US2728815A - Color television image tube utilizing electroluminescence - Google Patents

Description

Dec. 27, 1955 M. v. KALFAIAN COLOR TELEVISION IMAGE TUBE UTILIZING ELECTROLUMINESCENCE Filed June 3, 1954 CATHODE Fig-2 a FILTER-STRIPES g 2 11 v Q i 5 PHOSPHOR- ,5 E g DISPERSED j z B DIELECTRIC m m 8 -BEAM16 w 2 4. U a; :2 D g 3 3% o -1 u Lu U 25 2 2 2.1 2,0

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OLLECTOR 1 2 INVENTOR. 3 CV2 COLOR TELEVISION IMAGE TUBE UTILIZING ELECTROLUMINESCENCE Meguer V. Kalfaian, Los Angeles, Calif. Application June 3, 1954, Serial No. 434,157

2 Claims. (Cl. 178-5.4)

This invention relates to color television, and more particularly to the provision of electro-luminescent color screen in image reproducing cathode ray devices. Its main object is to provide an electro-luminescent color screen, which may be activated by an electron beam for the production of images in natural colors. Another object is to provide an electro-luminescent screen in elemental areas of difierent primary colors, each color-area of which is accompanied by a frequency-selective means for segregating different primary color areas of the screen in either simultaneous or sequential additive-color system. A further object is to provide an image reproducing color screen, the primaries of which may be selectively activated within the spot-area of a single electron beam, in either simultaneous or sequential additive system, without altering the direction of the beam from its normal deflection of forming a scanning raster on the screen. A corollary object is to provide a composite screen which is capable of forming images in difierent primary colors without the necessity of synchronous imaging process.

Cathode ray tubes for reproducing televised images in natural colors usually utilize some form of composite screen, comprising elemental primary-color component areas, in the path of the scanning beam. Among various forms, wherein direction-approach-sensitive color screens are utilized, a simultaneous system requires continuous control of the direction of approach of three separate electron beams impinging upon the color screen. In a sequential system, a single beam is utilized which is time shared among three arriving primary-color signals to achieve similar additive color reproduction. In either case, however, the direction of approach must be accurately controlled, in order to avoid color dilution; this meaning that extremely accurate instrumentations are involved in all of these systems. Thus in order to obviate these undesired control adjustments, the present invention contemplates to provide an image reproducing color screen, the primaries of which may be selectively activated by a single electron beam without control signals applied thereto. Conversely, Without altering the normal direction of approach of the beam, any one, or all of the primaries may be selected simultaneously or sequentially, within the single dot-area of an electron beam. 7 This condition closely approaches the simplicity of"conventionally utilized monochrome image reproducing cathode ray tubes.

In ordinary cathode ray devices, luminescence is effected by an electron beam bombarding the phosphorescent image surface; this action being termed as electronluminescence. Other methods of producing luminescence are also known and practiced, for example," by subjecting the phosphorescent material in a fluctuating electric field; this action being termed as electro-luminescence. -The device utilized for the latter practice comprises a phosphor dispersed thermoplastic dielectric matrix placed between two conducting electrodes, such as shown in Fig. l, wherein plate 1 represents the phosphor dispersed dielectric matrix, such as Lucite (by trade name) orthe like; plate ice 2 represents a metal conductor; and plate 3 represents a light-transparent conductor, such as Nesa (by trade name, as developed by Pittsburgh Plate Glass Co.). In

this structure, When an alternating voltage is applied to the electrodes 2 and 3, the phosphorescent cells in the dielectric sheet will glow, and appear as such through the light-transparent electrode 3. This type of structure is also termed as luminous capacitor, since the luminescence is produced in an alternating electric field between two plane parallel electrodes. The object of this invention, is accordingly, to provide an image forming screen that comprises a mosaic of elemental luminous capacitors, each of which may be activated independently in accordance with an imaging process. In order to realize how these elemental luminous capacitors may be activated individually in an imaging process, assume that the screen is constructed as shown in Fig. 2, wherein: 4 represents the phosphor dispersed thermoplastic dielectric; 5 represents a translucent conductor electrode; and the elemental secondarily-emissive electrodes 6 represent the capacitor plates with respect to the plate 5. In conjunction, there is projected a high velocity electron beam 7, emitted from cathode 8, upon the element 6, which in turn emits secondary electrons to be collected by collector anode .9. When the accelerating field is so adjusted that the ratio of secondary current to the primary current is greater than unity, the potential of bombarded element 6 may be raised equal to the positive potential of collector 9, where an equilibrium state is reached. Now, when an alternating voltage is applied to inductance 10, the potential of back plate 5 is varied with respect to the collector potential. But at this point, since the potentials of the upper two segments of electrodes 6 are stabilized with respect to the collector potential (due to the constant flow of primary electrons at these points), the upper two segments 6 will undergo charges and discharges with respect to the back plate according to the oscillatory voltage in coil 10, with corresponding electric fields therebetween. With the assumption that the thickness of the dielectric sheet 4 is less than the width of an electrode 6, transverse distribution of the electric field between the capacitive elements will be avoided, and accordingly, the electroluminescence will be confined only to the region of the upper two segments of electrodes 6; emitting through the translucent conductor 5. When the electron beam 7 is moved away from the upper two segments to the lowest segment of electrodes 6, the potentials of the upper segments are no longer stabilized with respect to the potential of the collector, and accordingly, the electro-luminescence is now shifted to the lowest segment. Thus for practicalpurposes, when the electro-luminescent screen just described is of large area, comprising plurality of rudimental electrodes 6, it is obvious therefore, that a scanning raster may be formed by the beam 7, and further by controlling the magnitude of oscillatory voltage in coil 10, in accordance with video signals, a complete monochrome imaging process may be eflected. Accordingly, this invention contemplates to provide a versatile imaging process which may be applied to either monochrome'or chromatic reproduction, for television, or for other useful purposes, such as for graphical observation of electrical phenomena.

When chromatic images are to be reproduced, the electrode 5 may be divided into three mutually insulated interleaved sections, each section aligned with a primarycolor filter, and three separate oscillatory voltages of dif ferent frequencies applied to these sections through frequency selective circuits. In this fashion, each one of the oscillatory voltages may be switched, on or oil, or varied according to simultaneous primary-color signals to produce additive color images. This particular function will be more clearly understood in the following specification when read in conjunction with the accompanying drawings, wherein: Fig. 1 is a perspective drawing of a luminous capacitor; Fig. 2 "is a longitudinal section of a coloritnage tube "(showing only essential parts) incorporating elect ro-lu' minescent image target; Fig. 3 is a schematic diagram of a frequency-selective circuit connected to a color-image reproducing target according to the invention; and Fig. 4 is a cross sectional drawing of the dilferen-t layers of materials comprising the colorimage forming target.

Referring to Fig. 3, the chromatic electro-luminesc'e'nt target is shown supported by a transparent face plate 11, which may serve as the end wall of the image tube, through which the image is viewed. A color-filtering film, 12, is mounted over the inner surface of the face plate. This contains a large number of very narrow color selective stripes, corresponding to suitable primary colors -e. g., green (G), red (R) and blue (B). Next to each stripe, and aligned therewith, is a translucent conductor strip 13. The conductor strips on stripes of each color are electrically connected to a corresponding inductor-e. g., those on green stripes to inductor L1, those on red stripes to inductor L2, and those on blue stripes to inductor L3. Next over the conductor strips 13 is a sheet of thermoplastic dielectric matrix 14, dispersed with phosphorescent luminous cells. Finally, a mosaic of mutually insulated conductor elements, 15, covers the dielectric sheet in the region to be scanned by the electron beam 16. In this assembly, the inductors L1 to L3 are separately energized by oscillatory waves at frequencies, f1, f2 and f3 respectively. When the electron beam 16 strikes one or several of the elemental electrodes 15, the secondary emission establishes an electron path between these elemental electrodes and the electrode strips 13 through the inductors and a collector anode (not shown) in the manner described by way of the illustration in Fig. 2. The oscillatory voltages are thus varied between the three sets of electrode-strips 13 and the elemental electrodes Within the given area of electron impingement.

The different layers of the color image forming target may be more clearly seen in the cross sectional drawing of Fig. 4, wherein, 20 represents the transparent base plate; 21 represents the striped color filtering film; 22 represents the transparent conductor strips, drawn in end View; 23 represents the phosphor dispersed dielectric matrix; and 24 represents the mosaic of secondarily emissive elements, the widths of which may be arranged either equal to the widths of the strips 22, or much smaller as desired.

For large screen image tubes, the thickness of the phosphor dispersed dielectric sheet may be made much less than the width of an elemental electrode 15, and accordingly, the transverse distribution of the electric field between each elemental electrode and the electrodestrips becomes negligible. When the three oscillations ft to f are of the same magnitude, it is apparent that the electric fields established between the strips adjacent to color stripes G, R, B, and the elemental electrodes within the spot area of the beam will be equally distributed, and accordingly, equal amounts of luminescence will emerge through the primary-color stripes 12; effecting white light. Whereas when the magnitudes of these oscillations are changed, the resultant hue may be changed at will. Thus, the oscillations ft to )3 may be amplitude modulated in modulators 17, 18 and 19 by simultaneous color signals g, r and b prior to application upon the inductors L1 to L3, and as the beam scans a raster across the electro-luminescent target, an image in natural colors will accordingly be produced. The oscillations ii to is may be locally generated by suitable means, but their frequency separations should be adjusted wide enough for proper band-pass selection, for example, they may be 30 mo, 40 me. and 50 mc., respectively.

In an image reproducing system of high image resolu- -t-ion, the number of interleaved strips should be substantially high. This means that the inherent capacitances Cd between adjacent strips will consequently be high, as they will necessarily be in close proximity; especially when the number of strips is so high that more than one strip (for each primary color) intercepts the beam simultaneously. This tends to cause cross fire between the signals representing different colors, and accordingly, special compensating arrangement 'is utilized in the form as shown schematically inFig. 2, wherein, the inherent capacitances are indicated by Cd connected between the upper ends of coils L1, L2, L3, and the neutralizing capacitors Cn connected between the upper end of one secondary coil, and the lower end of each of the other secondary coils. Each of these coils has a center tap (electrically connected to the collector anode of secondary emission, not shown) maintained at R.-F. ground potential, so that the R.-F. potential appearing at the lower end of the coil is opposite in polarity to that at its upper end, and when applied through acapacitance Cn ad justed to the proper'value (approximately equal to capacitance Cd), will balance out the effect of the potential applied through capacitor Cd. Conversely, although par-t of the current from any one of the secondary coils passes through capacitance Cd toward the upper end terminal of the other coils, a similar current passes through capacitor Cn toward the lower end terminals of said coils; and the two currents tending to flow in opposite directions cancel one another, producing no net effect on the three sets of conductor strips 13. Thus each set of the strips 13 is energized selectively corresponding to primary-color signals controlled by the modulations of the R .F. oscillations. With such capacitive neutralizing arrangement, it is obvious that the three frequencies f1, f2 and f3 maybe of a single frequency, whereas, without the capacitive neutralization the different frequencies would be imperative for signal selection.

Various techniques may be used in processing the electro-luminescent target. It may either be processed directly upon the inner surface of the face plate, or the target may be constructed separately; rolled into a tube of small diameter so that it may be inserted in the tube blank through its neck portion; and cemented upon the inner surface of the face plate by the aid of forceps; the alignment being non-critical for either round or rectangular face plates. As the thermoplastic dielectric sheet will be very thin, about microns thick, rolling into a small tube will not damage its original structure while inserting through the neck of the tube blank. When part-assembly is desired, the conductor strips may be assembled upon the inner surface of the face plate first, and then the dielectric sheet (having the mosaic electrodes 15 on its opposite surface) cemented over it, since no particular alignment of these electrodes is necessary. For example, the translucent conductor strips may be first bonded upon the inner surface of the face plate, and three output terminal connections secured mechanically. Two of these sets have their strips connected together at opposite ends, and accordingly, the strips themselves can lie in substantially a single plane; but to avoid cont-act with the first two sets, connections between strips of the third set must make a detour out of that plane. A simple arrangement for connecting the third set of strips is disclosed in co-pe'nding application Serial No. 277,632 filed March 20, 1952, by R. E. McCoy and myself for Color Television (Jarneras, and accordingly, it will not be repeated herein. For a simpler mode of electrical connections, however, the three sets of strips may be wound spirally (rectangularly if so desired), so that each terminal ending may be free for outgoing electrical connections; these windings may also be in zig-zag form. The color-filtering stripes may be aligned with the strips by photographic means, and itmay be sandwiched between the dielectric sheet and the conductor strips, without altering the final imaging performance. The name lucent conductor strips may be coated by evaporation'of uniform layer, and etching the strips after photographic exposure. The conductor siips may also be of conductor glass, such as Nesa (by trade name), which offers may be eliminated by employing a secondarily emissive dielectric sheet dispersed with phosphorescent material. Also, in order to eliminate transverse distribution of the secondarily-emitted electrons, a barrier screen, or grid, may be placed in front of the electro-luminescent target, intercepting the primary electron beam. In various applications, barrier grids have been utilized and described, and as an example, one form may be referred to an article by Kazan et al. in RCA Review December 1951, p. 703. The barrier screen may also act as the collector anode by applying a positive potential to it, in which case, the distance of travel of the secondarily emitted electrons will be substantially uniform throughout the region of the scanning raster.

Previous tests have shown that the brightness of electro-luminescence varies with frequency, and since three different frequencies are utilized, in one case, to energize the composite screen in the present invention, three different adjustments are utilized; but such arrangement is not shown in the drawing, as these are of common practice in electronic applications. Similarly, it has been shown that the color of luminescence varies somewhat with variation of applied frequency. Since however, the applied frequencies are substantially constant, the primaries of color filtering stripes 12 may be pre-arranged accordingly. In a second case, however, when only a single frequency is utilized for the energization of the composite screen, these control adjustments are not required. As further modification, the color-filtering stripes may be dispensed with, by constructing the thermoplastic dielectric sheet in narrow stripes of different primary colors, such as, by tinting the dielectric material, or dispersing with phosphors of different primary colors.

Electroluminescent phosphors having characteristics of luminescing in different colors have been known, for example, they may be zinc sulfides, activated by combinations of lead, copper, chloride, and manganese, and can be made in a range of colors from deep blue through green to yellow and orange. By using a mixture, composed mainly of blue and yellow phosphors, white light of any desired color temperature between 2,500 K. and 25,000 K. also may be produced. In the making of the electroluminescent layer, the desired phosphor powder may be mixed (by stirring) with the dielectric material, for example, Lucite in its viscous state, and pressing between two smooth metal surfaces into a sheet of about 100 microns thick.

While so far the foregoing disclosure had been limited to the preferred embodiment of this invention, it is to be understood that numerous substitutions of parts, adaptations and modifications are possible and will suggest themselves readily to the skilled in the art without departing from the spirit and scope of what is hereinabove set forth. As an example, beam velocity modulation may be utilized, in conjunction with beam deflection compensatory means therefor. The beam spot may be adjusted smaller than an elemental image size, and auxiliary vertical or horizontal deflection applied to the beam, for example as described by Schlesinger on page 97 of Electronics, September 1951, and elsewhere. With these few examples in View, the limitations of this invention will accordingly be defined only try the appended claims.

I claim:

1. A system of electro-luminescent image formation, which comprises means for projecting an electron beam; an electro-lurninescent screen in the path of said beam comprising a sheet of phosphor dispersed dielectric matrix, a first electrode comprising light-transparent conductor on one of its planar surfaces remote from the beam, second electrode comprising a mosaic of elemental electrodes on its other planar surface facing the beam, whereby forming a mosaic of elemental capacitive elements between the opposite surfaces of said dielectric sheet; electron-beam deflection means, and means therefor for forming a scanning raster upon the'second electrode with said projected beam; an impedance means connected at its one terminal to the first electrode; means for forming oscillatory energy in said impedance means; means for forming electron path between the second electrode and the other terminal of said impedance means at points of electron impingement by said beam, whereby constraining alternating electric field between the first and second electrodes at points of said electron impingement of the raster; and means for varying the magnitude of said oscillatory energy according to elemental image formation, whereby varying the magnitude of said electric field for varying the intensity of electro-luminescence at said points of electron impingement.

2. The system as set forth in claim 1, wherein said first electrode is divided into a plurality of mutually insulated adjacently positioned stripe-like translucent electrodes; means for dividing last-said electrodes into first, second and third interleaved sections; said impedance means comprises first, second and third impedance means, having means therefor for electrically connecting one end terminals of same to said first, second and third sections, respectively; means for forming said oscillatory energy in said first, second and third impedance means independent of each other; means for forming said electron path between said second electrode and the other terminals of last mentioned impedance means at points of said electron impingement by said beam; means for varying the magnitudes of said oscillatory energies in the first, second and third impedance means according to first, second and third image forming signals, respectively, whereby varying the intensity of electro-lurninescence of said screen, at points of said beam impingement, in the first, second and third independent sections of said first electrode; means for substantially cancelling out the capacitive intercouplings between said first, second and third interleaved sections, whereby rendering them independent of each others operation; and means for dispersing the phosphor cells of phosphor dispersed dielectric matrix having characteristics of phosphorescent glow of first, second and third primary colors, in stripe-like sections adjacent the aforementioned first, second and third interleaved sections, respectively, whereby identifying said first, second and third signals in first, second and third primary-color light representations on said image forming screen.

References Cited in the file of this patent UNITED STATES PATENTS 1,779,748

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