US2900562A

US2900562A - Electron beam controlling apparatus

Info

Publication number: US2900562A
Application number: US482445A
Authority: US
Inventors: Jr Leslie L Burns
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1955-01-18
Filing date: 1955-01-18
Publication date: 1959-08-18
Anticipated expiration: 1976-08-18

Description

Aug. 18, 1959 L. BURNS, JR 2,900,562

ELECTRON BEAM CONTROLLING APPARATUS BY 0m Hmm/fg Allg- 13, 1959' L. 1 .,BURNS, .AR 2,900,562

ELEcTRoN BEAM coNTRoLLrNG APPARATUS Filed Jan. .8, 1955 2 Sheets--Sheet 2 VVV l +15 Imm/f BY @yd/Lm United States Patent O ELEcrRoN BEAM coNrRoLLING APPARATUS Leslie L.. Burns, Jr., Princeton, NJ., assgnor to Radio Corporation of America, a corporation of Delaware Application January 18, 1955, Serial No. 482,445

12 Claims. (Cl. 315-18) The present invention relates to novel television imagescanning apparatus and, particularly, to such apparatus wherein a target screen made up of a plurality of areas m of respectively different characteristics is scanned by one I' m01' e electron beams.

Certain forms of color television image-reproducing apparatus, for example, include a cathode ray tube having a screen made up of a plurality of groups of horizontally disposed strips of elemental size and of respectively different component color light emitting characteristics and employ one, or more electron beams which scan along the strips in a predetermined fashion, parallel thereto, to reproduce the television image. In the case of such arrangements, exactness of scanning or tracking of the strips by the beam or beams is necessary for proper image rendition. One general form of tracking arrangement is that which provides suitable indicia in the target screen which produce tracking index signals in response to electron beam impingement, with the location of such indicia in relation to strips of predetermined characteristics being preselected in order to give sense or direction to the index signals thus produced.

One problem which is present in many tracking schemes involving elements which provide index signals in response to electron impingement is that of crosstalk between ythe image-representative video signals and the index signals. That is, for example, where the intensi-ty or the timing of the index signals is intended to aiford information regarding the extent of tracking deviation or error, it has been found that the intensity of the video signals has an undesirable effect upon the index signals lidelity, so that erroneous information as to tracking position results.

It is, therefore, a primary object of the present invention to provide novel electron beam tracking means.

Another object of the invention is that of providing means for tracking one or more electron beams in a scanning cathode ray tube, which means are responsive substantially solely to beam position.

A further object of the invention is the provision of means for tracking one or more electron beams in a scanning tube, which means are substantially free of the inuence of extraneous information such as image content.

In general, the present invention provides, in accordance with an illustrative embodiment, an electron beam tracking arrangement in which tracking-signal indicia afford signals representative of beam scanning position in response to electron impingement. Means are provided for elfectively preventing the tracking apparatus from responding to information other than that actually representative of beam positioning. In this manner, the tracking function is rendered independent of irrelevant factors such as image content and the like.

As applied to a color kinescope tracking arrangement, for example, in which the relative brightness values of the component colors of the image have an error-producing effect upon the tracking function, means are pro- Patented Aug. 18, 1959 ICC vided for unbalancing the tracking circuits in accordance with the intensity ofthe color or colors likely to have such effect. Thus, the invention will be understood as eifectively subtracting image signals from the tracking index signals.

Additional objects and advantages of the present invention will become apparent to those skilled in the art from a study of the following detailed description of the accompanying drawing, in which:

Fig. 1 illustrates, by way of a block and schematic diagram, a color television receiver embodying the principles of the present invention in accordance with one form thereof;

Fig. 2 illustrates certain wave forms to be described;

Fig. 3 is a schematic diagram of circuitry suitable for use in performing certain of the functions indicated in Figi. 1 in accordance with one form of the invention; an

Figs. 4 and 5 are schematic diagrams of additional forms of the invention.

Referring to the drawing and, particularly, to Fig. 1 thereof, -there is shown an illustrative color television receiver which may be of any suitable type. An antenna 10 intercepts broadcast signals which may, for example, be of the presently standardized color television variety and which may be viewed as comprising a rst carrier wave which is amplitude-modulated by black and white image information and a sub-carrier wave which is phase and amplitude-modulated by information regarding the hue and saturation of the television subject. Such signals are applied by the antenna to the receiver section 12 which is represented diagrammatically as a block containing the usual RF amplifer, converted, IF amplifier and second detector stages. The detected output signals from the receiver section 12 are applied to suitable color translator circuits 14 which provide simultaneous red, green and blue color representative video signals at the output leads 16, 18 and 20. Circuitry suitable for deriving simultaneous red, green and blue signals from signals standardized by the Federal Communications Commission on December 19, 1953 may be found, for example, in the book entitled Practical Color Television for the Service Industry, revised edition, April 1954 (second edition, rst printing), published by the RCA Service Company Inc.

In the interest of simplicity of presentation, Fig. l illustrates the apparatus 21 for applying such simultaneous signals to the color image reproducing kinescope 22 as comprising a commutator device having four

stationary sectors

24, 26, 28 and 30 and a rotating contact member 32 which successively contacts the stationary sectors. In practice, the apparatus 21 would comprise electronic sampling means. The red, green and blue signals are applied, respectively, to the

sectors

24, 26 and 28 and the fourth sector 30 is also provided with the same green video signals as those applied to the sector 26, for reasons which will become apparent. The contact member 32 is electrically connected, by way of illustration, to the cathode 34 of the kinescope whose control electrode 36 is illustrated as connected to a suitable background potential source 38. An electrostatic focusing electrode 40 for focusing an electron beam 42 produced by the cathode 34 is connected to a suitable positive potential terminal. A nal anode 44, which may be in the form of a conductive coating on the interior of the kinescope cone portion, is also provided with a high positive operating potential from the terminal 46. A conventional electromagnetic dellection yoke 4S comprising horizontal and vertical deflection windings is energized with deflection sawtooth currents of television line and eld frequencies from scanning circuits 50 which receive synchronizing pulses derived from the received signals in the Section 12.

The color image reproducing color kinescope 22 also includes a target screen 52 which is, by way of illustration, of the horizontal line phosphor strip variety shown more clearly in the enlarged fragmentary view of Fig. 2. That is, the target screen 52 is made up of a plurality of triads of phosphor strips, horizontally disposed, with thestrips arranged in the sequence R, G, B, R, G, B. The kinescope is additionally provided with an auxiliary deflection coil 54 for producing a high frequency wobbling of the electron beam, so that the beam is caused to trace a pattern (e.g., sinusoidal) with respect to the phosphor strips of a triad, such as that indicated in Fig. 2(a) by the dotted line `56. Specifically, -and by way of example, the coil `54 may be energized from a wobble oscillator 57 which provides a color sub-carrier frequency wave (e.g., 3.6 megacycles). The oscillator 57 may be synchronized with the color sub-carrier wave by means of the color synchronizing bursts which occur during the horizontal blanking intervals of the blanking signal irnmediately following the horizontal scanning synchronizing pulses. Reference may be made to an article entitled The NTSC Color-TV synchronizing Signal which appeared in the February 1952 issue of Electronics (Mc- Graw-Hill Publishing Company, Inc.), for a detailed description of color synchronizing bursts. While the foregoingdoes not constitute a part of the present invention, it may be noted briefly that, since the color information in accordance with present standards is transmitted as phase and amplitude-modulation of a sub-carrier wave, it is necessary to provide some means for synchronizing the receiver color decoding or translating circuits with the encoding apparatus of the transmitter so that selection of the several color signals may be made. The bursts, therefore, comprise several cycles of sub-carrier wave frequency of xed phase, whereby to provide a reference phase for the color translating sections of the receiver.

By virtue of the high frequency wobble of the electron beam 42, the beam is caused to traverse the phosphor strips in the sequence R, G, B, G, R, G, B. Since the beam traverses the green phosphor strip twice as often as it does each of the other color phosphor strips, the two green commutator sectors 26 and 30 are provided. With the commutator member 32 rotated at the subcarrier rate of 3.6 megacycles (in synchronism with the wobble frequency), the red, green and blue color video signals are caused to control the intensity of the beam at the same time that the beam is on the corresponding phosphor strips of the target 52.

As has been stated, color image reproducing arrangements of the type described normally require means for insuring that the electron beam of the kinescope properly tracks the phosphor strips. In accordance with one form of tracking arrangement illustrated herein by way of example, each of the green phosphor strips G is provided with a backing layer 60 of a material capable of emitting ultra-violet light in response to electron impingement. A photocell 62 receives the ultra-'violet light through a window 64 and provides a current in the lead 66 indicative of the traversal of the ultra-violet strips 60 by the sinusoidally Wobbled electron beam. This current is applied to a servo amplifier and associated tracking control circuits included generally within the block `68, which circuits also receive a reference subcarrier wave from the wobble oscillator `57. The output of the tracking control circuits comprises, in the usual operation of such arrangements, a signal in the nature of a correction voltage which may be applied to a correction coil 70 for causing the electron beam to be repositioned vertically so as to track the phosphor strips in a desired manner. The correction winding 70 may be of any suitable type capable of producing vertical shifting of the position of the electron beam 42,

As described thus far, the receiver shown in the drawing is capable of producing color images by virtue of the application of color 'video signals in synchronism with the beam wobble. Such image reproduction, however, depends upon proper beam tracking, as will be appreciated. In order that the utility of the present invention as -applied to such apparatus may be better appreciated, the general operation of one form of tracking control arrangement will be described briey. As will be seen from Fig. 2, the electron beam spot 42 travels along a sinusoidal path '56 and, when properly tracking, crosses the ultra-violet index strip 60 of a given triad twice during each wobble cycle. The output signal of the phototube 62, therefore, during proper tracking will comprise a series of pulses 74 which are equally spaced in time and which occur at twice the wobble frequency, or at the rate of 7.2 megacycles per second. When the electron beam 42 is erroneously shifted upwardly to an extreme position so that the negative peaks of the sine wave 56 fall on the ultra-violet strip 60, the tracking index signals will occur, as shown in Fig. 2(c), at the rate of 3.6 megacycles per second and phased as shown by the pulses 74. The tracking control circuits 68 derive a correction signal by comparing the phase of the received pulses with the reference wave from the oscillator 56 and apply the correction voltage to the winding 70 for moving the beam downwardly to its proper position.

Conversely, if the electron beam is erroneously shifted downwardly so that only the positive peaks of the sine wave 56 strike the ultra-violet light-emitting index strip 60, the pulses from the phototube 62 will be as indicated by the pulses 74 in Fig. 2(d). The pulses 74" occur at the rate of 3.6 megacycles per second and are phased differently (i.e., displaced) from the pulses 74 which were produced by the beam in its uppermost erroneous position. In response to the pulses 74, the tracking control circuits produce a correction voltage which, when appliedto the coil 70, produces upward repositioning of the electron beam 42.

It has been found in connection with beam tracking arrangements of the type generally described above that the operation of the tracking control circuits is subject to the influence of the content of the video signals. That is to say, the usual electron distribution of a scanning beam is of the so-called Gaussian type and the cross sectional area of such a beam increases with beam current. Since beam current is a function of the intended brightness of a given color in a tube of the type in question, it will be understood that the cross sectional area of the beam varies as the brightness content of the image being reproduced. Moreover, as the intensity of the beam is increased in order to reproduce a bright color, red, for example, the number of peripheral or tail electrons which will undesirably impinge upon the adjacent phosphor strip also will increase. Translating the foregoing into terms of its effect upon tracking accuracy, it will be seen that, for example, when the image being reproduced constitutes a bright red area, the electron beam when in the position shown by the spot 42 in Fig. 2(a) will be of high intensity and a portion of the beam electrons will unavoidably impinge upon the adjacent ultra-violet lightemitting strip 60. A pulse corresponding to such impingement upon the ultra-violet strip will appear in the output of the phototube `62 for application to the tracking control circuits y68. Since the tracking control circuits cannot normally distinguish between the pulses produced by actual passage of the beam across the green phosphor strip G and those produced by fringe electrons from the beam, a correction signal is produced by the tracking control circuits and applied to the correction winding 70, thereby causing the beam to be shifted upwardly. That is, the pulses produced in response to the impingemcnt of the ultra-violet light strip 60 by peripheral electrons from the beam when it is reproducing the red information cause the tracking control circuits to sense, albeit incorrectly, that the beam is too low, with a resultant undesirable upward repositioning of the beam. The same kind of error, but of the opposite sense, results when the image being reproduced contains a bright blue area, in which event peripheral electrons from the beam (when it traverses the blue phosphor strip) impinge upon the ultra-violet strip v60 to produce erroneous tracking information. J

The exact manner in which such error may be inadvertently caused by the video content of an image being reproduced will be more apparent from a consideration of the schematic diagram of Fig. 3 which illustrates one specific form of tracking control arrangement. Current pulses from the phototube 62, such as those shown in wave forms (b), (c) and (d) of Fig. 2 are applied to the terminal 66 in Fig. 3. The pulses are amplified by a stage 78 and are limited in amplitude by a limiter circuit 80 prior to application to the control grid 82 of a phase-splitter 84. Opposite phases of the pulses produced by the phototube are thus applied via the capacitors 86 and 88 to the control grids 90 and 92, respectively, of

comparator tubes

94 and 96 whose cathodes may, as shown, be connected to ground potential and whose anodes 98 and 100, respectively, are connected together at the common load terminal 102 at the upper end of the load resistor 104. The suppressor grid 108 of the comparator 94 receives a wave of the same phase and frequency as that of the wobble wave applied to the wobble coil 54, while the suppressor grid 106 is supplied with a wave of the opposite polarity (i.e., wobble phase plus 180). The control grids 90 and 92 of the comparator tubes are connected to suitable bias potential terminals 110 and 112, respectively, through grid-

leak resistors

114 and 116. The common load terminal 102 of the comparators is connected via a coupling capacitor 118 to the control electrode of an output'ampliier 120 which is of conventional form and which includes the beam position correction winding 70 in the load circuit of its anode 122.

Assuming that the winding 70 which is in circuit with the tube 120 is so oriented with respect to the kinescope 22 that increased current through the winding moves the electron beam 42 upwardly, while decreased current moves the beam downwardly, the operation of the circuit of Fig. 3 as described thus far will be as follows:

The amplifier 78 may include an even number of stages, so that the polarity reversal of an amplifier may be disregarded. The output signal of the amplifier 78 will, therefore, be understood as being a signal of the same phase as the current produced by the photocell 62 which, as pointed out supra, is illustrated by wave forms (b), (c) and (d) of Fig. 2. After passage through the limiter stage 80, the amplied photocell signal is applied to the comparator `96 and the opposite phase is applied to the comparator 94, the phase reversal being accomplished in the phase splitter 84. Assuming that the beam 42 has shifted upwardly so that the negative peaks of the wobble wave occur on the ultra-violet strip 60 which is super-imposed on the green phosphor strip, the output current pulses of the photocell will comprise the pulses 74 which are of the opposite phase from the wobble Wave described by the beam. The

comparator tubes

94 and 96 are so biased that, normally, the current through the winding 70 is sufficient to maintain the beam in a centered position. When the input signal to the control grid of the comparator 94 is in phase with the wave applied to the suppressor grid 108, however, that tube will conduct more heavily, Ias will the tube 96, causing the voltage at the terminal 102 to decrease, thereby lowering the potential of the control grid 120 of the output amplifier 120, with the result that current through the winding 70 is decreased in an amount sufficient to move the beam 42 downwardly to its correct position.

Conversely, if the beam erroneously moves downwardly in the scanning process, the photocell 62 will produce current pulses 74 (wave form (d) of Fig. 2), with the result that the pulses applied to the control grids and 92 of the comparator tubes will be substantially of the opposite polarity from the 3.6 megacycle wave applied to their suppressor grids. Conduction of both of the comparator tubes will, therefore, decrease, causing the potential of the terminal 102 to increase, thereby applying a more positive potential to the control electrode 10 of the output amplifier. The current conduction of the amplifier will thus increase to move the beam 42 upwardly to its proper position.

With the foregoing description in mind, it should be apparent that, for example, when the image being reproduced is a bright red scene so that the intensity of the electron beam 42 while it is traversing the red phosphor strip R is high such that peripheral beam electrons undesirably impinge upon the adjacent ultra-violet strip, pulses of current in the phototube will occur at the time of the pulses 74", causing the tracking control circuits to act as though the beam were too low. 0n the other hand, when a bright blue field is being reproduced, peripheral or fringe electrons from the beam while it traverses the blue phosphor strip will produce pulses in the phototube circuit of the phase of pulses 74', tending to cause the tracking circuits to move the beam upwardly. The present invention, therefore, and in ord'er to render the tracking control circuits substantially insensitive to such spurious signals as have been shown to result from video content, provides means which may be thought of generally as nnbalancing or counteracting the action of the tracking control circuits in accordance with the video content of the image being reproduced, so that those l circuits act only on photocell signals which are truly indicative of beam positioning. VIn the embodiment of Fig. 3, and as indicated generally by the leads 16' and 20' in Fig. l, a version of each of the red and blue video signals is applied to the tracking control circuits in such manner as to produce the desired unbalancing Specifically, the red and blue video signals are applied, with sync pulses extending in the positive direction, to the control electrode terminals and 132 of an amplifier 134 and a cathode-follower amplifier 136, respectively. The anode load terminal 138 of the amplifier 134 is coupled via a capacitor 140 to a point 142 on the grid bias resistor 114 of the comparator 94. Similarly, the cathode load terminal 144 of the amplifier 136 is connected via a capacitor 146 to a point 148 on the grid resistor 116 of the comparator tube 96. The

amplifiers

134 and 136 are so associated with the

comparator tubes

94 and 96 that conduction of the amplifiers varies the grid bias potentials applied to the comparator tubes. That is, for the condition of a bright red elds being reproduced by the kinescope 22, such that the tracking control circuits would otherwise tend erroneously to shift the beam upwardly, the negative-going video signal on the grid of the amplifier 134 will cause the potential at the terminal 138 to increase, thereby rendering the bias on the control electrode 90 less negative than the normal bias applied to the terminal 110. Such a decreased negative bias will increase conduction of the comparator tube 94, thereby increasing its conductivity. That is, the comparator 94 would, in the absence of the control bias applied via the amplifier 134, and in response to spurious photocell signals produced by a bright red spot, tend to decrease the potential of the terminal 102 in order to increase conduction of the output amplifier 120 to cause upward shifting of the beam. By virtue of the controlled bias applied to the comparator 94 in accordance with the invention, however, that tube conducts more heavily so that the potential at terminal 102 is decreased with an attendant decrease in conductivity of the output amplifier 120. The amount by which the conduction of the amplifier 120 is decreased as a result of the controlled bias applied to the comparator 94 may be adjusted to counteract substantially exactly the undesirable tendency of the tracking circuit to shift the beam up when a bright red field is being reproduced.

By reason of the cathode follower action of the amplifier 136, the reverse effect is caused to take place in the comparator 96. That is, when the image being reproduced is bright blue, so that the tracking circuits would otherwise undesirably tend to shift the beam downwardly, the negative-going blue video signal applied to the terminal 132 of the cathode follower 136 will produce a corresponding negative potential at the terminal 144 which, in turn, will increase the negative bias on the amplifier 96, thereby decreasing conduction in that tube to increase the positive potential at the terminal 102. Conduction of the output amplifier 120 is correspondingly increased in an amount sufficient to counteract the tendency of the tracking circuit to shift the beam downwardly.

From the foregoing it will be recognized that the embodiment of the invention shown in Fig. 3 produces unbalancing of the tracking circuits by varying the control electrode bias of the phase comparator tubes which serve to perform the tracking control function. In this manner, the normal tendency of the tracking control circuits to shift the beam up when a bright red field is being produced and to shift the beam down when a bright blue field is being produced is substantially counteracted. It will further be recognized that control of the comparator tubes as a function of the red and blue video signals is dictated in the embodiment thus far described by the fact that the red and blue phosphor strips are adjacent to the tracking index signal producing element or ultraviolet strip 60. Where the tracking index signal element is adjacent to color light producing elements other than red and blue, the video signals representative of such other colors would be employed in unbalancing the tracking control circuits.

Fig. 4 illustrates another form of the invention as applied to a horizontal line screen color kinescope of the type shown in Fig. 1. In the arrangement of Fig. 4, the comparator tubes 94 and 96' correspond to the

comparators

94 and 96, respectively, of Fig. 3 and the terminal 102' is the same as the load terminal 102 of Fig. 3. Again, as in the case fo the apparatus of Fig. 3, red and blue representative video signals are applied to the correction apparatus with the sync pulses extending in the positive direction. Specifically, such video signals are applied to the input terminals 150 and 152 of a difference amplifier comprising the

tubes

154 and 156, connected as shown. The cathodes of the

tubes

154 and 156 are connected to a common resistor 158, the anode of the tube 154 being connected directly to a source of +B potential, while the anode of the tube 156 is connected to +B through a load resistor 160 and, via a lead 162, to the load terminal 102' of the comparators.

Assuming the same facts as those set forth illustratively in describing the operation of the apparatus of Fig. 3, when the image being reproduced is bright red, the video signal applied to the terminal 150 will cause the potential at the cathode end of the resistor 158 to decrease in potential, thereby causing a corresponding decrease in potential at the anode lead 162. Since the lead 162 is connected to the load terminal 102', the conduction of the output amplifier 120" (corresponding to the amplifier 120 of Fig. 3) will be correspondingly decreased and the amount by which conduction of the amplifier 120" is thus decreased may be adjusted to counteract the amount by which it would otherwise be caused to increase by the action of the comparator tubes in response to the spurious signals produced in the photocell by the fringe electrons of the electron beams.

In the case of a bright blue image, the negative-going video signals applied to the terminal 152 will cause a decrease in conduction of the tube 156, thereby increasing the potential at its anode. The increased positive potential is applied to the load terminal 102 via the lead 162 to increase the conductivity of the output amplifier in an amount sufiicient to counteract the decrease in its conductivity which would otherwise be brought about by the action of the comparator tubes. It will thus be apparent that, in accordance with the form of the invention shown in Fig. 4, the video signal or image content compensating action takes place directly at the control electrode of the output amplifier which passes the beam shifting current through the correction coil 70.

Fig. 5 illustrates a further form of the invention by means of which compensation for the error-producing effect of image content is brought about. In the apparatus of Fig. 5, the compensating or unbalancing of the tracking control apparatus is accomplished by supplying a greater amplitude of error signal to the tracking control circuits of one of the error-indicating phases of photocell signal. That is, as has been explained supra, the comparator tubes of the tracking control circuits shown operate in response to the amplitude and phase of the signals derived by the phototube. When the photocell Signals are of the phase sho/wn by wave form (c) of Fig. 2 (i.e., pulses 74'), the tracking circuits tend to decrease the current in the correction winding 70 in order to shift the beam down. Conversely, pulses of the phase shown in wave form (d) of Fig. 2 cause the comparator tubes to increase the current through the correction winding for a corresponding upward shift of the electron beam. As has also been pointed out, the normal tendency of the tracking circuits is that of shifting the beam upwardly when the image being produced is bright red and shifting the beam downwardly when the image is bright blue.

A pair of mixer pentodes 164 and 166 are connected, as shown, with their cathodes joined at a common load terminal 168. The suppressor grid of the tube 164 is supplied with a 3.6 megacycle wave of the wobble phase (i.e., corresponding to the phase of the pulses '74" of Fig. 2) while the suppressor grid of the tube 166 is supplied with a 3.6 megacycle wave of the opposite polarity. Red and blue video signals of sync-positive polarity are applied, respectively, to the control electrodes and 172 of the tubes 164 and 166. The common load terminal 168 is coupled via a capacitor 174 to a point 176 on the grid-leak resistor 178 of an amplifier tube 180 which may, for example, be one of the two amplifier stages described in connection with Fig. 3 as following the phototube 62. Thus it will be understood that in Fig. 5, the block 78' is representative of one of the amplifier stages included in the block 78 of Fig. 3 and that the limiter 80, phase splitter 84,

comparators

94 and 96 and output amplifier 120 correspond to the same elements of the apparatus of Fig. 3.

In *the operation of the form of invention shown in Fig. 5, the conduction of the tubes 164 and 166 is balanced so that substantially no energy of 3.6 megacycles is present at the terminal 168. When the image being reproduced is bright red, for example, the negativegoing video signal applied to the control electrode 170 decreased the conductivity of the tube 184 so that there will appear at the terminal 168 a certain amplitude of 3.6 megacycle energy of the opposite polarity from the wobble phase.

In other words, the signal appearing at the terminal 168 and applied via the capacitor 174 to the control electrode of the amplifier 180 will be of the phase of pulses 74 in Fig. 2 and of sufiicient amplitude as to balance the effect of the spurious pulses produced in the photocell circuit by fringe electrons. Thus, the normal tendency of the tracking control circuits to cause a downward shift of the beam during a red field will be counteracted. On the other hand, when the image produced is bright blue, the negative-going video signal applied to the control electrode 172 of the tube 166 will decrease the conductivity of that tube to permit a greater amount of 3.6 megacycle energy of wobble phase to be 9 applied to the amplifier I180, thereby causing the tracking circuits to balance out the error which would otherwise result from the video content of the television subject.

While the invention has been described in accordance with certain speciiic embodiments indicated as applicable to a particular form of a tracking control arrangement, it will be understood that the principles of the invention are applicable to other types of tracking control circuits in which video compensation is desirable or necessary. For example, where an image reproducing kineoscope employs a plurality of beams for scanning simultaneously along strip-like elements of a target screen, one or more of the beams being modulated by a tag signal useful in identifying its position as determined by a phototube or the like, the present invention may be employed to counteract the inherent tendency of tracking control circuits (responsive to the amplitude of such a tag signal) to respond erroneously to an increased amplitude of derived tag information resulting from increased image brightness.

Hence it will be appreciated that the invention nds application in apparatus which includes a tracking arrangement for a plurality of beam components which scan a screen made up of a plurality of areas of respectively diierent characteristics and in which the tracking function depends upon 'the production of index signals which, in turn, depend upon the intensity of the beam components, regardless of whether the beam components comprise separate electron beams or a single beam which traverses diierent screen areas successively, as illustrated, for example, on the drawing.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

l. In image reproduction apparatus of the type comprising arcathode ray tube having means for causing a plurality of electron beam components to scan across a target screen made up of a plurality of areas of respectively different characteristics and tracking index signal-producing elements associated with the screen in a xed relation to selected ones of such areas for providing signals in response to electron impingement indicative of the relative position of at least one of the beam components with respect to the index elements, means for intensity-modulating such beam components respectively by signals representative of such respectively different characteristics; tracking control means associated with each tube for receiving such index signals and operative to correct the position of such beam components in accordance with such index signals, said index signals being undesirably subject to spurious eiects from such intensity modulation of said beam components so as to cause said tracking control means to respond erroneously to such spurious effects; means for providing a signal proportional to the diierence between the respective intensities of one of such modulating signals and another of such modulating signals; and means coupled to said tracking control means for counteracting the action of said tracking control means in response to a difference between the respective intensities of one of such modulating signals and another of such modulating signals, such counteraction being in such direction as to overcome the erroneous response of said tracking control means.

2.y Image reproduction apparatus comprising: a cathode ray tube having means for causing a plurality of electron beam components to scan across a target screen made up of a plurality of areas of respectively different characteristics and tracking index signal producing elements associated with the screen in a fixed relation to selected ones of such areas for providing signals in response to electron impingement indicative of the relative position of at least one of the beam components with respect to the index elements, and means for intensity modulating such beam components respectively with signals representative of such respectively different characteristics, tracking control means associated with such tube for receiving such index signals and operative to correct the position of such beam components in accordance with such index signals, said index signals being undesirably subject to spurious effects from such intensity modulation of said beam components so as to cause said tracking control means to respond erroneously to such spurious effects; means for providing a signal proportional to the difference between the respective intensities of one of such modulating signals and another of such modulating signals; and means coupled to said tracking control means and to said modulating means for counteracting the action of said tracking control means in response to a diierence between the respective intensities of one of such modulating signals and another of such modulating signals, such counteraction being in such direction as to overcome the erroneous response of said tracking control means.

3. In image reproduction apparatus of the type comprising a cathode ray tube having means for causing a plurality of electron beam components to scan across a target screen made up of a plurality of areas of respectively different characteristics and tracking index signal-producing elements associated with the screen in a fixed relation t0 selected ones of such areas for providing signals in response to electron impingement indicative of the relative position of at least one of the beam components with respect to the index elements; means for intensity-modulating such beam components respectively with signals representative of such respectively diEerent characteristics such that such index signals are inherently subject to spurious effects resulting from the intensity of such modulating signals, tracking control means associated with such tube for receiving such index signals and operative to correct the position of such beam components in accordance with the intensity of such index signals, said tracking control means being undesirably responsive to such spurious eiects; means for providing a signal proportional to the difference in intensity between selected ones of such modulating signals; and means coupled to said tracking control means and to said last named means for controlling the action of said tracking control means in response to and in accordance with a difference between the respective intensities of one of such modulating signals and another of such modulating signals, thereby to overcome the undesired response of said tracking control means to such spurious elects.

4. In image reproduction apparatus of the type comprising a cathode ray tube having means for causing a plurality of electron beam components to scan across a target screen made up of a plurality of areas of respectively diierent characteristics and tracking index signal-producing elements. associated with the screen in a iixed relation to selected ones of such areas for providing signals in response to electron impingement indicative of the relative position of at least one of the beam components with respectl to the index element, tracking control means associated with such tube for detecting error signals from said index signals and operative to shift the position of such beam components in a direction tending to correct the position of such beam components and in accordance with the intensity of such error signals, means for modulating such beam components respectively in intensity by signals representative of such respectively different characteristics such that spurious index signals are produced when one of such beam components is modulated by high-intensity signals so that said control means responds erroneously to said error signals to move said beam components in an amount proportional to the intensity of such modulation; means for producing a compensating signal proportional to the intensity of such modulation; and means coupled to said track control means and to said compensating signal producing means for counteracting the action of said tracking control means as a function of the intensity of one of such modulating signals, such counteraction being in the direction of overcoming the erroneous response of said tracking control means.

5. In image reproduction apparatus of the type comprising a cathode ray tube having means for causing a plurality of electron beam components to scan across a target screen made up of a plurality of areas of respectively different characteristics and tracking index signal-producing elements associated with the screen in a fixed relation to selected ones of such areas for providing signals in response to electron impingement indicative of the relative position of at least one of the beam components with respect to the index elements, correction means associated with such tube for identifying such index signals and operative to shift the position of such beam components in the direction of correcting the position of such beam components and in accordance with such index signals, means for modulating such beam components respectively in intensity by signals of such respectively different characteristics such that spurious index signals are produced when one of such beam components is modulated by high-intensity signals, said correction means being undesirably responsive to such spurious index signals; means coupled to said modulating means for producing a compensating signal proportional to the intensity of one of such modulating signals; and means coupled to said correction means for counteracting the action of said correction means as a function of the intensity of one of such modulating signals, such counteraction being in the direction of overcoming the undesirable response of said correction means to such spurious index signals.

6. Color image reproduction apparatus comprising a cathode ray tube having means for causing a plurality of electron beam components to scan across a target screen made up of a plurality of areas of respectively different color characteristics and tracking index signal producing elements associated with the screen in a fixed relation to selected ones of such areas for providing signals indicative of the relative position of at least one of the beam components with respect to the index elements, means for intensity modulating such beam components by signals representative of such respectively different color characteristics, said index signals being undesirably subject to spurious effects from such intensity modulation of said beam components; tracking correction means associated with such tube for receiving such index signals and operative to shift the position of such beam components in the direction of correcting the position of such beam components and in accordance with such index signals, said tracking correction means being undesirably responsive to said spurious effects such as to cause an erroneous shift of the position of said beam components, means coupled to said modulating means for producing a compensating signal which varies as a function of the intensity of at least one of such modulating signals, and means coupled to said tracking correction means and to said last-named means for counteracting the action of said tracking correction means as a function of the intensity of at least one of such modulating signals, such counteraction being in the direction of overcoming the undesirable response of said correction means to such spurious effects.

7. The invention as defined by claim 6 wherein said means for causing a plurality of electron beam components to scan said target screen comprises a source of a single electron beam and deflection means associated with said tube for causing said beam to undulate vertically as it scans and in such manner as to impinge successively, during such undulation, upon said areas of different color characteristics and at least one index element.

8. Image reproduction apparatus comprising a cathode ray tube having means for causing a plurality of electron beam components to scan across a target screen made up of a plurality of areas of respectively different characteristics and tracking index signal producing elements associated with the screen in a fixed relation to selected 'ones of such areas for providing signals indicative of the relative position of at least one of the beam components with respect to the index elements, means for intensity modulating such beam components by signals representative of such respectively different characteristics; tracking control means associated with such tube for receiving such index signals and operative to correct the position of such beam components in accordance with such index signals, said index signals being undesirably subject to spurious effects from such intensity modulation of said beam components such as to cause said tracking control means to respond erroneously to such spurious effects; means coupled to said modulating means for providing a compensating signal which varies as a function of the intensity of at least one of such modulating signals, and means coupled to said tracking control means for counteracting the action of said tracking control means as a function of the intensity of at least one of such modulating signals, such counteraction being in the direction of overcoming the erroneous response of said tracking control means.

9. The invention as defined by claim 8 wherein said means for causing a plurality of electron beam components to scan said target screen comprises a source of a single electron beam and deflection means associated with said tube for causing said beam to undulate vertically as it scans and in such manner as to impinge successively, during such undulation, upon said areas of different color characteristics and at least one index element.

10. Image reproduction apparatus comprising a cathode ray tube having a target screen made up of a plurality of groups of horizontally oriented strip-like elements, each group including at least first and second strip-like elements of respectively different characteristics and means for causing a plurality of electron beam components to scan across said screen horizontally, there being a beam component for each of said first and second striplike elements of a group; means responsive to the impingement of one of such beam components upon such first strip-like element of a group for producing a tracking index signal; tracking correction means associated with said last-named means for identifying such index signals and shifting the vertical position of such beam components vertically in the direction indicated by said index signals and in an amount which is a function of the intensity of such index signals; means coupled to said cathode ray tube for intensity modulating said beam components with signals representative of such respectively diierent characteristics, said index signals being undesirably subject to spurious inuence by such intensity modulation of said beam components; and means coupled to said modulating means and to said tracking correction means for applying signals from said modulating means to said tracking correction means to control the action of said tracking correction means as a measure of the intensity of the signal modulating the beam component which impinges upon such second strip-like element of the same group and in such manner as to compensate for the spurious influence of said beam component intensity modulation upon said index signals.

l1. Image reproduction apparatus comprising a cathode ray tube having a target screen made up of a plurality of groups of horizontally oriented strip-like elements, each group including at least first and second strip-like elements of respectively different characteristics and means for causing a plurality of electron beam components to scan across said screen horizontally, there being a beam component for each strip-like element of a group; and index signal producing element associated with said first strip-like elements of a group for producing a tracking index signal in response to electron impingement;

correction means associated with said last-named means for identifying such index signals and shifting the vertical position of such beam components as a function of the intensity of such index signals; means coupled to said cathode ray tube for intensity modulating said beam components with signals representative of such respectively dierent characteristics; said index signals being undesirably subject to spurious effects from such intensity modulation of said beam components so as to eause said correction means to respond erroneously to such spurious effects; means for providing a signal proportional to the intensity of the signal modulating that beam component which impinges upon such second strip-like element of the same group and means coupled to said last-named means and to said correction means for applying signals from said last-named means to said correction means to control the action of said correction means as a measure of the intensity of the signal modulating the beam component which impinges upon such second strip-like element of the same group, thereby to overcome the erroneous response of said correction means to said spurious effects.

12. Image reproduction apparatus comprising a cathode ray tube having a target screen made up of a plurality of groups of horizontally oriented strip-like elements, each group including at least rst, second and third striplike elements of respectively dierent characteristics arranged one above the other and means for causing a plurality of electron beam components to scan across said screen horizontally, there being a beam component for each strip-like element of a group; means responsive to the impingement of electrons upon such second striplike elements of a group for producing a tracking index signal; correction means associated with said last-named means for identifying such index signals and shifting the vertical position of such beam components as a function of such index signals; means coupled to said cathode ray tube for intensity modulating said beam components with signals representative of such respectively diterent characteristics, said index signals being undesirably subject to spurious effects from such intensity modulation of said beam components so as to cause said correction means to respond erroneously to such spurious effects; and means coupled to said modulating means for producing a compensating signal which is a measure of the intensities of the signals modulating the beam components which impinge, respectively, upon said first and third strip-like elements of the same group; and means coupled to said last-named means and to said correction means for applying said compensating signal to said correction means thereby to overcome such erroneous response of said correction means.

References Cited in the tile of this patent UNITED STATES PATENTS 2,490,812 Human Dec. 13, 1949 2,530,431 Huffman Nov. 21, 1950 2,664,520 Wiens Dec. 29, 1953 2,706,216 Lesti Apr. 12, 1955 2,777,087 Fromm Jan. 8, 1957