A pulse width modulation（ PWM） readout method

with self-adaptive reference voltage is introduced to enlarge dynamic range of digital image sensor. The pixel array is divided into blocks with the same pixel numbers

and each block generates its reference voltage through the voltage generator

which makes it related to illumination intensity within the block. It can double the dynamic range from 48 d B of typical PWM digital image sensors to96 d B in theory

and the simulation shows it can achieve dynamic range of 88. 16 d B. Main noise sources within the pixel block and the deviation brought in by sampling capacitance are studied. A pixel block circuit of 4 × 4 is achieved by 65 nm CMOS process. Comparison of outputs and theory values are made under high and low luminance

and the reason which cause errors is analyzed.