Avalanche photodiode gain control

An avalanche photo-diode (APD) circuit, comprising:

• a first APD configured to detect light;
• a bias circuit configured to control a gain of the first APD, and includes:
• a second APD;
• a reference voltage source configured to bias the second APD;
• a metal layer configured to shield the second APD from the light;
• and
• a bias voltage generation circuit configured to generate a bias voltage for biasing the first APD based on dark current output by the second APD.

A light detection circuit, comprising:

• an avalanche photo-diode (APD) array configured to detect light, and including:
• a first APD;
• and
• a transimpedance amplifier coupled to first APD;
• and
• a bias circuit coupled to the APD array, and configured to control a gain of the first APD, the bias circuit including:
• a second APD;
• a reference voltage source configured to bias the second APD;
• a metal layer configured to shield the second APD from the light;
• a current multiplier circuit coupled to the second APD, and configured to provide an output current that is a predetermined multiple of a dark current output by the second APD;
• and
• a bias voltage generation circuit configured to generate a bias voltage for biasing the first APD based on the output current of the current multiplier circuit.