A 64 × 64 CMOS Active Pixel Sensor Operative at a Very Low Illumination Level

A CMOS image sensor that focuses on very low illumination applications is described. The sensor uses a 0.35 μm 2-poly 4-metal standard CMOS process and is realized as a 64 × 64 array of 7.8 × 7.4 μm 2 active pixels with a fill factor of 33%. The unit pixel contains 3 NMOSFETs and a gate-body tied PMOSFET photodetector. The image sensor features highly sensitive characteristics because of the photodetector which has a maximum photo-responsivity of 2.5 × 10 2 A/W, and a pixel configuration with a voltage gain of about 1.3 and a pixel sensitivity of 1.2 × 10 V/lx·s. Furthermore, this sensor has a well-defined output voltage at a very low illumination level of sub-10 lx, such as with a photo-sensitivity of 35mV/lx without adjusting gain and integration time.