US3447023A - Electron tube for both transmission and reception of visual information - Google Patents

Description

y 27, 1969 SHOICHI MIYASHIRO 3, ,023

ELECTRON TUBE FOR BOTH TRANSMISSION AND RECEPTION Filed April 18, 1966 OF VISUAL INFORMATION Sheet INVENTOR BY Syn/cm MIYASHIRO May 27, 1969 s HOICHI MIYASHIRO 3,447,023 ELECTRON TUBE FOR BOTH TRANSMISSION AND RECEPTION OF VISUAL INFORMATION Filed April 18, 1966 Sheet 3 0:3

y 27, 1969 SHOIGHI MIYASHIRO 3 447,023

ELECTRON TUBE FOR BOTH TRANSMISSION AND RECEPTION OF VISUAL INFORMATION Filed April 18, 1966 Sheet 3 of s INVENTOR.

United States Patent Office US. Cl. 315-12 5 Claims ABSTRACT OF THE DISCLOSURE An evacuated envelope contains an electric charge image storage target consisting of a conductive back electrode and a storage face layer having high resistivity, a photocathode, an electron gun, and a fluorescent screen, said tube being so adapted that either an image carrying photoelectric current produced by projecting an optical image on the photocathode or an electron beam emitted from the electron gun and modulated by externally fed video signals may be directed to the said image storage target so as to form a corresponding charge image on the target which then may be either scanned by the electron beam emitted from the electron gun or irradiated by flood photoelectrons originating at the photocathode, thereby producing modulation of either the scanning electron beam or the flood photoelectrons which may be caused to strike the fluorescent screen, either for taking video signal current out of the tube or for the reproduction of the Original image or scene.

The present invention relates to a novel electron tube unit having an excellent image storage target which may be used both for transmission and reception of visual informations.

In prior art practice of transmission and reception of television pictures it is required to employ two separate apparatuses: one for picture transmission including means such as an image pickup tube, and the other for picture reception including such means as a cathode ray tube. As is well known, in the conventional broadcast television practice which is typical of visual information transmission and reception systems, a single television picture is resolved into a very great number, for instance about 300,000, of picture elements, to produce sequential video signal of the televised scene. The produced video signals are transmitted via a channel having a frequency range several megacycles wide to the receiving station where incoming video signals are synthesized into a succession of frames which are reproduction of continuously televised scenes to be displayed on the fluorescent screen, whereby continuous motion may be observed with a minimum of flicker on the receiver as the result of the residual image effect of vision.

However, under restricted conditions, where a bandwidth of only about several 'kilocycles is the. case available as is in the video telephone practice, limitation on the picture repetition rate is unavoidable. Stated in another way, it is necessary to utilize slow-speed scanning.

One of the disadvantages accompanying these restricted conditions that appertains to the transmitter side is a much longer exposure time required for photoelectric conversion of light into video signals, which tends to render the reproduced picture obscure and distorted.

A disadvantage pertaining to the receiver is the fact that in the extreme cases of slow scanning a light spot only will move progressively across a screen and it is diflicult for the moving light spot to be observed as a 3,447,023 Patented May 27, 1969 complete picture with the aid of the residual image effect of vision alone.

To overcome the above difliculties in the slow-speed television practice it is necessary to provide sufficient stored image retaining capacity to both transmitting and receiving apparatus. Heretofore, the above difiiculties have been minimized, for example, by relying upon a vidicon camera tube having a great retaining capacity for the transmitter. For better performance, a rapid scan vidicon tube is combined with a signal conversion-type storage tube, the latter being adapted to achieve slow-speed scanning from the output of the former. At the receiver use has been made of a storage-type cathode ray tube, or incoming slow-speed scanning video signals are converted by means of a signal conversion-type storage tube into rapid scanning signals which are then fed to a cathode ray tube to reproduce the original visual information. Also by way of example, the so-called electrophotographic recording is carried out by utilizing a movement of a stylus for slow-speed scanning and the resultant electric discharge phenomena.

All the above arrangements, however, have such drawbacks as insufficient performance, complexity of the arrangement and the consequent high cost and so forth.

It is an object of the present invention to simplify both the transmission and reception of televised information. According to one aspect of the invention there is provided a single electron tube which may be used both for image pickup (in other words transmission) and for reception of electrical signals and reproduction of the picture by switch-over of the operations.

Another aspect of the present invention is to provide a novel electron tube unit which assures simple and reliable means for transmission and reception of visual information through slow-speed scanning.

The invention is now described in conjunction with several embodiments thereof, reference being had to the drawings in which:

FIG. 1 is a schematic view illustrating the principal (construction of a typical embodiment of the electron tube according to the invention;

FIGS. 2a through 2 are schematic representations illustrating the function of the electron tube shown in FIG. 1;

FIG. 3 is a diagram illustrating the interconnection of the electron tubes shown in FIG. 1 in a video-telephone system;

FIGS. 4, 5, 6, 7 and 8 are schematic views illustrating the principal constructions of other embodiments of the electron tube according to the invention.

Referring now to the drawings and particularly to FIG. 1, there is illustrated an electron tube comprising an evacuated glass envelope 1. The inner surface of one end face of the envelope 1 is provided with a photocathode 3 and the inner surface of the other end face is provided with a fluorescent screen 4. Next to the fluorescent screen 4 there is disposed an image storage target 2 and next to which on the side remote from the fluorescent screen is disposed a collector mesh electrode 6. Between the photocathode 3 and collector 6 there are interposed several substantially cylindrical electrodes 7. The envelope 1 has an integral tubular extension 9 in the vicinity of the photocathode 3 and inclined a certain angle with respect to the axis of the main portion of the envelope 1. Within the extension tube 9 there are disposed an electron gun 5 and deflecting means 8. Although not shown in the figures, it is to be understood that there are also provided leads connected to individual electrodes and extending out of the tube. The image storage target 2 comprises a net-like metal member 212 possessing about 750 meshes per square inch which is arranged nearer to the fluorescent screen side and is coated on the side nearer to the photocathode with an insulating material 2a such as calcium fluoride by evaporation to have a thickness of about several microns. Alternatively netlike member of an insulating material having suitable thickness such as glass mosaic may be used which corresponds to the insulating material 2a of the previous arrangement and which may be deposited on one side with a thin membraneous pattern of a suitable metal corresponding to the back electrode 2b. The electron gun is provided with a grid 5' upon which are impressed video signals for modulating the electron beam. The fluorescent screen may preferably be provided with aluminium backing. It is also possible to provide a shutter grid mesh electrode immediately in front of the photocathode, for the purpose of shutting out photoelectrons from the photocathode. Though the specific embodiment of FIG. 1 uses an electrostatic focussing and deflection system for focussing and deflecting photoelectrons from the photocathode 3 and the electron beam from the electron gun 5, an electromagnetic system may also be employed.

The operation of the above described tube is now described in detail referring to FIGS. 2a through 2f.

(a) Preliminary operation for signal writing operation:

FIGS. 2a and 2b illustrate the preliminary operation for video signal writing. Initially, the signal storage target face layer 2a must be brought to a certain uniform potential throughout the face area. The operation comprises two steps. The first step is to erase previously written or stored signal images (FIG. 2a). Uniform luminous flux is projected on the fluorescent screen 4 and the resultant flood of photoelectrons are caused to strike the image signal storage face 2a with such a velocity that the secondary electron emission ratio is more than unity. This is accomplished, for example, by placing the photocathode 3 at zero potential and applying 300 volts to the collector 6 and 340 volts to the back electrode 2b. As a result of the emission of secondary electrons, the storage face 2a assumes a uniform potential slightly lower than the potential of the back electrode, for instance in the neighbourhood of 335 volts, and any previously written old image is rapidly erased. The second step is the preparation for the subsequent writing operation as shown in FIG. 2b, by increasing the potential difference between the back electrode 2b and the storage face 2a to a value necessary for the writing operation. By decreasing the back electrode potential to volts with the other electrode potentials kept unchanged, the potential of the storage face 2a falls to +10 volts by virtue of its capacitance coupling with the back electrode 2b. A distributed, or flood of photoelectric current is once again applied to the storage face 2a; this time the secondary electron emission ratio is less than unity and therefore the potential of the storage face 2a eventually approaches the photocathode potential, i.e. zero potential, the preparation for the writing operation is thus completed.

(b) Signal writing operation:

There are two methods of writing out charge images on the storage target: one method resorts to photoelectrons and the other uses the electron beam from the electron gun. At first, the former case is described. As shown in FIG. 20, an optical image is projected on the photocathode 3 (at zero potential) and the resultant image carrying photoelectric current is focussed and stored on the storage target by means of an electron lens. In this case the collector 6 potential is applied with a voltage of 300 volts and the back electrode 2b is applied with 340 volts similar to the case of the erasing step, so that the storage face 2a which is thus made to be at a potential of 325 volts due to capacitance coupling gives off secondary electrons by the bombardment of photoelectrons, thereby assuming a positive charge pattern corresponding to the original optical image. Similarly to the case of the above described erasing, the maximum potential resulting from the positive charging is approximately 335 volts while the potential of the part of the storage face where dark portion of the image occupies is about 325 volts. The amount of positive charging depends upon the light intensity of the projected optical image, and it is preferable to adjust exposure or storage time, illumination, brightness of the lens employed and so forth such that the storage face potentials roughly range from 325 to 330 volts.

The second writing method uses the electron beam from the electron gun. As shown in FIG. 2d, video signals are fed to the electron gun 5 thereby producing a modulated electron beam which scans the storage target. With a similar arrangement of zero volt at the cathode of the electron gun, 300 volts at the collector 6, and 340 volts at the back electrode 212, an electric charge image similar to that of the former case is stored on the storage face when the electron beam scanning has been completed.

(c) Signal reading operation:

As shown in FIG. 2e a uniform luminous flux (flood light) is projected on the photocathode 3 at zero-volt potential to produce flood reading photoeleetron current. Also, a potential of 5,000 volts is placed on fluorescent screen 4. By keeping the collector potential at 300 volts and changing the potential of the back electrode 2b to +10 volts the storage face is made to have an image potential distribution ranging between 0 to 5 volts. With this setup the flood photoelectric current reaching the storage target undergoes modulation when passing through target meshes in accordance with the distributed potential of each point over the storage face. The modulated photoelectric current is then caused to impinge upon the fluorescent screen 4 maintained at 5 kilovolts to achieve reproduction of the original scene.

The reproduction of the picture may also be accomplished by replacing photoelectrons with the scanning of a reading electron beam from an electron gun whose cathode is placed at zero potential as shown in FIG. 2]. In this connection an electron gun which is capable of switching over from the emitting of the reading electron beam to the generation of a flood of electrons and vice versa may, of course, serve this purpose. In the electron beam scanning, the electron beam having passed through the target and reaching the fluorescent screen 4 may be taken out of the screen through a lead as video signals which may be transmitted to a remote station. If it is desired to obtain only video signal current but not to have the fluorescent screen fluoresce then it is not necessary to apply a high voltage to the screen. Further, it is possible to produce video signal current by the beam scan while at the same time reproducing the corresponding picture on the fluorescent screen by means of the above-described flood photoelectric current. When so doing, the output current will contain D-C component which, however, does not cause any trouble, even when only taken out video signals.

As has been described in the foregoing, the electron tube according to the invention enables storing for a desired period of time a charge image corresponding to an optical image projected on the photocathode or to video signals fed to the electron gun on the storage target, and subsequent reading or reproduction of the stored image by means of electrons emitted either from a photocathode or an electron gun and/or producing video signals of the said stored image.

The principal operative functions of the electron tube as have been described above will find various applications. The typical example is the application in videotelephone using a slow-speed scan. A video-telephone system utilizing electron tubes according to the invention is now described with reference to FIG. 3. In this illustrative example Mr. A and Mrs. B are on their respective apparatus interconnected via a single tel phone line. Each of them performs the preliminary operation (a) above. Then, for instance, Mrs. B projects her own portrait on the photocathode of her tube B through an optical system B and writes it on the storage target by the above described writing operation. This operation may be made in about 0.3 second. Then she reads her own charge image on the target with the scanning beam from the electron gun and sends out video signals of the scanned image by means of a transmitting circuit B a switch 35 and a transmission line 33 to Mr. A. Mr. A receives the incoming video signal through a receiving circuit A coupled to an electron gun which generates a modulated electron beam carrying video signals for scanning the signal image storage target of his tube A to write a charge image of her portrait on the target. The transmitting process of a single picture takes about 3 seconds. Likewise Mr. A sends out his own portrait to Mrs. B to be stored in her tube. Then both Mr. A and Mrs. B are now able to reproduce at the same time the portrait of the opposite party by generating flood photoelectron current by means of the luminous flux from a flood light source A at Mr. As station and from a source B at Mrs. Bs station. When the reproduced static pictures are continuously displayed on the screens at the opposite stations there is no video signal through the transmission line 33, so that the intercommunication of speech using usual telephone receivers A and B is possible during this time. Also by suitably prearranging after an optional interval of time a switching over may be made for transmitting a fresh picture or information from Mr. A to Mrs. B and vice versa or for interchanging fresh informations of each other.

Since the electron tubes according to the invention have ample stored image retaining capacity, there arise no obstacles against reasonably long continuation of the static image reproduction as well as a few seconds of scanning operation. Also a single tube suffices both transmission and reception of pictures unlike the conventional complicated apparatus for this purpose.

Hereinafter is described a variety of embodiments of the electron tube according to the invention.

FIG. 4 shows an electron tube Whose construction is similar to that of the tube of FIG. 1, but which is so constructed that the modulated electron current emerging from the storage target 2 may be subjected to the influence of the electrostatic lens 40 to be caused to spread over an enlarged screen 4 for reproducing a picture of a larger size convenient for watching.

With the electron tube shown in FIG. 1, it is rather difiicult for the electron beam from the electron gun to strike the fluorescent screen at right angles, thus tending to cause shading. This is because the fact that both the photocathode 3 and the electron gun 5 which are the electron sources must be located on one side of the target 2. Even with this arrangement it is possible in fact, to prevent shading by applying a shading correction voltage of a suitable waveform to the cathode of the electron gun. The tube shown in FIG. 5 provides an example of the construction where such shading is taken into account. In this arrangement the electron gun 5 is disposed on the side of the fluorescent screen 4. Although both the electron gun 5 and the fluorescent screen 3 are inclined with respect to the axis of main tubular portion of the tube, a magnetic field derived from a magnet 50 and established midway between both ends of the tube serve to cause the electron beam from the gun 5 to proceed in a direction parallel to the tube axis on the one hand and to deflect photoelectrons having passed through the target 2 upwards so as to have them perpendicularly strike the fluorescent screen on the other hand. FIG. 6 shows a further embodiment of the tube where the electron gun 5 is aligned with the axis of the main portion of the tube. The operation of this tube is almost the same with that of the tube shown in FIG. 5, with photoelectrons coming from the target being deflected in travelling through a region 60 where a magnetic field is set up upward towards the fluorescent screen. The tubes shown in FIGS. 5 and '6 are of advantage in video-telephone application when it is desired to arrange vision downwardly to the reproduced picture. The design of the optical system for projecting the users own portrait on the photocathode is simplified.

The other arrangements FIGS. 7 and 8 illustrate still further embodiments where both the photocathode and the fluorescent screen are disposed on one side of the target 2. The arrangement shown in FIG. 7 places both the photocathode 3 and the fluorescent screen 4 side by side while the arrangement of FIG. 8 places both ele ments 3 and 4 one behind the other, with the electron gun 5 being placed on the opposite side of the target 2 in each case. Both these embodiments employ electromagnetic focussing and deflection system, and so are respectively equipped with a focussing coil 71 and a deflection coil 72. The advantage of these tubes over the previous embodiment lies in the fact that both projection and reproduction of the optical image may be made at one end of the tube. In the tube of FIG. 8 the fluorescent screen 4 is coated on a transparent supporting member such as glass mosaic and the other side of the screen facing toward the electron gun 5 is provided with the aluminum backing 81. The part designated at 82 is a shield mesh electrode.

As has been described in the foregoing, the electron tube according to the invention comprises an evacuated envelope which at least contains an electric charge image storage target consisting of a conductive back electrode and a storage face layer having high resistivity, a photocathode, an electron gun, and a fluorescent screen said tube being so adapted that either an image carrying photoelectric current produced by projecting an optical image on the photocathode or an electron beam emitted from the electron gun and modulated by externally fed video signals may be directed to the said image storage target so as to form a corresponding charge image on the target which then may be either scanned by the electron beam emitted from the electron gun or irradiated by flood photoelectrons originating at the photocathode, thereby producing modulation of either the scanning electron beam or the flood photoelectrons which may be caused to strike the fluorescent screen, either for taking video signal current out of the tube or for the reproduction of the original image or scene. Thus, the electron tube according to the invention is able to transmit and receive visual informations either separately or concurrently, thus complexity in the conventional slow-speed scan television practice. As a typical example when it is employed in a video telephone system utilizing ordinary telephone line, a pronounced simplification of the system will be realized.

While the invention is described in connection with some embodiments thereof it is, of course, to be understood that changes and modifications in the details of the tube may be made without departing from the spirit and scope of the invention as sought to be defined by the following claims.

What is claimed is:

1. An electron tube in which, during an image pickup operation, an optical image is projected on the tube, to be converted to video signals, and during an image reproduction operation, video signals are applied to the same tube to cause an image to appear thereon, said tube being useful for both conversion of optical information to electrical signals and reproduction of images by conversion of electrical signals to visual information comprising an evacuated envelope;

at photocathode; said photocathode producing a flood photoelectron current during a first operation and an image carrying photoelectric current corresponding to an optical image projected thereon during a reproducing operation;

means energizing said photocathode to produce said 7 8 flood photoelectron current during the first operation; 3. An electron tube according to claim 1, wherein said an electric charge image storage target comprising a photocathode and said fluorescent screen are arranged mesh-type conductive back electrode and a storage side by side on the same plane on one side of said storface layer of high resistivity; age target and said electron gun is disposed on the other an electron gun, said electron gun emitting a scanning side of said target.

electron beam; means selectively modulating said 5 4. An electron tube according to claim 1, wherein said beam by (a) externally fed video signal to emit a fluorescent screen is interposed between said photocathode modulated electron beam for storing an electric and said storage target facing toward said photocathode, charge image corresponding to said video signals dursaid fluorescent screen being coated on a mesh-type transing the reproducing operation and (b) further selec- 10 parent supporting member on said target side, and said tively inhibit modulation of said scanning beam durelectron gun is disposed on the side of said target oppoing an impage pickup operation; site to the photocathode side.

a fluorescent screen located to be impinged by said elec- 5. An electron tube according to claim 1 wherein said tron current, said electron current being selectively means energizing said photocathode to produce said flood derived from said electron beam or said flood photo- 15 photoelectron current includes a light source directing electron current, as modulated by said charge image light unto said photocathode. on said target so as to display a visual image corresponding to said charge image on said fluorescent References Cited f f d k d I f UNITED STATES PATENTS an means or pro ucing pic up v1 e0 signa s rom 2O said scanning electron beam as modulated by said 22 22 3 charge image on said target.

2. An electron tube according to claim 1 wherein said 2520507 8/1950 MIMCY 178 68 3 385 995 5/1968 Miyashiro 315-12 photocathode is disposed at one end of said evacuated 3388283 6/1968 0 315 12 envelope, said fluorescent screen is disposed at the other 5 43 4 8/1950 gzzyg g' end of said envelope, said storage target 1s disposed mid- 2,699,511 1/1955 Sheldon way between both ends of the tube, said electron gun is dis sed adjacent said fluorescent screen and is so orient efl that the electron beam emitted therefrom is direct- JAMES LAWRENCE Primary Exammer' ed toward said storage target, and means for establish- 30 LAFRANCHI, Assistant Examiner ing a magnetic field for deflecting passing electrons is provided in the neighbourhood and on said electron gun side of said storage target. 178-6.8; 3l3-65; 315-11

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