Abstract: An automatic gain control (AGC) circuit for performing an AGC for a picture signal. The AGC circuit includes an amplifier for amplifying the picture signal, a clamping circuit for fixing a tip-end level of a synchronous signal component of the picture signal, a synchronous detection AGC loop constituted of the amplifier, the clamping circuit, a synchronous detection circuit and a first filter, a peak detection AGC loop constituted of the amplifier, the clamping circuit, a peak detection circuit and a second filter, and a precharging means connected between the first filter and the second filter for charging the second filter by a voltage followed to a voltage charged on the first filter when the synchronous detection AGC loop is activated but the peak detection AGC loop is deactivated.

Abstract: A differential switch circuit having an input circuit being responsive to an input signal for providing switch instructions corresponding to the level of the input signal, a bias circuit coupled to the input circuit for generating bias signals respectively corresponding to the switch instructions, and a differential transistor circuit coupled to the bias circuit for providing a plurality of outputs in accordance with the potential of each of the bias signals. The input circuit includes comparators which respond to three levels of the input signal and provide the switch instructions in a manner so that the switch instructions respectively correspond to the levels of the input signal. The bias circuit includes three bias sources. Each of the bias sources generates one of the bias signals according to the switch instructions.