| 摘要 |
PURPOSE:To control a limit voltage with high accuracy by amplifying the temperature fluctuation of a terminal voltage of a temperature-sensing element and applying temperature control of a limit voltage to suppress the temperature change in the limit of a multiple rate of an APD. CONSTITUTION:An output signal level of a photodetector 1 photoelectrically converting an incident optical signal is kept always constant by controlling a bias voltage of the photodetector 1 so as to control the multiple rate. The photodetecting circuit equipped with the function above is provided with a limiter circuit 8 limiting the bias voltage controlling the multiple rate of the photodetector 1 lower by a prescribed value when the level of the input optical signal is lowered to limit the abnormal rise of the multiple rate of the photodetector 1. Thus, the limit voltage of the limiter circuit 8 is limited in response to the temperature change of the multiple rate of the photodetector 1 by using a temperature-sensing element 11. For example, a differential amplifier 12 amplifies the change in the terminal voltage of the element 11 due to temperature fluctuation and the temperature fluctuation of the limit value of the multiple rate of an APD 1 is suppressed by applying temperature control of the limit voltage of the limiter circuit 8. |
