Abstract
In this thesis, we present a novel imager that uses high performance Phototransistor Photodetectors (PTPD). This work is different from other CMOS imagers which have to sense the voltage drop after the integration time because of low photocurrent. PTPD has linear wide-dynamic-range photocurrent (~ pA to ~ μA) under wide-dynamic-range illumination (0 lux. to 10000 lux.). So we can sense the photocurrent directly without accumulating charges. The imager is constructed by: (1)PTPD that converts the light intensity into the photocurrent; (2)logarithmic amplifier that obtains the wide dynamic range photocurrent from the pixel and outputs the voltage signal after cancelling the dark current; (3)Correlated Double Sampling(CDS) circuit that cancels the fixed-pattern noise(FPN) which results from process variations. There are two PTPDs (one is covered with metal to perform a dark current sensor) in each pixel for automatic cancellation of the dark current. The design has been fabricated in TSMC 3-poly, 3-metal, 0.35μm SiGe BiCMOS technology. Experimental results confirm the ability to convert the wide dynamic range photocurrent to the voltage signals.