【作者】 叶春逢；

【导师】 安琪； 赵雷；

【作者基本信息】 中国科学技术大学 ， 物理电子学， 2014， 博士

【摘要】 飞行时间质谱仪是探测物质结构的一种常用工具。质谱数据获取系统是飞行时间质谱仪的核心部件之一,其性能指标对质谱仪性能有着重要的影响。本论文以国家同步辐射实验室宽压力层流预混火焰实验平台(简称火焰实验平台)的飞行时间质谱仪数据读出电子学为需求,开展高精度大测量范围时间测量技术研究,设计了完整的飞行时间质谱仪数据获取系统,主要包括：快定时放大器、质谱数据采集板、质谱数据获取系统软件。目前,飞行时间质谱仪的数据获取系统主要有两条技术路线,一是基于高速模拟数字转换(ADC)技术；二是基于时间数字转换(TDC)技术。高精度时间测量对高速ADC的采样速率、数据传输带宽以及数据处理能力要求较高,并且在离子信号事件率不高的时候,其使用效率较低。本课题则采用TDC技术进行质谱仪数据获取系统的设计。TDC设计可以基于模拟电路方法或专用集成电路(ASIC)的方法进行,然而,采用模拟的方法很难进行高集成度设计,调试也较为麻烦；采用ASIC方式则需要较长的设计周期,其功能和设计模式固定并且很难快速升级。本设计的定时甄别电路采用恒比定时电路结构,时间测量基于多相时钟的时间内插技术构建细时间测量单元,并通过多级时间数据缓冲技术将粗时间测量时钟频率进一步降低。粗时间测量单元则由计数器来执行。整个系统在单片FPGA内完成。经测试,本数据获取系统的时间测量范围不小于107s；在采样时钟为320MHz时,基于四相时钟的时间内插设计,其分辨率为781ps,RMS好于390ps,平均RMS为304ps,DNL在-0.01LSB到+0.01LSB之间,INL在-0.002LSB到+0.025LSB之间；基于八相时钟的时间内插设计,其分辨率为390ps,RMS好于195ps,平均RMS在150ps左右,DNL在-0.10LSB到+0.05LSB,INL在-0.10LSB到+0.01LSB之间。在质谱数据获取系统与火焰实验平台的联合测试中,待测样品甲苯、丙酮和正庚烷的质谱测试结果表明本设计完全满足设计需求。各章节内容如下：第一章对飞行时间质谱仪的关键技术发展进行回顾,并阐述本论文的研究目的和基本构想。第二章介绍了飞行时间质谱仪的原理,对影响质谱分辨率的各种因素进行探讨。同时,对飞行时间质谱仪数据获取系统的两种主要技术路线在这里进行了分析。第三章介绍了常用定时甄别方法和常用时间测量方法,并以此为基础,对时间内插测量方法和基于FPGA的时间测量方法进行探讨。第四章是系统方案设计和实现的部分。先是阐述了系统设计指标,接着对快定时放大器设计方案、定时系统方案、基于FPGA的多相时钟时间内插高精度时间测量方案、软件系统等部件的设计进行描述。为了评估系统的指标和性能,第五章介绍了主要电子学模块的测试性能指标和测量方法,并将质谱仪数据获取系统和火焰实验平台构建完整系统进行联合测试,并根据获取到的待测样品的质谱对本系统进行评估。第六章为论文的总结,并对下一步工作进行展望。更多还原

【Abstract】 The time-of-flight (TOF)mass spectrometry is one of the most widely used techniques to get knowledge of the composition and structure of compounds.The data acquisition system is one ofthe important parts in modern TOF mass spectrometers. Based on the requirement of the pressure-dependence laminar premixed flame facility at the National Synchrotron Radiation Laboratory (NSRL) in Hefei, a complete research and design of the data acquisition system for TOFmass spectrometry is presented in this dissertation.There are two main techniques to acquire the repetitive spectra rapidly in today’s TOF mass spectrometry, one is waveform digitization (WFD)based on high-speed analog-to-digital conversions (ADCs); the other is the technique based on time-to-digital conversions (TDC). In this work the TDC is employed.Time-to-digital conversion is often implemented with analog circuitry or application-specific-integrated-circuits (ASICs). However, it is difficult to achieve a high density with the analogapproach, while ASICs require a long design cycle and the function cannot be easily revisedfor different applications. In this paper, we present a highly flexible, accurate, and low costdesign of time digitizer based on a field-programmable-gate-array (FPGA) and timeinterpolation method. Test results indicate that the bin size of this time digitizer is390ps withan average standard deviation about150ps. The differential non-linearity is in the range of-0.1+0.05LSB, and the measurement range is larger than107seconds. Compared with othertechniques, this method reduces the system complexity and provides a good flexibility. Thistechnique can also accommodate one or more STOP pulse measurements for each START pulsereference, enabling measurement of multiple times-of-flight with a common start trigger.Besides, a time stamp is recorded for each input pulse, rendering this time digitizer versatile inother applications. Moreover, because of the programmable characteristic of the FPGA, morefunctions can be integrated in the time digitizer, such as trigger function, data transferinterface; the parameter like number of channels and the measurement range can also bemodified according to different requirements.In the first chapter, the key techniques of the TOF mass spectrometry are reviewed,and the research purpose of this dissertationand the basic idea are also presented.InChapter2, the principle of TOF mass spectrometry is introduced, and various factors influencing the mass resolution arepresented. At the same time, two basic techniquesof data acquisition system for TOF mass spectrometry are discussed and analyzed here.InChapter3, the methods of regular time discrimination and TDCare presented.In this part, the TDC based on FPGA devices is reviewed in details.The fourth chapter introduces the system design and implementation.At first the system design specificationsarepresented; then the fast signal amplifier design, time measurement scheme based on FPGA with the multi-phase clock time interpolation method, and software design are described.To evaluate the the system performance, we conducted the tests on this data acquisition system, which are presented in Chapter5.The tests includethe electronics test in the laboratory and the commissioning test with the TOF MS.The results indicate the performance of this system is beyond the requirement.Finally, Chapter6summarizeswhat have been achieved in the work and gives the outlook in the future.更多还原