Position Readout Circuit Study Of Far Ultraviolet Photon Counting Imaging Detector Based On Charge Division Anode

Since many celestials emission is extremely faint ultraviolet radiation (about10nm~400nm range of electromagnetic wavelength), the application of ultravioletphoton counting imaging detect in astronomy, deep space exploration, remotesensing and other areas of the ionosphere has a very important significance andneeds. With the success of "Chang E" Three of the launch, the two-dimensionalposition sensitive ultraviolet photon counting imaging detectors have a greatapplication in deep space exploration.The far ultraviolet photon counting imaging detector developed by our projectteam mainly contains four parts components: micro-channel plate (MCP) stackcoated with cesium iodide (CsI) cathode, position sensitive charge anode,positionreadout circuit and data acquisition software. The detector works as follows: theultraviolet photons incident on the CsI cathode are converted into photoelectrons andthe optoelectronics are multiplier to106~107forming the electron cloud after MCPstack. Electron cloud generated after the resistance of the WSA anode receiving onits back induced charge pulses which are input to the subsequent position readoutcircuit. The position of the electron cloud centroid or of the incident ultravioletphotons is determined by the signals of pulse.The research of position readout circuit is an important part of the far-ultraviolet photon counting imaging detectors’ work, but also is the focal point ofthis paper. It is divided into two parts: analog processing circuitry and a dataacquisition circuit. Its role is to amplify the charge signals output from the anode andto maintenance and acquisition the signals. This paper introduces the structure ofphoton counting detector based position sensitive anode. Followed is the design of asystem based on FPGA+USB2.0data acquisition and transmission circuit system.Then detailed analysis of various components and working principle of the circuit isintroduced, and the relevant hardware and software design is given. Finally, thedebugging of the data acquisition circuit, and with its resolution of the detector wastested on the test occurred during the image smearing and blurring are analyzed andpresented solutions.Experimental results indicate that the performance of the circuit and theimaging detector developed by ourselves is well. It shows that a clear image can beobtained with a resolution of5lp/mm when the photon counting rates are under100kcounts/s. The FUV detector meets resolution requirements of practicalapplication.Innovation of this paper is twofold: first, the part of peak hold module ofvoltage pulse in the analog processing circuit is removed in the far ultravioletdetector. Instead, an A/D converter chip with sampling and holding function is usedto achieve accurate sampling, which reduces the analog processing circuit designdifficulty; Second, the developed data acquisition circuit can completely replaceNational Instruments (NI) company’s data acquisition card and the detector systemsengineering to meet future needs.