Patent ID: 7368773

Claim:
A photodetector device, comprising: a photodiode for generating an electrical signal corresponding to an amount of incident light; and a logarithmic conversion transistor for subjecting a voltage value of the electrical signal to logarithmic conversion, wherein the logarithmic conversion transistor comprises a first electrode which is one of a source electrode and a drain electrode, a second electrode which is the other of the source electrode and the drain electrode, and a gate electrode, the first electrode is connected to the photodiode, a first voltage is applied to the second electrode so that the logarithmic conversion transistor operates in a subthreshold region, and the photodetector device further comprising a section for causing a voltage of the gate electrode to be in a floating state when the logarithmic conversion transistor subjects the voltage value of the electrical signal to logarithmic conversion, wherein a capacitance between the first electrode and the gate electrode is larger than a capacitance between the second electrode and the gate electrode.