Thomson Licensing S.a.

Thomson Consumer Electronics Inc.

Rca Inc.

Thomson Multimedia Licensing S.a.

Thomson Licensing

Dal Frank Griepentrog

Jeffrey Owen Allender

Leroy S Wignot

Brian Jonathan Cromarty

John Barrett George

William A Lagoni

Gene K Sendelweck

David Ross Jackson

An apparatus and a method for protecting a video display device, having an anode and a cathode, against excessive beam current conditions. In particular, the present invention protects the video display device against zero-biasing of the device, wherein the cathode driver circuit is supplied by a plurality of power supplies and the loss of anyone of the power supplies causes zero-biasing of the cathode. The invention provides, in a video display device () having an anode () and a cathode () for generating and controlling beam currents in the display device, a protection circuit comprising: a source of video signals (); a driver circuit () coupled to the source of video signals and the cathode (), the driver circuit coupled to a driver circuit power supply (+12V,+215V), the driver circuit causing a cathode voltage to be generated on the cathode in response to the video signals and the driver circuit power supply; a high voltage power supply (X) coupled to the anode () for providing high voltage accelerating potential in the display device; and a shutdown circuit () coupled to the driver circuit power supply and the high voltage power supply, the shutdown circuit disabling the high voltage power supply if the driver circuit power supply voltage decreases below a threshold level.

Video display protection circuit

A signal processor which provides non-linear transfer functions provides a processor output and non-linear inflection points that are referenced to a common bias. The processor output and the non-linear inflection points each exhibit rejection to time variant common-mode variations.

Non-linear signal processor

A video processing system includes a video output driver stage which is capable of automatically self-regulating the peak beam current output provided to a display. The system includes a video output driver stage with a video signal input and a video signal output for providing an amplified video signal. The video output driver stage comprises means for amplifying the video signal input to form the video signal output and conveying the amplified video signal output to the image reproducing display device. The system further comprising a sensing output for providing thereat a sensed signal representative of current conducted by said image reproducing display device. The system also includes a sensing and control means for sensing the sensed signal and for providing a feedback signal to an input component of the video output driver stage for limiting the current conducted by said image reproducing display device to a predetermined value.

Video output stage with self-regulating beam current limiting

A method and system for implementing a screen saver function is described. A peak value of a characteristic such as beam current magnitude of a video signal being processed is determined. An average value of the same characteristic of the video signal is also determined. Changes in this average value is additionally monitored. Therefore, the characteristic of the video signal is adjusted only if the peak value exceeds a first threshold and a change less than a second threshold is detected in the average value.

Automatic screen saver

Unintentional emissions are controlled responsive to the spectral content of the display signal. A video display apparatus comprises a cathode ray tube responsive to a video signal. A processor controls a bandwidth of the video signal coupled to the cathode ray tube in response to an emission control signal. A generating device is coupled to the processor for generating the emission control signal responsive to a component of the video signal.

Emission control in a video display

Generation of unintentional emissions are controlled by analysis of display signal content processed for scanning beam velocity modulation. An apparatus for scanning beam velocity modulation comprises a scanning velocity modulation signal processor for generating an scanning velocity modulation deflection signal responsive to a scanning velocity modulation signal. A generator supplies a feed forward signal to the processor for controlling the scanning velocity modulation deflection signal amplitude in response to a component of the scanning velocity modulation signal.

Emission control with scanning beam velocity modulation

Unintentional emissions are controlled responsive to the spectral content of the display signal. A video display apparatus comprises a cathode ray tube for video image display. A processor controls a magnitude of a video image display signal coupled to the cathode ray tube for display in response to an emission control signal. A generating means is coupled to the processor for generating the emission control signal responsive to a component of the video image display signal.

Control of emission in a video display

Display apparatus includes a kinescope cathode current sensor (,) coupled to a load (,) for developing a beam current measurement pulse during a beam current measurement interval. Overshoots in the pulses are suppressed by a pulse correction circuit (,) comprising a first capacitor (Ca) coupled from the load circuit (,) to a source of reference potential (Gr) via a switch (Q,); and a control circuit (Ca, Ra, Rb), responsive to the presence of the overshoot, for closing the switch for a predetermined length of time and for opening the switch otherwise. In an advantageous implementation of the pulse correction circuit the switch comprises a bipolar transistor (Q,) having an emitter (E) coupled to the source of reference potential (Gr) and having a collector (C) AC coupled to the load circuit (,) via the first capacitor (Ca); and the control circuit comprises a second capacitor (Cb) for AC coupling said load circuit to a base (B) of the bipolar transistor and a resistor (Ra) for DC coupling said base (B) to said source of reference potential (Gr). In an alternative irrplementation of the pulse correction circuit the switch comprises a field effect transistor (,A) provided with a gate (G) to drain (D) bypass diode (D,).

Apparatus for suppressing overshoots in kinescope beam current measurement pulses

A grid kick circuit for applying beam cut-off bias to the grid of a kinescope to provide spot burn protection. The circuit includes a first switching circuit having an output coupled to a first electrode of a grid kick capacitor and a second switching circuit having an output coupled to a second electrode of the capacitor and the grid. When beam blanking is not desired, charging current is supplied to the capacitor through a first current path from a first voltage source while the second switching circuit regulates the voltage at a second electrode of the capacitor and the grid. Current for the second switching circuit is provided by a second current path which is coupled to the first voltage source and is independent of the first path. When beam cut-off is desired, the first switching circuit clamps the first electrode of the capacitor to ground, the second switching circuit decouples the second electrode of the capacitor from the second voltage source, and the cut-off voltage developed across the capacitor is applied to the grid of the kinescope. Advantageously, the first and second current paths provide improved capacitor charging efficiency, the active pull down of the capacitor voltage provides increased cut-off speed and the grid bias voltage is regulated during normal operation when cut-off is not desired.

An AKB interface apparatus in a display system (,), includes a video signal processing IC (,) having outputs coupled via respective kinescope driver ICs (,) to respective kinescope cathodes (K,,K,,K,) for display of a color image, the signal processing IC having an input,for receiving an AKB input signal, the driver ICs having respective outputs (,) providing respective cathode current indicating signals (RP,GP,BP) An interface circuit (,) couples the cathode current indicating signals to the AKB input of the signal processing IC. The interface circuit comprises a load circuit (,) for generating a load voltage (Vo) in response to at least one of the cathode current indicating signals. A leakage correction circuit (,), responsive to said load voltage (Vo), feeds back a leakage correction current (Io) to the load circuit. The leakage correction circuit includes a keyed comparator (Q,,Q,,Q,) for comparing the output voltage of the load (,) with a reference potential during a vertical retrace pulse interval to provide a leakage indicating signal; and a controllable current source (Q,,Q,) is coupled to the keyed comparator and responsive to the leakage indicating signal for feeding back the leakage correction current (Io) to the load circuit (,). In one application the cathode current indicating signals are first combined (,) and then subjected to leakage compensation (,) for application to the processing IC AKB input. In another application, the cathode current indicating signals are individually leakage compensated and then combined (,) for application to the processing IC.

AKB interface circuit for kine driver IC

Supplementary grid blanking and spot burn protection are provided in a receiver/monitor (,) by a grid bias control circuit (,) including a blanking signal generator (,) that produces a blanking output signal (S,) devoid of any picture representative component whenever a vertical blanking signal (VB) or a horizontal blanking signal (HB) is present. A capacitor (C,) strips DC from the blanking signal and the resultant signal (S,) is applied to a modulation input (,) of a grid bias generator to produce an output grid bias reference voltage (Vr) modulated by the AC component of the blanking signal. The reference voltage (Vr) is coupled via a spot burn protection circuit (,) and a grid coupling circuit (,) to the control grids of three projection kinescopes (,). Distortions which may tend to appear in the grid blanking pulses are corrected by a high frequency correction circuit (,) coupled between an output (,) of the composite blanking generator (,) and an input (,) of the grid coupling circuit (,).

Television apparatus with supplementary kinescope blanking and spot burn protection circuitry

A direct current focus voltage applied to a focus electrode of a cathode ray tube that produces a blue image is set to slightly defocus the blue image for increasing the blue beam spot size. The increase in the blue beam spot reduces the saturation and allows brighter blue and increased blue video drive range. A passive network is coupled between an ultor electrode and the focus electrode to provide tracking of focus voltage-to-ultor voltage ratio. The tracking prevents voltage fluctuation of the ultor voltage produced by video loading from disturbing uniform defocussing in the entire blue image.

Focus voltage tracking circuit

Video signals to be displayed are applied via a video driver amplifier to the cathode electrode of a kinescope. A beam current sensor, also coupled to the cathode electrode, provides a beam current indicating signal. An AKB regulator, responsive to the beam current indicating signal, supplies a black level correction signal to the driver amplifier for regulating the black level of images displayed by the kinescope. A screen grid supply system is provided for controlling the G-2 (screen grid) voltage of the kinescope as a predetermined function of the black level correction signal thereby forming with the AKB regulator a dual feedback loop for providing black level regulation by both the driver amplifier and the screen grid thereby maximizing or extending the overall black level control range. Consequently, the high voltage screen control potentiometer normally required for setting screen grid bias may be completely eliminated if desired, or, in applications where it is retained, no adjustments are required subsequent to an initial adjustment.

Video display system with AKB responsive screen grid supply

A television receiver includes a scan velocity modulation circuit. An amplitude correction circuit couples vertical and horizontal parabola signals to the scan velocity modulation circuit so as to vary scan velocity modulation with displacement of beam position from the center of the screen. The parabola signals may be derived from a pincushion correction circuit of the television receiver, for example, from a diode modulator. The position-indicating parabolas may control amplifier gain within the scan velocity modulation circuit, output level limiting, or the amplitude of the differentiated luminance signal applied to the amplifier to provide scan velocity modulation reduction away from screen center.

Scan velocity modulation circuit

A microprocessor generates an output signal in accordance with user controlled sharpness selection. The output signal is supplied to a video processor and to a scan velocity modulation circuit for concurrently varying in the same sense the amount of picture sharpness produced by the scan velocity modulation circuit and by the video processor.

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Indianapolis, IN, United States of America

Dal Frank Griepentrog