Research And Design Of The Data Acquistion System ForTime-of-Flight Mass Spectrometry

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.