| 摘要 |
<p>PURPOSE:To suppress the noise at the time of the special reproduction of a laser disk or the like and at the time of cutting off input signals by adjusting synchronization protective length at the time of cancelling synchronization corresponding to a noise amount included in reception television signals. CONSTITUTION:When the noise amount detected from a noise amount detection circuit 3 is less than a prescribed level, the synchronization protective length value of a synchronization protective length adjusting circuit 4 is switched to a shortened value (a) by changeover control signal and the synchronization protective length at the time of the cancellation of a synchronization pull-in/cancellation circuit 7 is shortened. Thus, noise generation at the time of cancelling the special reproduction of the laser disk or the like and at the time of inputting signals can be prevented. On the other hand, when the detected noise amount is more than the prescribed level, the synchronization protective length of the synchronization protective length circuit 4 is switched to an extended value (b) by the changeover control signal and the synchronization protective length is extended. Thus, synchronization is prevented from being cancelled, sound interruption due to unnecessary mute is prevented, a synchronization pull-in operation length is shortened by the adjusting means of a synchronization pull-in operation period and synchronization pull-in is facilitated.</p> |
