Patent ID: 7696463
Filing Date: 2010-04-13
Classification: H04N

Abstract:
1. A photosensor circuit comprising: a photoelectric conversion element for converting a light signal into a current signal; a first MOS transistor for converting the current signal, output by said photoelectric conversion element, into a voltage signal having a logarithmic characteristic in a weak inversion state; a first capacitor element connected to a voltage detection terminal of said photoelectric conversion element; a second capacitor element for keeping the voltage signal; a second MOS transistor for controlling electrical charge transfer between said first capacitor element and said second capacitor element; and control means for supplying gate voltages and drain voltages to said first MOS transistor and said second MOS transistor, said control means performing voltage control to: set the drain voltage of said first MOS transistor at a high drain voltage value (VdH) and the gate voltage of said first MOS transistor at a high voltage value (Vg then set the drain voltage of said first MOS transistor at a low drain voltage value (VdL) after turning off said second MOS transistor to place said second capacitor element in an opened state and set the gate voltage of said first MOS transistor at a medium potential (Vg then set the drain voltage of said first MOS transistor at the high drain voltage value (VdH) and then, after passage of a third predetermined time, set the gate voltage of said first MOS transistor at a low voltage (Vg then, after passage of a predetermined time, set the gate voltage of said second MOS transistor at a predetermined voltage value (Vg then set a terminal voltage of said second MOS transistor as a sensor output signal after turning off said second MOS transistor to place said second capacitor element in the opened state.