OPTICAL SIGNAL RECEIVER AND DUTY CONTROL CIRCUIT

摘要

PROBLEM TO BE SOLVED: To provide the optical signal receiver where a duty factor is not deteriorated even if a burst optical signal with an excessively high amplitude is received. SOLUTION: An optical signal including a signal component is converted by a photoelectric converter 1 and given to a preamplifier 2. The preamplifier 2 outputs a differential electric power of the electric signal to an automatic threshold level adjustment circuit 3 via a variable attenuator 5. A bottom detector 6 and a bottom level identifying circuit 7 detect a bottom position of power and its value outputted from the automatic threshold level adjustment circuit 3. An attenuation selection circuit 8 controls the attenuation of the variable attenuator 5 based on the detected bottom value so as to have a threshold level in the automatic threshold level adjustment circuit 3 approach a center level of the differential power outputted from the preamplifier 2.