OPTICAL RECEPTION CIRCUIT

摘要

PURPOSE:To obtain a circuit wit a wide dynamic range without deterioration in the band distortion characteristic by allowing an APD to keep a constant output level, changing a multiplication factor only for a specific range and varying a gain of a variable gain amplifier circuit for another range. CONSTITUTION:A voltage control circuit 3 controls a multification factor of an avalanche photodiode(APD) 1 by varying a voltage applied to the APD 1 to vary the multification factor for range in which an output level of the APD 1 used to convert an optical signal into an electric signal is kept constant and its band distortion characteristic is not deteriorated. In this case, the gain of the variable gain amplifier circuit 7 is kept constant. The multification factor is kept constant by the voltage control circuit 3 for a range of a maximum light receiving level from an upper limit of compensating the band distortion characteristic by the APD 1 and a constant output level without distortion is obtained by the variable gain amplifier circuit 7. With an optical input larger than the maximum light receiving level, a protection circuit 6 is operated to reduce the multification factor and for a range below the lower limit for compensating the band distortion characteristics, the multification factor is kept constant.