Optimization of pixel structure for reducing knee point variation in the logarithmic response of linear-logarithmic CMOS image sensor

Abstract

We propose a linear-logarithmic CMOS image sensor with a modifiable dynamic range by adjusting the reference voltages. To implement these characteristics, a photogate and a MOS cascode are integrated with the pixel structure in conjunction with the photodiode. The new linear-logarithmic pixel is based on a conventional 3-transistor active pixel sensor structure. In addition, we propose the optimized pixel with reduced knee point variation in the logarithmic response. The proposed pixel has been designed and fabricated using a 0.35-μm 2-poly 4-metal standard CMOS process.