| Linear array image sensor is a special kind of image sensor that uses a line of effective pixels to obtain two-dimensional image information with high resolution.The line image sensor is particularly suitable for applications in the high-tech fields,such as space imaging and medical imaging.Time delay integration(TDI)image sensor is a special kind of line image sensor with high signal-to-noise ratio and sensitivity under conditions of high scanning speed and low illumination.The design of low noise accumulator is one of the key techniques to realize the time delay integration in CMOS image sensor technology.Based on the principle of the traditional analog accumulator for TDI CIS,this paper studies the noise of the analog accumulator and the optimal stages with a fixed silicon area.Firstly,the noise model of the device,the representation and calculation method,and the simulation methods of the noise are studied.The noise characteristics of three simple switched capacitor circuits are analyzed and the results are verified by the PSS and PNoise simulation of Spectre.The various exposure modes and the principle of analog accumulator are analyzed in this paper,and the key techniques to eliminate amplifier offset and charge injection effect are described in detail.Finally,the relationship among the improved SNR,the stages and the input noise is obtained by analyzing the noise characteristics of the analog accumulator and the relationship between the silicon area,capacitance and stages.Thus the relationship between the optimal stages and the input noise is obtained.As an example,when the fixed silicon area is 122500?m~2,and the noise of the input signal is greater than 2mV,the optimal stages are 120 stages.And then a fast transient noise simulation model(TNSM)is proposed and shown to be effective by transient noise simulation(TNS).Compared with the speed of transient noise simulation,that of TNSM is improved by 200 times.Finally the numerical analysis is verified by the TNSM. |
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