METHOD AND CIRCUIT FOR CLAMPING

摘要

PURPOSE:To attain an optimum clamping operation by using the broadcast/non- broadcast discriminating code output detected out of a MUSE signal to switch the time constant of a clamping circuit set at the preceding stage of an A/D converter. CONSTITUTION:A control signal detecting circuit 20 outputs a broadcast/non- broadcast discriminating code signal of a low level through a terminal 20a. A clamping time constant changeover switch 14 is opened by the broadcast/non- broadcast discriminating code signal. Then a clamping time constant circuit consisting of a 1st resistance 10 and a capacitor 3 sets a large clamping time constant. A clamp switch 8 is closed by a timing signal (horizontal clamp pulse) synchronous with a horizontal synchronizing signal and supplies the clamp voltage to a signal line to perform a clamping operation based on the clamping time constant. As a result, the clamping level has not large fluctuation even though the drop-out occurs in a horizontal synchronizing period.