Research On Signal Readout Circuit Based On CdZnTe Pixel-lated Radiation Detector

As a typical representative of Ⅱ-Ⅵ compound semiconductor materials,CdZnTe crystal has attracted extensive attention from domestic and foreign research institutions in the field of nuclear radiation energy spectrum detection and imaging detection due to its high resistivity,plateau sub-number and excellent energy resolution performance at room temperature.At present,relevant institutions have made significant breakthroughs in the processing of CdZnTe materials,so that CdZnTe detectors are also widely used in nuclear physics diagnosis,nuclear medical imaging,astrophysics and other related research fields.Firstly,this paper analyzed and summarized the current research status of CdZnTe detector by domestic and foreign researchers,and briefly introduced the principle and detection system of CdZnTe pixel array detector,and also introduced the detector signal readout electronics system,and determined the main research work of this paper.Secondly,we analyzed the signal characteristics of the front-end electronic circuit of the detection system.Because the output signal of CdZnTe crystal irradiated by high-energy X-ray is instantaneous weak pulse electric signal,and the time is very short,the basic principle of the preamplifier was analyzed in this paper.A functional circuit of charge sensitive preamplifier wasdesigned based on the basic structure of the traditional charge sensitive preamplifier.The circuit structure can change the attenuation time constant of the output signal without changing the feedback resistance and capacitance,and the sensitivity have been improved.Finally,by setting up the test platform,the analysis shows that the output signal of the designed charge-sensitive preamplifier has a rise time of about 10ns and a fall time of about 150μs.Compared with A250 and 142A,the charge-sensitive preamplifier designed in this paper has a certain application prospect.Then,according to the characteristics of the output signal of the preamplifier,a shaping amplifier circuit was proposed to amplify and shape the signal linearly.In the field of nuclear electronics,the shaping of nuclear pulse is usually aimed at quasi-gaussian waveform.On the basis of understanding the principle of filter shaping amplification circuit,this paper adopts LMH6628,a high bandwidth and high speed operational amplifier,and then adopts the polar-zero cancellation circuit,DC bias correction circuit,2-level Sallen-Key active filter and drive circuit to complete the design of filter shaping amplification circuit.Finally,the experimental platform was built based on the accurate pulse source of nuclear imitation to complete the experimental verification of charge-sensitive preamplifier and two-stage quasi-gaussian filter shaper amplifier.The output pulse waveform of the designed and prepared circuit wasconsistent with the simulation results of the circuit,which meet the requirements of the high resolution semiconductor energy spectrum measurement system.The energy resolution and peak efficiency of CdZnTe detector were tested by Cs¹³⁷ on CdZnTe crystal.The energy resolution of each pixel was mainly distributed in 6.25%⁷.5%.The peak efficiency of all pixels in the detector system was mainly distributed in 65%⁷2.5%and mainly concentrated in about 67.5%.