| 摘要 |
<p>PURPOSE:To obtain an economical frame synchronism protecting circuit using a digital circuit, by protecting the frame synchronism with lock-in in case coincidence/discordance pulses are produced more than the threshold level within a prescribed frame period. CONSTITUTION:A control circuit 7 sends a signal to a coincidence/discordance circuit 1 and then transmits a coincidence pulse when the coincidence is obtained between the circuit data fed through a terminal 9 and a frame synchronous pattern supplied from a synchronous pattern generating circuit 2. Then the coincidence pulses at the specific position of each frame are counted by a counting circuit 3 which is reset with an 8-frame period. When the count value of the circuit 3 exceeds the threshold level given from a threshold level generating circuit 5, an output of comparison is delivered. Receiving this output, the circuit 7 decides that the lock-in is over and then feeds signals to the circuits 1 and 5. Then the discordance pulse is generated from the circuit 1. When the count value of the circuit 3 exceeds the threshold level of the circuit 5, the generation of step out is decided. Then coincidence pulses are transmitted from the circuits 1 and 5.</p> |
