| 摘要 |
PURPOSE:To sample a synchronizing signal with high accuracy even from a video signal of adverse quality by applying pulse clamp except the 9-line vertical period where distortion is often caused easily thereby correcting leakage current caused during the 9-line vertical period. CONSTITUTION:A high frequency component is eliminated from an input video signal at first by an LPF, the result is fed to an amplifier 1, where the level is amplified and a built-in limiter eliminates the signal of the picture part above the slice level. A DC bias control circuit 2 to ensure the operation of the amplifier 1 is provided. The pedestal part in the output of the amplifier 1 is fixed in terms of DC to ensure the elimination of the signal of the picture part. The pedestal part of the output of the amplifier 1 is clamped to a ground level by using a clamp FETQ2. In such a case, since the synchronizing signal itself is often distorted during the 9-line vertical period, a leakage current correcting circuit 3 is provided to inhibit the DC bias control and clamping operation and to suppress the fluctuation of the DC level during this period.
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