This paper reports a CMOS active pixel sensor (APS) of 128/spl times/128 resolution designed for high quantum efficiency. This kind of image sensor can be operated under 3.3 V, and use a new structure of shared-pixel and split-path readout direction. This method has the advantage that the number of transistors in each pixel is reduced to increase the fill factor by enlarging the photo-sensing area; on the other hand, it also raises the speed of readout, and is twice as fast as traditional single direction readout. In addition, we use a delta-difference sampling (DDS) for readout circuit to suppress the fixed pattern noise (FPN). The complete CMOS image sensor is implemented based on TSMC 0.35 /spl mu/m 1P4M CMOS technology.