| 摘要 |
PURPOSE:To clamp a color difference signal at an optimum DC level by balance- modulating the color difference signal twice by a continuous wave signal and a signal obtained by inverting the continuous wave signal by 180 deg. every prescribed period and detecting the difference of the DC components of the two outputs. CONSTITUTION:The color deference signal inputttede from a terminal 1 is clamped by an automatic clamping circuit 2, the output of the circuit 2 is balance-modulated with a color signal obtained from a carrier generating circuit 6 by a balance modulator BM3 and the color signal is outputted from a terminal 9. The output of the circuit 6 is inverted by 180 deg. at its phase every horizontal period by a phase inverting circuit 7 based on a signal from a timing circuit 8 and the output signal form the circuit 7 and the output signal from the BM 3 are balance-modulated by a BM4. The difference of the DC components in the output signal of the BM4 every horizontal period of a horizontal blanking section of the color difference signal is detected by a detecting circuit 5 based on the signal obtained from the circuit 8 and the DC level of the circuit 2 is controlled by the detecting signal of the circuit 5. Consequently, the color difference signal can be always clamped at the optimum DC level free form carrier leakage and encoded.
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