| 摘要 |
PURPOSE:To stably and exactly separate and extract a control signal and a synchronizing signal, even when the synchronization is unstable, by setting the first and the second reference levels, based on a pedestal level and the minimum value level, when the synchronization is stable, and setting the first and the second reference levels, based on only the minimum value level, when the synchronization is unstable. CONSTITUTION:In a pedestal level detecting circuit 13, a pedestal level of a digitized video signal is detected, and in the minimum value detecting circuit 20, the minimum value level in a prescribed period of the digitized video signal is detected. When a synchronization formation discriminating signal has been supplied from a system controller 18, namely, when the synchronization is stable, a selector 144 selects the first and the second reference levels VTH1, TTH2 which has been generated by reference level generating circuits 140, 141, and in other case, namely, when the synchronization is unstable, the first and the second reference levels VTH1, VTH2 which have been generated by reference level generating circuits 142, 143 are selected.
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