| 摘要 |
PURPOSE:To suppress the increase of noise and to avoid the mistake of communication resumption by holding constant the gain of automatic gain control for previously decided time when a reception device receives power cut information. CONSTITUTION:When the reception device 22 receives power cut information from a transmission device 21, it is converted into an electric light input signal in a light/electricity conversion circuit 11, and a synchronism detection circuit 24 executes synchronization. An alarm mask signal outputted from a control signal separation circuit 25 is outputted to a timer circuit 12 and an AGC control signal is outputted to the circuit 11 for previously decided time. When the AGC control signal is inputted, the circuit 11 stops automatic gain control, maintains the gain at that time and the increase of noise occurring when the gain is improved as the level of an optical input signal drops can be prevented. When the power of the transmission device 21 is intentionally cut, the occurrence of alarm is securely masked and the mistake of communication resumption can be avoided. |
