A Dark Pixel Calibration System Design Based On CIS

CMOS image sensor has many advantages,such as high level of integration,low prices,low power consumption,light weight and short development cycle,compared with CCD image sensor.So,the CMOS image sensor is used more and more widely,especially in the mobile phone camera,digital camera,industrial camera,etc.But the CMOS image sensor has more random noise,fixed pattern noise(FPN,fixed pattern noise)and dark current noise,causing a CMOS image sensor figure with the disadvantages of small dynamic range and low SNR,which have restricted the applications of CMOS image sensor in the field of high-end situations.Above all,How to improve the figure quality of CMOS image sensor has a very high research value.Firstly,this paper presents an overview of CMOS image sensor,including the development,and the comparison with CCD image sensor.Then the type and the principle of the noise in CMOS image sensor,especially the dark current noise,has been introduced.Besides,the research status of how to eliminate the dark current and several typi cal algorithms of the dark pixel calibration have been shown,which leads to the dark pixel calibration algorithm adopted by this paper.In order to eliminate the dark current noise of CMOS image sensor(CIS),which affects the quality of the images in a large degree,an adaptive calibration circuit of dark current in CMOS image sensor has been proposed in this paper.What's more,the calibration circuit can achieve median filtering function,resulting in the decrease of the peak in dark current noise.Meanwhile,the design can accomplish 3 modes,including the single frame calibration correction,the multiple frames and the negative feedback correction calibration,which makes the algorithm to adapt to different occasions,and different calibration results.At the same time,different calibration value of the maximum,minimum,average value or median can be adopted with the measure of statistics.After completing the design,the circuit has been compiled and the clock gating strategy has been used to decrease the power consumption and the area.Debussy,LEDA,ncverilog,Formality and various EDA tools have been used to validate the circuit while the C model has been established for data comparison.The design of dark pixel calibration system of CMOS image sensor has been tested in the hardware chip.The test results show that the accurate dark current value has been obtained with the method and the fixed pattern noise introduced by dark current is eliminated,which brings about the great improvement of the image quality.