Study On Techniques To Enhance The Dynamic Range Of CMOS Image Sensors

CMOS image sensor is a very large-scale mixed integrated system, integrated with photodetectors, analog circuits and digital circuits. Compared with CCD technology, CMOS image sensor can be fabricated with the standard CMOS processes. The main advantages of CMOS image sensors are their high level of integration, random accessibility, and low-voltage, low power operation. Application prospect of CMOS image sense is abroad.Firstly, the paper analyzed the principle of silicon photoeffect, CMOS compatible photodetectors and limits from the CMOS image sensor. Secondly, random noise sources and fixed pattern noise sources from CMOS image sensor are analyzed in detail, and then fixed pattern noise was calculated in theory.Dynamic range is a critical figure of merit for image sensors. Often a sensor with higher dynamic range is regarded as higher quality than one with lower dynamic range. Since a sensor with higher dynamic can detect a wider range of scene illumination than one with lower dynamic range, it can produce images with greater detail. Dynamic range of silicon is often not wide enough to satisfy the requirements of application. It is necessary to study techniques of enhancing dynamic range of CMOS image sensor. It is necessary to study techniques of enhancing dynamic range of CMOS image sensor. Three techniques of enhancing dynamic range from three levels was investigated in the paper: Firstly, technique of photoelectric logarithmic response was studied, and the method changed the pixel structure and belonged to pixel level; Secondly, the technique of automatic gain control was researched, and the method is realized by adjusting the gain of pre-amplifier and belonged to the level of analog preprocessing; Finally, the technique of adaptive adjusting exposure was investigated, and the method is implemented by adjusting exposure time to adapt scene illumination and belonged to System-On-Chip(SOC) system level of CMOS image sensor.The paper is a part of research work on Tianjin technological key project"Study on CMOS image sensors with large dynamic range and high performance", and it also is a part of the project, supported by National Natural Science Foundation of China,"Study on key techniques of large dynamic range and tens of mega pixels CMOS image sensor based on the deep submicron processes".