A dark photodiode that is optically isolated from the signal photodiode and having a dark current in the absence of photons. A reference generating circuit configured to produce a reference voltage based on voltage at an anode of the signal photodiode. A voltage regulator circuit configured to regulate dark photodiode voltage at an anode of the dark photodiode based on the reference voltage. A current mirror circuit configured to produce, at an anode connecting to the signal photodiode, a mirrored current that is a mirrored version of a portion of the dark current.