CRT TUBE SONY TRINITRON 570HB22 VIEW.
Note the convergence assy on the deflection joke assy and the beam SVM (scan velocity modulation) unit on the neck of the tube and the H-STAT Regulator on the HV side.
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Trinitron is Sony's brand name for its line of aperture grille based CRTs used in televisions and computer monitors. One of the first truly new television systems to enter the market since the 1950s, the Trinitron was announced in 1966 to wide acclaim for its bright images, about 25% brighter than common shadow mask televisions of the same era. Constant improvement in the basic technology and attention to overall quality allowed Sony to charge a premium for Trinitron devices into the 1990s.
Patent protection on the basic Trinitron design ran out in 1996, and it quickly faced a number of competitors at much lower price points. Sony responded by introducing their flat-screen FD Trinitron designs (WEGA), which maintained their premier position in the market into the early 2000s. However, these designs were surpassed relatively quickly by plasma and LCD designs. Sony removed the last Trinitron televisions from their product catalogs in 2006, and ceased production in early 2008. Video monitors are the only remaining Trinitron products being produced by Sony, at a low production rate, although the basic technology can still be found in downmarket televisions from 3rd parties.
The name Trinitron was derived from trinity, meaning the union of three, and tron from electron tube, after the way that the Trinitron combined the three separate electron guns of other CRT designs into one.Trinitron
In the autumn of 1966 Ibuka finally gave in, and announced he would personally lead a search for a replacement for Chromatron. Susumu Yoshida was sent to the U.S. to look for potential licenses, and was impressed with the improvements that RCA had made in overall brightness by introducing new rare earth phosphors on the screen. He also saw General Electric's "Porta-color" design, using three guns in a row instead of a triangle, which allowed a greater portion of the screen to be lit. His report was cause for concern in Japan, where it seemed Sony was falling ever-farther behind the U.S. designs. They might be forced to license the shadow mask system if they wanted to remain competitive.[10]
Ibuka was not willing to give up entirely, and had his 30 engineers explore a wide variety of approaches to see if they could come up with their own design. At one point Yoshida asked Senri Miyaoka if the in-line gun arrangement used by GE could be replaced by a single tube with three cathodes; this would be more difficult to build, but be lower cost in the long run. Miyaoka built a prototype and was astonished how well it worked, although it had focussing problems.[10] Later that week, on Saturday, Miyaoka was summoned to Ibuka's office while he was attempting to leave work to attend his weekly cello practice. Yoshida had just informed Ibuka about his success, and the two asked Miyaoka if they could really develop the gun into a workable product. Miyaoka, anxious to leave, answered yes, excused himself, and left. That Monday Ibuka announced that Sony would be developing a new color television design, based on Miyaoka's prototype.[11] By February 1967 the focusing problems had been solved, and because there was a single gun, the focusing was achieved with permanent magnets instead of a coil, and required no after manufacturing manual adjustments.
During development, Sony engineer Akio Ohgoshi introduced another modification. GE's system improved on the RCA shadow mask by replacing the small round holes with slightly larger rectangles. Since the guns were in-line, they would shine onto the back of the tube onto three rectangular patches instead of three smaller spots, about doubling the lit area. Ohgoshi proposed removing the mask entirely and replacing it with a series of vertical slots instead, lighting the entire screen. Although this would require the guns to be very carefully aligned with the phosphors on the tube in order to ensure they hit the right colors, with Miyaoka's new tube this appeared possible.[11] In practice this proved easy to build but difficult to place in the tube – the fine wires were mechanically weak and tended to move when the tubes were bumped, resulting in shifting colors on the screen. This problem was solved by running fine tungsten wires across the grille horizontally to keep them in place.
The combination of three-in-one electron gun and the replacement of the shadow mask with the aperture grille resulted in a unique and easily patentable product. Officially introduced by Ikuba in April 1968, the original 12 inch Trinitron had a display quality that easily surpassed any commercial set in terms of brightness, color fidelity, and simplicity of operation. The tube was also flat vertically, a side-effect of the vertical wires in the aperture grille, which gave it a unique and appealing look. It was also all solid state, with the exception of the picture tube itself, which allowed it to be much more compact and cool running than designs like GE's Porta-color.
Ikuba ended the press conference by claiming that 10,000 sets would be available by October, well beyond what engineering had told him was possible. Ikuba cajoled Yoshida to take over the effort of bringing the sets into production, and although Yoshida was furious at being put in charge of a task he felt was impossible, he finally accepted the assignment and successfully met the production goal.[12] The KV-1310 was introduced in limited numbers in Japan in October as promised, and in the U.S. as the KV-1310U the following year.
In spite of Trinitron and Chromatron having no technology in common, the shared single electron gun has led to many erroneous claims that the two are similar, or the same.[13]
Despite the statement above claiming that there were no valves inside Trinitron TV sets, for a brief period in the United Kingdom between 1969 and 1971/72, the KV-1320UB was fitted with 3AT2 valves for the extra high tension. Later on, the KV-1320UB was redesigned internally and externally to become all solid-state. Despite containing vacuum tubes, the first version of the KV-1320UB was promoted as being all solid-state. The later version of this model is identified as having no wooden outer-shell. These early color sets intended for the UK market had a PAL decoder that was different from those invented and licensed by Telefunken of Germany, who invented this color system. The decoder inside the UK-sold Sony color Trinitron sets, from the KV-1300UB to the KV-1330UB had an NTSC decoder adapted for PAL. The decoder used a 64 microsecond delay line to store every other line, but instead of using the delay line to average out the phase of the current line and the "remembered" line (as with "Deluxe PAL"), it simply repeats the same line twice. Any phase errors can then be compensated for by using a Tint control on the front of the set.
The Trinitron design incorporates two unique features: the single-gun three-cathode picture tube, and the vertically aligned aperture grille.
The single-gun consists of a long-necked tube with a single electrode at its base, flaring out into a horizontally-aligned rectangular shape with three vertically-aligned rectangular cathodes inside. Each cathode is fed the amplified signal from one of the decoded RGB signals.
The electrons from the cathodes are all aimed toward a single point at the back of the screen where they hit the aperture grille, a steel sheet with vertical slots cut in it. Due to the slight separation of the cathodes at the back of the tube, the three beams approach the grille at slightly different angles. When they pass through the grille they retain this angle, hitting their individual colored phosphors that are painted in vertical stripes on the inside of the tube. The main purpose of the grille is to ensure the beams are properly registered with the phosphors.
Advantages
In comparison to early shadow mask designs, the Trinitron grille cuts off much less of the signal coming from the electron guns. RCA sets built in the 1950s cut off about 85% of the incoming signal, while the grille cuts off about 25%. Improvements to the shadow mask designs continually narrowed this difference in the two designs, and by the late 1980s the difference in performance, at least theoretically, was eliminated.
Another advantage of the aperture grille was that the distance between the wires remained constant vertically across the screen. In the shadow mask design the size of the holes in the mask is defined by the required resolution of the phosphor dots on the screen, which was constant. However, the distance from the guns to the holes changed; for dots near the center of the screen the distance was its shortest, at points in the corners it was at its maximum. To ensure that the guns were focused on the holes, a system known as dynamic convergence had to constantly adjust the focus point as the beam moved across the screen. In the Trinitron design the problem was greatly simplified, requiring changes only for large screen sizes, and only on a line-by-line basis.
For this reason, Trinitron systems are easier to focus than shadow masks, and generally had a sharper image. This was a major selling point of the Trinitron design for much of its history. In the 1990s new computer controlled real-time feedback focusing systems eliminated this advantage, as well as leading to the introduction of "true flat" designs.
Visible Support Wires
Even small changes in the alignment of the grille over the phosphors can cause the coloring to shift. Since the wires are thin, small bumps can cause the wires to shift alignment if they are not held in place. Monitors using this technology have one or more thin tungsten wires running horizontally across the grille to prevent this. Screens 15" and below have one wire located about two thirds of the way down the screen, while monitors greater than 15" have 2 wires at the one-third and two-thirds positions. These wires are less apparent or completely obscured on standard definition sets due to larger scan lines of the video being displayed. On computer monitors, where the lines are much closer together, the wires are often visible. This is a minor drawback of the Trinitron standard which is not shared by shadow mask CRTs.
CATHODE-RAY TUBE - CRT TUBE SONY TRINITRON ELECTRON GUN TECHNOLOGY OVERVIEW:
In a cathode ray tube, for example, a color picture tube in which a plurality of electron beams are made to converge or cross each other substantially at the optical center of an electrostatic focusing lens by which the beams are focused on the electron-receiving screen of the tube; the focusing lens includes first and second axially spaced, annular electrodes extending around the tube axis and being at the same potential, and a third annular electrode assembly extending between the first and second electrodes and which includes an axial array of at least three annular electrode portions, the electrode portions at the ends of the axial array being at a different potential than the first and second electrodes to establish the focusing electric field and at least one of the electrode portions intermediate the end portions being at a potential that deviates from the potential of the end electrode portions in a direction toward the potential of the first and second electrodes to modify the electric field so that its equivalent optical lens has relatively flatter surfaces for further reducing aberrations of the beam or beams focused thereby.
1. In a cathode ray tube having beam producing means generating at least one electron beam and a phosphor screen positioned to have the beam impinge thereon; electron focusing lens means for focusing the beam on the screen comprising: 2. A cathode ray tube according to claim 1, in which: 3. A cathode ray tube according to claim 1, in which: 4. A cathode ray tube according to claim 1, in which: 5. A cathode ray tube according to claim 1, in which: 6. A cathode ray tube according to claim 1, in which: 7. A cathode ray tube according to claim 6, in which:
In cathode ray tubes having an electron gun of the unipotential type, each electron beam is passed through the electric field of the electrostatic focusing lens so as to be focused thereby on the screen, and such lens usually comprises first and second axially spaced, annular electrodes extending around the tube axis and being at the same potential, and a third annular electrode extending between the first and second electrodes and being at a different potential, for example, at a substantially lower potential, to establish the focusing electric field. In order to minimize spherical aberrations of the beam focused on the screen, it is desirable that the electrostatic focusing lens be equivalent to an optical lens of large diameter and having relatively flat surfaces, that is, surfaces with large radii of curvature:
In an electrostatic focusing lens, the surface curvatures of the equivalent optical lens are dependent upon the gradient of the potential along the optical axis between the first and second electrodes, and the gradient of the potential is, in turn, dependent upon the potential difference between the first and second electrodes and the third or intermediate electrode and also upon the axial distance between the first and second electrodes and the diameter of the third electrode. Since the electron gun is positioned within the neck of the cathode ray tube envelope, it will be apparent that the diameter of the third or intermediate electrode of the electrostatic focusing lens is limited by the diameter of the neck. Thus, the diameter of the equivalent optical lens can be increased by increasing the diameter of the intermediate electrode only to a limited extent. If the axial distance between the first and second or end electrodes of the electrostatic focusing lens is reduced to decrease the potential gradient in the field along the optical axis, and hence to increase the radii of curvature of the surfaces of the equivalent optical lens, the focusing effect of the lens is decreased and, therefore, it is necessary to undesirably increase the distance from the focusing lens to the screen and also the overall length of the tube. If the potential difference between the intermediately electrode and the end electrodes is to be reduced, it becomes necessary to apply a relatively high voltage to the intermediate electrode, bearing in mind that the end electrodes are usually at the anode voltage which is generally in the range of from 13 to 20 kv. The application of a relatively high voltage, such as, a voltage of 4 to 5 kv. or more, to the intermediate electrode is disadvantageous in that it requires additional circuitry for producing that high voltage, and further in in that there is the possibility of discharges occurring between the closely spaced leads and pins that supply the voltages to the intermediate electrode and to the grids by which the beam is produced and modulated.
The need for an electrostatic focusing lens of single-gun, equivalent to an optical lens of large diameter and having surfaces of large radii of curvature is particularly acute in the case of single-gun, plural-beam cathode ray tubes of the type disclosed in U.S. Pat. No. 3,448,316, issued June 3, 1969, and having a common assignee herewith.
In such single-gun, plural-beam cathode ray tubes adapted for use as a color picture tube in a television receiver, a cathode structure emits electrons which are formed into a plurality of electron beams and such beams are made to converge or cross each other substantially at the optical center of an electrostatic focusing lens which is common to all the beams and focuses the beams on the electron-receiving screen. The fact that all of the beams pass through the center of the focusing lens diminishes the aberrations introduced by the latter as compared with earlier proposed arrangements in which at least two of the beams pass through the focusing lens at substantial distances from the optical axis. However, optimum reduction of aberration again requires that the electrostatic focusing lens for focusing the beams which converge to cross each other at its optical center be equivalent to an optical lens of large diameter having surfaces of large radii of curvature.
One suitable method of achieving an electrostatic focusing lens equivalent to an optical lens of large diameter and having surfaces of large radii of curvature is disclosed in my copending patent application, Ser. No. 846,533, filed July 21, 1969 corresponding to Japanese Pat. application No. 93589/68, filed Dec. 19, 1968; wherein an auxiliarly electrode is disposed within the intermediate electrode of the lens to reduce the potential gradient in the focusing electric field; however, there are other suitable methods of achieving this result without the necessity of utilizing an auxiliary electrode.
Accordingly, it is an object of this invention to provide a unipotential, focusing type electron gun for a single-beam or plural-beam cathode ray tube in which the electrostatic focusing lens is made equivalent to an optical lens of large diameter having surfaces of large radii of curvature, without unduly increasing the diameter of the tube neck or the length of the tube and further without reducing the focusing effect of the lens.
In a cathode ray tube according to an aspect of this invention, for example, a color picture tube in which a plurality of electron beams are made to converge or cross each other substantially at the optical center of an electrostatic focusing lens by which the beams are all focused on the electron-receiving screen of the tube; the electrostatic focusing lens is constituted by first and second axially spaced, annular electrodes extending around the tube axis and being at the same potential, for example, approximately the anode voltage of the tube, and a third annular electrode assembly extending between the first and second electrodes and which includes an axial array of at least three annular electrode portions, the electrode portions and the ends of the axial array being at a different potential than the first and second electrodes, for example, a voltage substantially lower than the anode voltage, to establish the focusing electric field, while at least one of the electrode portions intermediate the end portions is at a potential that deviates from the potential of the end electrode portions, in a direction toward the potential of the first and second electrodes, for example, the same potential of approximately the anode voltage of the tube, so as to reduce the potential gradient in the focusing electric field and thereby make the electrostatic lens equivalent to a large diameter optical lens having surfaces with large radii of curvature.
In an electrostatic focusing lens for a cathode ray tube, as aforesaid, the axial array preferably comprises an odd number of electrode portions spaced apart from each other, with the one electrode portion being in the middle of the array.
The above, and further object, features and advantages of the invention, will appear from the following detailed description of illustrative embodiments of the invention which is to be read in conjunction with the accompanying drawings, in which:
FIG. 1 is a diagrammatic axial sectional view of a conventional single-beam, unipotential focusing electron gun;
FIG. 2 is a fragmentary axial sectional view of an electrostatic focusing lens in accordance with an embodiment of the present invention;
FIG. 3A is a graphical illustration of the variations of potential along the tube axis in focusing lenses according to the prior art and this invention, respectively;
FIGS. 3B and 3C are graphical illustrations of the lines of equal potential in focusing lenses according to the prior art and this invention, respectively;
FIG. 4 is a fragmentary axial sectional view of a color picture tube employing an electrostatic focusing lens according to the present invention.
Referring to the drawings in detail, and initially to FIG. 1 thereof, it will be seen that a conventional single-beam unipotential electron gun 10 for a cathode ray tube is there shown to include a cathode 11 constituting an electron beam generating source, first and second control grids 12 and 13 having aligned apertures 14 and 15, respectively, and an electrostatic focusing lens 16. The lens 16 includes first and second end electrodes 17 and 18 which are annular, axially spaced from each other and coaxial with the tube axis x--x, and a relatively larger diameter third or intermediate annular electrode 19 which is also coaxial with the tube axis and extends between end electrodes 17 and 18 and axially overlaps the latter.
In operating the electron gun 10, appropriate voltages are applied to grids 12 and 13 and to electrodes 17, 18 and 19. For example, with the voltage of cathode 11 as a reference, a voltage of 0 to -400 v. is applied to first grid 12 for modulating the beam, a voltage of 0 to 500 v. is applied to grid 13 to cause the bundle of electrons of the single-beam to converge to a point source substantially within aperture 15, a voltage of 13 to 20 kv. is applied to the intermediate electrode 19.
The voltage applied to electrodes 17 and 18 may conveniently be anode voltage applied to the conductive layer 24 at the inner surface of the tube which further has a phosphor screen 23 for receiving the electrons of the single beam 25. With the distribution of applied voltages, as given above, the bundle or rays of electrons of beam 25 which diverge from the tube axis x--x after passing through aperture 15 are converged or focused at a point on screen 23 by passage through the electric field thus established within electrode 19 between electrodes 17 and 18, and which is
equivalent to an optical lens represented in broken lines at L on FIG. 1 and centered between electrodes 17 and 18.
When the axial distance between electrodes 17 and 18 is sufficient to ensure that the overall length of the tube is not undersirably large and the diameter of electrode 19 is suitable to permit a reasonable diameter of the tube neck, the field of electrostatic focusing lens 16 has a steep potential gradient as indicated by the curve P on FIG. 3A which represents the potentials along the tube axis x--x at various distances from the plane y--y passing through the optical center of lens 16 or its equivalent optical lens L. With such a steep potential gradient, the equivalent optical lens L is of limited diameter and has surfaces with relatively small radii of curvature. As shown graphically on FIG. 3B, the small radii of curvature of the surfaces of equivalent optical lens L result from the steep gradient of the lines p of equal potential within the electric field of electrostatic focusing lens 16, which lines p as shown, are at substantial angles with respect to axis x--x.
Thus, in focusing beam 25, the conventional electrostatic lens 16 may impart spherical aberrations to the beam with resultant poor resolution of the picture produced when the beam is made to scan screen 23, as by the usual deflection yoke (not shown).
In accordance with this invention, the above-mentioned spherical aberrations are substantially diminished by providing an axial array of at least three electrode portions in place of the conventional single intermediate electrode of the electrostatic lens 16, with the electrode portions at the ends of the array being at a different potential than the end electrodes of equal potential and with at least one intermediate electrode portion being at a potential different from the end portions and approaching the potential of the end electrodes to reduce the angles of the lines p' (FIG. 3C) of equal potential with respect to the tube axis x--x and to decrease the potential gradient along such axis, as indicated at P' on FIG. 3A, whereby to make the electrostatic lens equivalent to an optical lens L' (FIG. 3A) of relatively large diameter and having surfaces of large radii of curvature.
As shown on FIG. 2, in which the several parts of an electrostatic focusing lens 16a are identified by the same reference numerals employed in connection with the above description of FIG. 1, but with the letter "a" appended thereto, the electrostatic focusing lens 16a provided according to this invention is there shown to be comprised of end electrodes 17a and 18a, and an intermediate electrode assembly, generally indicated by the reference numeral 19a, in the form of an axial array of three electrode portions 30, 31, and 32. Although assembly 19a is shown for purposes of illustration to have three electrode portions, a larger, preferably odd number of electrode portions may be provided.
In the illustrated embodiment, the end electrode portions 30, 32 of the axial array constituting electrode 19a are at a potential substantially different from the potential of the end electrodes 17a and 18a, and may be connected to each other by a conductor 33. More specifically, the potential of electrode portions 30 and 32 may be substantially lower than the potential of end electrodes 17a and 18a, and may typically be 0 v. to 600 v. compared to 13 kv. to 20 kv. for end electrodes 17a and 18a. The potential difference provides an electric focusing field between the end electrodes 17a, 18a and the intermediate electrode assembly 19a.
The intermediate electrode portion 31 of the axial array is at a potential which deviates or is different from the potential of end electrode portions 30, 32 in the direction toward the potential of end electrodes 17a and 18a, and may typically be at the same relatively high potential, such as the anode voltage applied to the conductive layer at the inner surface of the tube, as is applied to end electrodes 17a and 18a. The means for applying this deviating potential to intermediate electrode portion 31 may be a separate source of potential (not shown) or, when it is desired to apply the same potential to intermediate electrode portion 31 as is applied to end electrodes 17a and 18a, electrode portion 31 may be connected to the end electrodes 17a and 18a by a conductor 35 connected to the end electrode interconnection 20a.
The overall effect of the intermediate electrode assembly 19a, with the potential differences associated with its various electrode portions 30, 31, 32, is to very substantially reduce the potential gradient along the tube axis between electrodes 17a and 18a and to decrease the angles with respect to the tube axis of the lines of equal potential within the field, with the result that the equivalent optical lens L' (FIG. 3A) is of large diameter and has surfaces of large radii of curvature, as is desired.
The electrode portions 30, 31, 32 comprising intermediate electrode assembly 19a are shown spaced apart from each other in the axial array and, when assembly 19a has an odd number of at least three electrode portions, as is preferred, at least the intermediate electrode portion situated at the middle of the axial array is at a higher potential than the end electrode portions.
Of course, the surface radii of the equivalent optical lens can also be changed by changing the distance between electrodes 17a and 18a, the potential difference between electrodes 17a and 18a and end electrode portions 30 and 32, and the potential difference between end electrode portions 30 and 32, and the intermediate electrode portion 31. Thus, the invention permits an electrostatic focusing lens to be obtained that is equivalent to an optical lens with precisely desired surface radii.
Although the invention has been described above with reference to its application to single-beam cathode ray tubes, reference to FIG. 4 will show the application of the invention to a single-gun, plural-beam cathode ray tube of the type disclosed in detail in U.S. Pat. No. 3,448,316. In the cathode ray tube of FIG. 4, three electrically separated cathodes K R , K G , and K B have "red", "green"
and "blue" video signals respectively supplied thereto. The three cathodes are arranged with their electron emitting surfaces in a straight line so as to be aligned with similarly arranged apertures in a first grid G 1 . A second cup-shaped grid G 2 has an end plate disposed adjacent grid G 1 and formed with apertures aligned with the apertures of first grid G 1 . Arranged in order following the grid G 2 in the direction away from control grid G 1 are an open-ended tubular electrode 117, an electrode assembly 119 consisting of an axially array electrode portions 130, 131, 132, and an open-ended tubular electrode 118 constituting an electrostatic focusing lens 116. Electrode 117 includes a relatively small diameter end portion 117a, and is supported with such end portion extending into cup-shaped grid G 2 and spaced radially from the side wall of the latter.
When voltages similar to those indicated for the cathode ray tube of FIG. 1 are applied to grids G 1 and G 2 and electrodes 117, 118, and to the portions of electrode assembly 119 in a manner in accordance with the invention, beams B R , B G , and B B emitted by cathodes K R , K G , and K B are modulated with the three different video signals applied between grid G 1 and the respective cathodes. Grid G 2 and the end portion 117a of electrode 117 cooperate to provide an electric field defining an electrostatic beam converging lens illustrated in broken lines by its optical equivalent 1 and which is operative to converge beams B R and B B toward beam B G so that the three beams cross each other substantially at the location of the optical center of the focusing lens 116.
In order to cause convergence of the beams B R and B B which emerge from electrode 118 along divergent paths, the electron gun of FIG. 4 further has deflecting means 36 that includes shielding plates 37 and 37' provided in spaced opposing relationship to each other and extending axially away from the free end of electrode 118. Deflecting means 36 further includes converging deflector plates 38 and 38', which may be flat, as shown, or outwardly convexly bent or curved, and which are mounted in spaced opposing relation to the outer surfaces of shielding plates 37 and 37' respectively. The plates 37 and 37' and the plates 38 and 38' are disposed so that the beams B B , B G , and B R pass between the plates 37 and 38, between the plates 37 and 37' and between the plates 37' and 38', respectively. The outer plates 38 and 38' may be mounted by attachment to electrode 118, as shown, while plates 37 and 37' are supported from plates 38 and 38' and insulated therefrom, as by insulating supports 39.
A high anode voltage V p , for example of 13 to 20 kv., provided by a source 40 is applied by way of an anode button 41 to the usual conductive layer 42 lining the tube envelope, and a spring contact 43 extends from plate 37 into engagement with layer 42. The high voltage V p thus applied to plate 37 is transmitted to plate 37' by a conductor 44 therebetween. A voltage (V p -V c ) which is lower than the voltage V p by 200 to 300 v., constituting a convergence voltage, is applied to outer plates 38 and 38'. The source of the convergence voltage V c is indicated at 45 and may provide a static convergence voltage and also, if desired, a dynamic convergence voltage varied in accordance with the scanning action. As shown, the voltage (V p -V c ) may be applied by way of a button 46 in the tube neck 47 and a conductor 48 to electrode 117 of focusing lens 116. Further, electrode 118 and intermediate electrode portion 131 are connected with electrode 117 by conductors 49, 50 to receive the voltage (V p -V c ) and, since outer plates 38 and 38' are mounted directly on electrode 118, plates 38 and 38' also receive the voltage (V p -V c ). Thus, convergence voltage differences V c are applied between plates 37 and 38 and between plates 37' and 38' so that beam B B and B R will cross each other and beam B G at a common spot on an aperture grill or mesh 51 and diverge therefrom to strike respective color phosphors b, r and g arranged in suitable arrays to constitute the color screen 52 on the face plate 53 of the tube. A deflection yoke 54 is also provided to cause beams B R , B G , and B B to simultaneously scan screen 52 in the usual manner. The end electrode portions 130, 132 may be electrically connected with a source at low potential, as previously described with respect to similar electrode portions 30, 32 of FIG. 2, by a conductor 55 and may be electrically connected together by another conductor 56 so as to have the same potential applied to both portions 30, 32. The conductor 55 may be electrically connected to one of the pins of the tube, which in turn may be connected to the source of low potential (not shown). Since beams B R , B G and B B all pass substantially through the optical center of electrostatic focusing lens 116 so as to be focused thereby on screen 52, lens 116 imparts diminished aberration to the resulting beam spots on the screen as compared with earlier arrangements in which, for example, beams B R and B B pass through the focusing lens at substantial distances from its optical axis. However, since beams B R and B B pass through lens 116 at substantial angles to the optical or tube axis, optimum reduction or avoidance of aberrations of the beam spots requires that lens 116 be equivalent to a large diameter optical lens having surfaces with large radii of curvature. Thus, in accordance with this invention, the optical lens L' equivalent to electrostatic focusing lens 116 is made to have a large diameter and surfaces with large radii of curvature by providing lens 116 with the intermediate electrode assembly 119 comprised of an axial array of at least three annular electrode portions 130, 131, 132, having the potential differences associated therewith, as previously described. Since the middle electrode portion 131 of the array is at a different potential than end electrode portions 130, 132, the effect is to reduce the potential gradient of the electric field of lens 116, and thus to provide the latter with the desired optical equivalent of a lens of large diameter and large radii of curvature.
Although illustrative embodiments of electrostatic lenses according to 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 made therein by one skilled in the art without departing from the scope or spirit of the invention.
ELECTRON GUN DEVICE FOR COLOR TUBE SONY TRINTRON CRT TUBE TECHNOLOGY:
An electron gun device for color television picture tubes. The electron gun has three cathodes and a plurality of grids. Means are provided for equalizing the cutoff voltages of the cathodes by equalizing the intensity of the electric field reaching the cathodes from the grids. Equalization preferably is obtained by making one or more of the apertures in the first and second grids of a diameter different from that of the other apertures, or by making the distances of one or more of the cathodes from the grids different from the corresponding distances of the other cathodes, or by a combination of both of these arrangements.
1. An electron gun device for a color picture tube comprising two side cathodes and a central cathode therebetween having beam generating surfaces arranged substantially in a row for emitting electrons generally in parallel directions, first and second grids spaced successively in the axial direction away from said beam generating surfaces and having apertures respectively aligned with the beam generating surfaces and through which the emitted electrons are collimated into respective electron beams, and a plurality of electrodes maintained at different potentials and arranged axially following said second grid to provide an electric field defining a main lens means by which said beams are focused and cooperating with said second grid to provide another electric field defining an auxiliary lens means by which the beams from said side cathodes are converged with respect to the beam from said central cathode for passage of all of the beams through the center of said main lens means, the angle of a cone that can be projected to the center of said beam generating surface of said central cathode from the peripheries of the respective aligned apertures of said grids being smaller than the angles of the corresponding cones for said side cathodes for equlizing the effects of said other electric field at said beam generating surfaces of said cathodes so that the latter will have equal cutoff voltages. 2. An electron gun according to claim 1, in which at least one of the apertures of said first and second grids which are aligned with said central cathode is of a size smaller than the sizes of the apertures of said grid aligned with said side cathodes. 3. An electron gun according to claim 1, in which said beam generating surface of the central cathode is at a distance from the aligned aperture in at least one of said first and second grids that is greater than the distance from the beam generating surfaces of said side cathodes to the corresponding apertures of the grids.
In certain prior color picture tubes having multiple cathodes, the cutoff voltages of the cathodes are not equal to one another. The result of this imbalance is that the gamma characteristics of the three colors in the picture produced by the tube are different and the colors are not natural.
In view of the foregoing, a major object of this invention is to provide a plural-cathode electron gun device whose cathodes have the same cutoff voltages. A further object of the invention is to provide a relatively simple and inexpensive means for equalizing the cutoff voltages of such cathodes.
In accordance with the present invention, the foregoing objects are met by the provision of means for equalizing the cathode cutoff voltages by equalizing the intensity of the electric field reaching the cathodes from the grids of the electron gun. The equalization means selectively limits the amount of flux reaching one or more of the cathodes. In the preferred embodiment of the invention, equalization is accomplished by making one or more of the apertures in the first and second grids of a diameter different from that of the other apertures, or by making the distances of one or more of the cathodes from the grids different from the corresponding distances of the other cathodes, or by a combination of both of these arrangements.
Further objects and advantages of the invention will be pointed out or made apparent in the following description and drawings.
In the drawings:
FIG. 1 shows a typical color television picture tube in which the electron gun of this invention can be used;
FIG. 2 is an enlarged, broken-away partially schematic view of a portion of the electron gun shown in FIG. 1;
FIGS. 3A, 3B, 4A, 4B and 4C are views similar to that of FIG. 2, each showing a different embodiment of the invention;
FIG. 5 is an enlarged detailed view of the preferred embodiment of the invention; and
FIG. 6 is a graph illustrating certain performance characteristics of the electron gun of the present invention.
FIG. 1 of the drawings shows a single-gun, plural-beam color picture tube 10 which is described in detail in U. S. Pat. application Ser. No. 697,414, filed on Jan. 12, 1968, and assigned to the same assignee as this application. The color picture tube 10, which is known by the name "Trinitron," includes a glass envelope 11 (indicated in broken lines) having a neck 12 and cone 13 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 grid or shadow mask G P . Disposed within the neck 12 is an electron gun A having cathodes K R , K G , and K B , each of which is a beam-generating source with its thermal electron-emitting surface disposed as shown in a plane which is substantially perpendicular to the longitudinal 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 substantially horizontal planes, with the alignment of the central beam B G being coincident with the axis of the gun.
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 assembled positions shown in the drawings by means of suitable non-illustrated support means of an insulating material.
For operation of the electron gun A 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 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 of electron gun which has a single cathode and first and second single-apertured grids.
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 100 V are applied to the cathodes K R , K G and K B , and bias voltages of 0V, 300V, 20KV, 200V and 20KV may be applied, respectively, to the first and second grids G 1 and G 2 , and the electrodes G 3 , G 4 and G 5 .
Further included in the electron gun A 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'. More specifically, a voltage V P which is equal to the voltage applied to the electrode G 5 , may be applied to both shielding plates P and P', and a voltage V Q , which is some 200 to 300V 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 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 at the center of the main lens L. 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 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 between adjacent grid wires g P of the beam selecting grid 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 and S B with each of the arrays or sets of color phosphors forming a color picture element as in a chromatron type color picture tube. Thus, it will be understood that the common spot of beam convergence corresponds to one of the thusly formed color picture elements.
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 in conventional manner through a non-illustrated graphite layer which is provided on the inner surface of cone 13 of the tube envelope. The grid wires of screen grid G P may have a post-focusing voltage V M ranging, for example, from 6 to 7KV applied thereto as indicated.
To summarize the operation of the depicted color picture tube of FIG. 1, the respective electron beams B B , B G and B R will be converged at screen grid G P and will diverge therefrom in such manner that electron beam B B wll strike the "blue" phosphor S B , electron beam B G will strike the "green" phosphor S G and electron beam B R will strike the "red" phosphor S R of the array or set corresponding to the grid aperture at which the beams converge. Electron beam scanning of the face of the color phosphor screen is effected in conventional manner, for example, by horizontal and vertical deflection yoke means indicated in broken lines at D and which receives horizontal and vertical sweep signals whereby a color picture will be provided on the color screen. Since, with this arrangement, the respective electron beams are each passed, for focusing, 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 said main lens, whereby improved color picture resolution will be provided.
FIG. 2, which is an enlarged view of the cathode region of the tube 10 shown in FIG. 1, shows thermal electron emitting surfaces 14, 15 and 16 of three cathodes K R , K G and K B which are arranged in a plane 21 which is perpendicular to the longitudinal axis of the tube. The first grid G 1 is arranged in a similarly perpendicular plane 22 which is located at a distance D 1 from the plane 21. The three circular apertures g 1R , g 1G and g 1B of grid G 1 have equal diameters φ 1R , φ 1G , and φ 1B . The second grid G 2 is arranged in another similarly perpendicular plane 23 which is located at a distance D 2 from the plane 22. The three apertures g 2R , g 2G and g 2B of grid G 2 have equal diameters φ 2R , φ 2G and φ 2B .
Applicants have discovered that when a high voltage is applied to the third grid G 3 , the intensity of the electric field reaching the center cathode K G is greater than the intensity of the electric field reaching the other cathodes on both sides, and that the cutoff voltage (absolute value) of the cathode K G is greater than the cutoff voltages of the other cathodes K B and K R . This difference in cutoff voltages causes the problems set forth hereinabove. That is, although the video signal voltages applied to the cathodes K R , K G and K B may be selected to have the same voltages to produce a white picture, because of the cutoff voltage imbalance, the video signal voltages must be changed with respect to each other according to the differences in their cutoff voltages.
Two arrangements are shown in FIGS. 3A and 3B for providing the same cutoff characteristics for the cathodes K R , K G and K B .
The arrangement shown in FIG. 3A, the electric field reaching the cathode K G through the aperture g 1G is reduced by selecting the diameter φ 1G of the central aperture g 1G in the first grid G 1 to be smaller than the diameters φ 1B and φ 1R of the other apertures g 1B and g 1R in the first grid.
The arrangement of FIG. 3B is like that of FIG. 3A except that the diameter φ 2G of the central aperture g 2G of the second grid G 2 also is smaller than the diameter of its neighboring apertures.
Other arrangements for the same purpose are shown in FIGS. 4A, 4B and 4C. In each of these arrangements, the diameters of the apertures in grids G 1 and G 2 are uniform, but the distances D 1 and/or D 2 relating to the central electron beam (green) is made greater than the corresponding distances for the other electron beams (blue and red) in order to equalize the intensity of the electric field reaching each cathode.
In the FIG. 4A arrangement, the intensity of the electric field reaching the central cathode K G is reduced by locating the beam-emitting surface 15 of that cathode farther away from grids G 1 and G 2 than the other cathodes by a distance D' 1 . Of course, this has the effect of locating cathode K G at a greater distance from the control electrode G 3 .
In the FIG. 4B arrangement, the same effect is achieved by bending the metal plate forming grid G 2 away from grid G 1 by a distance D' 2 in the vicinity of the central aperture g 2G .
In the FIG. 4C arrangement, the structural features shown in FIGS. 4A and 4B have been combined to give an even greater reduction in the electric field intensity at the surface 15 of cathode K G .
FIG. 5 shows one specific example of the gun device described in the foregoing description. The material of which the grids G 1 , G 2 and G 3 ar
e formed is stainless steel of 0.2 mm. thickness. Other dimensions and the voltages applied to the grids are shown in FIG. 5. It can be seen that the FIG. 3A arrangement is used in the FIG. 5 structure; that is, the diameter φ 1G is 0.77 mm, and φ 2G is greater, 0.8 mm.
FIG. 6 shows experimentally observed relationships between various voltages observed in the structure shown in FIG. 5. In FIG. 6:
Ekco is the cutoff voltage between the cathode K and the first grid G 1 ; that is, the negative voltage necessary to be applied to G 1 to cause cathode cutoff;
Ec 2 is the voltage applied to the second grid G 2 . The cutoff characteristics of the side beams are shown as line A in FIG. 6. Line B represents the cutoff characteristic of a structure like the FIG. 5 structure except that both φ 1G and φ 2G are equal to 0.8 mm; that is, a structure in which the diameters of the center apertures of the first and second grids G 1 and G 2 are equal to diameters of the corresponding side apertures. It is seen from FIG. 6 that there is a difference of about eight volts between the cutoff characteristic curves A and B throughout the section labeled "operating range."
In the gun device actually shown in FIG. 5; that is, one having a center aperture of the first grid G 1 whose diameter φ 1G is smaller than the diameter of its neighboring apertures, the cutoff characteristics of the center beam are shown as Line C. The differences between the cutoff voltages of the center beam and the side beams are so small as to be negligible in the "operation range." Thus, the problem of differing cathode cutoff voltages has been solved.
In each of the embodiments of this invention, the relative reduction in the diameter of the apergure g 1G and/or the aperture g 2G (FIGS. 3A and 3B), or the increase of the distance from the beam generating surface 15 of the central cathode K G to the portion of grid G 1 having the corresponding aperture g 1G and/or to the portion of the grid G 2 having the corresponding aperture g 2G , serves to relatively decrease the angle of the cone that can be projected from the peripheries of the apertures to the center of the beam generating surface 15. Thus, although the electric field constituting the auxiliary lens L' (FIG. 1) is most intense at the axis of the gun, the effect of that field at surface 15 of central cathode K G is minimized so as to be equalized with the effect of the field at surfaces 14 and 16 of side cathodes K B and K R .
The above description of the invention is intended to be illustrative and not limiting. Various changes or modifications in the embodiments described may occur to those skilled in the art and these can be made without departing from the spirit or scope of the invention as set forth in the claims.
A support for the grid structure of a cathode-ray tube in which the support is stressed to compensate for any expansion of the grid wires due to heating, the support having a pair of opposed parallel arms with the grid wires attached to and extending transversely between the arms, and a pair of braces supporting the arms at the Bessel points, the braces being stressed in a direction substantially parallel to the direction of the grid wires so that as the grid wires expand due to heat the braces will expand a
corresponding amount to maintain a substantially constant tension of the grid wires.
1. A support for the grid elements of a cathode ray tube comprising a pair of opposed parallel arms, a plurality of said grid elements affixed to said arms and extending transversely therebetween, a pair of generally C-shaped braces supporting said arms and attached thereto substantially at the Bessel points and formed to lie in surfaces substantially parallel to the surface defined by said grid elements, said braces being stressed a sufficient amount in a direction substantially parallel to the direction of said grid elements whereby as said grid elements expand said braces expand a corresponding amount to maintain the tension on all of said grid elements substantially uniform.
2. A support for a grid structure of a cathode ray tube comprising a pair of opposed parallel arms, a plurality of flexible grid wires affixed to said arms and extending therebetween, a pair of mechanically resilient braces supporting said arms and attached thereto at locations inwardly spaced from the ends of said arms substantially at the Bessel points, and said braces being stressed in a direction substantially parallel to the direction of said flexible grid wires to apply tension stress to said grid wires whereby as said flexible grid wires expand due to heat generated during the operation of the tube, said braces expand due to their resiliency and their being stressed a corresponding amount to maintain the tension on all of said flexible grid wires substantially uniform.
3. A support in accordance with claim 2 wherein said braces are substantially C-shaped.
4. A support in accordance with claim 2 wherein a damping rod extends over said flexible members to substantially eliminate mechanical vibration of said flexible members.
5. A support in accordance with claim 4 wherein said damping rod is stretched between said braces.
6. A support in accordance with claim 5 wherein said damping rod is flexible and is attached substantially to the center of said braces.
7. A support according to claim 6 wherein the damping rod is inclined relative to flexible grid wires.
8. A support in accordance with claim 6 wherein said damping rod resiliently presses against said flexible members.
9. A support according to claim 8 wherein said damping rod has a diameter of between 30 and 50 microns.
As is well known in the prior art, color cathode ray tubes employ, for electron beam postdeflection and focusing, a grid structure such that a plurality of parallel grid wires are stretched across a parallelogramic frame between a pair of opposed sides. Such a grid structure is produced in the following manner. A plurality of parallel grid wires are stretched on a master frame under predetermined taut conditions and a grid frame is put on the grid wires from inside of the master frame.
The grid wires are then fixed to a pair of opposed supports of the grid frame and are thereafter severed along the margins of the grid frame. In this case, the grid frame is prestressed inwardly by a turnbuckle to apply a maximum tension to the grid wires secured to the central portion of the opposed supports of the grid frame and a smaller tension to those fixed to end portions of the supports, ensuring that all the grid wires are subjected to substantially uniform tension by the restoring force of the prestressed grid frame after disassembling it from the master frame.
Such a grid structure may be regarded as one where a plurality of grid wires are stretched at substantially uniform tension on a parallelogramic frame prestressed in a manner to be displaced the most at the center of the frame. When a predetermined positive potential is applied to such a grid structure and electron beams are emitted from the electron gun of a cathode ray tube toward the fluorescent screen thereof, electron beams of several to 10-odd percent strike against the grid wires and are discharged therethrough to thereby heat the grid wires. As a result of this, the temperature of the grid wires is raised several-10 degrees and the wires expand. An examination of the expanded grid wires shows that since the displacement of the frame is greatest at the center thereof, elongation of the grid wires of that portion due to thermal expansion is cancelled by the restoring force of the prestressed frame as if the grid wires had not been elongated. Accordingly, the grid wires are still subjected to substantially the same original tension, and hence do not sag. The elongation of the grid wires lying on both sides of the central grid wires cannot be absorbed with the displacement of the frame at those particular portions, since the displacement is basically small. Consequently, when the elongation of the grid wires exceeds the displacement of the frame, the grid wires are likely to sag. Even if the grid wires do not sag, they are not pulled at a predetermined tension and are readily vibrated at great amplitude to lower the picture quality of the reproduced picture when subjected to accidental small shocks.
The above can easily be understood from the fact that when all the grid wires have substantially the same length 1, their elongation resulting from thermal expansion is 1 and the amount of restoration of the distorted frame is 1 at the center thereof, the amount of restoration of the frame on both sides of the center thereof is smaller than that at the central portion.
This defect is remarkable especially in the grid structure of a color cathode ray tube of the type where a plurality of ribbonlike grid elements are stretched in parallel with phosphor strips and function as a kind of shadow mask. In this type of structure three electron beams are impinged upon three different color emissive phosphor strips through slits defined between adjacent grid elements.
A grid structure such as described above has been proposed in an attempt to increase the electron beam transmission factor of the so-called shadow mask in which a plate having bored therethrough a plurality of apertures is used as a mask for the electron beam. In such a grid structure, however, the grid elements are secured only at both ends to the frame, so that the grid elements heated by electron beams striking thereon radiate heat mainly through the ends fixed to the frame. Further, the transmission factor of the electron beam through such a grid is 10-odd to 20-odd percent and the temperature of the grid elements rises up to 100° to 130° C. Consequently this type of grid structure encounters the same problems as in the Chromatron (Registered Trademark) type color cathode ray tube.
In addition to the sag of the grid elements, nonuniformity in the tension applied to the grid elements raises another problem in such a grid structure as mentioned above. Even slight nonuniformity in the tension causes the grid elements to twist and the space between adjacent grid elements becomes wider in a direction normal to the incident direction of the electron beam, although the pitch of the grid elements remains unchanged. As a result of this, there is the possibility that the electron beam strikes on a phosphor strip other than a predetermined one, especially a phosphor strip adjacent the predetermined one to cause unnecessary color emission. Therefore, the nonuniformity in the tension applied to the grid elements should be avoided.
Accordingly, one object of this invention is to provide a grid structure which is adapted such that the grid elements are always subjected to a predetermined tension and do not sag during operation, though heated by electron beams.
Another object of this invention is to provide a grid structure for shadow-mask type color cathode ray tubes in which the grid elements heated by electron beams do no sag during operation to thereby ensure uniformity in the spacing between adjacent grid elements and hence prevent unnecessary bombardment of the phosphor strips by the electron beam.
Still another object of this invention is to provide a grid structure which is constructed such that the grid elements are protected from shocks applied from the outside and caused by electron beam bombardment.
Other objects, features and advantages of this invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:
FIGS. 1 and 2 are schematic diagrams for explaining the present invention;
FIG. 3 is a plan view showing one example of a grid structure for color cathode ray tubes produced according to this invention;
FIG. 4 is a side view of the grid structure illustrated in FIG. 3;
FIG. 5 is a plan view illustrating another example of the grid structure of this invention;
FIG. 6 is a schematic diagram showing the manner in which the grid elements are mounted on a grid frame;
FIG. 7 is a plan view showing another modified form of the present invention;
FIG. 8 is a cross-sectional view taken along the line A--A in FIG. 7;
FIG. 9 illustrates in perspective the plate supports employed in the example of FIG. 7;
FIG. 10 similarly shows in perspective a resilient support;
FIG. 11 is a plan view showing still another modification of the present invention;
FIG. 12 is a side view of the grid structure depicted in FIG. 11; and
FIG. 13 is a perspective view of the grid structure shown in FIG. 11.
FIG. 1 is a schematic diagram showing displacement (indicated by broken lines) of a bar 1 of a length L having two fulcra 2A and 2B when subjected to a uniformly distributed load 3 acting substantially perpendicular to the bar. In order to minimize the displacement of the bar 1, the fulcra 2A and 2B are located at such positions that the displacement δ 1 of both end portions of the bar 1 is equal to the displacement δ 2 of the central portion. Such positions of the fulcra are referred to as the Bessel points, and when the distance from the end of the bar 1 to the fulcrum 2A or 2B is taken as b, b/L=0.223. The length L of the bar does not indicate the actual length but a range over which the load 3 is applied.
If a pair of such bars are arranged in parallel relation as a pair of opposed frame members of a grid frame, a plurality of grid wires or elements stretched between the frame members at substantially uniform tension are subjected to the aforementioned uniformly distributed load 3. In other words, where a pair of bars 1 and 1' (not shown) of a length L constituting two frame members are arranged in parallel relation and a plurality of parallel grid wires or elements are stretched between the bars substantially at right angles thereto under approximately uniformly tensioned conditions and fulcra 2A, 2B and 2A', 2B' (not shown) respectively supporting the bars are located at positions satisfying the aforementioned requirement b/L=0.223, the bars are deformed to be bent at both ends and between the fulcra by the load caused by the tension of the grid wires or elements in a direction of the tension but the displacement ratio, that is, the displacement per unit load is at minimum. Consequently, the displacement ratio of the frame of this invention (indicated by the broken line B in FIG. 2) is far smaller than that of the conventional grid frame (indicated by the full line A in FIG. 2) of the type where the fulcra are located at both ends of two bars constituting the frame members, and accordingly the grid frame of this invention virtually deformed as compared with the deformation of the conventional grid frame. If the rigidity of the bar 1 is increased up to maximum, the deformation of the frame can be neglected.
The tension of the grid wires or elements stretched between the two bars 1 and 1' (not shown) corresponding to the load 3 shown in FIG. 1 is produced by pressing the two bars with a resilient support (not shown) in a direction opposite to the load 3 in a manner to force away the two fulcra 2A and 2A' (2A' not shown) and 2B and (2B' not shown) from each other.
Referring now to FIGS. 3 to 10, the construction of the grid structure of this invention will be described in detail by way of example.
As clearly shown in the figures, the grid structure of this invention comprises a frame of a predetermined configuration which consists of bar supports 4 and 4' corresponding to the aforementioned bars 1 and 1' and a pair of substantially C-shaped resilient supports 5 and 5' supporting the bar supports 4 and 4' at or in the vicinity of the Bessel points B A , B B and B A ', B B ' thereof, and a plurality of ribbon-shaped grid elements of, for example, stainless steel are stretched between the bar supports 4 and 4' at a predetermined pitch under predetermined distribution of tension. Reference numeral 7 indicates generally the grid structure.
The bar supports 4 and 4' may be formed of a metal such as iron, stainless steel or the like and in the illustrated example the bar supports 4 and 4' are square in cross section and are bent to conform to the panel to which the grid structure will be attached. The resilient supports 5 and 5' may be formed of a metal such as iron, stainless steel or the like and are substantially C-shaped so as not to disturb the irradiation of the phosphor screen by the electron beam emitted from the electron gun of a cathode ray tube. It is a matter of course that the supports 5 and 5' may be configured at will so long as they do not disturb the electron beam directed to the fluorescent screen of the cathode ray tube. The grid elements 6 may also be formed of a metal such as iron, stainless steel or the like.
With such an arrangement, since the pair of bar supports 4 and 4' constituting one portion of the frame are jointed to the resilient supports 5 and 5' as a unitary structure at or in the vicinity of the Bessel joints B A , B B and B A ', and B B ', the bar supports 4 and 4' may be regarded as a rigid body with respect to the load caused by the tension of the grid elements. Accordingly, when the grid elements 6 that are stretched between the bar supports 4 and 4' uniformly at a predetermined tension expand by heat resulting from the electron beam bombardment thereon, the bar supports 4 and 4' are pulled outwards by the resilient supports 5 and 5' in a parallel relationship by a distance corresponding to the length of the grid elements which have been extended by the thermal expansion. Consequently, although the absolute value of the tension is different from the initial one, the initial distribution of the tension over the entire grid elements remains unchanged.
The foregoing description has been made in connection with a grid structure in which the grid elements are of substantially the same length at the both end portions and central portion of the bar supports and hence they are expanded substantially equally due to thermal expansion. According to our experiments on a grid structure in which the bar supports of square cross section were made of stainless steel and had a size of about 10 mm. × 10 mm. × 240 mm. and 400 grid elements 0.5 mm. wide, 0.1 mm. thick and about 180 mm. long (the length of the grid elements on the end portions of the bar supports were 175 mm. and that of the elements of the central portion: 185 mm.) were stretched between the bar supports at a tension of about 350 g. for each grid element, it has been ascertained that although the grid elements were heated by electron beams and extended due to thermal expansion during operation, accidents such as vibration of the grid elements due to nonuniformity of the tension or color contamination due to irregularity of the space between adjacent grid elements were not caused. Further, it has been found that the deviation from the initial distribution of the tension of the grid elements caused by the thermal expansion thereof resulting from the collision of the electron beam therewith were compensated for by the stretch or shrinkage of the grid elements or slight restoring force of the bar supports.
In addition, it has also been found that if the deviation of the length of the grid elements is in a range of ±20 percent relative to its mean value, the length of the grid elements extended by the thermal expansion is extremely short and the initial distribution of the tension of the grid elements is maintained during operation by the stretch and shrinkage of the grid elements or by compensation due to the restoring force of the bar supports.
In the prior art a very complicated device is required for stretching grid elements on a grid frame, but this can be readily achieved by the following method. As shown in FIG. 5, for example, a thin stainless steel plate 8 of a predetermined size is first prepared and is subjected to etching to remove selected areas, thus providing metal strips 8a arranged at a predetermined pitch. At the same time, slits 8b are formed for a predetermined number of metal strips 8a (every three metal strips in the figure) in the plate 8 at both marginal portions thereof. In a similar manner, slits 8c are formed in the plate 8 on both sides of the metal strips 8a. Portions 8d separated by the slits 8b are then respectively held by chucks 9A and 9B as shown in FIG. 6. In this case, the number of the chucks 9A and 9B corresponds to that of the portions 8d. The chucks 9B are supplied with a moderate tension in accordance with the thickness and the quality of material of the portions 8d, but such tension may be applied to both of the chucks 9A and 9B. Substantially the same tension is applied to the metal strips by means of, for example, a coiled spring 10 as shown in the figure. Under such taut conditions, a pair of bar supports 11 and 11' are disposed under the plate 8 at predetermined positions and the plate 8 is welded to the bar supports. In this case, the bar supports 11 and 11' are supported by a pair of resilient supports at or in the vicinity of their Bessel points, though not shown, and the resilient supports are slightly bent inwardly so as to apply a predetermined tension to the metal strips when the portions 8d are released from the chucks 9A and 9B. It is preferred that the force for bending the two resilient supports be equal to the tension (the total tension of all the metal strips) applied to the metal strips 8a by the spring 10. In such a case when the chucks 9A and 9B are removed, the tension of the metal strips 8a due to the spring 10 is applied to the strips 8a by the resilient supports, so that the tension of the metal strips 8a remains unchanged before and after the removal of the chucks.
Subsequent to the welding of the plate 8, the portions 8d projecting outside of the bar supports 11 and 11' are cut off and both end portions of the slits 8c are also cut off. The slits 8c are provided for facilitating the cutting of the plate 8, and hence they are not always necessary. In the manner described above, the metal strips 8a can readily be stretched between the bar supports 11 and 11' with predetermined distribution of the tension. In this case, the metal strips 8a are coupled together at both ends. It is possible, of course, that the end portions of the metal strips 8a are welded to the bar supports 11 and 11'. The slits 8b are provided for preventing the plate 8 from becoming creased when applying a tension to the edges of the plate 8 and for ensuring uniformity of the tension applied to each metal strip 8a. In the absence of the slits 8b, it is extremely difficult to apply the tension to the metal strips 8a with the predetermined distribution.
While the metal strips 8a are subjected to substantially equal tension by the chucks 9A and 9B in the above example, the distribution of the tension may be changed as desired in accordance with the shapes of the bar supports and the resilient supports and the condition of the resilient supports welded to the bar supports in the vicinity of the Bessel points thereof to ensure uniformity of the tension applied to the metal strips by the resilient supports.
The electron beam transmission factor depends upon the width of the metal strips or the diameter and the pitch of the metal wires, which are usually selected to render the electron beam transmission factor approximately 20 percent in view of the relationship to the width of each phosphor strip of the fluorescent screen of cathode ray tubes.
I
n FIGS. 7 and 8 there is illustrated another example of this invention, in which reference numeral 15 designates generally a grid structure. A pair of plate supports 12 and 12' are supported by a framelike resilient support 13 at or in the vicinity of their Bessel points to provide a frame of a predetermined configuration, and grid elements 14 in the form of, for example, metal strips are stretched between the pair of platelike supports 12 and 12'.
The plate supports 12 and 12' may be formed of a metal such as iron, stainless steel or the like and, as shown in FIG. 9, one marginal edge of each plate support is curved so as to conform to the surface of the panel of a cathode ray tube with which the finished grid structure will be assembled. The resilient support 13 may also be formed of a metal such as iron, stainless steel or the like and this support 13 has projections 13a at places substantially corresponding to the Bessel points of the plate supports 12 and 12' as illustrated in FIG. 10. Further, the support 13 has L-shaped plate support-retaining members 13b formed integrally at places corresponding to the projections 13a.
The pair of plate supports 12 and 12' are mounted on the retaining members 13b of the resilient support 13 in such a manner that the projections 13a of the support 13 engage the plate supports 12 and 12' at or in the vicinity of their Bessel points, and the plate supports and the resilient supports are held together by predetermined jigs in a manner to produce a predetermined pressure at or in the vicinity of the Bessel points of the plate supports 12 and 12' by the projections 13a of the resilient support 13. Then, the grid elements 14 are stretched between the pair of plate supports 12 and 12' at a predetermined distribution of tension.
With such an arrangement, the pair of plate supports 12 and 12' are supported by the projections 13a of the resilient support 13 at or in the vicinity of their Bessel points, so that the equilibrium of the tension is very stable after the grid elements 14 have once been stretched at the predetermined distribution of the tension. Accordingly, the equilibrium of the tension is not lost by a slight variation in the tension after stretching the grid elements 14 and the grid frame is not deformed. Further, the equilibrium of the tension is difficult to loose by thermal expansion of the frame or the grid elements 14 due to a temperature rise during operation, and even if the equilibrium of the tension is lost, the tension promptly balances, so that deformation of the frame is very slight. Consequently, the position of the grid elements 14 is not shifted and the electron beam always impinges upon the fluorescent screen accurately at a predetermined location, so that phenomenon such as color contamination is not caused thereby ensuring reproduction of a clear picture. In addition, since the grid structure described above is simple in construction, its fabrication is easy and the yield is greatly increased. Even if the grid elements 14 are stretched between the plate supports 12 and 12' at substantially uniform tension, the deformation of the frame is very slight as indicated by the dotted line B in FIG. 2. Accordingly, there is no possibility that the position of the grid elements 14 is shifted by a slight deformation of the frame and by thermal expansion of the grid elements or the frame due to a temperature rise. That is, even if the grid elements 14 are stretched at uniform tension, the aforementioned many advantages can still be obtained.
The assembling of the grid structure with the panel of a cathode ray tube can readily be achieved by the same means as mentioned previously or by other known means, and accordingly no description will be given. Further, it is needless to say that the aforementioned method can be used for stretching the grid elements, and the metal wires may be stretched as the grid elements 14 at a predetermined pitch in place of the metal strips.
The foregoing description has been made in connection with only several examples of this invention, and the material, shape and the like of the bar supports, plate supports, grid elements, resilient supports and so on can be suitably selected at will, if necessary. However, the bar supports and the plate supports are desired to be formed of a conductive material so as to establish electric fields between the supports and the grid elements. Further, these supports are not restricted to the bar and plate supports.
When the grid structure is used in color picture tubes the grid elements are caused to vibrate by mechanical vibration due to external shocks or electron beam bombardment. In FIGS. 11 to 13 there is shown still another example of this invention in which the grid structure is designed to prevent such unwanted vibration of the grid elements.
In the figures reference numerals 21A and 21B indicate a pair of bar supports, and 22A and 22B represent substantially C-shaped resilient supports supporting the bar supports 21A and 21B at or in the vicinity of their Bessel points to constitute a grid frame generally designated by 23. Reference numeral 24 identifies grid elements such as ribbonlike metal strips which are stretched between the pair of bar supports 21A and 21B at a predetermined tension distribution and pitch. These members are identical with those described in the foregoing examples.
In the present example, a damping rod formed of, for example, a metal wire is provided in contact with the grid elements 24.
For example, resilient pieces 26A and 26B are planted on the outside of the resilient supports 22A and 22B substantially at the center thereof, and the damping rod 25 is stretched between the resilient pieces 26A and 26B. In this case the damping rod 25 is stretched in a direction of the lines of the raster (in the electron beam-scanning direction) and it is preferred that the damping rod 25 be stretched obliquely in a range of 30° to 45° relative to the electron beam scanning direction.
With such an arrangement, the grid elements 24 are resiliently pressed by the damping rod 25, and hence are not likely to be caused to vibrate by mechanical shocks from the outside and electron beam bombardment. Even if vibration occurs, it is immediately suppressed by the damping rod 25, thus preventing a bad influence by the vibration of the grid elements. The provision of the damping rod 25 avoids not only the vibration of the grid elements but also irregularity in the spacing thereof which results from twisting of the grid elements. Namely, when the grid elements 24 are heated by collision of the electron beam therewith and are to be twisted due to thermal expansion, the damping rod 25 presses the grid elements 24 to prevent twisting of the grid elements to hold the space between adjacent grid elements as predetermined, ensuring that the electron beam impinges only on a predetermined phosphor strip. Further, the provision of the damping rod 25 is only to stretch it in contact with the surfaces of the grid elements and hence can be achieved with great ease. The damping rod 25 may be a mechanically strong metal wire of, for example, tungsten, stainless steel, inconel or the like. The use of such a mechanically strong wire avoids breakage of the damping rod or insufficient pressing of the grid elements as with conventional damping rods of glass fiber in grid structures for the Chromatron (Registered Trademark) type picture tubes.
The damping rod 25 formed of the above-mentioned metals or other ones is preferred in terms of mechanical strength and is free from secondary electron beam emission by the electron beam. It is preferred that the diameter of the damping rod 25 to 30 to 50 microns. With a diameter of, for example, 100 microns, the mechanical strength of the damping rod increases but the reproduced picture is adversely affected by the damping rod. With a diameter of less than 30 microns, the mechanical strength of the rod 25 decreases and its pressing effect of the grid elements becomes weak. With a smaller diameter damping rod, the bad influence on the reproduced picture is decreased correspondingly, but the influence of a damping rod 50 microns in diameter on the reproduced picture is hardly noticeable. According to our experiments, a tungsten wire of a diameter from 30 to 50 microns yields good results. In the foregoing example, the damping rod 25 is stretched between the two resilient pieces 26A and 26B but either or both of them may be dispensed with. The shape and position of the resilient pieces are not limited to those in the above example. For example, it is possible that resilient wires are stretched on the frame on both sides of the grid elements instead of the resilient pieces and the damping rod is stretched between the resilient wires. Further, the damping rod 25 may be attached to the grid elements 25.
It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of this invention.
Electron beam scanning velocity modulation (svm) In beam scan velocity modulation (SVM) system for a television receiver,
in brief ,
a video signal is applied to a differentiator followed by a limiting differential amplifier. A driver amplifier coupled to the limiting amplifier drives an output stage that supplies current to an SVM coil. Certain video signals with large high frequency content may tend to produce excessive dissipation in the devices of the output stage. To prevent this, a current source for the differential amplifier is controlled by a voltage which is a measure of the average current through the output stage. The magnitude of the current source is varied to thereby vary the peak-to-peak signal output from the limiting amplifier to prevent overdissipation of the output devices. The presence of random noise in the video signal can produce unwanted SVM operation which can impair the viewed image. The unwanted noise component in the video signal can be reduced in amplitude by coring. The coring is unaffected by the variable limiting.
Video signal reproducing apparatus with electron beam scanning velocity modulation further explanation and overview:
In a video signal reproducing apparatus having a cathode ray tube in which at least one electron beam is made to scan a screen in line-scanning and vertical directions while the intensity of the beam is modulated to establish the brightness of a video picture to be displayed on the screen, and in which bright picture portions are represented by respective high level portions of a video signal; a waveshaping circuit receives the video signal and acts thereon to provide a compensated video signal in which the width of each high level portion between the respective rising and falling edges is increased, the compensated video signal is employed to control the intensity of the electron beam, and the rising and falling edges of each high level portion of the compensated video signal are detected, as by a differentiating circuit or a delay line circuit, to provide respective output signals by which the scanning velocity of the beam in the line-scanning direction is modulated. The waveshaping circuit for providing the compensated video signal may be constituted by a delay line and an OR circuit having inputs to which the original video signal and the delayed video signal are applied, or by a differentiator receiving the original video signal and having its output applied to a polarity equalizer. a source of a video signal representing at least the brightness of a video picture and in which bright picture portions are represented by video signal portions of high level defined between respective rising and falling edges;
waveshaping means receiving said video signal from said source for providing a corresponding compensated video signal in which the width of each of said high level signal portions between said respective rising and falling edges is increased, said wave shaping means including delay means receiving said video signal from said source for providing a delayed video signal, and OR gate means having inputs receiving said video signal from said source and said delayed video signal, respectively, and an output at which said compensated video signal appears;
a cathode ray tube having a screen, an electron gun including beam producing means directing an electron beam generally along the axis of the tube toward said screen for impingement on the latter and being controlled in response to said compensated video signal from said waveshaping means so that the intensity of the beam is modulated in accordance with said compensated video signal, and deflection means for causing said beam to scan said screen in line-scanning and vertical directions, respectively;
detecting means also receiving said compensated video signal from said waveshaping means and detecting said rising and falling edges of the high level signal portions of said compensated video signal for providing output signals in correspondence to the detected rising and falling edges; and
beam velocity modulation means for modulating the scanning velocity of said electron beam in said line-scanning direction in accordance with said output signals from said detecting means.
2. A video signal reproducing apparatus according to claim 1; in which said OR gate means includes first and second transistors having respective collector-emitter paths connected in parallel between an operating voltage source and said output of the OR gate means, said first and second transistors further having respective base electrodes constituting said inputs receiving said video signal from said source thereof and said delayed video signal, respectively. 3. A video signal reproducing apparatus according to claim 1; in which said detecting means includes means differentiating said compensated video signal so as to provide said output signals in correspondence to said detected rising and falling edges. 4. A video signal reproducing apparatus comprisinga source of a video signal representing at least the brightness of a video picture and in which bright picture portions are represented by video signal portions of high level defined between respective rising and falling edges;
waveshaping means receiving said video signal from said source for providing a corresponding compensated video signal in which the width of each of said high level signal portions between said respective rising and falling edges is increased, said waveshaping means including differentiating means for differentiating the video signal from said source of the latter, polarity equalizing means acting on the differentiated signal from said differentiating means for providing a differentiated signal of one polarity, and adder means adding the video signal from said source thereof and said differentiated signal of one polarity to provide said compensated video signal;
a cathode ray tube having a screen, an electron gun including beam producing means directing an electron beam generally along the axis of the tube toward said screen for impingement on the latter and being controlled in response to said compensated video signal from said waveshaping means so that the intensity of the beam is modulated in accordance with said compensated video signal, and deflection means for causing said beam to scan said screen in line-scanning and vertical directions, respectively;
detecting means also receiving said compensated video signal from said waveshaping means and detecting said rising and falling edges of the high level signal portions of said compensated video signal for providing output signals in correspondence to the detected rising and falling edges; and
beam velocity modulation means for modulating the scanning velocity of said electron beam in said line-scanning direction in accordance with said output signals from said detecting means.
5. A video signal reproducing apparatus according to claim 4; in which said polarity equalizer includes a first diode connected in parallel with a series connection of an inventer and a second diode. 6. A video signal reproducing apparatus according to claim 4; in which said detecting means includes means differentiating said compensated video signal so as to provide said output signals in correspondence to said detected rising and falling edges. 7. A video signal reproducing apparatus comprisinga source of a video signal representing at least the brightness of a video picture and in which bright picture portions are represented by video signal portions of high level defined between respective rising and falling edges;
waveshaping means receiving said video signal from said source for providing a corresponding compensated video signal in which the width of each of said high level signal portions between said respective rising and falling edges is increased;
a cathode ray tube having a screen, an electron gun including beam producing means directing an electron beam generally along the axis of the tube toward said screen for impingement on the latter and being controlled in response to said compensated video signal from said waveshaping means so that the intensity of the beam is modulated in accordance with said compensated video signal, and deflection means for causing said beam to scan said screen in line-scanning and vertical directions, respectively;
detecting means also receiving said compensated video signal from said waveshaping means and detecting said rising and falling edges of the high level signal portions of said compensated video signal for providing output signals in correspondence to the detected rising and falling edges, said detecting means including means differentiating said compensated video signal so as to provide said output signals in correspondence to said detected rising and falling edges; and
beam velocity modulation means for modulating the scanning velocity of said electron beam in said line-scanning direction in accordance with said output signals from said detecting means.
8. A video signal reproducing apparatus comprisinga source of a video signal representing at least the brightness of a video picture and in which bright picture portions are represented by video signal portions of high level defined between respective rising and falling edges;
waveshaping means receiving said video signal from said source for providing a corresponding compensated video signal in which the width of each of said high level signal portions between said respective rising and falling edges is increased;
a cathode ray tube having a screen, an electron gun including beam producing means directing an electron beam generally along the axis of the tube toward said screen for impingement on the latter and being controlled in response to said compensated video signal from said waveshaping means so that the intensity of the beam is modulated in accordance with said compensated video signal, and deflection means for causing said beam to scan said screen in line-scanning and vertical directions, respectively;
detecting means also receiving said compensated video signal from said waveshaping means and detecting said rising and falling edges of high level signal portions of said compensated video signal for providing output signals in correspondence to the detected rising and falling edges; and
beam velocity modulation means for modulating the scanning velocity of said electron beam in said line-scanning direction in accordance with said output signals from said detecting means, said beam velocity modulation means including a tubular electrode on said axis of the tube for the passage of said electron beam axially through said tubular electrode between said beam producing means and said screen, said tubular electrode being in two parts which are axially separated along a vertical plane that is inclined relative to said axis of the tube, and means for applying said output signals from the detecting means across said two parts of the tubular electrode.
9. A video signal reproducing apparatus according to claim 8; in which said tubular electrode is included in electron lens means for focusing said beam at said screen, and said electron lens means further includes at least another tubular electrode arranged coaxially in respect to the first mentioned tubular electrode, with a relatively low potential being applied to said first tubular electrode and a relatively high potential being applied to said other electrode for producing an electrical field which effects said focusing of the beam.
1. Field of the Invention
This invention relates generally to video signal reproducing apparatus, such as, television receivers, and more particularly is directed to providing such apparatus with improved arrangements for effecting electron beam scanning velocity modulation so as to significantly enhance the sharpness of the reproduced picture or image.
2. Description of the Prior Art
When the phosphor screen of a video signal reproducing apparatus, such as, the screen of the cathode ray tube in a television receiver, is scanned by an electron beam or beams so as to form a picture or image on the screen, the beam current varies with the luminance or brightness level of the input video signal. Therefore, each electron beam forms on the phosphor screen a beam spot whose size is larger at high brightness levels than at low brightness levels of the image so that sharpness of the reproduced picture is deteriorated, particularly at the demarcation between bright and dark portions on areas of the picture. Further, when a beam scanning the screen in the line-scanning direction moves across the demarcation or edge between dark and bright areas of the picture, for example, black and white areas, respectively, the frequency response of the receiver does not permit the beam intensity to change instantly from the low level characteristic of the black area to the high level characteristic of the white area. Therefore, the sharpness of the reproduced image is degraded at portions of the image where sudden changes in brightness occur in response to transient changes in the luminance or brightness of the video signal being reproduced. The increase in the beam current and in the beam spot size for bright portions of the reproduced picture or image and the inadequate frequency response of the television receiver to sudden changes in the brightness or luminance level of the incoming video signal are additive in respect to the degradation of the horizontal sharpness of the reproduced image or picture.
It has been proposed to compensate for the described degradation of the horizontal sharpness of the picture or image by employing the so-called "aperture correction or compensation technique," for example, as described in "Aperture Compensation for Television Camera," R. C. Dennison, RCA Review, 14,569 (1953). In accordance with such aperture correction or compensation technique, the intensity of the electron beam is first decreased and then increased at those portions of the picture image at which the brightness changes from a low level to a high level. Such modification or compensation of the electron beam intensity can be achieved by twice differentiating the original video signal so as to obtain a compensation signal which is added to the original video signal for obtaining a compensated video signal applied to the cathode of the cathode ray tube and having high level portions with relatively more steeply inclined rising and falling edges. However, with the foregoing aperture compensation technique, the peak luminance or brightness levels of the compensated video signal are increased and, as applied to the cathode of the cathode ray tube, result in beam currents that are increased relative to the maximum beam currents resulting from the original video signal so that the beam spot size is actually increased. By reason of the foregoing, the aperture compensation technique or method is insufficient for achieving really sharp definitions between light and dark areas of the reproduced picture or image, particularly in the case of relatively large screen areas, even though the described technique creates a visual edge effect which, to some extent, and particularly in the case of relatively small screens, registers psychologically as improved edge sharpness.
In order to avoid the above-described disadvantage of the aperture correction or compensation technique, it has been proposed to employ the so-called "beam velocity modulation method or technique" in which transient changes in the brightness level of the video signal are detected, and the scanning velocity of the electron beam in the line-scanning direction is modulated in accordance with the thus detected transient changes, for example, as described in detail in U.S. Pat. Nos. 2,227,630, 2,678,964, 3,752,916, 3,830,958 and 3,936,872, with the last two enumerated patents having a common assignee herewith.
More particularly, in the known beam velocity modulation technique or method, the original video signal representing brightness or luminance of a video picture and which incorporates "dullness" at abrupt changes in the luminance level due to the inadequate frequency response of the television receiver circuits to such abrupt changes in luminance level, is applied directly to the cathode or beam producing means of the cathode ray tube for modulating the intensity of the electron beam or beams, and such original video signal is also differentiated to obtain a modulation signal which is employed for effecting a supplemental horizontal deflection of the beam or beams in addition to the main or usual horizontal deflection thereof. The modulation or compensation signal may be supplied to the main deflection coil or yoke or to a supplemental deflection coil which is in addition to the main deflection coil with the result that the overall magnetic field acting on the beam or beams for effecting horizontal deflection thereof is modulated and corresponding modulation of the beam scanning velocity in the line-scanning direction is achieved. As is well known, the effect of the foregoing is to improve the sharpness of the image or picture in the horizontal direction. Since the original video signal is applied directly to the cathode or beam producing means of the cathode ray tube without increasing the level thereof at sharp changes in the brigheness level of the video signal, as in the aperture correction or compensation technique, the beam velocity modulation technique does not cause changes in the beam spot size so that sharpness of the image or picture in the horizontal direction is conspicuously improved.
However, it is a characteristic or inherent disadvantage of existing beam velocity modulation arrangements that the improved horizontal sharpness of the reproduced image or picture is achieved at the expense of a reduction in the width of the bright or white areas of the reproduced image or picture so that such bright or white areas are slimmer or more slender than would be the case if the depicted scene were accurately or precisely reproduced.
Accordingly, it is an object of this invention to provide a video signal reproducing apparatus with an improved arrangement for effecting beam scanning velocity modulation and thereby achieving enhanced sharpness of the reproduced image or picture, particularly at the demarcations between relatively dark and light picture areas, without reducing the widths of such light picture areas.
Another object is to provide an arrangement for effecting beam scanning velocity modulation, as aforesaid, which is relatively simple and is readily applicable to video signal reproducing apparatus, such as, television receivers.
In accordance with an aspect of this invention, in a video signal reproducing apparatus having a cathode ray tube in which at least one electron beam is made to scan a screen in line-scanning and vertical directions while the intensity of the beam is modulated to establish the brightness of a video picture to be displayed on the screen, and in which bright picture portions are represented by respective high level portions of an original video signal; a waveshaping circuit receives the original video signal and acts thereon to provide a compensated video signal in which the width of each high level portion between the respective rising and falling edges is increased, the compensated video signal is employed to control the intensity of the electron beam, and the rising and falling edges of each high level portion of the compensated video signal are detected to provide a respective output or modulation signal by which the scanning velocity of the beam in the line-scanning direction is modulated.
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.
FIGS. 1A and 1B are diagrammatic views representing reproduced video pictures including bright and dark areas;
FIGS. 2A-2D are waveform or graphic views to which reference will be made in explaining the aperture correction or compensation technique of the prior art;
FIGS. 3A-3E are waveform or graphic views to which reference will be made in explaining the beam velocity modulation technique of the prior art and the disadvantage inherent therein;
FIG. 4 is a schematic view illustrating a circuit according to an embodiment of the present invention for effecting beam velocity modulation in a video signal reproducing apparatus;
FIG. 5 is an axial sectional view of an electron gun in a cathode ray tube which is particularly suited for use with a beam velocity modulation arrangement according to this invention;
FIGS. 6A-6F are waveforms or graphic views to which reference will be made in explaining the operation of the circuit according to this invention as shown on FIG. 4;
FIG. 7 is a schematic view illustrating another embodiment of a portion of the circuit shown on FIG. 4 for effecting beam velocity modulation according to this invention;
FIGS. 8A-8D are waveforms or graphic views to which reference will be made in explaining the operation of the embodiment of this invention illustrated by FIG. 7;
FIG. 9 is a diagrammatic view illustrating a circuit that may be used for one of the components shown on FIG. 7; and
FIG. 10 is a wiring diagram illustrating another embodiment of a portion of the circuit shown on FIG. 4 for effecting beam velocity modulation in accordance with this invention.
Referring to the drawings in detail, and initially to FIG. 4 thereof, it will be seen that the present invention is related to a television receiver or other video signal reproducing apparatus 10 having a cathode ray tube 11 in which a beam producing means including a cathode 12 directs an electron beam B generally along the axis of the tube envelope toward a phosphor screen S on the faceplate of the tube. In the apparatus 10, the intensity of electron beam B, and hence the brightness of the beam spot produced at the location where the beam B impinges on screen S, is modulated in accordance with a video signal applied to cathode 12 and representing at least the brightness of a video picture to be reproduced on screen S. The cathode ray tube 11 is further shown to include the conventional deflection means or yoke 13 by which beam B is made to scan screen S in the line-scanning or horizontal and vertical directions, respectively. The simultaneous modulation of the beam intensity by the video signal applied to cathode 12 and the scanning of screen S by beam B in response to sweep signals applied to yoke 13 will result in the reproduction of an image or picture on screen S. The image or picture reproduced on screen S may be constituted by at least one white or bright picture portion, for example, in the form of a rectangle as shown at 14a on FIG. 1A, 
or in the form of a vertical line as indicated at 14b on FIG. 1B, and relatively darker picture portions. In any case, it will be understood that, in each line or horizontal interval of a video signal received by a television receiver and utilized in the cathode ray tube of the latter for reproducing a horizontal increment of an image or picture at a vertical position in the latter which is included in the bright or white area 14a or line 14b, the respective bright picture portion is represented by a corresponding high level video signal portion defined between rising and falling edges 15r and 15f, respectively (FIG. 2A). If the transmitted video signal S T is to represent a white or bright shape or area surrounded by a black or very dark background with a sharp demarcation therebetween, the rising and falling edges 15r and 15f of the high level signal portion will be precipitous, that is, substantially vertical, as shown, so as to represent the desired high frequency change in luminance level. However, the usual television receiver circuit, for example, comprised of RF and IF amplifiers and a video detector, and by which the video signal to be used in the cathode ray tube is derived from the received television signal, has a frequency response that is inadequate to accommodate the mentioned high frequency components of the transmitted video signal S T . Thus, the video signal S O (FIG. 2B) which is available in the television receiver for controlling the intensity of the electron beam or beams in the cathode ray tube is relatively "dull" that is, it has decreased high frequency components, as represented by the illustrated sloping, rising and falling edges 16r and 16f of the high level signal portion. Such relatively dull video signal S O is hereinafter referred to as the "original video signal," and such terminology is reasonable when considered from the point of view of the input side of the cathode ray tube. Further, the term "original video signal" has often been used in the prior art in the same sense that it is used herein.
The decrease in the high frequency components of the original video signal S o as compared with the transmitted video signal S T causes a decrease in the horizontal sharpness of the reproduced image or picture, that is, the sloping, rising and falling edges 16r and 16f (FIG. 2B) result in a gradual change from dark to bright and from bright to dark, respectively, rather than in the sudden changes in brightness represented by the transmitted signal S T (FIG. 2A). Horizontal sharpness of the reproduced image or picture is furthermore decreased by the fact that, in the cathode ray tube, the electron beam current varies with the luminance or brightness level of the video signal applied to the cathode ray tube and, when the luminance level is high, for example, to represent a bright or white area of the picture, the beam spot size caused by impingement of the electron beam on the phosphor screen is enlarged to further decrease or deteriorate the sharpness of the reproduced picture.
In seeking to compensate for the above-described lack of sharpness of the reproduced picture by the known aperture correction or compensation technique, the original video signal S O (FIG. 2B) is differentiated twice so as to obtain a compensation signal S B (FIG. 2C) which is added to the original video signal S O for providing a compensated video signal S C (FIG. 2D). As shown, the compensated video signal S C has rising and falling edges 17r and 17f which are more steeply inclined than the corresponding rising and falling edges 16r and 16f of the original video signal S O . However, when the compensated video signal S C is applied to the cathode of a cathode ray tube for controlling the intensity or beam current of the electron beam or beams therein, the sharpness of the reproduced picture is not conspicuously improved. The foregoing results from the fact that, by adding the compensation signal S B to the original video signal S O for obtaining the compensated video signal S C applied to the cathode of the cathode ray tube, the maximum beam current corresponding to the peak luminance level of signal S C is increased, as compared with the maximum beam current corresponding to the peak luminance level of original video signal S O , with the result that the beam spot size resulting from compensated video signal S C is enlarged. Such enlargement of the beam spot size causes a decrease in sharpness of the reproduced picture, as previously noted, and thus substantially defeats any increase in sharpness that might result from the relatively more steeply inclined rising and falling edges 17r and 17f of the compensated video signal S C .
In the known beam velocity modulation technique for improving horizontal sharpness of the reproduced image or picture, the dull original video signal S O (FIG. 3A) is applied, without alteration, to the cathode or beam producing means of the cathode ray tube for determining the intensity or beam current of the electron beam or beams in the cathode ray tube. The original video signal S O is also subjected to differentiation to obtain a compensation signal S A (FIG. 3B). The compensation signal S A is applied to a supplemental deflection means which is in addition to the main deflection coils or yoke so that the horizontal deflection field for effecting scanning movement of each beam in the line-scanning direction is modified or compensated, as shown on FIG. 3C. As a result of such modified or compensated horizontal deflection field, the beam scanning velocity in the line-scanning direction, is modulated as shown on FIG. 3D. It will be appreciated that, during each period T a on FIG. 3D, the beam scanning velocity is increased so that a decreased amount of light is emitted from the phosphor dots or areas on the screen that are impinged upon during each period T a . On the other hand, during each period T b , the beam velocity is decreased so that an increased amount of light is emitted from the phosphor dots or areas impinged upon by the electron beam during each period T b . Therefore, the variation, in the horizontal direction across the screen, in the amount of emitted light, is substantially as indicated on FIG. 3E, from which it will be apparent that the sharpness of the reproduced image or picture in the horizontal direction is improved. Since the original video signal S O is still applied to the cathode of the cathode ray tube for controlling the beam intensity, the beam spot size is not changed or increased by reason of the beam velocity modulation and, therefore, the improvement in sharpness in the horizontal direction is not adversely affected by increasing beam spot size, as in the aperture correction or compensation technique. However, the conventional beam velocity modulation technique still has the disadvantage that the width of each white or bright portion of the picture or image reproduced on the screen is less than that which would result from the original video signal S o in the absence of the beam velocity modulation, as is apparent from the comparison of FIG. 3E with FIG. 3A.
Generally, in order to avoid the foregoing disadvantage of the previously known beam velocity modulation technique, the present invention employs a waveshaping circuit receiving the original video signal and providing a corresponding compensated video signal in which the width of each high level signal portion is increased relative to the corresponding width of the original video signal. The compensated video signal from the mentioned waveshaping circuit is applied to the cathode or beam producing means of the cathode ray tube for modulating the intensity of the electron beam or beams therein in accordance with the compensated video signal, while the rising and falling edges of the high level signal portions of the compensated video signal are detected to provide a corresponding output or modulating signal applied to the beam velocity modulation means for modulating the scanning velocity of the electron beam or beams in accordance with such output signal.
Referring in detail to FIG. 4, it will be seen that, in the video signal reproducing apparatus 10 according to this invention, as there shown, an antenna 18 receives a television signal which includes the transmitted video signal S T (FIG. 2A) and applies the same to conventional video circuits indicated schematically at 19 and which include the usual RF and IF amplifiers and video detector for deriving the original video signal S O (FIG. 6A) from the received television signal. As noted, the video circuits 19 of television receiver 10 are conventional so that no detailed explanation thereof will be included herein. The video signal from circuit 19 is supplied through a video amplifier 20 to a waveshaping circuit 21 which, in accordance with this invention, is operative to increase the width of each high level portion of the original video signal S O from video amplifier 20.
The waveshaping circuit 21 is shown to include a pair of transistors 22 and 23 having their collectors connected together to an operating voltage source +V cc , while the emitters of transistors 22 and 23 are connected together to one end of a resistor 24 having its other end connected to ground. The original video signal S O (FIG. 6A) 
is applied to the base of transistor 22 from video amplifier 20 through a resistor 25, and the base of transistor 22 is further connected to ground through a resistor 26. The original video signal S O from video amplifier 20 is further applied through a resistor 27 and a delay line 28 to the base of transistor 23 which is further connected to ground through a resistor 29. The resistors 27 and 29 provide impedance matching for the delay line 28, while the resistors 25 and 26 are provided for level adjusting purposes, that is, to ensure that the level of the original video signal S O applied to the base of transistor 22 from video amplifier 20 will be equal to the level of the delayed video signal S D (FIG. 6B) applied to the base of transistor 23 and which is delayed by the time τ in respect to the original video signal. Finally, the output of waveshaping circuit 21 is derived from a connection point between the emitters of transistors 22 and 23 and resistor 24.
It will be apparent that, during the period T A (FIG. 6C), the level of original video signal S O applied to the base of transistor 22 is higher than the level of the delayed video signal S D applied to the base of transistor 23, so that transistor 22 is turned ON and transistor 23 is turned OFF. During the next period T B , at which time both original video signal S O and delayed video signal S D are at the same level, transistors 22 and 23 are both turned ON. Finally, during the concluding period T C , the level of delayed video signal S D is higher than the level of original video signal S O , so that transistor 22 is turned OFF and transistor 23 is turned ON. Thus, as is apparent on FIG. 6C, the level of the compensated video signal S K obtained across resistor 24, that is, at the output of waveshaping circuit 21, is equal to the level of the input video signal S O during the period T A , is equal to the level of either the original video signal S O or the delayed video signal S D during the period T B , and is equal to the level of the delayed video signal S D during the period T C . In other words, transistors 22 and 23 of waveshaping circuit 21 operate as an OR gate circuit in respect to the original video signal S O and the delayed video signal S D applied to the two inputs of such OR circuit defined by the base electrodes of the two transistors. Further, by comparing the compensated video signal S K (FIG. 6C) with the original video signal S O (FIG. 6A), it will be appreciated that the effect of waveshaping circuit 21 is to increase the width of each high level portion of the original or incomming video signal.
Referring again to FIG. 4, it will be seen that the compensated video signal S K is applied through a video amplifier 30 to the cathode electrode 12 of cathode ray tube 11 for modulating the intensity of electron beam B therein. Simultaneously, the rising and falling edges of the high level signal portions of compensated video signal S K are detected to provide a corresponding output or modulating signal by which the scanning velocity of the electron beam B in the line-scanning direction is modulated. More particularly, in the television receiver 10 of FIG. 4, the compensated video signal S K from waveshaping circuit 21 is applied to a differentiation circuit 31 which acts as a detector for detecting the rising and falling edges of the compensated video signal and which provides a corresponding output signal in the form of a differentiated signal S V (FIG. 6D). Such differentiated signal S V is applied to a beam velocity modulation means, for example, in the form of the supplemental deflection device 32 of FIG. 4, for modulating the scanning velocity of the electron beam B in the line-scanning direction in accordance with the differentiated signal S V from differentiator 31. The supplemental deflection device 32 may be constituted, as shown, by two spaced apart plate-like electrodes 32a and 32b directed vertically in cathode ray tube 11 and arranged for the passage of electron beam B therebetween, with the differentiated signal S V being applied across the plate-like electrodes 32a and 32b so as to produce a corresponding electrical field by which the scanning velocity of the beam, in the line-scanning direction, is modulated, for example, as shown on FIG. 6E.
Although the beam velocity modulation means is, in the embodiment of FIG. 4, constituted by a supplemental deflection device 32 in the form of a pair of plate-like electrodes 32a, 32b across which the output of differentiation circuit 31 is applied, the present invention is preferably employed in connection with a cathode ray tube of the type disclosed in detail by U.S. Pat. No. 3,936,872, and having an electron gun provided with a special focusing electrode to also function as the beam velocity modulating means, as shown on FIG. 5. More particularly, in the cathode ray tube 11A of FIG. 5, the neck portion 33 of the tube envelope is shown to contain an electron gun structure including a cathode 12a, a control electrode or grid 35, an acceleration electrode or grid 36, a first anode electrode 37, a focusing electrode 38 and a second electrode 39 all arranged successively in axial alignment along the central axis 40 of the cathode ray tube. The focusing electrode 38 is shown to be tubular and to be formed in two parts 38a and 38b which are axially separated along a vertical plane that is inclined relative to the axis 40 of the tube. For the operation of electron gun 34, appropriate static or bias voltages are applied to grids 35 and 36 and to electrodes 37, 38 and 39. Thus, for example, a voltage of zero to -400 V. may be applied to grid 35, a voltage of zero to 500 V may be applied to grid 36, a relatively high voltage or potential, for example, an anode voltage of 13 to 20 KV. may be applied to electrodes 37 and 39, and a relatively low voltage or potential of zero to only several KV. may be applied to parts 38a and 38b of electrode 38, with all of the foregoing voltages being upon the bias voltage applied to cathode 12a as a reference. With the foregoing voltage distribution, an electron lens field is established around the axis of electrode 38 by the electrodes 37, 38 and 39 to form a main focusing lens by which the electron beam is focused at the screen of the cathode ray tube. Furthermore, the differentiated or modulation signal S V from differentiation circuit 31 of FIG. 4 is applied between parts 38a and 38b of electrode 38 in superposed relation to the static or bias voltage applied to electrode 38 for forming the focusing lens. It will be apparent that, by reason of the described diagonal separation between parts 38a and 38b of focusing lens electrode 38, the application of the differentiated signal or modulation signal S V across electrode parts 38a and 38b results in a respective electric field which is operative to deflect the electron beam or beams in the horizontal or line-scanning direction. Thus, the beam velocity in the line-scanning direction is modulated accordingly.
Whether the velocity modulation signal S V is applied to the plates 32a and 32b of supplemental deflection device 32, or across the parts 38a and 38b of focusing electrode 38, it will be seen that, in accordance with this invention, such velocity modulation signal S V (FIG. 6D) for effecting beam velocity modulation in the line-scanning direction is derived from the compensated video signal S K (FIG. 6C) in which the width of each bright or white signal portion is enlarged as compared with the width thereof in the original video signal S O (FIG. 6A). Therefore, the intensity of light emission is changed or varied in the horizontal direction across the screen in the manner represented by FIG. 6F, from which it is apparent that the sharpness of the reproduced image or picture in the horizontal direction is substantially improved. Furthermore, from a comparison of FIG. 6F with FIG. 6A, it will be apparent that, by a proper selection of the delay time τ of delay line 28, the width of the white or bright portion of the reproduced image or picture is not substantially decreased and may be made to accurately correspond to the width of corresponding high level portion of the original video signal. Therefore, the previously described disadvantage of the known technique for effecting beam velocity modulation has been avoided by the present invention.
Referring now to FIG. 7, it will be seen that, in accordance with another embodiment of this invention, a waveshaping circuit 21' which can be substituted for the waveshaping circuit 21 in the apparatus 10 of FIG. 4, includes a differentiation circuit 41, a polarity equalizer 42 and an adding circuit 43. The original video signal S O (FIG. 8A) 
from video amplifier 20 on FIG. 4 is applied directly to one input of adding circuit 43 and also to differentiation circuit 41 which provides a corresponding differentiated signal S A (FIG. 8B). The differentiated signal S A from circuit 41 is applied to polarity equalizer 42 in which the negative polarity portion of the differentiated signal S A , which corresponds to the falling edge of the original video signal S O , is inverted so as to have a positive polarity. The resulting polarity equalized signal S E (FIG. 8C) is applied to another input of adder circuit 43 so as to be added in the latter to the original video signal S O and thereby obtain the compensated video signal S K (FIG. 8D). Such compensated video signal S K shown on FIG. 8D corresponds generally to the compensated video signal S K previously described with reference to FIG. 6C, and is similarly applicable to amplifier 30 and differentiation circuit 31 of FIG. 4. It will be apparent that the compensated video signal S K (FIG. 8D) obtained from waveshaping circuit 21' also has the width of its high level signal portions enlarged relative to the widths of such signal portions in the original video signal S O . Therefore, when the compensated video signal S K from waveshaping circuit 21' is applied through amplifier 30 to cathode 12 of cathode ray tube 11 and also to differentiation circuit 31 to form therefrom the beam velocity modulation signal S V applied to the supplemental deflection device 32, the resulting beam velocity modulation is performed in the same manner as described above with reference to FIG. 4 so as to obtain improved horizontal sharpness of the resulting reproduced picture or image without narrowing of the bright or white areas of such image or picture.
As shown on FIG. 9, the polarity equalizer 42 employed in the waveshaping circuit 21' of FIG. 7 may simply consist of a first diode 44 connected in parallel with a series connection of an inverter 45 and a second diode 46. The diodes 44 and 46 both have the same polarity so that the positive polarity portion of the differentiated signal S A passes through diode 44, while the negative polarity portion of signal S A , after being inverted by inverter 45, passes through diode 46.
In the embodiment of the invention described above with reference to FIG. 4, the differentiation circuit 31 is employed for detecting the rising and falling edges of the high level signal portions of the compensated video signal S K and for providing output signals or beam velocity modulation signals in correspondence to the detected rising and falling edges. However, reference to FIG. 10 will show that a circuit 31' of a type disclosed in detail in U.S. Pat. No. 3,936,872, may be employed in place of differentiation circuit 31 for providing the desired beam velocity modulating signal. More particularly, circuit 31' is known to contain a single delay line 47 having input and output ends 47a and 47b, with the compensated video signal S K being applied to input end 47a by way of a transistor 48 of collector-common configuration which acts to amplify the signal without altering the phase thereof. More specifically, as shown, the compensated video signal S K is applied to the base electrode of transistor 48 which has its collector connected to ground, while the emitter of transistor 48 is connected through a resistor 49 to an operating voltage source +V cc , and through a resistor 50 to the input end 47a of delay line 47. Further, as shown, the output end 47b of delay line 47 is connected through a bleeder resistor 51 to ground, and is also connected to a transistor 52 of base-common configuration which acts as an impedance converter. More specifically, transistor 52 is shown to have its emitter connected to the output end 47b of delay line 47 while its base electrode is connected to ground through a capacitor 53 and also connected between biasing resistors 54 and 55 which are connected in series between operating voltage source +V cc and ground. Finally, a resistor 56 is connected between the operating voltage source and the collector of transistor 52, and output terminals 57 and 58 are respectively connected to the input end 47a of delay line 47 and to the collector of transistor 52.
In circuit 31', bleeder resistor 51 is dimensioned to provide a relatively small current flow therethrough, while the input impedance, that is, the base-emitter impedance of transistor 52 is very small in respect to the impedance of resistor 51. Therefore, in response to a transient or sharp change in the compensated video signal transmitted along delay line 47, the output end 47b of the latter is shorted to ground so as to cause a negative reflected wave to travel back along delay line 47 to its input end 47a. As a result of the foregoing, the resistor 56 detects the short circuit current at the output end of delay line 47, and more precisely at the collector of transistor 52, so as to provide a corresponding voltage or signal S K1 at output terminal 58 which corresponds to the compensated video signal S K once delayed by the delay line 47. Further, the reflected wave returning to the input end of delay line 47 in response to a transient change in the compensated video signal S K results in a signal S K2 that corresponds to the signal S K twice delayed by the delay line 47. Therefore, in response to a transient change in the signal S K , there is obtained at output terminal 57 a signal S V1 equal to the difference between compensated video signal S K and the twice delayed signal S K2 . When using the circuit 31 of FIG. 10 in place of the differentiation circuit 31 in the apparatus of FIG. 4, the output signal S K1 is applied to the cathode 12 of the cathode ray tube 11 for controlling the intensity of the electron beam, while the output signal S V1 is applied from circuit 31' to supplemental deflecting device 32 for effecting the beam scanning velocity modulation.
In the above described embodiments of the invention, the signal S V or S V1 for controlling the beam scanning velocity modulation has been applied across the plates 32a and 32b of the supplemental deflection device 32 or across the parts 38a and 38b of the focusing lens electrode 38. However, it will be understood that, in all of the described embodiments of the invention, the signal S V or S V1 from circuits 31 or 31', respectively, can be superimposed on the horizontal sweep or deflection signal and applied with the latter to the horizontal deflection coil of the main deflection yoke 13 so as to again modulate the beam scanning velocity in the line scanning direction.
Further, in FIGS. 4 and 5 of the drawings, the invention has been illustrated as applied to a monochrome television receiver for modulating the beam scanning velocity of a single electron beam in the cathode ray tube 11 or 11A. However, it will be understood that the invention is similarly applicable to a color television receiver in which the luminance component of the color television signal is the video signal that is compensated in circuit 21 or 21' and then detected in circuit 31 or 31'.
In any event, it will be apparent that, in a television receiver or other video signal reproducing apparatus according to this invention, the sharpness of the reproduced image or picture is improved without a decrease in the width of the relatively bright or white areas of the reproduced picture.
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 of the invention, as defined inthe appended claims.
SONY TRINTRON CRT COLOR TUBE HAVING ASYMETRICAL ELECTROSTATIC CONVERGENCE CORRECTION SYSTEM / H-STAT CORRECTION SYSTEM TECHNOLOGY.In a single-gun, plural-beam color picture tube in which two beams emerge from a focusing lens along paths that diverge from a central beam emerging along the optical axis of the lens by which all of the beams are focused on the color screen, and the divergent beams are deflected to converge with the central beam by passage through respective electrical fields established between first spaced plates, at opposite sides of the central beam path, and second plates spaced outwardly from the first plates; such plates are disposed closely adjacent to the main deflection yoke by which the beams are made to scan the screen so that the length of the tube can be minimized, and the misconvergence of the beams that may result from the magnetic field produced between the first plates by reason of a current flow induced in the first plates by flux change of the magnetic field of the main deflection yoke is corrected by providing the second plates with different dimensional relationships to the first plates, for example, different distances from the first plates or different distances along the first plates, so that the deflecting effects of the electrical fields are correspondingly different.
1. A plural beam color picture tube comprising a color screen having arrays of color phosphors and beam selecting means with apertures corresponding to said arrays, beam-generating means for directing a plurality of electron beams toward said color screen for impingement on respective phosphors of each array through the corresponding aperture, lens means for focusing said electron beams on said color screen and having an optical center through which all of said beams are passed with one of said beams passing through said lens means along the optical axis of the latter and two of said beams being angled with respect to said optical axis to emerge from said lens means along paths divergent to said axis, electron beam convergence deflecting means interposed between said lens means and said beam selecting means for deflecting said two beams emerging along said divergent paths so as to achieve convergence of all of said beams at an aperture of said beam-selecting means, and magnetic yoke means also interposed between said lens means and said beam-selecting means to produce a magnetic field by which said beams are simultaneously deflected to scan said screen; said convergence deflecting means including first interconnected plates which are spaced apart for the passage of said one beam therebetween, second plates spaced outwardly from said first plates so that each of said two beams passes between a first plate and a second plate and means to apply one voltage to said first plates and a different voltage to said second plates so that the voltage difference between said first plates and said second plates produces electrical fields therebetween for effecting said convergence, said convergence deflecting means being disposed closely adjacent to said magnetic yoke means so as to reduce the necessary length of the tube and as a result of which said magnetic field of the yoke means induces a current flow through said interconnected first plates producing a magnetic field between said first plates which acts on said one beam to cause misconvergence of the beams, and said misconvergence being corrected by providing one of said second plates with different dimensional relationships to its corresponding first plate than the other of said second plates has to its corresponding first plate so that said electrical fields exert unequal deflecting effects on said two beams in coaction with the field of said magnetic yoke means for restoring the convergence thereof with said one beam.
2. A plural-beam color picture tube according to claim 1, in which said second plates are spaced from the respective first plates by different distances so that the flux densities of said electrical fields are different.
3. A plural-beam color picture tube according to claim 1, in which said second plates extend for different distances along the respective first plates in the direction of said beams therebetween so that said two beams pass for different distances through the respective electrical fields.
4. A plural-beam color picture tube according to claim 1, in which said convergence deflecting means and said magnetic yoke means overlap in the direction of the axis of the tube.
In plural-beam color picture tubes of the described type, for example, in the single-gun tube as specifically disclosed in the copending U.S. application Ser. No. 697,414, filed Jan. 12, 1968 now U.S. Pat. No. 3,448,316 and having a common assignee herewith, three laterally spaced electron beams are emitted or originated by a beam generating or cathode assembly and directed in a common substantially horizontal or vertical plane with the central beam coinciding with the optical axis of the single electron focusing lens and the two outer 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 between the focusing lens and the color screen is an electrostatic convergence deflecting means by which the beams divergent from the optical axis are deflected substantially in the plane of origination thereof for causing all of the beams to converge at a common location on a beam-selecting means, such as an aperture grill, and to pass therethrough for impingement on respective color phosphors of a color screen. Further, between the focusing lens and the beam-selecting means, the beams are acted upon by the magnetic fields resulting from the application of horizontal and vertical sweep signals to a main deflection yoke, whereby the beams are made to scan the screen in the desired raster. The convergence deflecting means of the foregoing color picture tube conveniently comprises a first pair of interconnected, spaced plates between which the central beam is passed, and a second pair of plates spaced outwardly from the first plates so that the divergent beams are passed between the first and second plates to be deflected for convergence by electrical fields provided therebetween when one voltage is applied to both first plates and a different voltage is applied to both second plates.
If the above convergence deflecting plates are to be remote from the magnetic fields of the main deflection yoke, the length of the neck of the tube envelope is undesirably increased and requires a corresponding increase in the depth of the television receiver cabinet to accommodate the tube. On the other hand, if the neck portion of the tube is shortened, which requires that the convergence deflection plates extend closely adjacent to the main deflection yoke, a magnetic field of the latter induces a current flow in the closed path constituted by the interconnected first plates between which the central beam is passed, and such current flow produces a magnetic field that deflects the central beam away from accurate convergence with the other two beams.
Accordingly, it is an object of this invention to provide a plural-beam color picture tube of the described type in which the convergence deflection plates are closely adjacent to, or even axially overlapped with respect to the main deflection yoke so as to minimize the necessary length of the neck portion of the tube envelope, and further in which any misconvergence that would result from the proximity of the convergence deflection plates to the main deflection yoke is avoided.
In accordance with an aspect of this invention, the misconvergence that would result from the proximity of the convergence deflection plates to the main deflection yoke is compensated for by providing the second or outer convergence deflection plates with different dimensional relationships to the respective first convergence deflection plates so that the electrical fields established between the first and second plates exert unequal deflecting effects on the beams passing therethrough. The different dimensional relationships mentioned above may involve different spacings between the first and second plates for deflecting one of the divergent beams and between the first and second plates for deflecting the other divergent beam, so that the flux densities are different in the electric fields traversed by the two divergent beams. Alternatively, or in combination with the foregoing, the different dimensional relationship may be provided by giving the second plates different dimensions in the direction along the respective first plates so that the two divergent beams pass for different distances through the respective electric fields.
The above, and other objects, features and advantages of this invention, will be apparent in the following detailed description of illustrative embodiments thereof which is to be read in connection with the accompanying drawing, in which:
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 fragmentary sectional view taken in the same plane as FIG. 1, and which shows the structural arrangement of a portion of such tube in order to reduce the length of the neck portion of the tube envelope;
FIG. 3 is a transverse sectional view taken along the line 3-3 on FIG. 2; and
FIGS. 4 and 5 are fragmentary sectional views showing the arrangements of the convergence deflection plates in a tube as shown on FIGS. 2 and 3 in order to avoid misconvergence in accordance with two respective embodiments of this 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 10 of the type to which this invention may be applied comprises a glass envelop
e (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 apertured beam-selecting grill or shadow mask G P . 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. 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 or other common 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 400 v. 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.
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 focusing lens L, again as indicated in dashed lines. In a typical use of electron gun A, bias voltages of 100 v., 0 v., 300 v., 20 kv., 200 v. and 20 v. 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 .
Further included in the electron gun of FIG. 1 are electron beam convergence deflecting means F which comprise a first pair of shielding plates P and P' disposed in the depicted spaced, relationship at opposite sides of the gun axis, and a second pair of 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 electrode 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 , may be 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 convergence deflecting voltages between plates P' and Q' and plates P and Q and it is, of course, this convergence deflecting voltage V C which will produce electric fields to impart the requisite convergent deflection to electron beams B B and B R .
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 respective electron beams will then pass through the common auxiliary lens L' to cross each other at the 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 intended to be so arranged that 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 G P and then 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. It will be understood that the common spot of beam convergence corresponds to one of the thusly formed color picture elements.
Electron beam scanning of the face of the color phosphor screen is effected by horizontal and vertical deflection yoke means indicated in broken lines at D and which receives horizontal and vertical sweep signals whereby a color picture will be provided on the color screen. Since, with this arrangement, the electron beams are each passed, for focusing, through the center of the main lens L of 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 main lens, whereby improved color picture resolution will be provided.
As shown on FIGS. 2 and 3, the plates P and P', in a structural embodiment of the tube schematically illustrated on FIG. 1, may be supported, at the sides of their ends closest to electrode G 5 , by angle members
12 and 13 secured to a flange 11 at the adjacent end of a tubular extension of electrode G 5 which is, in turn, supported within tube neck N by insulating discs 24 and 25 having getter rings 22 and 23 suitably mounted therebetween. The forward ends of plates P and P' are joined, at the sides of the latter, by bracing members 21 extending therebetween. The voltage V P is applied to plates P and P' through a contact spring 18 extending from one of the bracing members 21 into engagement with a conductive coating 17 which is applied to the inner surface of the cone portion C of the tube envelope and extends into the adjacent neck portion thereof. The voltage V P is applied to coating 17 by way of an anode button (not shown) provided in cone portion C, and is applied to electrode G 5 from plates P and P' by way of angle members 12 and 13. From electrode G 5 , the voltage V P may be applied to electrode G 3 by way of a suitable conductor (not shown). The voltage V P may also be applied to aperture grill G P , as an anode voltage, by way of coating 17.
Posts or pins 14 extend outwardly from plates P and P' and, at their outer ends, carry glass beads 15 by which plates Q and Q' are supported while being insulated with respect to plates P and P'. The voltage V Q is applied to plate Q by a conducting lead 20 extending from a button 19 in neck N and the voltage V Q is applied to plate Q' by way of a conducting lead 16 extending between plates Q and Q' and being spaced from plates P and P'.
In order to reduce the necessary length of neck N of the tube envelope, the convergence deflecting means F is located closely adjacent to the main deflection yoke D, and may even axially overlap the location of the latter as shown on FIG. 2. However, when convergence deflecting means F is thus located, it is disposed within the magnetic field with vertical lines of flux produced by main deflecting yoke D for causing the beams to horizontally scan the color screen. Since plate P, bracing members 21, plate P', angle members 12, 13 and electrode G 5 form a closed loop, the magnetic flux changes in such magnetic field of yoke D induces a current to flow in the closed loop, and the induced current, in turn, produces a magnetic field between plates P and P' that acts on the central beam B G in the direction opposed to the horizontal scanning movement of the beams. Since the other beams B R and B B are not acted upon by the magnetic field between plates P and P' resulting from the induced current, at any instant during each horizontal scan the point at which beam B G reaches the aperture grill G P will lag behind the point on the latter at which beams B R and B B converge, whereby misconvergence results.
In accordance with this invention, such misconvergence is avoided or corrected by providing the convergence deflecting plates Q and Q' with different dimensional relationships to the respective shielding plates P and P' so that the electrical fields between plates P and Q and between plates P' and Q', respectively, will have different deflecting effects on beams B B and B R , respectively, and thus cause such beams to reach the aperture grill at the same point as beam B G notwithstanding the fact that beams B R and B B are not subjected, during horizontal scanning, to the magnetic field acting on central beam B G between plates P and P'.
As shown on FIG. 4, the different dimensional relationships of plates Q and Q' with respect to plates P and P' may refer to the distances by which plates Q and Q' are spaced from plates P and P', respectively. Thus, on FIG. 4, the distance d between plates P and Q is larger than the distance d' between plates P' and Q', from which it follows that the flux density or intensity of the electrical field between plates P' and Q', and hence the deflecting force acting on beam B R , will be greater than the flux density
or intensity of the electrical field between plates P and Q, and hence the deflecting force acting on beam B B . Thus, the convergence deflection of beam B R will be greater than the convergence deflection of beam B B to cause beams B R and B B to converge at a common point with beam B G at the aperture grill.
As shown on FIG. 5, the mentioned different dimensional relationships of plates Q and Q' with respect to plates P and P' may alternatively refer to the distances along plates P and P' that the plates Q and Q' respectively extend. Thus, on FIG. 5, the plate Q is shown to have a length l in the direction of the tube axis that is smaller than the length l' of the plate Q' in the same direction. In view of the foregoing, beam B B will traverse a distance in passing through the electric field between plates P and Q that is greater than the distance traversed by beam B R in passing through the electric field between plates P' and Q'. Thus, once again the convergence deflection of beam B R will be greater than the convergence deflection of beam B B so as to restore proper convergence of the three beams B R , B G and B B at a common point on the aperture grill.
It is also apparent that the measures according to this invention for correcting the described misconvergence as shown on FIGS. 4 and 5 can be combined, that is, for example, the plate Q may be spaced further from the plate P than the distance of plate Q' from plate P' and the length of plate Q may be made shorter than the length of plate Q'.
Although illustrative embodiments of the invention have been described in detail herein with reference to the 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.
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