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Electron discharge device

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Publication number
US2887594A
US2887594A US50478455A US2887594A US 2887594 A US2887594 A US 2887594A US 50478455 A US50478455 A US 50478455A US 2887594 A US2887594 A US 2887594A
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Prior art keywords
target
electron
envelope
photocathode
image
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Alexander A Rotow
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RCA Corp
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RCA Corp
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    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J31/00Cathode ray tubes; Electron beam tubes
    • H01J31/08Cathode ray tubes; Electron beam tubes having a screen on or from which an image or pattern is formed, picked up, converted, or stored
    • H01J31/26Image pick-up tubes having an input of visible light and electric output
    • H01J31/28Image pick-up tubes having an input of visible light and electric output with electron ray scanning the image screen
    • H01J31/34Image pick-up tubes having an input of visible light and electric output with electron ray scanning the image screen having regulation of screen potential at cathode potential, e.g. orthicon
    • H01J31/36Tubes with image amplification section, e.g. image-orthicon

Description

May 19, 1959 A. A. RoTow ELEcTaoN DISCHARGE DEVICE Filed April 29.A 1955 .lwlmwllllllll INVENTOR. l 1 v ruilnldzv fram/ff United States Patent lC F 2,887,594 ELEcTRoN DISCHARGE DEVICE Alexanderli. Rotow, Lancaster, assignor to Radio yCorporation of America, a corporation of Delaware This invention relates to television pickup, or camera tubes. In particular this invention relatesto an improved image orthicon type of television camera tube.

n image orthicon .tube-normally includes, within an evacuated envelope, an electron gun for producing an kelectron beam. The electron beamhis directed upon one side .of -a storage target.v v.Within theother end of `the envelope is a photocathode the photoemission from which is directed onto the other side of the target to produce charge patterns on the target that are discharged by the electron beam to provide outputsignals from the tube.

When utilizing an image orthicon type of camera tube, there are instances when it is desirable to obtain greater resolution ofthe scene being televised than has been possible heretofore. It is known that the resolution of the image orthicon type of vtube is limited primarily by the size of the targetrrather thanYthe-size ofthe photocathode. One solution to this resolution problem has been to utilize an image orthicon having a target and photocathode of greater diameter. However, whenutilizing photocathodes of larger diameter `it is necessary to utilize a camera'lens system, which includes expensive lenses 'such as the telephoto and zoomer lenses, of a size to match the largerphotocathode. Thisincreased size of lens 'system is considerablymore expensive than the 'equivalents in the'smaller universally used size of lens systems. v

It is therefore an object of this invention to provide an improved image orthicon type of tube having improved resolution.

It is anotherlobjectof this invention to provide a new and improved image orthicon type of tube which can be used with relativelyinexpensive lens systemsl and one which has improvedresolution. t

These and otherl objects are accomplished in accordance with this invention by providing an image orthicon type of pickup tubecomprising an evacuated envelope. In one end of the envelope is an electron gun and an electron multiplier section having a conventional dynode structure. In the central portion of the envelope there is provided a scanning section which may comprise deection and focus coils badjacent to the tube as is Well known. Within the other'lend of the envelope there is provided `an image section including a target and photocathode.

Also, a tube in accordance with this invention includes v a conical shield and a cylindrical shield both of which are `provided to produce a smooth transition of electric elds between the small photocathode and the larger target.

The novel features of this invention arepointed out in the appended claims. 'l'helinvention itself now be l g 2,887,594 Patented May 19, 1959 ice 4 2 described in greater detail in connection with the accom panying single sheet of drawings, wherein:

Figure 1 is a partial sectional view of an image orthicon type of tube in accordance with this invention,

Figure 2 is a fragmentary schematic view showing of Athe magnetic lields produced in the tube shown in Figure 1 and; L

Figure 3 Vis a fragmentary sectional view of an embodiment of the invention.

Referring speciically now to Figure 1 there is shown a partial sectional view of an image orthicon type of vtube 10 in, accordance with this invention. the image orthicon tube 10 comprises an evacuated envelope 11 having an electron gun assembly 12 in one end of the envelope. The electron gun assembly 12' includes a conventional heater, cathode, control grid and accelerating electrode structures (not shown) for producing an electron beam 15. Surrounding the gun-12 is an electron multiplier structure '19.' An additional accelerating electrode 14 is formed as a wall coating on the inner surface .of the envelope. 'I'he accelerating electrode 14 is utilized for accelerating the electron beam `15 toward a target electrode 16 enclosed within an image section 13.

. APairs of `horizontal and vertical deflection coils are formed into a yoke structure 17 surrounding the tube envelope 1.1. The deflection coils provide fields perpendicular to each other and to the axis of the envelope` 11 and are connected to appropriate sources -of potential (not shown) for providing frame and line scanning of the electron beam 15 over the surface of target 16. Such deilection systems' are well known and further description thereof is not deemed necessary.

Surrounding the envelope 11 is a focus coil 20 fo providing a magnetic eld having lines of force substantially parallel to ytheaxis of the tube'lt] and extending from the end of the electron gun-structure 12 to the opposite end of the image'sect-ion of envelope 11 as shown. Duringtube operation, theield' produced by focus coil 20 `provides a focusing action on the electrons of beam 15 to bring 'these electrons to awell defined point of focus on the target 16. Also surrounding the envelope, and adjacent to the gun v12, is .a compensating coil 21 having a iield perpendicular tothe axis of tube 10. By adjusting coil 21 around the axis of tube 10, any slight miscentering ofthe beam 15, due to mechanical imperfections, can be eliminated; Surrounding the other end of envelope `11 is a divergence coilm22, in accordance with this invention, the purpose of `'which will be explained hereinafter. l I

A decelerator electrode 18, which is formed as a ring, is mounted immediately in front of target 16 and adjacent the scanned surface thereof.

In the other end of the envelope 11 there is provided an insulating target 16. Thetarget 16 comprises a sheet 28 of insulating material, such as glass, and a ne'me'sh screen 26. Extending fromv vthe outer periphery of the target 16 and inwardly toward the other end of the envelope 11 is a target cup 23 that is tubular and has a conically shaped end that decreases in diameter as it extends toward the other end of the envelope 11. Adfjacent to the smaller end of the conical target cup,l or electron shield 24,`is supported an accelerator electrode 25 which includes a pair of hollow tubular shaped members 27 and 29. As can be seen from Figure l, the hollow tubular shaped members 27 and 29 are spacedapart' and electrostatically screen an evaporator filament. 31 vfrom the end of envelope 11. Due to the fact that the Ctubular members 27 and 29 are spaced apart there is provided a slot between these members through which .an alloymaterial is evaporated from the filament ,31 to form a photocathode. 33 on the end wall ofptube 1 0,

,Photocathode 33). isja semi-transparent coating of light Generally,

aanwas with a conductive electrode border 34. One example of awphotocathode material Vis facesiatedj jlayer` owfl `silver bismuth alloy. 3 r l `During operation of tube. 10,*pliotoelectrons *are image, and are directed'towardtargetl` `These photo- `electrons `travel `at a yhigh velocity along the magnetic lines of force provided by focusing coil onto the un- 'scanned side .of the glassdarget 16.3"'Tl1'es`e `photoelecsensitive,electron emissive' material-supported onf-the y inner surface of the end ofenvelope 11y and in contact.

structure is shown in Figure 3wherein.the focusing coil 20 is wound with a largerk number ofk turns per unit of area near the photocathode 33 than the number of turns around the balance of tube; 10. When this alternative emitted from `time photocathode 33, response to an y,

trons forma positive charge patternjonthe unscanned f surface of target `16 corresponding to the light density of theoriginal scene projected onto the photocathode 33. Assuming a condition -whenno 4light is directedonto photocathode 33, low energy `electrons `from V`thepriinary electron Abeam 15la`nd onthe surface of target 16which is exposed tothe electronbeam; and: drive) this surface 'of target 16 substantially to ground, or cathodepotential;

"A`t thisV time, the remaining electrons iny beam 15 *are reflected-back, as a return election beam' 152; toward gun" 12.` f -When Ia light pattern is directed onto photo- 'cathode' 33, they photoelec'trons arey `emitted *from each i elemental` portionY of photocathode 33 in -an lamounty proi portional to `the light ,p and shade of the `original Scene.`

The photoelectrons strike 'the' surface of target 16 and initiatesecbndaryemissiontherefrom.' Dueto the velocity of-the photoelectrons this `secondary `emission hasfan 'emissionratio greater thanfnnity from the bombarded areas, which drives -theseareasdn a. positive direction.

Due Ito the thinness of target' 16, with the' re'sultingfhigh struct-ure is utilized the divergence: coil 22 is omitted since its function, is replaced `by the larger number of turns in the focusing coil 20.

It can be 1 shown electron optically` that, in order to minimize image.distortion` in a tube ofthis` type, the diverging or spreadingoiy .the `magnetic lines of force 35, i.e. the magnetic ield which. determinesthe diverging electron paths between the photocathode 33 and the target '16, shouldr be. a smooth rflow without sharp bends or strong diversions. same time to obtain` considerable image magnication, the distance from the photocathode `33 tothe target 16 is greater in tubesl built inaccordance: withthis invention than in standard tubes.

` Electron optical considerations alsshowthat,` in order to minimize image; distortion,` the yelectrostatic `lines of force, as Well as the 1magneticlines of` force, must be f assrnooth as possible and free of sharp bends. To achieve 25 accordance with this l invention. A The conical yshaped this "object .the conio'alshaped shield 24 is` introducedfin f shield 24 provides ia. Smoothtransition `of electrostatic `lines efforce from the target 16ste the accelerator elec- `trodeZS. l

, involved .in thisinventioniisy shown below. It should be capacity betweentthe two sides,th'e saine potential pat- 1 tern is`established on the` scanned, or electrongun," side f `of target 16. Accordingly, the potential offthe scanned surface of target 16 will vary frornip'oint topoinnfrona substantiallyzero volts to severalvolts positive potential.r When the electron beam 1ISapproaches targetl, at n la -verylow "velocity immediately in Vfront "of target 16,

the gunnlZ. In this manner, as the electron beam is p scanned "over the surface of target y16, it is reected toward the gun 12 as a modulated return beam15'.` The modulated return beam 15' Vfc` llows`substantally the same path as the incident beam 15 and strikes `the end `of gun 12 which is formed as a dynode electrode and is the first stage` of the electron multiplier section 19.1 The multiplier section may be any *conventional type where the modulated return beam 15' is converted into output signal voltagesfromV a collector electrodein the multiplier elecfrode. In `conventional tubes of, this type, the photoelectron image is converged fromthe photocathode to the target. `In other words, the useful area of the target is smaller ,than the useful area of` the photocathode even though physicallythe photocathode and target Vare'` the Asame size, However, in accordancewith this invention the photoelectron image is diverged from the photocathode 33 tothe target `plt. Thus, tubes builtin accordance with this invention permit the use of a universally used lens system with the relatively small photocathode 33, in 'cooperation With'thehigher resolution of the relatively large target `16.

Thediverging photoelectron path coniiguration in accordancewith this invention is provided by means `of a div'er'gingcoil 22, around the image Section13, which produces a magnetic eld `density that is "greater adjacent `not be limited to thisparticlar example. e

An leirample'of specifick dimensionsof the components understood that this is merely an example of a tube which has `been successfully operated and `the invention should structures in4 the image section, tubesi'n accordance with this invention permit the use oflthe` universally used size of lens system coupled with improved resolution. What is claimed is: l y

l. A camera tube comprising `an"'evacuated envelope, a target cup supporting atargetwithin said envelope, `a `portion of said target cup extending inwardlytoward the axis of said envelope, ahollow tubular electrode spaced adjacent to the end of saidlportion of said"target cup, a photocathode spaced "adjacenttoithefother end of said hollow tubular electrode, thefelctron receiving area ofsaid target "being substantially larger "than the electron emissivearea of saidphotocathodafand means around said envelope for directlyfocussing an electron image from said photocathode onto 'saidtarget andfor enlarging said electron image `from`sad`photocathode ontosaid target. p p

2. A television cantera tube comprising an `evacuated envelope, `electrtm `beam"lproducin'g"means in one end of said envelope, atarget within said "envelope Tand-inthe `path of theelectif'bnbeam, a targetfcup-electrode said target being spportedacross an aperture in saidtarget cupelectro'de, a'portion of said target cup electrode extending outwardly` from adjacent the" peripheryfof said `target to adjacenttiie` wall Aot said envelope, another porend of said other portion"of"`said""'target cup, a photo- Tosatisfy this conditiomand at the Inches cathode on said end of said envelope, said target being substantially larger in electron receiving area than said photocathode is in electron emitting area, a focusing coil around said envelopev and extending at least between 'said target and said photocathode for focussing an electron image from said photocathode directly onto said target, and a divergence coil around said focusing coil adjacent .to said photocathode for enlarging said electron image from said photocathode onto said target.

References Cited in the ile of this patent UNITED STATES PATENTS Ruska Mar. 21, 1939 Morton Feb. 6, 1940 Lubszynski June 11, 1940 Lubszynski Aug. 8, 1950 FOREIGN PATENTS Germany Sept. 17, 1953

US2887594A 1955-04-29 1955-04-29 Electron discharge device Expired - Lifetime US2887594A (en)

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3052809A (en) * 1958-09-13 1962-09-04 Fernseh Gmbh Focusing system for storage tubes with image section
DE1197919B (en) * 1963-06-14 1965-08-05 Fernseh Gmbh Coil system for Superorthikonroehren with large deflection angle
US3296485A (en) * 1962-12-20 1967-01-03 Bosch Gmbh Robert Image orthicon pickup tube using metal evaporator filament to deflect return beam
US3424997A (en) * 1966-01-05 1969-01-28 Spectra Physics Gas laser with gas storage electrode
DE1562301B1 (en) * 1963-12-06 1970-08-20 Tokyo Shibaura Electric Co Coil system for magnetic focus for Superorthikonroehren
DE1462582B1 (en) * 1966-10-21 1971-06-03 Fernseh Gmbh Television camera with a superorthikonroehre with improved signal rauschverhaeltnis

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2151530A (en) * 1935-10-15 1939-03-21 Firm Fernseh Ag Braun tube
US2189319A (en) * 1935-11-30 1940-02-06 Rca Corp Electro-optical device
US2203734A (en) * 1937-05-20 1940-06-11 Emi Ltd Electron lens
US2518434A (en) * 1945-07-12 1950-08-08 Emi Ltd Electron discharge device such as a television transmitting tube
DE890098C (en) * 1944-07-23 1953-09-17 Fernseh Gmbh A process for producing a conductive connection in Vakuumgefaessen

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2151530A (en) * 1935-10-15 1939-03-21 Firm Fernseh Ag Braun tube
US2189319A (en) * 1935-11-30 1940-02-06 Rca Corp Electro-optical device
US2203734A (en) * 1937-05-20 1940-06-11 Emi Ltd Electron lens
DE890098C (en) * 1944-07-23 1953-09-17 Fernseh Gmbh A process for producing a conductive connection in Vakuumgefaessen
US2518434A (en) * 1945-07-12 1950-08-08 Emi Ltd Electron discharge device such as a television transmitting tube

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3052809A (en) * 1958-09-13 1962-09-04 Fernseh Gmbh Focusing system for storage tubes with image section
US3296485A (en) * 1962-12-20 1967-01-03 Bosch Gmbh Robert Image orthicon pickup tube using metal evaporator filament to deflect return beam
DE1197919B (en) * 1963-06-14 1965-08-05 Fernseh Gmbh Coil system for Superorthikonroehren with large deflection angle
DE1562301B1 (en) * 1963-12-06 1970-08-20 Tokyo Shibaura Electric Co Coil system for magnetic focus for Superorthikonroehren
US3424997A (en) * 1966-01-05 1969-01-28 Spectra Physics Gas laser with gas storage electrode
DE1462582B1 (en) * 1966-10-21 1971-06-03 Fernseh Gmbh Television camera with a superorthikonroehre with improved signal rauschverhaeltnis

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