JPS6449393A - Chrominance signal processing circuit - Google Patents

Abstract

PURPOSE:To oscillate a voltage control type oscillating circuit in an APC circuit with a free-run frequency and to stably operate a frequency converting circuit to utilize the oscillating output signal or other circuits by separating the loop of the APC circuit when the level of a burst signal in a chroma signal goes to be lower than a prescribed value. CONSTITUTION:Out of color video signals impressed to an input terminal 1, only the burst signal in the chroma signal to pass through a band-pass filter 2 is extracted in a burst gate circuit 14 in correspondence to a burst gate pulse from a terminal 6 and impressed to an ACC detecting circuit 15 and a gain control signal is obtained. The gain control signal is compared with a reference voltage in a comparator 18. When the level of the burst signal goes to be small, the level of the gain control signal goes to be small, the control signal of an L level is generated to the output of the comparator 18 and a switch 20 is opened. Thus, the burst gate pulse is not impressed to a burst gate circuit 5 and the output signal of the burst gate circuit 5 goes to be zero. Thus, a VXO8 is oscillated with the prescribed free-run frequency determined by a crystal oscillator and the oscillating output signal is impressed to a second frequency converting circuit 9.