Abstract
We present a novel image sensor that uses the new read out circuit. This work is different from other CMOS imagers which have to sense the voltage drop after the integration time because of low photocurrent charging parasitic capacitance. New read out circuit converts wide range photo current into narrow range voltage, and contributes it to the usage of backend circuit. The photodiode fabricated in 0.35 um SiGe BiCMOS technology has linear wide-dynamic-range photocurrent (~ pA to ~ 40 uA) under wide-dynamic-range illumination (0.0lux. to 460000 lux.). So we can sense the photocurrent directly without accumulating charges. The novel image sensor is constructed by: (1) Photodiode, whose detecting region is base-collector (BC) junction, converts the light intensity into the photocurrent. (2) New read out circuit that obtains the wide dynamic range photocurrent from the pixel and outputs the voltage signal. (3) Correlated Double Sampling (CDS) circuit that cancels the fixed-pattern noise (FPN) which results from process variations. (4) Constant gm bias circuit contributes supply- independent-biasing to the imager. (5) Peripheral digital control circuit is integrated with analog circuit and pixel array, which achieves the system-on-a chip design. This work has been fabricated in TSMC 0.35 um SiGe BiCMOS technology. Experimental results confirm the ability of the wide-dynamic range readout circuit.