Abstract: In a method of black level and gain control setting, including the steps of applying (42) at least two mutually differing control values (Vd1, Vd2) in a first predetermined ratio, and controlling (35, 3, 7, 15) the black level and gain in response to the at least two mutually differing control values (Vd1, Vd2), at least two mutually differing reference values (Iref1, Iref2) in a second predetermined ratio and corresponding to the at least two mutually differing control values (Vd1, Vd2) are applied (47) to the controlling step (35, 3, 7, 15), where a predetermined relationship exists between the first predetermined ratio and the second predetermined ratio, a first error value depending on a first control value (Vd1) and a first reference value (Iref1) is integrated (43) to obtain a black level setting value, and a second error value depending on a second control value (Vd2) and a second reference value (Iref2) is integrated (44) to obtain a gain setting value.

Abstract: An amplifier (60) provides an amplified video signal in response to a video input signal supplied thereto. A cathode current sensor (Q3), couples an output of the amplifier to the cathode of a kinescope (20) and also provides an output current (Ik) proportional to the kinescope cathode current. A feedback path (82) applies a portion of the sensed cathode current provided by the cathode current sensor to a circuit node (65 or 63) in the amplifier for imparting gamma correction to images produced by the kinescope. In one application the cathode current is apportioned (Q3, Q5) to provide gamma correction for the kinescope and to provide automatic kinescope bias (AKB) control.

Abstract: A transient improvement circuit is disclosed for cathode ray tube (CRT) amplifiers with automatic kinescope bias feedback circuits. An NPN transistor and a PNP transistor are provided, each having a collector, an emitter and a base. A video input signal is applied to the base of the NPN transistor. A first collector resistor is connected between the collector of the NPN transistor and a power supply voltage, the collector of the NPN transistor also being connected to the base of the PNP transistor. A first emitter resistor is connected between the emitter of the NPN transistor and ground, and the first emitter resistor has, connected in parallel therewith, a filter capacitor and a second emitter resistor connected in series with the filter capacitor.

Abstract: A cathode ray tube display in which a signal for detection of a cathode current is inserted into a part of the vertical blanking period of the video signal to be displayed, a cathode current corresponding to the signal for detection is detected, and a cathode voltage or a grid voltage is negative feedback controlled so that the detected cathode current becomes constant, thereby stabilizing the cathode current. The display has a local overscan circuit for executing a vertical scan on the screen with a width larger than a predetermined scan width only at a timing of the cathode current detecting signal inserted for a vertical blanking period, and even in the case where an underscan system to scan by a width smaller than a predetermined display screen width is used as a scan system of the screen display. The invention prevents a harmful visible display image by the cathode current detecting signal appears on the screen.

Abstract: A controllable current source in an AKB circuit applies a measurement current to a kinescope driver amplifier during selected lines of the vertical interval of a video input signal to induce a beam current in a kinescope coupled to the driver amplifier. A comparison circuit compares samples of the beam current obtained during the selected lines with a reference signal and applies a correction current to the driver amplifier for regulating a parameter (e.g., black level) of images displayed by the kinescope. A signal source, coupled to the measurement current source, inhibits production of the measurement current during retrace portions of the selected lines and enables production of the measurement current during trace portions of the selected lines. Advantageously, the signal source provides suppression of visual artifacts due to AKB operation when using direct view or projection kinescopes of a type in which pincushion correction is not applied during line retrace intervals.

Abstract: Control circuitry, in an AKB sample pulse generator, enables charging of a capacitor upon initiation of a vertical retrace pulse, initiates discharge of the capacitor in response to termination of the retrace pulse and concurrently produces an AKB output pulse having a width (W) determined by an RC time constant and having a delay time (Td) relative to initiation of the retrace pulse that is equal to the length (L) of the retrace pulse and that is independent of the value of the RC time constant. Advantageously, the AKB sample pulse delay time tracks variations, if any, of the retrace pulse and is unaffected by parameter variations of the RC components. Additionally, the sample pulse width can be controlled with analog simplicity and can be increased, for the same amount of overscan as compared with systems in which both pulse delay and width exhibit component sensitive delay times, thereby providing improved AKB control accuracy due to the increased "aperture" or sampling time.

Abstract: Known display devices include a video signal processing circuit with a black level setting circuit. This black level setting circuit measures the black level of the video signal, for example, during the field retrace interval by making use of an extra output of the video output stage. However, the measured black level has a line-frequency interference component which is caused by a parasitic capacitance in the display tube. The line-frequency interference component is fully compensated for by coupling one side of a secondary winding of a transformer, required for the focusing voltage to be generated, to a first capacitor, the other terminal of which is connected to the measuring input of the black level setting circuit, and by coupling at least a second and a third capacitor across the secondary winding of the transformer.

Abstract: A receiver includes a kinescope, a driver amplifier and an integrated automatic kinescope bias (AKB) circuit. A soft start circuit includes a timing capacitor, external to the integrated circuit, and a control circuit within the integrated circuit which limits the AKB current adjustment range during turn-on to a time determined by the external capacitor. The capacitor is effectively isolated from the integrated circuit to prevent discharge thereof by protection diodes of the IC whereby the time constant of the overall AKB circuit is substantially the same for both hot start conditions and cold start conditions thereby avoiding undesirable visual start-up artifacts such as black level and contrast shifts during warm-up of the kinescope for either a cold start condition or a hot start condition.

Abstract: A method for detecting the warm-up of a television CRT includes the following steps during a warm-up phase of the tube: providing the CRT with warm-up signals during predetermined line periods at the initial portion of frames; and detecting the cathode current of the tube during the occurrence of windows in correspondence with the predetermined line periods in order to enable black level regulation loops. The windows have a width smaller than a line period and are approximately centered on the line periods.