谱仪放大器中滤波成形电路的一种改进设计

对改进的5阶Butterworth滤波器网络进行了更深入的分析和仿真,并设计出了Sallen-key型有源滤波网络作为谱仪放大器中的滤波成形电路,在Protel DXP中进行了电路仿真,输出的结果满足设计要求.     

参数最优化数字核能谱获取系统研究

为建立最优能量分辨的数字化核能谱装置,探讨了一种参数最优化数字核能谱获取系统的设计原理及软件实现,通过对核信号预采样和自学习,给出最优化滤波方案和前端条件线路最佳参数。与相同条件下模拟多道系统获取的能谱相比,该数字化能谱获取系统优于模拟系统。     

基于实时数字脉冲处理技术的核谱仪研究

本文提出一种基于80 MHz ADC的数字化γ能谱系统。系统由探测器、前端电路、ADC和数字处理单元组成。数字处理在FPGA中完成,主要包括FIR数字滤波、脉冲梯形成形、幅度甄别、数据通讯。为减小高速ADC在采集过程中引入的噪声信号,在数字处理单元实现FIR数字滤波,对数字脉冲信号先进行滤波处理,再进行脉冲梯形成形,得到高分辨率的能谱数据。测量系统中模拟信号全部采用直流耦合,数字脉冲宽度为1.6μs,对137 Cs的能量分辨率达6.88%。     

Minimum-Noise Filters with Good Low-Frequency Rejection

A nuclear pulse spectrometer should have both low noise and minimal sensitivity to slow disturbing signals, e.g. base-line fluctuations due to long CR-couplings. A bipolar filter weight-function (or step response) with area balance is advantageous for the latter, but generally involves increased noise and/or resolving time. This paper derives the optimum area-balanced waveform giving least noise for a defined overall width. Optimum waveforms are illustrated and the noise/signal performance is compared with that of the finite-width unipolar cusp and also with several practical bipolar systems in common use.     

Ultra-Low Noise Charge Sensitive Preamplifier for Scintillation Detection with Avalanche Photodiodes in PET Applications

The need for compact, fast, low-noise front-end electronics in high resolution positron emission tomography (PET) has prompted this effort to design a preamplifier suitable for avalanche photodiode-based scintillation detectors. Due to the small signals from the detectors (< .03 pC/MeV), a preamplifier with ultra-low noise performance in the 5 to 20 MHz range is essential to achieve the timing resolution required by the PET application. Out of many available technologies, a new third generation MOSFET wqas selected and implemented as input transistor in an original charge sensitive (CSP) design. Performance among the best reported to date are obtained. The new design was implemented as a dual-channel preamplifier in high density hybrid (thick film) technology.     

Pulse Die-Away Experiment in Small Graphite Prisms with the “Cold” Neutron Source

Abstract

Recently a remarkable progress has been made in fast ADCs such as flash ADCs. This paper shows a method of applying these fast ADCs to the radiation measurements. Direct sampling and digitizing of output signal from preamplifier were examined using the weighted sum of sampled data in order to obtain the energy of incident radiations. As a result, this method is applied to r-ray spectroscopy by a Nal(Tl) scintillation counter to give sufficient performance. Because the present method treats the signal waveform itself, the standard waveform of input signals can be measured. After the standard waveform was obtained by preliminary measurement, a trial was made to select the similar waveforms to the standard waveform using the resembrance factor. With this selection, improvement of energy resolution was observed in the measurement of ⁶⁰Co γ-ray.     

A Comparison of Various Filter and Discriminator Techniques on Timing with Ge(Li) Detectors

An experimental examination of the effect of several filters and two discriminator techniques on the time measurement of the signals from coaxial Ge(Li) detectors is presented in this paper. The signal to the filters and discriminators was obtained from the output of the charge-sensitive preamplifier in order not to degrade the energy resolution of the system. The discriminators used were a level discriminator for leading-edge discrimination and a fast zero-crossing discriminator. The filters examined for leading-edge discrimination were four RC time-invariant and four RC time-variant filters, and the filters for zero-crossing discrimination were three time-invariant RC filters. A comparison of time-invariant and time-variant filters reveals two advantages of the time-variant filter. These advantages are smaller timing errors and lower discrimination levels. The lower discrimination levels allow the reduction of energy dependent timing errors. Likewise, zero-crossing discrimination provides several improvements over leading-edge discrimination. By a compensation method, timing errors due to charge collection variations are reduced; and, due to the invariancy of the zero-crossing point as a function of amplitude, energy-dependent timing errors are also reduced.     

CR-RC~m滤波器数字化研究

从RC高低通滤波电路输入输出电压之间的线性常系数微分方程出发,推导出数字化CR高通和RC低通滤波器的系统传递函数,进而推导出数字化CR-RC~m成形滤波器的系统传递函数。对数字化CR-RC~m滤波器的频域特征和时域成形特征进行分析和测试,并通过实验,对数字化CR-RC~m成形滤波器滤波成形前后不同脉冲信号的能谱及能谱全能峰能量分辨率进行了测试。实验结果表明,该滤波器可对数字化的核信号成形成高斯型,使脉冲信号的上升沿变缓,峰顶变得更加平坦,提高信噪比,进而提高系统能量分辨率。     

磁质谱仪离子收集器数字化读出系统的研制

研制了一个用于磁质谱仪法拉第筒阵列离子收集器的高精度数字化读出系统,实现对离子束中离子成分的分析与诊断。数字化读出系统由前端处理电路和数据获取模块组成,前端处理电路采用门控积分器将418通道微弱电荷信号转换为电压信号,数据获取模块将电压信号数字化后,通过以太网接口将数据上传到远程上位机。该读出系统实现了电荷范围为0.1~120 pC的数字化读出,非线性误差小于1.95%（全量程）。现场应用测试结果表明,该数字化读出系统完全满足实验需求。该系统还可广泛用于核物理实验和加速器系统中微弱电流或电荷信号的测量。     

共面栅碲锌镉探测器读出电路设计及性能研究

为有效读出共面栅碲锌镉(CPG-CZT)探测器的核脉冲信号,本文结合CPG-CZT探测器工作原理及国内外研究,设计了可用于CPG-CZT探测器的读出电路,主要包括高压偏置电路、前置放大电路、增益调节及减法电路。为研究读出电路性能,本文测试了各单元电路的性能及探测系统能量分辨率随偏置电压、增益调节电路中两路信号的相对增益G的变化规律。结果表明：高压偏置电路两路输出偏压与输入偏置电压的相关系数R²均为0.998;前置放大电路输出噪声为5 mV;增益调节及减法电路输出信号噪声为10 mV;输入偏置电压、相对增益G的变化均会影响探测系统能量分辨率,当偏置电压为-1650 V、相对增益G为0.7时对¹³⁷Cs源产生的γ射线能量分辨率最佳,可达3.65%,且无明显拖尾现象。     

A fast, programmable, stand-alone pulse generator emulatingspectroscopy nuclear events

The design of a fast, programmable, stand-alone pulse generator emulating spectroscopy nuclear events is described. The generator is one unit in a system aiming to test the validity of the simulation and theoretical work relating to the shaping, acquisition, and processing of spectroscopy signals in different experimental situations arising from different technical and scientific fields. The generator output, which also includes piled-up shapes, can be used in many different ways. For example, it can be used: (1) as an input to a charge sensitive preamplifier and shaping amplifier system; (2) as an input to a module for real-time digital shaping of spectroscopy pulses; and (3) it can generate a digital sequence emulating a digitally sampled analog pulse. The signals that it can emulate include those from simple charge sensitive preamplifiers, from more refined analog shapers, and the signals generated directly from scintillation detectors. The main element of the generator is the Analog Devices 21060, a fast and flexible digital signal processor (DSP). This paper considers various generator configurations arising from the need to reach a compromise among generator speed, shape resolution, and memory requirements. It is possible to program both the emulated average counting rate and the time interval between two consecutive samples (tns) using a predetermined pulse shape. The minimum tns value is equal to 10 ns in parallel configurations     

基于阵列式吸收发光CT法的辐射场实时测量系统的研究

分析了已有的各种核辐射剂量场测量方法的基础上, 利用闪烁体吸收发光特点并结合计算机实时成像处理技术,提出了对剂量场分布进行实时成像测量的新方法——阵列式吸收发光ＣＴ 法。研制出闪烁光纤阵列构成的探测器及其伺服控制系统, 用高灵敏度的电荷耦合器件（ＣＣＤ）拾取探测器产生的微弱闪烁光信号,并采用定点采集的方法对视频信号进行数据的快速采集。在图像重建方法上, 提出了迭代滤波反投影重建方法和利用非完全投影进行数据修复,对获取的投影数据进行变换和处理,并通过选择滤波函数及其适当的参数, 可获得最佳滤波效果,以重建剂量场的二维场分布,从而建立了剂量场的实时、高精度的成像测量系统。     

模型试验研究SPECT滤波函数的最佳选择

目的：为了寻找临床应用中ＳＰＥＣＴ滤波函数的最佳选择，方法，我们用Ｊａｓｃｚａｋ模型进行了模拟试验，模拟的主要参数为信息量和空间分辨，信息量用高计数和低计数模拟，空间分辨改变滤波器函数种类和滤波参数模拟，共模拟８种条件，结果：８种条件中，低计数以Ｂｕｔｔｅｒｗｏｒｔｈ０．５截止频率为最佳，高计数时以Ｂｕｔｔｅｒｗｏｒｔｈ０．７截止频率为最佳，结论：临床ＳＰＥＣＴ滤波不能单用Ｒａｍｐ滤波函数Ｂｕｔｔ     

羊八井大型水契伦科夫探测器中双增益大动态范围前放的研制

介绍了羊八井大型水契伦科夫探测器中前置放大器的预研设计,分析了该前放的设计原理,介绍了测试方法和性能指标。该前放接收光电倍增管输出信号,采用双增益和差分输出设计方案。对该前置放大器原型电路的测试结果表明,该前放两通道增益分别为2倍和34倍,-3 dB带宽均大于150MHz,可满足0.5 mV～2 000 mV的输入信号大动态范围及远距离传输信号的实验需求。     

用于硅多条阵列探测器的48路前置电荷灵敏放大器的研制

介绍了一套用于硅多条阵列探测器中的高密度多通道电荷灵敏放大器的研制和阵列探测器电子学的发展现状和工作原理,提出了设计原则和设计思路,特别介绍了一个新开发的用于硅多条探测器中的48路电荷灵敏前置放大器的设计和实际测量结果.它具有低成本、高密度的特点,好于1%的能量分辨和良好的长期稳定性.     

ICON, a current mode preamplifier in CMOS technology for use withhigh rate particle detectors

The ICON current mode preamplifier intended for use in experiments at high-rate hadron colliders is described. The transient response and noise performance are analyzed. One chip has been made using an ICON circuit with resistive feedback to produce a preamplifier with a peaking time of below 10 ns. This fast preamplifier has a gain of 870 mV/pC and a power dissipation of around 1 mW. Another chip was made using the ICON circuit as the front-end to a dual-port analog memory. The noise measured is between 2400 e^- and 3000 e^-. An important characteristic of ICON is that it can tolerate a detector leakage current of 10 μA at the DC-coupled input. Therefore, it is very suitable for silicon detector systems under severe radiation conditions     

Design and simulation of charge sensitive preamplifier with CMOS FET implemented as feedback capacitor Cfp

In this paper,to design a new preamplifier for optimum performances with charged-particle or heavy-ion detectors,the CMOS FET is implemented as a feedback capacitor Cfp.so that the entire system should be built only with MOSFET.This work is a revolution design because to realize an ASIC for a preamplifier circuit,the capacitor will also be included.We succeed after a simulation to maintain a rise time less than 3 ns,the output resistance less than 94 Ω and the linearity almost good.     

数字化多道脉冲幅度分析技术研究

多道脉冲幅度分析技术正在朝数字化方向发展,基于数字信号处理技术的数字化多道具有脉冲处理能力强、速度快、稳定性高和灵活性强等特点。文章分析了数字核脉冲处理关键技术,利用MATLAB完成了梯形成形、数字基线估计、数字极零零极补偿、极零点识别等核心算法的模拟。给出了数字化多道初步总体设计方案,探讨了工程没计中的关键技术问题,为研制国产数字化核谱仪打下了基础。     

ASD IC for the thin gap chambers in the LHC Atlas Experiment

An amplifier-shaper-discriminator (ASD) chip was designed and built for Thin Gap Chambers in the forward muon trigger system of the LHC Atlas experiment. The ASD IC uses SONY Analog Master Slice bipolar technology. The IC contains 4 channels in a QFP48 package. The gain of its first stage (preamplifier) is approximately 0.8 V/pC and output from the preamplifier is received by a shaper (main-amplifier) with a gain of 7. The baseline restoration circuit is incorporated in the main-amplifier. The threshold voltage for discriminator section is common to the 4 channels and their digital output level is LVDS-compatible. The IC also has analog output of the preamplifier. The equivalent noise charge at input capacitance of 150 pF is around 7500 electrons. The power dissipation with LDVS outputs (100 Ω load) is 59 mW/ch     

数字化核能谱获取中信号处理方法的研究

介绍了将核辐射能量信号离散化后进行数字极零识别及补偿、基线扣除、低通滤波、脉冲成形和幅度分析等一系列数字化信号的处理方法，将长尾指数衰减信号成形为梯形波或三角波信号。用所述方法对实测波形进行离线处理后的结果表明，所获能谱的能量分辨率好于模拟式多道系统的测量结果。