Abstract: A DC coupled system for automatically controlling the high frequency peaking content of a video signal is disclosed. The system includes a DC coupled control path comprising a peak detector for developing a control voltage representative of the high frequency content of the video signal exclusive of video signal DC components. The detector is preceded in the control path by a frequency selective network comprising an amplifier and a filter for shaping the frequency response of the control path such that high frequency video signal components exclusive of DC video signal components are passed to the peak detector. The frequency selective network comprises the cascode combination of a video signal amplifier transistor and a current source transistor which provides quiescent operating currents for the amplifier transistor. The filter is coupled to the junction of the amplifier and current source transistors, and includes a DC blocking network coupled between the junction and a point of reference potential.

Abstract: A television receiver includes means for generating a peaking component which is combined with a video signal to produce a peaked video signal, and a control circuit responsive to the peaked video signal during prescribed control intervals for automatically controlling a reference level of the video signal. The peaking component is attenuated during the control intervals to prevent the control network from responding to spurious signals including noise, which would otherwise be enhanced by the peaking generator and distort an output control voltage from the control circuit. In a system wherein the control circuit is arranged in a feedback loop with a peaking generator comprising a delay line, such attenuation also serves to stabilize the feedback control loop against oscillation.

Abstract: In a video signal processing system, an input capacitor AC couples video signals to a DC coupled video signal path, and to a DC coupled peaking signal path for generating a peaking component which is combined with video signals from the video path to develop a peaked video signal. A feedback control voltage for controlling the DC level of the video signal is stored by the input coupling capacitor, and is DC coupled to both the video path and the peaking path in a manner to reduce the likelihood of a DC offset error when the video signal and peaking component are combined. In an embodiment, the control voltage is coupled to the storage capacitor via a delay line included in the video path and which is coupled across the differential inputs of a differential amplifier with which the delay line coacts to generate the peaking component.

Abstract: The DC output level of a video signal amplifier is compensated to remain constant as the amplifier is gain controlled in response to a gain control voltage supplied from a gain control circuit which also supplies a DC compensation voltage to the amplifier. The DC compensation is preserved by means of an additional network which senses the DC bias of both the amplifier and the gain control circuit, and corrects a deviation of the amplifier bias and the gain control circuit bias from a prescribed mutual relationship. The sensed DC bias of the gain control circuit is also used to establish a black reference level for the video signal.

Abstract: Input video signals are applied to a video signal processor via an AC coupling capacitor and an input impedance. A gated control circuit operates periodically to develop a DC control voltage for establishing the DC black reference level of the video signal, at which time the control circuit forms a feedback loop with the video processor. The DC feedback control voltage is coupled via a feedback impedance to the AC coupling capacitor, which stores the control voltage, at the video processor input. The AC coupling capacitor exhibits a low impedance at signal frequencies, such that the input and feedback impedances form a voltage divider for sufficiently reducing the AC signal gain of the feedback loop to prevent the feedback control loop from oscillating at AC signal frequencies.

Abstract: An automatic kinescope beam current limiter for a television receiver includes a source of derived beam current representative voltage, a keyed sampling circuit for developing an output beam current control voltage on a charge storage capacitor in response to the derived voltage, and an auxiliary current path including an impedance coupled between the output capacitor and the source of derived voltage. In a normal beam limiting control mode, the control voltage from the sampling circuit serves to modify the television signal in response to the derived voltage in a direction to limit excessive beam current. In an abnormal control mode such as when the sampling circuit is inoperative due to disrupted keying, current is conducted via the auxiliary current path in response to the derived voltage to modify the control voltage on the capacitor with a sense and at a rate for limiting excessive beam current, to thereby preserve beam limiting capability.

Abstract: A circuit for generating a composite keying signal includes a burst gate circuit, a clipping circuit, and a voltage divider, in a color television receiver also including means for deriving horizontal and vertical blanking signals and a horizontal sync pulse from a composite color television signal containing a color burst component. The burst gate circuit responds to the lagging edge of the horizontal sync pulse to develop a burst gate pulse encompassing the burst interval. The clipping circuit and the voltage divider serve to clip and translate both the horizontal and vertical blanking signals, which are then combined with the burst gate pulse to produce a composite keying signal. The composite keying signal comprises a first pulse component of desired magnitude as determined by the clipping and voltage divider circuits and occurring during the blanking intervals, and a second pulse component as provided from the burst gate circuit, superimposed on the first pulse and encompassing the burst interval.

Abstract: A first resistive current path is DC connected between respective output terminals of push-pull color demodulator. A second resistive current path is DC connected between respective output terminals of a second push-pull color demodulator. An output color-difference signal is formed by a differential amplifier having one input DC connected to an asymmetrically positioned point in first resistive current path, and a second input DC connected to an asymmetrically positioned point in second resistive current path. Output color-difference signal corresponds to a combination of the demodulated signals, with a polarity relationship and magnitude ratio determined by the asymmetry of positioning of the takeoff points in the respective current paths. Output quiescent voltage is independent of the asymmetry of positioning of the takeoff points.

Abstract: A circuit for generating a composite keying signal comprises a burst gate circuit and a voltage translating network in a color television receiver also including keyed signal processing circuits and means for deriving horizontal and vertical blanking signals and a horizontal sync signal from a composite color television signal containing a color burst component. The burst gate circuit responds to the horizontal sync signal to develop a burst gate pulse encompassing the burst interval. A voltage level developed by the translating network in response to the horizontal and vertical blanking signals is combined with the burst gate pulse to produce a composite keying signal. The composite keying signal comprises a first pulse component of a desired level as determined by the translating network and ocurring during the blanking intervals, and a second pulse cmponent as provided from the burst gate circuit, superimposed on the first pulse and encompassing the burst interval.

Abstract: An automatic kinescope beam current limiter for a television receiver comprises a source of signal representative of kinescope beam current conduction, a first transistor responsive to the representative signal over first, second and third ranges of excessive beam currents above a threshold level, and a second transistor. A first control signal derived from the first transistor modifies the video signal peak-to-peak amplitude (contrast level) when beam currents above the threshold level occur. The output of the first transistor is selectively coupled to an input of the second transistor when beam currents beyond the first range occur. A second control signal derived from the second transistor modifies the video signal D.C. component (brightness level) to limit beam currents beyond the first range, whereby both the peak amplitude and D.C. components are modified over the second range.

Abstract: A video signal image reproducing system including a video signal processing channel, a kinescope driver for supplying amplified video signals to an image reproducing kinescope, a source of potential to which signals processed by the kinescope driver are referenced, and an adjustable brightness control network which provides a range of brightness reference voltages including a given voltage corresponding to a threshold conduction condition of the kinescope driver. The brightness network is biased from a voltage source from which the signal reference potential is derived. The signal reference potential is coupled to the kinescope driver, and to the brightness network such that the given voltage is produced when the brightness control is at a mid-range setting.

Abstract: Brightness control apparatus for a video signal image reproducing system including a video signal processing channel, a kinescope driver for supplying video signals to an image reproducing kinescope, and a source of substantially fixed potential to which signals processed by the kinescope driver are referenced. A comparator senses the substantially fixed reference potential and a blanking level which occurs during periodic blanking intervals of the video signal, and provides an output control signal indicative of the voltage difference between the reference potential and the blanking level. The control voltage is applied to the video channel for translating the blanking level in a direction to minimize the voltage difference, to thereby establish the conduction of the kinescope driver during image intervals of the video signal at a level corresponding to a desired image black level condition when such condition is manifested by the video signal.

Abstract: An image brightness control arrangement for a color video signal processing system including a plurality of amplifiers each responsive to luminance and separate color difference signals for developing color representative output signals. A brightness control (e.g., a potentiometer) also is included for varying a brightness determinative D.C. level of the luminance signal. A locally generated periodic keying signal, occurring during periodic image blanking intervals of the video signal and of a magnitude which may vary undesirably, is coupled to each of the amplifiers for establishing a reference level for the color difference signals, as described in U.S. Pat. No. 3,970,895. A derived signal indicative of the magnitude of the keying signal is coupled to the brightness control for establishing a brightness control range thereof.

Abstract: A beam current limiter for a kinescope responsive to video signals coupled to the kinescope via a video signal transmission channel comprises means for providing a control signal representative of the magnitude of kinescope beam current above a predetermined level. The control signal is related to the amount by which the beam current exceeds the predetermined level. When beam current exceeds the predetermined level by an amount within a first range of beam current, the control signal is coupled to the signal transmission channel to vary the peak amplitude of the video signal to inhibit beam current above the predetermined level. When beam current exceeds the predetermined level by a relatively greater amount within a second range of beam current, the control signal is coupled to the signal transmission channel to vary both the peak amplitude and the D.C. level of the video signal to inhibit beam current above the predetermined level.

Abstract: A service switch in a color television receiver for simulating quiescent signal conditions to permit set-up adjustment of a color image reproducing kinescope responsive to luminance and chrominance signals processed by luminance and chrominance channels of the receiver. Separate, adjustable image brightness and contrast control networks are coupled to the luminance channel for respectively varying a D.C. level and peak-to-peak amplitude of the luminance signal. The switch has "normal" and "service" positions and is coupled to the chrominance channel, brightness and contrast networks, and a vertical deflection circuit of the receiver. In the "service" position, the switch renders the chrominance channel inoperative to process the chrominance signal, and disables vertical scanning of the kinescope. The switch also causes the brightness and contrast networks to establish predetermined values of the D.C.