US2910615A - Photoelectrical control system for color television receivers - Google Patents

Description

Oct. 27, 1959 5, w, MQULTQN T 2,910,615

PHOTOELECTRIC CONTROL SYSTEM FOR COLOR TELEVISION RECEIVERS Filed May 31, 1955 2 Sheets-Sheet 2 Low PASS 42 VARIABLE nun PHASE nc) SHIFTER HORQIVERT.

DEFLECTIOI 57 40 CIRCUITS REOElVER- H AAAA IQJVVQ (s-muc) SHIETER 44 45 Q 46 PHASE smmn coLon CONERED H207) aunsr OSCILLATOR MIXER 5B SEPARATOR (5.5mm "use smmn M) 47- OSCILLATOR uoouc) T0 car cm :1

LV w :/"L16 v B+ 4 g F74 2. mm L) RECEIVER +L 36 g I f $rPfiJ A r0- r l: MELVIN 5. fi/mr/N nun PHOTOELECTRICAL CONTROL SYSTEM FOR COLOR TELEVISION RECEIVERS Stephen W. Moulton, Hatboro, and Melvin E. Partin, Philadelphia, Pa., assignors to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application May 31, 1955, Serial No. 511,858

6 Claims. (Cl. 315-10) This invention relates to an improved color television system and, more particularly, to a color television receiver system of the type which utilizes the screen structure of a single cathode ray tube for the formation of the colored image.

Screen structures suitable for the aforenoted purpose are formed of a large number of minute phosphor elements, different ones of which are responsive to electron impingement to emit light in different primary colors, e.g. red, green and blue. These phosphor elements are arrayed in such manner that the electron beam, during its normal scanning traversal of the screen structure, impinges upon elements emissive of light of these different colors in rapidly recurrent sequence. It is apparcut that, in a receiver system utilizing such a screen structure, the electron beam intensity must be controlled by means of a signal which represents intelligence concerning a particular color during the same intervals during which the electron beam impinges upon phosphor elements emissive of light of that same color. Furthermore, in order to obtain visual blending of the light emitted from successively impinged phosphor elements, these elements must be impinged in extremely rapid succession. As a result the time interval during which the electron beam dwells upon any particular phosphor element is obviously extremely short. This, in turn, makes it difiicult to maintain the desired synchronism between the time intervals during which beam intensity is controlled by a signal representative of a given color and the time intervals during which the beam impinges upon screen elements emissive of light of that color. To overcome this difliculty it has been proposed to derive, from the screen structure, indications of electron beam impingement upon portions of the screen structure bearing predetermined geometrical rela tionship to the colored light emissive phosphor elements. This has been done by photoelectric or by secondary electron emissive means disposed so as to sense such impingement and to produce electrical signals (called indexing signals) indicative thereof. The indexing signals thus produced were then utilized to control the rate of application of color representative signals to the electron beam in such manner as to provide the desired synchronism.

It is apparent that, in the absence of further precautions, the aforementioned indexing signals vary not only as a function of beam position but also as a function of beam intensity (as determined by the picture content of the televised scene). Since the presence of these variations due to picture intelligence reduces the utility of the indexing signals in producing the desired synchronism, elaborate precautions were taken to eliminate tube, all for the purpose of rendering the indexing sig- 2,910,615 Patented Oct. 27,1959

nals more readily distinguished from contaminating signals. Such precautionary measures complicated the receiver system and rendered the same more costly as Well as more diflicult to adjust and to maintain in adjustment over prolonged periods of operation.

Accordingly it is a primary object of the invention to provide an improved and simplified color television receiver.

It is another object of the invention to provide an improved and simplified color television receiver characterized by the use of a single cathode ray tube screen structure to reproduce a televised image in full color.

It is still another object of the invention to provide a color television receiver characterized by the use of a single cathode ray tube screen structure for the formation of the televised image in full color and further characterized by the utilization, in a new and improved manner, of electrical signals derived from this screen structure in response to electron beam impingement thereon.

To achieve the foregoing objects, as well as others which will appear, we provide a color television receiver which includes a screen structure of the multi-color phosphor element type hereinbefore briefly described with apparatus which is responsive to electron beam impingement upon phosphor elements emissive of light in the different colors to produce different electrical signals, respectively representative of the times during which the beam impinges on these different elements and also of the intensities with which such impingements take place. We provide additional means for comparing each of these different beam impingement representative signals with a signal derived from the received color television signal and representative of received picture information concerning the same color as the particular beam impingement representative signal involved in the comparison. We also provide means which are responsive to the existence of a discrepancy between the aforedescribed signals under comparison to modify the beam impingement representative signal so as to reduce this discrepancy (and preferably so as to eliminate the same entirely). From the separate modified signals thus produced we derive a combined signal corresponding to the algebraic sum of the individual modified signals and we supply this combined signal to the cathode ray tube as its beam intensity control signal.

The details of construction and operation of specific apparatus embodying the aforedescribed principles will be better understood from the following discussion taken -in conjunction with the accompanying drawings wherein:

Figure 1 illustrates those portions of a color television receiver which embody one form of my invention;

Figure '2 shows an improved form of certain portions of the system of Figure l; and V Figure 3 showsa preferred embodiment of my invention in a color television receiver.

Referring now to the embodiment of Figure 1 the color television receiver system illustrated therein comprises a receiver portion 10 which is supplied with signals intercepted by an antenna 11. In the discussion which follows, these intercepted signals are assumed to be of the form which is now standard for this country. However it will be understood that our invention is broadly applicable to any form of color television signal, since any such signal must necessarily contain the same sort of information as the standard signal. This receiverportion 10 may be of any conventional form suitable for converting the received signal into three separate output signals, which appear respectively in output leads 12, 13 and 14 and which represent respectively the different primary color components of the televised scene (eg the red,

green and blue components). Thus receiver portion may comprise a radio frequency amplifier, a heterodyne detector for converting the received radio frequency signal into an intermediate frequency signal, an appropriate number of intermediate frequency amplifier stages and a second detector, all of which may be of any conventional form. In addition receiver portion 10 may include conventional synchronous demodulators, matrixing circuits this connection.

Another component of the receiver system of Fig. l which may be of conventional construction is the cathode ray tube 15. More particularly this cathode ray tube may comprise a conventional cathode 16, a beam intensity control grid 17, afirst anode 18 which is supplied with a suitable positive potential from a conventional source A+ of such potential, a second anode 19 which may be in the form of a conductive coating on the interior of the funnel shaped portion of tube and which is supplied with a suitable positive potential from a conventional source A++ of such a potential, and a screen structure 20. This screen structure 20 may be composed of a large number of parallel phosphor strips disposed with their longitudinal axes transverse to the horizontal line scanning direction of the electron beam projected from cathode 16. Different ones of these strips are made of phosphor materials responsive to electron impingement to emit light in the same three primary colors (red, green and blue in the present example) as are represented by the signals appearing respectively in output leads 12, 13 and 14 of receiver portion 10. These phosphor strips are disposed in recurrent sequence across the screen structure, so that the electron beam impinges upon phosphors emissive of light of the different colors in rapidly recurrent sequence during its horizontal line scans across the screen structure. The aforedescribed phosphor strips are diagrammatically illustrated in Fig. 1 by vertical lines 21. It will be understood that, in practice, a much larger number of phosphor strips forms the screen structure of the cathode ray tube than is represented by the vertical lines 21. In fact the number of phosphor strips is preferably coordinated with the rate of horizontal beam deflection across the screen structure in such manner that the electron beam traverses successive strips emissive of light of any particular primary color at a rate of approximately 7 megacycles. In the case of a screen structure approximately 16 inches wide by 12 inches high, this requires the provision of a screen structure having approximately 400 phosphor strips of each color.

The cathode ray tube 15 is also equipped with conventional deflection coils 22 which are, in turn, supplied with the usual horizontal and vertical deflection signals from a source 23 of such signals. The source of deflection signals receives synchronizing signals in the usual manner from receiver 10.

In accordance with our invention there are disposed, in light communicating relationship with the screen structure 20, three photosensitive devices, designated 24, and 26, respectively, each of which is of such construction that it responds only to light of one of the three different primary colors emitted by the phosphor strips of the screen structure. More particularly photosensitive device 24 may be constructed to be responsive substantially exclusively to blue light emitted from the screen structure, while device 25 may be made responsive to green light and device 26 to red light. These photosensitive devices may be of any desired conventional form. For example they may consist of conventional phototransmissive of light only within the desired portions of the color spectrum. The output circuits of these photosensitive devices are respectively connected to three high pass filters 27a, 27b and 27c and also to three detectors 28a, 28b and 28c. The output circuits of the high pass filters are connected to limiters 29a, 29b and 290 respectively and the output circuits of these limiters are re spectively connected to one input circuit of each of modulators 30a, 36b and 30c. The output circuits of the detectors, on the other hand, are respectively connected to one input circuit of each of subtractors 31a, 31b and 310 and the output circuits of the subtractors are in turn connected respectively to the other input circuit of each of modulators 30a, 30b and 300. The output circuits of all three modulators are connected to the beam intensity control grid electrode 17 of cathode ray tube 15. The output leads 12, 13 and 14 of receiver portion 10 which, as will be recalled, bear the red, green and blue color representative signals, respectively, are connected to the second input circuit of subtractors 31c, 31b and 31a, respectively. Each of the aforementioned detectors, subtractors, high pass filters, limiters and modulators may be of any conventional form and need therefore not be described further.

The aforedescribed system operates as follows. Consider, for example, the blue light responsive photosensitive device 24. This device receives a flash of blue light from the screen structure 20 each time that the electron beam, during its scanning of the screen structure, traverses a phosphor strip emissive of blue light. The intensity of this flash of blue light will, of course, depend upon the intensity of the blue light emitted by the phosphor strip and therefore also upon the blue light content of the particular picture element which is being reproduced at that instant. Because of the aforementioned coordination between the number of phosphor strips in the screen structure and the rate of scanning of this screen structure, successive ones of these flashes of blue light will occur at a rate of approximately 7 megacycles. Accordingly there will be produced in the output circuit of photoelectric device 24 :a signal component of approximately 7 megacycle frequency subject to amplitude variations which reflect intensity variations in the blue light flashes from screen structure 20. The time phase position of this signal component will correspond to the time phase position of successive traversals of the blue light emissive phosphor strips by the electron beam. Passage of this signal from photosensitive device 24 through high pass filter 27a (which is constructed in conventional manner to transmit only signals in excess of approximately 6.5 megacycles) and through limiter 29a (which is conventionally constructed to suppress all amplitude variations in the signal supplied thereto from high pass filter 27a) will produce, at the input of modulator 30a, a 7 megacycle signal having the time phase position determined by the output signal of photoelectric device 24 and having a fixed amplitude. On the other hand, application of the same output signal from photoelectric device 24 to detector 28a (which is conventionally constructed to produce a unidirectional output signal having variations indicative of the variations in the amplitude of the 7 megacycle signal from the photoelectric device) and subtractive combination in subtractor 31a of this detected signal with the blue light representative signal supplied from receiver 10 by way of lead 14, will pro duce at the output of the subtractor a signal which represents the extent to which the intensity of blue light emitted by the screen from a particular picture element departs from the intensity with which it is desired to have this element of the screen structure emit (the desired value being, of course, represented by the amplitude of the received, blue light representative signal). This error signal from subtractor 31a is then utilized, in modulator 30a, to modulate the amplitude of the fixed amplitude'7 multiplier tubes, respectively equipped with optical filters megacycle signal supplied to this modulator from limiter 29a, thereby producing, at the output of modulator 30a,

I a signal having a component at approximately 7 meg-acycles whose time phase position is determined by time phase position of successive actual traversals of the blue light emissive phosphor strips by the electron beam of the cathode ray tube and whose amplitude is precisely such that subtractor 31a will produce zero output, thus designating the production of blue light in the screen structure with precisely the intensity indicated by the received signal.

The operation of the circuits connected to green responsive photosensitive device 25 and to red responsive photosensitive device 26, respectively,is similar to that described for the circuit connected to the blue light responsive photosensitive device 24. Accordingly the three modulators 30a, 30b and 300 will produce, respectively, the proper output signals for driving the beam intensity control grid electrode 17 in such manner as to cause the emission of red, green and blue light of proper intensity from the screen structure. As a result there will be reproduced, on screen structure 20, an image in full color which is an accurate replica of the televised scene, as represented by the red, green and blue light representative output signals from receiver 10.

Whenever certain simple forms of photoelectric devices, such as, for example, conventional two-electric photoelectric tubes are used for the photoelectric devices 24, 25 and 26 in a receiver system embodying our invention, the comparatively complicated signal utilization circuits illustrated in Fig. l are necessary. However we have found that considerable circuit simplification may be obtained by using a more advanced form of photoelectric device to observe the cathode ray tube screen structure. The manner in which these simplifications may be Carried out is illustrated in Fig. 2 of the drawings to which reference may now be bad. There is shown in Fig. 2 only that portion of the entire receiver system which differs from the system of Fig. 1, together with the necessary indications of how these portions are connected with those portions of the system of Fig. 1 which have not been illustrated in Fig. 2. More particularly there are shown in Figure 2 three photo- multiplier tubes 35, 36 and 37, each of which is of conventional construction and therefore comprises the usual photoemissive cathode, a multiplicity of dynodes, and an anode. These photo-multiplier tubes are disposed in those positions with respect to the screen structure of the receiver cathode ray tube which are occupied by the photoelectric devices 24, 25 and 26 in Figure 1tl1at is, they are positioned so as to be illuminated by light emanating from this screen structure as the electron beam scans its conventional raster upon the screen. In addition, the photomultiplier tubes of Fig. 2 are also constructed so that they are respectively responsive substantially exclusively to diflerent ones of the three primary colors of light emitted by the screen structure. This photo-multiplier tube 35 may be constructed to respond substantially exclusively to blue light, while photo-multiplier tube 36 responds to green light and photo-multiplier 37 responds to red light.

To this end the photoemissive cathodes of the respective photo-multiplier tubes may be constructed of suitably color responsive substances or, alternatively, appropriately color-selective filters may be interposed in the path of light falling from the screen structure upon these photo-cathodes. The anodes of all of the photomultiplier tubes are connected to a low-pass filter 38 which may be conventionally constructed to transmit only .signal variations emanating from the individual photomultiplier tubes at frequencies up to about 7 megacycles.

'The output of the filter 37 is, in turn, connected to the 'beam intensity control grid electrode 17 of the cathode ,a suitable load resistor, to a source of conventional positive potential B+, and different ones of these last dynodes are connected to different ones of the output leads 12', 13 and 14 of the receiver 10 of Fig. 1. More particularly the last dynode of photo-multiplier tube 35 is connected to lead 14 which, it will be recalled, bears the blue representative portion ofthe received intelligence signal. The last dynode of photo-multiplier 36, on the other hand, is connected to output lead 13 and is therefore supplied with green representative signals and the last dynode of photo-multiplier tube 37 is supplied with red representative si nals by way of lead 12. It may be shown that, by appropriate adjustment of the values of the resistors connecting these dynodes to their respective sources of positive potential B+ and by appropriate selection of the values of these positive potentials, the aforedescribed circuitry will effect a modulation of the 7 megacycle signal flowing from each photocathode to the anode of the corresponding photo-multiplier tube which is substantially analogous to the modulation of the 7 megacycle signal in modulators 30a, 301) or 30c of Fig. 1. More particularly, at the last dynode of each photo-multiplier tube there will be formed a difference voltage between the average value of the 7 megacycle signal developed by the corresponding photoemissive cathode and the corresponding color representative signal from the receiver, and this difference voltage will modulate the entire photo-multiplier anode current and hence the 7 megacycle component thereof.

In each of the receiver systems of Figures 1 and 2 it is necessary to derive, from the received signal, separate signals respectively representative of the different primary colors of the televised scene. While, as has been indicated, this can readily be accomplished by means of entirely conventional apparatus it is sometimes preferable to utilize the received signal in a form which requires less modification. More particularly it is well known that the standard color television signal which is now standard for this country is composed of a component occupying principally the 0 to 3 megacycle frequency range, whichis representative of the luminance of the televised scene, and a component in the form of a subcarrier wave of approximately 3.58 megacycle nominal frequency which is subject to amplitude and phase modulation representative of the chrominance of the televised scene. This latter component has sidebands extending approximately 0.6 megacycles on either side of the nominal 3.58 megacycle carrier frequency. In addition the received signal includes the usual horizontal and vertical scanning synchronizing pulses, as well as so-called color synchronizing bursts each of which consists of a few cycles of a carrier wave having the same frequency as the unmodulated chrominance snbcarrier and having reference phase and amplitude therefor. Each such color burst is superposed on the trailing portion or backporch of a horizontal line blanking pulse, the leading portion of which is occupied by the conventional horizontal line synchronizing pulse. All of the foregoing is well known and is recapitulated here only for completeness of description.

A receiver system embodying our invention in which a signal of the aforedescribed form is utilized without decomposition of the same into separate signals, respec tively representative of the different primary colors of the televised scene, is illustrated in Figure 3 of the drawings to which reference may now be had.

The system there illustrated comprises a receiver por tion 40 which includes those portions of the receiver system up to and including the second detector. Thus the receiver portion 40 may include the usual radio frequency amplifiers, converters, intermediate frequency amplifiers and second detector, all of which may take any one of a variety of conventional forms. As a result of the conventional operation of these elements, a standard signal intercepted by antenna 41 and supplied to receiver 40 appears at the output of the latter reduced to its 'stantial exclusion of all other signals.

' components and is therefore made transmissive of signals in the 3 to 4.2 megacycle frequency range to the sub- Finally color burst separator 44 is constructed to separate the aforementioned color synchronizing bursts from the remainder of the signals. A variety of circuits suitable for this latter purpose are known. For example, color burst separator 44 may include a triode biased sufliciently negative so that only the application of the horizontal line blanking pulses drive the same into conduction, and a filter transmissive only of signals of 3.58 megacycle frequency to the substantial exclusion of signals at all other frequencies. The intermittent signal of 3.58 megacycles frequency and of reference amplitude and phase for the modulated chrominance subcarrier, which is produced by color burst separator 44, is utilized to synchronize, in frequency and phase, a cohered oscillator 45 which may be of any conventional construction and which will produce a continuous output signal also of reference frequency and phase for the chrominance sub-carrier. The output signal from this cohered oscillator 45 is supplied to a mixer 46 in which it is hererodyned with the output signal from an oscillator 47, which may be of any conventional construction suitable for the production of a signal at a frequency substantially in excess of any video frequency encountered in the receiver system, e.g. at 100 megacycles. The sum frequency heterodyne component produced by the operation of mixer 46 is selectively derived from this mixer and is supplied to a second mixer 48 in which it is heterodyned with the chrominance signal derived from bandpass filter The resultant difference frequency heterodyne components are then supplied, by way of a variable phase shifter 49, to one dynode 50 of a photo-multiplier tube 51 having there separate photoemissive cathodes 52, 53 and 54 so disposed within the photo-multiplier tube that their emission currents flow through a common set of dynodes including dynode 50 to a common anode 55. This photo-multiplier tube 51 is disposed in such spatial relationship to a cathode ray tube 56 (which may be exactly identical in every respect with the cathode ray tube of the systems of Figs. 1 and 2) as to be impinged by colored light emitted from screen structure 57 thereof. In addition provisions are made so that the photoemissive cathode 52 of the photo-multiplier tube 51 is responsive only to blue light emanating from the screen structure of the cathode ray tube while the photoemissive cathode 53 is responsive substantially exclusively to green light and photoemissive cathode 54 is responsive only to red light. This may again be accomplised either by appropriate construction of the respective photoemissive cathodes or by the interposition of optical filters in the path of the light falling thereupon. Assuming an equal spacing between the different phosphor strips constituting the screen structure 57 of cathode ray tube 56, the photoemissive cathodes are further supplied with signals from oscillator 47 diifering in phase from each other by 120 degrees. More particularly, if a blue light emissive phosphor strip is disposed so as to be flanked by a red light emissive phosphor strip in the direction of approach of the scanning electron beam and by a green light emissive phosphor strip in the direction of the receding electron beam, then the blue light responsive photo-cathode 52 may be supplied with the signal from oscillator 47 directly, without phase shift while the signal supplied to photo-cathode 53 delayed by 120 degrees in phase shifter 58 and the signal supplied to-photoemissive cathode 54 .is advanced by 120 degrees in phase shifter 59, both of which may be of entirely conventional construction. The anode 55, which receives the emission currents from all three photo-emissive cathodes (as has been indicated), is connected by way of a variable phase shifter 60 to the beam intensity control grid electrode 61 of cathode ray tube 56, to which is also connected the output circuit of low pass filter 42.

The operation of the aforedescn'bed system is as follows. At the output of low pass filter 42 there is produced the received luminance signal which is then applied to beam intensity control grid electrode 61. At the output of mixer 48 there is produced the received chrominance signal superposed, not upon the 3.58 megacycle subcarrier upon which it is received and transmitted by bandpass filter 43, but rather upon a megacycle subcarrier derived from oscillator 47 by the double heterodyning action of mixers 46 and 48. This chrominance signal at 100 megacycles nominal frequency is further heterodyned with certain sum and difference frequency heterodyne components present in the stream of electrons flowing through the dynodes of photo-multiplier tubes by the application of the chrominance signal to dynode 50 in the manner previously described. These heterodyne components of photo-multiplier current are generated by the interaction, at the three photoemissive cathodes of the tube, between the 7 megacycle variation in the photoemitted current in response to scanning of the screen structure by the electron beam of cathode ray tube 56 and the 100 megacycle signals supplied to these photoemissive cathodes fro-m oscillator 47, also in a manner hereinbefore described. The aforedescribed interaction between the 100 megacycle signals and the 7 megacycle signals at the photoemissive cathodes will produce sum and frequency heterodyne components at nominal frequencies of 93 and 107 megacycles, respectively, each modulated in phase and amplitude with time phase information concerning the rate of scan of the electron beam across the different phosphor strips of the screen structure 57 and with information concerning the intensity of the light emitted from these different phosphor strips. The aforenoted heterodyne interaction between these sum and frequency heterodyne components and the 100 megacycle subcarrier wave modulated with chrominance intelligence from mixer 48 will result in the production, at the common anode 55, of a 7 megacycle component constituted of (1) the sum frequency heterodyne component between the 93 megacycle component and the 100 megacycle chroma modulated component and (2) the difierence frequency heterodyne component formed by interaction between the 107 megacycle component and the 100 megacycle chrominance modulated signal. In addition there will appear at the common anode of photomultiplier tube 51 a 7 megacycle component equal to the sum of the original 7 megacycle components of electron stream intensity variations produced by the scanning of the screen structure by the electron beam of cathode ray tube 56. It may be shown that, by appropriate phasing adjustment of variable phase shifter 49 and variable phase shifter 60, there will be produced, as a result of all of the aforedescribed interactions, a signal at the output of variable phase shifter 60 which is in the form of a carrier wave of nominal frequency equal to the rate at which the electron beam of the cathode ray tube 56 traverses phosphor strips emissive of light of a particular color, and which bears such amplitude and phase modulation as will cause the emission, from the screen structure, of light of all three primary colors corresponding precisely to that intensity of these three primary colors which is indicated by the received color television signal.

In each of the aforedescribed embodiments the apparatus for deriving indications of the intensity with which ill? filfictron beam of the cathode ray tube impinges upon portions of its screen structure which are emissive of light of different colors has included devices which are sensitive to that light itself. It will be understood, however, that other devices may be used for this purpose. More particularly it is entirely feasible to incorporate, in the screen structure of the cathode ray tube, strip-like elements disposed in geometrical coincidence with the phosphors emissive of light of difierent colors respectively and responsive to electron impingement to emit different invisible radiations such as, for example, different Wave lengths within the ultra-violet spectrum. The radiation from the screen structure would then be sensed by appropriately sensitized devices which would operate to produce signals similar to those produced by the photoelectric devices illustrated and which would be utilized in a similar manner. In fact the aforementioned ultraviolet light emissive substances may be incorporated directly in the phosphor strips of the screen structure by iixing them with the phosphors prior to their deposition, in which case geometrical registry between the ultraviolet light emissive substances and the proper phosphor strips will be inherently assured.

The use of such separate materials for energizing the beam perceptive devices may prove particularly desirable because the phosphors themselves preferably have long radiation persistence whereas short radiation persistence is desirable to excite the maximum 7 megacycle component within the beam perceptive devices. Accordingly it may be advantageous to use ultra-violet light emissive substances having much shorter radiation persistence than the phosphor materials themselves.

It will be apparent that still other modifications of the particular apparatus illustrated will occur to those skilled in the art without departing from our inventive concept and accordingly we desire the latter to be limited in scope only by the appended claims.

We claim:

1. In a color television receiver which includes a cathode ray tube adapted for the emission of different radiations in response to impingement of the electron beam sequentially upon different portions of its screen structure, said radiations being emitted with intensities determined by the intensity of said beam: means for producing at least one electrical signal indicative of the intensities of said radiations and of the intervals during which they occur; means for comparing said produced signal with a signal indicative of the desired intensities of said radiations during corresponding time intervals; means responsive to the existence of a discrepancy between said compared signals to modify said produced signal; and means for utilizing said modified signal to control the intensity of said beam.

2. In a color television receiver which includes a cathode ray tube adapted for the emission of light of different colors in response to impingement of the electron beam sequentially upon dilferent portions of its screen structure, said light being emitted with intensities determined by the intensity of said beam: means responsive to emissions of light of at least one of said colors to produce at least one electrical signal indicative of the intensities of said emissions and of the intervals during which they occur; means for comparing said signal with a signal indicative of the desired intensities of said emissions during corresponding intervals; means responsive to the existence of a discrepancy between said compared signals to modify said produced signal; and means for utilizing said modified produced signal to control the intensity of said beam.

3. In a color television receiver which includes a cath ode ray tube adapted for the emission of different radiations in response to impingement of the electron beam sequentially upon different portions of its screen structure, said radiations being emitted with intensities determined by the intensity of said beam: means for producing at least one electrical signal indicative of the intensities of said emitted radiations and of the intervals during which they occur; means for comparing said produced signal with a signal indicative of the desired intensities of said radiations during corresponding intervals; means responsive to the existence of a discrepancy between said compared signals to modify said produced signal and to reduce said discrepancy; and means for utilizing said modified signal to control the intensity of said beam.

4. In combination: a cathode ray tube having a source of an electron beam and a screen structure with different portions respectively responsive to electron beam impingement to emit different radiations, each with intensity determined by the intensity of the impinging electron beam; means for deflecting said beam so as to cause it to impinge upon said different portions during different intervals; means responsive to said radiations to produce at least one electrical signal indicative of the intensities of said radiations and of the intervals during which they are emitted; means for comparing said signal with a signal indicative of the desired intensities of said radiations during corresponding intervals and for producing an error signal indicative of discrepancies between said signals; means responsive to said error signal to modify said radiation produced signal; and means for utilizing said modified signal to control the intensity of said beam.

5. The combination of claim 1 characterized in that said means responsive to said radiations comprises photosensitive devices disposed in radiation communicating relationship to said screen structure and responsive to the emissions of said radiations to produce said electrical signal indicative of the intensity of radiation.

6. In combination: a cathode ray tube having a source of an electron beam and a screen structure with different portions respectively responsive to electron beam impingement to emit different radiations, each with intensity determined by the intensity of the impinging electron beam; means for deflecting said beam so as to cause it to impinge upon portions emissive of the same radiation at a predetermined rate and to impinge upon portions emissive of different radiations during intervals occupying predetermined relative time-phase positions; an electron multiplier tube disposed in radiation communicating relation to said screen structure, said tube having a plurality of cathodes respectively responsive to different ones of said radiations to emit electrons in numbers determined by the intensities of said radiations, a common anode for intercepting electrons flowing in said tube, and a common set of dynodes between said cathode and said anode; means for applying to said cathodes, respectively, alternating signals of the same frequency and in the same relative phases as said impingements of different screen portions by said electron beam; means for applying to one of said dynodes an alternating signal of said predetermined frequency and representative at time intervals during any given cycle which are also in said relative time phase positions of the desired values of said diiferent radiations; means for deriving, from said anode, an alternating signal having a nominal frequency equal to said rate of beam traversal of successive portions emissive of the same radiation; and means for applying said derived signal to said cathode ray tube to control the intensity of said electron beam.

References Cited in the file of this patent UNITED STATES PATENTS 2,635,141 Bedford Apr. 14, 1953 2,648,722 Bradley Aug. 11, 1953 2,664,520 Wiens Dec. 29, 1953 2,697,742 Evans Dec. 21, 1954 2,701,850 Blayney Feb. 8, 1955

Images