A New Sampling Scheme for High-Sensitivity, Extended-Dynamic-Range Complementary Metal Oxide Semiconductor (CMOS) Imaging Pixel Sensors

A new sampling scheme for extending the dynamic range of a high-sensitivity complementary metal oxide semiconductor (CMOS) image sensor is proposed. The photodiode-type CMOS pixel imager, consisting of a transfer gate transistor for transporting photoelectrons from a sensing region to a readout region, is highly sensitive but suffers form a poor dynamic range. The new sampling scheme and a ratiometric processing circuit can improve the dynamic range of the pixel imager by about 24 dB by making use of the photo response of the readout node. Optimization of the sensing region area/readout region area can be applied to specific applications such as low-light imaging and high-speed imaging applications. Experimental results indicate that this pixel can maintain high sensitivity at low illumination while obtaining an extended dynamic range about 10 dB higher than that of the conventional 3-transistor (3-T) photodiode-type CMOS pixel imager.