Abstract: An automatic color tuning system includes a counter controlled oscillator that is started in the middle of its controllable frequency range. If the counter counts around and no color burst signal is detected, the oscillator is stopped. Whenever the oscillator is sweeping, an automatic phase control circuit is operated at low gain for assuring that the oscillator will be close to the frequency of the color burst signal when lock-up occurs. Whenever the oscillator is stopped, the automatic phase control circuit gain is made high. Once the automatic phase control circuit locks up the oscillator to a color burst signal, a subsequent loss of the color signal does not re-initiate the counter.

Abstract: A PNP turnaround circuit includes a common base lateral PNP transistor connected to the output of a high gain amplifier having a resistor coupled thereacross. The input is supplied from a differential pair of NPN transistors havng their emitters connected to a current source. One transistor of the differential pair has its collector connected to the collector of the PNP for supplying a push/pull output. In another embodiment the collector of the PNP is returned to ground through a load resistor and a DC level shifted output signal is developed.

Abstract: A luminance peaking circuit includes a common and differential mode amplifier comprising a first differentially coupled pair of transistors coupled to a current source and functioning in a differential mode and a second differentially coupled pair of transistors functioning in a common mode. The bases of the second pair of transistors are connected together and to the base of one of the first pair of transistors. The inputs to the amplifier comprise a common mode signal and a differential mode signal and the outputs are matrixed to produce common mode signal components with opposite polarity differential mode components. The amplifier is characterized by a differential mode gain that is independent of common mode signal level and a common mode gain that is independent of differential signal level.

Abstract: An automatic beam current limiting circuit for a color television receiver comprises means for individually monitoring the three cathode currents developed in response to the green, blue and red video drive signals. The video processing unit of the receiver is automatically adjusted in response to any one of the cathode currents exceeding a predetermined level for reducing the video drive signals to limit the excessive cathode current to the predetermined level. As a result, the individual cathode currents are limited to the predetermined level while the combined cathode currents are allowed to substantially exceed this level.

Abstract: Disclosed is a DC-coupled video amplifier with AGC feedback having a stable operating point. Shifting of sync tip DC level resulting in a loss of synchronization of the video signal is compensated for by means of a feedback loop in the video amplifier thus providing a level video output signal.

Abstract: A tint control circuit is described for use in a color television receiver. The circuit generates four currents having substantially equal D.C. components, and having respective 3.58 MH.sub.z subcarrier components of four different quadrature phases. The phase of each such current is preferably variable over a range of .+-.45 degrees. In a preferred embodiment, the four currents are coupled to a matrixing network for developing a pair of subcarrier output voltages whose phases differ by more than 90 degrees and whose D.C. components are substantially equal. As the phases of the four currents are varied, the phases of the subcarrier output voltages vary accordingly, but maintain their phase relationship to each other.

Abstract: A chroma amplifier and color killer are described for use in a color television receiver. In a preferred embodiment, the chroma amplifier comprises a first pair of emitter-coupled transistors receiving a current source which has a D.C. operating component and an A.C. chroma signal component. A second pair of emitter-coupled transistors receives another current source which has only a D.C. operating component substantially equal to that received by the first pair of transistors. A variable ACC voltage and a substantially fixed bias voltage are applied to selected base terminals of the transistors such that one of the first pairs of transistors develops a gain controlled A.C. chroma signal output and one of the second pair of transistors develops an ACC-varied D.C. output signal free of chroma component. The latter signal drives a low power color killer for quenching color reproduction when the color component of the broadcast signal is missing or is of very low amplitude.

Abstract: A DC restoration circuit for an AC coupled television receiver includes means for converting an input video voltage signal to a corresponding video current signal and for abstracting from the video current signal a DC current feedback signal, the remaining video current signal being reconverted to a corresponding output video voltage having a DC voltage component. A feedback loop including a clamp capacitor is operable during the back porch of the horizontal blanking interval for establishing the level of the DC current feedback signal to equalize the values of the DC component of the output video voltage and a black level reference voltage derived from a manually operable brightness control.