Patent ID: 7868701

Claim:
A transimpedance amplifier comprising: a first transimpedance amplifier core circuit which includes an input terminal and an output terminal, amplifies a current input to the input terminal with a desired gain, and outputs the signal as a voltage signal from the output terminal; a second transimpedance amplifier core circuit which has the same arrangement as that of said first transimpedance amplifier core circuit with an open input terminal; an inter-stage buffer circuit which differentially amplifies voltage signals output from said first transimpedance amplifier core circuit and said second transimpedance amplifier core circuit and outputs the signals as a differential output signal; and a gain switching determination circuit which receives the differential output signal output as a comparative input voltage from said inter-stage buffer circuit, and outputs a gain switching signal for switching gains of said first transimpedance amplifier core circuit and said second transimpedance amplifier core circuit on the basis of a result obtained by comparing/determining the comparative input voltage with a first hysteresis characteristic, wherein said first transimpedance amplifier core circuit and said second transimpedance amplifier core circuit switch gains on the basis of the gain switching signal output from said gain switching determination circuit.