A 256 X 256 CMOS photo-gate active pixel image sensor is presented. The image sensor uses four MOS transistors within each pixel to buffer the photo-signal, enhance sensitivity, and suppress noise. The pixel size is 20 micrometers X 20 micrometers and was implemented in a standard digital 0.9 micrometers single-polysilicon, double-metal, n-well CMOS process; leading to 25% fill-factor. Row and column decoders and counters are monolithically integrated as well as per column analog signal correlated double-sampling (CDS) processors, yielding a total chip size of approximately 4.5 mm X 5.0 mm. The image sensor features random accessibility and can be employed for electronic panning applications. It is powered from a single 5.0 V source. At 5.0 V power supply, the video signal saturation level is approximately 1,200 mV with rms read-out noise level of approximately 300 (mu) V, yielding a dynamic range of 72 dB (12 bits). The read-out sensitivity is approximately 6.75 (mu) V per electron, indicating a read-out node capacitance of approximately 24 fF which is consistent with the extracted value. The measured dark current (at room temperature) is approximately 160 mV/s, equivalent to 3.3 nA/cm2. The raw fixed pattern noise (exhibited as column-wise streaks) is approximately 20 mV (peak-to-peak) or approximately 1.67% of saturation level. At 15 frames per second, the power dissipation is approximately 75 mW.