A Novel Linear-Logarithmic Active Pixel CMOS Image Sensor with wide dynamic range

Abstract

Many image sensor applications require high dynamic range under both high and low illumination environments. Hence, a novel active pixel architecture is proposed using TSMC 0.18μm 1P6M 1.8V mixed signal processing. The proposed sensor differs from the linear pixel sensor (3T APS) and the logarithmic pixel sensor (Logarithmic Pixel). The framework proposed in this paper achieves a dynamic range of up to 160 dB. It can be applied to the high dynamic range CMOS image sensors. In terms of circuit design, in order to achieve high dynamic range, this paper adopts a linear-logarithmic active pixel architecture as the base. The main purpose is to pass the output of the source follower back to gate of transistor, which is in the logarithmic architecture. When the photocurrent is large, the output of the source follower is lowered, thereby increasing the output current of the transistor to delay the voltage drop rate of the sensing terminal of the photodiode and improve the dynamic range of the pixel sensor. In addition, due to the low complexity of the circuit, this architecture also has a higher fill factor. It can be as high as 55%, which is much higher than that of the conventional high dynamic range sensors.