Abstract
In this dissertation, some factors that influence the performance of 4-T photodiode type CMOS imagers are studied through experiments and simulations. High sensitivity of this imager can be achieved by carefully designing the area of readout diode, area ratio of sensing diode to readout diode and the readout scheme. However, tradeoff between sensitivity and dynamic range in this imager is inevitable. We then propose a new readout scheme to extend the maximum non-saturating input signal at high light intensity while maintaining the high sensitivity performance at low light intensity. Experimental results show that high sensitivity can be obtained with a small readout diode area at the cost of large dark signals. In addition, the newly proposed readout scheme achieves good performances of both high sensitivity at low light intensity and extended dynamic range.