CMOS active pixel sensor with variable dynamic range using a double-photodiode feedback structure

A double-photodiode feedback structure to extend the dynamic range (DR) of the CMOS active pixel sensor (APS) has been proposed in this paper. Since the proposed APS requires one additional photodiode and two additional nMOSFETs in comparison with a conventional 3-transistor (TR) APS, the size of pixel is slightly larger than that of conventional 3-TR APS. However, extension of the dynamic range is much easier than conventional methods by adjusting the reset voltage and photo current of the additional photodiode. The proposed APS exhibits a wide and variable dynamic range with high sensitivity at low illumination and low sensitivity at high illumination.