US2320977A - Photoelectric tube and circuit - Google Patents

Description

June 1, 19 3. A. M L. NICOLSON PHOTOELECTRIC TUBE AND CIRCUIT Original Filed Jan. 29, 1938 Curved Scan 7; zny General;-

INVENTOR ALEXANDER McLEAN NICOLSON ATTORNEY :tube. from a dark area of the scene to a lighter area,

Patented June 1, 1943 UNITED STATES ATNT' orgies PHOTOELECTRIC TUBE AND CIRCUIT Alexander McLean Nicolson, New York, N. Y., as-

signor to Communication Patents, Inc., New York, N. Y., a corporation of Delaware 5 Claims.

This invention relates to improvements in photosensitive devices of the class whose elements include an anode, a cooperating lightsensitive cathode, and the interconnections therefor. More specifically the invention relates to photoelectric tube arrangements of the type used in television systems, such as, for example, the system disclosed in my application filed July 7, 1930, Serial No. 466,079, now Patent No. 2,108,827, dated February 22, 1938, although the invention is not limited to that use. p

This application is a division of my application Serial No. 187,758, filed January 29, 1938, now Patent No. 2,220,115, dated November 5, 1940, which is a division of my Patent No. 2,108,827.

In the system disclosed in Patent No. 2,108,827 the image of a distant or near scene is focused upon the cathode of a photoelectric tube having a non-linear characteristic. The focusing of the image on the cathode causes a steady total emission of electrons to the anode of the tube, and produces a steady electric current in the input circuit of the photoelectric current amplifier. A scanning ray of light, produced in any well known manner, but preferably in the form of an electrodynamic are along electrode rails in a magnetic field, i. e., an actinic ray, is employed for scanning the image on the cathode. Since the intensity of the light of the scamiing ray is substantially constant, variations in the current output of the tube are obtained through the non-linear characteristic of the photoelectric Thus, when the scanning ray is shifted the current output of the tube will be greater.

This variation in current in accordance with the variations in light and dark areas of the scanned image will reproduce the image at a receiving station. The definition of all areas of the reproduced image at the receiving station is greatly enhanced, as well as the efficiency and rapidity of response of the system, by the use of the photoelectric tube arrangement of the present invention.

In accordance with the present invention. a circuit is provided for a photoelectric tube arrangement having a non-linear characteristic. in which the cathode is translucent and will transmit light through it as well as being able to hold the image of a scene projected thereon, intercepting sufficient light for that purpose. The

cathode is sensitized on its opposite surfaces for response to the character of the light to be projected thereon, one surface being adapted to be position by thumb-screw Hi.

responsive to the spectrum light of the image projected thereon, and the opposite surface being adapted to be responsive to the scanning ray, which preferably is actinic, the cathode being translucent to both optical functions. An anode is positioned adjacent each surface of the cathode and the anodes are so constructed as not to materially intercept the projection of theimage light or the scanning light on the corresponding surfaces of the cathode. Since the distance between the source of the scanning ray and the cathode is short because of space requirements, the cathode and the complementary anodes are preferably curved about the source of the scanning ray, so that the scanning is uniform over every unit of area of the cathode and blurring of the image at its borders, due to irregular scanning, as is common with flat cathodes, is avoided.

The output circuits of the cell in accordance with the present invention are preferably ar ranged with a regenerative feed back coupling for increased efficiency. Details of construction and further advantages of the photoelectric tube and the circuit of this invention will become apparent upon examination of the accompanying drawing, which is a cross-section of the tube and scanning arrangement with a diagram of the external electrical circuits. Referring to the drawing, numeral l0 designates a camera casing divided into two chambers H and [2 by a partition l3. Chamber II contains a specially designed photoelectric tube i4 supported on a suitable base It: and locked thereon in vertica-llyadjus'ted The chamber 12 contains an electrodynamic arc screen i? supported on a suitable base l3 in which it is locked in vertically adjusted position by thumb-screw 19. The screen ll is positioned in alignment with tube I4 and a focusing lens'combination 20 in the partition I3 directs the scanning ray from the screen ll on the tube M. A focusing lens combination 2! in the opposite wall of the chamber directs the image 0, such asthe scene to be transmitted, upon the tube It.

The tube It comprises an evacuated or gasfilled transparent envelope or tube 22 containing a cathode 23 and symmetrically arranged anodes 24 and 25 positioned on opposite sides of the cathode 23. The cathode 23 has a'spherical curvature about the focus of the camera lens combination 2%] and the anodes 2t and 25 and the opposite surfaces of the envelope 22 are complementarily curved as shown. The advantage'of the curved cathode 23 isthat the projection path of the ray of light from the scanning screen I! is always a constant distance from the cathode 23 and the image thereon. In this manner the intensity of the normal light is maintained constant at the image, so that a small and compact camera may be provided without distortion of the image and out-of-focus blurring at the borders, as is commonly the case with flat cathode tubes. The screen ll thus may be fixed relatively to the cathode 23 for scanning all sorts of images.

The cathode 23 of the tubelfl is translucent and Will transmit light through it as well as being able to hold the image of the scene projected thereon, intercepting sufficient light for that purpose. The opposite surfaces oi-the cathode 23 are provided or coated with active light-sensitive material, such as potassiumor the like, well known in the art, the material on each cathode surface being responsive to the character ofthe light projected thereon, and being con tinuous, i. e., substantially uniformly conductive as compared to individual, insulated photosensitive cells The anodestE-i and 25 are so constructed, such as: of fine wire as shown, as not to materially. intercept the light directed on the opposite surfaces of the cathode, the light from the object 0 being projected on the lefthancl side of the cathode 23, while the scanning ray of the screen I! is projected on the righthand sid of the .cathode, as seen in the drawings. The double anode arrangement with the translucent cathode provides a very efiicient tube, as Well as an advantageous arrangement from the mechanical point of view.

The screen 1'! produce a strong scanning ray of substantially constant intensityin anywell known manner, but preferably the ray is produced in the form of an electrodynamic arc-along electrode rails 25 in a magnetic field producing actinic light as compared to the spectrum light reflected from the object 3. Scanning systems of this natur are shown in greater detail in my Patents Nos. 1,839,696 and 1,863,278. A shown in the'drawing, a field winding 21, in series with the electrode rails 25, is provided for producing the magneticfield. This winding2l is enclosed in a jacket 28 packed with suitable heat dissipating material'23,such as steel wool or the like,

and containing a passage-33 through which a suitable heat-conducting fluid is circulated to maintain the screen electrode rails 2E at a constant temperatureas well as for cooling the field winding '21. V

The external electricalcircuits which-embody the present invention include a photoelectric tube amplifier having either two tubes, or a single tube 3| with a double anode,-as shown. For example, the grid 32 is connected to thecathode 23 of the photoelectric tub I l, while one anode 24 of the tube I4 is connected through avariable inductance 33 to an anode 34 of the amplifier tube 3|. Similarly, the other anode 25 of the tube I4 is connected through a variable inductance 35 to the anode 36 0f the amplifier tube 3!.

A variable resistance 37 is connected between the grid 32 and the filament of the tube-3i for controlling th operation of the tube 14, and the tube 3|. A plate potential 38 for the amplifier tube 3i, supplies also the operating voltage s for photoelectric tube l4 through the primary of the output transformer 39, choke coils 49 and 4|, in parallel, the variable inductances 33 and 35 in parallel, tube anodes 24 and 25 in parallel, cathode 23, and grid 32. It will beobserved that t-wo interdependent regenerative circuits ar thus formed, one including the anode 24 and the cathode 23 and the other including the anode 25 and the cathode 23.

An increase in electron emission of the cathode 23 to either of the anodes 24 or25 of the tube will produc an increase in the voltage of the input circuit of the amplifier tube 3|, which will be transmitted through the output transformer 39 to a suitable amplifier 42. This output circuit has a tuning inductance 43 connected therein which is employed for feed-back purposes and, with inductances 33 and 35, may be used to produce a certain amount of regeneration. With a circuit of the type described above, the tube I 4 may be operated on alternating current thereby greatly simplifying th circuit and eliminating the need for rectifying and filtering circuits.

The scanning electrode rails 26 and field coil 21 are supplied from a suitable scanning generator 44 through conductors 45. The output of the amplifier 42 is also-connected to conductors 45, for the purpose of increasing'the intensity of the scanning ray producing arc as thegphotoelectric tube l4 output currents are increased. This action will produce regeneration by. increasing the intensity of the scanning ray in proportion to the increase in photoelectric'tube current. That is, should the tube output'current. be considerably increased by the scanning ray falling on a highly illuminated area of the cathode 23, this increase will be augmented by the substantially simultaneous-increase, in the scanning ray intensity. When the. ray fallson a less illuminated area, the contrastwill thus bemuch greater than with the normal scanning ray.

The photoelectric tub l4 output currents and the are producing currentsare segregated by a filter 46 in the output circuit of the system. The-output terminals 4'! may beconnected to suitable transmission apparatus 48. The impulses from the scanning generator 44 aretransmitted along with the photoelectric tube l4 output currents for synchronizing the remote receiving screen with th transmitter 48. With the scanninggenerator 44 a direct current source, it is unnecessary .to employ a filter.

The photoelectric tube. arrangement .of this invention is particularly:adaptable:to.the television systemdescribed :in the aforementioned copending parent application. In sucha system,

the tube I4 is preferably disposed between the scen il being televised and the scanning ray source ll. Since the cathode-23 is translucent, light refiected from the scene!) impinges on both sensitized surfaces, and lightfrom the scanning source IT also impinges onboth-sensitized surfaces, so that the efiiciency of conversion from radiant to electrical energy'is much higher in this photoelectric tube than in other photoelectric cells used heretofore for this purpose.

It is evident that theeiiicienc'y; of this novel photoelectric tube'arra-ngement may be still further increased bycoating each side of the cathode with photosensitive material which is most sensitive to the luminous radiation falling on it; For example, in the above-described'television"scanning system where visible light isfocusedon one side of the. cathode anda scanning beam of actinic radiation is focused on the other. side of the cathode, the side of the cathodenearest the scene may be coated Withphotosensitive material which is responsive to light fromthe sun or any artificiallighting ystem, and the side .nearestthe scanning source may be coated with material especially sensitive to actinic radiation.

Obviously, the use of a photoelectric tube with a translucent cathode and its associated circuit is not limited to the television art, but is capable of adaptation to many other fields in which the transmission of light, either visible or invisible, through the cathode of a photoelectric tube may be desirable. Furthermore, the novel photoelectric tube and circuit are capable of modification in form and detail, and are not to be limited in any way by the embodiment described in the specification except as defined in the appended claims.

I claim:

1. In a photoelectric device, the combination of a photoelectric cell having a non-linear characteristic and including a translucent cathode, photosensitive material on the opposite surfaces of said cathode, the said material on one surface of said cathode being activated by radiations of the visible spectrum, the said material on the opposite side of said cathode being activated by actinic radiations, and amplifying means electrically connected to said cathode and responsive to the activation of said material.

2. In a photoelectric device, the combination of a photoelectric cell having a non-linear characteristic, a cathode pervious to radiations in the visible spectrum and actinic radiations, photosensitive material on said cathode adapted to be activated by radiations directed on opposite sides of said cathode, an anode spaced in cooperative electronic relation to each of said opposite surfaces of said cathode and two regenerative circuits, responsive to activation of said photosensitive material each including said cathode and one of said anodes.

3. In a photoelectric device, the combination of photosensitive tube having a non-linear characteristic and including a cathode pervious to actinic radiations and radiations in the visible spectrum, photosensitive material on said cathode adapted to be activated by radiations directed on opposite sides of said cathode, an anode spaced in cooperative electronic relation to each of said opposite surfaces of said cathode and two regenerative circuits responsive to activation of said photosensitive material, each including said cathode, one of said anodes and a variable inductance.

4. In a photoelectric device, the combination of photosensitive tube having a non-linear characteristic and including a cathode pervious to actinic radiations and radiations in the visible spectrum, photosensitive material on said cathode adapted to be activated by radiations directed on opposite sides of said cathode, an anode spaced in cooperative electronic relation to each of said opposite surfaces of said cathode, a vacuum tube having a filament, two anodes and a pair of grids interposed between said filament and said anodes, one electrical connection including a variable inductance between one anode of said photosensitive tube and one anode of said vacuum tube, another electrical connection including a variable inductance between the other anodes of said tubes and an electrical connection between said cathode and said grids.

5. In a photoelectric device, the combination of a photoelectric cell having a non-linear characteristic and including a cathode pervious to radiations in the visible spectrum and actinic radiations and having a pair of opposite surfaces, photosensitive material on said cathode, adapted to be activated by radiations directed on either of said opposite surfaces of said cathode, an anode spaced in cooperative electronic relation to each of said opposite surfaces of said cathode and on opposite sides of said cathode, and electrical connections including said cathode and anodes and responsive to said activation of said photosensitive material, said electrical connections including a regenerative circuit.

ALEXANDER MCLEAN NICOLSON.

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