US2689926A - Electron beam tubes - Google Patents

Description

Sept. 21, 1954 D. s. BOND ELECTRON BEAM TUBES Filed Feb. 25. 1950 n m m n A Patented Sept. 21, 1954 '-ELECT'RQN BEAM TUBES JDonaflxlfS. ""Bond; V"Princeton, N. J., assignor to "RadioGorporation of America, a corporation of .Application-February 25, 1950, Serial No.14;6,282

` fClaims.

VIn electron-lbeam tubes Ofithe kind lin which I am especially interested, l the target vcomprises a multiplicity of subselerrrental phosphor areas or lines. When thetubeisofthe c'olor-kinescope variety, each phosphorline emits .lightofa Dar- `ticular color component. .In'colorikinescopes' as in other line-target tubes, the 'bigproblemis to vkeep l the `beam in register with the phosphor lines.

One 'solution of'4 the problem of'.be'am=toline 4 registry in color-kines'copes is set forth byZWory- Vkin in his U.' S. Patent:2,41'5,'059," issued. January 28, 1947. "'Zworykinteaches"the'use of control signals generated ."b'y `'a number 'of photo'cells. Each photocellis sensitive to'on'e ofthecolors emitted bythe; phosphorflines. vThe"c`ontrolsig nais are employedtoacc'elerate or' deceleratethe deflection of thebeam'fin"accordance 'with its I obviate"'tlre 'above-described *and* other -less o apparent objections to `present" dayb'eam-tof-line registry' systems` byproviding -a'catl'iederayr tube containingran electronesensitiv-e screen or-'target having' 'discrete' lightremisste Yand signal-generatingr areas. I'dispcsel thesignaligenerating"area "adjacent to amarginaledgeofthe light-'emissive area. -'IIence' theY beam in traversing the signal-'generating indicia may Ibe endowed (by the grid 'of' they gun Aof the'4 tube) f-With yany'constant intensity "required togenerate fvernier control signals of a uniformly*"usablel amplitude.

In traversingVv the light-'emissive area, the beam may be varied in intensity,` as `dictated-by Video signals 'appliedf'to the" grid. Without affecting' the amplitudeof'V tne"`controlffsignals picked7 up l from thesignal-generating area.

I achieve greater Vaccuracy of bea'incontrol 'when I provide separate beam-deiecting -elements. for the""scanning and" Vernier Hdeeoting -forces. Thus, "although I may apply `the horizontal `and" vertical scanning forces 4to the beam inthe usual "Way (e: g., through amagnetic yoke disposed on the exterior of the tube) -Iv 'prefer to` apply' the Vernier deflecting Yforces toone' of a pairof auxiliary electrodes.

2 Allof theseieatures of myV invention vare Villus- Vtrated in the accompanying `drawing, wherein:

Fig. l is a partly sohematicVbroken-away View in perspective of an electron-'imagetubecontaining a target er screen electrodehavingr vdiscrete signal-.generating and light-emssive areas. The tube is provided with a pair of defiecting electrfodes` to which Vernier deflecting forces, `derived from `the signal-generating target area, 'are applied t0 the beam;

FgjZ is an enlarged View in perspective'ofa portion of' thecolor screen. A part of themetallized surface of the screen is rolled'back Vrto reveal its phosphor lines;

Fig. 3 is a chart of'a portion ofthe surface of the screen showing various .possible positionsv of the beam; and

Fig. l is a curve to which I refer in explaining the operation of my tubeunder the conditions ,indicated in Fig. 3.

In applying my inventionv to `acolor-kinescope, Imay use a conventionalimage-tube'envelope'i having a bulbous portion i and a rearwardly extending neckportion 3. The vacuous space between the 'bulb and Ineck is continuous. I prefer toY employ the rear surface il of a separate glass plate '5 as `the foundation of my biepart screen. I-Iov/ever, I may use the Vinner surface or" the window 6 as the foundation. Alternatively, .fthewindow andneck ofthe envelope-are suitablyoriented, I may employ a non-transparent foundation plate (not shown). Inany event, the screen ccmprisesa light-emissivearea'l and a discrete signabgenerating area il. The 'signalgenerating area-ii is disposed along a marginal edge of the light-emissive-area l. Both of these screen areas 'E ands-are accessible to theelectron-beamV t when the beam is Vsubjected to -a conventional scanning movement. Thescanning movement results from-horizontal and 'vertical deflecting forces supplied by electromagnetic coils .le and il. These coils are disposed at right angles to each other on the neck i of the tube.

An opaque coating l2 on the back of the signalgenerating area 8. of the plate 'conceals that area from theview of an observer looking into the Window.

The source of the beam il is a conventional electron-gun. The gun which is shown here comprises an'indirectly heated cathode I3, agrid-ifl and a rst anode l5. The grid vcontrols thelintensity of the beam duringfits'excursion across both areas `'i andS ofthescreen. :Apcrtion of the-inner surface of the neck and-*bulb f'ZLhas 1 a ccnductivelcoatingi it. vflhiscoating;is the.l sec ond anode of the device. The outer surface of the light-emissive area 'l may comprise a transparent aluminum nlm il (Fig. 2). This conductive iilrn il may be connected, as by a lead l, to the second anode i5.

A strip-like conductor I9 is supported, as on insulating beads 29, along the outer edge of the signal-generating area 8. A pair of deecting plates 2l, 22 is disposed, in front of the electrongun, in horizontal planes on opposite sides of the path of the beam 9. The metal strip le collects the electrified particles or signals emitted by the signal-generating area 8 when it is hombarded by the beam 9. The signals impinging upon the collector electrode are applied through an appropriate servo circuit 23 to the deflecting plate 2|. The other plate is maintained at a high positive potential, for example by connecting it to the second anode I6. When thus applied, the signals operate to impart Vernier vertical deilecting forces to the beam. Alternatively, as suggested by Zworykin Patent 2,415,959 (previously mentioned) and Zworykin 2,304,755,

' the Vernier or correcting signals may be applied to an appropriate one of the magnetic deflection coils l or il. In this later connection, however, I call attention to the fact that the coils Il) and Il are current (as distinguished from voltage) actuated devices of high inductance and that the correcting force of the Vernier signals is usually a voltage containing relatively high frequency components. Therefore, the servo circuit 23 may be simplied by applying this voltage directly to one of the electrostatic plates 2|, 22, instead of converting it into current of the amplitude required to produce an appropriate magnetic deflecting force. One such servo circuit is claimed in co-pending application Ser. No. 146,230, in the name of Donald G. Moore. Another is claimed in application Ser. No. 146,283, now U. S. Patent 2,634,325, in my name jointly with Donald G. Moore. Said patent applications are led concurrently with the subject case.

In making the screen, I provide its foundation surface 4 with a number (say, two hundred and forty) of groups of (say, three) narrow phosphorstripes or lines, R, B and G. Each line is capable of emitting light of a particular color component when bombarded by electrons.

As taught by Leverenz in U. S. Patent 2,310,863, when the phosphor lines which make up the clifferent groups are to emit blue, green and red light, respectively, the materials of which the lines are composed may comprise: Silver-activated zinc sulfide and zirconium silicate for the blue lines B. Alpha-willemite activated with manganese or zinc cadmium sulfide activated with silver for the green lines G. Chromium-activated aluminum berylliate or zinc cadmium sulfide activated by silver for the red lines R.

The parallel phosphor-lines R, B and G preferably, though not necessarily, extend horizontally. In the space between the ends of the lines R, B and G and the edge of the foundation surface li, I provide a number (in this case, two) or parallel columns C, C of signal-generating indicia. In the instant case, the indicia take the form of line-segments, Rl, R2 etc., B1, B2, etc. They are arranged in register with the blue (B) and the red (R) lines of each of the several groups of phosphor lines.

The particular (line-segment) contour and (two-element) code arrangement of the signal-generating indicia here shown is especially llsuited for use in connection with conventional phosphor-line screens. This is so because the simplicity and economy of the code indicia facilitate both the manufacture of the screen and the design of the control circuits which may be associated therewith.

I may employ any of a variety of ray-emissive materials in the signal-generating area 8. I prefer, however, to use secondary-electron emissive materials in preference to light-emissive or ultraviolet-ray or X-ray or infra-red ray emitters. The use of secondary-electron emissive materials simplifies the problem of collecting the signalbearing emanations from the code indicia. Thus, as previously pointed out, I may employ as the signal-collector electrode a single strip of metal I9. I may dispose an additional collector electrode (not shown) between the second column C' of indicia and the adjacent terminals of the light-emissive strips, though this is usually unnecessary. The collector electrode or electrodes should not prevent the beam from impinging upon any portion of the signal-generating or light- 4emissive areas. This condition is avoided, in the instant case, by mounting the collector i9 along the edge of the glass plate 5 in a plane normal to its foundation surface 4.

One might assume that I should form the indicia Rl, Bl etc. of a material having the highest obtainable secondary-electron to primaryelectron emissive ratio. Such, however, is not necessarily the case. The principal requirement is that there be a usefully great difference in the emissive-ratios of the code marks and the surface 24 immediately surrounding the same. Thus, I may make the code marks Bl, Rl etc. of a material (e. g. glass or carbon-black) having a secondary-to-primary electron emissive-ratio of less than unity, providing I make the surrounding surface 2li of a material (e. g. silver or aluminum) having an emissive ratio greater than that of the other. In the interests of simplicity, however, I prefer to make the code marks or" the more highly emissive material and to use the surface of the glass foundation plate 5 as the contrastingly less-emissive area 2d.

I i'lnd it convenient to refer to the chart of Fig. 3 and to the curve of Fig. d in explaining the manner in which the secondary-electron emissive indicia Bl, Rl, etc. operate to generate signals capable of eiecting the up or down Vernier adjustment required to bring the beam 9 into register with a particular phosphor line.

Let use assume that the beam starts its movement across the signal-generating area at the various points indicated by the beam spots 9, Sa, 9h, 9c or 9d. Let us also assume that the phosphor line upon which the beam should impinge is the green line G. In the particular arrangement or code of the signal-generating indicia here shown, there is a code-mark opposite each of the blue and red phosphor lines (B and R) but none opposite the green line (G). l-Ience, if the beam 9 is moving along an axis afwhich coincides with the longitudinal axis of the phosphor line G, it will pass through the signalgenerating area 8 without encountering either the indicia B1 or R1. Thus, no control signal will be generated. Nor is any required, since the beam is where it should be, i. e., in register with the line G. This condition of no signal is indicated by the point 9 on the curve of the chart.

If the beam should start its excursion across the signal-generating area at one of the points indicated by the beam spots da or 9b, i. e., above the central axis :v -r, it will encounter the indicia or code mark Bl. Hence, secondary-electrons will be released in a quantity proportional to the percentage of the total beam area impinging upon the code mark B1. As a result, a Vernier beam-delecting signal of the magnitude required to move the beam the proper distance into register with the line G Will be generated. This condition is indicated by the points 9a and 9b on the curve of the chart. The information necessary to ensure the proper direction of this movement is supplied to the time-discriminating means of the servocircuit 23 (Fig. 1) by reason of the fact that in the columnar arrangement of the indicia, the rst column (C) is allotted to the down movement.

If, as indicated by the beam spots 9c and 9d, the beam strikes the signal-generating area at a point beneath the line :v -m, it will encounter a secondary-electron emission code-mark when it reaches the first column, C, where it will strike the mark R2. Here again a beam-deliecting signal of the magnitude (indicated by points 9c, 9d on the left or red curve of the chart) and (upward) direction required to move the beam the proper distance into register with the green phosphor-line G.

I have described the screen of the tube of my invention as containing a signal-generating code of a simple yet practical pattern. My disclosure in this respect is intended as illustrative. I may use other signal-generating line or dot codes for the same purpose (i. e., beam-toline register), or indeed for other purposes, for example, controlling the focus or the timing of the beam, or for securing linear, vertical, radial or other directional scanning of a high order of precision.

I claim as my invention:

1. The combination with an electron-beam tube of the type provided with horizontal and vertical beam-deecting means and containing a target having discrete light-emissive and signal-generating areas upon which the beam may successively and repeatedly be directed by said horizontal and vertical beam-deliecting means, of auxiliary beam-deflecting, means disposed adjacent to the path of said beam for applying to said beam Vernier deecting forces derived from said signal-generating area of said target.

2. The invention as set forth in claim 1 and wherein said auxiliary beam-deecting means comprises a pair of electrodes disposed in substantially horizontal planes on opposite sides of the path of said beam Within said tube, whereby said Vernier defiecting forces serve to deflect said beam in a vertical direction only.

3. The invention as set forth in claim 2 and wherein said first-mentioned beam-deecting means are of the magnetic type and are disposed on the exterior of said tube intermediate said target and said pair of horizontally disposed electrodes.

4. An electron-discharge device comprising an evacuated envelope containing an electron-sensitive screen having a light-emissive area and a secondary-electron emissive signal-generating area, a collector electrode disposed adjacent to said signal-generating area in a position to collect secondary-electrons from said area, an electron gun for generating a beam of electrons, said gun being disposed in a position to activate said light-emissive and signal-generating areas of said screen, horizontal and vertical beam-deflecting elements disposed exterior of said envelope intermediate said gun and screen, and auxiliary beam-deflecting elements mounted within said envelope for applying Vernier deecting forces to vsaid beam in accordance with signals picked up by said collector electrode from said secondaryelectron emissive signal-generating area of said screen.

5. The invention as set forth in claim 4 and wherein said light-emissive area of said screen comprises a plurality of sub-elemental phosphor areas, and said signal-generating area comprises a plurality of secondary-electron emissive signalgenerating indicia individual to said sub-elemental phosphor areas.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,305,646 Thomas Dec. 22, 1942 2,441,296 Snyder, Jr May 1l, 1948 2,446,440 Swedlund Aug. 3, 1948 2,463,535 Hecht Mar. 8, 1949 2,490,812 Huffman Dec. 13, 1949 2,496,633 Llewellyn Feb. 7, 1950 2,518,200 Sziklai et al. Aug. 8, 1950 2,621,245 Kell Dec. 9, 1952 2,630,548 Muller Mar. 3, 1953 FOREIGN PATENTS Number Country Date 868,403 France Sept. 29, 1941

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