Abstract
This thesis presents a dual-mode CMOS image sensor suitable for visible light communication. The dual-mode operation of the proposed imager is image mode and communication mode. There are several innovations in this thesis. First, a compact four transistors pixel structure provides the dual-mode operation. Second, a background cancelling function in communication mode can eliminate the undesired background information and avoid suppressing the output voltage headroom. Third, photo-sensing current summation scheme with a programmable array area is implemented to improve the photo-sensitivity, where the array area is defined by the proposed real-time light source tracking function. The prototype dual-mode CMOS imager chip consisting of 64 × 64 4-T pixel array with n+/p-sub photodiode and pixel pitch as 10 × 10 μm2 with 54.9% fill factor and 3.3V operation has been designed and fabricated in TSMC 0.18μm CMOS 1P6M standard process. The measured results achieve raw image data output in image mode with 1.3V/lux•s sensitivity, and real-time output in communication mode with tunable gain of photo-sensitivity from ×1 to ×64 by proposed current summation feature and maximum receiver bandwidth of 1MHz with 10-9 bit-error rate, respectively. The revised dual-mode CMOS imager chip consisting of 64 × 64 4-T pixel array and pixel pitch as 7.6 × 7.6 μm2 with 45% fill factor and 3.3V operation has been designed and fabricated in TSMC 0.18μm CMOS 1P6M standard process. In image mode, the measured results achieve 1.136V/lux•s sensitivity at 120 fps with 1.093mW power consumption. In communication mode, the measured results achieve a real-time tracking with 5000fps tracking rate and maximum receiver bandwidth of 6MHz with 3.8×10-9 bit-error rate with a reliable background cancelling function.