US2777087A - Means for obtaining a sensing signal for a servo-controlled color television viewing tube - Google Patents

Description

Jan. 8,- 1957 N. FROMM 2,777,087

CONTROLLED K. MEANS FOR OBTAINING A SENSING .SIGNAL FOR A SERVO- COLOR TELEVISION VIEWING TUBE Filed Jan. 22, 1952 "Ill Hill Sensing' Signal so 6 Fug. 2. 1e

Signal Input I V Transparent Red l2 Blue Green 26 Sensing Signal l M Tronsporenl- Conducting Strip lNVENTOR Kenneth N. Fromm.

United States Patent f) Kenneth N FrommyFortWaynmlni, .assignor to Westinghouse Electric GorporatiomEast.Pittsburgh, Pa, a corporation of Pnnsylvania Application JanuaryaZZ; L195Z',-Seria1 No.:267,60&:

3 Claimsn ((1315-12) My invention relates'to-television tubes and; more particularly, to means for obtaining a sensing signal fromra phosphorscreen of a television tube;

Iris-an object of my invention to provide an-improved color'television' tube andci rcui t therefor.

Anotherobiect of my 'invention-is-to' provide-a cathode ray tube and circuit producing; a reliablesensing signal;

Still another'object of my-invention'isto provide a cathode: ray tube having'a' plurality ofstripsof-phosphor material'near an end thereof and having means for pro ducing a change. inisecondary electron emission when the cathode ray 'leaves the desired path.v

Still anotherobject' of my'invention is to provide, a color television tube having a plurality of phosphor strips whereby the secondary emission from any group ofstrips isdifferentfrom thesecondary emission of the strips immediately adjacenttheretoh An ancillary. object of my invention is to provide means for registering the secondary emission produced inthe regionbf saidphosphor strip.

Thenovel features which I consider characteristic of my. invention are set forthwith more particularity in the appended claims. The invention, however, with respect to both the organization and the operation thereof; together with other objects and advantages. may. be best understood'from the following description of specific embodiments when read in connection withthe accompanying drawing, in which:

Figure 1' is a schematic showing of an apparatusbuilt in accordance with one. embodiment of my invention wherein the tubeanode serves as the secondary emission collector;

. Fig. 2" is a schematic showing of an apparatus built. in accordance with another embodiment of. my invention wherein a secondary emission collector electrode is pro.-

vided'which is separated from the anode;.and.

ated envelope 4 havingan end plate 6 of transparent materiall This end' plate 6 comprises the picture area of the tube. At the opposite; end of; the tube 4 from the end plate6, an electron gun 8 is provided for producing a stream of electrons; The-electron gun is a device well known in the art andwill'notbedescribed in detail here. Between-the electron gun 8- and the end plate: 6; there is l'ocated inside" the tubeenvelope4 an anode 10': Betweenthe electron gunfi and the anode 10 in accordance with principles well known inthe art, deflection electrodes 12'are-placcd so-as-toeffect; in accordance with asignal, a horizontal'or vertical acceleration inthe electronbeam which is producedbytheclectrongun and accelerated by the field between'theelectron gun and the anode, By means of the deflectionelectrodes 12, in accordance with principleswell'known in the art, the electronbeam may; becaused to scan the viewing area. Fastened to the'inside ofthe-enve1ope4- at the viewing end of the tube 2; isalayer of electrically conducting transparent material 14; whiclrcoverssubstantially all of that' end-of the tube envelope -4.- This electricaly conducting transparent material14 may'beany of several materials which-arewell known in the art; such as'the transparent conducting glass produced by Pittsburgh Plate Glass Company under-the trade name Nesa; Coated on the inside'of the transparent conducting coating: 14 are a large number of strips16; 17, 18- ofaphosphor material. In the drawing; only a fewsuch-strips are shown, but thesestripsare meant to be indicativeof" the organizationof the much larger number'of strips which-would'actually be employed in practice. These strips of phosphor material 16,-17;' and 18am organized in accordancewithoneembodiment of my invention so 'that-a-fi'rst strip16-comprises a-phosphor material capable of producing-red-light inresponseto electrons' irnpinging*thereon; such as zincphosphatezMn: A. second phosphorstrip' 17 isprovided adjacent the first phosphorstrip' and is-capable ofproducing-a blue light when electrons impinge thereon. An example of thissecond phosphor wouldbe-zinc sulfidezAg. A third phosphor1-strip'18is provided adjacent-the secondphos: phor-stripwhichis capable of" emitting green light. By way of example, the thirdphosphorrnaterialmight be comprised of zinc orthosilicatezMn; A fourth strip- 19 islocated parallel-to the thirdstrip 18 but separateda substantial-distance therefrom so that'a strip of the trans parentconducting coating 14- is exposedbetween. the third phosphor strip 18 and the fourth phosphorstrip 19; The strip of exposed transparent-material14 between" the third-strip. 18 and the fourthstrip 19; thereforejhas a different coeflicientof secondary emission from the cm efficient of either the-third-strip 18- or the fourth strip 19;

Insome instances, it maybe desirable to employ a mixture of'a-phosphor-and another material such as AgzO having a high secondary emission coefficient.

In the embodiment shown in Fig. 1, a, high voltage source of'potential 20 is connected between the electron gun 8 and the anode 10; and a low voltage source of potential 22' in series with a resistance 24 is connected between the anode" 10 and the transparentconducting layer 14. An output terminal 26 for the sensing signal is connected through a condenser 28 to the transparent icon.- ducting-layer 14;

In the operation of the apparatus shown, in Fig; 1, electrons produced by the electron gun 8" are accelerated by the anode 10 so as to impinge on the screen comprising the phosphor strips' 16 to 19 and the transparent conducting layer 14. The electrons which have been formed in a beam of small cross-sectional area bypthe. electron gun 8 are deflected by the deflection electrodes 12 in accordance with an input signal so that the point at which the electron beam impinges on. the screen is caused to scan the screen. The electron beam is preferably caused to scan the first phosphor strip 16' first and then scan the second phosphor'strip 17;

The path of the scanning beam is preferably sinusoidal as, for example, is shown by the curve 36 in Fig. 3. Let; us assume now that the third phosphor strip is being scanned. As the beam scans the third phosphor strip 18, it may leave its desired course and move over onto the strip of exposed transparent conducting material betweenthe third phosphor strip 18 and the fourth phosphor strip 19. If thisoccurs, the number of'secondary electrons emitted per unit time will change.

The secondary electrons emitted by the screen are attracted toward the anode 10 since the anode 10 is more positive than the transparent conducting layer 14. These electrons impinging on the anode 10 cause a. current pulse between thcanode 10 andthe transparent'conducting layer 14. When. the scanning beam ceases tov scan the third'phosphor strip ls'and starts to scan the strip of exposed transparent material 14,there will be a change in the number of the secondary electrons impinging on the anode per unit time because of the difference in secondary emission coefficients of the third strip 18. and the transparent material 14. This change in the number of secondary electrons striking theanode 10 per unit time causes a change in the current between the anode 10 and the transparent conducting layer 14. A pulse of current is thus produced which changes the output through the condenser 28. Thus, the current pulses which pass out through the condenser 28 comprise a sensing signal which indicates the position of the scanning beam. This sensing signal may then be employed to correct the potenials applied to the deflection electrodes so as to cause the electron beam to change its direction. a

In the embodiment shown in Fig. 2 a separate secondary emission collector electrode, 30 is provided for collecting the electrons eniitted by the screen in response to electrons impinging thereon. The secondary electron collector 30 is connected to the anode 10 through a source of potential 32 and a resistance 34 in series. A change in the number of secondary electrons impinging on the collector electrode 30 will produce a change in the current across the resistance 34. An output pulse is therefore produced which varies in response to variations in the secondary emission.

A system as described herein has a particular advantage-that a very high ratio of sensing signal current to noise current may be obtained. For'example letus assumethat the secondary emission coefiicient of the three phosphors which are separated periodically by a strip of exposed conducting material is so chosen thatthe number of electrons per unit time impinging on the phosphor is equal to the secondary emission electrons leaving the phosphors per unit time. Under these conditions, the current through the conducting layer adjacent the phosphors will be zero when the electrons of the scanning beam are impinging on the phosphor. If the secondary emission coefiicient of the exposed conductive strip is any quantity other than one, that is, if either more or less electrons leave the conductive strip per unit' time than impinge thereon, a current will flow between the conductive strip and the electron gun. Thus, the ratio ofcurrent from the conductive strip to current from the phosphors will be equal to a finite quantity divided by zero. The ratio of the currents is therefore infinite. I a

In accordance with another embodiment of my invention, the fourth phosphor strip 19 may be composed of the same materials as the first phosphor strip 16. However, the phosphor materials are so chosen that each strip has a secondary emission coefiicient when bombarded with electrons, which is susbtantially different from the secondary emission coefficients of the strips immediately adjacent thereto; For example, the third phosphor strip 18 is so chosen that a secondary emission coefiicient-is substantially different from either the secondary emission coefiicient of the second phosphorstrip 17 or the secondary emission coefficient of the exposed area of the transparent conducting material 14located between the third phosphor strip 18 and the fourth phosphor strip 19.

It is understood also that the strip of exposed transparent conducting material 14 could beeliminated and the phosphor strips 16 to 18 so chosen that one of the strips of phosphor, as, for example, the green strip 18, has a different coefiicient of secondary emission from the red and blue strips 16, 17. A different pulse would, therefore, be produced when the electron beam impinges on the green strip 18 from that produced when it impinges on the red or blue strips 16 or 17.

Although I have shown and described specific embodimerits of. my invention, I am aware that other modifications thereof are possible. My invention, therefore, is

second phosphor strip capable of emitting light of .a sec ond wave length adjacent said first strip, a third phosphor strip capable of emitting light of a third wave length in response to electrons impinging thereon adjacent said second strip, a fourth phosphor strip capable of emitting light of said first wave length extending parallel to said third phosphor strip .but being separated therefrom by a substantial distance, output means responsive to the secondary emission of electrons produced by bombardment of said phosphors and the area between said third phosphor and said fourth phosphor with high velocity electrons.

2. In combination, a television .tube having therein near an end thereof a layer of transparent conducting material, a first phosphor strip on said layer capable of emitting light of a first frequency, a second phosphor strip on said layer capable of emitting light of a second frequency, a third phosphor strip on said layer capable of emitting light of a third frequency, a fourth phosphor strip coated on said layer parallel to said third phosphor strip but separated therefrom by a substantial distance which is capable of emitting light of said first frequency, a secondary emission collector ring located inside said tubenear said layer, means for maintaining saidsecondary collector at a higher potential than said layer, means for obtaining a signal responsive to the rate at which said first strip, a third strip of phosphor material capable of emitting light of a third frequency coated on said collector electrode adjacent said second strip, a fourth strip of phosphor coated on said collector electrode parallel to said third strip but separated therefrom by a substantial distance and capable of emitting light of said first frequency, said second phosphor having a different secondary emission coeificient from said first phosphor and said third phosphor, and all of said phosphors having a different coetficient of secondary emission from the coefficient of the region between said third phosphor strip and said fourth phosphor strip, means for obtaining a signal from said anode which is responsive to the rate at which secondary electrons impinge thereon.

References Cited in the file of this patent V UNITED STATES PATENTS 2,178,238 Massa et al. Oct. 31, 1939 2,250,528 Grayv -1 July 29, 1941 2,343,825 Wilson Mar. 7, 1944 2,446,440 Swedlund Aug. 3, 1948 2,458,291 Munster et a1 J an. 4, 1949 2,463,535 Hecht Mar. 8, 1949 2,516,314 Goldsmith July 25, 1950 2,602,145 Law July 1, 1952 2,630,548 Muller Mar. 3, 1953 2,631,259 Nicoll Mar. 10, 1953 2,644,855 Bradley July 7, 1953 2,648,722 Bradley Aug. 11, 1953 2,667,534 Creamer et a1 Jan. 26, 1954 2,689,269 Bradley Sept. 14, 1954

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