A 3.9-μm pixel pitch VGA format 10-b digital output CMOS image sensor with 1.5 transistor/pixel has been developed for mobile applications. The newly developed CMOS pixel architecture realizes the minimum number of the transistors in one pixel. Small pixel size and sufficient fill factor are achieved by using the shared pixel architecture and floating diffusion driving. High conversion gain, low random noise, and low dark current are achieved by buried photodiode with complete charge transfer capability and correlated double sampling (CDS) circuit. The image sensor is fabricated in a thin planarized 0.35-μm single poly-Si double-metal customized CMOS process in order to provide good image performance. The image sensor achieves low noise floor of 330 μV and low dark current of 50 pA/cm 2 at 45 °C. This image sensor also realized various functions by on-chip digital and analog circuits.