Light detection circuit

A photodetection circuit, comprising:

• a photodetector configured to output a signal current in response to incidence of signal light;
• a current-to-voltage converter having a signal input terminal and a signal output terminal and configured to convert the signal current input to the signal input terminal into a first signal voltage and output the first signal voltage from the signal output terminal, the signal input terminal being connected to the photodetector;
• a first current removal circuit connected to the photodetector and configured to extract a first current from the signal current;
• and
• a second current removal circuit connected to the photodetector and configured to extract a second current from the signal current,
• wherein the signal current includes a signal component and a low-frequency component having a lower frequency than the signal component or having a constant magnitude, the first current removal circuit is configured to determine a magnitude of the first current based on the magnitude of the low-frequency component at a predetermined timing and to maintain the magnitude of the first current, and
• the second current removal circuit includes:
• a feedback circuit connected to the signal output terminal of the current-to-voltage converter and configured to output a second signal voltage having a magnitude corresponding to the first signal voltage;
• a smoothing capacitor configured to smooth the second signal voltage;
• and
• a second transistor configured to extract, from the signal current, the second current having a magnitude corresponding to the second signal voltage smoothed by the smoothing capacitor.