The CHASSIS FM 100-20 DH delivers a totally uncommon Frame deflection system, derived from previous chassis types. (YEARS 1978)
Plus the E/W Correection circuit uses the same Technology.
It's a system called S.S.V.D. which stays for Synchronized Switched Vertical Deflection.
The system is highly reliable and does dissipate energy like linear amplifier types like A class or AB class Types and should not be confused with D Class amplifier.
Abstract:
In a switched vertical deflection circuit, two SCR switches couple horizontal retrace pulses to a capacitor. A modulator couples pulse width modulated gating pulses to the SCR's. The SCR's couple to the capacitor successively smaller portions of the horizontal retrace pulses during a first part of the vertical trace interval and successively larger portions during a second part for developing in a vertical deflection winding a sawtooth vertical deflection current. The modulator couples gating pulses to one of the SCR's during the vertical retrace interval for substantially loading the horizontal deflection circuit during the vertical retrace interval for preventing undesired oscillations within the horizontal deflection circuit.
What is claimed is:
1. A switched vertical deflection system comprising:
a horizontal deflection circuit including first means for generating horizontal rate energy signals;
a vertical deflection winding;
energy storage capacitance means coupled to said vertical deflection winding;
first and second switching means coupled to said first means and said energy storage capacitance means; and
second means coupled to said first and second switching means for switching conductive states of both of said switching means for coupling successively smaller portions of said horizontal rate energy signals to said energy storage capacitancemeans during a first part of a vertical trace interval and successively larger portions of said horizontal rate energy signals during a second part of said vertical trace interval for developing a vertical deflection current in said vertical deflectionwinding during said vertical trace interval,
said second means causing said first switching means to conduct during a vertical retrace interval for coupling substantial portions of said horizontal rate energy signals to said energy storage capacitance means during said vertical retraceinterval for preventing undesired oscillations within said horizontal deflection circuit.
2. A system according to claim 1 wherein said first and second switching means comprise controlled semiconductors, said second means coupling first and second signals to said first and second switching means for switching conductive states ofboth of said controlled semiconductors.
3. A system according to claim 2 wherein said second means includes transformer means for coupling said first signals to said first switching means.
4. A system according to claim 3 wherein said first switching means comprises a silicon controlled rectifier, a secondary winding of said transformer means coupled between the gate and cathode electrodes of said silicon controlled rectifier.
5. A system according to claim 2 including vertical signal means coupled to said second means for generating a vertical rate signal for modulating said first and second signals at a vertical rate.
6. A system according to claim 5 wherein said vertical signal means includes first circuitry for generating a component of said vertical rate signal that inhibits conduction of said second switching means during said vertical retrace interval.
7. A system according to claim 6 wherein said first circuitry comprises an RC differentiating circuit.
8. A system according to claim 7 wherein the time constant of said differentiating circuit is selected to provide a duration for said component of said vertical rate signal substantially equal to said vertical retrace interval.
9. In a television receiver including a horizontal deflection circuit comprising a horizontal deflection generator and a horizontal output transformer, a switched vertical deflection circuit comprising:
a vertical deflection winding;
energy storage capacitance means coupled to said vertical deflection winding;
first and second controllable switches coupled to said capacitance means and to respective secondary windings of said horizontal output transformer for coupling horizontal retrace signals to said capacitance means; and
a modulator coupled to said first and second controllable switches and responsive to a source of vertical rate signals for providing to said controllable switches during said vertical trace interval horizontal rate signals modulated at a verticalrate for varying the amount of each horizontal retrace signal coupled to said capacitance means for generating a vertical deflection current in said vertical deflection winding during said vertical trace interval, said switched vertical deflectioncircuit substantially loading said horizontal deflection circuit at the beginning and end of said vertical trace interval,
said modulator providing signals to said first controllable switch during said vertical retrace interval for coupling said horizontal retrace signals to said capacitance means during said vertical retrace interval for substantially loading saidhorizontal deflection circuit during said retrace interval for preventing undesired oscillations within said horizontal deflection circuit.
10. A circuit according to claim 9 wherein said vertical rate signals cause said modulator to provide for conduction of said first controllable switch during said vertical retrace interval and for inhibiting conduction of said second controllable swith during said vertical retrace interval.
Description:
BACKGROUND OF THE INVENTION
This invention relates to switched vertical deflection circuits for a television receiver.
In a switched vertical deflection circuit of the type disclosed in U.S. Patent Application Ser. No. 595,809, now U.S. Pat. No. 4,048,544, filed July 11, 1975, by Peter Eduard Haferl, entitled, SWITCHED VERTICAL DEFLECTION SYSTEM, horizontalrate energy, in the form of horizontal retrace pulses from a horizontal output transformer of a horizontal deflection circuit, charges a capacitor in parallel with a vertical deflection winding. A first switch, such as an SCR, couples successivelysmaller portions of the horizontal rate energy to the capacitor during a first part of the vertical trace interval and a second switch, such as another SCR, couples successively larger portions of the horizontal rate energy during a second part of thevertical trace interval. The voltage across the capacitor is integrated by the vertical deflection winding into a sawtooth vertical deflection current. The conduction of the two SCR switches is controlled by horizontal rate pulse width modulated pulsescoupled from a modulator to the SCR gate electrodes.
At the start of vertical retrace, the second SCR switch which had previously been conducting is maintained in cutoff. The vertical deflection winding and the capacitor form a resonant retrace circuit. A disconnect diode coupled to the gate ofthe first SCR switch is reversed biased, maintaining the SCR in cutoff independent of the gating pulses generated by the modulator. With both SCR's nonconducting, resonant retrace of the current in the vertical deflection winding is accomplished. Atthe start of the subsequent vertical trace interval, the disconnect diode is no longer reverse biased. Pulse width modulated gating pulses to the first SCR enable the SCR to couple the horizontal retrace pulses to the capacitor for generating thesawtooth deflection current in the vertical deflection winding.
Both SCR's conduct relatively large amounts of current at the beginning and end of the vertical trace interval, respectively. Neither SCR conducts during the vertical retrace interval. Accordingly, loading of the horizontal deflection circuitby the switched vertical deflection circuit will be greatest at the beginning and end of the vertical trace interval, with substantially no loading occurring during the vertical retrace interval. Such load interruption during the vertical retraceinterval may cause undesirable modulation of the horizontal deflection current and undesirable oscillations within the horizontal deflection circuit. These oscillations may appear, for example, in the "S" shaping capacitor or in the horizontal outputtransformer windings as the load impedance of the vertical deflection circuit abruptly changes. It is, therefore, desirable to provide a switched vertical deflection circuit in which undesirable oscillations within the horizontal deflection circuit areprevented.
SUMMARY OF THE INVENTION
A switched vertical deflection circuit comprises a horizontal deflection circuit including apparatus for generating horizontal rate energy signals, a vertical deflection winding, an energy storage capacitance, first and second switches and aswitching circuit coupled to the switches. The switching circuit switches the conductive states of the switches for coupling successively smaller portions of the horizontal rate energy signals to the energy storage capacitance during a first part of thevertical trace interval and successively larger portions during a second part for developing a vertical deflection current in the vertical deflection winding during the vertical trace interval. The switching circuit causes the first switch to conductduring the vertical retrace interval for coupling substantial portions of the horizontal rate energy signals to the energy storage capacitance during the vertical retrace interval for preventing undesired oscillations within the horizontal deflection circuit.
To permit use of a circuit in which the energy derived during horizontal flyback is used to control vertical deflection, without damage to the vertical deflection system upon vertical flyback, the vertical deflection output stage is dimensioned to have a time constant which is less, preferably about half, of the time constant of the sawtooth wave generator controlling vertical deflection. The vertical deflection output stage forms, in essence, a parallel oscillatory circuit which, to provide the lesser time constant, is damped.
1. In a television receiver,
having means (1, 2) coupling out a portion of the energy delivered by the horizontal deflection circuit during line flyback or retrace;
a vertical deflection output stage (V) including deflection means (LV1, LV2) and a charge capacitor element (C);
and a sawtooth wave generator (S), which controls application of the coupled-out energy derived from the horizontal deflection circuit to the vertical deflection means (LV1, LV2), a method to control vertical deflection
comprising, in accordance with the invention, the step of
additionally controlling application of the energy to the vertical deflection means by the sawtooth wave generator during the vertical flyback or retrace interval by reversely re-charging said capacitor element during said interval.
2. Method according to claim 1, wherein the re-charging step is carried out continuously.
3. Method according to claim 1, wherein the re-charging step is carried out linearly.
4. Method accordi
ng to claim 1, wherein the vertical deflection output stage includes, vertical deflection coil elements (LV1, LV2) and forming with said charge capacitor element (C) said deflection means, a feedback resistor element (R) and a vertical correction circuit element (4), said charge capacitor element and said other elements being connected to form a parallel oscillatory circuit; said method including the step of controlling the damping of the parallel oscillatory circuit by controlling the relative parameters of said elements.
5. In a television receiver, a vertical deflection system including means (1, 2) coupling out a portion of the energy delivered by the horizontal deflection circuit during line flyback or retrace;
a vertical deflection output stage (V) including vertical deflection means (LV1, LV2);
and a sawtooth wave generator (S) controlling application of the coupled-out energy to the vertical deflection means during the flyback interval
and wherein, in accordance with the invention,
the time constant (τS) of the sawtooth wave generator (S) is longer than the time constant (τV) of the vertical deflection output stage (V).
6. Vertical deflection system according to claim 5, wherein the time constant of the vertical deflection output stage is about twice as long as that of the sawtooth wave generator (S).
7. Vertical deflection system according to claim 5, wherein the ratio of time constants (τS /τV) is between about 1.5 to 2.5.
8. Vertical deflection system according to claim 5, wherein the vertical deflection output stage (V) includes a charge capacitor element (C), vertical deflection coil elements (LV1, LV2) forming said vertical deflection means, a feedback resistor element (R) and a vertical correction circuit element (4), said elements being connected to form a parallel oscillatory circuit;
and wherein said oscillatory circuit is a damped oscillatory circuit.
9. Vertical deflection system according to claim 8, wherein the elements of said oscillatory circuit are dimensioned to provide a time constant which is about half of the time constant of the sawtooth wave generator (S) and is in the order of about 0.5 ms.
The present invention relates to a deflection circuitry for television receivers, and more particularly to a deflection circuit in which energy contained in the horizontal flyback is used in the vertical deflection system.
Video scanning in television receivers is effected, as well known, by a vertical deflection circuit. A pulse generator is synchronized by pulses included in the video signal. The pulses are then applied over a pulse generator, a driver and an output stage to deflection systems, usually deflection coils.
Various types of solid-state circuits have been proposed; for example, U.S. Pat. No. 4,048,544 describes a transistorized vertical deflection circuit with additional circuitry to stabilize the pulses. The time constant of the pulse generator and of the driver stage of such circuits is less than the time constant of the output or final power stage of the vertical deflection circuit. Such vertical deflection circuits have some disadvantages, particularly in that the transistors are operated at high voltages which may result in flash-over and thus damage or destruction of the transistor. The power required to control the final output transistors is already substantial and thus the overall operating efficiency of such a vertical deflection circuit is low.
In earlier developments, a vertical deflection circuitry was proposed which avoids some of the disadvantages of this transistorized circuit; in this earlier circuit, a portion of the energy contained in the horizontal flyback is coupled out and is directly utilized in order to supply current for the vertical deflection coils. To control application of current, a controlled sawtooth wave generator is connected to the final output stage of the vertical deflection circuit, the sawtooth wave generator having a short retrace or flyback time. These vertical deflection circuits also have some disadvantages. The energy derived for vertical deflection is obtained from the horizontal flyback; thus, changes in loading in the vertical deflection circuitry affect the horizontal output stage. The vertical deflection circuit is subject to substantial changes in loading during the vertical flyback or retrace since, in accordance with the previously known circuit, the vertical deflection circuit is not controlled during the vertical flyback or retrace. The lack of control of the vertical deflection circuit causes abrupt changes in loading which result in undesired spurious oscillations in the vertical output stage. These oscillations can so feed back or react on the horizontal output stage that the horizontal flyback pulses are overloaded, the vertical stage starts to oscillate, and high voltages may occur therein during the vertical flyback. This, necessarily, degrades the image quality of the reproduced video picture. High-voltage flash-over may occur and electronic components, particularly solid-state semiconductor elements can be destroyed thereby.
It is an object of the present invention to provide a vertical deflection circuit for television receivers, which has the advantages of utilizing a portion of the energy contained in the horizontal deflection circuit during horizontal flyback without causing abrupt changes in loading on the horizontal output stage and preventing undesired spurious and uncontrolled oscillation of the vertical output stage.
Briefly, the sawtooth wave generator which controls charging of a charge capacitor of the vertical output stage is controlled to in turn control the charge on the capacitor also during vertical retrace; in accordance with a feature of the invention, this control is obtained by so arranging and relatively matching the time constants of the sawtooth wave generator and of the parallel oscillatory circuit formed by the vertical deflection coils of the T.V. receiver and the charge capacitor that the time constant of the vertical deflection output stage is less, preferably about half that of the time constant of the sawtooth wave generator. This matching can be obtained by so selecting the values of the components of the vertical deflection output stage that the resulting oscillatory circuit formed by the capacitor, resistance elements in the circuit, and the vertical deflection output stage form a damped oscillatory circuit.
The invention will be described by way of example with reference to the accompanying drawings, wherein the single FIGURE is a schematic diagram of a vertical deflection output stage in which the method of the present invention is carried out, and utilizing the system thereof.
A horizontal deflection output stage 1 is connected to a horizontal output transformer 2 which has coupling windings W 1 and W 2 to derive a portion of the energy contained in the line retrace. This energy is stored in the inductances L 1 and L 2 and then applied through thyristors Th 1 and Th 2 to a charge capacitor C. A control circuit 3 is provided triggering the thyristors Th 1 and Th 2 in such a manner that the charge capacitor C is positively charged during the first half of the video scan and negatively during the second half of the video scan. The charge capacitor C is discharged through the vertical deflection coils L V1 and L V2 , a vertical correction circuit 4 for vertical correction and a feedback resistor R. The voltage drop across feedback resistor R is fed back to the control circuit 3 in order to ensure exact triggering of the thyristors Th 1 and Th 2 and to control the desired deflection current.
Positive deflection current is obtained during the first half of the video scan by the triggered thyristor Th 1 ; negative deflection current is derived during the second half of the video scan by the triggered thyristor Th 2 . The thyristors Th 1 and Th 2 can be triggered during a portion of the video scan simultaneously to result in a linear deflection and provide overlapping, opposite deflection currents.
The control circuit 3, together with the thyristors Th 1 and Th 2 , and the inductances L 1 and L 2 , forms a sawtooth wave generator S. The vertical deflection output stage V is formed of the vertical deflection coils L V1 , L V2 , the vertical correction circuit 4, the charge capacitor C and the feedback resistor R. As can be seen from the FIGURE, the capacitor C on the one hand, and the deflection coils, the correction circuit 4 and the resistor R on the other hand form a parallel oscillatory circuit.
The circuit, as far as the diagram is concerned, is known. Uncontrolled, undesired and spurious oscillations in the horizontal output stage can be avoided, in accordance with the invention, by reverse re-charging the capacitor C also during the vertical retrace interval. This re-charging of the capacitor C preferably is carried out continuously and desirably linearly. The controlled re-charging of the capacitor C can be readily obtained by arranging the relative values of the components in the sawtooth wave generator S and in the vertical output stage V such that the time constant τ S of the sawtooth wave generator is longer than the time constant τ V of the vertical deflection output stage. Mathematically: τ S >τ V (1)
preferably, the quotient of the time constants should be between 1.5 and 2.5, most desirably about 2, mathematically: 1.5>τ S /τ V <2.5 (2)
if the time constants of the respective circuits are properly arranged, the thyristors Th 1 and Th 2 can be precisely triggered also during the short time interval of the vertical flyback or retrace. Due to the short time constant, the vertical deflection circuit can then follow the control from the control circuit 3 exactly; the voltage dropped across the feedback resistor R will permit precise triggering, with respect to time, of the thyristors Th 1 and Th 2 also during the vertical flyback. In the first half of the video scan, the thyristor Th 2 is triggered; in the second half, thyristor Th 1 is triggered. This ensures linear flyback.
The time constant τ V is essentially determined by the vertical deflection coils L V1 , L V2 , the correction circuit 4, and the feedback resistor R which, together with the capacitor C, form a parallel oscillatory circuit. A short time constant corresponds to high damping of this parallel oscillatory circuit. Thus, in accordance with a feature of the present invention, by suitably arranging the ratio of the time constants, the parallel oscillatory circuit will not start undesired uncontrolled oscillations which could interfere with image reproduction quality, or proper operation of the components of the T.V. receiver. The ratio of the time constants can be selected by suitable adjustment of the damping of the oscillatory circuit.
The vertical deflection circuit has an essentially continuous, uniform and even power requirement. This avoids abrupt changes in loading during the vertical retrace. Excessive over-compensation of horizontal flyback pulses, and resulting high voltages which may lead to undesired distortion of the reproduced image and possibly to damage or destruction of components of the video system are avoided. The vertical deflection circuitry, as described, can be readily manufactured and has high operating reliability. The efficiency is high and the power requirement is low.
Various changes and modifications may be made within the scope of the inventive concept.
In a typical T.V. receiver using vertical deflection coils of 20 millihenry inductance, a suitable time constant τ V is 0.5 ms. In such a circuit, the resistor R can have a value 1 Ω capacitor C a value of 1.5 μF. and the reflected impedance of correction circuit 4 a value of 1 Ω.
The sawtooth wave generator has a time constant of 1 ms, providing for a slow rise time for 20 milliseconds. The circuit 3 is well known and described in U.S. Pat. No. 4,048,544.
A side pincushion correction circuit having an impedance circuit in series with the deflection coil. A controlled switch coupled in a branch of the impedance circuit is operated at times during the second half of the horizontal retrace interval which are progressively advanced during the first half of vertical interval and retarded during second half of vertical interval. Enhanced inside pincushion distortion correction is provided when the impedance circuit includes a capacitor coupled in series with the switch.
1. A pincushion correction circuit for a kinescope deflection apparatus including horizontal and vertical deflection generator systems, comprising:
a horizontal deflection winding coupled to the horizontal deflection generator system for accepting scanning current therefrom;
an impedance circuit for presenting an impedance between first and second terminals and further including a third terminal, and first coupling means for coupling said first terminal to said third terminal;
second means for serially coupling said first and second terminals of said impedance circuit with said deflection winding;
controllable switch means including a control electrode and a controlled current path coupled between said second and third terminals;
control means coupled to the horizontal and vertical deflection generator systems and to said control electrode for operating said controllable switch means at a time during the second half of the horizontal retrace interval which time is progressively advanced during a first portion of the vertical scan interval and which is progressively retarded during a second portion of the vertical scan interval for altering said scanning current in a manner to reduce pincushion distortion.
2. A pincushion correction circuit in accordance with claim 1 wherein said first coupling means comprises a direct connection.
3. A pincushion correction circuit in accordance with claim 1 wherein said impedance circuit comprises first inductance means coupled between said first and second terminals.
4. A pincushion correction circuit in accordance with claim 3 wherein said first coupling means comprises capacitance means coupled between said first and third terminals.
5. A pincushion correction circuit according to claim 3 wherein said first coupling means comprises:
capacitance means;
second inductance means;
means for serially coupling said capacitance means with said second inductance means; and
means for coupling the serial combination of said capacitance means and said second inductance means between said first and third terminals.
6. A pincushion correction circuit according to claim 3 wherein said coupling means comprises second inductance means coupled between said first and third terminals.
7. A pincushion correction circuit according to claim 6 further comprising means for magnetically coupling said first inductance means with said second inductance means.
8. A pincushion correction circuit according to claim 7 further comprising capacitance means serially coupled with said second inductance means.
9. A pincushion correction circuit according to claim 8 wherein said first and second inductance means have substantially the same self-inductance.
1
0. A pincushion correction circuit according to claim 1 wherein said controllable switch means comprises a controllable rectifier including said control electrode and said controllable current path, a unidirectional current conducting device, and wherein said controllable current path is coupled in parallel with said unidirectional current conducting device. 11. A pincushion correction circuit according to claim 10 wherein the anode of said unidirectional current conductive device is coupled to the cathode of said controllable rectifier and the cathode of said unidirectional current conducting device is coupled to the anode of said controllable rectifier.
12. A pincushion correction circuit according to claim 1 wherein said control means comprises gating pulse generator means coupled to said controllable switch and to the horizontal and vertical deflection generator systems for producing repetitive switch gating pulses during the second half of each horizontal retrace pulse interval, said gating pulses terminating substantially at the termination of said horizontal retrace pulse and initiating at a time which is progressively advanced during a first portion of the vertical scan interval and progressively retarded during a second portion of the vertical scan interval.
13. A pincushion correction circuit according to claim 12 wherein said gating pulse generator means comprises:
parabola generating means coupled to the vertical deflection generator system for generating a parabolic signal at the vertical deflection rate;
means coupled to the horizontal deflection generator system for generating a horizontal rate signal during the horizontal retrace pulse period;
modulating means coupled to said horizontal rate signal generating means and to said parabolic signal generating means for generating a horizontal rate pulse width modulated by said parabolic signal; and
gating means coupled to said horizontal rate signal generating means and to said modulating means for generating switch gating pulses representative of the absence of said horizontal rate signal and of said horizontal rate pulse.
14. A pincushion correction circuit according to claim 12 wherein said gating pulse generator means comprises: parabola generating means for generating a parabolic signal at the vertical deflection rate; means for generating a horizontal rate signal during the horizontal retrace pulse interval; and
comparator means coupled to said parabola generator means and to said horizontal rate signal generating means for producing said repetitive gating pulses.
15. A pincushion correction circuit according to claim 14 wherein said comparator means comprises: differential amplifier amplitude comparison means having a first and a second input;
said first input being coupled to said parabola generating means; and
said second input being coupled to an output of said horizontal rate signal generating means and said horizontal rate signal comprises a ramp.
16. A pincushion correction circuit for a kinescope deflection apparatus including horizontal and vertical deflection generator systems, comprising:
a horizontal deflection winding coupled to the horizontal deflection generator system for accepting scanning current therefrom;
an impedance circuit including a capacitor coupled in parallel with an inductor;
means for serially coupling said impedance circuit with said deflection winding;
controllable switch means including a control electrode and a controlled current path serially coupled with a branch of said impedance circuit; and
control means coupled to the horizontal and vertical deflection generator and to said control electrode for operating said controllable switch means at a time during the second half of the horizontal retrace interval which time is progressively advanced during a first portion of the vertical scan interval and which is progressively retarded during a second portion of the vertical scan interval for altering said scanning current in a manner to reduce pincushion distortion.
17. A pincushion correction circuit according to claim 16 wherein said controllable switch is serially coupled in the capacitive branch of said impedance circuit.
18. A pincushion correction circuit according to claim 17 wherein the inductive branch of said impedance circuit comprises an autotransformer.
19. A pincushion correction circuit according to claim 18 wherein said controllable switch comprises a controllable rectifier, a unidirectional current conducting device and having said controllable current path coupled in parallel with said unidirectional current conducting device.
20. A pincushion correction circuit according to claim 19 wherein the anode of said unidirectional current conducting device is coupled to the cathode of said controllable rectifier and the cathode of said unidirectional current conducting device is coupled to the anode of said controllable rectifier.
21. A p
incushion correction circuit according to claim 16 wherein said control means comprises gating pulse generator means coupled to said controllable switch and to the horizontal and vertical deflection generator systems for producing repetitive switch gating pulses during the second half of each horizontal retrace pulse interval, said gating pulses terminating substantially at the termination of said horizontal retrace pulse and initiating at a time which is progressively advanced during a first portion of the vertical scan interval and progressively retarded during a second portion of the vertical scan interval. 22. A pincushion correction circuit according to claim 21 wherein said gating pulse generator means comprises:
parabola generating means coupled to the vertical deflection generator system for generating a parabolic signal at the vertical deflection rate;
means coupled to the horizontal deflection generator system for generating a horizontal rate signal during the horizontal retrace pulse period;
modulating means coupled to said horizontal rate signal generating means and to said parabolic signal generating means for generating a horizontal rate pulse width modulated by said parabolic signal; and
gating means coupled to said horizontal rate signal generating means and to said modulating means for generating switch gating pulses representative of the absence of said horizontal rate signal and of said horizontal rate pulse.
23. A pincushion correction circuit according to claim 21 wherein said gating pulse generator means comprises: parabola generating means for generating a parabolic signal at the vertical deflection rate; means for generating a horizontal rate signal during the horizontal retrace pulse interval; and
comparator means coupled to said parabola generator means and to said horizontal rate signal generating means for producing said repetitive gating pulses.
24. A pincushion correction circuit according to claim 23 wherein said comparator means comprises: differential amplifier amplitude comparison means having a first and a second input;
said first input being coupled to said parabola generating means; and
said second input being coupled to an output of said horizontal rate signal generating means and said horizontal rate signal comprises a ramp.
25. A television kinescope deflection apparatus comprising:
a vertical deflection generator coupled to a vertical deflection coil for producing vertical scanning current therethrough;
a horizontal deflection generator system for generating horizontal rate current;
a horizontal deflection winding coupled to said horizontal deflection generator for accepting horizontal rate current therefrom for scanning;
impedance means;
controllable switch means; first coupling means for coupling said horizontal deflection winding with a first terminal of said impedance means so as to form a series circuit, said impedance means having a second terminal remote from said first terminal; second coupling means coupling a first end of the controlled current path of said controllable switch means with said first terminal, and third coupling means for coupling the other end of the controlled current path of said controllable switch means with said second terminal; and
control means coupled to said vertical and to said horizontal deflection generator systems and to said controllable switch means for operating said controllable switch means at a time during the horizontal retrace interval which is progressively advanced during a first portion of the vertical scan interval and which is progressively retarded during a second portion of the vertical scan interval for altering said scanning current in a manner to reduce pincushion distortion.
26. A television kinescope deflection apparatus according to Claim 25
wherein
said control means closes said controllable switch means at a time during the horizontal retrace interval which is progressively advanced during the first half of the vertical scan interval and progressively retarded during the second half of the vertical scan interval.
27. A television kinescope deflection apparatus according to claim 26 wherein said impedance means comprises first inductance means coupled between said first and second terminals.
28. A television kinescope deflection apparatus according to claim 27 wherein said second coupling means comprises capacitance means coupling said first terminal of said impedance means to said first end of said controllable switch means.
29. A television kinescope deflection apparatus according to claim 27 wherein said second coupling means comprises second inductance means coupling said first terminal of said impedance means to said first end of said controllable switch means.
30. A television kinescope deflection apparatus in accordance with claim 27 wherein said second coupling means comprises second inductance means coupling said first terminal of said impedance means to said first end of said controllable switch means and further comprising magnetic coupling means for magnetically coupling said first inductance means with said second inductance means.
31. A television kinescope deflection apparatus according to Claim 27 wherein said second coupling means comprises capacitance means and second inductance means.
32. A television kinescope deflection apparatus according to claim 31 wherein said first and second inductance means have substantially the same self-inductance.
33. A television kinescope deflection apparatus according to claim 31 wherein said capacitance means and said second inductance means are serially coupled.
34. A television kinescope deflection apparatus according to claim 31 further comprising magnetic coupling means for magnetically coupling said first and second inductance means.
35. A tel
evision kinescope deflection apparatus according to claim 31 wherein said first and second inductance means are windings of an autotransformer. 36. A television kinescope deflection apparatus in accordance with claim 25 wherein said controllable switch means comprises a controllable rectifier including a control electrode and a controllable current path, a unidirectional current conducting device, and wherein said controllable current path is coupled in parallel with said unidirectional current conducting device.
37. A television kinescope deflection apparatus according to Claim 36 wherein the anode of said unidirectional current conductive device is coupled to the cathode of said controllable rectifier and the cathode of said unidirectional current conducting device is coupled to the anode of said controllable rectifier.
38. A television kinescope deflection apparatus according to Claim 25 wherein said control means comprises gating pulse generator means coupled to said controllable switch and to said horizontal and vertical deflection generators for producing repetitive switch gating pulses, said gating pulses terminating substantially at the termination of said horizontal retrace pulse.
39. A television kinescope deflection apparatus according to Claim 38 wherein said gating pulse generator means comprises: parabola generating means coupled to the vertical deflection generator for generating a parabolic signal at the vertical deflection rate; means coupled to said horizontal deflection generator system for generating a horizontal rate signal during said horizontal ratrace pulse period; modulating means coupled to said horizontal rate signal generating means and to said parabolic signal generating means for generating a horizontal rate pulse width-modulated by said parabolic signal.
40. A television kinescope deflection apparatus according to Claim 39 wherein said modulating means comprises: comparator means coupled to said parabola generator means and to said horizontal rate signal generating means for producing said repetitive gating pulses.
41. A television kinescope deflection apparatus according to Claim 40 wherein said comparator means comprises: differential amplifier amplitude comparison means having a first and a second input; said first input being coupled to said parabola generating means; and said second input being coupled to an output of said horizontal rate signal generating means and wherein said horizontal rate signal comprises a ramp.
42. A television kinescope deflection apparatus comprising: a vertical deflection generator coupled to a vertical deflection coil for producing vertical scanning current therethrough; a horizontal deflection generator system for generating horizontal rate current; a horizontal deflection w
inding coupled to said horizontal deflection generator for accepting horizontal rate current therefrom for scanning; impedance means; controllable switch means; means coupling said impedance means and said controllable switch means in series with said deflection winding for defining a path for said horizontal rate current; control means coupled to said vertical and to said horizontal deflection generator systems and to said controllable switch means for operating said controllable switch means at a time during the horizontal retrace interval which is progressively advanced during the first half of the vertical scan interval and which is progressively retarded during the second half of the vertical scan interval for altering said scanning current in a manner to reduce pincushion distortion. BACKGROUND OF THE INVENTION
This invention relates to a kinescope pincushion distortion correction circuit.
It is known in the art that side or East-West pincushion distortion of the raster on a kinescope such as utilized in a television receiver may be substantially eliminated by modulating the horizontal rate deflection current amplitude through the horizontal deflection coils by a substantially parabolic current component at a vertical scanning rate. Generally the desired modulation has been accomplished by passive currents in which a control or primary winding of a saturable reactor or transformer is energized by vertical rate energy and a secondary winding is placed in circuit with the horizontal deflection winding. The horizontal deflection current amplitude is modulated by the vertical deflection current such that the raster width is reduced at the top and bottom of the raster.
Another known arrangement for side pincushion distortion correction involves a capacitor coupled in parallel with the vertical deflection winding. As is disclosed in copending application Ser. No. 07161/75 for Peter E. Haferl and entitled "VERTICAL DEFLECTION SYSTEM", the capacitor is charged by energy from the horizontal retrace pulse under the control of switches. In both the passive saturable reactor circuits and in the switched vertical deflection circuit according to the aforementioned copending application, side pincushion correction is obtained by loading the high voltage transformer of the horizontal deflection system during the horizontal retrace time. In order to obtain correctly shaped side pincushion correction the loading of the high voltage transformer is modulated at the vertical deflection rate, as by the vertical deflection current. Thus, maximum loading occurs at the top and bottom of the picture and minimum loading occurs at the center of the picture.
The variable loading of the horizontal retrace pulse at the vertical rate results in the generation of a further pincushion distortion, known as inside pincushion distortion to distinguish from the outside or peripheral pincushion distortion ordinarily referred to. This further pincushion distortion occurs within the raster as a result of time modulation of the start of horizontal scan caused by the vertical rate loading. Increased trace duration resulting from time modulation of the horizontal retrace pulse at the top and bottom of vertical scan increases the portion of the resonant period of the deflection coil 26 with S correction capacitor 28 subtended during trace. Thus, the inside pincushion distortion appears in the region between the center line and the extreme left and right sides of the picture as an insufficient pincushion correction.
The amount of inside pincushion correction depends upon the geometry of the picture tube and on the amount of outside pincushion distortion requiring correction. With the advent of wide-angle large viewing screen picture tubes it has been found that the inside pincushion distortion may be objectionable to the point that correction is required.
A prior art arrangement for the solution of the inside pincushion correction problem, in addition to structure utilized for conventional pincushion correction, uses a separate saturable reactor or transductor in series with the horizontal deflection winding. The control winding of the saturable reactor is driven by a vertical deflection rate signal and modulates the inductance of the horizontal deflection circuit to correct for the change in "S" shaping and thereby correct the inside pincushion distortion. This prior art solution has disadvantages which include critical design of the saturable reactor, temperature dependence of the saturable reactor, cost of the saturable reactor, and a control range so limited as to often be insufficient to compensate for construction tolerances.
SUMMARY OF THE INVENTION
A pincushion correction circuit includes an impedance coupled in series with a horizontal deflection winding. The impedance circuit contains two branches, one of which is always in series with the deflection winding. The second branch of the impedance circuit is paralleled with the first branch by a controllable switch. The controllable switch is gated on at a time during the second half of the horizontal retrace interval. The time during the second half of the horizontal retrace interval at which the switch is gated on is progressively advanced during a first portion of the vertical scan interval and is progressively retarded during the second portion of the vertical scan interval.
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