In optical communications, an avalanche photodiode (APD) is used as a receiver probe. Its characteristics of high sensitivity and high bandwidth have been widely recognized by designers. When APD works, a reverse junction pressure is required. When radiation is received, electron-hole pairs are generated. The electron-hole pairs collected by the applied electric field are converted into electric current, and the intensity of the electric current is proportional to the intensity of the rays.

　　 When the APD avalanche photodiode works, the reverse bias voltage applied to the device will cause the avalanche effect, and the avalanche gain can be adjusted by changing the bias voltage. Then adjust the avalanche gain to get better fiber receiving sensitivity. However, in order to obtain satisfactory avalanche gain, many APDs require high reverse offset pressure, most of which are in the range of 40V to 60V, and some even reach 80V.

One disadvantage of 　　APD is that as the temperature changes, the avalanche gain changes and is also affected by the manufacturing process. So in a typical system, if the APD needs to work with a constant gain, then in order to compensate for the avalanche gain changes caused by temperature and manufacturing process, the high-voltage bias power supply must be able to change. Under normal circumstances, the temperature coefficient of the APD power supply is about +0.2%/°C, which is approximately equal to 100mV/°C, in order to obtain a constant gain.

　　 In order to compensate the gain drift of the APD photodiode due to temperature, there are many ready-made methods that can be used to adjust the output voltage of the power supply. The temperature measuring elements contained in the APD module, such as thermistors, can be directly connected to the power supply to adjust the output voltage. In some systems, it is also possible to read the resistance value through a single-chip microcomputer, and then issue an instruction to adjust the bias voltage to the power supply.