note:THE SONY SG-613 HORIZONTAL OUTPUT, special Thyristor SG-613 technology called Silicon-Controlled Switch (SCS) SG-613
The silicon controlled switch (SCS) is the next step beyond the silicon controlled rectifier (SCR). It is still a four-layer diode, but this time all four regions are accessible to the external circuit.
The basic construction of the SCS is the same as for the SCR, with the addition of a second gate lead. We thus have an anode, a cathode, an anode gate, and a cathode gate. The equivalent circuit is the same as shown to the right, and even the schematic symbol of the SCS is similar to the SCR symbol.
The SCS has two advantages over the SCR and the four-layer diode. First, because both gate regions are accessible, they can be biased so as to completely cancel the rate effect we described with the four-layer diode. Second, since we can now control both end junctions, we can actively turn the SCS off without having to reduce the applied voltage or current. Thus, the SCS really is a switch, and can be used as one.HORIZONTAL DEFLECTION CIRCUIT SONY KV-2202ET CHASSIS SCC-137C-A :
What is claimed is
1. A horizontal deflection circuit including a high voltage producing circuit comprising:
2. A horizontal deflection circuit according to claim 1, in which the third electrode of said gate-controlled switching device is directly grounded.
3. A horizontal deflection circuit according to claim 1, comprising, in addition, a resistor, one end of said series connection of the diodes being connected to the third electrode of said semiconductor switching device and the other end being grounded through a resistor.
4. A horizontal deflection circuit according to claim 3, in which said coupling means comprises a capacitor and a resistor connected in parallel to each other.
5. A horizontal deflection circuit according to claim 4, in which said semiconductor switching device comprises a second gate-controlled switching device, the gate of said second gate-controlled switching device being connected to said driving signal source.
6. A horizontal deflection circuit according to claim 3, in which said semiconductor switching device comprises a transistor, the base and emitter electrodes of said transistor being connected to said driving signal source.
7. A horizontal deflection circuit according to claim 1, in which said coupling means comprises an additional signal source.
8. A horizontal deflection circuit according to claim 7, in which said coupling means further comprises a parallel connection of a capacitor and a resistor coupled in series with said additional signal source.
9. A horizontal deflection circuit according to claim 8, in which said driving signal source and additional signal source comprise a driving transformer having a plurality of windings.
10. A horizontal deflection circuit according to claim 9, in which said semiconductor switching device comprises another gate-controlled switching device.
11. A horizontal deflection circuit according to claim 9, in which said semiconductor switching device comprises a transistor having an additional current path provided between the base and emitter electrodes thereof.
Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to horizontal deflection circuits for a television receiver or the like and more particularly to a solid-state horizontal deflection circuit including a high voltage producing circuit and using a gate-controlled switching device for applying a deflection current to a horizontal deflection coil.
2. Description of the Prior Art
In solid-state horizontal deflection circuits for use in television receivers or the like, a switching element employed in the horizontal output stage is required to withstand a high voltage and must be capable of carrying large current. It is the practice in the art to employ a specially selected, expensive transistor of large current carrying capacity and high inverse voltage. In order to avoid the use of such an expensive transistor, a proposal has been made to employ a cheaper thyristor, for example, a semiconductor device referred to as a gate-controlled switch (GCS). This GCS is sometimes called a GTO (a gate turnoff switch). The GCS consists of a first P-type semiconductor layer, a first N-type semiconductor layer, a second P-type semiconductor layer and a second N-type semiconductor layer. The first P-type layer serves as an anode; the second N-type layer, a cathode; and the second P-type layer, a gate. A gate current is applied between the gate and cathode to control the conductivity between the anode and cathode. Once the switch has been turned on or off by the gate current between the gate and cathode, it remains in the on or off state even without continuing to apply the gate current to it, so that it is capable of being switched by a low power source and is suitable for use as a switching element of the horizontal deflection circuit. Further, generally, a horizontal deflection pulse produced by the operation of the switching element of the horizontal deflection circuit is boosted by a flyback transformer and rectified to serve as the high voltage for the cathode ray picture tube. However, prior horizontal deflection circuits using such a thyristor have defects such as complexity in the construction for operating the thyristor, deterioration of the horizontal deflection current, and so on.
It is one object of this invention to provide an improved solid-state horizontal deflection circuit using a gate-controlled switching device.
Another object of this invention is to provide a horizontal deflection circuit using a gate-controlled switching device effectively controlled by an improved gate current applying system.
A further object of this invention is to provide a horizontal deflection circuit using a gate-controlled switching device and producing a horizontal deflection current of high quality.
Still a further object of this invention is to provide a solid-state horizontal deflection circuit including a high voltage producing circuit in which a gate-controlled switching device and another semiconductor switching device are provided for producing, respectively, a horizontal deflection current and a pulse voltage to make a high voltage applied to a cathode ray tube and both switching devices are coupled with each other to operate with improved efficiency.
Other objects and aspects of this invention will be apparent from the following specification, together with drawings.
SUMMARY OF THE INVENTION
This invention is directed to a horizontal deflection circuit employing such a GCS as abovementioned in which a switching element for supplying a horizontal deflection current to a deflection coil and a switching element for generating a pulse voltage necessary for producing a high voltage to be supplied to a cathode ray tube are separately provided and at least the former switching element is a GCS.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a connection diagram showing one example of a horizontal deflection circuit of this invention;
FIGS. 2A-2I are a series of waveform diagrams for explaining the operation of the circuit exemplified in FIG. 1;
FIGS. 3 and 4 are connection diagrams illustrating modified forms of the horizontal deflection circuit of this invention;
FIGS. 5A-5H are a series of waveform diagrams for explaining the operation of the circuit depicted in FIG. 4; and
FIG. 6 is a connection diagram showing another modified form of the horizontal deflection circuit of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to FIG. 1 a horizontal deflection circuit of this invention with hereinafter be described in detail. A driving transistor 1 is supplied with a rectangular wave signal produced by a horizontal oscillating circuit, which may be of standard construction and is, therefore, not shown, synchronized wiJh a horizontal synchronizing signal. Reference numeral 2 designates a transformer having a primary winding 3a, a secondary winding 3b, and a tertiary winding 3c. A high voltage generating circuit 4 is connectdd to the transformer 2 and comprises a fly-back transformer 5 that has primary and secondary windings 6a and 6b. A switching element 7, which, in the present example, is a GCS, is connected to the primary 6a. A damper diode 8 and a capacitor 9 are also connected to the primary 6a. A rectifier 10 connects the secondary 6b to a cathode ray tube 11. The secondary winding 3b of the driving transformer 2 is grounded through a parallel circuit 25 consisting of a capacitor 24 and a resistor 23. Reference numeral 12 indicates generally a horizontal deflection current generating circuit that includes a horizontal deflection transformer or choke 13, a horizontal deflection coil 14, and a capacitor 15 connected in series thereto. A damper diode 16, a capacitor 17, and a GCS 18 are connected in parallel with the series connected coil 14 and capacitor 15. A direct voltage source 19 furnishes power for the circuit 4, and a second source 20 furnishes power for the circuit 12.
With such an arrangement, when a rectangular wave voltage S 1 , such as is shown in FIG. 2A, is applied through the transistor 1 to the primary winding 3a of the transformer 2, rectangular wave voltages S 2 and S 3 , such as are depicted in FIGS. 2B and 2C, are derived at the
secondary and tertiary windings 3b and 3c. Accordingly, when the voltage S 2 rises at a time t 1 , a gate current i 0 of the GCS's 7 and 18, such as shown in FIG. 2D, flows in a circuit along the path P 0 to turn on the GCS's 7 and 18. The anode currents I 1 and I 2 (currents flowing between the anodes and cathodes) of the GCS's 7 and 18, shown in FIGS. 2E and 2F, flow therethrough from the time t 1 to t 2 (the positive half cycle of the voltage S 2 ). The waveform of the current I 2 is identical with that of a current flowing in the horizontal deflection coil 14 of the horizontal deflection current generating circuit 12. In this case, at the rising of the rectangular wave voltage S 2 , the gate current i 0 is about to flow through the diode 22, but the voltage S 3 induced in the tertiary coil 3c is opposite in sense to that S 2 in the secondary coil 3b and is impressed through the gate and cathode of the GCS 18 to the diode 22 to put it in reverse biased condition and hence hold the diode 22 nonconductive. Accordingly, the aforementioned gate current i 0 does not flow to the diode 22 and the voltage S 2 induced in the winding 3b biases the GCS in the forward direction between its gate and cathode to put it in the "on" state. The voltages S 3 and S 2 induced in the windings 3c and 3b are superimposed on each other to bias the GCS 18 in the forward direction between its gate and cathode to cause it to conduct. As the gate current i 0 and the anode current I 1 of the GCS 7 flows in the aforementioned path and charges the capacitor 27, the anode potential of the diode 22 gradually rises to bias the diode 22 in the forward direction to cause it to conduct. Therefore, one portion of the gate current i 0 and almost all of the gate current I 1 of the GCS 7, which gradually increases because of its being a sawtooth wave, flow in the diode 22. The diode 22 plays an important role to provide a path which prevents the anode current of the GCS 7 from flowing in the GCS 18 except at its rising.When the rectangular wave voltage S 1 falls at the time t 2 , the aforementioned voltage S 2 also falls and a gate current i 0 ' flows in a path opposite in direction to the path P 0 of the gate current i 0 . The current i 0 ' flows for a period of time during which the so-called recovery currents of the diodes 21 and 22 flow. The GCS's 7 and 18 are thereby turned off to stop the flow of the anode currents I 1 and I 2 of the GCS's 7 and 18. In this case, the value E c of the voltage S 3 produced across the tertiary winding 3c is selected to be smaller than the value V 1 of the breakdown voltage between the gate and cathode of the GCS 18. Mathematically, E c < V 1 . The sum of the value E b of the voltage S 2 produced across the secondary winding 3b and the aforementioned voltage value E c is selected to be greater than the sum of the value V 2 of the breakdown voltage between the gate and cathode of the GCS 7 and the aforementioned voltage value V 1 . That is, E b + E c > V 1 + V 2 . Under such conditions the gate current is applied to the GCS's 7 and 18 for the time of circulation of the aforementioned recovery current. Moreover, the diodes 21 and 22 are put in the reverse biased condition at the time t 2 when the rectangular wave voltage S 2 falls and the recovery current of the diodes 21 and 22 flows, as the gate current i 0 ' for the GCS 7, from the diode 22 to the resistor 23 through the diode 21, the cathode and gate of the GCS 7 and the secondary winding 3b of the transformer 2, by which the GCS 7 is turned off substantially at the time t 2 . At that time, no current flows from the cathode of the GCS 18 to the diode 21 through the gate of the GCS 18, the winding 3c and the resistor 26 due to the aforementioned relationship E c < V 1 .
However, the forward current flowing in the diode 22 when the GCS's 7 and 18 are in the "on" state is less than the forward current flowing in the diode 22, so that the time during which the recovery current of the diode 22 flows is shorter than that during which the recovery current of the diode 21 flows. Therefore, the reverse current flowing in the diode 22 stops at the time t 3 , after which the recovery current of the diode 21 flows as a gate current i 0 ", shown in FIG. 2G, through the path P 0 of the current i 0 , by which the GCS 18 is turned off substantially at the time t 2 due to the aforementioned relationship E b + E c > V 1 + V 2 . The recovery current of the diode 21 stops at the time t 4 .After a time t 5 , a current I 3 , such as depicted in FIG. 2H, flows in the deflection coil 14 through the damper diode 16 and at a time t 6 the voltage S 1 rises again. Thereafter the same operations as above described are repeatedly carried out to supply the deflection coil 14 with a current I 4 , shown in FIG. 21. Further, the primary winding 6a of the flyback transformer 5 of the high voltage producing circuit 4 is supplied with a pulse voltage by the on-off operation of the GCS 7, so that the pulse is boosted by the secondary winding 6b and is rectified by the diode 10 to provide a high voltage, which is supplied to the anode of the cathode ray tube 11.
FIG. 3 illustrates another embodiment of this invention in which elements similar to those in FIG. 1 are marked with the same reference numerals and in which the GCS 7 of the high voltage producing circuit 4 is replaced with a transistor 31. The transistor 31 is turned on and off by the rectangular wave voltage S 2 induced in the secondary winding 3b of the drive transformer 2, but the GCS 18 is turned off by the recovery current of the diode 21 as is the case in FIG. 1. The other operations are the same as those in the example of FIG. 1, and, accordingly, no detailed description will be repeated. Reference numeral 29 indicates a diode connected between the base and emitter of the transistor 31, which is provided for preventing breakdown of the transistor 31 when its recovery current flows, but this diode is not always necessary.
In the present invention, since the output currents from the secondary and tertiary windings 3b and 3c of the transformer 2 are superimposed on each other and applied to the control electrodes of the switching element 7 and the GCS 18, that is, to the gate current path as above described, the GCS's 18 and 7 can be turned on and off without fail. In the illustrated example, the parallel circuit 28 is interposed between the connection point of the diodes 21 and 22 and the tertiary winding 3c but may be connected between the gate of the GCS 18 and the tertiary winding 3c.
In the example of FIG. 1, the connection point of the horizontal deflection coil 14 and the capacitor 15 is connected through the capacitor 30 to the connection point of the secondary winding 3b and the parallel circuit 25. With such a connection, a parabolic voltage generated at the connection point of the horizontal deflection coil 14 and the capacitor 15 is applied to the connection point of the secondary winding 3b and the parallel circuit 25, thereby to facilitate turning on and off the GCS 7. Due to this parabolic voltage, the gate potential of the GCS 7 is raised at the time of turning on the GCS 7 and lowered at the time of turning it off.
FIG. 4 illustrates another embodiment of this invention in which the tertiary winding 3c of the drive transformer 2 in the example of FIG. 2 is not employed and the connection point of the diodes 21 and 22 is connected directly to the gate of the GCS 18 through the parallel circuit 28 of the resistor 26 and the capacitor 27. Further, the cathode of the diode 22 is grounded through a resistor 32. The on-off and other operations of the GCS's 7 and 18 are also substantially the same in this embodiment as in the embodiment of FIG. 2. However, the present example is different from that of FIG. 2 in that the gate current of the GCS's 7 and 18 and the anode current of the GCS 7, having passed through the diode 21, are shunted from a path leading to the diode 22 and the resistor 32 to a path leading to the gate of the GCS 18 through the parallel circuit of the resistor 26 and the capacitor 26. The resistor 32 is provided to direct the shunted current to the gate of the GCS 18 and its resistance value is selected to permit flowing of the shunted current as a gate current enough to turn on the GCS 18.
At the time t 2 when the rectangular wave voltage S 1 falls, the rectangular wave voltage S 2 becomes negative and the gate current i 1 is stopped and, at the same time, the diodes 21 and 22 are put in reverse biased condition, so that the recovery current of the diodes 21 and 22 flow as a gate current i 1 ' of the GCS 7 through the resistor 32, the diodes 22 and 21, the cathode and gate of the GCS 7, the secondary winding 3b and the parallel circuit 25 of the resistor 23 and the capacitor 24, thereby turning off the GCS 7. Therefore, the anode current I 1 of the GCS 7 stops substantially at the time t 2 . In this case, the forward current flowing in the diode 22 from the time t 1 to t 2 is less than the forward current flowing in the diode 21 by the amount corresponding to the gate current i 2 of the GCS 18. Consequently, the time during which the recovery current of the diode 22 flows is shorter than that of the diode 21. Accordingly, while the recovery current of the diode 21 is still flowing, that of the diode 22 stops flowing at a time t 3 and the recovery current of the diode 21 flows as a gate current i 2 ' of the GCS 18 through the cathode and gate of the GCS 18, the parallel circuit 28 of the resistor 26 and the capacitor 27, the diode 21 and the GCS 7, causing the GCS 18 to be turned off. Consequently, the anode current I 2 of the GCS 18 stops flowing substantially at the time t 3 . The flow of the recovery current of the diode 21 stops at a time t 4 . Thereafter, a damper current I 3 , such as depicted in FIG. 5G, flows from a time t 5 , so that the deflection coil 14 is supplied with a horizontal deflection current I, such as shown in FIG. 5H. Further, the primary winding of the flyback transformer 5 is supplied with a pulse of a predetermined width which is generated when the anode current I 1 of the GCS 7 stops. The pulse is derived from the secondary winding of the flyback transformer 5 after being boosted and then it is rectified to provide a high voltage. Thereafter, the rectangular wave voltage S 1 rises again at a time t 6 and the foregoing operations are repeated.
FIG. 6 shows another example of this invention which employs the transistor 31 in place of the GCS 7 of FIG. 4, as is the case with FIG. 3, and which is the same in operation as the example of FIG. 3. Therefore, no detailed description will be given, but, in this case, the recovery currents of the diodes 21 and 22 do not flow in the transistor 34 through the short path 33.
As has been described in the foregoing, in the present invention a series circuit of two diodes is connected to the cathode of, for example, a GCS serving as a first switching device of a high voltage generating circuit and a GCS serving as a second switching device of a horizontal deflection current applying circuit is connected to the series circuit and the switching of both of the switching devices is controlled by a voltage derived from the secondary winding of a drive transformer. In this invention, the series circuit is provided for coupling the switching devices in the current path of the secondary winding of the drive transformer, so that the circuit construction is simple as a whole. Further, since the two switching devices, at least one of which is a GCS, are controlled only by the voltage induced in the secondary winding, the horizontal deflection circuit of this invention is low in power dissipation and hence is economical.
It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of this invention.
SONY KV-2202ET CHASSIS SCC-137C-A CONVERGENCE DEFLECTION SYSTEM FOR A SONY COLOR PICTURE TUBE
In a color picture tube in which a plurality of beams are made to intersect each other at a location between the beam generating sources and the color screen and are focused on the latter by a main focusing lens positioned to dispose its optical center substantially at the location where the beams intersect so that beams emerge from such lens along divergent paths, first and second spaced plates are disposed at opposite sides of each of the divergent paths to electrostatically deflect the respective beam and cause convergence of all of the beams at a common area on the screen when the first and second plates are at different potentials, a high voltage is generated from a horizontal deflecting pulse provided for causing the beams to scan the screen and such high voltage is applied to an anode electrode of the tube and also to each first plate, and a static convergence deflecting voltage is obtained by dividing the aforementioned high voltage and is applied as the potential difference between the first and second plates by which the respective beam is to be deflected. Further, a dynamic convergence deflecting voltage, comprising both parabolic and sawtooth voltages is generated in response to the horizontal deflecting pulse and is superimposed on the static convergence deflecting voltage with provision being made for separately adjusting both deflecting voltages.
1. In a single-gun, plural-beam cathode-ray tube which includes a beam-receiving screen, beam-generating means for directing a plurality of electron beams toward said screen, and lens means for focusing said electron beams on said screen and having an optical center through which said beams are all passed with at least two of said beams emerging from said lens means along paths which are divergent to the optical axis of the latter; electron beam convergence-deflecting means to deflect said beams emerging along said divergent paths for convergence of said beams at a common area of said screen, said convergence-deflecting means comprising first and second spaced plates disposed at opposite sides of each of said divergent paths for electrostatically deflecting the respective beam when at different electrical potentials, high voltage-generating means receiving a horizontal deflecting pulse and operative to generate a high voltage therefrom, means to apply said high voltage as an anode voltage in said tube and also to said first plate associated with each divergent path, voltage-dividing means dividing said high voltage to produce a static convergence deflecting voltage, and means to apply said static convergence voltage between said first plate and said second plate associated with each divergent path and thereby establish the potential difference therebetween for deflecting the respective beam.
2. A single-gun, plural-beam cathode-ray tube according to claim 1, in which said voltage-dividing means includes first and second series connected resistors having said high voltage applied thereacross so that said static convergence-deflecting voltage appears across one of said resistors.
3. A single-gun, plural-beam cathode-ray tube according to claim 2, in which one of said resistors is variable to permit adjustment of said static convergence-deflecting voltage obtained by dividing said high voltage.
4. A single-gun, plural-beam cathode-ray ray tube according to claim 2, in which capacitors are respectively connected in parallel with said first and second resistors for stabilizing the voltages appearing thereacross.
5. A single-gun, plural-beam cathode-ray tube according to claim 2, in which there are provided means to generate a dynamic convergence-deflecting voltage, and means to superimpose said dynamic convergence voltage on said static convergence voltage.
6. A single-gun, plural-beam cathode-ray tube according to claim 5, in which said means to superimpose the dynamic convergence voltage on the static convergence voltage is an isolating transformer connected to said means to generate the dynamic convergence-deflecting voltage and to said voltage-dividing means.
7. A single-gun, plural-beam cathode-ray tube according to claim 6, in which said isolating transformer has a primary winding connected with said means to generate the dynamic convergence-deflecting voltage and a secondary winding connected in series between said first and second resistors of said voltage dividing means.
8. A single-gun, plural-beam cathode-ray tube according to claim 6, in which said isolating transformer has a primary winding connected with said means to generate the dynamic convergence-deflecting voltage and a secondary winding connected at one end to a connecting point between said first and second resistors of said voltage-dividing means and at the other end to said second plate associated with each of said divergent paths.
9. A single-gun, plural-beam cathode-ray tube according to claim 5, in which the tube has a horizontal deflection coil to cause the beams to horizontally scan the screen when a horizontal deflecting current of sawtooth configuration flows through said coil, and in which said means to generate a dynamic convergence-deflecting voltage includes means to derive from said horizontal deflecting current flowing through said coil a voltage of parabolic waveform, means operating in synchronism with said horizontal deflecting current to produce a voltage of sawtooth waveform and means to combine the voltages of parabolic and sawtooth waveform for constituting said dynamic convergence deflecting voltage.
10. A single-gun, plural-beam cathode-ray tube according to claim 9, in which means are provided to separately adjust the magnitude of said voltage of parabolic waveform and the magnitude and wave shape of said voltage of sawtooth waveform.
11. A single-gun, plural-beam cathode-ray tube according to claim 9, in which a capacitor is connected in series with said horizontal deflection coil to produce a voltage of parabolic waveform across said capacitor, capacitive means divides said voltage across said capacitor to provide said voltage of parabolic waveform to be combined with said voltage of sawtooth waveform, and variable inductor means is connected between said capacitance means and said means to superimpose the dynamic convergence voltage on the static convergence voltage to adjust the magnitude of said voltage of parabolic waveform thus combined.
12. A single-gun, plural-beam cathode-ray tube according to claim 11, in which said means to produce the voltage of sawtooth waveform includes a flyback transformer driven in synchronism with said horizontal deflection current and having a secondary winding, a potentiometer having a resistance and a slider movable therealong, and an inductor connected in series with said potentiometer resistance across said secondary winding to produce a voltage of sawtooth configuration across said resistance, with said voltage of sawtooth waveform to be combined with said voltage of parabolic waveform appearing at said slider of the potentiometer.
13. A single-gun, plural-beam cathode-ray tube according to claim 12, in which said means to superimpose said dynamic and static convergence voltages includes an isolating transformer having a primary winding connected to said slider of the potentiometer and to said variable inductor means.
14. Horizontal dynamic convergence voltage-generating means for a cathode-ray tube having a horizontal deflection coil to effect horizontal beam scanning in response to the passage therethrough of a horizontal deflecting current of sawtooth configuration, comprising means operating in synchronism with said horizontal deflecting current to produce a voltage of sawtooth waveform, a capacitor connected in series with said horizontal deflection coil to produce a first voltage of parabolic waveform across said capacitor, capacitive means dividing said first voltage across said capacitor to provide a second voltage of parabolic waveform, means to combine said second voltage of parabolic waveform with said voltage of sawtooth waveform, and variable inductor means connected between said capacitance means and said means to combine said second voltage of parabolic waveform with said voltage of sawtooth waveform to adjust the magnitude of said second voltage of parabolic waveform thus combined.
15. Horizontal dynamic convergence voltage-generating means according to claim 14, in which said means to produce the voltage of sawtooth waveform includes a flyback transformer driven in synchronism with said horizontal deflection current and having a secondary winding, a potentiometer having a resistance and a slider movable therealong, and an inductor connected in series with said potentiometer resistance across said secondary winding to produce a voltage of sawtooth configuration across said resistance, with said voltage of sawtooth waveform to be combined with said voltage of parabolic waveform appearing at said slider of the potentiometer.
16. Horizontal dynamic convergence voltage-generating means according to claim 15, in combination with means to produce a static convergence-deflecting voltage, and means to superimpose said dynamic convergence-deflecting voltage on said static convergence-deflecting voltage including isolating transformer means having a primary winding connected, at its ends, to said variable inductor means and to said slider, respectively.
Accordingly, it is an object of this invention to provide a color picture tube of the described type with an improved circuit arrangement by which the convergence-deflecting voltages are generated.
Another object is to provide a circuit arrangement, as above, which produces a static convergence voltage from a high voltage applied to the tube anode, and wherein variations in the anode voltage are accurately reflected in corresponding charges in the static convergence voltage so as to maintain the proper convergence of the beams.
Another object is to provide a circuit arrangement, as above, which produces a horizontal dynamic convergence voltage superimposed on the static convergence voltage while isolating the source of such dynamic convergence voltage from the static convergence voltage.
Still another object is to provide a circuit arrangement, as above, and in which the static and dynamic convergence voltages can be individually controlled without danger from high voltages.
A further object is to provide a circuit arrangement, as above, with improved means for producing the dynamic convergence voltage.
In accordance with an aspect of this invention, the high voltage applied to an anode electrode of the color picture tube and to one of the convergence deflecting plates associated with each divergent path is generated from a horizontal deflecting pulse provided for causing horizontal scanning of the beams, and the static convergence-deflecting voltage applied between the convergence-deflecting plates associated with each divergent path is obtained by dividing the mentioned high voltage.
Further, in accordance with the invention, the dynamic convergence-deflecting voltage which is superimposed on the static convergence-deflecting voltage is generated in response to the horizontal deflecting pulse.
The above, and other objects, features and advantages of the invention, will be apparent in the following detailed description of illustrative embodiments thereof which is to be read in connection with the accompanying drawings, wherein:
FIG. 1 is a schematic sectional view in a horizontal plane passing through the axis of a single-gun, plural-beam color picture tube and which is shown provided with a convergence deflection system according to one embodiment of this invention;
FIGS. 2A-2E are graphic representations of the wave forms of the static and dynamic convergence deflection voltages produced according to this invention; and
FIG. 3 is a diagrammatic view showing a modification of the convergence deflection system of FIG. 1.
Referring now to the drawings in detail, and initially to FIG. 1 thereof, it will be seen that a single-gun, plural-beam color picture tube of the type to which this invention is applied may comprise a glass envelope (not shown) having a neck and a cone extending from the neck to a color
Screen S provided with the usual arrays of color phosphors S R , S G and S B and with an aperture grill G P or beam-selecting means, such as a so-called shadow mask. Disposed within the neck is a single electron gun A having cathodes K R , K G and K B , each of which is constituted by a beam-generating source with the respective beam-generating surfaces thereof disposed as shown in a plane which is substantially perpendicular to the axis of the electron gun. In the embodiment shown, the beam-generating surfaces thereof are arranged in a straight line so that the respective beams B R , B G and B B emitted therefrom are directed in a substantially horizontal plane containing the axis of the gun, with the central beam B G being coincident with such axis. A first grid G 1 is spaced from the beam-generating surfaces of cathodes K R , K G and K B and has apertures g 1R , g 1G and g 1B formed therein in alignment with the respective cathode beam-generating surfaces. A common grid G 2 is spaced from the first grid G 1 and has apertures g 2R , g 2G and g 2B formed therein in alignment with the respective apertures of the first grid G 1 . Successively arranged in the axial direction away from the common grid G 2 are open-ended, tubular grids or electrodes G 3 , G 4 and G 5 , respectively, with cathodes K R , K G and K B , grids G 1 and G 2 , and electrodes G 3 , G 4 and G 5 being maintained in the depicted assembled positions thereof, by suitable, nonillustrated support means of an insulating material.For operation of the electron gun of FIG. 1, appropriate voltages are applied to the grids G 1 and G 2 and to the electrodes G 3 , G 4 and G 5 . Thus, for example, a voltage of 0 to minus 400 v. is applied to the grid G 1 , a voltage of 0 to 500 v. is applied to the grid G 2 , a voltage of 13 to 20 kv. is applied to the electrodes G 3 and G 5 , and a voltage of 0 to 400v. is applied to the electrode G 4 , with all of these voltages being based upon the cathode voltage as a reference. As a result, the voltage distributions between the respective electrodes and cathodes, and the respective lengths and diameters thereof, may be substantially identical with those of a unipotential single beam-type electron gun which is constituted by a single cathode and first and second, single-apertured grids.
Further included in the electron gun of FIG. 1 are electron beam convergence deflecting means F which comprise shielding plates P and P' disposed in the depicted spaced, relationship at opposite sides of the gun axis, and axially extending, deflector plates Q and Q' which are disposed, as shown, in outwardly spaced, opposed relationship to shielding plates P and P', respectively. Although depicted as substantially straight, it is to be understood that the deflector plates Q and Q' may, alternatively, be somewhat curved or outwardly bowed, as is well known in the art.
The shielding plates P and P' are equally charged and disposed so that the central electron beam B G will pass substantially undeflected between the shielding plates P and P', while the deflector plates Q and Q' have negative charges with respect to the plates P and P' so that respective electron beams B B and B R will be convergently deflected as shown by the respective passages thereof between the plates P and Q and the plates P' and Q'. More specifically, a voltage V P which is equal to the voltage applied to the electrodes G 3 and G 5 , may be applied to both shielding plates P and P', and a voltage V Q , which is some 200 to 300 v. lower than the voltage V P , is applied to the respective deflector plates Q and Q' to result in the respective shielding plates P and P' being at the same potential, and to result in the application of a deflecting voltage difference or static convergence deflecting voltages V C between the respective plates P' and Q' and P and Q and it is, of course, this convergence-deflecting voltage V C which will impart the requisite convergent deflection to the respective electron beams B B and B R .
In operation, the respective electron beams B R , B G and B B which emanate from the beam-generating surfaces of the cathodes K R , K G and K B will pass through the respective grid apertures g 1R , g 1G and g 1B , to be intensity modulated with what may be termed the "red", "green" and "blue" intensity modulation signals applied between the said cathodes and the first grid G 1 . The respective electron beams will then pass through the common auxiliary lens L' to cross each other substantially at the optical center of the main lens L and to emerge from the latter with beams B R and B B diverging from beam B G . Thereafter, the central electron beam B G will pass substantially undeflected between shielding plates P and P' since the latter are at the same potential. Passage of the electron beam B B between the plates P' and Q' and of the electron beam B R between the plates P and Q will, however, result in the convergent deflections thereof as a result of the convergence-deflecting voltage applied therebetween, and the system of FIG. 1 is so arranged that the electron beams B B , B G and B R will desirably converge or cross each other at a common spot centered in an aperture of the aperture grill G P or other beam selecting means so as to diverge therefrom to strike the respective color phosphors of a corresponding array thereof on screen S. More specifically, it may be noted that the color phosphor screen S is composed of a large plurality of sets or arrays of vertically extending "red", "green" and "blue" phosphor stripes or dots S R , S G and S B with each of the arrays or sets of color phosphors forming a color picture element. Thus, it will be understood that the common spot of beam convergence corresponds to one of the thusly formed color picture elements.
The flyback transformer 25 is shown to have a secondary winding 25b connected to a high voltage-generating means 28 receiving pulses from winding 25b in synchronism with the horizontal driving pulse supplied to terminal 22', and the high voltage-generating means 28 includes a rectifier 28a to produce, from the received pulses, a constant high voltage V P which appears between output terminal 29 and ground. This high voltage V P is, as described above, applied to an anode of the picture tube, the electrodes G 3 and G 5 and also the convergence-deflecting plates P and P' by way of a terminal 33.
A resistor 30, the secondary winding 31b of an isolating transformer 31 and a variable resistor 32 are connected in series between the output terminal 29 and the ground so that the high voltage V P is divided by resistors 30 and 32 into the static convergence voltage V C and the voltage V Q , with the voltage V C appearing across resistor 30 and being easily adjustable by means of the variable resistor 32. Further, capacitors 44 and 45 are connected in parallel with resistors 30 and 32 for stabilizing the voltages V C and V Q .
The flyback transformer 25 is further shown to include an additional secondary winding 25c across which an inductance 35 and the resistance of a potentiometer 36 are connected in series to function as an integration circuit 37. Series connected capacitors 38 and 39 are connected between ground and the connection point between capacitor 27 and the horizontal deflection coil 26, that is, capacitors 38 and 39 are connected in parallel with capacitor 27, and the connecting point between capacitors 38 and 39 is connected to a middle tap 40 provided on the resistance of potentiometer 36. The connecting point 41 between capacitors 27 and 38 is connected to one end of the primary winding 31a of isolating transformer 31 through a variable inductor 43, and the other end of winding 31a is connected to the output terminal 42 of potentiometer 36 from which there extends the slider or movable tap 42'. The variable inductor 43 is provided to permit adjustment of the voltage developed at connecting point 41. Finally, a terminal 34 extending from the connecting point between winding 31b of the isolating transformer and variable resistor 32 is connected to plates Q and Q'.
The above-described circuits operate as follows:
It will also be seen that, since the static convergence-deflecting voltage V C is produced by dividing the anode voltage V P in accordance with the ratio of resistors 30 and 32, which ratio remains constant in the absence of adjustment of resistor 32, the voltage V C will be varied in accordance with variations in the anode voltage V P . Thus, if, for example, the anode voltage V P decreases with an increase in the anode current, the voltage V C will correspondingly decrease to maintain the ratio V C /V P at a constant value so as to maintain the proper convergence of the beams.
Referring now to FIG. 3, it will be seen that the circuit arrangement there shown is generally similar to that of FIG. 1 and has its several components identified by the same reference numerals. However, in the circuit of FIG. 3, the secondary winding 31b of isolating transformer 31 is not connected in series between resistors 30 and 32, but rather has one end connected to the connecting point 57 between those resistors and its other end connected to terminal 34. Thus, the static convergence-deflecting voltage V C is produced across resistor 30, that is, between terminal 33 and connecting point 57, and the horizontal dynamic convergence-deflecting voltage e c is produced across winding 31b, that is, between connecting point 57 and terminal 34, with the result that the combined convergence-deflecting voltage V C +e c again appears between terminals 33 and 34. As in the first described embodiment, terminal 33 is connected to the electrodes G 3 and G 5 , the anode and the plates P and P' of the tube (not shown), while the terminal 34 is connected to the plates Q and Q' of the tube.Although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention.
SONY KV-2202ET CHASSIS SCC-137C-A SONY TRINITRON CONVERGENCE DEFLECTING DEVICE FOR SINGLE-GUN, PLURAL-BEAM COLOR PICTURE TUBE
In a color picture tube of the single-gun, plural-beam type in which a central beam and two side beams originate in a common horizontal plane and are all made to pass through the center of an electron lens for focussing the beams on the color screen with the central beam emerging from the lens along the optical axis of the latter and the side beams emerging from the lens along paths that are oppositely divergent from the axis, the divergent side beams are acted upon by an electrostatic convergence deflecting device constituted by pairs of horizontally spaced plates arranged along the divergent paths and having voltages applied thereacross to produce electric fields by which the divergent side beams passing therethrough are deflected to converge at a common spot with the central beam on the apertured grill or mask associated with the screen, and a main deflection yoke produces magnetic fields by which the beams are deflected horizontally and vertically, respectively, for causing the beams to scan the screen; the horizontal distances between the plates of each pair are varied in the vertical direction from a maximum at the common horizontal plane to minimums at the opposed edges of the plates remote from such common plane so as to correspondingly vary the strengths of the electric fields and thus correct distortions in the rasters of the side beams.
1. A single-gun, plural-beam color picture tube comprising a color screen, beam generating means directing a central beam and two side beams in a common horizontal plane toward said screen, electron lens means defining a focusing field having a center through which the beams pass and by which the bundle of electrons in each of the beams are focused on said color screen with the central beam emerging from said lens along the optical axis of the latter and said two side beams emerging from said lens along paths that are oppositely divergent from said central beam, electrostatic convergence deflecting means including a pair of horizontally spaced plates arranged along each of said divergent paths, said spaced plates of each pair being disposed at the inside and outside, respectively, of the side beam in the related divergent path and having voltages applied thereacross to produce an electric field by which the respective side beam passing therethrough is deflected horizontally to converge at a common spot with said central beam and the other of said side beams, and a main deflection yoke producing magnetic fields by which said beams are deflected horizontally and vertically respectively, for causing the beams to scan said screen and produce respective rasters on the latter; said convergence deflecting means being located within the field produced by said yoke to deflect said beams vertically so that said beams are similarly deflected vertically within said convergence deflecting means, and the horizontal distance between said plates of each of said pairs varying progressively in the vertical direction normal to said common horizontal plane from a maximum at said common horizontal plane to minimums at the opposed edges of the plates remote from said common plane so as to correspondingly vary the strength of the respective electric field for changing the rasters of said side beams with respect to the raster of said central beam and thereby compensating for deviations between said rasters as produced by said magnetic fields of the main deflection yoke. 2. A single gun, plural-beam color picture tube according to claim 1, in which the inner plate of each of said pairs which is closest to said central beam is flat, and the other plate of the respective pair is convex at the side thereof facing away from said inner plate. 3. A single-gun, plural-beam color picture tube according to claim 1, in which the plates of each of said pairs are convex at the sides thereof facing away from each other.
In single-gun, plural-beam color picture tubes of the described type, for example, as specifically disclosed in U.S. Pat. No. 3,448,316, issued June 3, 1969, and having a common assignee herewith, three laterally spaced electron beams are emitted by a beam generating or cathode assmebly and directed in a common substantially horizontal plane with the central beam coinciding with the optical axis of the single electron focussing lens and the two outer or side beams being converged to cross the central beam at the optical center of the lens and thus emerge from the latter along paths that are divergent from the optical axis. Arranged along such divergent paths are respective pairs of convergence deflecting plates constituting a convergence deflecting device and having voltages applied thereacross to produce electric fields which laterally deflect the divergent beams in a substantially horizontal plane for causing all beams to converge at a common spot on the apertured beam selecting grill or shadow mask associated with the color screen. Further, arranged between the convergence deflecting device and the screen is a main deflection yoke which, in response to its reception of horizontal and vertical sweep signals, produces horizontal and vertical magnetic deflection fields acting on all of the beams to cause the latter to scan the color screen in predetermined rasters. Since the beams are horizontally spaced and non-parallel during their passage through the horizontal deflection field, the distances that the side beams travel through such field will be respectively greater and less than the distance that the central beam travels through the field when the beams are deflected toward one side or the other side of the screen. If the horizontal deflection field has a uniform flux density thereacross, the side beam traveling therethrough for the greater distance will be deflected to a greater extent than the side beam traveling the shorter distance through the field and misconvergence of the beams will result. Even if the horizontal deflection field is given a non-uniform flux density thereacross, misconvergence of the beams can be thereby avoided only when the beams are deflected toward one side or the other of the screen midway between the top and bottom of the screen, that is, when the common plane of the beams passing through the horizontal deflection field is directed horizontally, that is, substantially perpendicular to the vertical lines of magnetic flux of the horizontal deflection field. However, when the common plane of the beams passing through the horizontal deflection field is substantially inclined from the horizontal, that is, when the vertical deflection field deflects the beams to cooperate with the horizontal deflection field in directing the beams toward an upper or lower corner of the screen, the difference between the distances traveled by the side beams through the horizontal deflection field is further increased and hence may not be compensated by the non-uniform flux density established across the horizontal deflection field. Thus, the rasters of the side beams may have shapes that are oppositely distorted with respect to the shape of the raster of the central beam.
Accordingly, it is an object of this invention to provide a single-gun, plural-beam color picture tube in which the rasters of the several beams are free of distortion with respect to each other.
Another object is to provide a single-gun, plural-beam color picture tube in which distortions of the rasters of the several beams are avoided by a particular construction of the convergence deflecting device.
The above, and other objects, features and advantages of this invention, will be apparent in the following detailed description of illustrative embodiments which is to be read in connection with the accompanying drawing, wherein:
FIG. 1 is a schematic sectional view in a horizontal plane passing through the axis of a single-gun, plural-beam color picture tube of the type to which this invention is preferably applied;
FIG. 2 is a diagrammatic view to which reference is hereinafter made in explaining the invention;
FIG. 3 is a diagrammatic view showing the possible relative distortions of the rasters of the several beams, as seen from the viewer's side of the tube screen, and which are to be avoided by this invention;
FIG. 4 is a diagrammatic, transverse sectional view through the convergence deflecting device of a color picture tube according to a first embodiment of this invention; and
FIGS. 5-8 are views similar to FIG. 4, but showing other embodiments of the invention.
Referring to the drawings in detail, and initially to FIG. 1 thereof, it will be seen that a single-gun, plural-beam color picture tube of the type to which this invention may be applied comprises a glass envelope (indicated in broken lines) having a neck N and cone C extending from the neck to a color screen S provided with the usual arrays of color phosphors S R , S G and S B and with an apertured beam selecting grill or shadow mask G P . Disposed within neck N is an electron gun A having cathodes K R , K G and K B , each of which is constituted by a beam-generating source with the respective beam-generating surfaces thereof disposed as shown in a plane which is substantially perpendicular to the axis of the electron gun A. In the embodiment shown, the beam-generating surfaces are arranged in a straight line so that the respective beams B R , B G and B B emitted therefrom are directed in a substantially horizontal plane containing the axis of the gun, with the central beam B G being coincident with such axis. A first grid G 1 is spaced from the beam-generating surfaces of cathodes K R , K G and K B and has apertures g 1R , g 1G and g 1B formed therein in alignment with the respective cathode beam-generating surfaces. A common grid G 2 is spaced from the first and grid G 1 and has apertures g 2R , g 2G and g 2B 1 . Successively arranged in the axial direction away from the common grid G 2 are open-ended, tubular grids or electrodes G 3 , G 4 and G 5 , respectively with cathodes K R , K G and K B , grids G 1 and G 2 , and electrodes G 3 , G 4 and G 5 being suitably maintained in the depicted, assembled positions thereof.formed therein in alignment with the respective apertures of the first grid G
For operation of the electron gun A of FIG. 1, appropriate voltages are applied to the grids G 1 2 and to the electrodes G 3 , G 4 and G 5 . Thus, for example, a voltage of 0 to minus 400V is applied to the grid G 1 , a voltage of 0 to 500V is applied to the grid G 2 , a voltage of 13 to 20KV is applied to the electrodes G 3 and G 5 , and a voltage of 0 to 400V is applied to the electrode G 4 , with all of these voltages being based upon the cathode voltage as a reference. As a result, the voltage distributions between the respective electrodes and cathodes, and the respective lengths and diameters thereof, may be substantially identical with those of a unipotential-single beam type electron gun which is constituted by a single cathode and first and second, single-apertured grids.
and G
With the applied voltage distribution as described hereinabove, an electron lens field will be established between grid G 2 and the electrode G 3 to form an auxiliary lens L' as indicated in dashed lines, and an electron lens field will be established around the axis of electrode G 4 , by the electrodes G 3 , G 4 and G 5 , to form a main lens L, again as indicated in dashed lines. In a typical use of electron gun A, bias voltages of 100V, 0V, 300V, 20KV, 200V and 20V may be applied respectively to the cathodes K R , K G and K B , the first and second grids G 1 and G 2 and the electrodes G 3 , G 4 and G 5 .
In operation, the electron beams B R , B G and B B which emanate from the beam generating surfaces of the cathodes K R , K G and K B will pass through the respective grid apertures g 1R , g 1G and g 1B , to be intensity modulated with what may be termed the "red", "green" and "blue" intensity modulation signals applied between the said cathodes and the first grid G 1 . The electron beams will then pass through the common auxiliary lens L' to cross each other at the center of the main lens L. Thereafter, the central electron beam B G will pass substantially undeflected between sheilding plates P and P' since the latter are at the same potential. Passage of the electron beam B B between the plates P' and Q' and of the electron beam B R between the plates P and Q will, however, result in the convergent deflections thereof as a result of the convergence deflecting voltage V Q applied therebetween, and the system of FIG. 1 is so arranged that the electron beams B B , B G and B R will desirably converge or cross each other at a common spot centered in an aperture of the beam selecting grill or mask G P so as to diverge therefrom to strike the respective color phosphors of a corresponding array thereof on screen S. More specifically, it may be noted that the color phosphor screen S is composed of a large plurality of sets or arrays of vertically extending "red", "green" and "blue" phosphor stripes or dots S R , S G B with each of the arrays or sets of color phosphors forming a color picture element. Thus, it will be understood that the common spot of beam convergence corresponds to one of the thusly formed color picture elements.and S
The voltage V P may also be applied to the lens electrodes G 3 and G 5 and to the screen S as an anode voltage as well as to the aperture grill G p . Electron beam scanning of the face of the color phosphor screen is effected in conventional manner, for example, main deflection yoke means indicated in broken lines at D and which receives horizontal and vertical sweep signals to produce horizontal and vertical deflection fields by which the beams are made to scan the screen for providing a color picture thereon. Since, with this arrangement, the respective electron beams are each passed, for focussing, through the center of the main lens L of the electron gun A, the beam spots formed by impingement of the beams on the color phosphor screen S will be substantially free from the effects of coma and/or astigmatism of the same main lens, whereby improved color picture resolution will be provided.
In accordance with the present invention, such distortions of the rasters of side beams B B and B R relative to the raster of central beam B G are avoided by suitably varying, in the direction perpendicular to the common plane in which the beams originate, for example, in the vertical direction for the tube of FIG. 1, the distances by which plates P and Q and plates P' and Q' are spaced from each other. For example, in the embodiment shown by FIG. 4, plates P and P' are made flat or planar while plates Q and Q' are outwardly concave in the vertical direction or the direction across the plates, whereby the distances between plates P and Q and between plates P' and Q' are relatively small at the horizontal plane 21 containing the tube axis and such distances between the plates increase progressively in the direction of vertical plane 22 upwardly and downwardly from horizontal plane 21 in which the beams all originate.Since convergence deflecting device F is disposed adjacent the main deflecting yoke D (FIG. 1), it will be apparent that the vertical deflection field of yoke D will extend into device F, and thereby influence the vertical positions of the beams B B , B G and B R in passing through device F. Thus, when the vertical and horizontal deflection fields of yoke D are effective to direct the beams toward a corner of the screen, the vertical deflection field of yoke D will vertically displace beams B R , B G and B B either upwardly or downwardly from plane 21 within convergence deflection device F. By reason of the increased distance betweeen plates P and Q and plates P' and Q' at such displaced positions of beams B B and B R , the parts of the electric fields then acting on such beams will be of relatively reduced intensity thereby to similarly reduce the convergent deflections imparted to beams B B and B R . Thus, for example, when the beams are horizontally and vertically deflected by yoke D so as to be directed at the upper or lower left-hand corner of the screen, as seen from the viewer's side thereof, the left-ward deflection of beam B B by the field between plates P and Q will be reduced and the right-ward deflection of beam B R by the field between plates P' and Q' will be similarly reduced, whereby to bring the left-hand sides of the rasters L B and L R , as seen on FIG. 3, into agreement with the left-hand side of the raster L G . Similarly, when the beams are horizontally and vertically deflected by yoke D so as to be directed at the upper or lower right-hand corner of the screen as viewed on FIG. 3, the left-ward and right-ward deflections of beams B B and B R , respectively, by the fields between plates P and Q and plates P' and Q' will be reduced whereby to bring the right-hand sides of rasters L B and L R into agreement with the right-hand side of raster L G . Thus, distortions of the rasters L B and L R relative to the raster L G can be effectively avoided by suitably selecting the position of convergence deflecting device F relative to yoke D and the shapes of plates Q and Q'.
Of course, in the foregoing, it has been assumed that the distortions of rasters L B and L R relative to raster L G that are to be corrected are those shown on FIG. 3. However, a situation may arise, for example, by reason of a particular configuration of the horizontal deflection field produced by yoke D, in which the raster of beam B B has the shape indicated at L R on FIG. 3 while the raster of beam B R has the shape indicated at L R . In the latter case, the plates P and Q and the plates P' and Q' are shaped so that the distances therebetween are maximum at the horizontal plane containing the axis of the tube and decrease progressively therefrom in the vertical direction, that is, in the direction perpendicular to the common plane in which the beams originate. In achieving such variations in the distances between the plates, plates P and P' may be flat or planar and plates Q and Q' may be outwardly convex (FIG. 6), or plates P and P' may be inwardly convex and plates Q and Q' may be outwardly convex (FIG. 8).
Further, in each of the above described embodiments of this invention, the convergence deflection device F consists of only a single pair of plates P and Q or P' and Q' acting on each of the beams B B and B R to deflect the respective beam in the direction for convergence with the central beam B G . However, the invention can also be applied to color picture tubes, for example, as disclosed in the copending U.S. application Ser. No. 718,738, filed Apr. 4, 1968, and having a common assignee herewith, in which the beams following paths diverging from the tube axis upon emerging from the focussing lens are each successively acted upon by two pairs of deflecting plates, with the first pair of plates establishing an electric field therebetween by which the respective beam is further diverged from the tube axis and the second pair of plates establishing a field therebetween by which the beam is deflected in the direction for converging with the other beams. The foregoing arrangement makes it possible to increase the angles of incidence of the side beams B B and B R at the beam selecting apertured grill or mask G P , whereby to permit a decrease in the distance of the latter from screen S for facilitating the accurate locating and mounting of the grill or mask G P relative to the screen S. Where each of the side beams B B and B R is successively acted upon by two pairs of deflecting plates, as aforesaid, one or the other of such pairs of plates, and preferably the pair of plates closest to the location of the main deflection yoke, is provided with a distance between the plates that varies in the direction perpendicular to the common plane in which the beams originate so as to avoid distortion of the raster of the respective beam in accordance with this invention.
SONY TRINTRON DYNAMIC CONVERGENCE CIRCUIT
1. Field of the Invention
This invention relates generally to dynamic convergence circuits for plural electron beam display apparatus such as a color television receiver, and is more particularly directed to an improved dynamic convergence circuit of reduced complexity provided together with a horizontal deflection circuit.
2. Description of the Prior Art
In most color cathode ray tubes employed in color television receivers for commercial use at present, plural electron beams, for example, three electron beams are utilized. In such a color cathode ray tube, respective electron beams emitted from its electron gun are deflected for beam scanning by a deflection yoke provided around the neck portion of the tube. An aperture mask is provided in the tube in front of the color phosphor screen for determining the impinging positions of the electron beams on the color phosphor screen. The respective electron beams impinge on the positions corresponding to red, green and blue color phosphors in response to their incident angles to the aperture of the mask. Thus, the electron beams scan the color phosphor screen under the control of the deflection yoke to form separate images of different primary colors and hence to display a full color image on the color phosphor screen. In order to form a correct full color image on the screen it is required that the plural primary color images should be formed on the screen with a superposition relation over all the points on the screen. To this end, arriving positions of the plural electron beams on the screen are required to be in superposition. This superposition is achieved by not only a static correction means but also by a dynamic correction means generally called a convergence means.
To correct or compensate for the misconvergence of the electron beams, an additional dynamic convergence coil is provided as a dynamic convergence means in addition to the deflection yoke for beam scanning. The additional dynamic convergence coil is supplied with a current in accordance with a beam position to correct or compensate for the beam deflection state. To this end, a waveform of a generally parabolic shape with horizontal and/or vertical scanning period repetition is used as the current supplied to the dynamic convergence coil. Thus, the plural electron beams are deflected by the beam deflection field of the dynamic convergence coil to be converged correctly at all of points on the screen.
In the prior art, it has been proposed that the current having a waveform of parabolic shape with a repetition which is the same as the horizontal scanning period and which is fed to the dynamic deflection coil be formed by a circuit in which a horizontal pulse appearing at an output transformer of the horizontal deflection circuit is integrated by a series connection of a coil and a capacitor. The voltage of sawtooth waveform obtained across the capacitor is then fed to the dynamic convergence coil so as to apply the current of parabolic shape waveform. Such a circuit, however, is required to provide means for deriving the horizontal pulse from the horizontal output transformer, means for integrating the thus obtained horizontal pulse, means for adjusting the integrated pulse in amplitude and so on, separately, so that the circuit becomes complicated in construction.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide an improved dynamic convergence circuit of reduced complexity for a plural beam color cathode ray tube.
Another object of this invention is to provide an improved dynamic convergence circuit which is simplified by being designed together with a horizontal deflection circuit.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of certain preferred embodiments of the invention, taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic circuit diagram showing one embodiment of a dynamic convergence circuit according to the present invention;
FIGS. 2 and 4 show waveforms used for explanation of the present invention; and
FIGS. 3, 5, 6 and 7 are schematic circuit diagrams respectively showing other embodiments of dynamic convergence circuits according to the present invention.
DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS
FIG. 1 is a circuit diagram for illustrating an embodiment of this invention. In the figure reference numeral 1 designates a horizontal driving circuit whose output terminal is connected to the base electrode of an NPN-type transistor 2 which forms a horizontal output circuit. The emitter electrode of the transistor 2 is grounded while its collector electrode is connected through a horizontal output winding 3 and a dynamic convergence coil 13 to an electric power source terminal 4 which is supplied with a DC voltage from an external source (not shown). The collector electrode of the transistor 2 is grounded through a parallel circuit of a damper diode 5 and a capacitor 6 and also through a series circuit of a horizontal deflection coil 7 and a deflection current wave compensation capacitor 8.The dynamic convergence coil 13 is connected in series between the power source terminal 4 and the end of the horizontal output winding 3 remote from the transistor 2. A series circuit of a capacitor 11 and a variable resistor 12 is connected in parallel with the dynamic convergence coil 13. A variable resistor 14 for correction of the amplitude of a parabolic waveform current is also connected in parallel with the dynamic convergence coil 13. In this case, the capacitance of the capacitor 11 may be selected, for example, as 0.022 micro-Farads (μF), the resistance value of the variable resistor 12 may be selected within a range of from 220 ohms (Ω ) to 500 ohms (Ω ) and the inductance value of the dynamic convergence coil 13 may be selected to be 14 milli-Henries (mH) to resonate with a signal with a frequency of 15.75 KHz.
As mentioned above, with the circuit shown in FIG. 1 the parabolic shape waveform current flows through the dynamic convergence coil 13 without the provision of a separately provided coil for integration, so that the circuit construction is simplified.
Further, according to this invention if the resistance value of the variable resistor 12 is adjusted the phase or tilt of the parabolic shape waveform current i c can be controlled as shown in FIG. 2 by a dotted line. If the resistance value of the variable resistor 14 is adjusted the amplitude of the parabolic shape waveform current i c for the dynamic convergence compensation is controlled. In this case, it should be noted that, it is possible to adjust the amplitude and the tilt of the parabolic shape waveform current independently, which is an advantage of this invention.
FIGS. 3 and 5, respectively show other embodiments of this invention in which horizontal and vertical convergence compensations are both performed. In these figures reference numerals similar to those of FIG. 1 designate similar elements so that their description is omitted for the sake of brevity.In the embodiment of FIG. 3, the collector electrode of the transistor 2 for the horizontal output circuit is connected directly to the power source terminal 4 and the parallel circuit of the damper diode 5 and capacitor 6 is connected between the collector and emitter electrodes of the transistor 2. The series circuit of the horizontal deflection coil 7 and capacitor 8 for deflection current wave compensation is also connected between the emitter and collector electrodes of the transistor 2. The emitter electrode of the transistor 2 is grounded through the series circuit of the horizontal output winding 3 and dynamic convergence coil 13. The connection point between the winding 3 and the coil 13 is grounded through the series circuit of the capacitor 11 and variable resistor 12 and also through the variable resistor 14. Thus, a parabolic shape waveform current flows through the horizontal dynamic convergence coil 13 in the same manner as in FIG. 1. The connection point between the horizontal output winding 3 and the dynamic convergence coil 13 is further connected to a coil 15, which servies as a horizontal frequency stopper, such that a parabolic shape waveform current with horizontal scanning period repetition is obtained at the coil 15 and is blocked from being applied to a point a.
In FIG. 3 reference numeral 16 indicates a vertical driving circuit whose output terminal is connected to base electrode of an NPN-type transistor 17. The collector electrode of the transistor 17 is connected through the base-collector junction of a transistor 18 to the base electrode of a transistor 21, which forms a SEPP-type output stage together with a transistor 20. The collector electrode of transistor 17 is also connected to the cathode of a diode 19 whose anode is connected to the base electrode of the transistor 20. The connection point between the emitter electrode of the transistor 20 and the collector electrode of the transistor 21 is connected to the emitter electrode of transistor 18 and through a series circuit of a vertical deflection coil 22, capacitors 23 and 24 to the emitter electrode of the transistor 17. A sawtooth waveform current flows through the vertical deflection coil 22 so that a parabolic shape waveform current with a vertical scanning period repetition is delivered to the connection point a between the two capacitors 23 and 24.
With the circuit shown in FIG. 3 a current i' c , in which the parabolic shape waveform current with the vertical scanning period repetition for vertical dynamic convergence compensation is superimposed on the parabolic shape waveform current with the horizontal scanning period repetition for horizontal dynamic convergence compensation is obtained as shown in FIG. 4 to perform both vertical and horizontal dynamic convergence compensation.
In the embodiment of FIG. 5 a parabolic shape waveform current with the vertical scanning period repetition is obtained at the emitter electrode of the transistor 21 as described above in reference to the embodiment of FIG. 3. The connection point between the horizontal output winding 3 and the horizontal dynamic convergence coil 13 is connected through the coil 15, serving as a horizontal frequency stopper, to the common connection point a' of the emitter electrode of the transistor 21, a resistor 25 and a capacitor 26. The connection point between the emitter electrode of the transistor 20 and the collector electrode of the transistor 21 is connected through the vertical deflection coil 22 to another electric power source terminal 4' which is supplied with a DC voltage. The other circuit elements are connected in a manner similar to FIG. 3. The embodiment of FIG. 5 operates to attain the same effect as that of the embodiment of FIG. 3.FIGS. 6 and 7, respectively show further embodiments of this invention in which reference numerals similar to those of the foregoing figures indicate similar elements. In these embodiments a pin-cushion compensation signal, which is applied to the horizontal deflection circuit for compensation of pin-cushion distortion of the raster, is used for vertical dynamic convergence.
In the embodiment constructed as above, the parabolic shape waveform current with the vertical scanning period repetition for pin-cushion compensation is applied to the base electrode of the transistor 28, which is connected in parallel to the dynamic convergence coil 13, through the input terminal 28a, so that a first parabolic shape waveform current with a vertical scanning period repetition such as, for example, shown in FIG. 4, flows through the dynamic convergence coil 13 where a second parabolic shape waveform current, with the horizontal scanning period, is superimposed on the first parabolic shape waveform current. Accordingly, it should be apparent that the vertical and horizontal convergence compensations are achieved by this embodiment as in the embodiments shown in FIGS. 3 and 5.
Since the parabolic shape waveform current with the vertical scanning period repetition for pin-cushion compensation is used in the embodiment of FIG. 6 as mentioned above, a separate circuit for producing the parabolic shape waveform current can be dispensed with.
The embodiment shown in FIG. 7 is similar to that shown in FIG. 6 except that the dynamic convergence circuit of FIG. 6 is connected to the power source side of the horizontal output transistor 2. It will be easily understood that this embodiment performs the same effect as that mentioned above.The terms and expressions which have been employed here are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions, of excluding equivalents of the features shown and described, or portions thereof, it being recognized that various modifications are possible within the scope of the invention claimed.
SONY TRINTRON Convergence means for color cathode ray tube
1. A convergence correction system for a color cathode ray tube comprising a fluorescent screen and means to produce three electron beams, said system comprising a deflection yoke to deflect said beams at line repetition rate in a raster pattern repeated at field repetition rate on said screen, and system further comprising:
static convergence correction means to cause said beams to be substantially fully converged to common points at certain outer regions of said screen and to be only partially converged at the central region of said screen; and
magnetic, dynamic, convergence correction means comprising a coil and current-generating means connected thereto to supply to said coil a magnetic convergence correction current that has a repetitive waveform with a maximum magnitude when said beams strike the central region of said screen and a lesser magnitude when said beams are deflected to strike said certain outer regions of said screen to cause said coil to produce a magnetic convergence field of greatest intensity when said beams strike said central region, whereby said beams are substantially fully converged at said central region.
2. The convergence correction system of claim 1 in which said static convergence correction means comprises:electrostatic deflection means within said tube and positioned therein between said means to produce said beams and the location of said deflection means; and
substantially constant voltage means connected to said electrostatic deflection means to apply thereto deflection voltages of magnitudes sufficient to cause said beams to converge to common points at the outer region of said raster pattern and less than sufficient to cause said beams to converge to a common point at the center of said raster pattern.
3. The convergence correction system of claim 1 in which said vurrent-generating means comprises means to generate a correction current in which said repetitive waveform comprises parabolic segments of substantially equal amplitude and the same repetition rate as said line repetition rate. 4. The convergence correction system of claim 3 in which said current-generating means generates a current having second substantially parabolic waveform segments at a repetition rate equal to the field repetition rate of said raster, said first-named correction current and said second current being connected additively to said magnetic dynamic convergence correction means and the additive value of said first-named current and said second current being substantially equal to zero when said beams are deflected substantially to the corners of said raster. 5. A convergence correction system for a color cathode ray tube comprising a fluorescent screen and means to produce three electron beams directed generally toward said screen, said system comprising a magnetic deflection yoke located on said tube in a region between said means to produce said beams and said screen to deflect said beams in a raster pattern on said screen in response to deflection currents applied to said deflection yoke, said deflection yoke producing an electron lens with a strength that is a function of the deflection current and is substantially zero at the center of said raster, said system further comprising:electrostatic static convergence deflection plates in said tube in a region between said means to produce said beams and said region on which said deflection yoke is located, said deflection plates having a fixed voltage applied thereto to produce a static convergence field to converge said beams in combination with the focusing effect of said yoke when said beams are deflected by said yoke to the outermost parts of said raster;
magnetic dynamic convergence means defining a lens field and comprising a coil; and
means to generate a convergence correction current to be applied to said coil to cause said magnetic dynamic convergence means to produce a magnetic electron lens having different horizontal and vertical strengths, the magnitudes of said strengths being a function of the magnitude of said current and varying from substantially zero when said beams are deflected to the outermost parts of said raster to a maximum when said beams are not deflected from the center of said raster, whereby said beams are converged at the center of said raster by the combined effects of said statis convergence field and said lens field of said magnetic dynamic convergence means when said deflection current in said yoke is substantially zero.
6. A convergence correction system for a color cathode ray tube comprising a fluorescent screen and means to produce three electron beams, sais system comprising a deflection yoke to produce a deflection field to deflect all of said beams simultaneously in a rectangular raster pattern comprising a plurality of substantially parallel lines generated on said screen at line repetition rate, said system further comprising:static convergence means to produce, in cooperation with the deflection field of said yoke, a convergence field to cause said beams to be substantially fully converged to common points only when said beams are deflected to outer regions of said raster pattern;
magnetic dynamic convergence correction means comprising a coil and current generating means connected thereto to supply to said coul a convergence correction current comprising a parabolic waveform repetitive at said line repetition rate, said current having a maximum magnitude when said beams are directed to the central region of said screen and substantially zero magnitude when said beams are deflected to said outer regions of said raster pattern.
7. The method of correcting convergence of electron beams on a color cathode ray tube screen, said method comprising the steps of:statically converging the beams near outer regions of the screen; and
imposing additional dynamic magnetic convergence fields on selective ones of said beams, said dynamic magnetic convergence fields having maximum intensity when the beams are in the central region of the screen to converge the beams in said central region.
8. The method of correcting convergence of a plurality of electron beams disposed in spaced relation substantially in a common plane and deflected along a series of lines defining a rectangular raster, said lines being substantially parallel to said plane and being the points of interception of said beams with a cathode ray tube screen, said method comprising:statically deflecting said beams selectively parallel to said plane to cause all of said beams to converge at the corners of said raster; and
selectively imposing on said beams dynamic magnetic convergence fields having maximum intensity when the beams strike the central region of the raster, said dynamic convergence fields applying converging force to said beams in a direction parallel to said plane and substantially perpendicular to said beams.
9. The method of claim 8 in which said dynamic, magnetic, convergence fields have minimum intensity when beams are deflected to each end of each of said lines. 10. The method of claim 8 in which said dynamic magnetic convergence fields have minimum intensity only when said beams are deflected to the corners of said raster.BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to convergence correction apparatus for color cathode ray tubes and particularly to apparatus that includes static and dynamic convergence correcting devices, at least the latter of which is a magnetic correcting device.
2. Description of the Prior Art
It has been the practice heretofore to provide proper focusing and convergence of the electron beams of a color cathode ray tube at the center of the screen when the magnetic deflection fields are not present and therefore are not contributing to any distortion of the beam or to any misconvergence. However, as the beams are deflected away from the center of the screen and particularly at the most distant locations in the four corners of the screen, the beams are subjected to magnetic fields and in some cases to electrostatic fields that cause the beams to strike different locations instead of being converged to a small area and further cause the cross sections of the beams to be distorted. Both of these effects cause the quality of the image to be deteriorated at the corners of the picture.
In addition, the change of beam size due to distortion affects the current density. Steps taken to correct the misconvergence at the corners still may leave the current density uncorrected. Since the luminance of the different phosphors is relatively linear only up to a certain maximum amount and is then saturated, and the point of saturation is different for the different phosphors, the hue of the image will be incorrect at the corners due to the fact that one of the phosphors will start to saturate first.
OBJECTS AND SUMMARY OF THE INVENTION
It is one of the objects of this invention to provide a simpler and better convergence arrangement for a color cathode ray tube.
Another object is to provide more uniform color balance over the entire cathode ray tube screen.
A further object is to provide improved convergence of the beams of a multibeam color cathode ray tube without producing high distortion of the beams.
Further objects will become apparent from the following description including the drawings.
In accordance with this invention a multibeam color cathode ray tube, particularly a tube of the general type shown and described in U.S. Pat. No. Re 27,751, has a static convergence correction device, such as a set of electrostatic deflection plates with applied voltages of the magnitude to cause static convergence of the beams at the corners of the cathode ray tube. The result is misconvergence at the center. However, the misconvergence at the center is corrected by a dynamic correction device that causes the beams to converge at a time when the beams are not also being subjected to the magnetic deflection fields.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified cross sectional view of the electron gun region and part of the convergence and deflection coils of a color cathode ray tube.
FIG. 2 illustrates the relationship between the dynamic convergence apparatus and the electron beams in the device in FIG. 1 when operated according to the prior art.
FIGS. 3 and 4 illustrate two types of misconvergence of electron beams on a cathode ray tube screen in a tube of the type represented in FIG. 1.
FIG. 5 is a waveform of correction current applied to the dynamic correction device in FIG. 1 according to the prior art.
FIG. 6 is a waveform of a modified correction current to correct for the misconvergence shown in FIG. 4.
FIG. 7 illustrates the proper cross sectional shape of an electron beam in a tube of the type shown in FIG. 1.
FIG. 8 shows a typical distortion of the cross sectional shape of the beam in FIG. 7.
FIG. 9 shows a beam pattern similar to that in FIG. 3 but with static correction applied according to the present invention.
FIG. 10 shows a beam pattern corresponding to that in FIG. 4 but with proper static convergence according to the present invention.
FIG. 11 is a waveform of dynamic convergence correction current to effect convergence of the beams having the type of misconvergence shown in FIG. 9.
FIG. 12 is a waveform of the current applied to a dynamic convergence correction device according to the present invention to correct misconvergence of the type illustrated in FIG. 10.
FIG. 13 is a graph of luminance versus beam current for different phosphors .
DETAILED DESCRIPTION OF THE EMBODIMENTS
The cathode ray tube in FIG. 1 includes means for forming three electron beams. In the embodiment illustrated the tube is provided with three cathodes K R , K G and K B as the origin of the three beams. The cathodes are supported by insulating means within a control grid G 1 that has appropriately spaced apertures for the three beams. In front of, and spaced slightly from, the first grid is a second grid G 2 that also has appropriately spaced apertures. Beyond the second grid G 2 , that is, to the right of that grid as shown in FIG. 1, is the beam focusing structure that includes a three-element electron lens consisting of three generally cylindrical electrodes identified as G 3 , G 4 and G 5 . Commonly electrodes G 3 and G 5 are directly electrically connected together and are operated at or close to the most positive voltage of the tube.
Beyond the electrode G 5 is an electrostatic convergence structure 1 comprising an inner pair of deflection plates 2 and 3 juxtaposed, respectively, with a pair of outer deflection plates 4 and 5. The plates 2 and 3 are electrically connected together to a voltage terminal E b and the plates 4 and 5 are electrically connected together to a terminal E c .
External to the tube in FIG. 1 are an electromagnetic convergence device 6 and part of a deflection yoke 7. The latter is arranged to deflect the electron beams, for the most part, after they have been subjected to convergence forces by the structure 1 and the structure 6.
The cathodes K R , K G and K B are preferably located in the same plane, which may be considered to be the plane of the drawing. The cathode K G is at the center at the axis of the tube and the other two cathodes are parallel to the cathode K G and equally spaced from it on opposite sides. The beams originally emitted from the cathodes are substantially parallel until they reach a lens identified as L S , formed generally by electrostatic fields in the region between the second grid G 2 and the anode, or third grid, G 3 . This lens is commonly called an auxiliary lens. The focal length of the auxiliary lens is such that it causes the three beams to intersect in the lens region L M approximately centrally located in the three-element lens formed by the electrodes G 3 -G 5 . As is now well known, this permits the three beams identified as R, G and B to be focused by nearly the same electrostatic field in the three-electrode lens so as to minimize distortion of the spots produced by the electron beams at the screen (not shown). After passing through the lens field L M and being focused thereby (an action which is not illustrated), the beams diverge along continuations of the lines by which they entered the lens field L M . The beam that will eventually strike green phosphor elements and is therefore identified by the reference character G, continues along the tube axis midway between the deflection plates 2 and 3. Since these plates are at the same voltage, the beam G is not substantially affected by the voltage on those plates. The beam B passes between the plates 2 and 4 and the beam R passes between the plates 3 and 5. Since these beams originate at points that are symmetrically displaced with respect to the beam G, and since the deflection plates of the structure 1 are also substantially symmetrically arranged, voltages applied to the terminals E b and E c deflect the beams B and R to intersect the beam G once more at the region of the screen of the cathode ray tube. In accordance with prior technology, if the screen has a 22 inch size, the voltage E b , which is considered the anode voltage of the tube, is approximately 1300 volts higher than the voltage E c . This voltage brings the three beams together at the center of the cathode ray screen and is referred to as the static convergence correction condition. It is illustrated in either FIG. 3 or FIG. 4 by the single dot at the center of the screen S of those two figures.
The dynamic convergence correction device 6 is located at substantially the same point on the Z-axis of the cathode ray tube as the static convergence correction device 1. As shown in FIG. 2, the dynamic convergence correction device 6 comprises two U-shaped magnetic cores 8 and 9. A coil 10 is wound on the core 8 and a similar core 11 is wound on the core 9. The coils are connected in series and are polarized so that the current of a given polarity following through them will produce magnetic fields in the cores 8 and 9 to result in north and south magnetic poles N and S as illustrated in FIG. 2. The direction of flux across the poles of the core 8 and across the poles of the core 9 is indicated by the reference character H 1 . Flux between the upper ends of the cores 8 and 9 and between the lower ends of these cores is denoted by reference character H 2 . The arrangement of the cores 8 and 9 is called a four-pole construction. The forces produced by magnetic fields of the cores 8 and 9 acting on electron beams B, G and R are indicated as the forces F 1 and F 2 . The force F 1 is produced by the flux H 1 and the force F 2 is produced by the flux H 2 . In the simplified representation in FIG. 2, these forces are illustrated as being substantially perpendicular to the respective magnetic fields that cause them, and the combined effect of these forces is to flatten the beams vertically and to spread them apart horizontally.
The beam pattern produced on the screen S of a cathode ray tube in accordance with the prior art is indicated in FIG. 3. At the center of the screen S, the three beams are caused to converge to a single dot by electrostatic fields on the deflection plates 2-5. These plates are not illustrated in FIG. 2, but would be located in a manner consistent with the cross sectional view illustrated in FIG. 1 so that the electrostatic fields acting upon the beams B and R would both be horizontally inward in FIG. 2 to cause them to intersect at the center of the screen S in FIG. 3. The type of misconvergence illustrated in FIG. 3 varies only horizontally and not vertically and, in accordance with the teachings of the prior art, has heretofore been corrected by applying a parabolic current of the type shown in FIG. 5 to the coils 10 and 11 in the dynamic convergence correction structure 6 in FIG. 2. This parabolic current has a periodicity of 1H corresponding to the horizontal deflection frequency.
FIG. 4 shows another typical misconvergence pattern, and FIG. 6 shows the prior art convergence correction current applied to the coils 10 and 11 in FIG. 2. The misconvergence illustrated in FIG. 4 has both a horizontal and a vertical component and therefore the correction current waveform in FIG. 6 includes a parabolic horizontal component 1H and a parabolic vertical component 1V. The combined currents reach a maximum when the beams are deflected to the four corners of the screen S.
FIG. 7 represents the cross section of any one of the beams R, B or G when the current flowing through the dynamic convergence correction structure 6 in FIG. 2 is zero under the conditions of the prior art. That is, the correction current applied to the coils 10 and 11 in the structure 6 is zero and the beams are not deflected from the center of the screen S. However, when the beams are deflected toward the corners under the conditions of the prior art, which requires that the current through the coils 10 and 11 be at the peak values shown in FIG. 5 to correct the type of misconvergence in FIG. 3 or at the peak values shown in FIG. 6 to correct the type of misconvergence in FIG. 4, the beams are flattened as illustrated in FIG. 8. This is due to the force F 1 pulling the electron beams horizontally so as to spread them apart and the force F 2 compressing the beams vertically. This distortion of the beams adversely affects the quality of the television picture, mainly by adversely affecting the focus of the beams at the outer part of the screen.
The present invention overcomes the disadvantage of the prior art by changing the convergence correction fields. In accordance with the present invention, an anode voltage E b supplied to the inner deflection plates 2 and 3 of the static convergence device 1 and the convergence voltage E c applied to the outer deflection plates 4 and 5 are more nearly at the same level than in the prior art. For example, the difference between the voltage E b c may be lower, thus creating a different convergent lens than the prior art. This can be accomplished by making the voltage E c only about 1100 volts lower than the anode voltage E b for a 22 inch color cathode ray tube instead of 1300 volts in accordance with the prior art. This causes the beams to be properly converged at the outer sides of the screen S in the case of a cathode ray tube having a misconvergence only in the horizontal direction as shown in FIG. 9. The dynamic correction current applied to the coils 10 and 11 from a source 12 is of the type shown in FIG. 11, which has the same parabolic waveform shown in FIG. 5 but which reaches zero value when the electron beams are deflected to the edges of the screen. This parabolic current has a negative value that reaches a maximum value when the beams are at the center of each horizontal line, and little or no dynamic convergence force is applied by the magnetic field when the beams are at the ends of each line. and the voltage E
In the case of a tube having both horizontal and vertical components of misconvergence, the reduction in the voltage difference between the inner deflection plates 2 and 3 and the outer deflection plates 4 and 5 eliminates misconvergence at the corners of the screen S as shown in FIG. 10. The correction current applied to the coils 10 and 11 from a source 12 must be of the type illustrated in FIG. 12. This current has the same waveform as the correction current shown in FIG. 6 but reaches zero value at the corners of the screen and a maximum negative value at the center of the middle line of the raster.
The current values required for dynamic convergence correction in accordance with this invention and as illustrated in FIGS. 11 and 12 do not necessarily have the same magnitudes as the current values in FIGS. 5 and 6. When the beams are in the exact center of the screen, they are not subjected to any deflection fields, which, when present, have not only a deflecting effect but a focusing effect that is a function of the deflection current and of the configuration of the deflection yoke 7. As a result dynamic convergence current may be less than in the case of the maximum dynamic convergence current in FIGS. 5 or 6. The magnetic field produced in the structure 6 in FIG. 2 is, in effect, a magnetic lens that has unequal horizontal and vertical effects on the beams. In the case of the present invention, this lens has maximum power due to maximum current when the beams are at the center of the screen and are thus not subjected to the combined lens and prism effects of the deflection yoke 7 shown in FIG. 1. As a result the beams B, G and R are not distorted in the manner shown in FIG. 8 or at least are distorted less than under the conditions of the prior art. This produces a picture of relatively uniform high resolution, not only at the outer part of the screen, but in the central region.
FIG. 13 shows the relationship between luminance and beam current for three typical phosphors used in color cathode ray tubes. For low beam currents the luminance of all three phosphors varies substantially linearly with the beam current. At a certain beam current the green phosphor begins to saturate so that additional current does not produce a corresponding additional green luminance. In the absence of any correcting circuits, if the beam current extends to a high enough value for all three phosphors so that the green phosphor is saturated, an image of a white object would take on a magenta hue due to an excess of red and blue light with respect to the green.
When the convergence correction device 6 is used in accordance with the prior art, maximum distortion of the beam spots occurs at the outer parts of the screen S. The beam distortion concentrates the beams at the outer parts of the screen and thus produces the effect of excess beam current, even if the current remains constant. The reason is that the constant current is concentrated into a smaller area by the distortion and thus the phosphor elements are subjected to increased current density. This produces the same adverse effect on hue as if the current had simply been increased without beam distortion.
By correcting the beam convergence according to the present invention, there is relatively little distortion of the beams at any part of the screen S and thus there is less tendency to have a high density that will adversely effect the color balance.
SONY TRINITRON E/W Pincushion distortion correction apparatus CIRCUIT:
A pincushion distortion correction saturable reactor is a saturable transformer comprising a core having four legs, controlled and control coils being coupled to the core legs in a perpendicular relation to each other. The core gap for the controlled coil is provided in an unbalanced form, and a parabolic current at the vertical scanning frequency (or at horizontal scanning frequency) containing a superimposed DC component is supplied through the control coil to modulate the inductance of the controlled coil. The inductance of the controlled coil is thus reduced in a region where the magnetomotive force produced by the control coil is greater than that produced by the control coil to preclude deflectional distortion in the neighborhood of the center of the reproduction on the screen and improve the horizontal linearity.
1. A pincushion distortion correction apparatus for television receivers comprising;
a saturable transformer including a ferromagnetic core forming a cubic magnetic loop path structure, said ferromagnetic core consisting of two ferromagnetic core pieces having four legs and two common portions, a controlled winding wound on the first and second ones of said four legs of the core, a control winding wound on the second and third ones of said four legs of the core, and a space gap means provided between said two ferromagnetic core pieces;
a deflection coil being connected in series with said controlled winding; and
a signal source for supplying a control parabolic signal to said control winding.
2. A pincushion distortion correction apparatus according to claim 1, wherein said two pieces constituting ferromagnetic core have respectively four legs and a common portion, and said space gap means is provided between the first and second legs of said two pieces of cores. 3. A pincushion distortion correction apparatus according to claim 1, wherein one piece of said ferromagnetic core has four legs and a common portion and the other core is a ferromagnetic core plate, and also wherein said space gap means is provided between the top of the first and second legs of said one core and said core plate. 4. A pincushion distortion correction apparatus for television receivers comprising;a saturable transformer including a ferromagnetic core forming a cubic magnetic loop structure, said ferromagnetic core consisting of two core pieces and, said cubic magnetic loop having four magnetic legs and two common portions, a horizontal winding wound on the first and second legs of the core, a vertical winding wound on the second and third legs of the core, and a space gap means provided between said first and second legs of one of the ferromagnetic core pieces and the other core piece;
a horizontal deflection coil connected in series with said horizontal winding; and
a signal source for supplying a vertical parabolic signal to said vertical winding.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to pincushion distortion correction apparatus and, more particularly, to an apparatus to this end having a control coil and a controlled coil, these coils being coupled to a saturable magnetic core in a perpendicular relation to each other.
2. Description of the Prior Art
A prior-art saturable reactor apparatus for correcting pincushion distortion in a television receiver has a construction as shown in FIG. 1.
In the pincushion distortion correction transformer 21 shown in FIG. 1, saturable E and I type cores 22 and 23 are held in face to face relationship to each other with a predetermined gap l g provided between them, a control coil 27 is wound on a central leg 24 A of the E type core 22, and first and second controlled coils 28 B and 28 C are wound on the respective opposite end legs 24 B and 24 C of the same core such that they operate differentially with respect to each other. For correcting horizontal pincushion distortions, a parabolic current changing at the vertical scanning frequency is caused through the control coil 27 to modulate the horizontal deflecting current flowing through the controlled coils 28 B and 28 C , thus obtaining a correction such that the horizontal deflection current becomes maximum at the center of the vertical scanning portion. The inductance L H of the transformer 21 is given as ##EQU1## where N H1 and N H2 are respectively turns numbers of the first and second controlled coils 28 B and 28 C (N H1 =N H2 ), l is the average length of the magnetic path, S is the sectional area of the core, and μ e is the effective magnetic permeability while μO is the magnetic permeability of a vacuum.
FIG. 2 shows a pincushion distortion correction transformer disclosed in a earlier patent application filed by the same applicant, and it is mentioned here for the purpose of faccilitating the understanding of the present invention. In this transformer 31, a control coil 37 and a controlled coil 38 are wound in a perpendicular relation to each other on legs 34 and 35 of a pair of four leg cores 32 and 33. The core 32 has a square or rectangular plate-like base portion 34 E and four legs 34 A to 34 D extending from the four corners of the base portion. The four legs have equal sectional area. Likewise, the core 33 has a base portion 35 E and four legs 35 A to 35 D . In FIG. 2, the legs 34 D and 35 D are concealed and not shown. The cores 32 and 33 having this construction are held such that the ends of the legs 34 A to 34 D of the former are respectively brought into contact with the corresponding legs 35 A to 35 D of the latter through predetermined gaps to define a constant space l g . The control coil 37 is wound on the legs 34 B and 34 D of the core 32 as a set, and the controlled coil 38 is wound on the legs 35 A and 35 B of the core 33 as a set. The inductance of this perpendicular transformer 31 is given as ##EQU2## N H in equation (2) is the turns number of the controlled coil 38 having almost half the turns of FIG. 1, and this means that for the example in FIG. 2 substantially the same variable inductance characteristic can be obtained with one half the turns number compared with the prior-art example of FIG. 1.
However, these pincushion distortion correction saturable reactor apparatus shown in FIGS. 1 and 2, have disadvantages; for example, raster shrinkage occurs in the neighborhood of the center of the screen, and the horizontal linearity is inferior.
FIG. 3 is a graph showing the variable inductance characteristic of the perpendicular transformer 31 shown in FIG. 2. In this graph, the abscissa represents the horizontal deflecting current I H (in A), and the ordinate represents the inductance L H (in μH). The vertical deflecting current I V (in mA) is taken as the parameter, and characteristic curves for 0,10,20,40 mA respectively are shown. When the inductance characteristic is as shown in FIG. 3, the reproduction on the screen has a character as shown in FIG. 4. The reproduction shown in FIG. 4 is obtained when a reference pattern consisting of a plurality of uniformly spaced vertical lines is reproduced on the television screen after the horizontal pincushion distortion correction using the transformer 31 mentioned above. The ratio of the interline space in the reproduction of FIG. 4 with respect to the interline average space in the reference pattern (in %) is as shown in FIG. 5. It will be seen that the raster shrinkage is produced in the neighborhood of the center of the screen, particularly in a horizontal deflecting current region between from -1 to +1 A. Due to this shrinkage, the horizontal linearity is inferior. Therefore the dynamic range of the variable inductance defined by the DC superimposition characteristics thereof becomes narrow.
SUMMARY OF THE INVENTION
The present invention seeks to overcome the aforementioned drawback inherent in the prior art, and its object is to provide a pincushion distortion correction saturable reactor apparatus, which is simple in construction and can improve the variable inductance characteristic and preclude the distortion of deflection in the neighborhood of the center of the reproduction, thus permitting wide improvement of the horizontal linearity and extension of the DC superimposition variable inductance dynamic range.
In accordance with an aspect of present invention, the apparatus for correcting pincushion distortion comprises a core having a gap, a control coil and a controlled coil, the control and controlled coils being wound on the core in a perpendicular relation to each other, the gap having an unbalanced configuration in the path of magnetic flux produced by the controlled coil, the control coil supplying a parabolic current for pincushion distortion correction, and the controlled coil supplying a deflecting current to be corrected.
The above and other objects, features and advantages of the illustrated embodiments of the invention will appear from the description given below, which is to be read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing a prior art example.
FIGS. 2 through 5 illustrate information concerning a transformer, given for the purpose of facilitating the understanding of the present invention, and of which FIG. 2 is a perspective view of the transformer;
FIG. 3 is a graph showing the variable inductance characteristic in FIG. 1 or 2;
FIG. 4 is a plan view showing the reproduction on a television screen in example FIG. 1 or 2;
FIG. 5 is a graph showing the horizontal linearity;
FIGS. 6 and 7 show a first embodiment of the present invention, and of which FIG. 6 is a perspective view showing the apparatus before the assembly, and FIG. 7 is a perspective view showing the apparatus after the assembly.
FIGS. 8 through 13 show a second embodiment of the present invention, and of which FIG. 8 is a perspective view showing the apparatus before the assembly thereof, FIG. 9 is a perspective view showing the apparatus after assembly, FIG. 10 is a fragmentary perspective view of the apparatus for illustrating the operation thereof, FIG. 11 is a graph showing the variable inductance characteristic, FIG. 12 is a plan view showing the reproduction on a television screen, and FIG. 13 is a graph showing the horizontal linearity.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now, a preferred embodiment of the present invention will be described in conjunction with some preferred embodiments thereof with reference to the accompanying drawings.
FIGS. 6 and 7 show a first embodiment of the pincushion distortion correction saturable reactor apparatus 1 according to the present invention. FIG. 6 shows a perspective view of the apparatus before the assembly thereof, and FIG. 7 shows a perspective view of the apparatus after assembly. In these Figures, the apparatus comprises cores 2 and 3 having an identical shape and made of a ferrite material. The core 2 has a plate-like base portion 4 E , for instance having a square or rectangular shape, and four legs 4 A ,4 B ,4 C and 4 D perpendicularly projecting from the four corners of one side of the base portion and having an equal sectional area. Likewise, the other core 3 has a base portion 5 E and four leg portions 5 A ,5 B ,5 C and 5 D . These cores 2 and 3 are arranged such that the legs 4 A to 4 D of the former abut on the corresponding legs 5 A to 5 D of the latter. More particularly, an adjacent two of the four legs of the core 2, for instance legs 4 A and 4 B are coupled to the corresponding legs of the other core, for instance legs 5 A and 5 B via a spacer 6. Thus, the faces of the legs facing each other are inclined with respect to each other, and the gap is increased toward the reader. The thickness of the spacer 6 is set substantially to 2 l g , i.e., double the gap interval l g in the afore-mentioned prior-art construction. A control coil 7 is wound on a pair of legs, namely the leg 4 B of the core 2 in contact with the spacer 6 and the leg 4 D adjacent to the leg 4 B but not in contact with the spacer 6. A controlled coil 8 is wound on a pair of legs 5 A and 5 B of the other core 3 in contact with the spacer 6. Alternatively, the controlled coil 8 may be wound on pair legs 5 C and 5 D which are not in contact with the spacer 6. The magnetic flux produced by the current through the control coil 7 passes through a loop constituted by the legs 4 A and 5 A and legs 5 B and 4 B. The magnetic flux produced by the current through the controlled coil 8 passes through a loop constituted by the legs 4 A and 5 A and legs 5 C and 4 C . Since the facing faces of the individual pairs of legs constituting the path of magnetic flux set up by the controlled coil 8 are inclined due to the spacer 6 interposed between the legs 4 A and 5 A and also between the legs 4 B and 5 B , the gap between these facing surfaces is increased toward the reader in the FIG. 7, that is, the gap formed in the path of magnetic flux set up by the controlled coil 8 has an unbalanced form. In the afore-mentioned prior-art example (shown in FIG. 2), in which the facing surfaces of the individual pair legs are parallel, the gaps in the magnetic flux paths for both the control and controlled coils are balanced in form.
FIGS. 8 through 10 show a second embodiment of the present invention. In this embodiment of the pincushion distortion correction saturable reactor apparatus 11, a pair of cores 12 and 13 which have different shapes are used. The assembled form of the pincushion distortion saturable reactor apparatus 11 is practially the same as the apparatus of the first embodiment, but this embodiment is different from the first embodiment in the position, in which the core halves of the apparatus are coupled to each other, and the assembly can be more readily made.
More particularly, referring to FIGS. 8 and 10, the core 12 has a base portion 14 E , for instance having a square or rectangular shape, and four legs 14 A ,14 B ,14 C and 14 D perpendicularly projecting from the four corners of the base portion and somewhat a greater length (capable of accommodating two coils). The core 13, on the other hand, consists of a square or rectangular plate corresponding to the base portion of cores in the first embodiment.
These cores 12 and 13 are arranged such that they abut on each other with a spacer 6 provided in contact with two adjacent legs 14 A and 14 B of the core 12 to form a gap of an unbalanced form for the controlled coil 8. The coil 7 is wound on the set of legs 14 B and 14 D , and the controlled coil 8 is wound on a set of legs 14 A and 14 B in contact with the spacer 6. In this construction, the gap in the magnetic flux path for the controlled coil 8 varies for different portions of the facing surfaces and thus has an unbalanced form.
In the use of the first and second embodiments for the lateral pincushion distortion correction, parabolic current I V containing an appropriate DC bias is supplied to the control coil 7, and horizontal deflecting current I H is supplied to the controlled coil 8. In this case, the turns number N V of the control coil 7 is selected relatively large to reduce the exciting current I V so that a flux φ V within a saturating region is produced by the magnetizing force N V I V . For the control coil 8 a large diameter wire is used, and its turns number N H is set to a value necessary for obtaining the required variable inductance for the lateral pincushion distortion correction.
The first and second embodiments having the above constructions according to the present invention operate practically in the same way, so the operation of the second embodiment only will be described.
The flux φ V produced by the current I V through the control coil 7 passes through the leg 14 B , base portion 14 E and leg 14 A of the core 12 and the core 13 as shown by dashed arrows in FIG. 9. Also, although not shown, a flux is caused to pass through the leg 14 D , base portion 14 E and 14 C of the core 12 and core 13. On the other hand, the flux φ H produced by the current I H through the controlled coil 8 passes through a loop constituted by the leg 14 A , base portion 14 E and leg 14 C of the core 12 and the core 13 as shown by solid arrows in FIG. 9. These fluxes φ V and φ H do not link with each other, so that no induction voltage is produced. Thus, by causing a parabolic current at the vertical scanning frequency to flow through the control coil 7, the inductance of the controlled coil 8 can be varied to obtain the correction of the lateral pincushion distortion.
Now, the effects of the gap having the unbalanced form will be described. In a state when the magnetomotive force N V I V provided by the control coil 7 is less than the magnetomotive force N H I H provided by the controlled coil 8 (i.e., N V I V H I H ), the flux through the four legs 14 A to 14 D , and hence the magnetic permeability, is controlled by the magnetomotive force N H I H . Thus, in the neighborhood of the end faces of the legs 14 C and 14 D free from the spacer 6, the magnetic saturation in the core sets gradually in from the contact points of the legs 14 C and 14 D with the core 13, and substantially the similar variable inductance characteristic as that obtained with the balanced gap perpendicular transformer 31 shown in FIG. 2 can be obtained.
On the other hand, in a state when the magnetomotive force N V I V is greater than the magnetomotive force N H I H (i.e., N V I H >N H I H ), the saturation of the core in the neighborhood of the gaps defined by the end faces of the legs 14 C and 14 D is determined by the magnetomotive force N V I V . For the flux φ V , most flux flows in one loop through the legs 14 C and 14 D , because the other magnetic loop which includes the legs 14 A and 14 B has two wide gaps, therefore the magnetic reluctance of this loop is larger than that of the former. Therefore the large flux φ V concentrates at the contact points of the legs 14 C and 14 D . The concentration of flux makes the points saturate and, the saturated points act as the effective gaps. With the saturation in the neighborhood of the gaps defined by the legs 14 C and 14 D , the magnetic reluctance of the gaps is apparently increased. Also, the distance of the gap in the magnetic flux path for the controlled coil 8 is increased in the gaps defined by the legs 14 C and 14 D . The flux φ H and the apparent gap Δl g are shown in FIG. 10.
With the apparent increase of the magnetic reluctance (i.e., increase of the gap distance), the inductance is reduced to L H , which is expressed as ##EQU3## where l is the average length of magnetic path, S is the sectional area of the core, and μ e is the effective permeability, while μ O is the permeability of a vacuum.
FIG. 11 shows the variable inductance characteristics of the pincushion distortion correction saturable reactor apparatus having the above construction. In the graph of FIG. 11, the ordinate is taken as the variable inductance L H ' in μH, and the abscissa is taken as the horizontal deflecting current I H in A. Characteristic curves shown are obtained when the vertical parabolic current I V is respectively 0,10,20 and 40 mA. These characteristic curves have substantially M-shaped forms with the variable inductance L H , reduced in an I H range in the neighborhood of 0 corresponding to the central portion of the screen. Thus, in the reproduction, the deflectional distortion in the central portion of the television screen can be widely improved as shown in FIG. 12. FIG. 12 is similar to FIG. 4, showing the reproduction of a reference pattern consisting of uniformly spaced vertical lines. In this case, extremely improved horizontal linearity compared with that shown in FIG. 5 can be obtained as shown in FIG. 13. Also, the dynamic range for the control coil current I V and controlled coil current I H can be increased. Further, with the same outer case size and current I H , a larger CRT size correction is possible even with a reduced value of current I V . Furthermore, with the same amplitude of control current, a larger CRT where the horizontal deflecting current is higher is possible to correct.
The characteristics of the prior-art reactor apparatus of FIG. 1, as shown in FIGS. 3 through 5, and the characteristics of the reactor apparatus according to the present invention, as shown in FIGS. 11 through 13, are based upon data obtained from experiments using a 20-inch color television receiver with a deflection angle of 100 degrees for 10% pincushion distortion correction. The relevant conditions and performance are shown in table 1.
A signal source means S is indicated in FIG. 7 for supplying a control parabolic signal to the control winding 7, and a deflection coil means D is indicated in FIG. 7 as being connected in series with the controlled winding 8, for the sake of diagrammatic illustration.
| TABLE 1 |
| ______________________________________ |
| Present Item Invention Prior Art |
| ______________________________________ |
Core Data Gap 75μ (unbalanced) 38 (balanced) N V /N H (turns ratio) 1200 T /16 T 900 T /9 T + 9 T Outer dimensions 18 × 18 × 22 mm 19 × 21.5 × 30 mm of core Volume of core 4608 mm 3 9747 mm 3 Total weight 38.5 g 58.5 g Performance Horizontal linearity +1.4%.about.-2.7% +6.3%.about.-5.7% Controlled power 0.6 W 0.8 W Heat generation 20° C. 30° C. from core |
| ______________________________________ |
The data listed in Table 1 for the present invention are for the second embodiment. According to the present invention, the volume of the apparatus can be reduced to 0.58 times that of the prior-art apparatus. Also, the total weight can be reduced to 0.66 times that in the case of the prior art. Further, in the performance, the horizontal linearity can be improved, and the heat dissipation of the core can be reduced.
As has been described in the foregoing, with the pincushion distortion correction saturable reactor apparatus according to the present invention, which is a saturable transformer comprising a core having four legs and respective common portions (such as 4E, 5E, FIG. 7, and 13, 14E, FIG. 9), and controlled and control coils coupled to the core legs in a perpendicular relation to each other, the core gap for the controlled coil is provided in an unbalanced form, and a parabolic current at the vertical scanning frequency (or at horizontal scanning frequency) containing a superimposed DC component is caused, through the control coil, thus modulating the inductance of the controlled coil.
By the unbalance of the gap is meant that the gap distance varies with different portions of the facing surfaces defining the gap. This can be obtained by interposing a spacer between two of the four legs on which the controlled coil is wound as mentioned above or between the other two legs so that the surfaces forming the gap are inclined with respect to each other.
With this construction, the variable inductance is reduced in a region in which the magnetomotive force produced by the control coil is greater than that produced by the controlled coil and, as a whole, characteristic curves having M-shaped forms can be obtained. Thus, the deflectional distortion in the neighborhood of the center of the reproduction on the screen is reduced, so that horizontal linearity can be widely improved. In addition, the dynamic range of the variable inductance inclusive of the superimposed DC portion is extended, so that it is possible to obtain size reduction and wide cost reduction compared with the prior art. Further, it is possible to realize the reduction of heat dissipation of the core, reduction of the controlled power, reduction of the number of component parts connected to the transformer and also reduction of the area of the printed circuit board occupied by the transformer.
The above embodiments of the present invention are by no means limitative, and the invention may be applied to the top and bottom pincushion distortion correction as well. Also, various other changes and modifications are possible without departing from the scope and spirit of the present invention.
Side, or left and right pin-cushion distortions in the raster of a cathode ray tube, for example, of a color television receiver having an in-line arrangement of its electron beams, are corrected by connecting the horizontal deflection winding of the cathode ray tube, the collector-emitter path of a transistor and the output winding of a saturable reactor, in series, to a power supply source, and by applying to the base or control electrode of the transistor and to the input winding of the saturable reactor a correction signal having a parabolic waveform of the vertical scanning rate or frequency so that correction of the side pin-cushion distortions is effected satisfactorily at all portions of the raster.
1. A raster distortion correcting circuit for a television receiver including a cathode ray tube in which at least one electron beam is directed against a screen, a deflection yoke associated with said tube and having horizontal and vertical deflection windings, and horizontal and vertical deflection circuits for supplying horizontal and vertical deflection currents to said horizontal and vertical deflection windings, respectively, so that the resulting magnetic fields cause each said beam to scan horizontally and vertically for forming a raster on the screen: said raster distortion correcting circuit comprising a power supply source for supplying a power supply voltage to said horizontal deflection circuit; an active element having first and second electrodes and a control electrode for varying the effective resistance between said first and second electrodes in dependence on a control signal applied to said control electrode; a saturable reactor having input and output windings, means for generating a correction signal at the vertical scanning rate of said vertical deflection current; circuit means for connecting said first and second electrodes of the active element between said power supply source and said horizontal deflection circuit to connect said active element, said horizontal deflection winding of the yoke and said output winding of the saturable reactor in a series circuit connected to said power supply source; and circuit means for applying said correction signal to said control electrode of the active element as the control signal for the latter and to said input winding of said saturable reactor so that said active element and saturable reactor combine to correct a distortion of said raster over all portions of the latter. 2. A raster distortion correcting circuit according to claim 1; in which said correction signal is generated with a parabolic waveform at said vertical scanning rate for correcting side pin cushion distortions of said raster. 3. A raster distortion correcting circuit according to claim 1; in which said means for generating the correction signal includes a capacitor connected in series with said vertical deflection winding of the yoke, and said circuit means for applying said correction signal extends from between said vertical deflection winding and said capacitor. 4. A raster distortion correcting circuit according to claim 1; in which said active element is a transistor having collector, emitter and base electrodes which constitute said first, second and control electrodes, respectively. 5. A raster distortion correcting circuit according to claim 1; in which said horizontal deflection current is supplied from said horizontal deflection circuit to said series circuit at a location in the latter between said first and second electrodes of said active element and said horizontal deflection winding of the yoke. 6. In a horizontal deflection circuit for a cathode ray tube, including a horizontal deflection current output circuit for supplying horizontal deflection current to a horizontal deflection winding and a source of operating voltage adapted to be supplied to said output circuit, a raster distortion correcting circuit comprising a saturable reactor having an input winding to receive a correction signal whose frequency is equal to the vertical deflection frequency of said cathode ray tube, and an output winding connected in series with said horizontal deflection winding; an active element for supplying said operating voltage to said output circuit; and means for supplying said correction signal to said active element to thereby vary said operating voltage supplied to said output circuit as a function of said correction signal. 7. A raster distortion correcting circuit in accordance with claim 6 wherein said correction signal is generated with a parabolic waveform.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a raster distortion correcting circuit for a cathode ray tube, for example, of a color television receiver.
2. Description of the Prior Art
In a television receiver having a cathode ray tube, a deflection yoke is positioned about the neck of the cathode ray tube, and deflection circuits associated with such deflection yoke cyclically vary currents which are made to flow through windings of the yoke so that the windings generate varying electromagnetic fields by which each electron beam of the cathode ray tube is deflected vertically and horizontally to scan a respective raster on the screen of the cathode ray tube. In general, the raster formed by each electron beam is desired to be substantially rectangular. However, various types of scanning distortions may occur so as to cause the configuration of the generated raster to deviate from the desired rectangular shape. One of the types of raster distortions that may occur is the so-called "pin-cushion" distortion which may appear in respect to the top and bottom or left- and right-hand sides of the raster, and this invention is particularly concerned with providing corrections for the side, or left and right pin-cushion distortions.
Heretofore, such side, or left and right pin-cushion distortions in the raster of a cathode ray tube have been corrected by one or the other of several methods. One of the most frequently employed methods for achieving correction of side pin-cushion raster distortion involves varying or modulating the power supply voltage for the horizontal deflection circuit of the cathode ray tube in accordance with a parabolic wave having the vertical scanning rate or frequency. Another frequently employed method for achieving the foregoing raster correction involves the use of a saturable reactor having an output winding connected in series with the horizontal deflection winding of the yoke and an input winding to which there is applied a correction signal in the form of a parabolic wave having the vertical scanning rate or frequency so that the horizontal deflection current is again varied or modulated by such parabolic wave. Each of the foregoing methods that are frequently employed for correcting side, or left and right pin-cushion distortions in the raster of a cathode ray tube has its inherent advantages and disadvatages, as hereinafter described.
In the case where the power supply voltage for the horizontal deflection circuit is varied or modulated, as aforesaid, the horizontal deflection current I h flowing through the horizontal deflection winding of the yoke is expressed by the following equation: ##EQU1## in which V cc is the power supply voltage, L is the inductance value of the deflection winding, and t is time.
It will be apparent from the above equation that, when the power supply voltage V cc is varied or modulated in accordance with a correction signal having a parabolic waveform at the vertical scanning rate, the amplitude of the horizontal deflection current is varied in accordance with such parabolic waveform so that correction of side pin-cushion distortions in the raster is achieved. Such correction of side pin-cushion distortions in the raster is advantageous in that the circuit required therefor is very simple and inexpensive. However, with this method, the horizontal deflection current is varied only at the vertical scanning rate, and not within each horizontal or line scanning period, so that, if a single horizontal scanning line is considered, the same correction is effected adjacent the center and adjacent the opposite or left- and right-hand sides of the screen. The foregoing characteristic of the described method is disadvantageous, particularly when applied to a color cathode ray tube having a wide deflection angle, and the disadvantage, as hereinafter described, is most serious in the case of a color cathode ray tube having an electron gun structure with a so-called in-line arrangement of the plural electron beams issuing therefrom.
In a color cathode ray tube having an electron gun structure with an in-line arrangement of the plural electron beams issuing therefrom, it is desirable that the electromagnetic field for effecting horizontal deflection or scanning of the beams have a pin-cushion shape and that the electromagnetic field for effecting vertical deflection or scanning of the beams have a barrel shape, that is, that the horizontal and vertical deflection fields be non-uniform, so as to correct or compensate for misconvergence of the plural electron beams as the latter are deflected horizontally and vertically from the center of the screen, for example, as disclosed in U.S. Pat. No. 3,500,114, issued Mar. 10, 1970, and having a common assignee herewith. When such non-uniform deflection fields are employed so as to correct or compensate for misconvergence of the electron beams, it has been determined experimentally that correction of side pin-cushion distortions of the raster by means of varying the power supply voltage for the horizontal deflection circuit as mentioned above, is insufficient, particularly in respect to the extent of the correction effected at the central portion of each horizontal scanning line. Therefore, in the case being described, a side pin-cushion distortion may still remain adjacent the central portion of the raster.
On the other hand, when a saturable reactor is employed for correcting side pin-cushion distortions, as aforesaid, such distortions are fully eliminated even near the central portion of the raster by reason of the fact that the inductance value of the output winding of the saturable reactor is varied in response to the correction signal applied to the input winding of the reactor and having a parabolic waveform at the vertical scanning rate, and the inductance value of the output winding of the saturable reactor is also varied at the horizontal scanning rate in response to the horizontal deflection current flowing through such output winding. However, when the side pin-cushion distortions are corrected only by means of the described saturable reactor, the apparatus required for correction of side pin-cushion distortions becomes bulky, heavy and expensive, particularly when applied to a color cathode ray tube having a relatively large deflection angle. Further, when side pin-cushion distortions of the raster are corrected only by means of the described saturable reactor in the case of a color cathode ray tube having a relatively wide deflection angle, it has been found that the desired linearity of the horizontal deflection of the beam or beams if seriously deteriorated.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide an improved circuit for correcting side pin-cushion raster distortions which avoids the above mentioned disadvantages inherent in the arrangements previously employed for that purpose.
More specifically, it is an object of this invention to provide a side pin-cushion raster distortion correcting circuit which is relatively small in size and weight and also inexpensive, and which is effective to fully eliminate such distortions near the central portion of the raster as well as near the opposite sides thereof.
Another object is to provide an improved side pin-cushion raster distortion correcting circuit, as aforesaid, which is suitable for a color cathode ray tube with a relatively wide deflection angle.
Still another object is to provide an improved side pin-cushion raster distortion correcting circuit which is particularly adapted for use with a color cathode ray tube having an electron gun structure with a so-called in-line arrangement of the plural electron beams emitted thereby.
In accordance with an aspect of this invention, side pin-cushion distortions in the raster of a cathode ray tube are eliminated by varying or modulating the power supply voltage for the horizontal deflection circuit in accordance with a correction signal having a parabolic waveform at the vertical scanning rate, and by simultaneously applying such correction signal to the input winding of a saturable reactor which has its output winding connected in series with the horizontal deflection winding of the cathode ray tube. By reason of the foregoing arrangement, the horizontal deflection current is modulated in accordance with the parabolic waveform at the vertical scanning rate by the combined action of a transistor or other active element employed for varying or modulating the power supply voltage and of the saturable reactor, and the horizontal deflection current is further modulated in response to the flow of such current through the output winding of the saturable reactor which varies its inductance in accordance with the horizontal deflection current flowing therethrough.
The above, and other objects, features and advantages of the invention, will be apparent in the following detailed description of illustrative embodiments which is to be read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic view illustrating the side pin-cushion distortion that may remain near the central portion of the raster on the screen of a cathode ray tube when correction for the side pin-cushion distortion is effected only by varying or modulating the power supply voltage in accordance with a correction signal having a parabolic waveform at the vertical scanning rate;
FIG. 2 is a schematic elevational view of a saturable reactor that may be used in a raster distortion correcting circuit according to this invention;
FIG. 3 is a circuit diagram of a basic or simplified raster distortion correcting circuit in accordance with an embodiment of this invention;
FIGS. 4 and 5 are graphical representations of characteristics of the saturable reactor shown on FIG. 2; and
FIG. 6 is a circuit diagram showing a practical application of a raster distortion correcting circuit according to this invention in association with horizontal and vertical deflection circuits of a typical cathode ray tube.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings in detail, and initially to FIG. 1 thereof, it will be seen that, when side pin-cushion distortions in the raster of a cathode ray tube are sought to be corrected or removed only by the known method of varying or modulating the power supply voltage for the horizontal deflection circuit in accordance with a parabolic waveform at the vertical scanning rate, the distortion is not fully corrected or removed near the central portion of the raster. Generally, in accordance with this invention, the side pin-cushion distortion of the raster is, for the most part, removed or corrected by varying or modulating the power supply voltage of the horizontal deflection circuit in accordance with a parabolic waveform at the vertical scanning rate, while the side pin-cushion distortion which remains uncorrected near the central portion of the raster is corrected or removed by modulating the horizontal deflection current in accordance with the horizontal scanning rate. Generally, the horizontal deflection current is modulated or varied in accordance with the horizontal scanning rate for removing the side pin-cushion distortion remaining near the central portion of the raster by means of a saturable reactor 1 having its output winding connected in series with the horizontal deflection winding of the cathode ray tube so that the horizontal deflection current, in passing through the output winding of the saturable reactor, will vary the inductance value of such output winding in accordance with the horizontal scanning rate.
As shown on FIG. 2, the saturable reactor 1 employed in a raster distortion correcting circuit according to this invention may include an E-shaped core 2 and an I-shaped core 3 which are both formed of a magnetically saturable material, and which are arranged relative to each other so that core 3 extends across the free ends of the legs of core 2 with a small gap g therebetween. Saturable reactor 1 further is shown to include an output winding constituted by two windings Lh 1 and LH 2 which are respectively wound on the outer legs of core 2, and an input winding Lv wound on the central leg of core 2. The directions in which windings Lh 1 and Lh 2 are respectively wound on the outer legs of core 2 are selected so that, when such windings are connected in series to constitute the output winding, the compound magnetic fluxes generated by the windings Lh 1 and Lh 2 in the central leg of core 2 are effective to oppose or cancel each other. Since saturable reactors of the type shown on FIG. 2 are well known, the construction and operation thereof will not be further described. However, it may be noted that the satuable reactor 1 for use in a raster distortion correcting circuit according to this invention may, for example, have a length l of 20mm, 11 turns in each of windings Lh 1 and Lh 2 , 500 turns in input winding Lv, and a gap g between cores 2 and 3 of about 50 microns.
Referring now to FIG. 3 in which only the basic or essential components of a circuit according to this invention for correcting or compensating for side pin-cushion distortions of the raster are illustrated, it will be seen that, in such circuit, the windings Lh 1 and Lh 2 constituting the output winding of saturable reactor 1 are connected in series with the horizontal deflection winding or windings 4 of the deflection yoke of a cathode ray tube. A transistor 5, which forms the output of a horizontal deflection circuit, receives a horizontal driving signal at its base electrode, while the emitter electrode of transistor 5 is connected to ground. The collector electrode of transistor 5 is connected to ground through a parallel circuit of a damper diode 6 and a tuning capacitor 7, and further connected to ground through the series connection of horizontal deflection winding or windings 4, the output winding of saturable reactor 1 and a capacitor 8 which is provided to correct for S-letter distortions. In accordance wtih this invention, an active element 9, shown in the form of a transistor, has its collector-emitter path connected in series with the primary winding 10 of a horizontal output transformer (which is not otherwise illustrated) between a power supply source or terminal 11 to which a positive DC voltage +B is applied, and the collector electrode of transistor 5. The base electrode of transistor 9 is connected to a terminal 12 which receives a correction signal having a parabolic waveform of the vertical scanning rate or frequency, and which may be generated as hereinafter described in detail. Such correction signal having a parabolic waveform of the vertical scanning rate is also applied to input winding Lv of saturable reactor 1.
The raster distortion correcting circuit of FIG. 3 operates as follows:
The correction signal having a parabolic waveform of the vertical scanning rate, when applied to terminal 12, varies the conductance of the collector-emitter path of transistor 9 so that the voltage at the emitter electrode of transistor 9, that is, the power supply voltage for transistor 5 forming the output of the horizontal deflection circuit is varied in accordance with such parabolic waveform. Therefore, the amplitude of the horizontal deflection current attains maximum values during horizontal scanning across the center of the raster or screen, considered in the vertical direction, and is relatively reduced during horizontal scanning across the upper and lower edge portions of the screen so that a correction for side, or left and right pin-cushion distortion is effected.
While the above described correction is being effected by the operation of transistor 9, the correction signal having a parabolic waveform of the vertical scanning rate is being simultaneously applied to input winding Lv of saturable reactor 1 having its output winding Lh 1 , Lh 2 connected in series with horizontal deflection winding 4. As indicated by the line l 1 on FIG. 4, the compound inductance Lh of the windings Lh 1 and Lh 2 of saturable reactor 1 has a substantially linear relationship to a DC current Iv which flows through the control or input winding Lv of the saturable reactor. Of course, the value of the compound inductance Lh will become saturated when the current Iv reaches a sufficiently high value (not shown). Therefore, when a correction signal having a parabolic waveform, as indicated at Iv' on FIG. 4, is applied to input winding Lv with an appropriate DC voltage, the value of the compound inductance Lh of output windings Lh 1 and L h 2 undergoes a corresponding parabolic variation, as indicated at Lh' on FIG. 4. Since horizontal deflection winding 4 is connected in series with windings Lh 1 and Lh 2 of the saturable reactor, the horizontal deflection current Ih flowing through horizontal deflection winding 4 is also varied in accordance with the parabolic waveform of the correction signal applied to input winding Lv. Therefore, saturable reactor 1 also operates to provide a correction for a side or left and right pin-cushion distortion, which correction is added to that provided by the transistor 9, as previously described.
In the raster distortion correcting circuit according to this invention, the correction for side or left and right pin-cushion distortion is effected mainly by transistor 9, and only to a relatively smaller extent by saturable reactor 1. For example, from 70 to 80% of the required correction may be provided by the operation of transistor 9, while the remaining 30 to 20% of the required correction is provided by saturable reactor 1.
Referring again to FIG. 4, it will be apparent that the linear relationship between the compound inductance Lh of the output windings of saturable reactor 1 and the signal Iv applied to the input winding, as represented by the line l 1 , assumes that the current through windings Lh 1 and Lh 2 of the saturable reactor is constant. However, in the circuit according to this invention as shown on FIG. 3, the connection of windings Lh 1 and Lh 2 in series with horizontal deflection winding 4 causes the current through windings Lh 1 and Lh 2 to be equal to the horizontal deflection current Ih which, of course, varies at the horizontal scanning rate so that the Lh-Iv characteristic curve of the saturable reactor is also changed in accordance with the varying value or amplitude of the horizontal deflection current Ih. More specifically, when the horizontal deflection current Ih increases, the saturable reactor 1 is directed to a more saturated condition, so that the compound or total inductance L h decreases and the rate of change of the inductance Lh relative to the input current or signal Lv also decreases. For example, on FIG. 5, the lines l 2 , l 3 , l 4 and l 5 represent the Lh -Iv characteristics of the saturable reactor 1 for progressively increasing values of the horizontal deflection current Ih.
By reason of the foregoing, it will be apparent that the correction or compensation for side pin-cushion distortion provided by saturable reactor 1 is at its maximum when each electron beam is directed at the center of the screen, considered in the horizontal direction, and is relatively reduced when each electron beam is directed toward one or the other of the opposite side edges of the screen. Thus, the side pin-cushion distortion which remains near the central portion of the screen when the power supply voltage for the horizontal deflection circuit is varied in accordance with a parabolic waveform at the vertical scanning rate, as by the transistor 9, may be completely removed by suitably selecting the parabolic waveform and the DC voltage level of the signal Iv' applied to the input winding of saturable reactor 1.
From the foregoing, it will be apparent that, in accordance with the present invention, side pin-cushion distortions are removed by modulating the power supply voltage applied to the collector of transistor 5, as by transistor 9, in accordance with a parabolic waveform at the vertical scanning rate and by similarly modulating the input signal to the winding Lv of saturable reactor 1, while the side pin-cushion distortion near the central portion of the screen is corrected or removed by saturable reactor 1 by reason of the connection of its output winding Lh 1 , Lh 2 in series with the horizontal deflection winding 4.
In theory, the input winding Lv of saturable reactor 1 may have applied thereto merely an appropriate DC voltage, rather than the described correction signal having a parabolic waveform at the vertical scanning rate. In that case, transistor 9 of the circuit shown in FIG. 3 has to be relied upon to provide the full correction for side pin-cushion distortions, while saturable reactor 1 then operates only to correct the pin-cushion distortion which remains near the central portion of the screen or raster. However, it is preferred that the input winding Lv of saturable reactor 1 also receive the correction signal having a parabolic waveform, as explained above, so that the saturable reactor can also operate to provide at least a portion of the correction for the side pin-cushion distortion, and thereby relieve a portion of the load on transistor 9.
When saturable reactor 1 is employed to provide only a portion of the correction for side pin-cushion distortion and to remove the remaining distortion near the center of the screen or raster, as in accordance with this invention, such saturable reactor can be relatively small and light in weight. For example, it has been found that a saturable reactor having a length of 30mm and the other dimensions given above will operate satisfactorily to perform the stated functions in connection with a color cathode ray tube having a screen with a 17 inch diagonal dimension and a 114° deflection angle. On the other hand, if the side pin-cushion distortion for such a color cathode ray tube is to be corrected only by a saturable reactor, rather than by the latter in combination with the modulating transistor 9, as shown on FIG. 3, such saturable reactor would have to be substantially larger, for example, have a length of 50mm, and have a mass or weight that is approximately five times greater than the saturable reactor with a length of 30mm which may be used in accordance with this invention.
Referring now to FIG. 6 in which circuit elements corresponding to those described above with re
ference to FIG. 3 are identified by the same reference numerals, it will be seen that a raster distortion correcting circuit according to this invention is there shown associated with typical horizontal and vertical deflection circuits for a cathode ray tube. More specifically, on FIG. 6, the horizontal deflection circuit is shown to include an input terminal 13 which receives horizontal driving pulses, for example, from a horizontal oscillator (not shown), a horizontal driver transistor 14 having its base electrode connected to terminal 13, and a horizontal drive transformer 15 having its primary winding connected in series with the collector-emitter path of transistor 14 between a power supply terminal and ground. The secondary winding of transformer 15 is connected to the control electrode of a semiconductor device 16, for example, to the gate electrode of a GCS (gate controlled switch), as shown, which functions as a horizontal output switching device and corresponds to the transistor 5 on FIG. 3.
The typical vertical deflection circuit 17 illustrated on FIG. 6 is shown to include an input terminal 18 which receives a saw-tooth wave signal at the vertical scanning rate, that is, in synchronism with the vertical synchronizing signal, for example, from a vertical oscillator (not shown), and transistors 19A and 19B which are connected, as shown, to form a single ended, push-pull output amplifier. The vertical deflection winding 20 of the deflection yoke associated with the cathode ray tube and a charge-discharge capacitor 21 are connected in series between the emitter electrode of transistor 19A and ground so that the desired correction signal having a parabolic waveform at the vertical scanning rate is obtained across capacitor 21. Such correction signal is applied to the base electrode of transistor 9 by way of terminal 12 so that transistor 9 will correspondingly modulate the power supply voltage applied to the horizontal output switching device 16, and hence the horizontal deflection current supplied to horizontal deflection winding 4, in the same manner as in the circuit of FIG. 3. In the circuit of FIG. 6, a variable resistor 22 is provided for adjusting the DC bias voltage applied to the base electrode of transistor 9, and thereby controlling the width of the horizontal deflection.
The correction signal having a parabolic waveform obtained across capacitor 21 is also applied to the base electrode of a transistor 26 through a variable resistor 23 and capacitor 24, with the variable resistor 23 serving to control the amplitude of the parabolic waveform as applied to the base electrode of transistor 26. A variable resistor 25 is connected in the base circuit of transistor 26 for adjusting the DC voltage or level of the correction signal having a parabolic waveform as applied to the input winding Lv of saturable reactor 1. A variable resistor 27 and a capacitor 28 are connected in series between the movable tap of variable resistor 23 and the ground so as to form a wave-shaping circuit for the correction signal having a parabolic waveform.
The input winding Lv of the saturable reactor 1 is connected in the collector circuit of transistor 26 so as to receive the correction signal with a parabolic waveform, as adjusted by the elements 23-25, 27 and 28. The output winding Lh 1 , Lh 2 of saturable reactor 1 is connected in series with the horizontal deflection winding 4 and with a coil 29 which is provided to achieve horizontal linearity compensation.
Although the circuit according to this invention for correcting side pin-cushion distortions is shown on FIG. 6 in association with typical horizontal and vertical deflection circuits of a cathode ray tube, which circuits do not appear on FIG. 3, it will be understood that the raster distortion correcting circuit according to this invention, as shown on FIG. 6, operates in the same manner as has been described above with reference to FIG. 3.
Having described specific embodiments of the present invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.
(AFC) Automatic frequency control circuit:
An automatic frequency control (AFC) circuit is disclosed which comprises an oscillating circuit
for generating repetitive pulses, a generator for generating comparison signals having a slope portion in response to the repetitive pulses, and a phase comparison circuit which compares the comparison signals, and synchronous (sync) signals and based on the comparison supplies control signals to the oscillating circuit. The AF circuit further comprises a limiting circuit connected between the comparison signal generator and the phase comparison circuit which limits the maximum and minimum levels of the comparison signals to predetermined levels, and thereby predeterminedly limits the control range of the AFC circuit.
1. An automatic frequency control signal generating circuit, comprising:
an oscillating circuit for generating repetitive pulses;
means for receiving said repetitive pulses and generating comparison signals having sloped portions and maximum and minimum levels in response to said repetitive pulses;
a source of reference signals;
phase comparison means having a first input terminal supplied with said comparison signals, a second input terminal supplied with said reference signals and an output terminal for supplying automatic frequency control signals to said oscillating circuit for controlling its frequency within a control range; and
limiting means connected between said comparison signal generating means and said phase comparison means for limiting said maximum level and said minimum level of said comparison signals to first and second predetermined levels respectively, thereby limiting said control range of said automatic frequency control signal generating circuit to a predetermined range.
2. An automatic frequency control signal generating circuit according to claim 1; wherein said comparison signal generating means comprises integrating means for generating saw-tooth wave signals as said comparison signals in response to said repetitive pulses. 3. An automatic frequency control signal generating circuit according to claim 1; wherein said limiting means comprises a series circuit including sources of first and second reference potentials, first and second diodes connected together and respectively connected to said first reference potential and said second reference potential, the connecting point of said first and second diodes being connected to an output terminal of said comparison signal generating means. 4. An automatic frequency control signal generating circuit for a television receiver, comprising;a source of reference signals;
an oscillator for generating control pulses;
an output circuit for producing repetitive pulses in response to said control pulses;
an integrating circuit for generating saw-tooth wave signals having maximum and miniumum levels in response to said repetitive pulses from said output circuit;
a phase comparator for comparing the phase of said saw-tooth waves and the phase of said reference signals, and supplying output signals to said oscillator as automatic frequency control signals; and
an amplitude limiting circuit connected between said integrating circuit and said phase comparator, for limiting said maximum and minimum levels of said saw-tooth wave signals to first and second predetermined levels.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an automatic frequency control (AFC) circuit and more particularly to an AFC circuit, preferably is used in a television receiver, which has a predeterminedly limited control range.
2. Description of the Prior Art
I
n a prior art horizontal AFC circuit of a television receiver, as shown in FIG. 1, the output from a horizontal oscillator 1 which can be, for example, a control pulse is supplied to a horizontal output circuit 2 and a flyback pulse therefrom is fed to a saw-tooth wave generator 3. Though not shown, the horizontal output circuit 2 comprises a deflection circuit and a high voltage generating circuit. The saw-tooth wave signal from saw-tooth wave generator 3 is supplied, as a comparison signal, to a phase comparator 4 which is also supplied with a horizontal synchronizing (sync) signal H through a terminal 5. In phase comparator 4 the saw-tooth wave signal is compared with the horizontal sync signal H to detect the phase difference between the saw-tooth wave signal and the horizontal sync signal. The detected phase difference is applied to horizontal oscillator 1 as an AFC voltage e c . As shown in FIG. 2, when the horizontal sync signal H is coincident with the center φ 0 of the downward sloping portions of the comparison signal, that is, when the phase difference between the comparison and sync signals is 0 (zero), the synchronization is maintained for phase differences of which corresponds to the ends of the downward sloping portion of the comparison signal. For phase differences of ±φ cm , the AFC output voltage e c has a maximum value of ±e cm .
If the AFC control sensitivity is taken as β, the maximum frequency range within which the f cm oscillating frequencies are controlled, hereinafter referred to as the control range, is: f cm =±2πβe cm
When the value of e cm in the above formula is need constant, regardless of frequency variation, then the value of f cm is constant.
Generally, the comparison signal, which is supplied by saw-tooth wave generator 3, is provided by integrating the flyback pulse. Both the width of the flyback pulse, which is determined by an LC resonance of horizontal output circuit, and the inclination of the rising portion of the comparison signal, which is determined by an RC time constant of the sawtooth generator, are constant. Therefore, the value of e cm varies with the frequency resulting in a variable value of f cm .
For example, as shown throughout FIGS. 3A, 3B, and 3C, both the width of the downward sloping portion and the inclination of the rising portion of the comparison signals are constant. As a result, when the frequency becomes high (FIG. 3A) as compared with its reference state (FIG. 3B), the value of e cm becomes small as represented by e' cm and when the frequency becomes low (FIG. 3C) as compared with the reference state (FIG. 3B), the value of e cm becomes large as represented by e" cm .
Therefore, when the frequency of the horizontal output signal is high, the differences between the minimum and maximum control signal amplitudes, hereinafter referred to as the amplitude range become smaller resulting in a reduced control range f cm . In contrast thereto, when the frequency of the horizontal oscillator signal is low, the amplitude range becomes larger resulting in an increase of control range f cm .
Typically for a variable control range as described heretofore, the AFC circuit is designed with the smaller control range, corresponding to high oscillating frequencies, as a reference. Such a reference, however, results in the control range at lower oscillating frequencies becoming either too large or at least larger than necessary.
When the control range at the lower oscillating frequencies is too large, the amplitudes of the control signals, that is, the values of ±e cm , are too high or low to be applied to horizontal oscillator 1 and thereby results in an unacceptable frequency correction. Such unacceptably high or low values of e cm can occur, for example, when the sync signal disappears during switching of television channels resulting in the oscillating frequency becoming too low and thereby creating a voltage in the horizontal output circuit that is abnormally high. Therefore, it is necessary that the control range of the AFC circuit be made as small as possible for lower frequencies.
Further, if the control range is too large, the AFC circuitry may unnecessarily adjust the oscillating frequency when noise is present on a weakly received signal.
Accordingly, an AFC circuit should necessarily have as small a control range as possible. Such a small control range is possible by providing maximum and minimum values of e cm irrespective of frequency variation.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an AFC circuit which avoids the drawbacks of the prior art.
More specifically, it is an object of the present invention to provide a new and improved AFC circuit whose control range is constant.
It is another object of the present invention to provide a new and improved AFC circuit which limits the maximum and minimum values of the amplitude range.
According to an aspect of the present invention, an AFC circuit comprises:
an oscillating circuit for generating repetitive pulses;
means for receiving said repetitive pulses and generating comparison signals having a slope portion and maximum and minimum levels in response to said repetitive pulses, said generating means having an output terminal;
a source of reference signals;
phase comparison means having a first input terminal supplied with said comparison signals, a second input terminal supplied with said reference signals and an output terminal for supplying said automatic frequency control signal to said oscillating circuit for controlling its frequency within a control range; and
limiting means connected between said comparison signal generating means and said phase comparison means for limiting said maximum level and said minimum level of said comparison signals to first and second predetermined levels respectively, thereby limiting said control range of said automatic frequency control signal generating circuit to a predetermined range.
The above, and other objects, features and advantages of the present invention will become apparent from the following description which is to be read in conjunction with the accompanying drawings, in which like reference numerals designate like elements and parts.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a prior art AFC circuit;
FIG. 2 and FIGS. 3A to 3C are waveform diagrams used to explain the operation of the prior art circuit shown in FIG. 1;
FIG. 4 is an embodiment of saw-tooth wave generating and limiter circuitry in accordance with the present invention;
FIGS. 5A, 5B, and 5C illustrate respectively input and output waveforms of the saw-tooth wave generator and the output waveform of the limiter shown in FIG. 4;
FIG. 6 is an alternative embodiment of circuitry which replaces the circuitry of FIG. 4 and produces a comparison signal in accordance with the present invention; and
FIGS. 7A and 7B illustrate respectively an input waveform supplied to and an output waveform produced by the circuitry shown in FIG. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be hereinafter described with reference to the attached drawings.
FIG. 4 includes an in
put terminal 11 connected to horizontal output circuit 2 (not shown) and an input capacitor 12. Input capacitor 12 is connected to resistors 13 and 14. Capacitor 12 and resistors 13 and 14 form a bias circuit which biases a base of an NPN-type transistor 15. Transistor 15 has a grounded emitter and a collector connected through a resistor 16 to a power supply terminal 17 which is at a voltage V cc and through a series connection of a resistor 18 and a capacitor 19 to ground. The connection point between resistor 18 and capacitor 19 is connected to power supply terminal 17 through a series connection of a capacitor 20 and a resistor 21. The connection point of capacitor 20 and resistor 21 is connected to power supply terminal 17 through a resistor 22 and a diode 23 wherein the cathode and anode of diode 23 are respectively connected to terminal 17 and resistor 22. The connection point of capacitor 20 and resistor 21 is also connected to ground through resistor 22 and a series connection of a diode 24 and a capacitor 25 which is grounded wherein the cathode and anode of diode 24 are respectively connected to the connection point of resistor 22 and diode 23 and to capacitor 25. The connection point of diode 24 and capacitor 25 is connected to the connection point of voltage dividing resistors 26 and 27. Resistors 26 and 27 are connected between terminal 17 and ground. The connection point between diodes 23 and 24 is connected to a base of an NPN-type transistor 28 whose collector is connected to power supply terminal 17 and whose emitter is grounded through a resistor 29 and connected to an output terminal 30. Output terminal 30 is connected to an input terminal of phase comparator 4 (not shown).
Diodes 23 and 24 form a limiter circuit and capacitor 25 and resistors 26 and 27 form a direct current (d.c.) voltage source having a voltage level of E.
When a repetitive pulse, such 
as a flyback pulse, as shown in FIG. 5A, is applied to input terminal 11, a saw-tooth wave (FIG. 5B) is generated at the connection point of capacitor 20 and resistor 22 which in turn is fed to the limiter circuit which produces a waveform as shown in FIG. 5C. That is, the value e cm is limited to an upper level V cc +V D and a lower level E-V D (where V D is the forward voltage drop of diodes 23 and 24).
Since the value e cm is within a fixed range, the control range is constant resulting in a desired control range which is fixed regardless of frequency. That is, the present invention provides a control range which is constant irrespective of the frequency and thereby avoids the possibility of an unnecessary expansion of the control range at low frequencies and the resulting erroneous operation caused by the expanded control range.
An alternative embodiment of the present invention is shown in FIG. 6 which includes input terminal 11 connected through capacitor 12 to the base of a PNP-type transistor 31, which is biased by the resistors 13 and 14. Transistor 31 has an emitter connected to power supply terminal 17 and collector grounded through a parallel circuit of a resistor 32 and a capacitor 33. The collector of transistor 31 is also connected through a series connection of a capacitor 34 and a resistor 35 to an emitter of an NPN-type transistor 36. A base of transistor 36 is connected to a voltage dividing point of resistors 37 and 38 and a collector thereof is connected to power supply terminal 17 through a resistor 39. An emitter of transistor 36 is grounded through a resistor 40. Output terminal 30 is connected to the collector of transistor 36.
A repetitive pulse, such as a flyback pulse as shown in FIG. 7A, is supplied from the horizontal output circuit 2 and is applied to the input terminal 11. During those periods of each cycle when there is no flyback pulse, transistor 31 turns ON which charges capacitor 33 resulting in voltage at the emitter of transistor 36 rising and thereby causing transistor 36 to turn OFF. During periods when transistor 36 is turned off, output terminal 30 is at a voltage level of V cc as shown in FIG. 7B. During that portion of each cycle when a flyback pulse occurs, transistor 31 turns OFF, allowing capacitor 33 to discharge through resistor 32. As a result, the potential at the emitter of transistor 36 gradually lowers and transistor 36 turns ON resulting in the output voltage at output terminal 30 gradually lowering to ground potential. When the period of the flyback pulse terminates, once again transistors 31 turns ON, charging capacitor 33 immediately, turning transistor 36 OFF and charging the voltage at output terminal 30 to V cc . That is, a signal is produced having a magnitude of V cc when the flyback pulse is absent and gradually lowering to ground potential during the flyback pulse period.
Thus the comparison signal, e cm , magnitude is restricted to a range between V cc and ground potential and thereby provides a desired control range regardless of the frequency. More particularly, in either embodiment the present invention provides a predetermined control range.
The present invention, as described heretofore has used the downward sloping portion of the comparison signal during phase comparison with a reference signal. However, the present invention can be applied as well to circuitry which provides a comparison signal having a rising slope portion during flyback pulse periods wherein control signal e cm is selected from the rising slope portion.
Although illustrative embodiments of this invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the spirit and scope of the invention, as defined in the appended claims.
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