Design Of Ultraviolet Single Photon Counting Imaging System Based On Avalanche Photodiode

UV single photon detection technology is a new photoelectric detection technology,which can be widely used in national defense,industrial and agricultural production,scientific exploration,environmental monitoring and other fields.The research of imaging systems based on SiC UV single photon detectors is of great significance in promoting the wide application of this technology.Based on the 1×8 SiC APD solar-blind UV array detector assembly,a UV imaging system covering wavelength band which range from 240 nm to 280 nm is designed.The corresponding pixel protection circuit is designed considering the reliability of APD.Firstly,the characteristics of surface solar radiation and its effects on the performance of solar-blind ultraviolet detection systems are analyzed.At the same time,the principle of optical-mechanical-scan imaging and the working principle of APD are introduced.Then the importance of the protection circuit for APD arrays is described and several kinds of devices and typical structures for high voltage protection are compared.In the design of UV imaging system,serial and hybrid scanning method is used according to the size of APD linear array and the characteristics of the imaging target,and object scanning is realized through the two-dimensional scanning turntable.In the design of protection circuit that is in UV detection module,a new type of clamp protection circuit structure with diode and resistor cross-combination is adopted,in which common diodes and Zener diodes are used as clamping structures for comparative study.Finally,the design of circuit and layout are completed based on the CSMC 0.18?m high voltage process;UV lens and filter are used in the pre-optical system for optical focusing and shielding the solar background radiation respectively.In the data acquisition system,the technology of waveform digitization based on data acquisition card and upper computer is used to realize the data acquisition of the chip.At the same time,the UV and visible images are obtained by APD array and CCD camera respecttively,and the whole system is finally assembled.In addition,the LabVIEW software platform has been adopted in the controlling programing of the imaging system and is used to realize the function of the stage scanning,real-time data acquisition and image display?In the high-voltage protection circuit,the validity of the protection structure is verified through tests.The output voltage of both types of protection circuits are lower than the gate oxide breakdown voltage of MOS transistor when the input voltage is 170 V,in which the structure of Zener diode is more effectively;it is initially verified that the imaging system can sense the ultraviolet light and realize photon counting imaging in the imaging demonstration experiment,at the same time,the relative positions of the two light sources can be distinguished and the relative position of the ultraviolet light in the background image can be det ermined.This provides an environment for the test of readout circuit chip.Finally,the corresponding design improvement strategy is provided for the existing shortcomings.