A UNIT PIXEL OF CMOS IMAGE SENSOR

摘要

A unit pixel of a CMOS(Complementary Metal Oxide Semiconductor) image sensor is provided to compensate a dark current generated in a photo diode by detecting an output voltage of a drive transistor and supplying a compensation current to the photo diode when the output voltage is reduced at a predetermined level or less. A photo diode(PD) generates and stores an optical charge. A gate of a drive transistor(Q2) receives the charge stored in the photo diode(PD), and a source of the drive transistor(Q2) outputs the received charge as a voltage value. A drain of the drive transistor(Q2) receives a power supply voltage. A saturation sensing device having an inverter(21) and a feedback line(22) receives the source voltage of the drive transistor(Q2), and judges a current state as a saturation state when the source voltage is lower than a predetermined reference voltage. A switching transistor(Q4) short-circuits/opens connection of the power supply voltage and the gate of the drive transistor(Q2) according to the saturation state judgment of the saturation sensing device.