Patent ID: 7579915

Claim:
An electronic circuit comprising: a control circuit that controls a gain of a transimpedance amplifier by taking part of an input current to be input to the transimpedance amplifier, based on an output voltage of the transimpedance amplifier; a differential amplifier; and a PIN diode that is provided between an input of the transimpedance amplifier and the control circuit, and is connected in a forward direction with respect to the current to be drawn into the control circuit, wherein an input terminal of said differential amplifier is in communication with an output of said transimpedance amplifier, and another input of said differential amplifier is in communication with a reference voltage; wherein an output of said differential amplifier is connected to an input of said control circuit; wherein the input current is an output current from a light receiving element; and wherein an undoped semiconductor layer provided between a cathode layer and an anode layer of the PIN diode has the same film thickness as an undoped semiconductor layer provided between a cathode layer and an anode layer of a PIN photodiode serving as the light receiving element.