US2256462A - Television transmitting device - Google Patents

Description

Sept. 16, 1941.

H. A. IAMS 2,256,462

TELEVISION TRANSMITTING DEVICE Filed May 15, 1940 2 Sheets-Sheet 1 DEF CIRCUIT I |IIl|III|I|------III|I|I|IIIIIIIIIIIIII INVENTOR. HARLEY A. JAMS c ATTORNEY.

Sept. 16, 1941. H. A. IAMS TELEVISION TRANSMITTING DEVICE Filed May 15, 1940 2 Sheets-Sheet 2 4 4 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 0 00000000 avvvnwvvw u000?. uuvvvvvvvbk INVEN TOR. HARLEY A. JAMS w ATTORNEY.

Patented Sept. 9, 1941 UNITED STATES PATENT OFFICE 2,256,462

TELEVISION TRAN SIWITTING DEVICE were J., assignor to'Radio a corporation or Dela- Application May 15, 1940, Serial No. 335,211

9 Claims. (01-. 250-150) My invention relates to cathode ray tubes of the television transmitting type and particularly to an improved type of tube utilizing electron image amplification. In many cathode ray tubes of the television transmitting type it is customary to generate an electron image corresponding in electron distribution to elemental areas of light and shade of an optical image and to project this electron image upon one side of a mosaic electrode of the double-sided type, the opposite side of which is scanned by a high velocity electron beam. The construction of double-sided mosaic electrodes is exceedingly complex and the use of a high velocity scanning beam produces a spurious signal known as dark spot which is very difiicult to eliminate from the signals representative of elemental areas of the optical image. While Albert Rose and I in our copending application, Serial No. 276,106, filed May 27, 1939, now U. S. Patent 2,213,175, have described a type of television transmitting tube whereby this last-mentioned spurious signal may be eliminated, it has been desirable in such tubes to provide a mosaic electrode of the semi-transparent type which reduces the efiective light available for the generation of an electrostatic image from which the television signals are derived. Furthermore, it is mor diificult to get high photosensitivity with a discontinuous structure such as a mosaic electrode than with a continuous structure such as a-conventional photocathode.'

It is an object of my invention toprovide a television transmitting tube wherein all of the advantages attendant upon the use of low velocity scanning, a single-sided mosaic electrode and a continuous photocathode may be obtained without the introduction of distortion in the signals generated by the tube. It is a further objector my invention to provide a tube wherein 'an electronimage may be intensified by secondary emission while retaining the advantages of low velocity electron beam scanning, and it is a still further object to provide 'a tube of the type described having increased signal output and wherein this output is proportional to the intensity of the optical image for which transmission is desired. In'accordance with my invention, electrons forming an electron image are directed from one electrode to another positioned at opposite ends of a semi-circular path and focused over the length of the pathby a cylindrical magnetic field to produce on one of the electrodes an electrostatic image having shear distortion and displaced from the optical-image producing the electron image. Further in accordance with my invention, I'generate and scan an electron beam to form a scanning field of electrons which is' subjected to the magnetic field to produce similar shear distortion and displacement of the electron the area of the electrostatic image. More particularly,

I generate an electron image having an electron distribution corresponding to the distribution of light over elemental areas of an optical image, subject the electron'image to a curved magnetic field to displace the electron image and form an electrostatic image which is scanned by an electron beam' deflected over a scanning pattern which is similarly displaced tion with the accompanying drawings in which:

Figure 1 is a plan view in section of a television transmitting tubeembodying my invention,

Figure 2 is a side elevation in section, taken along the lines 2-2 of Figure 1, showing the olfcenter arrangement of certain of the electrodes of my transmitting tube,

Figure 3'is a sectional view of a portion of the tube shown in Figure 1 taken along the lines 33, and

Figure 4 is a plan view of one modification of the tube shown in the preceding figures.

' Referring to the drawings and particularly to Figure 1 which shows a plan view of my improved television transmitting tube, the tube comprises a highly evacuated. envelope comprising two abutting sections, a toric segment '2 closed at one end by a window 3 abutting a cylindrical section 4 at the opposite end from the window 3. Within the envelope and adjacent the window 3 is positioned a fiat photocathode 5 of the semi-transparent type so that it may have focused thereon an optical image from an object represented by lens system I. At the opposite end of the toric segment 2 from the .window 3 and adjacent the abutting end of the cylindrical section 4 I provide a target electrode such as the mosaic electrode 8 having a mosaic of mutually separated and insulated particles facing in the direction of the photocathode. Th cylindrical section 4 of the envelope" contains an electron sun 9 to scanning field over the arrow 6 through the.

generate an electron beam and direct the beam toward the mosaic electrode 8.

Surrounding the envelope sections, I provide a magnetic coil ll, one portion of which is in the form of a toric segment surrounding and coaxial with the toric envelope segment 2 and another portion of cylindrical formation surrounding the cylindrical section 4 of the envelope. This focusing coil preferably extends over the space between and slightly beyond the positions occupied by the photocathode 5 and electron gun Q and may be constructed of two or more parts to facilitate its placement over the envelope.

The photocathode 5 may be of a conventional type including a semi-transparent conductor photosensitized on the side facing the interior of the envelope. Such semi-transparent photocathodes are well known in the art and will not be described in detail. The electron gun at the opposite end of the tube and the structure for deflecting the electron beam have been described in the above-referenced copending application and comprise a cathode II from which electrons may be drawn to form an electron beam controlled in intensity by a conventional control grid M, an anode it provided to accelerate the electrons, and a pair of deflection plates 14 to provide horizontal deflection of the electron beam. The electron beam may be vertically deflected in a further direction by a pair of deflection coils It surrounding a portion of the space between the deflection plates and the mosaic electrode. To simplify the drawings, the

coils I5 are shown displaced 90 from their actual position during use. The operation of this portion of the tube in generating and deflecting an electron beam in the presence of an axial magnetic field such as generated by the cylindrical portion of the coil I I is believed well described in the above-mentioned application.

In accordance with my invention and as best shown in Figures 1, 2 and 3, I provide a target electrode having a mosaic surface offset from the longitudinal axis of the electron gun and deflection system and provided with an opening for the passage of the deflected electron beam from the gun and deflection system. The mosaic electrode 8 preferably comprises a sheet of insu-' lating material such as the sheet of mica it provided with a large aperture or opening II. A portion of the sheet of mica II is provided with a great number of mosaic particles IS on the side thereof facing in the direction of the photocathode 5. On the electron gun side of the sheet of mica and co-extensive with the area covered by the mosaic particles I provide a conductive coating which may be of metal or any other conducting material such as Aquadag to form a signal plate I! which is in capacitive relationship with the mosaic particles It. Between the photocathode 5 and the mosaic electrode 8 I provide a series of conductive coatings on the inner wall of the toric segment 2 comprising a principal wall coating 20 and a ring-shaped electrode. 2| adjacent the photocathode and a second ring-shaped electrode 22 adjacent the mosaic electrode 8 to control the flow of electrons flowing from the photocathode to the mo- 1 sale electrode. One or more of these conductive potential highly negative with respect to the cathode II, and the ring electrode 2| is supplied with a potential intermediate the photocathode potential and that of the wall coating 20 which is maintained positive with respect to the cathode II. The signal plate I! is connected to the input of a translating device such as a thermionic amplifier 23 and to ground through an output impedance :4 so that the average potential of the signal plate corresponds to ground potential. In all prior television transmitting tubes using a single-sided mosaic it has been necessary to provide semi-transparent mosaic electrodes or to position the electron gun on the same side of the mosaic as the optical system, which latter construction necessitates displacement of the electron gun and optical axes so that complicated keystone correction circuits were necessary. With a tube made in accordance with my invention, however, the electron beam is first made to pass to one side of and beyond the mosaic electrode and caused to return to the mosaic electrode. In operating my tube, the light represented by the arrow 6 is focused upon the photocathode by the lens system 1 to liberate electron streams from elemental areas of the photocathode corresponding in intensity and distribution to the light and shade'areas of the optical image. This distribution of electrons flowing from the photocathode may be termed an electron image of the optical image. The electrons liberated from the photocathode are directed along curved paths by the magneticfleld generated by the toric segment portion of the magn'etic coil II and accelerated to a relatively high velocity and caused to impinge upon the mosaic particles It with sufficient velocity to liberate v secondary electrons from the mosaic particles. The number of secondary electrons liberated from elemental areas of the mosaic electrode occupied by the particles is directly proportional to the number of photo-electrons, and since the wall coating 20 is maintained at a positive potential with respect to the signal plate I9, these secondary electrons are ,collected, resulting in the formation of an electrostatic image of positive charges corresponding in charge distribution to the light intensity of elemental areas of the optical image.

The toric segment portion of the coil l0 generates a cylindrical magnetic fleld over the space separating the photocathode from the mosaic electrode". Such a magnetic field may be defined as one in which the magnetic lines of flux are arcs of circles having their centers on a common axis and drawn in planes perpendicular to that axis. I have found that if an electron receiving target is placed at the junction between the toric segment 2 and the cylindrical section 4 of the envelope, considerable shear distortion results and that an electron image incident upon the target electrode and originating from the phoshape of the electron image so that if the original optical image on the photocathode 5 is rectangular; the resulting electron image and produced electrostatic image on the target such as the mosaic electrode 8 is actually rhombcidal. The displacement and the amount of shear may be controlled by the potentials applied to the 2,256,462 tube electrodes and by controlling the intensity of the magnetic field over the toric segment 2.

In accordance with my invention, the electron beam from the electron gun is scanned over the area of and through the opening IT in the mosaic electrode 8, these electrons passing into the cylindrical magnetic field generated by the toric segment portion of the coil in where the scanning pattern of the electrons is similarly displaced and sheared. Since the photocathode is maintained at a negative potential with respect to the oathode II, the beam electrons lose velocity as they approach the photocathode and, being constrained in their paths by the cylindrical magnetic field, are, in efiect, reflected by the photocathode and re-directed in a direction toward the mosaic electrode. The potentials applied to the various electrodes are preferably so chosen that the velocity of the beam electrons bears a definite relationship with the velocity of the photoelectrons liberated by the photocathode 5. I have found that if the beam electrons are caused to have a velocity, expressed in volts, approximately one-fourth as great while passing from the plane of the mosaic electrode in the direction of the photocathode as the velocity of the photo-electrons flowing in the opposite direction, then the displacement and shear distortion imparted to the scanning pattern of the beam electrons is the same as the displacement and shear distortion imparted to the photo-electrons. However, since the beam electrons do not travel for as great a distance between the planes of the mosaic electrode and photocathode as do the photo-electrons due to the fact that the beam electrons merely approach but do not reach the photocathode, this velocity ratio is somewhat less than one to four, such as one to 3.7. I therefore refer to this ratio as approximate, and it is to be understood that a reference to the one to four ratio allows a slight variation from the exact numerical ratio. In this manner the electron image and consequently the electrostatic image on the mosaic electrode are made to conform in shape to the scanning pattern of the beam electrons on the same side of the mosaic electrode. The electron image and scanning pattern are made to coincide in position by adjustments of the voltages on the rings 2i and 22, as.

will be described later.

Instead of providing a. fixed ratio of beam velocity to photo-electron velocity, I may obtain the corresponding shearing action of the electron beam pattern with respect to that of the electron image by rotating the horizontal deflection means, such as the plates M, with respect to the vertical deflection means, such as the deflection coils l5. In this manner the line scanning of the pattern passing through the opening I! in the mosaic electrode is non-perpendicular to the frame scanning at this position. In this mode of operation the pattern of the beam scanning in the plane of the mosaic electrode over an area of the opening is rhomboidal but sloping in an opposite direction with respect to the rhomboidal electron image and the resulting electrostatic image formed by electrons from the photocathode when the beam velocity is higher than the onefourth ratio referred to above, and in the same direction when the beam velocity is less than this ratio. As the beam electrons continue beyond themosaic electrode and along paths approaching and then receding from the photocathode, the electron beam pattern is displaced and sheared to correspond with the displacement and shear of the electron image withoutrecourse to the specific four to one velocity ratio referred to above. I have found that the electron image adjacent, the photocathode and mosaic electrode may be rotated by controlling the electrostatic field adjacent these electrodes. This co trol of rotation of the electron image may be ut zed to align the electron image with the scanning beam pattern. Thus the potentials applied to the ring electrodes 2! and 22 may be adjusted to super-' pose the electron image and scanning pattern over the same area on the mosaic electrode. I prefer to provide means such as the adjustable taps 25 and 26 to vary the potentials applied to these ring electrodes from a direct current source represented by the battery 21. Under typical operating conditions the photocathode may be maintained 450 volts negative with respect to ground, the average potential of the signal plate and the potential of the cathode H being at ground. The wall coating 20 may be at 150 volts positive with respect to ground and the ring electrode 2i potential variable over the range of potentials applied between the photocathode and wall coating 20, the potential of the ring electrode 22 being variable from ground to the potential of the wall coating 20. It will be noted that these operating potentials will produce a four to one ratio of electron velocities. With the above potentials a tube made in accordance with my invention may be operated with a magnetic field along the center line of the tube equal to approximately 50 gausses, and under such conditions a rectangular optical image, such as shown by the dashed lines 28 in Figure 3, produces an electron image and resulting electrostatic image at the mosaic electrode substantially as by the dashed lines 29 enclosing a rhomboidal area on the mosaic electrode. The pattern of the scanned electron beam in the plane of the opening I7 will be as shown by the fine broken lines 30 of Figure 3. As the beam electrons fiow around the toric segment 2 of the envelope in a direction toward the photocathode, as best shown in Figures 1 and 2, the scanning lines are displaced and the entire group of lines as a scanning pattern is sheared so that the electrons, upon returning to the plane ofthe mosaic, form a pattern rhomboidal in shape coincident with the rhomboidal pattern of the electrostatic image. Since the cathode ll ismaintained at the same potential as the average potential of the signal plate l9, the beam electrons lose velocity as they approach the mosaic surface and are incapable of liberating secondary electrons. However, since the electrostatic image consists of positive charges, the beam electrons progressively neutralize these charges and capacitively produce signalling impulses in the signal plate circuit which are applied to the translating device or amplifier 23, whereupon the signals may be further amplified and applied to a transmitting network in the conventional manner.

While I have described my invention with particular reference to the tube shown in Figures 1-3 and wherein the photocathode is coplanar with but displaced from the mosaic electrode, the tube shown in Figure 4 may have definite advantages when used in certain applications. The tube shown in Figure 4 is identical in operation and construction with that shown in the previous figures except that the photocathode is positioned in a plane normal to the plane of the mosaicelectrode. Such a tube has a definite advantage in certain television'camera apthe mosaic electrode in the direction of the photocathode as the velocity of the photo-electrons flowing in the opposite direction and that this ratio might be somewhat less than the factor one to four because of the difference in the length of the paths of the beam electrons and photo-electrons. In a tube of the type shown in Figured the difference in this ratio from the theoretical one to four value may be somewhat greater because the percentage difference in length of the paths in the tube of Figure 4 is somewhat greater than that in the tube where the photocathode and mosaic electrode are co- Planar.

In both of the tubes made in accordance with my invention an optical replica of the optical image may be recreated in true rectangular, coordinates, since the signals generated across the output impedance 24 have a time displacement corresponding to the rate of scanning of the electron beam as produced by the deflection plates and the coils l5. It is therefore obvious from the above description of my improved transmitting tube that the shear distortion and displacement imparted to the electron image in the course of producing a displaced electrostatic image is matched by the shear distortion and displacement of the scanning pattern traced by the electron beam so that the output signals are generated in a time and space sequence such that a replica corresponding in shape to the original optical image may be recreated.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

I claim:

1. A television transmitting tube comprising an evacuated envelope, an' electron source to liberate electrons forming an electron beam, a target offset to one side of the normal path of I said electron beam to allow said beam to pass beyond said target, a mosaic of mutually separated particles on the surface of said target facing away from said electron source, an electrode in capacitive relation with said particles, means including a photocathode exposed along arced paths to said particles to liberate electrons and develop an electrostatic image representative of information to be transmitted on said mosaic of mutually separated particles and means including said photocathode and magnetic field generating means to substantially reverse the direction of flow of said electron beam and direct the electron beam following its passa e beyond said target to said target to neu tralize said electrostatic image.

2. A television transmitting device comprising an evacuated envelope, a photocathode to liberate streams of electrons to form an electron image, a target electrode spaced from and exposed along arced paths to said photocathode. a mosaic of mutually separated particles on the side of said target electrode exposed to said photocathode to receive electrons of said electron image, magnetic means surrounding said arced paths to direct said electron image on said mosaic, an electron gun positioned to project an electron beam from the side of said target opposite the side bearing said mosaic, past one edge of said target electrode, beyond said target electrode with respect to said gun and into the space between said photocathode and said target, and means including said photocathode to sub stantially reverse the direction of flow of said electron beam and direct the streams of said electron image and said electron beam along coextensive paths upon said mosaic electrode to produce signals representative of the electron density of said electron image.

3. A television transmitting device comprising a photocathode to liberate streams of electrons in response to an optical image focused thereon, a target electrode having a mosaic of mutually separated particles on one side thereof positioned to receive said streams of electrons from said photocathode along arced paths, means to generate a cylindrical magnetic field having lines of force intercepted by said photocathode and said target to direct said streams of electrons on said mosaic and form an electrostatic image thereon, an electron gun facing the opposite side of said target to generate an electron beam' and project said beam along paths extending to one side of beyond said target and into said field and means along said aths and between said gun and said target to scan said beam over an area in space displaced from and coplanar with said target and means between said photocathode and said target to generate an electrostatic field to direct the electron beam upon said mosaic electrode to neutralize said electrostatic image and generate signals corresponding to the charge distribution of said electrostatic image.

4. A television transmitting tube comprising an evacuated envelope, an electron gun to develop a beam of electrons adjacent one end of said envelope, a photocathode adjacent the opposite end of said; envelope to liberate streams of electrons in response to an optical image focused thereon, a mosaic target of mutually separated particles intermediate said gun and said photocathode offset to one side of the normal undeflected path of said beam of electrons the said particles facing away from said gun, means to scan said beam of electrons over an area coplanar with and offset to the said one side of said mosaic electrode, means to direct said beam of electrons from the region of said mosaic electrode and toward said photocathode, and magnetic cylindrical fleld generating means to focus said streams of electrons and said beam of electrons on said mosaic particles on the surface thereof facing away from said electron 5. A television transmitting tube comprising an evacuated envelope, an electron gun to generate a beam of electrons, a mosaic electrode having a plurality of mosaic particles facing away from said gun and offset to one side of the normal undeflected path of said beam of electrons to allow the said beam of electrons to flow beyond said mosaic electrode with respect to said electron gun, a photocathode in the path of said beam of electrons to liberate photoelectrons in response to an optical image formed thereon and to reflect the electrons of said beam toward said mosaic electrode, means to accelerate said photo-electrons in the direction of said mosaic electrode, means to accelerate said beam of electrons in the direction of said photocathode at such a velocity that the said beam of electrons will not be collected by said photocathode and magnetic cylindrical field generating means to direct said photo-electrons and said beam of electrons to said plurality of mosaic particles.

6. A television transmitting device comprising a photocathode to develop an electron image of an optical image focused thereon, a mosaic electrode having. a mosaicsurface facing said photocathode, an electron gun on the opposite side of said mosaic electrode from that facing said photocathode to form a beam of electrons, means between said electron gun and said mosaic electrode to deflect said electron beam over an area in the plane of but displaced to one side of said mosaic electrode, electrode means to direct said electron beam beyond said mosaic electrode with respect to said electron gun and toward said photocathode and magnetic means to generate a cylindrical magnetic field between said photocathode and said mosaic electrode to direct said electron beam and electrons forming said electron image upon said mosaic electrode.

7. A television transmitting device comprising an electron gun to generate an electron beam, a photocathode ofiset from the normal undefiected path of said beam to generate a flow of electrons, a mosaic electrode having a mosaic surface exposed to the electron flow from said photocathode and being along but ofiset to one side of the undefiected path of said beam and means to generate a cylindrical magnetic field intercepted by said photocathode and said mosaic electrode to direct said electron beam and said flow of electrons upon the mosaic surface of said mosaic electrode to generate television signals representative of said flow of electrons.

8. A television transmitting device including an electron gun to generate a beam of electrons, a photocathode ofiset to one side of the undeflected path of said beam of electrons to liberate photo-electrons, an electrode between said electron gun and said photocathode having a plurality of mutually separated particles facing said photocathode to receive electrons from said gun and said photocathode on the said particles, and a magnetic coil having a cylindrical portion enclosing the space between said electron gun and said mosaic electrode and a toric segment portion enclosing the space between said photocathode and said mosaic electrode to generate an axial magnetic field over said first portion and,

a cylindrical magnetic field over said lastnamed portion to direct said photo-electrons and said electron beam upon said mosaic electrode.

9. A television transmitting device comprising toric segment portion, a magnetic coil surrounding said envelope to' generate an axial magnetic field over said cylindrical portion and a cylindrical magnetic field over said toric segment portion, a mosaic electrode intermediate the two portions of said envelope the major portion of said mosaic electrode being displaced from the longitudinal axis of said cylindrical portion, a photocathode to liberate electron streams in response to an optical image focused thereon adjacent the opposite end of said toric segment portion from said mosaic electrode, an electron gun adjacent the opposite end of said envelope from said photocathode the longitudinal axis of said gun being ofiset from the axis of said cylindrical portion and passing to one side of said mosaic electrode to direct a beam of electrons beyond said mosaic electrode,

into the toric segment portion of said envelope and toward said photocathode, whereby the beam of electrons will be directed to the surface of said mosaic electrode facing said photocathode.

HARLEY A. IAMS.

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