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 integratable third harmonic signal generator comprises an amplitude limiting amplifier, a linear amplifier, and a signal combining network. A sinusoidal input signal is coupled to the limiter and linear amplifiers. The limiting amplifier generates a square wave signal containing a first harmonic (fundamental) component at the frequency of the input signal, and higher order odd harmonics including a desired third harmonic frequency. The signal gain of the linear amplifier is set so that the magnitude of the output signal from the linear amplifier is sufficient to cancel with the first harmonic of the square wave output signal from the limiter amplifier, when these output signals are combined in the combining network. A resulting signal developed at the output of the combining network contains the desired third harmonic component, as well as higher order harmonics at acceptably reduced levels relative to the third harmonic component, to the substantial exclusion of the first harmonic component.

Abstract: An arrangement for symmetrically gain controlling a differential amplifier is disclosed. A control circuit including first and second similarly arranged transistors coupled between points of operating potential develops first and second control voltages of prescribed magnitude at collector outputs of the transistors. The first transistor is biased to provide the first control voltage at a fixed, prescribed level related to the gain control bias requirements of the amplifier. The second control voltage varies symmetrically with respect to the first control voltage in response to the setting of a potentiometer coupled to a bias circuit of the second transistor.

Abstract: A circuit is described for protecting a semiconductor junction device such as a transistor against damage from high voltage transients that can be produced by kinescope arcing in a television receiver. The protected device is coupled to a circuit point at which the transients can appear. The protection circuit comprises a normally nonconductive protection transistor with a collector coupled to a source of operating potential, a base coupled to a source of threshold conduction bias reference voltage, and an emitter connected to the circuit point at which high voltage transients are likely to appear. The base bias of the protection transistor is determinable independent of the bias of the protected device, and the protection circuit is connected to the protected device with substantially zero voltage offset between the circuit point and the protected device.

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 controlled oscillator comprises an amplifier including an active device, a filter network arranged in a feedback loop of the amplifier for providing regenerative feedback to sustain oscillation of the amplifier, and a source of control signals. Output oscillatory signals from the amplifier and output control signals from the control source are summed by a combining network to produce a resultant controlled signal, which is coupled to the filter network. Parasitic capacitances associated with output terminals of the amplifier and control source impart an unwanted phase shift to the controlled signal. A compensation signal derived from the oscillator is supplied to the combining network with a magnitude and phase to offset the unwanted phase shift, to thereby produce a phase compensated resultant controlled signal.

Abstract: A sample and hold detector arrangement suitable for construction in integrated circuit form as an automatic chroma gain control detector, or a color oscillator AFPC detector, or the like. A wide bandwidth analog multiplier circuit is supplied with an intermittent reference signal and a second signal, the phase or amplitude of which is to be sampled. In a preferred embodiment, the reference signal corresponds to the burst component of a composite color television signal and the second signal corresponds to a locally generated color subcarrier signal. The multiplier provides oppositely phased output signals which are coupled to first and second sample and hold circuits. Each sample and hold circuit is keyed to concurrently sample the respective multiplier outputs for the same sampling interval, and each provides substantially symmetrical bidirectional conduction to associated filter capacitors during the sampling interval and a high holding impedance during the remainder of each cycle.

Abstract: A video signal processing system is disclosed including a sample and hold comparator arranged in a closed control loop with a video channel including a video amplifier for the purpose of providing automatic brightness control, and an automatic kinescope beam current limiter. The beam current limiter is coupled to a first point in the amplifier for controlling the amplifier signal gain to limit excessive beam current demand in a first control mode. In a second control mode, the beam current limiter cooperates with the automatic brightness control network to control the D.C. output level of the video amplifier in the presence of excessive beam current demand. The comparator response time is slow relative to transient variations of the D.C. level at the amplifier output induced by beam limiter action in the first control mode, but is otherwise sufficient to permit compensation of relatively long term variations in the output D.C. level. Compensation of the transient D.C.

Abstract: Apparatus for automatically controlling the bias of an image reproducing color kinescope in a system incuding a plurality of video driver stages for supplying image representative video signals to respective intensity control electrodes of the electron guns of the kinescope. The output of each driver stage is coupled to an operating supply voltage via a load impedance. The electron gun currents (e.g., cathode currents) are sensed during image blanking intervals of the video signal to provide respective control voltages representative of the electron gun blanking current levels. The control voltages are respectively applied to control the output operating voltage of each driver stage, and thereby the electron gun bias, in a manner to reduce deviations of the blanking current level from a normally expected level. In one embodiment, each driver stage comprises a transistor with a video input base electrode, and a collector output electrode coupled to an electron gun.

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: Brightness control apparatus for a video signal image reproducing system including a video signal processing channel, a source of reference voltage for establishing a desired level of image brightness, and a keyed comparator circuit. The comparator forms a closed control loop with the signal processing channel, and is keyed during periodic blanking intervals of the video signal to sense the magnitude of the reference voltage and a brightness representative blanking level of the video signal which may vary undesirably. The comparator provides an output control signal indicative of a voltage difference between the reference voltage and the blanking level. The control voltage is applied to the signal channel for translating the blanking level in a direction to minimize the voltage difference, so that a desired relationship between the reference voltage and the blanking level is preserved.

Abstract: In a PAL color television system for processing a color signal including burst and chrominance components alternating in phase at the image line scanning rate, identification and control circuitry for rapidly correcting an incorrect mode of line to line color demodulator switching. A bistable circuit generates timing signals for controlling line by line switching of a selected color demodulator (e.g., R-Y). An identification signal representative of an incorrect line switching mode is derived from information contained in the burst component, and serves to reset the bistable circuit such that timing signals corresponding to a correct switching mode are produced. The identification signal is derived by a filter circuit exhibiting a fast response time relative to the line scanning time, in order to rapidly respond to the switching mode identification information occurring at the line rate and thereby rapidly restore the correct demodulator switching mode.

Abstract: Brightness control apparatus in a video system employing a sample and hold circuit including a charge storage capacitor. The sample and hold circuit forms a closed control loop with a signal processing channel, and is keyed during periodic blanking intervals of the video signal to sample the magnitude of a reference voltage and a brightness representative blanking level of the video signal. The sample and hold circuit provides an output control signal indicative of the voltage difference between the reference voltage and the blanking level. The control signal is applied to the signal channel for translating the blanking level in a direction to minimize the voltage difference, so that a desired relationship between the reference voltage and the blanking level is preserved.