A Charge Compensation Phototransistor for High-Dynamic-Range CMOS Image Sensors

This paper presents a charge compensation phototransistor for high-dynamic-range CMOS image sensors (CIS). With a built-in charge compensation mechanism, the photoresponse of the proposed device can switch between the linear mode and the logarithmic mode automatically, according to the incident light intensity. In particular, the device does not saturate until approximately 0.5 W/cm
²
, almost 5 times the brightness of the sun. Therefore, CIS with this proposed phototransistor demonstrates a measured dynamic range of 167 dB, and an output swing of more than 2 V without amplification. The nonideal behavior of the proposed device due to the thermal effect and the parasitic resistances is investigated when exposed with high incident light intensity. In addition, the nonuniform response of the pixel array is exhibited and analyzed.