Research On Key Techniques Of TDI CMOS Image Sensor Based On Mixed-domain Accumulation

Time-Delay-Integration (TDI) image sensor is a particular visual sensor, which cancapture image information in the form of two dimensions array working as thescanning mode of one line pixels. And the TDI image sensor achieves higher scanningspeed and higher resolution compared to traditional array image sensor, so it isespecially suitable for applications in space image, aerial photography, industrialdetection and security. As the scaling of CMOS standard process technology andincreasing of integration in processing circuit, the TDI image sensor based on CMOSprocess technology becomes the most popular issue in the field of imaging system.Therefore, this paper will focus on the mixed-domain-accumulation mode andprocessing circuit design, and research the key technology in the TDI CMOS imagesensor.Supporting by in-depth analysis of current research scheme in TDI image sensor, asystematic based on the mixed-domain-accumulation mode which can save the siliconarea and realize high speed readout is firstly proposed. Considering the feature and thedevelopment tendency, a linear current-mode pixel is designed. And a32stagesmixed-domain accumulator is designed based on the research of the readout circuit inTDI CMOS image sensor, and the noise characteristic is also analyzed. Finally, twotypes of column level analog-to-digital converters (ADCs) are proposed for the TDIreadout system. One is a single-slope ADC with error calibration, the other one is aCyclic ADC which can be used to digitalized current signal directly. In this paper, thecorresponding current-mode pixel and the readout circuit are discussed in detailthrough theoretical analysis, system modeling, circuit simulation and testing. Themain blocks have been fabricated and verified. The result of simulation and testingindicates that the proposed TDI CMOS image sensor works effectively.The creative work of the paper include:1. A structure of mixed-domain-accumulation is proposed based on the32stagesTDI CMOS image sensor. The new structure combines the advantages ofanalog-domain and digital domain, which can save the silicon area and relax therestrictions of the converting speed of ADC. The result of simulation indicates that thesignal-to-noise ratio can be improved as well as analog-domain or digital-domain.2. A low noise current accumulator is proposed based on the principle of TDI imagesensor and mixed-domain-accumulation mode structure. And the optimization designmethods of low noise current accumulator are derived.3. A current mode ADC which can be used to digitalized current signal is proposed.The power efficiency can be guaranteed without adding the silicon area or decreasing the precision. Meanwhile, a current-mode sample-and-hold circuit, which can be usedto remove the signal-dependent charge injection and suppress the signal-independentcharge injection, is adopted to improve the precision of the ADC.