Research On Background Suppression Circuit Of MCT Infrared Detector

Mercury cadmium telluride(HgCdTe,MCT)material has many advantages such as adjustable band gap,high quantum efficiency and so on,which is the mainstream material for infrared photodetectors.For infrared detectors working in high background environment,the background current may be greater than the signal current.The high background current and dark current will quickly saturate the integrated capacitor in the readout circuit,which will reduce the signal-to-noise ratio and the dynamic range.The dark current of the MCT detector reflects the essential characteristic of the detector.The dark current of the detector will increase as the area of the PN junction becomes larger.The dark current will increase the noise of the device.By reducing the dark current of the MCT infrared detector,the performance such as the signal-to-noise ratio of the focal plane can be improved.The main purpose of this thesis is to reduce the influence of the dark current and background current of the MCT infrared detector on infrared imaging.The research content of this paper includes:(1)the dark current mechanism of MCT infrared detector is studied through device simulation,which provides theoretical reference for process optimization of reducing device dark current;(2)the background suppression circuit is designed to reduce the dark current of the detector in the integrated signal and the background signal,which can reduce the influence of background noise on infrared imaging.For large-scale infrared focal planes,it is difficult to extend the integration time by increasing the integration capacitance in the limited unit circuit area.In the readout circuit,the dark current of detector and background radiation signal in the integral signal can be reduced by adding background suppression circuit.It can prolong the integration time and improve the signal-to-noise ratio of focal plane.In this paper,the dark current data for long-wavelength infrared detectors and medium-wavelength MCT infrared detectors are fitted and analyzed.Based on the dark current level of the medium and long wavelength HgCdTe infrared detector and the background environment in which the detector works,two kinds of background suppression circuits are designed,which are two-step background suppression circuit and multi-mode background suppression circuit.The two-step background suppression structure adopts the combination of common mode noise suppression and differential mode noise suppression,which can effectively reduce the fixed pattern noise and increase the dynamic range within a larger background noise range.The multi-mode background suppression circuit adopts an adaptive background suppression structure.The three readout modes can be selected according to the dark current and background current,dynamic range,non-uniformity and frame rate for this circuit.It has the characteristics of high flexibility and wide adaptability.The main representative innovations of this article are as follows:1.The dark current of HgCdTe infrared detector is measured and analyzed.Based on the measured results,the influence of the non-uniformity of dark current on infrared imaging is discussed.The dark current mechanism of medium-wavelength MCT infrared detectors is studied by using the method of variable implantation area.2.Based on the structure of common mode background suppression and differential mode background suppression,a two-step background suppression structure of long wavelength infrared readout circuit is designed and tested.Based on the differential mode background suppression,a signal amplification and reduction module is introduced to improve the memory accuracy of current storage background suppression module.It is verified that the common mode background suppression range is from 0?1.1 ?A expanded to 0?2.3 ?A at 80 K temperature.When the background current is greater than 130 n A,the accuracy error of differential mode background suppression is less than 1%.After the two-step background suppression function is turned on for the long-wave infrared focal plane arrays,the FPN value drops from 56.7 m V to 5.8 m V.3.A multi-mode adaptive background suppression readout circuit is designed.The readout mode and the self-compensation mode of the signal is simulated and analyzed,which can be selected according to the working environment.The dichotomy method is introduced to search the signal of the DAC to improve the memory efficiency in the background memory mode.The circuit simulation and layout design are completed.The output swing is 2.55 V and the background suppression range is 0.122?1 ?A?...