US3562409A - Circuit arrangements including a color display cathode-ray tube of the index type - Google Patents

Circuit arrangements including a color display cathode-ray tube of the index type Download PDF

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Publication number
US3562409A
US3562409A US736712A US3562409DA US3562409A US 3562409 A US3562409 A US 3562409A US 736712 A US736712 A US 736712A US 3562409D A US3562409D A US 3562409DA US 3562409 A US3562409 A US 3562409A
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tube
gate
output
indexing
during
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US736712A
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Kenneth George Freeman
Michael Compton French
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US Philips Corp
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US Philips Corp
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/12—Picture reproducers
    • H04N9/16—Picture reproducers using cathode ray tubes
    • H04N9/22—Picture reproducers using cathode ray tubes using the same beam for more than one primary colour information
    • H04N9/24—Picture reproducers using cathode ray tubes using the same beam for more than one primary colour information using means, integral with, or external to, the tube, for producing signal indicating instantaneous beam position

Definitions

  • a gate is provided to prevent application of video alms rawmg signals to the display tube during the first few lines of each [52] U.S. C1 l78/5.4 field, and during this time a control signal is produced from [51] Int. Cl H04n 9/22 the indexing signal corresponding to the desired black level. [50] Field of Search 178/52, The control signal thus produced is applied to the display tube 5.4, 5.4F, 5.4H for the remainder of the field.
  • a color display cathode ray tube of the index type normally comprises a series of vertical strips of phosphor on its screen. These phosphors are arranged to luminesce with different colors when excited by an electron beam and, in order that the correct phosphor should be excited atall times, it is necessary to have information as to the particular phosphor color which the beam is exciting at all times. In orderto do this so called indexing strips are provided between groups of color strips. Thus a signal derived from scanning the indexing strips will provide information as to the beam position relative to the color strips.
  • the indexing strips are usually arranged to emit ultraviolet radiation on being scannedlby the electron beam, and this radiation is picked up by an ultraviolet radiation-sensitive element provided inside or outside of the tube.
  • the output of the element is processed to provide an RF carrier signal which is modulated with the color information obtained from the transmitted color television signal. After further processing the signal is applied to thecontrol grid (or the cathode) of the cathode ray tube to provide the color drive.
  • Some indexing tubes employ a pattem 'of indexing strips whose repetition period is notthe same as that of the color strips.
  • the color strips may be arranged in groups of three while the indexing strips may be provided after every two or four color strips.
  • the result of scanning the screen of such a tube is the provision of an indexing signal whose frequency is only related to that of the groups of color strips and is not equal thereto.
  • a receiver employing such a tube has to include inter alia a frequency divider for processing the index signal and this results in a possible phase ambiguity between the output signal of the frequency divider and the indexing signal obtained from the ultraviolet-sensitive element.
  • This ambiguity can be overcome by modifying the structure of the indexing strips on the left-hand side 'of the cathode ray tube at a position corresponding in vtime with the start of each line scan of the tube.
  • This modified index structure of so called frun in strips provides two signals, one at the normal index frequency, and another at a lower frequency. Thesetwo signals. enable the frequency divider to be started, at the beginning of each line scan, always in the same phase relative to the index signal.
  • this minimum or black level” current should normally be about 2k/ua.
  • the black level” current may also be caused to fall below this value by variations in cathode ray tube heater or E.H.T. supply or grid-cathode voltage variations.
  • the invention provides a circuit arrangement for automati cally reducing fluctuations which would otherwise occur in the amplitude of a signal which would be derived from scanning the indexing strips of a color display cathode ray tube of the index type in the absence ofa video signal applied to the tube, said arrangement comprising said tube.
  • a video channel including a gate in series therewith and co pled to a control electrode of said tube, means for deriving a control signal from said tube during times when the gate is blocked, which control signal varies with said amplitude.
  • the circuit arrangement is made to cut off the video signal for a period at the start of several, for example each, field scan. This may be arranged to occur, for example for the first five lines of the scan of each field, or for lines three to ten of these scans, and during this time the tube current or the indexing signal derived from the tube can be sampled to obtain the control signal which is then used to maintain the effective black level constant.
  • the control signal can conveniently be derived from the output of the indexing amplifier (which normally would feed a frequency divider). This point is the closest one to the frequency divider input which can normally be used.
  • the field scan starting times must include times when at least a portion of a line lying on the tube screen at substantlally the start of a field is scanned (ovcrscanning being normally employed).
  • the means for deriving the control signal is conveniently only operative when the video channel gate is blocked and to this end it may include a second gate in series therewith. which second gate is arranged to conduct during said field scan staning times and to be blocked during said remainder of the lines of the fields.
  • FIG. 1 shows a block diagram of the embodiment
  • FIG. 2 shows some alternative points from which the control signal may be obtained
  • FIG. 3 shows a block diagram of the gating signal generato of FIG. 2;
  • FIG.'4 shows a circuit diagram of the gating signal generator of FIG. 2;
  • FIG. 5 shows possible input and output waveforms of the gating signal generator of FIG. 2;
  • FIG. 6 shows a block diagram of FIG. 2
  • FIG. 7 shows a circuit diagram of the control amplifier of FIG. 2.
  • a color display cathode ray tube 1 of the index type has a video channel comprising a video amplifier 2 and a gate 3 coupled to a control grid thereof.
  • the tube 1 is provided with ultraviolet-emitting indexing strips (not shown) and a photomultiplier 4 is positioned to pick up radiation from these indexing strips.
  • the indexing signal supplied by the photomultiplier 4 is amplified in an amplifier 5 and coupled thence inter alia to a frequency divider 6 which supplied an output suitable for processing the video signal supplied to the tube in the normal way.
  • the index amplifier 5 also supplies a second gate 7 and a gating signal generator 8.
  • the generator 8 supplies gating signals in a manner which will be described hereinafter to gate 3 and 7 so that the gate 3 is blocked during field flyback times and additionally during the first few lines of each subsequent field scan on the tube screen (field scan starting times) and the gate 7 is rendered conducting during these field scan starting the control amplifier of times.
  • the gate 7 feeds the index amplifier output to a control amplifier 9 during the field scan starting times (when the video channel gate 3 is blocked).
  • the control amplifier 9 is arranged to derive a control signal from this index amplifier output and to apply it, via the video amplifier 2. to the control grid of the tube I to maintain the output of the amplifier substantially constant during the field scan starting times.
  • the amplifier 9 includes an integration circuit so that the control signal supplied therefrom to the tube 1 is maintained during the scanning of the subsequent lines of each field on the screen.
  • the amplifier 9 is supplied with a DC reference voltage from a source in order that the magnitude of the amplifier 5 output may be absolutely determined.
  • the generator 8 is also supplied with the trailing edges of field fiyback pulses by means of a lead 11.
  • the video drive to the tube 1 is blocked by the gate 3 during each field flyback time and for the first few lines of the subsequent field scan on the tube screen.
  • the control amplifier measures the magnitude of the indexing signal supplied from the photomultiplier 4 and the amplifier 5 and compares it with the DC reference from the source 10.
  • the signal resulting from this comparison is integrated and applied as a DC control signal bias to the grid of the tube 1 in order to maintain the index amplifier 5 output substantially constant during these first few lines of the field scan.
  • the resulting correction is maintained during the remainder of the field scan on the screen by means of the integrating action of the amplifier 9 and thus maintains the black level of the video signal subsequently supplied to the tube substantially constant and ensures that the output of the index amplifier 5 to the divider 6 never falls below a predetermined minimum value during each line scan.
  • FIG. 2 shows some additional circuitry normally provided around the tube 1 and alternative positions from which the input to the gate 7 may be derived.
  • the point 12 at the immediate output of the photomultiplier 4 may be used. but in this case the resulting correction to the "black level" will not take into account any variations with time in the gain of the index amplifier 5.
  • the same objection would apply if a point 13 were chosen at the output of a run-in amplifier 14. or if a point 15 were chosen from which a sample of the cathode ray tube cathode current could be obtained.
  • a point 16 at the output of the frequency divider 6 could be used but the signal obtained at this point would not vary linearly with the output of the index amplifier 5 and thus additional complications would be caused.
  • the point 17 at the output of the amplifier 5 is preferred.
  • FIGS. 3 and 4 show a possible embodiment of the gating signal generator 8 of FIG. I.
  • the index amplifier 5 feeds a reset terminal of a bistable circuit 19 via amplifier 18 which may be tuned.
  • a trigger terminal of the circuit 19 is supplied with the trailing edges of field flyback pulses from the lead 11.
  • An output 20 of the circuit I9 feeds the gate 3 and an output 21 is coupled to a trigger input terminal of a monostable circuit 22 having an "on" period equal to the time it is desired to open the gate 7 each time.
  • the output of the circuit 22 is coupled to the gates 3 and 7 in order to block the gate 3 and to open the gate 7.
  • the gate 3 is also blocked by the output 20.
  • FIG. 4 shows a possible circuit diagram of some of the blocks of FIG. 3.
  • the semiconductors can be obtained under the type numbers given under the Registered Trade Mark Mullard".
  • the signal from the index amplifier 5 is fed to the arrangement of FIG. 4 by means of the lead 25.
  • the circuit of FIG. 4 includes an extra monostable circuit 23 which may be used if the field time base does not supply a flyback pulse at the correct time for triggering the bistable circuit 19. If this is so the flyback pulse from the field oscillator may be fed to the monostable circuit 23 by means of the lead 24. the trigger pulse for the bistable circuit appearing at the lead 26.
  • the output of the monostable circuit 22 is fed to the gates 3 and 7 by means of the lead 27.
  • FIG. 5 Some possible waveforms appearing in the circuit arrangement of FIG. 4 in operation are shown in FIG. 5. together with the index signal (denoted by reference numeral 28) appearing in the index channel. Pulses appearing on the lead 24 front the field time base are denoted by 29 and the resulting output from the monostable circuit 23 is denoted by 30. The trailing edge of the output of the monostable 23 results in a pulse 31 appearing at the output 20 of the bistable circuit I9. This pulse is brought to an end by the appearance of indexing signals 32 at the lead 25. The trailing edge 33 thus generated gives rise to an output 34 on the lead 27 from the monostable circuit 22. This output is terminated at 35 after a time dependent upon the on" time of this monostable circuit. Thus.
  • the gate 3 is blocked at the end of the field fiyback time by the pulse 31. 33 and then. during the time taken to scan on the tube screen the first few lines of the next field. by the pulse 34. 35. During this latter time the pulse 34. 35 also opens the gate 7.
  • the pulses 34. 35 may also be used to remove the elevated run-in signal normally provided for in indexing circuits.
  • the signal 30 may also be used for field fiyback suppression.
  • FIGS. 6 and 7 show in more detail how the control amplifier 9 and the source 10 may be constructed.
  • the output of the index amplifier 5 is fed via a lead 36 to a further indexing amplifier 37 which incorporates the gate 7 and is supplied with the gating signal from lead 27 (FIGS. 3 and 4).
  • the amplifier 37 in turn feeds a first peak detector 38 which incorporates a comparator for comparing its output with a variable DC reference voltage from a source 39.
  • the detector 38 has an integration time long with respect to the line scan period.
  • the comparator output is fed to a second peak detector 40 having an integration time long with respect to a field scan period.
  • the second detector 40 enables a substantially DC control voltage to be produced proportional to the peak amplitude of the signal supplied to the detector 40. and hence which varies with the signal supplied on the lead 36.
  • This DC signal is amplified in a DC amplifier 41 and in the video amplifier 2 whose output is DC coupled to the control grid of the tube 1 by means of the lead 42.
  • a diode clipping circuit 43 is connected to the output of the first peak detector.
  • the diode is returned to a variable DC reference source (in this case a further source included in the box 39) so that excursions of the control signal supplied by the circuit of FIG. 6 in the direction representing a high black level are limited by the bias voltage applied to the diode.
  • the further index amplifier 37 may comprise three synchronously tuned stages with an emitter follower interposed between the second and third stages to reduce collector-base feedback effects in the last stage (FIG. 7). This circuit may be arranged to give a suitable overall bandwidth sufficient to ensure that its gain is substantially independent of variations in the index frequency.
  • the gain of the amplifier is stabilized by employing emitter degeneration and driving each stage from a voltage source. The gating of the amplifier is accomplished by switching a transistor 44 in the emitter circuit to the final stage.
  • the output of the amplifier is transformer coupled into the first peak detector 38 so that the earthy side of the detector can be returned to a set-black-level" control 45.
  • the maximum positive excursion at the output of the detector is limited by a diode 46 connected between the output and a "set-uncontrolled-black-level” control 47.
  • the integrating circuit formed by the I00 k0 resistor and 390 pf. capacitor enables efficient detection of the line component of the input signal to the detector to be achieved without excessive damping of the output stage of the tuned amplifier.
  • the second peak detector may consist of two emitter followers shown connected in cascade with an integrating circuit composed of a k9 resistor and 200 uuf. capacitor in the emitter circuit of the second stage.
  • the coupling from the detector 40 to the amplifier 41 includes an RF filter formed by the 2 K 29m sistor and 4K 7 pf. capacitor in order to ensure that all RF signals may be suppressed at the input to the amplifier M.
  • the overall gain may be about I00.
  • the gain of the video amplifier 2 (not shown in the diagram of FIG. 7) may be about l0 so that the overall gain in the control loop may be about 1,000. This has been found sufficient in one receiver to control the index signal amplitude at black level to within i 25 percent of its nominal level under all normal operating conditions.
  • a circuit arrangement for automatically reducing fluctuations which would otherwise occur in the ampiitude of a signal which would be derived from scanning the indexing strips of a color display cathode ray tube of the index type in the absence of a video signal applied to the tube comprising said tube, a video channel coupled to a control electrode of said tube, characterized in that the circuit arrangement comprises a gate in series with the video channel and means for deriving a control signal from said tube during at least a part of the times when the gate is blocked, which control signal varies with said amplitude, means for coupling said control signal to said tube durir ig each line scan to reduce fluc tuations in said amplitude, and means for blocking said gate during field scan starting times and rendering it conducting during the scan of the remainder of the lines of the fields on the tube screen.
  • the field scan starting times include times when at least a portion of a line lying on the tube screen at substantially the start of a field is scanned, the arrangement including means for deriving an indexing signal in response to thescanning of the indexing strips by the tube electron beam, an amplifier for amplifying said indexing signal and a frequency divider, the inputs of said means for deriving a control signal and of said frequency divider being coupled with the output of said amplifier.
  • the means for deriving the control signal includes a second gate in series therewith, which second gate is arranged to conduct during said field scan starting times and to be blocked during said remainder of the lines of the fields.
  • An arrangement as claimed in claim 5 including means for deriving an output in response to the scanning of the index' ing strips by the tube electron beam and with its output coupled to a reset terminal of a bistable circuit, means for coupling the trailing edge of the field flyback pulses to a trigger terminal of said bistable circuit, an output of said bistable circuit being arranged to block the video channel gate, and an output of the bistable circuit being coupled to a trigger input terminal of a monostable circuit having an on period equal to the time it is desired to open the second gate each time, the output of the monostable circuit being arranged to block the video channel gate and to open the second gate.
  • the means for deriving a control signal comprises a peak-detector, a DC reference voltage source, and a comparator for comparing the peak-detector output with the DC reference, the resultant circuit coupling the peak-detector output with the tube having an integration time long compared with a field scan period.
  • a color television receiver of the type having an indexing type color display tube, a source of video signals, means applying said signals to said tube, means for deriving indexing signals from said tube, and a source of field flyback pulses; the improvement comprising means connected to said source of flyback pulses and said means for producing said indexing signal for producing a control signal responsive to the level of said indexing signals during only predetermined lines of each field, said means for applying said video signals to said tube comprising gate means, means for blocking said gate means during said predetermined lines, and means for maintaining current in said tube at a predetermined minimum level comprising means fonapplying said control signal to said tube during the remainder of the lines of each field.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Video Image Reproduction Devices For Color Tv Systems (AREA)
  • Processing Of Color Television Signals (AREA)
US736712A 1967-06-16 1968-06-13 Circuit arrangements including a color display cathode-ray tube of the index type Expired - Lifetime US3562409A (en)

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GB27918/67A GB1186067A (en) 1967-06-16 1967-06-16 Improvements in or relating to Circuit Arrangements including a Colour Display Cathode Ray Tube of the Index Type

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US2813273 Expired USRE28132E (en) 1967-06-16 1973-02-05 Circuit arrangement including a colour display cathode-ray tube of the index type

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AT (1) AT287091B (xx)
DE (1) DE1762430C3 (xx)
GB (1) GB1186067A (xx)
NL (1) NL6808353A (xx)
SE (1) SE337639B (xx)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3872348A (en) * 1972-07-26 1975-03-18 Crosfield Electronics Ltd Spot positioning control for display tubes
US3977022A (en) * 1972-01-03 1976-08-24 Sunstein David E Cathode-ray tube image presentation system of the indexing type and timing system useful therewith
US4207591A (en) * 1978-02-09 1980-06-10 Rca Corporation Gated automatic beam current limiter in a video signal processing system
US5268615A (en) * 1991-08-30 1993-12-07 Sextant Avionique Device for the [servo-] control of the cut-off voltage of a cathode-ray tube by measurement of luminance

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5544268A (en) * 1978-09-25 1980-03-28 Sony Corp Color television receiver

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2967210A (en) * 1955-06-30 1961-01-03 Rca Corp Delay-compensated indexing system
US3201510A (en) * 1959-05-22 1965-08-17 Philips Corp Circuit arrangement in a color television receiver of the beam index type
US3234324A (en) * 1960-08-10 1966-02-08 Philco Corp Color television receiver employing both ambiguous and unambiguous index signals
US3305628A (en) * 1963-03-08 1967-02-21 Hitachi Ltd Phase-correcting device in beam-indexing color television receiver

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2967210A (en) * 1955-06-30 1961-01-03 Rca Corp Delay-compensated indexing system
US3201510A (en) * 1959-05-22 1965-08-17 Philips Corp Circuit arrangement in a color television receiver of the beam index type
US3234324A (en) * 1960-08-10 1966-02-08 Philco Corp Color television receiver employing both ambiguous and unambiguous index signals
US3305628A (en) * 1963-03-08 1967-02-21 Hitachi Ltd Phase-correcting device in beam-indexing color television receiver

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3977022A (en) * 1972-01-03 1976-08-24 Sunstein David E Cathode-ray tube image presentation system of the indexing type and timing system useful therewith
US3872348A (en) * 1972-07-26 1975-03-18 Crosfield Electronics Ltd Spot positioning control for display tubes
US4207591A (en) * 1978-02-09 1980-06-10 Rca Corporation Gated automatic beam current limiter in a video signal processing system
US5268615A (en) * 1991-08-30 1993-12-07 Sextant Avionique Device for the [servo-] control of the cut-off voltage of a cathode-ray tube by measurement of luminance

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DE1762430C3 (de) 1978-06-29
SE337639B (xx) 1971-08-16
DE1762430A1 (de) 1970-06-18
GB1186067A (en) 1970-04-02
DE1762430B2 (de) 1977-11-17
NL6808353A (xx) 1968-12-17
USRE28132E (en) 1974-08-27
AT287091B (de) 1971-01-11

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