US2195489A - Television transmitting tube - Google Patents

Description

April 2, 1940. H. IAMS I TELEVISIONTRANSMITTING TUBE Filed Oct. 26, 1937 2 Sheets-Sheet 1 INVENTOR- HARLgY/l. IAMS ATTORNEY April 2, 194G. H. A. IAMS 7 2,395,489

' TELEVISION TRANSMITTING TUBE Filed Oct. 26, 1937 2 Sheets-Sheet j lalalnlrr INV EN TOR.

HARLEY A. JAMS $7 ATTORNEY.

Patented Apr. 2, 1949 hurrah sTaTss TELEVISION TRANSMITTING TUBE Harley A. Earns, Berkeley Heights, N. .l., assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application October 26, 1937, Serial No. 171,021 7 Claims. (o us-4.2)

My invention relates to electron discharge apparatus of the television transmitting type, and more particularly to improved cathode ray television transmitting tubes and methods of operating such tubes in transmitting systems.

In oneforrn of cathode ray transmitting tube an optical image of an object of which a picture is to be transmitted is formed upon a mosaic electrode consisting in general of an insulating sheet of a great number of discrete light sensitive elements on the front surface and aconductive coating on the other surface, the front surface being illuminated by an optical image and scanned by a cathode ray beam to produce currents which flow through. an output resistor connected between the conductive coating on the mosaic electrode and ground to generate picture signals. Because of the light absorbing properties of the signal electrode it has been found advantageous to project the optical image on the same side of the mosaic electrode which is scanned by. the cathode ray beam. When this is done the axis of the optical system for projecting the image is made perpendicular to the mosaic electrode in order to obtain uniform focus of the image over the surface of the electrode, but the axis of the electron gun for developing and directing the beam of electrons is of necessity disposed at an acute angle to the mosaic electrode. On account of this arrangement the outline of the area scanned by the cathode ray beam has a keystone shape rather than the desired rectangular shape. This distortion of the scanned pattern is manifested by a substantial and corresponding distortion of the reproduced image at the receiving station, the reproduced image being also the shape of a keystone with the vertical boundaries inclined toward each other. Such keystone distortion may be compensated for in the electron beam scanning system but such compensation requires the addition of undesirable circuit components which are relatively difiicult to control during the operation of the tube.

' Tubes utilizing a mosaic structure on a sheet of insulating material with a metal coating or signal plate on the opposite side of the sheet of insulation are susceptible to a certain amount of distortion which is known as black spot distortion. This is due to the fact that secondary electrons are liberated from the surface of the mosaic during scansion, which electrons are nonuniformly distributed over the surface of the mosaic, and since all of the particles forming the mosaic. are in capacitive relationship with the signal plate, electrical impulses representative of the .non-uniform distribution of secondary electrons are transmitted together with the transmissionof the desired picture impulses.

In the use of such tubes it is occasionally desirable to project two or more optical images upon the mosaic electrode forthe purpose "or producing dissolving views or background effects, such as various shaped borders and advertising material. The projection of two ormore such optical images is difficult in practice in that it is necessary to locate the image focusing means in different positions, thereby introducing optical distortion and corresponding distortion in the transmitted image. 7

It is an object of my invention to avoid the limitations inherent with the use of conventional types of signal electrodes.

Another object of my invention cathode ray television transmitting tube wherein keystone compensationis unnecessary. It is a further object of my invention to provide a tube suitable for transmitting images of two or more objects.

To'this end I provide a mosaic electrode, preferably of the photosensitive single sidedv type, which is light transmitting with meansto pI'O-. duce on. the surface of the mosaic electrode opposite the photosensitive surface a virtual signal plate which is incapable of light absorption so that light may be projected through the mosaic electrode and focused upon the photosensitive surface without appreciable light absorption. I Other objects, features, and advantages of my invention will appear from the following description taken in connection with the accompanying drawings in which,

Figure 1 is a longitudinal diagrammatic view of one embodiment of my invention, and

Figure 2 is a similar view of a preferred .embodiment of my invention.

Referring to the drawings, the tube shown in Fig. 1 comprises a highly evacuated envelope or is to provide a bulb I having a tubular arm or neck section entype and consists of a cathode '5, control electrode 3 connected to the usual biasing battery and a first anode 9 maintained positive with respect to the cathode i by a battery it. The electron stream leaving the first anode 9 is accelerated and concentrated into an electron scanning beam focused on the front surface of the mosaic elec' trode by a second or beam focusing anode H, which is preferably in two parts, one of which is connected to ground and the other to a translating device it and through the impedance l3 to ground. Deflection means such as the deflection coils M and it are provided for sweeping the beam in a horizontal and vertical plane, respectively, to scan the mosaic electrode. It is obvious, however, that electrostatic deflection plates may be substituted for either one or both of the deflection coils, if desired.

The mosaic electrode 3 may consist of a thin sheet of optically transparent insulating material such as the sheet of mica it having a multitude of photcsensitized silver particles 5? which are in effect discrete and each of which has a film of silver oxide and is made photosensitive by being coated with caesium in accordance with the practice of making photocells. The mosaic electrode 3 may be supported from the side walls of the tube and is not provided with electrical connections to any of the other components of the tube.

In accordance with my invention 1' provide be tween the mosaic electrode 3 and the window 5 and out of the path of the light rays from the object represented by the arrow Ll, means for projecting a cloud of electrons onto the rear side of the mosaic electrode to produce what is in effect a virtual signal plate which may be defined as an electrostatic charge on the rear surface of the electrode. Such means, as shown in Fig. 1, may comprise one or more cathodes i8 and 18a each with an associated anode l9. and i902, the longitudinal axis of each cathode and its associated anode intersecting the mosaic electrode along the longitudinal axis of the tube 5. The anodes H3 and Na may comprise a fine wire mesh of sufficient area to project a cloud of electrons having substantially uniform density over its cross-section on'the rear surface of the mosaic electrode. Each of the anodes l9 and 19a, however, may consist of an apertured metallic plate, the aperture having such an outline or configuration as to provide a beam of electrons at the surface of the mosaic of a corresponding outline or configuration. is shown with a keyhole shape, while the aperture in the anode I 9a is shown star shaped. The apertures may have any desired configuration depending on the desired outline of the virtual signal plate to be formed on the mosaic electrode by the bombardment of electrons from the cathodes I8 or Eda.

In operation the light forming an optical image is projected through the sheet of mica l6 and focused upon the mutually separated and photosensitized silver particles ll, which are scanned by an electron beam generated by the gun structure 2 and deflected by the magnetic deflection coils Hi and it. One or more cathodes such as the two represented in the figure as it and 18a, either separately or together focus an electron pattern or patterns on the rear surface of the mosaic electrode, the outline of the pattern or patterns corresponding to the outline of the aperture in each of the anodes l9 and 19a to form a The aperture of the anode i9v virtual signal plate on the rear surface of the mosaic electrode.

The photoelectrons liberated by the photosensitive silver globules H in response to the optical image projected upon the mosaic electrode 3, are collected by the portion of the beam focusing anode connected to the translating device IZ, and by the loss of the photoelectrons an electrostatic image corresponding in e1ectr0- static charge distribution to the elemental areas of light and shade of the optical image is formed on the front surface of the mosaic electrode. This electrostatic image is effectively utilized over the area of the mosaic on which electrons impinge on the rear surface thereof from the cathodes i8 or 18a, by scanning the front surface of the mosaic electrode with a beam of high velocity electrons. Under the influence of the high velocity scanning beam, secondary electrons modulated in accordance with the electrostatic charge on the particles are emitted by the particles, the secondary electrons being collected by the anode I I to produce signal voltage fluctuations across the impedance l3 which are applied to the input electrode of the translating device l2, whereupon the signals may be further amplified and applied to a transmitting network in a manner well known in the art.

In Figure 2, which shows a preferred modification of my television transmitting tube, the envelope or bulb 20 encloses a mosaic electrode 3, an electron'gun structure 2 and one or more cathodes l8, Ma and anodes i9, 9a as shown in 1. However, between the window 5 and the mosaic electrode 3 I provide one or more electron guns 2| and 2m in the tubular arm extensions 22 and 22a. whose longitudinal axes intersect the longitudinal axis of the tube 20 at the rear surface of the mosaic electrode 3. The electron guns 2! and Zla may be similar to the electron gun 2 as described in connection with Fig. l and comprises the cathodes 23 and 23a, control elec trodes 24 and 7.4a, the first anodes 25 and 25a and the second anodes 26 and 23a. Electromagnetic deflection coils similar to the coils l4 and I5 may be provided for each of the electron guns 2| and 25a to deflect the beam of electrons projected from the cathodes onto the rear surface of the mosaic electrode. The control elec trode 24 is connected through a source 27 of fluctuating potential to the usual biasing battery and the corresponding control electrode 24a of the electron gun 21a. may be connected to the same or a similar source.

In the operation of the tube shown in Fig. 2 the optical image of an object or" which a picture is to be transmitted is focused on the front surface of the mosaic electrode 3 to produce on the photosensitive particles H an electrostatic image representative of the degrees of light and shade of the optical image. The photosensitive particles are scanned with a cathode ray beam in a manner similar to that described" in connection with the tube shown in Fig. l. 1 The electron guns 2! and Zia are operated individually or collectively to form a cathode ray beam or beams which scan the rear surface of the mosaic electrode. The electromagnetic deflection coils on the neck sections 22 and 22a are energized in such a manner that the electron beams generated and focused by the electron guns 2! and 210. impinge on the rear surface of the mosaic electrode at a point opposite the point ofimpingement of the cathode ray beam from the electron gun 2.: The potentials applied tothe first and second anodes of the electron guns 2|. and 21a, such as by the batteries 28 and 28a, should be so adjusted to focus the beam of electrons on the rear surface of the mosaic electrode so that the diameterof the beam at the rear surface will be somewhat larger than the diameter of the beam generated and focused on the front surface by the electron gun 2. This is desirable in that the electronguns 2| and 2la. are disposed at a slightangle with respect to the longitudinal axis of the electron gun 2 and will obviate any need for keystone correction of the pattern swept out by the electron beams from the electron guns 2! and Zia. The necessity for keystone correction is avoided because some portion of the electron beam or beams from the electron guns 2! and 21a always impinges opposite the point of impingement of the beam from the gun 2 Whereas, if the beams from the guns 2| and Zla were of the same area as the beam from the gun 2 at the points of impingement on opposite sides of the mosaic electrode, the points of impingement would be slightly displaced one from the other. In the case of an equal area beam impinging on opposite sides of the mosaic electrode 3, keystone correction would be required to keep the points of impingement opposite each other at all times. The cathodes l8 and E811 and anodes l9 and l9a are energized either singly or collectively depending upon the outline of the virtual signal plate desired on the rear surface of the mosaic electrode and the control electrodes of the electron guns 2! and Zia are energized with fluctuating potentials which may be representative of the degrees of light and shade of any optical image which it is desired to combine with the image of the object such as represented by the arrow 4. In this manner, one or more electrostatic images may be superposed upon the optical image projected on the mosaic electrode so that the final transmission is a composite representation of the optical and electrostatic images. Such an arrangement is especially desirable for transmitting composite pictures, such as a studio scene which is optically projected on the mosaic electrode with a superposed background added to the scene by energizing the control electrodes of the guns 2! and Zia with signals representative of the desired background.

While I do not wish to be restricted to any particular theory of operation it seems probable that the operation of my new and improved transmitting tube depends upon the fact that the electrons focused on the rear surface of the mosaic electrode from the cathodes 18 or 180 produce a virtual signal plate so that transmission is eifected only for those portions of the optical image projected upon the mosaic electrode which are within the pattern or outline of the virtual signal plate. It seems probable that in operation the electrons projected upon the rear surface of the mosaic electrode produce upon impingement therewith secondary electrons which cause the rear surface of the mosaic electrode to acquire an electrostatic potential in accordance with the intensity of primary electron bombardment. Thus, when the rear surface of the mosaic electrode is bombarded by electrons it is established at a potential which depends upon the ability of the surface to emit secondary electrons and if the potential of the surface is changed, such as by the emission of photoelectrons from the front surface of the mosaic electrode a current now takes place to restore the potential of the rear surface to its original value.

If the rear surface of the mosaic electrode with its electrostatic charge or virtual signal plate is then bombarded with a highly concentrated beam of electrons at a point corresponding to the point being scanned by the electron beam on the opposite or front side of the electrode, the secondary electron emission occurring on the front surface under the influence of the scanning beam will be modulated in accordance with the intensity of the electron beam on the rear surface. Thus, if the beam impinging on the rear surface is modulated with picture signals the signal produced by the scamiing of the front surface with its superposed optical image will be accordingly modulated and the resultant image when recreated at a receiving station will be a composite of the optical image focused on the mosaic electrode and the image represented by the signal impulses applied to the electron gun or guns scanning the rear surface of the mosaic electrode.

From the foregoing description it will be apparent that various other modificationsmay be made in my invention without departing from thespirit 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:

1. A television transmitting tube comprising an evacuated envelope having a light transmitting window, a mosaic electrode exposed to said window to receive an optical image, said electrode including a sheet of insulating material with a number of mutually separated photosensitive particles on the front surface to establish on said photosensitive particles an electrostatic image representative of the light and shade of the optical image, means to scan the photosensitive particles with an. electron beam and means including a cathode and an anode exposed to the rear surface of said mosaic electrode to establish on the said rear surface a cloud of electrons to produce a signal plate consisting of electrostatic charges on said rear surface.

2. A television transmitting tube comprising an evacuated envelope, a mosaic electrode consisting of a sheet of insulating material with a number of mutually separated photosensitive particles on the front surface said electrode being positioned to receive an optical image, means to scan the photosensitive particles with an electron beam, and cathode ray means in cluding an electron emitting cathode and an associated anode exposed to the rear side of said mosaic electrode to project on said rear surface a cloud of electrons and form thereon a signal plate consisting of electrostatic charges.

3. A television transmitting tube comprising an evacuated envelope having a light transmitting window, a mosaic electrode exposed to said window to'receive an optical image, said electrode consisting of a sheet of insulating material coated on one side with a number of mutually separated photosensitive particles, a thermionic cathode adjacent and exposed to the uncoated side of said mosaic electrode, an apertured anode between said thermionic cathode and the uncoated side of said mosaic electrode to focus electrons from said thermionic cathode toward and upon the uncoated side to form a signal plate consisting of electrostatic charges on said uncoated side, an electron gun to project on the coated side of said mosaic electrode an electron beam, and means to scan said electron beam over said photosensitive particles.

4. A television transmitting tube comprising an evacuated envelope having a light transmitting window at one end and a cathode ray gun 1 ject on the uncoated surface of said mosaic electrode a cloud of electrons in the form of a pattern corresponding to the pattern of the aperture in said anode to produce a signal plate consisting of electrostatic charges on said uncoate surface. H

5. A television transmitting tube comprising an evacuated envelope, a portion of which is light transmitting, a mosaic electrode exposed to said portion and consisting of a sheet of insulating material with ,a number of mutually separated photosensitive particles on the front surface, means to project an optical image on the photosensitive particles to liberate photoelectrons therefrom and develop an electrostatic image corresponding in intensity and distribution to the light of the optical image, an electron gun exposed to said photosensitive particles, means to scan the photosensitive particles with an electron beam from said electron gun, means including an electron emitting cathode and an anode to project electrons upon a predetermined area of the rear surface of the mosaic electrode to produce a signal plate consisting of electrostatic charges on said rear surface, an electron gun positioned to project a modulated electron beam on said rear surface of the mosaic electrode, and means to scan said modulated electron beam over the rear surface of the mosaic electrode to produce on said surface an electrostatic image representative of the intensity of the modulated electron beam.

6. A television transmitting tube comprising in an evacuated envelope a mosaic electrode consisting of a sheet of insulating material with a number of mutually separated photosensitive particles on the front surface, means to project an optical image on the photosensitive particles to produce an electrostatic image thereon, an electron beam source, means to project on said photosensitive particles an electron beam from said source, means to scan said beam over said particles to liberate secondary electrons and neutralize the electrostatic image, a thermionic cathode adjacent the rear surface of said mosaic electrode to liberate electrons, apertured anode means to direct said electrons toward said rear surface and focus said electrons upon said surface ina pattern determined by the configuration. of the aperture of said means, means to generate and focus an electron beam on the rear surface of said mosaic electrode, means to scan said electron beam over the rear surface of said mosaic electrode in synchronism with the electron beam projected on said photosensitive particles, andmeans to vary the intensity ofthe electron beam scanning the rear surface of the mosaic electrode in accordance with a predetermined signal to produce a corresponding variation in the secondary electrons liberated from said photosensitive particles.

7. A television transmitting tube comprising in an evacuated envelope a mosaic electrode consisting of a sheet of insulating material with a number of mutually separated photosensitive particleson one'surface, means to project an optical image on the surface of the electrode bearing the photosensitive particles, means to project an electron beamv on said photosensitive particles, means to scan said electron beam over said particles in a predetermined pattern, means including an electron emitting cathode and an anode adjacent the surface of the electrode opposite that hearing the photosensitive particles to flood the said opposite surface of said mosaic electrode with a cloud of electrons to form a signal plate consisting of electrostatic charges thereon, means to project a second electron beam of varying intensity on the surface of the mosaic electrode opposite that hearing the photosensitive particles, and means to scan said second electron beam over said surface in the same predetermined pattern and in synchronism with the firstmentioned electron beam.

HARLEY A. IAMS.

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