| 摘要 |
PURPOSE:To remarkably reduce noise caused in a demodulated stereo difference signal by controlling the time constant of a low pass filter in a PLL circuit in response to a white noise level in a video signal. CONSTITUTION:A white level detection circuit 6 detecting the white level of a detected video signal is provided and the time constant of the low pass filter of the PLL circuit 4 is controlled in response to the output signal of the white level detection circuit 6. That is, since the white level of the video signal is detected to control the time constant of the low pass filter, if the white level is high and the noise is easily caused, the time constant is increased and even when the stereo pilot signal is affected by the horizontal synchronizing signal, the production of noise from a subchannel demodulation circuit is prevented.
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