| 摘要 |
PURPOSE:To realize the changeover of three stages of AGC as electric AGC-full AGC-electric AGC with more simple circuit constitution by controlling an equalizing amplifier with two signals as an output signal of a 1st analog switch and an output signal of a 2nd analog switch. CONSTITUTION:An inputted optical signal is converted into an electric signal by an avalanche photodiode APD 4, amplified by an equalizer amplifier 6 and outputted from an output terminal 8. Part Vin1 of the output signal is inputted to an AGC circuit 1, in which the signal is compared with a 1st reference voltage Vin2 corresponding to a 1st limit of a bias voltage to keep the band of the APD 4 to a normal state at a 1st analog switch 2 and a control signal Vout E1 to control the gain of the equalizing amplifier 6 is outputted in response to the result of comparison. An output Vout2 of the lst analog switch 2 and a 2nd reference voltage Vin3 corresponding to a 2nd limit of a bias voltage to keep the band of the APD 4 to a normal state are compared at a 2nd analog switch 3, and a control signal VoutE2 for the equalizing amplifier 6 and a control signal VotF for a DC/DC converter 10 are outputted according to the result of comparison. |
