PURPOSE: To obtain a video signal with a broad band and high picture quality by extracting a clock frequency component from a signal output and feeding back a DC level proportional to the amplitude of leakage clock to a correlation duplicate sampling circuit.
CONSTITUTION: A clock frequency is extracted at a BPF 1 from an output signal at an output point P1 of a correlation duplicate sampling circuit, the leakage component is subject to synchronization detection by a synchronization detection circuit 2 and a DC voltage proportional to the amplitude is converted. The voltage is given to a gate circuit 3, a signal is extracted by using a gate pulse GP, the signal is compared with a reference voltage Vf at a differential amplifier 4 and a comparison output is given to a loop filter 5, and the output is used as a reference voltage of a clamp circuit 42 and a negative feedback circuit is constituted as a whole. In the negative feedback circuit, the voltage Vf is set to an earth level and the converged value is controlled so that an output level of the circuit 2 is zero, that is, the clock frequency at a point P1 is controlled to be zero. Thus, the video signal with an excellent phase characteristic is obtained and a sufficiently wide band output signal is obtained.
AKIYAMA TOSHIYUKI
MIMURA ITARU
OZAWA NAOKI
MATSUMOTO TAKAHIRO
