US2699520A - Cathode-ray system - Google Patents

Description

Jan. 11, 1955 LUBCKE 7 2,699,520

CATHODE-RAY SYSTEM Filed NOV. 2, 1950 2 Sheets-Sheet 1 IN VEN TOR.

Jan. 11, 1955 H. R. LUBCKE CATHODE-RAY SYSTEM Filed Nov. 2, 1950 2 Sheets-Sheet 2 3 85' IN VEN TOR.

United States Patent CATHODE-RAY SYSTEM Harry R. Lubcke, Los Angeles, Calif., assignor to General Teieradio, Inc., Los Angeles, Calif., a corporation of California Application November 2, 1950, Serial No. 193,655 17 Claims. (Cl. 315-22) This invention relates in general to the art of reproducing plural-component information in plural manners and in a specific sense to a cathode ray system for reproducing multicolored images upon essentially a single surface.

While the optical simplicity of reproducing systems adapted to reproduce full-color images upon a surface is obvious, the structural complexity and precision required to accomplish this reproduction has been an obstacle in the prior art. It has been found necessary to construct multi-faceted or ridged colored-light-producing screens, to rule a screen with different phosphors, to dot a screen systematically with different phosphors and to dispose a matching perforated plate in the electron path thereto, or to alter the velocity of the impinging electrons so as to permeate layers of different phosphors.

These structures have been fraught with various difliculties. Vacuum envelopes with multiple necksand circuits for double keystone correction have been required. Auxiliary photoelectric apparatus has been proposed to keep the scanning electron stream upon the ruling of a given phosphor; alternately, there exists the danger of irreparable damage of voltage breakdown between ruled electrodes. Or the amplitude of scanning deflection must be changed with alteration of velocity of impinging electrons. Separate phosphor-coated grids impose optical alignment and sufliciency of detail problems.

The present invention overcomes these difficulties by invoking new functions in a simple structure. Briefly, a heterogeneously composed transducing screen is caused to function selectively by coaction of the electron stream at varying scanning velocities with the selected characteristics of the plural transducers of the screen. Advantage is taken of differing speed of response, intrinsic efliciency, efficiency variation as influenced by the method of this invention, secondary-emission, and/or insulation characteristics of the transducers employed. In physical appearance the cathode ray tube does not differ from the simple black and white tube of the prior art.

An object of this invention is to reproduce information of a given characteristic upon a surface capable of reproducing information of plural characteristics.

Another object of this invention is to produce a simple color television cathode ray tube.

Another object of this invention is to supply operating circuitry which intimately coacts with the requirements of the color cathode-ray tube on the one hand and the necessary color process circuitry on the other.

Another object of this invention is to excite phosphors selectively amongst a plurality of phosphors.

Another object of this invention is to provide means for exciting a transducer in relation to its inherent characteristics rather than according to its geometrical position in a device.

Another object of this invention is to provide a coloredlight reproducing screen in which the color fidelity does not change with changes in viewing angle.

Another object of this invention is to provide means for selectively exciting a transducer according to its speed of response, efficiency, variation of efliciency with temperature, secondary electron emission, operating voltage, insulation, conductivity, and/or treatment by or coaction with auxiliary matter.

Other objects of my invention will become apparent from further examination of this specification and the drawin See In the drawings:

Fig. 1 is an enlarged plan view of a portion of my transducing screen;

Fig. 2 is an elevation view of the same;

Fig. 3 illustrates a group of time-related waveforms concerned with velocity of scanning;

Fig. 4 illustrates the response of transducers as a function of time;

Fig. 5 shows a cathode ray tube according to this invention in combination with a deflection coil truncated-wave oscillator;

Fig. 6 is a schematic diagram of a relaxation truncatedwave oscillator;

Fig. 7 is an elevation view of an alternate form of transducing screen;

Fig. 8 illustrates time-related waveforms concerned with an alternate form of scanning velocity variation;

Fig. 9 illustrates time related waveforms concerned with variation of accelerating potential of the electron stream as a factor in variation of velocity of scanning;

Fig. 10 shows a differentiation and amplification circuit capable of accomplishing the processes illustrated in Fig. 9.

Referring to Fig. 1, the elemental form of the transducers is noted. The transducers are, for example, phosphor crystals 1, 2 and 3 which fluoresce in primary colors, say blue, green and red, respectively, upon bombardment by an electron stream. These are laid down at random upon a substrate 4, Fig. 2, by known methods of settling from a liquid suspension, by spraying or by dusting.

Selective excitation of transducers from amongst the above-described plurality is accomplished through coaction of the scanning velocity of the electron stream in traversing the plurality in relation to one or more-characteristics of the transducers.

Phosphors are known which have wide differences in excitation and decay rates, wide differences in efficiency, in variation of efliciency with temperature, in secondary emission ratio, in properties as an insulator or conductor, and in spectral response. These characteristics are partially inherent, partially controlled by the preparation process, by the activator and by the presence of auxiliary materials.

Fortunately, it is possible to select and to treat phosphors in such a manner that selective activation can be accomplished amongst a plurality of phosphors otherwise equivalently disposed and influenced. The advantages of simplicity in construction, ruggedness in operation and freedom from spurious structure in viewing, over geometrically-dependent phosphor structures, are evident.

One selection of phosphors for the structure of Fig. 1 includes zinc sulphide with approximately one-hundredth of one percent silver as an activator, the phosphor being hexagonally crystallized, for the blue-emitting phosphor 1 in the figure. This phosphor is fast in response, high in efliciency and relatively sensitive to temperature; an increase in temperature above a certain point resulting in a marked decrease in efliciency.

For the number 2 green-emitting phosphor zinc silicate can be used, having approximately one-third of one percent manganous oxide activator and being rhombohedrally crystallized. This material is also known as the mineral willemite. The speed of response is medium, the efiiciency medium and the temperature characteristic average.

For the number 3 red-emitting phosphor zinc sulphate can be used, having a few hundredths percent manganese sulphate activator and being ortho-rhombohedrally crystallized. The speed of response of this material is slow, the efliciency low and the temperature characteristics high before drop-off.

In the practice of present-day television the scanning velocity of the electron stream over the phosphor screen is uniform in the process of reproducing the image. Certain portions of the scan, such as the return strokes, may be executed more rapidly but these are blanked-out either in the transmitting or the receiving apparatus, or both, so that such strokes do not visually appear and are of no significance in the process.

By periodically altering this scanning velocity I am able to separately excite individual phosphors amid the Plurality upon the screen.

. 3 Referring to" Fig. 3', numeral 6 indicates a plot of a portion of the uniform horizontalscanning displacement; S, along a line of the television-image.

Time is the abscissa. Numeral 7 indicates a truncated triangular waveform having a frequency considerably higher than: that of waveform.6. Theresultof combining these waveforms is shown at 8.

It will be notedthat the waveform 6 has been modified to increased scanning. velocity at 9, remain the same as before at 10, and drop to zerovelocity at 11. The average velocityis-unchanged, thus the image scanning process is unaltered. Conveniently, the period of each inclination of the truncated waveform 7 is made equal to the period of transmission of information for one of the three primary colors. The intensity of the electron stream in Fig; 2 is thus controlled by, the grid in the electron gun in accordance with the information and thetruncated waveform is synchronized to color synchronizing information. This is known as the sampling frequency waveform in thedot sequential system of color television. For line or frame sequential color television the bias upon the electron gun is merely raised to cut-off on two of the three throws of the truncated waveform, this blanking being altered as to color for each line or frame by the color sequence synchronizing pulses provided for that purpose.

Because of the difference in the several characteristics of the phosphors chosen, only the blue phosphor is excited during the rapid traverse 9. During the traverse of average velocity 10, principally the green phosphor is excited. When the scanning spot is stationary at 11, the red'phosphor is excited.

The blue phosphor only is excited during the rapid traverse for the following reasons. The number of electrons that impinge upon any phosphor crystal depends upon the number of electrons that are in the electron stream and the velocity with which the stream traverses the crystal. During the rapid traverse 9 a thousand crystals may be swept over, whereas during the stationary period 11, fifty crystals may be continuously excited. The highly eflicient' blue phosphor will thus be excited whereas the less efficient green and red phosphors will not be excited.

It is known that the rate of response to electron excitation is proportional to the rate of decay of luminescence after excitation. In other words, a quick decay phosphor rapidly reaches equilibrium between the excitation supplied to it and its fluorescent light output. It is also known that this increase in output ceases (within a fraction of a microsecond) after electronic excitation ceases. Thereafter, the phosphorescent decay starts, continuing to produce light which is desired'and useful in this invention but which plays no part in the selective excitation of the phosphors according to the invention.

Referring to Fig. 4, the excitation and decay characteristics 12, 13 and 14 for the three phosphors 1,. 2 and 3 are shown, plotted as a function of time, t. The light output L is the ordinate.

At a brief interval of time At after t=0 it will be noted that the rapid response blue phosphor, curve 12, is fully excited and emitting maximum light. After the same interval of time the response of the green phosphor, curve 13, is small, only to point 15. The time At represents the time any phosphor crystal is excited during the rapid traverse 9 of Fig. 3. Since the response does not increase after the excitation ceases, the light output of green is negligibly small, only the area of the small-dash curve below point 15. In the same way the light output of red is even less, only the area of the small-dot curve below point 16.

We turn now to the mechanism for preventing blue light response during the periods of scanning traverse intended for the excitation of green and of red response.

Two properties of phosphors are relied upon to perform this function; the temperature characteristic and the secondary emission characteristic. The temperature characteristic of the ZnSzAg blue phosphor 1 previously described breaks rapidly above room temperature. At 100 C., for instance, the luminous efiiciency is only onefifth that at room temperature,

In order that this characteristic be evaluated for proper performance, attention is given to the sizes of the phosphor particles. Small sizes give greater elevation in temperature under bombardment than large sizes. A small size is something less than 1O millimeter and this size is used for the phosphors 1 and 2. Larger phosphor par- 4:- ticles contribute the reverse effect and also are known to emit light more slowly than small particles after excitation; both effects being required for phosphor 3.

Similarly, the coefiicient of secondary emission of phosphor 1 decreases with elevated temperature. When the electron stream is stationary or traversing at low velocity the elevation of temperature of'. the phosphor impinged is considerable, largely because of the power inherent in the electron stream and the small heat capacity of the small phosphor crystals.

The phenomenon of variation in secondary emission with the impinging velocity of the electron stream is also relied upon. The unity emission voltage is here defined as the highest voltage. obtaining in the operation of cathode ray tubes at voltages of the order of several thousands of volts at which the secondary emission from the screen equals the incident current of the primary electron stream.

The unity emission voltage of the fast and medium speed phosphors are one ofthe parameters upon which the phosphors are chosen. These are selected progres-, sively higher but reasonably lower than the unity ,emis. sion voltage of the slowphosphor, which is to emit adequate secondary electrons under prolonged bombardment.

The cathode ray tube is operated at a voltage somewhat higher than the unity emission voltage of the fast and medium phosphors. This causes these phosphors to charge negatively upon the longer electron stream impingements than are intended to produce luminosity of the phosphor involved. In other words, the fast phosphor 1 charges negatively suificiently to substantially cease emitting light during the medium and the slow traverses, 10 and 11, while the medium speed phosphor 2 does the same during the slow traverse only.

In the comparatively very long time between scansions of the same phosphor particles by the electron stream, as occurs once for each frame in a television scanning raster, the usual small leakage and conduction associated with. any insulator-like substance willresult in loss of the negative charge by the time of the next impingement of the electron stream. Thus, original datum conditions are restored.

In the practical application of the above recited phosphor mechanism attention must be given to variation in phosphor characteristics. While it is possible to reproduce phosphors having known characteristics with known techniques it is also possible to suffer considerable departures in characteristics by small variations in the preparation technique. Consequently, the worker will therefore select the particular batch of phosphor for use on the basis of best conformance to the characteristics recited.

Another control is available to the worker: namely, the relative amount" of'each phosphor present in the screen. The color the eye ascribes to a finite area of the screen surface is a chromatic integration of the areas and intensities of the component color particles. The area factor is affected by the relative amount of the phosphor present, and is a useful independent variable.

We pass now to apparatus for altering the scanning velocity of the electron stream.

Fig. 5 shows cathode ray tube 26 constructed according to this invention in coactive relation to a novel deflection coil truncated-wave oscillator also according to the invention. I have found that I secure superior functioning;

i. e., desired waveform of time variation of magnetic field at maximum amplitude for given circuit parameters, by deflecting the electron stream 21 by coils 22 and 23, both of which are in the plate circuit of vacuum tube 24. Together, these coils contain somewhat more turns than the grid circuit coil 25. tor, establishing the frequency of oscillation in combination with the effective inductance of coils 22, 23 and 25.

The waveform produced bythis oscillator is shown at 7 in Fig. 3. I shape the truncated portion (top) of the waveshape by a relatively low value of grid leak 28.

Without limitingmy invention, the following values have been found convenient in practice. For the truncated waveform a desirable frequency is of the order of one-third'of that which forms a dot upon the reproducing screen. This isequivalent to the frequency of commutation (or sampling) of a dot-sequential type color television system and the incoming video signal is comprised of the intensity of the primary colors existing in the field of view corresponding to the portions of waveform 8 of Fig. 3 identified as 9, 10 and 11. A commutation fre Capacitor 26 is the tank capaciquency of 3.58 megacycles per second is convenient for the television scanning standard now in use in the Umted States of 525 lines, 30 frames, 60 fields 2 to 1 interlaced. The values of capacitor 26 and coils 22, 23 and 25 are chosen to resonate at the commutation frequency.

For dash sequential color television the commutatlon frequency is lower and several adjacent elements are reproduced in the same color. The values for capacitor 26, and coils 22, 23 and 25 are correspondingly larger.

For either values a preferred value for the grid leak 28 is 22,000 ohms. The objective is to utilize a relatively small bias on the grid of tube 24; this condition of operation giving the truncating action sought. Capacitor 27 is merely of a sufliciently large value to have a small reactance at the oscillating frequency with respect to the resistance of resistor 28. Capacitor 29 is similarly constituted with respect to the impedance of the power supply, shown in Fig. 5 as battery 30. Vacuum tube 24 1s conveniently a triode, the cathode of which is connected to ground, as is one side of the grid coil 25. In the schematic diagrams of this invention the heater circuits for vacuum tubes are not shown, these being conventional. Power supplies can be substituted for the batteries.

Preferably, polychromatic video information is impressed upon the grid or control electrode 31 of electron gun 32 to alter the intensity of the electron stream in accordance therewith. Coils 22 and 23 are aligned with the horizontal or high frequency deflection coils (not shown) for creating the usual scanning raster formed upon screen 33. The magnetic flux of truncated triangular waveform caused by current flowing through coils 22 and 23 thus acts upon the electron stream 21 in the same direction as the traverse of the scanning lines across the screen. This is shown as composite waveform 8 of Fig. 3. All the components of Fig. 5 can be conveniently, though not necessarily, grouped around the neck of the cathode ray tube 20.

The integral coaction of elements of the circuitry and the cathode ray tube is to be noted.

*In operation, the average intensity of the electron stream 21 is adjusted by varying the potential of the grid element of the electron gun, or by other means, so that the intensity and the previously recited truncated variation of scanning velocity coact to selectively excite the several phosphors. In other Words, that adjustment of the pedestal or brightness is used which fits each portion of the truncated wave traverse-velocity variation to excite only the proper phosphor. Within this gross range the video or contrast signal changes determine the brightness of each particular colored element of the field of view.

The truncated Wave oscillator is most conveniently synchronized to color changes in the color television process by impressing the color synchronizing signal of the process upon the grid electrode of vacuum tube 24.

Having thus described one aspect of this invention I now turn to related alternates.

In practice, it is often necessary that the electron stream be deflected by a varying voltage rather than by a varying magnetic field. This is accomplished by the circuitry shown in Fig. 6.

Vacuum tubes 40 and 41 are arranged in a relaxation circuit. However, the voltage output waveform of this circuit is triangular, not rectangular as is usually the case. Tubes 40 and 41 can be sections of a miniature double triode. Resistor 42 is connected between grid and cathode of tube 40 and resistor 43 similarly connected to tube 41. The cathodes are connected to ground, or alternatively, together, and to one side of the output circuit. Resistors 42 and 43 are approximately equal in value and of the order of 5,000 ohms resistance. Resistors 44 and 45 are connected to the plates of triodes 40 and 41 respectively and to the source of anode voltage supply 46. Each of these resistor values are of the order of 5,000 ohms.

Capacitor 47 connects the plate of tube 40 to the grid of tube 41 and capacitor 48 the plate of tube 41 to the grid of tube 40. These capacitors have capacitances of approximately micromicrofarads.

The recited component values are for an operating frequency of approximately 3.58 megacycles. Lower operating frequencies can be reached by increasing the several values and vice versa. This specific operative embodiment has been necessarily set forth but it will be understood that various departures in values and details can electron emission. I

be made without departing from the teaching of this invention.

'It will be noted that the scaler value of the capacitative reactance of the capacitors at the operating frequency are of the same order as the value of the resistances in the relaxation circuit and that the value of the capacitative reactance of the stray circuit and vacuum tube electrodes is only somewhat higher than these values.

Diode 49 truncates the triangular voltage wave appearing at the plate of tube 41. Potentiometer 50 is connected across a voltage source 46 with negative grounded. The cathode 51 of the diode can then be placed at any desired positive potential by adjusting the movable contact of the potentiometer. By way of explanation, if this potential is made equal to that of the anode 52 of the diode upon the most positive excursions of the triangular waveform, the latter will not be truncated. For the desired truncation, the cathode potential is reduced until all the intercepts of the truncated waveform with the time axis are equal. (See waveform 7 of Fig. 3.) Other adjustments can be utilized to equalize the overall perporrnance of the system, if this is found necessary in any specific embodiment. Capacitors 53 and 54 are for bypass purposes and thus are to have a small reactance with respect to the imped-ances of elements 50 and 46 at the operating frequency.

At the anode 52 the truncated triangular voltage waveform appears. This is caused to influence the most rapid scan of the raster of the cathode ray tube 20 according to this invention. The usual electrostatic deflection plates can be employed, either in addition to or in common with those required for the rapid raster scan. As an alternate, the voltage waveform can be impressed directly on coils of the general nature and placement of coils 22 and 23 which also are to have small reactance at the operating frequency. As a further alternate, an essentially distortionless impedance step-down transformer can be connected between anode 52 and coils 22 and 23. Deflection plates and step-down transformers are known per se and thus do not require further description nor illustration herein.

The device is synchronized to the color changes of the color television process by applying the color synchronizing piulse to an electrode of tubes 40 or 41, preferably a gr1 Another important aspect of this invention has to do with the fabrication of the transducing screen. In the screen illustrated in Figs. 1 and 2 the inherent characteristics of the phosphors are relied upon for selective activation by the electron stream. These characteristics can be enhanced or supplemented by external factors as illustrated in Fig. 7.

Here numeral 4 identifies the structural substrate as before but an additional thin conductive deposit 60 is formed upon the inner surface. This deposit is essentially transparent to visual light and can be laid down by rapid evaporation of such metals as aluminum or antimony en vacuo, a thin black resulting which also performs the function of the dark screen cathode ray tube face in reducing the effects of spurious ambient light when viewing the image. The deposit is electrically connected to the electrode in the structure for forming the electron stream that has the highest potential, such as gun anode 32 or a conductive coating on wall 20 of the cathode ray tube of Fig. 5.

The phosphor of slowest response to excitation, 61, the red in previous examples, is deposited directly upon the conductive deposit. This is easily accomplished by depositing this phosphor first. Essentially the same result occurs should a simultaneous method be used, because the slow response phosphor is preferably composed of the largest particles, and these settle out of any liquid or gaseous suspension most rapidly. It is not necessary that a complete layer of the slow phosphor 61 be deposited, the object of my invention is achieved as long as the other phosphors are prevented from coming in contact with the conductive layer. Not only will this layer provide the most favorable conditions for prolonged excitation under a stationary spot from the standpoint of dissipation of negative electrical charge but it will also reduce phosphor temperature rise because of its thermal conductivity.

The screen is completed with medium phosphor 62 and rapid phosphor 63, which are treated to inhibit secondary Substances with which phosphor crystals canv be coated will exercise this effect. Silica is assume one such substance. It is known tohave a; low secondary emission ratio with respect to phosphors and to have: a;

ratio less than unity for accelerating potentials of the electron stream in excess ofv about5,,0.00 volts.

Silica can be coated upon phosphors by the known method of adding the phosphor to a warm dilute solution of potassium silicate, adding acetic acid and then turning alkaline with ammonia, upon which silica ispreoip'ia ta=ted from the solution onto the phosphor particles in a thin coating. The resulting solid is separatedfrom the solution, washed and dried.

Metals have low secondary emission ratios in compari: son with phosphors or other insulator-like transducers. A

thin coating of metal can be evaporated upon phosphor. particles en vacuo by heating a small piece of the metal. The phosphor. particles are.

tact with the conductive deposit 60 in Fig. 7. Should this occur the particles 62 and 63 could not collect and retain a negative charge while the electron stream is sweeping by.

Phosphors 62 and 63 are deposited at random. with sumcient premixing or agitation to. prevent appreciable areas of one phosphor only.

In operation, the fast phosphor 63 only is excited and (blue) light is emitted during, the rapid scanning traverse. 9"

(Fig. 3). The medium velocity traverse excites both; the fast and the medium speed phosphor for. a brief instant at any point but the. fast. phosphor charges. negatively quickly because of largely inhibited secondary emission. strike the fast phosphor are thus deflected a very small amount to adjacent medium-speed phosphor. particles. The essentially stationary spot. portion. of the traverse results in, both of the prior phosphors rapidly charging negatively and electron impingement upon only the slow phosphor particles.

Attention is directed to the fact that the above recited factors enhancing selective excitation of the phosphors are most properly combined with the original factors. The

functioning of a coordinated. plurality of properties of. matter to accomplish selective excitation amongstxaplu rality of transducers is an important aspect of' this invention. large plurality disclosed increases the selectivity.

It is to be noted that the residuum of. non-selective excitation of transducers is innocuous. Concurrent excitation of the primaries produces white light. This contributes to the effective presentation of an image according to the known printing technique. of superimposing a blackand white impression over color primaries for the purpose of accentuating detail. It2is. also known that the eye does not perceive detail in color but as a function of (polychromatic) brightness. By thus bringing about the coactive coordination of several factors I securea high degree of selective excitation of plural transducers which in the prior art has always resulted in a high degree of concurrent excitation.

it is also to be noted that in the. practice of color television a degree of miscoloration is often sought as a palliative for boiling efiects in the dot-sequential or dashseqnential systems. Such a polychromatic variation, intended to supplant an intensity variation, is automatically made a functional part of the cathode. ray tube reproducing system in this invention.

In certain circumstances a primary color other than: red may advantageously be reproduced during the stationary electron-stream phase of my color sequence; It is known that the green image in a color television trio supplies the major portion of the image detail. Although all selective excitation traverses in this invention are, of essentially elemental dimensions, the substitution of a slow green phosphor as one transducer for the slow red one maximizes the detail-traverse relation.

A suitable slow green phosphor isa cadmium and zinc sulphide. combination with copper activator. The ratio'of Electrons of the electron stream that would A duality will sulfice, but the coordination of. the

weight-and. the. activator concentration is less than 0.0002 parts. by,-weight. The material is preferably crystallized hexagonally. and large ,and otherwise. takes the place of phosphor 3 in. Fig. 1 or phosphor 61 inhFig. 7.

The efficiencyof the. phosphor is somewhat low and thetemperatureefiiciency relation is ideal, increasing with elevated temperature. The unity emission voltage is high, asrequired so that this factor will not enter into the selective excitation of the slow phosphor of the plurality.

When. green is the slow phosphor, red must be more rapid, say of. intermediate speed. A suitable phosphor is zinc sulphide with manganese asv activator, approximately four I percent by weight. should be of. moderatelysmall size. The speed of excitation and. decay are intermediate and the eificiency also intermediate.

The rapid phosphor of this group can be the silver activatecl. zinc sulphide asbefore.

In order to conform to a color changesequence or time of synchronizing, imposed by other conditions, blue might be, required as the slow phosphor. In this case, zinc silicatewith less than.0.0l part by weight of titanium silicate, rhombohedrally crystallized can'beused.

In the above. instance another color would be required for. therapid phosphor. This can be. green, as composed of. zinc sulphide 45 parts by weight, cadmium sulphide 55 parts and.- silver as activator, 0.01 part. This phosphor is efiicient and of rapidcxcitation and decay behavior. The temperature characteristic drops rapidly above room temperature: so that at somewhat. above the temperature of boilingwater it is only one-fifth as efficient. The'efficiency also decreases under strong excitation. so that the desired behavior under the stationary spotv will be secured.

As another alternate, red can be made the rapid phosphor with the crystallized.compositionof zinc sulphide 20. parts by weight, cadmium sulphide parts and silver as activator, 0.01 part. This phosphor has approximately the same characteristics as the abovegreenphosphor except for emission in the red instead of green light.

Other transducers are possible, such. as thin films having roughly the size of the phosphor crystals illustrated in Fig. 2 but consisting only of thesurface area; i. e., being hollow. Three kinds of films are provided, each havingv a different. thiclmess and: dyed with a somewhat heat resistant; dye in one of the three primary colors. The electron stream 5 impinges as shown. in Fig. 2,. causing incandescence of the films at the. points of impact. The emission of light iscolored according to the respective dye on theother side of the particle in the direction of the viewer, below the substrate 4. Roughly a single layer of the heterogeneous particles is preferable. Selective excitation occurs with dilferingrates of scanning traverse in that during the rapiditraverse only the thin films are raised to incandescence, and so on.

These groups of particles can also be treated with silica to inhibit secondary emission. on the fast ones. Moreover, other groups of particles capable of altering opacity to light transmission upon electron impact can be prepared andarranged according to the teaching of this invention for selective excitation. Such substances are potassium chloride and other alkali halides.

The effective velocity of scanning can be maximized for the rapid traverse of this invention by forming the electron stream of rectangular cross-section as it impinges upon the transducing screen; the. narrow dimension of the rectangle being in the direction of motion. Such a shape can be obtained by giving'the same shape to the defining aperture in the. electron gun 32, this aperture being refocused at the transducing. screen as known in the art of electron. optics.

(Considering a round spot and any given phosphor particle the latterisexcited for a finite time as the whole of the electron stream moves over it. With a narrow rectangular spot the duration of traverse is much shorter when the narrow dimension. is in the direction of motion. Since this'eiiect is not present duringthe stationary portion of the traverse sequence the ratio of excitation times between the' rapid and the medium traverses are increased over the stationary condition.

The effective velocity of scanning can also be maximized for the rapid traverse by altering thetraversing'waveform from the truncated shape; It is only necessary to reduce the value of capacitor 53 in Fig. 6, so as to only partially bypass. potentiometer 50' at the operating frequency, in

cadmium to zinc is approximately fifteentoeighty-five-by; ikorder, to: effectuate .this change. Modification of the Crystallization is cubic and.

truncated portion of the wave from a horizontal to an inclined slope results. This reduction can be, for example, from 0.25 microfarad to 50 micromicrofarads glen the potentiometer resistance is of the order of 25,000 ms.

Fig. 8 shows the resulting waveforms. The horizontal line scan 6 is the same as before (Fig. 3). Waveform 70 is the new asymmetric truncated waveform. When these are combined the upward slope of 70 adds to the upward slope of 6 to create an upward slope 72 of rapid traverse velocity in the resultant waveform 71. The asymmetric portion 'of 70 creates the stationary resultant 73. The downward slope of 70 and the upward slope of 6 combine at 74 to give a reverse intermediate slope 74. It will be noted that this is backward, rather than forward, as before; that the sequence of the respective traverses has been changed; and that the speed of the most rapid traverse.72 is greater than the previous corresponding traverse 9 in Fig. 3. The change in sequence makes convenient an additional number of color sequences with respect to time of synchronization, when variously combineddwith the several phosphor combinations previously recite A correlated mechanism for alternately or further varying the velocity of traverse between the rapid, intermediate and stationary phases lies in variation of the accelerating voltage of the electron stream. It should be clearly understood that the transverse scanningvelocity of the spot on the phosphor screen and not the speed of flight of electrons in the electron stream from gun to screen is referred to. The latter effect is incidental.

It is known that the amplitude of electron stream deflection varies inversely as the square root of the accelerating voltage employed in forming the stream when magnetic deflection is employed and inversely as the first power of that voltage when electrostatic deflection is employed. For a constant value of deflection energy the speed of writing upon the transducer screen is increased if the accelerating voltage is decreased, since the trace is longer Within the fixed period of time of a deflecting cycle. This same effect occurs incrementally if the accelerating voltage is lowered for an increment of the whole scanning traverse. By synchronizing this eflect with the truncated or asymmetric truncated waveforms the velocity variation of writing can be inhanced.

This process is carried outaccording to the waveforms of Fig. 9 and the apparatus of Fig. 10. In Fig. 9 curve 80 will be recognized as the derivative of curve 7 of Fig. 3, the basic truncated waveform. The first portion of the cycle of curve 7 has zero slope, thus the corresponding portion of curve 80 has a zero value. The second portion of curve 7 has a uniform negative slope, thus the second portion of curve 80 has a constant negative value. The third portion of curve 7 has a uniform positive slope, thus the third portion of curve 80 has a constant positive value.

In Fig. 10 point X connects to point X in Fig. 6. The waveform at this point is the truncated one 7 in Fig. 3. Capacitor 90 has high capacitative reactance at the operating frequency and resistor 91 a small value in relation to that reactance so that differentiation occurs. At the grid of vacuum tube 92 waveform 80 is to be found. Pentode 92 amplifies this waveform to a high level. Because of the phase reversing characteristic of the amplifier stage Waveform 81 of Fig. 9 appears at the plate 93 of the tube. Over plate resistor 94 and through capacitor- 95, the latter having small reactance at the operating frequency, waveform 81 is conveyed to the accelerating anode of cathode ray tube 20 in Fig. at point Y. This voltage, superimposed upon the usual accelerating voltage provided by battery 34 alters the acceleration of the electron stream 21 in accordance with waveform 81.

By the same process of combining the truncated waveform with the scanning waveform as illustrated in Fig. 3 a new waveform 82, Fig. 9, results in the present instance, instead of waveform 8. In the new operation, the amplitude of the truncated waveform is adjusted, as before, to give a stationary spot on one of the throws, this time on the throw 83 corresponding to the maximum value of waveform 81.

Since the truncated throw, prior, occurs at the intermediate value of waveform 81, throw 84 will be steeper than the corresponding throw 10 of Fig. 3. Similarly, since throw 85 occurs at the minimum value of waveform 81 it will likewise be steeper than throw 9 of Fig. 3. Thus, further means have been provided for increasing the range of traverse velocities for selective excitation of the plural transducers.

It will be further recognized that these means can be compounded. The asymmetric truncated waveform 71, Fig. 8, can be developed in one amplifier according to Fig. 10 (without differentiation) and fed to the deflection system of the cathode ray tube 20, Fig. 5, while a second amplifier according to Fig. 10 varies the accelerating voltage at Y in Fig. 5.

Modifications and other combinations of the preferred embodiments described above are possible which do not depart from the broad spirit and scope of this invention.

These it is also intended to cover in the scope and semantics of the following claims.

Having thus fully described my invention and the ways in which it can be practiced, I claim:

1. The method of selectively exciting plural comingled unlike transducers which comprises the steps of impacting electrons upon said transducers and varying the rate of traverse of said impacting electrons over said transducers a plurality of times greater than two during each said traverse.

2. The method of selectively exciting plural kinds of adjacently disposed phosphors which comprises the steps of causing electrons to impinge upon a limited area of said disposed phosphors, changing the location of said area, and altering the velocity of said change a plurality of times greater than two before again impinging electrons upon said limited area.

3. The method of uniquely and recurrently causing energy emission from each of a plurality of transducers having different characteristics which comprises the steps of impinging electrons upon an area that includes all the kinds of said transducers, deflecting said electrons to cause impingement upon another area, and cyclically altering the rapidity of said deflection a plurality of times greater than two before again impinging upon the first said area.

4. A cathode ray tube system comprising, means for forming an electron stream, a transducing surface in the path of said stream, cyclic means for deflecting said stream, plural transducers upon said surface each having uniquely distinguishing characteristics, said deflecting means constituted by speed of deflection in relation to said characteristics to excite one of said plurality of transducers to a greater extent than others of said plurality, and means to alter said deflecting means speed of deflection a plurality of times greater than two per cycle to excite another of said plurality rather than the one.

5. Means for selectively exciting a plurality of unlike phosphors, comprising, means for supporting said phosphors, means for causing electrons to strike a plurality of said phosphors, cyclically operative electron 'translative means to cause said electrons to strike said plurality at a place removed from that first mentioned, and means to vary more than twice per cycle the rate at which said electrons are translated from said first plurality to said plurality removed. i

6. Apparatus in accordance with claim 5, including in the rate varying means, plural means arranged to coactively alter the transverse deflection velocity of said electron stream, said alteration being accomplished by increasing the velocity by approximately linearly compounding the component velocities of said means in an additive sense for one element of time and compounding said velocities in a subtractive sense for another element of time.

7. In a device for accomplishing selective response from plural phosphors, means for producing an electron stream, means for deflecting said electron stream at more thantwo rates, said plural phosphors in the path of said deflected stream, each of said phosphors having different characteristics such that the response of one phosphor exceeds that of others of said plurality over a range of deflection velocity.

8. A device for selectively exciting one of a plurality of unlike transducers comprising, an evacuated envelope, said plurality disposed as a mixture within said envelope, means for causing particles capable of exciting said transducers to impinge thereupon to excite the same, means for deflecting said particles from one portion of said disposed plurality to another and. means for changing the rate of said deflection more than twice, each of said transducers responding at a different rate of traverse from said one portion to said other.

9. A device for selectively exciting a plurality of phosphors comprising, a plurality of phosphors heterogeneously arranged, means for producing an electron stream having a cross-sectional area smaller .than the total area .of said arranged phosphors, means for deflecting said stream over said phosphors at a varying velocity of more than two rates, said phosphors composed differently with respect to response to said stream at different velocities, one of said plurality having a rapid, eflicient and brief re sponse to excitation by said electron stream, another of said plurality having a less-rapid, less-eflicient and lessbrief response to said excitation and another of said plurality having a slow, inefficient and prolonged response to said excitation.

10. A color television cathode ray tube system compris ing, an evacuated envelope, means for producing a single electron stream therein, plural means for deflecting said to stream, one of said plural means constituted to cyclically deflect sa1d stream at more than'two -veloc1t1es in step with color change information, a transducer screen disposed within said envelope to receive the impact of said electron stream, a plurality of transducers distributed as a heterogeneous mixture upon said screen, there being one transducer for each color to be reproduced, said transducers differing in response to impact of said electron stream with respect tothe deflection velocity over said screen, one of said plurality of transducers having a rapid, efficient and brief response stimulable upon rapid traverse of said electron stream over said screen, another of said plurality having a less-rapid, less-efficient and less-brief response stimulable upon a less-rapid traverse of said stream over said screen, and another of said plurality having a slow, inefficient and prolonged response stimulable upon essentially a stationary interruption of the traverse of said stream over said screen.

'11. A color television reproducing system comprising, a cathode ray tube, means for producing an electron stream therein, said stream having a crosssection longer in one dimension than in that at right angles thereto, means for accomplishing television raster scanning, an oscillatory electron stream deflection means having a period a small fraction of the period of the more rapid scanning component of said television raster scanning means and substantially aligned in deflection with that of said rapid scanning component, said direction of alignment being at right angles to said longer cross-sectional dimension of the electron stream, said oscillatory deflection means constituted to deflect said electron stream at plural rates during one oscillation, means to synchronize said oscillatory deflection means with the color changes in said color television system, a phosphor screen in said cathode ray tube in the path of said electron stream, plural phosphors upon said screen each of distinguishing characteristics predominantly grouped in degree of efliciency of light output for excitation by said electron stream, rapidity of light response to said excitation, inhibition of secondary emission, deterioration of efliciency and of secondary emission with elevation in temperature, each of said phosphors being further characterized by a light output of different color.

12. A color television cathode ray tube system comprising, an evacuated cathode ray tube envelope, an elec tron gun therein for producing one electron -stream,-plural means for deflecting said stream, one of said plural means arranged to coact colinearly with another of said means to cyclically deflect said stream at more than two velocities, means to synchronize said one deflection means with color changes in the color television process, a phosphor screen disposed oppositely to said electron gun within said evacuated envelope and in the path of said electron stream, said screen composed of a plurality of phosphors, one for each color to be reproduced, each having different characteristics, one of said phosphors having relatively low efficiency, slow visual response to excitation by said electron stream, high capability of emitting secondary electrons, efliciency and secondary electron emitting capability not aifected adversely by elevated temperature, another phosphor having an intermediate value of effi ciency, intermediate speed of visual response to excitation by said electron stream, intermediate capability of emitting secondary electrons, efliciency and secondary electron emitting capability adversely afiected to an intermediate degree by elevated temperature, and another phosphor having relatively high efliciency, fast visual response to excitation by said electron stream, low capability of emitting secondary electrons and eificiency and '12 secondary electron emitting .capability adversely affected by elevated temperature, each of said phosphors emitting light of a different color and giving a maximum response to one of the .said cyclically deflected electron stream velocities.

13. In a device for selectively exciting plural unlike phosphors by an electron stream, means to deflect said stream at a plurality of rates greater than two comprising, a relaxation circuit, vacuum tubes having electrodes in said circuit, relaxation capacitors connected to said electrodes having capacitative reactances somewhat smaller than those associated with said electrodes, resistors connected to said relaxation capacitors having resistances approximately the same as the scalar value of said capacitative reactances, a voltage limiting device connected to said relaxation circuit, said device operative to limit the voltage excursion at one extreme, and means to influence said electron stream with said limited voltage waveform.

14. -In a device for selectively exciting plural unlike phosphors by an electron stream, means to deflect said stream at a plurality of rates greater than two comprising, a relaxation circuit for producing a triangular waveform, an amplitude limiting device connected to said circuit operative to limit excursions in one direction, a circuit having .amplitude and phase characteristics varying with frequencyconnected .to said device to alter the amplitude of said limited excursions, and means to influence said electron stream with said altered Waveform.

15. A .device for selectively exciting plural unlike phosphors by an electron stream, comprising, means for forming an electron stream, waveform means for deflecting said stream :at more than two velocities, plural phosphors in the path of said stream, means to difierentiate the waveform of said -prior means, means for altering the speed of the electrons in said stream according to said differentiated waveform, said latter means connected to said means for forming the electron stream.

16. A color television cathode ray tube system comprising, an evacuated cathode ray tube envelope, an electron gun structure therein for producing one electron stream, plural means for deflecting said stream in two dimensions to form a television raster, another deflection means of reduced .deflective capability with respect to said prior plural means, said .means comprising an oscillatory circuit, plural coils in said circuit, a capacitor connected to said coils, a vacuum tube, control and power electrodes therein, coils connected to said power electrodes and disposed adjacent to said electron stream for the deflection thereof colinearly with the more rapid of said plural raster deflecting means, means connected to said control t lectrode for limiting the amplitude of oscillatory current through said latter coils at one extreme of said amplitude thereby producing more than two rates of change of said current, means connected to said control electrodes to synchronize said deflection means with color changes 'in the color television process, a phosphor screen disposed oppositely to said electron gun within said evacuated envelope and in the path of said electron stream, an electrically-conductive optically-transmissive substrate electrically connected to said electron gun structure, a finely divided phosphor deposited upon said substrate having relatively low efflciency, slow visual response to excitation by said electron stream, high capability of emitting secondary .electrons, efliciency and capability of emitting secondary electrons not adversely affected by elevated temperature, said phosphor thereby adapted to give maximum visual response to said electron stream excitation when .the slowest change of said current occurs, another'finely divided phosphor disposed adjacent to said first phosphor and out of contact with said conductive substrate, said phosphor having an intermediate value of efliciency, intermediate speed of visual response to excitation'by said electron stream, an intermediate capability of emitting secondary electrons, efliciency and capability of emitting secondary electrons affected to an intermediate degree by elevated temperature, said phosphor thereby adapted to give maximum visual response to said electron stream excitation when an intermediate change of said current occurs, and another finely divided phosphor disposed adjacent to said prior phosphors and out of contact with said conductive substrate, said phosphor having a high value of efficiency, rapid visual response to excitation by said electron stream, low capability of em tt ng secondary electrons, efflciency and capability of emitting 0 secondary electrons adversely afiected by "elevated temperature, said phosphor thereby adapted to give maximum visual response to said electron stream excitation when the fastest change of said current occurs, each of said phosphors emitting light of a diflerent color.

17. A color television cathode ray tube system comprising an evacuated cathode ray tube envelope, an electron gun therein producing an electron stream, a phosphor screen disposed oppositely to said electron gun within said evacuated envelope and in the path of said electron stream, said screen composed of three different color phosphors, deflecting means for linear scanning said stream across said diiferent color phosphors and circuit means applied to said deflecting means to produce three difierent rates of scanning during a single linear scan whereby said color phosphors are suitably activated.

References Cited in the file of this patent UNITED STATES PATENTS Von Ardenne Oct. 26, 1937 Dawihl et al. Oct. 31, 1939 Leverenz May 27, 1941 Burnett Aug. 4, 1942 Sharpe Apr. 27, 1948 Shrader Aug. 3, 1948 Leverenz Oct. 26, 1948 Isbister et al Nov. 16, 1948 Szegho Dec. 7, 1948 Jeanne Dec. 27, 1949 Sziklai et al Feb. 27, 1951 Laws et a1 May 8, 1951 Watson et a1. May 8, 1951

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