基于同步自适应匹配的模拟前端暗电流补偿方法研究

Research on Dark Current Compensation Method of Analog Front End Based on Synchronous Adaptive Matching

为抑制像素阵列在曝光阶段的暗电流对图像传感器动态范围和输出图像质量的影响,基于同步自适应的暗电流跟踪机制,提出一种电路与系统级暗电流积分补偿方法。通过采样输出有效光电信号,在无源处理阶段同步进行暗电流消除。该方法不仅可以补偿不同区域暗电流对有效光电信号的影响,而且可解决传统暗电流消除方法对读出电路动态范围会造成衰减的问题。基于该方法,在55 nm CMOS工艺下设计了一种752×512阵列规模的CMOS图像传感器,实现了完整的电路设计、版图设计与后端物理验证。结果显示,采用集成暗电流补偿技术的采样放大电路对暗电流最小补偿精度可以达到12 bit,补偿范围最大可以达到500 mV,单列功耗仅有15.84μW,同时可实现1~4倍的增益,最小增益步进6.25%。实现了从模拟前端根除暗电流对CMOS图像传感器图像质量和动态范围的影响,为高端、高性能的CMOS图像传感器设计提供了一定的理论支撑。

In order to suppress the influence of dark current of pixel array in the exposure stage on the dynamic range and output image quality of image sensor,based on the synchronous adaptive dark current tracking mechanism,an integrated compensation method for dark current at the front of the readout circuit is proposed.While sampling and outputting the effective photoelectric signal,the influence of dark current was eliminated synchronously in the passive processing stage.This method not only compensated for the influence of dark current in different areas on the effective photoelectric signal,but also solved the attenuation problem of the dynamic range of the readout circuit by the traditional dark current elimination method.Based on this scheme,a 752×512 array scale CMOS image sensor was designed in a 55 nm CMOS process,including detailed circuit design,layout design and back-end physical verification.The verification results show that the minimum compensation accuracy of the sampling amplifier circuit with integrated dark current correction technology can reach 12 bit,the maximum compensation range can reach 500 mV,and the single column power consumption is only 15.84μW.At the same time,1-4 times of gain amplification can be achieved,and the minimum gain step is 6.25%.The effect of dark current on the image quality and dynamic range of CMOS image sensor is eliminated from the analog front-end,which provides a theoretical support for high-end and high performance CMOS image sensor design.