A CMOS Image Sensor with a Buried-Channel Source Follower

This paper presents a CMOS image sensor with a pinned-photodiode 4T active-pixel design (APS) that uses a buried-channel source follower (BSF) as the in-pixel amplifier. A prototype of the image sensor has been fabricated in a 0.18mum CMOS process. Measurements show that compared to a regular imager with a standard nMOS transistor surface-mode source follower (SSF), the new pixel structure reduces dark random noise by more than 50% and improves output swing by almost 100%.