US Patent 7809285 Receiving circuit and optical signal receiving circuit

A receiving circuit comprises a transimpedance amplifier 3 including an inversion amplifier 2 for amplifying an input current IN, and a feedback resistance R1 connected between an input and an output of the inversion amplifier 2, a comparison circuit 4 for comparing an output OUT of the transimpedance amplifier 3 with a certain desired reference value, and outputting a result of the comparison, and a control circuit for holding the comparison result, and generating an AGC signal 20 for adjusting a gain of the transimpedance amplifier 3. The transimpedance amplifier 20 has a function capable of gain adjustment in accordance with the input AGC signal 20. The control circuit 5 performs gain adjustment until the output OUT of the transimpedance amplifier 3 exceeds the reference value so that an appropriate gain is obtained. Therefore, even when an input has a wide dynamic range, it is possible to prevent signal saturation and a distortion in output waveform in the transimpedance amplifier, so that appropriate reception can be invariably performed and a signal having a stable duty can be output.