US2233888A - Charge storage amplifier - Google Patents

Description

Marfil'l 4, 1941- P. T. FlARNsI/VORTH 223,888

CHARGE STORAGE AMPLIFIER Filed July e, 1955y /lllllllnmllllllll @2 ,e4

ESM.

Patented Mar. 4, 1941 UNirEo srnrss Partnr orties CHARGE STORAGE AMPLFIER Application July 6, 1935, Serial No. 30,116

10 Claims.

My invention relates to a means and method for scanning a picture'i'leld, and more particularly to a means and method for electron beam analysis primarily adapted for use in television systems employing cathode ray dissection.

This applicati-on is a companion `application to, and embodies the same broad method as described and claimed in my application Serial No. 29,242, led July 1, 1935, for an Electron image amplifier, filed contemporaneously with the present case, and the tube structure herein described is also described and claimed in my application Serial No. 40,563, led September 14, 1935, for a Charge storage tube, led simultaneously with the present case, now matured into U. S. Patent No.12,100,842, issued Nov. 30, 1937.

Among the objects of my invention are: To provide a method of increasing the sensitivity of television transmission and dissecting cells; to permit the projection of television `pictures by reiiected light of ordinary intensity; toincrease the electrical output of a television dissector tube in order to provide satisfactory television signals Without the use of complicatedand sensitive amplifiers; to provide a television system wherein amplification of an electron image is accomplishedby the formation of a charge image; to provide a means and method whereby relatively large currents may be secured from atelevision transmitting tube; to provide an amplifying means which can be applied to a television tube; to provide an 'amplifier-of photoelectric currents wherein extremely high amplification may be obtained within the photo-electric tube itself; to provide a means 'and method for combining a non-uniform electron "stream with a uniform electron stream; to provide a means and method for forming a charge image'and neutralizing the charge image by a uniform electron stream to produce a train of television signals; toprovide a means and method for charging an insulator to produce modulation of a uniform electron stream; to produce a television dissector tube having a storage period; to provide a television dissector tube and method of operation whereby storage periods create gain in output; vto provide a television dissector `tube .having in effect a moving aperture; .toprovide a television dissector tube wherein stationary charges representing a single line of the picture field are scanned by a dimensioned cathode ray beam to produce a television signal; and to provide a simple and efficient television transmission tube capable of an amplified output.

Myinvention possesses numerous other objects and features of advantage, some of which, together with the foregoing, will be'set forth in the following description of specific apparatus embodying and utilizing my no-vel method. It is therefore tobe understood that my method is r applicable to other apparatus, and that I do not limit myself, in any way, to the apparatus of the present application, as I may adopt various other apparatus embodiments, utilizing the method, within the scope o-f the appended claims.

In my previous United States Patents, as follows:

Patent No. `Issued 1,773,980 Aug. 26, 1930 1,844,949 Feb. 16, 1932 1,941,344 Dec. 26, 1933 2,087,683 July 20, 1937 villumination of the picture field.

The electron stream forming this image may be deflected by means well known in the art, but preferably by magnetic fields, to pass over a stationary aperture in such a manner as to effect a scanning of the image. Selected portions of the electron stream passing through the aperture are collected to form a picture current or train of picture signals which may be amplified and modulated upon a radio wave or, if desired, transmitted by wire or other means.

This method of television transmission offers the advantage of having no moving mechanical parts and of being suitable for the electrical dissection of pictures, having any desired neness of detail. Tl e principal weakness of this method, however, lies in the fact that only a relatively small portion of the velectrons emitted from the total photoelectric area pass through the aperture at any given instant, and at the present time photoelectric emission is relatively small in intrinsic value.

Furthermore, as greater detail is required apertures must be made smaller as there are practical limits to the actual size of the photoelectric emitter. Smaller apertures receive fewer electrons. It is necessary, therefore, in operation of such devices for the highest possible sensitivity to be obtained from the photoelectric surfaces, and even then high gain amplifiers are necessary in order that satisfactory picture currents can be obtained; in fact certain devices of this sort operate with a maximum aperture collection of from zero to twenty electrons for full range operation. With such small output currents, therefore, attempts to amplify the signals above certain limits will bring in background noise, Shottke effect and other factors ordinarily negligible, which tend to make the amplified signals unsatisfactory and distorted. The received picture will therefore be lacking in the detail which it would have if such interference, due to extreme amplification, were not present.

In the present invention the fundamental principles of my previous inventions are retained. An electron image corresponding to the optical image is formed and is dissected as before. I utilize `the electron image, however, to produce a charge image which is then scanned by a separate uniform electron beam to neutralize the charges, and thus produce a train of signals.

Describing my present invention in general terms as relates to method, I prefer to form a stream of electrons in space, representing in cross sectional elementary densities the illumination of the coresponding elementary areas of the optical image. This electron stream is then scanned past an insulating surface to form a charge image of one complete line of the electron image thereon, the charge image being preferably formed perpendicularly to the direction of deiiection.

A stream of electrons is then created having a dimension of elementary extent, and this stream is then passed over the charge image to successively neutralize the charges in the image. The electrons necessary to neutralize the charge at various points along the charge image are then utilized to produce a train of picture signals.

I prefer to form the line charge image at the low frequency rate and to wipe the charges off the insulating material at a high frequency rate.

Brcadly, in terms of apparatus, my invention comprises a tube having a fine wire extending across the tube in the path of the electron image, this wire being coated with a thin layer of insulating material, preferably gl-ass. This wire will be a source of the television signal and preferably will be maintained at a voltage of the order of ten Volts negative with respect to the anode. The anode will preferably be a ring shaped wall coat adjacent the window of the tube. The insulated wire is placed so as to be perpendicular to the direction of low frequency scanning.

Perpendicularly to the wire an electron gun is positioned to project a low voltage cathode ray of small cross section and of elementary dimension across the wire. This ray is deflected back and forth along the wire to provide the high frequency scanning.

In one method of operation of the present device, the photoelectrons in the electron image are accelerated at sufficient velocity to knock secondary electrons out of the insulating coating on the wire, Thus a line of the electron image will be recorded in the form of positive charges bound upon the surface of the glass coating. These will be neutralized by electrons from the electron gun as the ray therefrom is swept along the length of the wire, and the discharge will produce surges of current in the wire in acordance with the capacitances between the charges on the surface of the glass and the Wire within. The velocity of the scanning electrons is preferably limited so that they do not cause secondary emission. Therefore they leave the surface uniformly negatively charged and ready for the next line of photoelectron charges.

In another method of operation I employ photoelectron velocities less than those required to produce secondary electrons, and a higher velocity in the scanning ray electrons. In this manner the photoelectric charges upon the wire are negative and they are neutralized by production of the positive condition of the surface when scanned by the gun. It is obvious, therefore, that the photoelectric charges are stored during the period of one high frequency scanning cycle, thus giving a multiplication on the order of several hundred, the multiplication depending upon whether the positive or' negative condition obtains. The method has the advantages of a mosaic without employing an actual mosaic surface, as the charges are bound and dissipated only by leakage. The method is of course adapted to a surface as well as to a wire, as a thin sheet of mica with a metal coating on the side opposite to the photocathode is of course a full equivalent of the wire described.

In the case where a surface is used, it is of course obvious that the scanning beam shall be of elemental dimension in all dimensions; in other words, of elemental cross section, and that both high and low frequency scanning shall be done with this beam.

In its broad aspect, therefore, in terms of method, my invention comprises directing a stream of photoelectrons against an insulated surface to produce fixed charges thereon, in accordance with the illumination intensities of an optical image, and utilizing the charges to create a current representing the image. This method is broadly covered in my copending application for an Electron image amplifier, Serial No. 29,242, filed contemporaneously with the present application, the system for practicing the method being somewhat modified herein.

In the following description and discussion the word photoelectron is used to designate the emission from a photoelectric surface in accordance with the illumination thereof by an optical image, it being understood that the electron image formed by the photoelectrons is at all times maintained in optical 'image relation. Scanning electrons shall be taken to mean electrons existing in a stream whose cross section has uniform electron densities.

In the drawing which accompanies this application and is made a part hereof:l

Figure 1 is a longitudinal section, partly in elevation, of a dissector tube utilizing a line charge image.

Figure 2 is a cross sectional view taken as indicated by the line 2-2 of Figure 1.

Figure 3 is a diagram reduced to simplest terms, showing how the tube of Figure 1 may be connected in operation.

Referring directly to the drawing for a detailed description of the specific embodiments of .my invention illustrated therein, and first referring to Figures 1 and 2 which illustrate a charge storage dissector tube wherein the charge influence of the anode potential.

is stored a line-at a time, an -envelope I is providedat one end with a photoelectric cathode 2, outside connection beingmade by-connection lead 4.

`I prefer in this case to make the cathodelof cup shape and depositen thewall of the tube a ring anode 5, the edges of the anode and cathode approaching but leaving la space-6 therebetween.

Across the end of the tube I prefer to position a horizontal tungsten rod `I which Yis provided with a thin glass coating 9, and-in order to allow the' passage therethrough of this composite electrode I prefer to remove a Aportion-of the 'anode film 5 to form apertures IIJ-IIB therein vwhere the wire passes through the Wall ofthe tube. The opposite end of the tube is provided with a window II through which an optical image of an object I2 may be projectedby means of a lens I4 on the cathode 2.

Positioned in the lower end of `the tube envelope inra side arm I5 and-in -the plane of the tungsten rod is an electron gun assembly adapted for supplying a ne line beam intersecting the composite electrode 'I-9. This gun comprises an indirectly heated cathode II and a perforated tent of the composite electrode.

The operation of the device is in accordance with two methods, but as the apparatus for creating the operation is similar, the diagrammatic hookup shown in Figure 3 will serve to illustrate both methods.

Here, the cathode 2 is connected to the anode '5 through an anode battery 2l] so that the anode is positive with respect to the photoelectric cathode. When the optical image from object I2 is focused by means of lens- I4 onto the photoelectric cathode, the latter emits electrons at every elementary area thereof in proportion to the illumination these areas receive, and these elec-- trons are drawn outwardly in space under the The electrons emitted from the photoelectric cathode are maintained in the electron image relation by means of a focusing coil 2l Whose held is produced bycurrent from a source 22 under the control of a rheostat 24 so that the electrons focus in the Y plane of the storage electrode 1 9, and the electron image is scanned across the storage electrode in a direction perpendicular thereto by means of the field of a low frequency magnetic deecting coil 25 supplied by a low frequency f oscillator 26. At the same time the'electron gun is energized, the cathode I'I by means of cathode battery 21, and the anode thereof by means of anode source 29, to project a beam of scanning electrons upon the insulating surface of the tungsten rod 1, and this scanning beam is deflected along the storage rod by means of charges placed upon the horizontal deflecting plates I9 from a high frequency oscillator 3l). The tungsten rod is connected through an output resistor 3l having output leads 32 thereacross to a point 34 intermediate the positive and negative end of the anode battery 29.

In one method of operation the photo-electrons are accelerated by means of the anode potential from source 2U to a suflicient velocity to knock secondary electrons out of coating 9 as the image is scanned thereacross. These secondary electrons are of course picked up by the anode 5, leaving charges which will represent a line of the electron image recorded in the form of positive charges bound upon the surface of the glass coating. After these charges have been formed, the electrons from the electron gun assembly comprised in the beam projected thereby, sweep across the length of the wire and discharge the positive charges on the Wire. This discharge of thecharges upon the wire in sequence as the beam sweeps across will produce in the tungsten rod "I surges of current in accordance with the capacitance between the surface charges and theA The other method of operation is to reduce the potentialon anode 5 to a point where secondary electrons are not produced.

be bound thereon, .and I then prefer to raise the voltage on the electron .gun I8 to a point where these electrons will cause secondary emission from the surface 9 which will then discharge the `charges on the surface in the opposite direction 'and vwill ieave the surface positively charged, Yready for the next negative charge to be supplied by the photoemission.

It is obvious `from the above description that the photoelectric charges will be stored during 'theperiod `of one scanning cycle of the scanning beam, thus giving a considerable multiplication,

`the multiplication being substantially equal in 4both cases inasmuch as the charges are stored endfbound upon the insulatingsurface. It is obvious that the charge pattern, in case a line storage is usecLwvill have a value which is de- -termined by the period of the vhigh frequency the charge storage surface rectangular and of .an area comparable to the whole of the electron image, and then scan the charge image with an 1 eiectronbeam-moving in'two directions. In this latter case the charge will be stored during the entire low frequency scanning cycle. In this latterinstance prefer to utilize a thin sheet of mica backed with a metal film for the charge storage electrode, the full functional equivalent of a photoelectric mosaic being produced, thus avoiding the difculties entering into satisfactory mosaic production.

I claim:

1. In a cathode ray tube containing a conductor having .an insulating surface, the method of creating a signal train which comprises projecting an electron image on said insulating .surface having elemental length and picture Width to produce a charge image thereon corresponding to a single line of said electron image, scanning the charged surface with an electron beam to produce equilibrium thereof, and utilizing the capacitance changes in said conductor dueto charge neutrali- The charges proy duced oninsulating surface 9 by the photoelectrons will therefore be negativecharges and will zation on said surface by said beam to produce said train.

2. In a cathode ray tube containing a conductor having an insulating surface, the method of image dissection which comprises storing a charge image on said insulating surface and scanning the charged surface with an electron beam of elemental dimension to successively neutralize said charges and to produce a charge equilibrium thereon, the relative velocities of the electrons in said image and said beam being such that one Will produce secondary electrons and the other will not, and repeating the cycle.

3. In a cathode ray tube containing a conductor having an insulating surface, the method of image dissection which comprises storing a charge image on said insulating surface .and scanning the charged surface with an electron beam of elemental dimension to successively neutralize said charges and to produce a charge equilibrium thereon, the relative velocities of the electrons in said image and said beam being such that one will produce secondary electrons and the other will not, and measuring the energy required for neutralization through said conductor.

4. In a cathode ray tube containing a conductor having an insulating surface, the method of image dissection which comprises storing a charge image on said insulating surface and scanning the charged surface With an electron beam of elemental dimension to successively neutralize said charges and to produce a charge equilibriu-m lthereon, the relative velocities of the electrons in said image and said beam being such that one will produce secondary electrons and the other Will not, and deriving said train from the succes-sive capacitance changes in said conductor.

5. In combination, means for producing an electron image, means for projecting said image on an insulating surface deposited on a conductor :to form a charge image thereon, means for scanning said surface with an electron 4beam of elemental dimension to successively neutralize the charges in said image, the relative velocities of the electrons in said image and said beam being such that one will produce secondary electrons and the other will not, and means for utilizing the current in said conductor varying in accordance with the energy required for neutralization of said charges.

6. In combination, means for producing 4an electron image, means for projecting said image on an insulating surface backed by and deposited on a conductor to form a charge image on said surface, means for scanning said surface with an electron beam of elemental dimension to successively neutralize the charges in said image, the relative velocities of the electrons in said image and said vbeam being such that one Will produce secondary electrons and the other will not, and an output circuit connected to said conductor.

7. In combination, means for producing :an electron image, means for projecting said image on an insulating surface :covering a linear conductor, said surface being of picture width and single line length to form a charge-image thereon representing a picture line, means for directing an electron beam of elemental dimension along said surface to successively neutralize said charges, the relative velocities of the electrons in said image and said beam being such that one will produce secondary electrons and the other will not, :and means for utilizing currents in said conductor due to neutralization of said charges.

8. In combination, means for producing an electron image, a conductor disposed transversely of said image, an insulating surface on said conductor, said conductor with said insulating surface being of a length at least equal to one dimensionof said electron image, and of a Width substantially equal to the Width of an elemental area of said image, an independent electron beam of .approximately elementary area in cross section, directed toward said insulating surface and capable of movement therealong, and means for imparting only unidirectional scanning movement to both said electron image and said independent electron beam over said insulating surface.

9. In combination, means for producing an electron image, a conductor disposed transversely of said image, an insulating surface on said conductor, said conductor with said insulating surface being of a length at least equal .to one dimension of ysaid electron image, and of a Width substantially equal to the Width of an elemental area of said image, an independent electron beam of approximately elementary area in cross section, directed toward said insulating surface and capable of movement therealong, means for impar-ting :a con-tinuous unidirectional scanning movement to said electron image past said composite electrode in a direction normal thereto, and means for simultaneously imparting a plurality of successive scanning movements to said independent electron beam along said composite electrode at 1a rate to, in effect, scan successive lines cf said electron image.

10. In combination, means for producing an electron image, a composite electrode disposed transversely of said image `and of a length at least equal to one dimension of said electron image, and of a Width substantially equal to the Width of an elemental area of said image, an independent electron beam of approximately. elementary area in cross section, directed toward said composite electrode and capable of movement therealong, and means for imparting unidirectional scanning movement to said electron image in a direc-tion normal to said composite electrode and means for imparting a plurality 'of successive scanning movements to said independent electron beam along said composite electrode duringl the period of said scanning movement of said electron image.

, PHILO T. FARNSWORTH.

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