Patent ID: 6157022
Filing Date: 2000-12-05
Classification: H01L

Abstract:
Bias voltage control circuitry for an avalanche photodiode (APD), comprising:a voltage varying circuit for controlling an input DC voltage in accordance with a voltage control signal to thereby output a varied voltage, said varied voltage being controlled and then output via an output terminal of said bias voltage control circuitry as a bias voltage to be applied to the APD;a temperature slope voltage outputting circuit for outputting a voltage corresponding to a temperature slope of a breakdown voltage of an opposite direction particular to the APD;a set voltage outputting circuit for outputting a set voltage for controlling a voltage of said output terminal to a preselected value; anda comparing and control circuit for setting a reference voltage based on said voltage corresponding to the temperature slope and said set voltage, generating said voltage control signal such that said reference voltage and a voltage input from said output terminal via a resistor coincide with each other, and feeding said voltage control signal to said voltage varying circuit;said voltage varying circuit comprising a digital variable resistor whose resistance is variable in accordance with a digital voltage control signal, said digital variable resistor outputting said digital voltage control signal by digitizing said voltage control signal and feeding said digital voltage control signal to said digital variable resistor, whereby a resistance of said digital variable resistor is set to control said input DC voltage.