JPS6449394A - Chrominance signal processing circuit - Google Patents

Abstract

PURPOSE:To attain the oscillation more exact than the oscillation with an abnormal frequency due to an unnecessary component by switching an oscillating circuit in in APC circuit to an oscillating frequency fixed type when the level of a burst signal in a chroma signal goes to be lower than a prescribed level. 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 by 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 and the control signal of an L level is generated to the output edge of the comparator 18. Then, a first amplifying circuit 22 of an oscillating circuit 20 obtains an operating condition by a mode changing-over switch 24 and a second amplifying circuit 23 stops the operation. Thus, the oscillating circuit of the fixed type determined by a crystal oscillator 21 and the first amplifying circuit 22 is constituted and the stable oscillating output signal is impressed from an output terminal 25 to a second frequency converting circuit 9.