Bias circuit for an avalanche photodiode

Abstract

A bias circuit accurately compensates temperature coefficient of an optical multiplication in an avalanche photodiode with low power consumption. Temperature coefficient voltage for compensating temperature coefficient of the multiplication of the photodiode is delivered from an emitter follower added a constant voltage to an input of an operational amplifier. The output of the operational amplifier is added, via a voltage regulating diode, to a base of a transistor of which emitter and collector are respectively connected to a terminal of the photodiode and a negative power source. Emitter voltage of the transistor is dividedly connected to another input terminal of the operational amplifier, wherein this connection is negative feedback. The temperature coefficient voltage generated at the emitter follower is amplified inversely proportional to the divided ratio of the emitter voltage of the transistor in order to compensate the temperature coefficient of the multiplication of the photodiode. A voltage across the photodiode can be adjusted by adjusting the constant voltage added to the emitter follower. Voltage drifts caused by temperature variations in the negative feedback loop including the operational amplifier, the voltage regurating diode, the transistor and the voltage divider are entirely eliminated with the negative feedback operation.

Dependencies are inferred from the claim text.