摘要:
A gain switching circuit (3) that switches a conversion gain of a preamp (2), which outputs a voltage signal upon amplifying an output current of a photo-detecting element (1) that converts a burst-form optical signal into an electrical signal and with which a series circuit, formed with a first resistor (6) and a first switching element (9), and a series circuit, formed with a second resistor (7) and a second switching element (10), are connected in parallel to a feedback resistor (2B), generates an operating signal for closing the first switching element (9) within a first gain switching period and generates an operating signal for closing the second switching element (10) within a second gain switching period.