The Research On The Key Techniques For CMOS Image Sensor In Surveillance Field

Since the beginning of the new century, the country’s comprehensive nationalstrength and people’s living standards are improved continuously. The state-ownedassets and the personal property and safety of the masses are in need of protection. Thesupervision and management network of the whole society must be improvedconstantly. So the security surveillance system is used widely, almost everywhere inthe city. The social life’s smoothness is effectively guaranteed by these equipments.With the development of the microelectronics, the image sensor plays an importantrole in the security surveillance system, likes the heart, and the performance of theimage sensor derectly decides the effect of the surveillance equipment. So this paperaims at the application of the security surveillance system, analyzes the key technicalproblems of CMOS image sensor, and puts forward the solution.First, against the low-noise requirement of the surveillance system, the mainnoise sources of CMOS image sensor are analyzed. And the theoretical methods andcircuit implementation of noise elimination are presented. Secondly, against the widedynamic range requirement of the surveillance system, the importance of the dynamicrange of CMOS image sensor is introduced, the main reasons of low dynamic range ofCMOS image sensor are analyzed and some methods to improve the dynamic rangeare presented. Again, against the high sensitivity requirement of the surveillancesystem, some methods for increasing the sensitivity of CMOS image sensor arerecommended. At last, through the actual chip test, the theory and methods which thispaper presents are proved that the sensitivity, noise and dynamic range are effectivelyenhanced.This paper has analyzed and improved the noise, dynamic range and sensitivitywhich are more important in CMOS iamge sensor in surveillance field and advancedthe some main creative points below.First, a new low noise and high PSRR circuit configuration is presented, whichreduces the analog circuit noise of CMOS image sensor and improves the imagequality. And according to the correlation of dark current, a method of eliminating thedark current noise by applicating dark current proportional coefficient matrix ispresented, which not only saves hardware resources, but also improves the imagequality under a dark condition.Second, On the basis of the theory that multiple exposures could enhance thedynamic range, a new interlaced multiple exposures way is creatively put forward. While the dynamic range effectively improved, this method also can guarantee theframe rate not to be slow down, and the hardware not to be excessive consumption.At last, for different applications, a new sensitivity boosting technology bychanging the capacitor of the floating node of the pixels is introduced, which achievesthe feasibility of that one chip can apply to the various surveillance conditions.