Current-Mode CMOS Imaging Sensor With Velocity Saturation Mode of Operation and Feedback Mechanism

We present a complementary metal-oxide-semiconductor (CMOS) imaging sensor containing two novelties in the field of current mode sensing. First, the in-pixel read-out transistor operates in velocity saturation mode and allows for high linearity between integrated photo charges and output current of the pixel. Second, the column parallel read-out circuitry includes a novel current conveyor with a feedback mechanism, which improves linearity of the output current and leads to improvements in fixed pattern noise. Correlated double sampling, a noise reduction technique, is performed on-chip via current mode circuits to improve spatial noise characteristics of the imager. A prototype of the proposed imaging sensor was fabricated in 0.18 μm triple well CMOS process. The sensor operation and measurements are presented.