| 摘要 |
PURPOSE:To easily compensate the temperature drift and time drift of the photodetecting amplifier including a photodetector as well only by adding a compensation circuit and to enable the compensation in the state of reducing the leak current of a capacitor at real time by deciding a feedback value for each no signal case of a repeating signal cycle. CONSTITUTION:When an optical signal is inputted to a photodetector 22, the signal is amplified by an amplifier 24, subjected to sample/hold at a sample/hold circuit 25, A/D conversion is executed at an A/D conversion circuit 26, and an output signal is taken out. When no optical signal is inputted, an analog switch 30 is changed over, the output of the amplifier is subjected to sample/hold and A/D conversion in the no signal case of the repeating signal, and the output is inputted to a flip-flop 27 and latched. When the optical signal is inputted, the analog switch 30 is changed over, the compensation signal latched at the flip-flop 27 in the no signal case is subjected to D/A conversion, and the dark current of a photoelectric conversion circuit including the photodetector as well, the temperature drift and the time drift of the offset output from the amplifier are turned to zero. |
