US3404308A

US3404308A - Cathode-ray signal-translating device

Info

Publication number: US3404308A
Application number: US551769A
Authority: US
Inventors: Burns Joseph
Original assignee: Fairchild Camera and Instrument Corp
Current assignee: Fairchild Semiconductor Corp
Priority date: 1961-12-04
Filing date: 1966-05-20
Publication date: 1968-10-01
Anticipated expiration: 1985-10-01

Description

Oct. l, 1968 J. BURNS CATHODE-RAY SIGNAL-TRANSLATING DEVIGE Original Filed Dec. 4, 1961 MULTI VI BRATOR United States Patent O 3,404,308 CATHODE-RAY SIGNAL-TRANSLATING DEVICE Joseph Burns, iequannoclr, NJ., assigner to Fairchild Camera and instrument Corporation, a corporation of Delaware @riginal application Dec. 4, 1961, Ser. No. 156,627. Divided and this application May 20, 1966, Ser. No. 551,769

2 Claims. (Cl. 315-12) ABSTRACT F THE DISCLQSURE A cathode-ray signal-translating device includes airst target comprising a thin glass substrate having a phosphor screen adhering to one side and a layer of photoemissive material, for example a photocathode of a caesium-antimony or silver-caesium alloy on the other side. A conventional electron gun and deflection system scans the phosphor screen with a signal-modulated cathode ray which causes the photocathode to develop a space-modulated electron beam representative of the input signal. The device further includes a barrier grid assembly disposed adjacent a target comprising a conductive plate on which is disposed a continuous layer of dielectric material having a substantial secondary electron emission ratio characteristic. interposed between this barrier grid assembly and the photoemissive layer is a collector electrode. A multivibrator is provided for shifting the potential of `the conductive plate between two desired potential levels. During application of a positive potential to the conductive plate, the electron beam from the photoemissive cathode is effective to write on the dielectric layer of the barrier grid assembly. When a negative poftential is applied to the conductive plate, the charge pattern on the dielectric layer is read out by scanning the first target with a beam from the electron gun.

This is a division of application Ser. No. 156,627, filed Dec. 4, 1961, now abandoned.

This invention relates to cathode-ray signal-translating devices and, while it is of general application, it is particularly applicable to so-called scan converters, that is, devices of the type including a storage target on which information is stored by a write gun and from which such information is derived either simultaneously or sequentially by a read gun.

In the conventional scan converter, a storage grid or target is scanned by a cathode-ray beam from the write gun and, through the process of bombardment induced conductivity, there is developed a charge pattern on the storage grid. If the storage grid is then scanned by a relatively low-potential reading cathode-ray beam, the backing electrode of the storage grid draws a capacitive current varying in accordance with the charge pattern as the read gun beam brings `the successive elemental areas of the target electrode to a uniform potential substantially that of the read gun cathode or the collector, depending upon the primary beam velocity, at the same time erasing the storage pattern. The scanning of the storage grid by the reading beam may be either simultaneous or sequential, that is, after one complete block of information is stored by the write gun, the read gun scans the storage grid to reconstitute the stored block of information.

Scan converters of the type described are frequently used to store high-frequency periodic information or highspeed transient information which can then be read out at a slower rate more compatible with the desired use to be made of the information. To permit high-speed writing, the write beam must have a high energy level,

3,404,38 Patented Oct. 1, 1968 that is, it must have a high density and a high accelerating voltage in order to store a significant amount of energy in each elemental area of the storage grid as it is rapidly scanned. However, it is well known that maximum secondary electron emission occurs between the first and second crossover points on the potential-secondary emission characteristic of the particular material, which, for the most efficient dielectric materials useful on the storage grid, occurs at a relatively low potential of the order of a few hundred volts. Thus, in prior scan converters, the accelerating voltage of the Write beam has been a compromise 'between these two conflicting criteria.

In the present invention, the foregoing compromise is avoided by providing two electron-optical transducers in cascade, effectively dividing the former method of forming a charge pattern on the storage grid into two steps each performed at optimum energy levels.

In accordance with the invention, there is provided a cathode-ray signal-translating device comprising an electro-luminescent first target, an electron-gun assembly for generating a focused signal-modulated cathode ray, means for scanning such first target with such cathode ray to form thereon a luminous representation of the signal, a layer of photoemissive material disposed closely adjacent such first target, a barrier grid assembly including a conductive plate having an adhering continuous layer of dielectric material and a grid near such dielectric layer, and means for transferring to the such dielectric layer the charge pattern developed on such photoemissive layer by the scanning of the first target. The signal-translating device further comprises a collector electrode means adjacent the dielectric layer, and means for scanning the photoemissive target with a constant-intensity, constant velocity cathode ray sequentially with the scanning thereof by the signal-modulated ray, whereby the collector electrode means reads off the charge pattern on the dielectric layer. The term signal-modulated cathode ray is used herein vand in the appended claims to refer to a cathode-ray beam modulated in intensity and having a constant defiection pattern or such a beam of constant intensity having a modulated scanning pattern. The term electro-optical responsive material is used herein and in the appended claims to refer to a material having an electrical property variable wit-h illumination, for example a photoemissive or a photoconductive property.

For a better understanding of the present invention, together with other 4and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawing, while its scope will be pointed out in the appended claims.

Referring now to the drawing:

FIG. 1 is a schematic representation of an embodiment of the invention in a scan converter utilizing a photoemissive material in place of a photoconductive material, while.

FIG. 2 is a schematic representation of the embodiment `of a modified form of the invention in a scan converter tube utilizing a single electron gun for writing and reading sequentially.

Referring now more particularly to FIG. 1 of the drawing, there is represented a cathode-ray signal-translating device responsive to a high-frequency wave signal. This device comprises an electroluminescent target which may be in the form of a thin transparent supporting member 1f), for example a thin plate of glass or a plate-like assembly of optical fibers. The member 10 has a layer 11 of electroluminescent material, such as a suitable phosphor, adhering to one face of the plate and preferably having an electron transparent conductive coating 12 in the form of a conventional aluminized backing overlying the phosphor layer 11. The other surface of the supporting member 16 has an adhering transparent conductive coating 45 on which is disposed a layer 4@ of photoemissive material of any Well-known type, for example a caesium-antimony or silver-caesiurn alloy.

The device of FIG. l also includes an electron-gun assembly fo-r generating a focused signal-modulated cathode ray. This electron-gun assembly includes the unit shown schematically as 13 comprising the usual cathode, control electrode, and accelerating electrodes forming an electrostatic focusing means. Alternatively, magnetic focusing means may be used if desired. There is also provided means for scanning the target with the cathode ray to form thereon a luminous representation of an input signal, This scanning means may be in the form of a series of spaced pairs of plates 15551, 141), and 14C adapted to be connected to the signal input source 17 through a conventional delay line 18 terminated in a resistor 19 having a value equal to the characteristic impedance of the l-ine. The plates 14a, Mb, and 14E-c are connected to suitable taps on the delay line 18 so located that the signals applied to the successive plates are delayed by intervals approximately equal to the transit time of the cathode-ray beam between the plates.

The cathode-ray device of FIG. l includes also an electron-charge storage target in the form of a grid or mesh 41 coated with a suitable dielectric material capable of emitting secondary electrons, for example magnesium tiuoride. The device also includes means for transferring to the target electrode 41 the charge pattern developed on the photoemissive layer 40 by the scanning of the phosphor layer 11. This means may be in the form of an accelerating grid or mesh electrode d2 disposed near the photoemissive layer 46, that is, between the target comprising the elements 11, 12, dit and the storage target 4l. There is also provided a decelerating grid electrode 43 disposed adjacent the storage grid 41 and between it and the electron-gun unit Z3 and a coliimating electrode in the form of an annular conductive ring te for collimating the cathode-ray beam from the electron gun 23 during the scanning of the targets as described. The accelerator electrode 42 may comprise also a collector for deriving an output signal varying with the charge pattern on the storage grid target 41 as it is scanned by the cathode-ray beam from the electron gun Z3. To this end, the accelerator electrode ft2 is connected to a suitable potential such as +500 V. through a load resistor 45 to which is connected an output terminal 45a. The conductive element of the storage grid t1 is adapted to be selectively connected via a switch 41a to a potential approximately v. above the potential of the layer dit), that is about +40 v., to a potential about 300 v. above that of the layer 40, that is about 320 v., or to approximately the potential of the layer 46, for example to ground, as illustrated. The decelerator grid S3 and the collimating electrode i4 are connected to adjustable taps on a voltage-divider resistor 15 connected across a suitable source -l-O v. If desired, a magnetic lens (not shown) may be disposed between the photoemissive layer and the storage target 41 to facilitate the transfer of the charge pattern without distortion.

The potentials applied to the several electrodes of the device of FIG. 1 will depend upon its particular design parameters and, to an extent, upon its intended use. However, typical electrode potentials may be of the order of those indicated in the drawing.

The operation of the cathode-ray signal-translating device of FIG. l may be as follows: Assume that the conductive element of the storage grid 41 is initially adjusted to approximately 20 v. above the potential of the photoemissive layer 40, that is, below the first crossover point on the secondary emission ratio characteristic 0f the storage grid 41. The phosphor layer 11 is then scanned with a defocused raster of constant intensity to bring the potential of the surface of the storage grid 41 to equilibrium potential. The potential of the conductive element d, of the storage grid 41 is then increased to approximately 300 v, above that of the photoemissive layer 40 and the information to be translated is utilized to Write on the phosphor layer 11 as described above. The electron pattern formed on the photoemissive layer 40 is transferred to the surface of the storage grid 41 by the accelerating grid 42 during the scanning process and, due to the fact that the dielectric layer of the storage grid l1 is above the second crossover p-oint on the secondary emission ratio characteristic, each elemental area of the photoemissive layer d@ which is caused to emit electrons produces a corresponding positively charged area on the storage grid 41. Y

In order to retrieve the information represented by the electron pattern on the photoemissive layer 455, the conductive element of the storage grid 41 is then `reduced substantially to the potential of the photoemissive layer 40 as it is scanned Vwith the focused nonmo-dulatcd cathode-ray beam from the electron gun 23. The electron charge Apattern now existing on the storage grid l1 is such that it permits the flow of electrons from the scanning beam in those areas which have become positively charged, as described above, and repels such electrons in other areas. The electrons from the scanning beam of the electron gun 23 passing through the storage grid 41 are collected by the accelerating electrode 42 and develop an output signal across the load resistor 45 which appears at output terminal 45a.

The cathode-ray signal-translating device of FIG. l has a number of advantages. The formation of the input signal wave form on the phosphor layer 11 may be at an extremely high speed, considerably greater than that possible in prior scan converter tubes, due to the substantial energy in the high-density cathode-ray beam from the gun 13 operating with a high accelerator potential. As pointed out above, such a high accelerator potential could not be applied directly to the storage grid d1 because of secondary electron emission effects. The speed of Writing the input signal on the phosphor layer 11 may be so high that it could not be utilized if it were attempted to apply it directly to other utilization circuits. However, by storing on the storage grid 41 this information Written at high speed on the phosphor layer 11, it may then be retrieved by relatively lower speed scanning of the grid 41 by the electron gun 23 for utilization in any convenient manner. Furthermore, by thus providing separate electrode elements for writing and reading, the optimum potentials for the two functions may be selected independently, thus resulting in a very much higher efficiency in the over-all signal-translating device and providing a gain in the electron amplier comprising the photoemissive layer 40 and the storage grid 41.

Turning now to FIG. 2, there is represented a modified form of the invention for utilizing the information formed as an electron pattern on the photoemissive layer 40 of FIG. 1. In this arrangement, there is provided a barrier grid assembly comprising a grid or mesh electrode 47 disposed adjacent a target comprising a conductive plate 48 on which is disposed a continuous layer 49 of dielectric material having a substantial secondary electron emission ratio characteristic. Interposed between the

target

48, 49 and the photoemissive layer 40 is a collector electrode in the form of a cylindrical conductive element 5?. The conductive plate 48 is connected to means for shifting its potential between two desired potential levels. This may be in the form of a multivibrator 51 having an output Wave of the form represented in the curve 52. The collector electrode 50' may be connected to a suitable source, such as v., through a load resistor 53, the output signal being taken from across the load resistor 53 and appearing at an output terminal 54. ln this embodiment of the invention, the same cathode-ray beam from the electron gun 13 is utilized both for writing and reading.

The operation of the barrier grid form of the invention illustrated in FIG. 2 is as follows: The barrier grid 47 adjacent the surface of the dielectric layer 49 acts both as a collector electrode, in addition to the collector 50, and establishes an equilibrium potential on the adjacent surface of the dielectric layer 49. It also prevents coplanar grid effects and prevents electron redistribution on the surface of the dielectric layer 49.

Initially, equilibrium potential on the surface of the dielectric layer 49 is established at l or 2 volts positive with respect to the barrier grid 47 which creates a negative barrier when the surface of the dielectric layer 49 tends to rise higher. A positive potential applied to the conductive plate 48 capacitively shifts the potential of the surface of the dielectric layer from its equilibrium value in preparation for writing. For example, if a positive pulse fromY the multivibrator 51 is applied to the conductive plate 48, the potential of its surface will shift positively by an equal amount due to capacitive coupling. Electrons from the photoemissive layer 40, as the phosphor layer 11 is scanned by the writing gun, can now land on the surface of the dielectric layer 49 in accordance with the modulation of the write gun beam. The written areas on the surface of the dielectric layer 49 are thus restored to its previous equilibrium potential.

After the input signal has been stored on the dielectric surface 49 by one scansion of the writing beam, a negative pulse from the multivibrator 51 is applied to the conductive plate 48, returning its surface to its original equilibrium potential by capacitive coupling. The charge pattern previously established during the writing cycle may be retrieved by again scanning the target 11, 40 with a beam from the electron gun 13 now operating as a constant-intensity read gun. The resulting constantintensity electron emission from the photo-emissive layer 40 now effectively scans the surface of the dielectric layer 49, returning the potential of the written areas to their equilibrium value and producing a secondary electron emission output modulated in accordance with the previously written information, which output is collected by the collector electrode 50, and producing an output signal across the load resistor 53 which may be derived from the output terminal 54. It is noted that the read-out, as described, is destructive of the charge pattern on the surface of the dielectric layer 49 formed during the writing cycle.

While there have been described what are, at present, considered to be the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein, without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A cathode-ray signal-translating device comprising:

an electroluminescent target;

a first electron-gun assembly for generating a focused signal-modulated cathode ray;

means for scanning said target with said ray to form thereon a luminous representation of the signal;

a layer of photoemissive material disposed closely adjacent said target;

a barrier grid assembly including a conductive plate having an adhering continuous layer of dielectric material and a grid near said dielectric layer;

means for transferring the charge pattern from said photoemissive layer to said dielectric layer;

collector electrode means adjacent said dielectric layer;

and means for scanning said target with a constant-intensity, constant-velocity cathode ray sequentially with the scanning thereof by said signal-modulated ray, whereby said collector electrode means reads off the charge pattern on said dielectric layer.

2. A cathode-ray signal-translating device comprising:

an electroluminescent target;

a layer of photoemissive material disposed closely adjacent said target;

collector electrode means adjacent said dielectric layer;

means for scanning said target with a constant-intensity, constant-velocity cathode ray sequentially with the scanning thereof by said signal-modulated ray, whereby said collector electrode means reads Off the charge pattern on said dielectric layer;

and means for switching the potential of said conductive plate synchronously with scanning means to determine whether a charge pattern is formed or erased on said dielectric layer.

References Cited UNITED STATES PATENTS 2,879,442 3/1959 Kompfner et al. 315--12 2,916,661 12/1959 Davis 315--12 X 2,919,377 12/1959 Hanlet 315--12 3,165,664 1/1965 Callick 315-12 RODNEY D. BENNETT, Primary Examiner.

M. F. HUBLER, Assistant Examiner.