| 摘要 |
PROBLEM TO BE SOLVED: To detect optical input interruption at a high speed. SOLUTION: When a reception signal 11 is interrupted, a timing extract circuit 2 cannot extract a reception clock signal 13 based on received data signal and conducts self-running and the output of the timing extract circuit 2 deviates from a substantial frequency. As a result, a phase difference is caused between the output of the timing extract circuit 2 and a reference clock 14. The phase difference is detected by a phase comparator circuit 3 and decides it to be input interruption when the phase difference reaches a prescribed value or over and outputs an interruption detection signal. |
