Research Of TDI-CMOS Imaging System And Design Of FPN Correction Method

Traditional linear-array image sensor adopts one-dimensional pixel array structure and captures two-dimensional images by scanning motion.Therefore,its imaging performance is limited by speed of relative movement and illumination intensity.Time-delay-integration(TDI)image sensor adopts two-dimensional pixel array structure.Pixels in different rows can implement multiple exposures on the same scene by means of scanning,equivalent to increasing the exposure time,thus effectively improving the signal-to-noise ratio and sensitivity of the image sensor.TDI-CMOS image sensor(TDI-CIS)has the advantages of being compatible with CMOS process,high integration level,low power consumption,resistance to radiation,etc.It has gradually become a research hotspot.In the process of the development of TDI-CIS,it is extremely important to carry out function test and performance analysis of the sensor.Therefore,the research of imaging quality and imaging system of TDI-CIS is of great significance.In order to eliminate the fixed-pattern noise(FPN)in the output image of TDICIS,the working principle of TDI-CIS is first studied.Then,a noise model of TDICIS is proposed based on the analysis of FPN,including its source,noise characteristics and influence on imaging quality.According to the noise model,a FPN correction method based on gray value compensation is designed.Firstly,a large number of sample images are captured under uniform illumination.Then,row FPN(RFPN)and column FPN(CFPN)are estimated based on the row-mean vector and column-mean vector of all sample images,respectively.Finally,RFPN are corrected by adding the estimated RFPN gray value to the original gray values of pixels in the corresponding row,and CFPN are corrected by subtracting the estimated CFPN gray value from the original gray values of pixels in the corresponding column.In order to validate the effectiveness of the proposed FPN correction method,an imaging system is first designed based on a 128-stage TDI-CIS with on-chip analog accumulator.The key techniques in the design of the system are studied,including the design of printed-circuit-board with TDI-CIS,system on a programmable chip(SoPC),and mechanical motion device with conveyor belt.The SoPC is the embedded control system of the imaging system,which is designed based on a FPGA development-board.Then,one hundred sample images are captured with the designed imaging system,and FPN estimation is accomplished in MATLAB.Finally,FPN correction is carried out.Experimental results show that,after correcting the FPN in the image captured under uniform illumination with the proposed method,the standard-deviation of row-mean vector decreases from 5.6798 to 0.4214 LSB,and the standard-deviation of column-mean vector decreases from 15.2080 to 13.4623 LSB;and both kinds of FPN in the real images are effectively corrected.The designed method can effectively eliminate the FPN in the output image of TDI-CIS.