Bias circuit for maintaining a constant potential difference between respective terminals of more than one avalanche photodiode

摘要

A bias circuit for applying a bias voltage to an avalanche photodiode APD2 for detecting light comprises a first diode APD1, a power supply VH connected to the first diode APD1, for applying a voltage to make the diode in breakdown between an anode and a cathode of the first diode APD1, and a constant voltage circuit V2 connected to the avalanche photodiode APD2 for detecting light, for applying a voltage difference of a breakdown voltage generated between the anode and the cathode of the first diode APD1 minus a constant voltage to the avalanche photodiode. The constant voltage is substantially independent from current flowing in the avalanche photodiode APD2 for detecting light to the avalanche photodiode.