| 摘要 |
PURPOSE:To ensure the normal production of a system synchronizing signal, by neglecting the track synchronizing signal in case the said synchronizing signal can not be detected or is not detected within a fixed time when the system synchronizing signal is produced. CONSTITUTION:The output of an OR circuit 39 is set at H level at a time point when a track synchronizing signal is first detected and then supplied to an OR circuit 41 after a fixed time leg given by a delay circuit 40. When the synchronizing signal is detected at all tracks within the delay time, the output of an AND circuit 33 is set at H level. Then the signals within the circuit 40 are cleared by a clear signal 42 of the circuit 40 as soon as a system synchronizing signal 31 is detected. In case no synchronizing signal is detected at all tracks within the delay time, the output of the circuit 39 is supplied to the circuit 41. Then a system synchronizing signal is delivered. As a result, it is possible to demodulate a data correctly owing to the production of a synchronizing signal even in case the normal synchronizing signal is not detected at several tracks due to continuous errors, etc. |
