US2713604A - Apparatus for applying signals to electrodes of an electron tube - Google Patents

Description

July 19, 1955 L. PENSAK 2,713,604 APPARATUS FOR APPLYING SIGNALS TO ELECTRODES OF AN ELECTRON TUBE Filed March 15, 1952 3 Sheets-Sheet l 5%" away/7' Edi/7019779! ATTORNEY July 19, 1955 PENSAK 2,713,604-

APPARATUS FOR APPLYING SIGNALS T0 ELECTRODES OF AN ELECTRON TUBE Filed March 15, 1952 3 Sheets-Sheet 2 ATTORNEY July 19, 1955 PENSAK 2,713,604

APPARATUS FOR APPLYING SIGNALS To ELECTRODES OF AN ELECTRON TUBE Filed March 15, 1952 s Sheets-Sheet s ATTORNEY aired States Patent 2,7 l fifil Patented duly 159, "i955 2,713,504 APPARA'HUS FUR APPLYING SIGNALS T0 ELECTRGEDES (3F AN ELECTRON TUBE Louis Pensak, Princeton, N. 5., assignor to Radio Corporation of America, a corporation of Delaware Application March 15, 1952, Serial No. 276,835

6 Claims. (Cl. 178-5.4)

This invention relates to age waves to electrodes of an electron discharge device in such manner as to minimize the loading eiTect of interelectrode or other stray capacitance.

In some types of color kinescopes employed in television the intensity of the selected component color re- :1?

produced is controlled by the application of video to an appropriate electrode or electrodes. In other types of color kinescopes one or another selected component color is produced in accordance with the instantaneous signals magnitude of a color selection signal that is applied to associated with each of t e electrodes. Because collectors are smaller than the electrodes, their interelectrode capacitance is lower than the interelectrode capacity of electrodes so that the collectors do not load the source of the voltage waves excessively. The capacitive coupling between the collectors and their corresponding electrodes is extremely small so that the electrodes are effectively isolated from the collectors and the sources of voltage waves. One convenient way of coupling the electrodes to the collectors is by the secondary electrons produced when portions of the electrode structure of which the electrodes form at least a part are bombarded by a beam of electrons.

The manner in which the above objective is attained by this invention may be more clearly understood after a detailed consideration of the drawings in which:

Figure 1 is a side view of a target embodying the principles of the present invention and employed in a color kinescope of the type wherein video signals are applied to the electrodes of the target so as to control the intensity with which different color phosphors of a phosphor screen luminesce.

Figure 2 is a view of the target shown in Figure 1 taken along a section AA of Figure 1;

Figure 3 illustrates by block diagram an arrangement that may be employed in conjunction with a target such illustrated in Figures 1 and 2;

Figure 4 is a top view of a means for connecting selected ones of the electrodes in desired sources of voltage waves;

Figure 5 is a front view of Figure 4;

Figure 6 illustrates the circuitry employed in accordapparatus for applying volthe invention will now be described as applied to a color kinescope of the first type mentioned above wherein component colors.

S. patent application bearing Serial No. 138,088 filed on January 12, 1950, in the name of Zworykin.

so as to be parallel to the lines of the raster scanned by the electron beam. in between successive pairs of ribs 3 are grooves 33, 3G, 3R, strips 4G, 4B, 4R, are mounted at the bottoms of the grooves 33, 3G, 3R etc. so as to be in contact with the metallic strip 2. The strips 4B, 4G, 4R, etc. that phosphor strips 8B.

in order that the drawing of Figure 1 may be clearly understood no connections are shown for coupling the various signals to their corresponding grid members.

The manner in which the various grid electrodes 58, 5G, and SR are coupled to their respective sources of video signals so as to reduce the capacitive loading of these sources in accordance with the principles of this invention is illustrated in Figure 2. Each pair of grid electrodes 5B are electrically connected together by a loop of conto pick up any electrons emitted by the loops 913, 9G and 9R respectively. each collector plate picks up only those electrons from the adjacent loop. All of the collector plates 10B are electrically connected to a source of blue video signals 13, all of the collector plates 10G are electrically connected to a source of green video signals 12, and all the collector plates 10R are connected to a source of video signals 11.

Secondary electrons are emitted by the loops 93, 9G and 9R in response to bombardment by an auxiliary beam of electrons 14 that is caused to scan in vertical synchronism with a main beam 15 in a manner to be discussed below. The present discussion relates to the effect of the auxiliary beam 14 and points out how the use of such a beam decreases the capacitive loading of the sources 11, 12 and 13 by a large amount. If the loops 98, 9G, 9R that connect the pairs of grid electrodes 58, G and SR respectively are comprised of material that is capable of emitting secondary electrons, those electrons will be picked up by the corresponding collector plates B, 106 and 10R. The electron coupling thus introduced causes the loops to assume the same potential as the corresponding collector plates and therefore to have the same potential variations as the video signals supplied by the sources coupled to the plates. The capacitive loading of the sources 11, 12 and 13 is reduced materially by a combination of two factors. In the first place the total distributed capacitance of all the collector plates connected to any one of the sources is much less than the distributed capacitance of the grid electrodes that in previous arrangements were connected to any one of the sources. In the second place, only the distributed capacitance of a relatively small number of the control electrodes 5 is added to the distributed capacitance of these 601180101 plates. The number of control electrodes Whose distributed capacitance is thus added depends upon the size of auxiliary beam 14. If this beam is such as to encompass three successive grid loops 9B, 9G and 9R, then the source 13, for example, is capacitively loaded only by the sum of all the distributed capacitance associated with the different collector plates 18B, and in addition only the distributed capacitance of one set of grid electrodes 5B. The same is true for the sources 11 and 12. Thus the essence of invention lies in providing means for coupling only a relatively small number of the control grid electrodes to any one of the sources, the coupling means itself having a much smaller total interelectrode capacitance than the total interelectrode capacitance of all the control electrodes that would normally be coupled to any one source.

The particular size of cross sectional area of the main beam that scans a raster on the metallic sheet 2 of Figure 1 depends upon the manner in which the final image is to be formed and upon the type of signals supplied by the sources 11, 12 and 13. For example, if the image is to be built up from a series of parallel color lines the main beam 15 may have a cross sectional area equal to the width of one of the strips 413, 4G or 41R, and may be caused to scan along these strips in sequence. Thus even though the signals provided by the sources 11, 12 and 13 are continuous, only those signals from one of the sources will control the number of electrons reaching a given phosphor strip 83, 8G or 8R during any one line scansion. On the other hand, if the cross sectional area of the main beam 15 is sufficient to encompass at least three strips, that is 413, 4G and 4R, the signals supplied by the sources 13, 12 and 11 could be of the line sequential type. In this case the blue video signals supplied by the source 13 would permit secondary electrons from the strip 4B to reach the blue phosphor strip 83, and the signals supplied by the sources 11 and 12 would prevent any electrons from reaching the phosphor strips 86 and SR. During the next line scansion the main beam 15 would not scan the top strip 4B but would encompass the next 3 lower strips that is 4G, 4R and the next lower strip 4B.

The physical arrangement is such that If it is desired to reproduce green light during this next line scansion, the green video signals from the source 12 permit electrons to reach the uppermost green phosphor strip 8G and the sources 11 and 13 of red and blue video signals respectively would prevent any secondary electrons from reaching the corresponding phosphor strips.

If it is desired to build up the final color image from a series of differently colored dots of light the signal supplied by the sources 11, 12 and 13 could be of the elemental sequential type and the main beam 15 could be of sufficiently large diameter to encompass at least three successive strips 4B, 4G and 4R. Other combina' tions of beam size and the type of signals provided by the sources 11, 12 and 13 could be devised by one skilled in the art so as to build up the final color image in any desired manner. The particular size of the main beam 15 is not important to the practice of the present invention. In the above discussion it is only intended to indicate other various ways in which the entire apparatus may be used.

Figure 3 illustrates a type of cathode ray tube and circuitry that may be employed in conjunction with the target structure shown in Figures 1 and 2 so as to achieve the desired results and advantages of the present invention. The color video signals may be detected by any suitable receiver and applied to a target structure 21 via leads 22, 23 and 24. The details of the target structure 21 are the same as those illustrated in Figures 1 and 2. The cathode ray tube 25 in which target 21 is mounted is equipped with a standard gun 27 and a standard yoke 28 that causes the beam emitted by the gun 27 to scan a raster on the target fashion. Between the gun 27, the yoke 28 on the one hand and the target 21 on the other is another electron gun 29 that is mounted so as to direct an auxiliary beam of electrons indicated in cross section by the numeral 14 in Figure l to one edge of the target 21. The vertical deflection of this beam is controlled by deflection plates 30 and focussing of the beam is brought about by a coil 31. Owing to the fact that the two guns are not the same distance from the focussing field established by the coil 31, one will be in focus at the target 21 and the other will be slightly out of focus. The current in the coil 31 is adjusted so as to focus the beam from the gun 27 from the target 21 and to cause the beam from the gun 29 to be slightly defocussed at the target 21. This means that the auxiliary beam will cover at least one of the loops 9 and in the practical case will cover more than one. As will readily be understood by those skilled in the art, the relative sizes of the cross sectional areas of the main and auxiliary beams can be controlled by changing the cathode potential. The synchronizing signals are separated from the output of the receiver 20 by a standard sync separator 32 and are applied to a horizontal sweep circuit 33 and a vertical sweep circuit 34 of conventional design. The output of the horizontal sweep circuit 33 is applied via an amplifier 35 to the horizontal deflection coils in the yoke 28. The output of the vertical sweep circuit 34 is applied via an amplifier 36 with vertical deflection coils in the yoke 28. These connections and circuits are standard. Inasmuch as the auxiliary beam emitted by the gun 29 is to scan only in a vertical direction, the yoke 30 is supplied with signals from only the vertical sweep circuit 34 via an amplifier 37. The gain of the amplifier 37 is so adjusted with respect to the gain of the amplifier 36 that the same vertical sweep voltages may cause the auxiliary beam emitted by the gun 29 to scan the same vertical distance at any given time as the main beam emitted by the gun 27.

Figures 4 and 5 illustrate another means whereby an auxiliary beam of electrons may be caused to land upon a few of the loops at any given instant. It would be apparent to those skilled in the art that the number of secondaries emitted in response to the auxiliary beam 21 in a normalof the type illustrated in Figure 2 will be proportional to the density of the beam. Whereas it is true that the electron density of the beam can be increased by increasing the voltage difference through which the beam passes, it is also true that the number of secondaries maximum in the neighborhood Any further increase in the density of the beam current that arrives at the target the electron gun and the target. In general, the greater the distance the greater must be the voltage differential to obtain a given electron density. However, as noted above, an increase in voltage beyond a predetermined amount causes the number of secondaries emitted to be reduced.

In Figure 4 an arrangement is shown whereby the distance through which the beam passes is greatly reduced so as to permit an optimum voltage in the order of 500 volts to be used. The target may be similar to that shown in Figures 1 and 2 and is generally indicated parallel to one edge of the target 4%). An accelerating anode 42 is mounted parallel to the rod 41 and has a slit 43 extending the full length of the rod 41. Any stand ard means may be employed for heating the cathode 41 shape deflection plates 44 of the slit 4-3 and ribbon. The

beam of electrons emerging from The ribbon beam 46 that is placed 45 and the target view of the Figure 4 AA, the mask 46 has a diagonal slot of electrons then encounters a mask between the deflection plates 44 and 47 cut through it. lector electrodes 14 are placed in such manner that any electrons passing through this slit 47 may strike It can be seen that if a voltage tion plates 44 and 45 that deflects the beam left that the beam will pass through any suitable receiver 51 and applied via leads 52, 53 and 54 respectively to different groups of collector electrodes in the target 40. In view of the fact that the target 40 is illustrated in detail in Figures 1 and 2, these details are omitted in and focussed by a to scan a raster on the emerging through the slit 47 of The beam is the loops associated with the grid electrodes that control main beam of electrons.

Figures 7, 8 and 9 illustrate the manner in which the invention reduces the capacitative loading of a source of keying signals that are applied to color selection electrodes. Further details of the tube employed in this arrangement may be found in the U. S. Patent No. 2,446,791 issued on August 10, 1948, in the name of Alfred C. Schroeder. Only those details of this tube that are essential to the application of this invention to this type of tube are shown. In this case the target is comprised of a sheet 70 75' are equal, electrons passing through the grid structure strike the green phosphor strips as indicated by a path '78.

When the lead 74 is made positive lead 75 these grid pair so as red phosphor. Those electrons passing through the next lower adjacent pair of grid Wires also strise a red phosphor but are deflected downward along a path 81.

strike a blue phosphor, and the electrons passing through as to strike a blue phosphor.

The target structure just described in Figures 7 and 8 components that represent the color information, a burst of energy that represents a standard color and the standard type of scanning sync signals. The scanning sync signals are separated from the output of the receiver 85 by any standard sync separating apparatus 86 and applied to vertical and horizontal sweep circuits 87 and 88 respectively. The outputs of these sweep circuits are applied to a deflection yoke 89 via amplifiers 90 and 91 so as to cause the electron beam projected by an electron gun 92 to scan a raster on a target 93. The target 93 is of the type set forth in detail in Figures 7 and 8. The burst of color synchronizing signals are separated from the rest of the signals by a burst separator 94 and applied to a color switching circuit 95 that is connected to the leads 74 and 75 so as to control the relative voltages applied to the different groups of grid wires 71 and 72. Assuming that the images are to be reproduced with three selected component colors, a continuous third harmonic of the burst frequency is generated by a harmonic generator 96, and the phase of the continuous harmonic is controlled by a phase control device 97. The video signals supplied by the receiver 85 are combined in an adder 98 with the output of the phase control device 97 and applied to a control grid (not shown) in an electron gun 99 that projects the main beam of electrons. The cathode (again not shown) of the gun 99 may be biased so that the main beam of electrons is cut off during the peaks of the continuous harmonic wave supplied by the phase control device 97. The phase control device 97 is adjusted so that the gun 99 is turned on whenever its beam is centered on a single color phosphor by the voltages supplied by the grid groups 71 and 72. A gun 10%) serves to direct an auxiliary beam of electrons towards the target 93 and both beams pass through a focussing field established by a coil 101. The current in the focussing coil 10% is adjusted so as to sharply focus the main beam projected by the electron gun 99 at the target 93 and to slightly defocus the auxiliary beam projected by the gun 190. The auxiliary beam is deflected in the vertical direction in synchronisrn with the vertical deflection of the main beam by application of the output of the vertical sweep circuit 37 to a set of deflection plates 1&2 through which only the auxiliary beam passes.

What is claimed is:

1. Apparatus for applying voltage waves to a plurality of electrode structures having a relatively large interelectrode capacity in such manner that the capacitative loading effect of the electrodes on the source of the voltage waves is minimized comprising in combination an electron gun for producing a beam of electrons, means to cause said beam to scan successively over portions of each of said electrode structures so as to cause said portions to emit secondary electrons, sep arate collector plates, each of said plates being mounted so as to collect secondary electrons from the portion of one of said electrodes struck by said beam of electrons, and means for coupling a plurality of said collector plates to said source of voltage waves so that said voltage waves are applied to particular ones of said electrodes only when said particular electrodes are emitting secondary electrons.

2. In conjunction with a cathode ray tube wherein a source of voltage waves is to be connected to a plurality of electrodes, and wherein the interelectrode capacity of said electrodes is large, apparatus for reducing the loading effect normally produced on said source by said interelectrode capacity comprising in combination separate means for collecting secondary electrons from a portion of each of said electrodes, said means having less interelectrode capacity than said electrodes, said means being coupled to the source of voltage waves, said means being arranged with respect to said electrodes in such manner that the voltages applied to said means are established on the corresponding ones of said electrodes only when said portions of said 1- so as to control the electrodes are emitting secondary electrons, and means for scanning said portions of the electrodes with electrons in such manner that said electrodes successively emit secondary electrons.

3. Apparatus for selectively applying voltage waves to one or more of a plurality of electrodes in such manner that the loading effect of the interelectrode capacity of said electrodes on the source of said voltage waves is materially reduced, comprising in combination a set of auxiliary electrodes, each of said auxiliary electrodes being adapted to be coupled to one of said electrodes, said auxiliary electrodes having less inherent capacity than said electrodes, means for coupling said voltage waves to said auxiliary electrodes, and electron dis- 1 charge means for selectively coupling at least one of said auxiliary electrodes to its corresponding electrode at any given time so that the voltage waves are applied to less than the whole number of said electrodes.

4. Cathode ray tube apparatus comprising in combination an evacuated envelope, a target having a plurality of segregated areas adapted to emit electrons from one side when struck by light from another, means adapted to direct a beam of uniform intensity toward said target, a screen, different areas of said screen being adapted to emit light of a difierent selected component color when struck by moving electrons, means for causing said beam of electrons to scan a raster on said target, a grid structure comprised of a plurality of groups of members mounted between said target and a said screen, a collector positioned with respect to each grid member so as to collect any secondary electrons emitted from a portion thereof, said collectors having less inherent capacity than the corresponding grid members, one group of said grid members being positioned flow of electrons from certain areas of said target to areas of said screen that luminesce with light of one selected component color, another group of said grid members being positioned so as to control the flow of electrons from other areas of said target to other areas of said screen that luminesce with a different selected component color when struck by electrons, means for applying video signals represent ing the intensity variation of one of said selected component colors to the collectors associated with the group of grid members adapted to control the flow of electrons from the target to the areas of the screen that luminesce in the same selected component color, means for applying signals representing a different selected component color to the collector associated with a group of grid members that control the flow of electrons from said target to areas of said screen that luminesce in said other selected component color when struck by electrons, means for generating another beam of electrons, means for causing said other beam of electrons to strike the portions of said grid members that are mounted so that secondary electrons emitted therefrom are gathered by said collectors, and means for causing said latter beam to strike said portion at a time when the first mentioned beam is striking the target at points where the same grids control the flow of electrons to the screen.

5. Apparatus for reproducing images in color comprising in combination, a cathode ray tube having a target, different segregated areas of said target being adapted to luminesce with light of a different selected component color, an electron gun adapted to direct a beam of electrons toward said target, means adapted to cause said beam to scan a raster on said target, a grid structure mounted in said tube, said grid being comprised of a plurality of groups of members, said groups of members being so positioned with respect to said target that the electrons from said gun strike segreated areas of said target determined by the voltages applied to said groups of grid members; a plurality of electron collectors, each collector being mounted so as to gather secondary electrons from a portion of a particular gnd member, the collectors thus associated bers in synchronlsm with the scanning of said other electron beam.

6, Apparatus as described in claim 5 wherein a source of color switching signals is connected between said groups of grid members.

References Cited in the file of this patent UNITED STATES PATENTS Schroeder Aug. 10, Chew Nov. 14, Oklicsanyi Dec. 5, Sziklai Feb. 26, Rose Nov. 11, Bradley July 7, Weimer Aug. 25,

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