| 摘要 |
PURPOSE:To widen the dynamic range of an automatic gain control circuit (AGC) by controlling simultaneously the multiplication factor of a photodetector of an optical system and the gain versus frequency characteristic of an electric system. CONSTITUTION:An avalanche photodiode (APD) 2 being a photodetector receives an optical input signal 1 and converts it into an electric signal and its multiplication factor varies with a control voltage from an APD bias circuit 9. The amplitude of an output pulse is detected by a peak detector 7, its control signal drives a voltage variable impedance conversion circuit 8 employing a voltage follower to produce a prescribed control voltage thereby controlling simultaneously a gain frequency characteristic automatic control circuit 4 and the APD bias circuit 9. Since the multiplication factor of the APD 2 and the gain frequency characteristic are controlled simultaneously, the dynamic range of the AGC is widened. |
