Signal processing device and signal processing method

A signal processing device comprising:

• an integrator configured to integrate an electrical charge corresponding to electromagnetic waves, the integrator including an integrating capacitor configured to store the electrical charge corresponding to the electromagnetic waves and a discharging circuit configured to discharge the integrating capacitor;
• an integration period setting unit configured to set a period of integration of the electrical charge with respect to the integrator;
• and
• an analog-to-digital converter including a comparator configured to compare an integration output and a predetermined threshold value and a counter configured to output, as digital data of the electrical charge, the number of times for which a value of the integration output becomes equal to or greater than the predetermined threshold value, the analog-to-digital converter being configured to discharge the integrating capacitor during the period of integration by supplying a comparison output of the comparator to the discharging circuit while a value of the integration value is equal to or greater than the predetermined threshold value.