Development Of X-ray Fluorescence Spectrometer Based On Digital Gaussian Shaping Technique

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.