【作者】 周伟；

【导师】 方方；

【作者基本信息】 成都理工大学 ， 核资源与核勘查工程， 2011， 博士

【摘要】 核分析技术具有高精度、高灵敏度、微量元素等特点,能够提供其他检测手段所不能提供的信息,为多种学科的基础研究提供了灵敏而精确的实验方法和分析手段。因此,核仪器的发展一直受到人们广泛关注。20世纪90年代以来,随着电子技术的高度发展及其在核分析仪器中的应用,数字化已成为核分析仪器发展的主要方向。核分析仪器数字化的关键技术是数字脉冲成形技术,已成为近年来核信号处理最为活跃的研究领域。数字化脉冲成形不仅可代替复杂的模拟滤波成形电路,提高系统稳定性,而且还能改善系统灵活性和自适应性。如果核分析仪器中探测器产生的电荷被瞬时收集,则探测器和电荷灵敏前置放大器系统的输出信号可描述为基于一个时间常数的指数衰减信号。而高斯波形的脉冲信号在提高信号噪声比、减小弹道亏损等方面具有良好的综合表现。因此,为了提高分析仪器的综合性能,脉冲成形单元需要将指数衰减信号滤波变换为高斯波形信号。现有的基于分立元件设计的模拟成形技术,在工作稳定性、测量一致性、参数通用性和后期维护性等方面存在着诸多缺陷。此外,真正的高斯脉冲成形具有反因果部分,模拟系统难以实现。论文瞄准核分析仪器数字化的迫切需要,从精密信号放大、高速数据采集、数字脉冲处理技术以及硬件描述语言等脉冲成形的关键技术入手,提出了一种新的高斯脉冲数字成形方法,并以FPGA为硬件平台完成了硬件实现,最后以此为基础研制了数字X荧光谱仪系统。Sallen-Key滤波器(以下简称S-K滤波器)是一种常用的有源滤波电路,具有高通S-K滤波器和低通S-K滤波器2种形式。由于采用了正反馈控制,S-K滤波器具有较大的品质因数。将其应用于指数衰减信号的成形,可以在较少的级数下得到高斯波形。脉冲成形以S-K滤波器为理论基础,将滤波器传递函数改进为离散化处理,从而脉冲信号的数字成形。数字X荧光谱仪系统以Actel公司ProASIC3系列FPGA芯片为核心平台,配备相应的辅助电路,可以独立完成脉冲信号的采集、成形、甄别、存储和传输等过程。性能测试及初步实验表明,论文涉及软硬件设计先进,方案合理,研究工作的技术路线正确。论文的研究工作和成果符合我国国情,易于推广使用,具有明显的经济效益、社会效益和环境效益。更多还原

【Abstract】 Nuclear analysis technique features as high precision, high sensitivity, trace, etc, and the nuclear analysis technique can provide the information which other detection means cannot, as well as provide sensitive and accurate analysis and experimental method for the fundamental research of multi-subjects. Therefore,the development of nuclear instrument has been widely drawn people’s attention. Since the 1990s, with the rapid development of electronic technique and its applications in nuclear analysis instruments, digitization has become the main development direction of the nuclear analysis instrument. The key of digitalizing the nuclear analysis instrument is digital pulse shaping technique, and it has become the most active field of research in nuclear signal processing in recent years. Digital pulse shaping technique can not only replace the complicated analog filtering shaping circuit and enhance the system stability, but also improve the flexibility and adaptability.If the electric charge was collected instantly which produced by the detector of the nuclear analysis instrument, so the output signal of detector and sensitive charge preamplifier system can be described as exponential decay signal which based on an time constant. While the pulse signal of Gaussian wave has a well synthetic performance in improving the signal noise ratio and reducing ballistic losses, etc. Therefore, in order to improve the combination property of analysis instrument, pulse shaping units need to filterable transform the exponential decay signal into Gaussian wave signal. Based on the existing discrete components design, the simulation shaping technique has many defects in working stability, measuring consistency, general parameter and late maintenance and so on. Moreover, the true Gaussian pulse shaping has the anti-causal part which result the analog system can hardly realize.The dissertation aimed at the urgent need of digital nuclear instruments. According to the precision amplification, high-speed data acquisition and processing technology of digital pulse and hardware description language etc as the key technology of pulse shaping, it developed a new kind of Gaussian pulse shaping and digital realization method, completed a digital pulse shaping system based on FPGA. Sallen-Key Filter(S-K Filter in short) is a common kind of active filter, has two forms: high pass filter and low pass filter. S-K Filter has a greater quality factor because of using a positive feedback control. When it applied to the shaping of exponential decay signal, w can get the Gaussian wave in the few series. The digital pulse shaping system use the Actel Ltd. ProASIC3 series FPGA chips as the core platform, equip with relevant auxiliary circuits, can independently complete the pulse signal’s collection, output and forming etc. The pulse shaping based on S-K Filter, improved the filter transfer function to differentiation, then digital pulse signal shaped.Performance testing and preliminary experiments show that the designs of the hardware and software involved in the thesis was advanced, the program was reasonable and the studying technical route was right. The research and its results were in line with China’s conditions, so it is easy to be promoted and it has obvious benefits of economic, social and environmental.更多还原