| 摘要 |
PURPOSE:To keep a loop gain of an AGC circuit with a sufficient quantity constantly by providing a timing pulse generating circuit and a sample and hold circuit in place of a smoothing circuit. CONSTITUTION:A video signal from an input terminal 7 is given to a VCO1 and a timing pulse generation circuit 2 via a subtraction circuit 8. The output of the VCO1 is detected by an AM detection circuit 3 and the waveform of the detected output (b), a portion corresponding from the tip level to the pedestal level of a synchronizing signal is restored. On the other hand, a generating circuit 2 generates a prescribed timing signal based on the synchronizing signal. The sample and hold circuit 4 uses the timing signal to sample and hold the detected output (b) thereby outputting a control signal (c). The control signal (c) is fed back negatively to a subtraction circuit 8 via an amplifier 5. Thus, a sufficient large control voltage (c) is obtained in comparison with that using a smoothing circuit. Thus, the loop again of the AFC circuit is increased and kept constant.
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