To stably and easily measure a free-run frequency of a voltage controlled oscillator without being affected by spurious radiation or noise from the voltage controlled oscillator by providing a means that minimizes the gain of an ACC amplifier circuit with an external signal in the case of measuring the free-run frequency to the title circuit.
In the case of measuring a free-run frequency of a voltage controlled oscillator circuit 9, even when a chrominance signal input terminal 1 has no input, a 1st changeover circuit 14 is thrown to the position of 14b by a control signal to apply a 1st reference voltage to a control terminal of an ACC amplifier circuit 2 so as to minimize, a gain of the ACC amplifier circuit 2 at all times. Thus, in the case of intrusion of spurious radiation or noise to the ACC circuit 2 through a sneak path from the voltage controlled oscillator circuit 9 to a power supply or ground, the amplification of the spurious radiation or noise by the ACC amplifier circuit 2 is eliminated thereby preventing the output of a error voltage between the spurious radiation or noise and a chrominance subcarrier to the output.
KINUGAWA HIROKI
KANEDA JINSAKU
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