EQUIVALENT AMPLIFIER CIRCUIT FOR OPTICAL RECEIVER

PURPOSE:To adjust automatically a band width in response to a change in a bit rate of an optical signal and to obtain an output of a prescribed level by providing an automatic gain control amplifier correcting a level fluctuation of an output signal of a band width variable preamplifier and obtaining an output of a prescribed level to the circuit. CONSTITUTION:A peak detection circuit 29 detecting a peak of an output signal of a preamplifier 26 connects to the peak detection circuit 29 and its output connects to a gain control input terminal of a main amplifier 27. A bit rate detection circuit 28 generates a voltage in response to a bit rate of an output signal of the preamplifier 26. Since a resistance of a variable resistive element 25 varies with a voltage applied thereto and a feedback quantity of the preamplifier 26 is changed, the band width and the gain result in a change. The peak detection circuit 29 detects a level fluctuation attended with a gain change based on the peak of the output signal and gives the result of detection to a gain control terminal of the main amplifier 27. The main amplifier 27 controls the level of the output signal to be made constant input terminal the signal given to the gain control terminal.