Signal processing device, including charge injection circuit, and photodetection device

A signal processing device that outputs an electrical signal having a value according to an amount of charge generated in a photodiode according to an amount of incident light onto the photodiode, comprising:

• an integration circuit including an integration capacitor element that accumulates a charge output from the photodiode, for outputting a voltage value according to an amount of the charge accumulated in the integrating capacitor element;
• a comparator circuit for comparing the voltage value output from the integration circuit and input thereto with a predetermined reference value, and when the voltage value has reached the reference value, outputting a saturation signal indicating that fact;
• a charge injection circuit for, based on the saturation signal output from the comparator circuit, injecting a constant amount of charge having a polarity opposite to that of the charge accumulated in the integrating capacitor element of the integration circuit into the integrating capacitor element;
• a counter circuit for, based on the saturation signal output from the comparator circuit, counting a number of times that the voltage value output from the integration circuit has reached the reference value;
• a holding circuit for holding and outputting the voltage value output from the integration circuit;
• an amplifier circuit for outputting a voltage value that is K times as large as the voltage value held and output by the holding circuit and input thereto (where K>1);
• an A/D converter circuit in which a voltage value that is K times as large as the reference value is set as a maximum input voltage value, for outputting a digital value corresponding to the voltage value output from the amplifier circuit and input thereto;
• and
• further comprising a reference value generating circuit for being input with a reference value to set the maximum input voltage value in the A/D converter circuit, and supplying a voltage value one K-th as large as this reference value to the comparator circuit as the reference value.