| 摘要 |
PURPOSE:To suppress the fluctuation of the blanking level of a color difference signal and to prevent influence such as a waveform flaw by detecting the color difference signal level of a vertical fly-back line period, comparing the color difference signal level of a signal period with a detecting level and adjusting the blanking level of the color difference signal. CONSTITUTION:A sample-and-hold circuit 62 samples an input signal according to signal (h). A differential amplifier 64 compares the output voltage of a sample-and-hold circuit 56 with the output voltage of the sample-and-holding circuit 62 and outputs a voltage indicating the difference. When there is a level difference in an offset between a (R-Y) line and a (B-Y) line in an input terminal 30, a potential difference is generated between the output voltage of the sample- and-hold circuit 56 and the output voltage of the sample-and-hold circuit 62. Accordingly, in order to eliminate the level difference in the offset, a level control circuit 66 follows the output of the differential amplifier 64 to apply a signal canceling the offset part of a signal inputting to clamping circuits 34, 36 to adders 60, 61.
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