The Research Of High-Speed Digital Sampling Into Spectrum Directly For Narrow Pulse Signal

In the field of particle physics, high energy physics and nuclear radiation environmental monitoring, spectral analysis is an important means to obtain the information of the radiation field energy, position information and time information. In applications of neutron scintillation detection, the key to discriminating the shape of narrow current pulse signal is high speed digital technology for narrow pulse signal in order to discriminating the neutron and gamma.In a highly radioactive environment, achieving dose distribution and nuclide information of the radiation field to accurate positioning source material and identify the source type has become the focus of the present study. The difficulties of design is making the output of detector to be narrow pulse signal, thereby decreasing pulse accumulation, and to realize high count rate multi-channel pulse amplitude analysis on this basis. So it is of great significance and value to develop high speed digital multi-channel pulse amplitude analyzer for a narrow pulse signal. Currently, the mainstream adoption of multi-channel pulse amplitude analysis is fully digital technology, which makes the high count rate energy spectrum analysis possibly. With the rapid development of the integrated chip manufacturing level, ultra high-speed AD converter, high frequency amplifier and mass rapid field programmable gate array(FPGA) chip are increasingly emerging, make the high-speed digital discrete and energy spectrum of nuclear pulse signal acquisition with the implementation.Aimed at problems of multi-channel pulse amplitude analyzer's low pass rate, the narrow bandwidth of analog, this article carry out the research and design high-speed analog front-end circuit, high-speed analog to digital conversion circuit and direct digital sampling into a spectrum based on high-speed FPGA.The research comes from the national natural science fund project "mathematics of nuclear pulse signal chain construction and high-speed real-time digital reconstruction technology research"(project number: 41474159). It is carried out for narrow pulse signal's high-speed discretization and spectral acquisition. The main research results of the paper:1. Design analog signal conditioning circuit in direct coupling and add high speed hardware gain adjustment, polar transformation and offset adjustment,and other functions in the signal processing circuit for analog signal, to adjust the high frequency pulse signal. For high counting rate and narrow pulse signal, the system designs high-speed analog front end to ensure the signal through without distortion. After the test, the large signal's-3 d B bandwidth is 110 MHz, small signal's bandwidth is up to 200 MHz.2. Low jitter sampling clock, high-speed analog-to-digital conversion(ADC) and high speed data transmission is the key to the system, but it is difficult to design. With ADI's high-speed, low power analog-to-digital conversion chip AD9434-500, the design realizes 500 MSPS high-speed discrete sampling, and only 690 m W power consumption in full speed.3. Using Xilinx company field programmable logic gate array(FPGA) chip XC4VFX20, implement an LVDS communication speed of 645 MHz. Then, the system need to complete high-speed LVDS routings between FPGA and ADC, according to the theory of signal integrity. The system realizes the high speed narrow pulse of discrete data acquisition, filtering, amplitude extraction, storage and so on in the FPGA.4. The system designs FPGA + SOPC(Power PC) architecture, achieving high performance embedded control system and simplifying the hardware design. The USB peripheral hangs on Power PC PLB bus, realizing high speed data transmission with PC software.5. From power supply topology, PCB layout, chip selection, circuit parameters selection, etc, to achieve a low noise, high efficiency, high current, rapid dynamic response power system, the noise is control to be 5 m V. It is can be realized to power up complex power system with single power supply only in DC-2.5 interface, with power supply range: 6.8V to 20 V.6. Based on D2 XX, SQLite library and Visual C++ 6.0's MFC platform, the design for PC software has been finished. And the experiment of software and hardware has been finished in this software platform, it proves the stable and reliable of the system.7. Through the experiment with signal source, the system counting rate can reach 10 Mcps, linearity is 0.9998. In this paper, connects Na I(Tl) scintillator, boron plastic scintillator, La Br3(Ce) scintillator, and other detectors to high-speed digital multi-channel analyzer, measures the spectral curve in direct sampling method, and verifies the practicability of high speed digital multi-channel analyzer.