System for automatically controlling reverse bias-voltage of avalanche photodiode (APD) by using noise and method for controlling same

The invention discloses a system for automatically controlling the reverse bias-voltage of an avalanche photodiode (APD) by using noise and a method for controlling the same. The system comprises an APD photoelectricity receiving circuit, an analog/digital (A/D) conversion module, a signal processor and a high-voltage generating circuit. The APD photoelectricity receiving circuit is used for converting a photo signal into an analog electricity signal and sending the analog electricity signal to the A/D conversion module; the A/D conversion module is used for converting the analog electricity signal into a digital signal and sending the digital signal to the signal processor; the signal processor is used for processing the collected signal, acquiring the noise level of the APD photoelectricity receiving circuit and outputting a control signal according to the noise level of the APD photoelectricity receiving circuit to regulate the voltage output of the high-voltage generating circuit; and the high-voltage generating circuit is used for providing the reverse bias-voltage for the APD photoelectricity receiving circuit. The system can ensure that the the reverse bias-voltage of the APD keeps the gain of the APD constant under different temperature.