Wide dynamic range CMOS active pixel sensor using a stacked-photodiode structure

In this paper, we propose a stacked-photodiode structure to extend the dynamic range of the CMOS active pixel sensor (APS). The proposed APS uses two photodiodes with different sensitivities and two additional MOSFETs in comparison with a conventional 3-transistor APS. Although the size of pixel is slightly larger than that of conventional 3-transistor APS, extension of the dynamic range is much easier than conventional methods by adjusting the reference voltage. The dynamic range of the proposed APS was greater than 103 dB. The designed circuit has been fabricated by using 0.35 μm 2-poly 4-metal standard CMOS technology and its characteristics have been evaluated.