US2201215A

US2201215A - Picture transmitter tube

Info

Publication number: US2201215A
Application number: US732750A
Authority: US
Inventors: Vladimir K Zworykin
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1934-06-28
Filing date: 1934-06-28
Publication date: 1940-05-21
Anticipated expiration: 1957-05-21

Description

PICTURE TRANSMITTER TUBE Filed June 28, 1934 PICTURE INVENTOR VladimirKZwory/iin ATTORNEY Patented May 21, 1940 UNITED STATES PATENT OFFICE PICTURE TRANSMITTER TUBE tion of Delaware Application June 28, 1934, Serial No. 732,750

8 Claims.

My invention relates to picture transmitting apparatus and particularly to cathode-ray transmitter tubes.

In one form of cathode-ray transmitter tube,

an image of the picture or scene to be transmitted is thrown upon a mosaic of light sensitive elements whereby photo-electrons are emitted therefrom to produce an electrical image upon the mosaic. The picture signals are generated by scanning the electrical image with the cathode ray, both'th'e cathode ray and the light from the picture striking what is referred to as the front side of the mosaic. It has been the usual practice to collect the photo-electrons by means of a screen electrode placed opposite the front side of the mosaic. When a screen electrode is used in this way, however, it interferes with the optical image and with the scanning beam or cathode ray.

An object of my invention, therefore, is to provide a cathode'ray tube of the above-mentioned type in which the photo-electrons are collected without involving the disadvantages referred to above.

A further object of my invention is to provide a cathoderay picture transmitter tube having the minimum number of electrodes.

Other objects, features, and advantages of my invention will appear from the following description, taken in connection with the accompanying drawing, in which Figure l is a view of a tube constructed in accordance with one embodiment of my invention and of its associated circuit;

Figure 2 is a view which is referred to in explaining the operation of my improved transmitter tube, and

Figure 3 is a view of another embodiment of my invention.

Referring to Figure l, the tube comprises a highly evacuated envelope I, in which is located an electron gun consisting of a cathode 3, a control electrode 5, and a first anode l. The anode I may be maintained at a suitable positive potential with respect to the cathode 3 by means of a battery 9 While the control electrode 5 may be maintained at a suitable negative potential by means of a battery I I.

The electrons leaving the first anode l are accelerated, and the electron beam focused to the desired small cross-sectional area by means of a second anode I 3, which may consist of a metallic coating on the inner surface of the envelope I. The second anode I3 is connected to ground and maintained at a comparatively high positive potential with respect to the cathode 3 by means of a battery H3 or other source of voltage connected in series with the battery 9.

A mosaic ll of light sensitive elements is sup Picture signals from the transmitter tube are impressed upon an amplifier 25 through an output resistor 21 and an inductance coil 29, which are connected between the mosaic l1 and ground, the coil 29 being provided to improve the high frequency response.

The mosaic H, which in itself is no part of the present invention, may be constructed in a variety of ways. In a preferred form it consists of a thin sheet of mica having a continuous metallic coating on the back side thereof which is electrically connected to the

output impedance units

21 and 29. This metallic coating will be referred to as the signal plate. The mosaic proper may consist of a multitude of silver globules each of which has a film of silver oxide thereon, the silver oxide film being coated with caesium. In such a mosaic, the light sensitive elements are electrically insulated from each other and from the metallic coating or signal plate on the back of the mica sheet. Another possible method of constructing a mosaic is' that of forming a lightsensitive layer upon. the front side of the mica and separating the light-sensitive material into a large number of elements insulated from each other by ruling the light sensitive film with a ruling machine. Still another method of making a mosaic is to form an exceedingly thin coating of light-sensitive material upon the mica, the coating not necessarily being discontinuous, but being so thin that the resistance between ele mental portions thereof is very high.

Each light-sensitive element of the mosaic acts as the cathode of a photo-electric cell which has the metallic coating l3 as its anode, the metallic coating l3 functioning not only as an accelerating and focusing electrode for the electron beam but also as a common photo-electric cell anode for the photo-electric cell cathodes in the mosaic.

The photo-electric cell circuit of the transmitter tube is shown in Figure 2 where parts similar to those in Figure 1 are indicated by the same reference numerals. Two light-sensitive globules or cathode elements of the mosaic are indicated at 3| and 33. The common anode [3 for the'cathodes, which is indicated schematically, is connected through the resistor I! and inductance coil 29 to the metallic coating or signal plate indicated at 35, which is on the back side of the mica sheet (not shown). It will be seen that the photoelectric cell cathodes 3i and 33 are connected to the metallic coating or signal plate 35 through the capacity between the silver globules and the said metallic coating. These capacity connections are represented by the

condensers

31 and 39.

It is my present theory that the operation of the transmitter tube depends upon the fact that when, during scansion, an optical image is formed upon the mosaic l1, each elemental light sensitive portion or globule acquires a positive charge having a value depending upon the intensity of the light striking it, whereby an electrical image is formed upon the mosaic. The positive charge, of course, is acquired as a result of the light sensitive element emitting photo-electrons which are collected by the electrode l3. When a light sen- 'sitive element acquires a positive charge, the condenser which it forms with the signal plate is likewise charged so that each time a light sensitive element is scanned by the electron beam, the condenser is discharged through the

output impedance

21 and 29. This discharge current, which has a value depending upon the intensity of light at a certain picture area, is the picture signal current.

It will be seen from the foregoing description that the electrode I3 is so positioned that it does not interfere with the optical image formed upon the mosaic and that, since it has a large opening therein which is positioned inline with and between the electron gun and the mosaic, it permits the scanning beam to pass therethrough and does not intercept it at any time.

In addition to collecting photo-electrons, the electrode l3 also collects the secondary electrons which are emitted from the mosaic as a result of its bombardment by the electrons in the scanning beam. In the embodiment of my invention shown in Figure 1, therefore, the electrode I 3 functions to accelerate and focus the electrons in the scanning beam, to collect secondary electrons from the mosaic and also to collect photoelectrons from the mosaic.

In the modification of my invention shown in Figiu'e 3, in which parts similar to those in Figure 1 are indicated by the same reference numerals, the electrode l3 functions only as a collector of photo-electrons and secondary electrons from the mosaic. An additional ring-shaped electrode 4| positioned between the first anode l and the electrode l3 functions as the second anode of the tube. The final step in focusing the electron beam is accomplished by means of the second anode 4|, the electrode l3 having no accelerating or focusing effect on the electron beam since it is maintained at the same potential as the second anode 4| by means of a direct connection 43 thereto.

If desired, one or more pairs of electro-static deflecting plates may be substituted for the defleeting coils 2| and 23 shown in Figure 1. In the embodiment illustrated, one pair of deflecting plates 45 has been provided, these deflecting plates being positioned inside the metallic coating which-forms the electrode l3, whereby they are shielded from external electric fields.

From the foregoing description it will be apparent that various other modifications may be made in my invention without departing from the spirit and scope thereof and I desire, therefore, that only such limitations shall be placed thereon as are necessitated by the prior art and set forth in the appended claims.

I claim as my invention:

1. A picture transmitting tube comprising a highly evacuated envelope, means therein including a first anode for producing a beam of electrons, a mosaic of elements so sensitized that they emit electrons when an image is formed thereon and so positioned that said beam may scan said elements and also so positioned that an image may be formed on said elements on the same side that is scanned by said beam, and an electron beam focusing electrode having an opening therein which is positioned in line with and between said first anode and said mosaic whereby said beam passes through said opening, the size of said opening being such that said electrode is not struck by said beam as it is caused to scan said mosaic, said electrode being positioned out of the path of the rays forming said image and functioning as a collector of photoelectrons from said mosaic.

2. A picture transmitting tube comprising an evacuated envelope, means including an electron gun therein for producing a beam of electrons,

a mosaic of elements so sensitized that they emit electrons when an image is formed thereon and so positioned that said beam may scan one side thereof to scan said elements and also so positioned that an image may be formed on said side to cause said elements to emit electrons, means for collecting said emitted electrons from said mosaic, said last means comprising an electrode positioned adjacent to said mosaic and out of the path of both said beam of electrons and the rays forming said image, and an electron beam focusing electrode which is maintained at substantially the same potential as said collecting electrode.

3. A tube according to claim 2 characterized in that said last means comprises an electrode which is ring-shaped in cross section.

i. In combination, an electric discharge tube comprising an evacuated envelope, means includin an electron gun therein for producing a beam of electrons, a mosaic of elements sosensitized that they emit electrons when an image is formed thereon and so positioned that said beam may scan the front side of said elements and also so positioned that an image may be formed on the front side of said elements, a metallic signal plate positioned close to but insulated from the back side of said elements, an electrode having an opening therein which is positioned in line with and between said gun and said mosaic whereby said beam passes through said opening, and an impedance unit connected between said signal plate and said electrode whereby picture signals may be taken off said impedance unit, the size of said opening being such that said electrode is not struck by said beam as it is caused to scan the mosaic.

5. In a picture transmitter, a transmitter tube comprising an evacuated envelope, means including an electron gun therein for producing a beam of electrons, a mosaic of light-sensitive elements so positioned that said beam may scan the front side of said elements and also so positioned that an optical image may be formed on the front side of said elements to cause them to release photoelectrons, a metallic signal plate positioned close to but insulated from the back side of said elem'ents, means for collecting said photoelectrons comprising an electrode having an opening therein which is positioned in line with and between said gun and said mosaic whereby said beam passes through said opening, the size of said opening being such that said electrode is not struck by said beam as it is' caused to scan the mosaic, an impedance device connected between said signal plate and said electrode, and an amplifier having an input circuit connected across said impedance device.

6. The invention according to claim 4 characterized in that the connection between said signal plate and said electrode is a direct-current connection.

7. The invention according to claim 5 characterized in that said signal plate and said electrode are maintained at approximately the same direct-current potential.

8. In a picture transmitter, a transmitter tube comprising an evacuated envelope, means including an electron gun therein for producing a beam of electrons, said electron gun including a cathode and a first anode, a mosaic of elements so sensitized that they emit electrons when an.

image is formed thereon and so positioned that said beam may scan the front side of said elements and also so positioned that an image may be formed on the front side of said elements, a metallic signal plate positioned close to but insulated from the back side of said elements, means comprising a second anode for accelerating and electrostatically focusing the electrons in said beam, means for maintaining said second anode at a high positive potential with respect to said cathode, means comprising a circuit connection including an impedance element for maintaining said signal plate and said second anode at approximately the same direct current potential as compared with said high positive potential, and

an amplifier having an input circuit connected 29 across said impedance unit.

VLADIMIR K. ZWORYHN.