| 摘要 |
PURPOSE:To prevent automatically a breakdown caused by an overcurrent of a photoelectric converting module by a simple constitution, by providing a decision circuit for deciding a photodetecting range from both an output of the first comparator and an output of the second comparator, and a voltage control circuit for controlling said photoelectric converting module use impressed voltage supplied from the outside, by an output of the decision circuit, and outputting it a voltage impressing circuit. CONSTITUTION:When a light is inputted to a photoelectric converting module (APD)1 at a time T1 in the figure, a voltage is generated in a load resistance 3, and amplified by a pre-amplifier 4. An amplified output of the pre-amplifier 4 is inputted to an AGC circuit 5, and a signal (a) obtained by peak-holding an amplitude is obtained in a terminal 15. As for an output of the terminal 15, the amplitude rises gradually. This signal is inputted in advance to the first comparator 11 for detecting the minimum photodetecting level and the second comparator 12 for detecting the maximum photodetecting level, sliced by each level shown by the signal (a), and output waveforms of (b) and (c) are obtained in an output of the first comparator 11 and an output of the second comparator 12, respectively. By each detected state in each time point, a decision circuit (EX-OR circuit)13 is operated, and by this exclusive OR output, a voltage control circuit 14 and a switching circuit 10 are controlled. |
