A CMOS image sensor with nearly unity-gain source follower and optimized column amplifier

This paper presents a CMOS image sensor with in-pixel nearly unity-gain pMOS transistor based source followers and optimized column-parallel amplifiers. The prototype sensor has been fabricated in a 0.18 μm CMOS process. By eliminating the body effect of the source follower transistor, the voltage gain for the pixel-level readout circuitry approaches unity. The use of a single-ended common-source cascode amplifier with ground rail regulation improves the PSRR of the column-parallel analog front-end circuitry and further the noise performance. Electrical characterization results show that the proposed pixel improves the conversion gain after the in-pixel source follower by 42% compared to that of the conventional structure. The prototype sensor with proposed readout architecture reaches a 1.1e
^-
input-referred temporal noise with a column-level ×16 analog gain.