Signal processing circuit, and light detecting device

A signal processing circuit comprising:

• an input terminal configured to receive an analog signal output from an avalanche photodiode operating in Geiger mode;
• a comparison circuit configured to compare information related to the signal received at the input terminal with a threshold to remove a noise component related to the signal input at the input terminal;
• an adjustment circuit configured to adjust a signal input to the comparison circuit;
• and
• a succeeding-stage circuit configured to process a signal output from the comparison circuit,
• wherein the comparison circuit outputs a signal based on a component that exceeds the threshold among components included in the signal input to the comparison circuit, and
• the adjustment circuit includes,
• an AC coupling unit that establishes AC coupling between the input terminal and the comparison circuit,
• a level shifter unit that, between the AC coupling unit and the comparison circuit, adjusts a voltage of the signal input to the comparison circuit to a value lower than a reverse bias voltage applied to the avalanche photodiode, and
• a reference value adjustment unit that adjusts a reference value of the signal input to the comparison circuit.