| 摘要 |
PURPOSE:To prevent unstable operations by operating a ghost erasing unit only when horizontal and vertical synchronizing signals of inputted TV signals have a prescribed frequency relation corresponding to normal broadcasting waves. CONSTITUTION:Input signals Vin are supplied at horizontal synchronizing separator circuit 24 and vertical synchronizing separator circuit 25, and horizontal synchronizing signals are applied to comparator circuit 28 through frequency divider 26 and window signal generator circuit 27. The comparator circuit generates signal P1 if vertical synchronizing signals exist during the period of window signals, and the comparator circuit generates signal P2 otherwise. These signals are supplied to counters 30 and 31, and these counters generate signals PN and PM when N-number M-number signals P1 and P2 are counted respectively. Consequently, FF 33 is reset to stop the ghost erasing operation when P2/ P1> M/N is true. In case of a normal TV signal, the ghost erasing operation is normally operated because horizontal and vertical synchronizing signals are stable and the relation above is not satisfied. |
