| 摘要 |
PURPOSE:To surely attain DC level recovery immune to noise in a short time by generating a clamp voltage similar to a part or all of horizontal reference signals included in an input picture signal so as to operate switching at a part or all periods of the horizontal reference signal. CONSTITUTION:A reference amplitude detection circuit 7 detects the reference amplitude from the horizontal reference signal component of the signal subjected to A/D conversion. A pattern generating circuit 8 generates a signal similar to the horizontal reference signal and the level difference of the flat portion of the signal is controlled to be the same as the detected reference amplitude. A picture signal changes between two flat portions during the horizontal reference signal period, the pattern generating circuit 8 generates a waveform similar to the horizontal reference signal and the result is fed to a switch circuit 4 via a D/A converter 9, then the potential difference of the outputs between the D/A converter 9 and a buffer circuit 1 hardly includes the change component of the horizontal reference signal. Thus, the switch circuit 4 is conductive during the horizontal reference signal period and sure clamping is applied in a short time.
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