Patent ID: 7880788

Claim:
An optical sensor circuit comprising: a photoelectrical converting device which includes an electrostatic capacitance element that stores charges, and which converts a light signal to a current signal; a converting MOS transistor for converting the current signal output from said photoelectrical converting device to a voltage signal having a logarithmic characteristic in a weak inversion state; and controlling means for supplying a gate voltage to a gate of said MOS transistor, and supplying a drain voltage to a drain of said MOS transistor, wherein said controlling means has initial setting means for performing initial setting in which said electrostatic capacitance element of said photoelectrical converting device is charged/discharged while setting the gate voltage of said converting MOS transistor to a high gate voltage value (VgH), only for a first predetermined time period, and setting the drain voltage to a low drain voltage value (VdL), only for a second predetermined time period, thereafter the drain voltage is set to a high drain voltage value (VdH), after elapse of a third predetermined time period, the gate voltage is set to a low gate voltage value (VgL), and wherein the high gate voltage value (VgH), the high drain voltage value (VdH), and the low drain voltage value (VdL) are set so as to satisfy relational expressions of “VgH−VdH<Vth and VgH−VdL>Vth where Vth: a threshold voltage of said converting MOS transistor”, and wherein a potential difference (W) between a value obtained by subtracting the threshold voltage (Vth) of said converting MOS transistor from a low gate voltage value (VgL) and a terminal voltage (VC) of the photoelectric converting device is set to be high, and the initial setting is performed such that the set potential difference (W) is constant in plural optical sensor circuits.