The Research Of Low Temperature ROIC Design For Infrared Imaging Systems

Infrared imaging technology is wildely used in military monitoring, resourceexploration, scientific research, industrial and agricultural fields, and so on. However,due to the response characteristic of detector materials and thermal noise, detectionsystems need to work in the cryogenic environment. The performance of thecryogenic readout integrated circuits (ROIC) has become an important factor for thethe overall detection system performance. Therefore, the design of cryogenic ROICfor low-temperature infrared applications is researched in this paper. The maincontents are as follows:First, through theoretical analysis and MOSFET low-tenperature testing, thecharacteristics of MOSFETs using Chartered0.35μm CMOS process are studied, andthe reason of the abnormal changes of the MOS I-V characteristics caused by carrierfreeze-out effect at ultra low-temperatures are explained. Meanwhile, the changes ofdigital and analog circuit performance resulting from MOSFETs I-V characteristics atlow-temperatures are analyzed. Then, based on the analysis of MOS characteristics atlow-temperatures, the MOSFET model for low temperature circuit simulation at80Kand135K is set up. The model is based on BSIM3model, and use correnctionparameters to describe carrier freeze-out effect at low temperatures to improve thefitting accuracy for low temperature MOSFET simulation.Secondly, a low power readout architecture for512×512infrared facol planearray (FPA) is proposed. Through low-temperature MOSFET model simulation, thecircuit can work in a wide temperature range from80K to300K. By using thehigh-gain cascode CTIA, charge transfer based column amplifier, a novel outputbuffer and optimazed column readout timing, the readout system can realize over10MHz ouptut rate, while consumes less than70mW.Thirdly, two cryogenic analog-to-digital converters (ADCs) is proposed forinfrared readout system applications. One is a cyclic ADC with mismatch correction.By using the optimized MDAC structure and improved RSD calibration technique,the operation amplifer offset and MDAC gain errors resulting from device mismatchare eliminated. Meanwhile, the tolerance of the camparator offset is improved. Theother one is a SAR ADC with temperature compensation. By using temperature compensated time-domain comparator, the stability of the conversion speed andaccuracy in80K to300K operated temperature range is improved.In the paper, the design of cryogenic ROIC and ADCs for infrared readoutsystems is discussed in detail through theoretical analysis, device modeling, circuitsimulaton and testing. The simulation and test results prove that the circuits fully meetthe needs of low temperature applications.