Design And Implementation Of Cavity Ring-down Signal Acquisition And Processing System Based On FPGA

Cavity ring-down spectroscopy technology is a kind of absorption spectrum detection technology, which can be self calibrated, and absolutely quantitative measurement, and not affected by the fluctuation of the light source fluctuation. Cavity ring-down spectroscopy technology has been widely used in the measurement of gas concentration. While accurate acquisition and processing of cavity ring-down signal is the basis of quantitative detection of gas concentration by cavity ring down spectroscopy. Therefore, it is necessary to develop a system, which is suitable for the data acquisition and processing of cavity ring-down signal. FPGA is a kind of programmable logic device with high integration and high density, which is powerful in system programming and parallel data processing. USB2.0 is a high-speed serial data communication standard, which has the properties of high performance, low cost and supporting hot plug. Based on this, this paper designs a cavity ring-down signal acquisition and processing system.The system uses FPGA as the main controller. Firstly, the system completes the data acquisition and caches the collected data to FPGA through the high-speed AD interface module in FPGA, realizes the corresponding point cumulative average processing of the collected cavity ring-down signal signal data through the data accumulation average processing module in FPGA, and completes the transmission of pre-processed data and command information data through the USB2.0 interface module in FPGA. Then the host computer software monitors and receives the data transmitted through USB2.0 by data receiving thread, and obtains cavity ring-down time by processing the received data. Finally, respectively getting the cavity ring-down time of having gas absorption in the cavity and the cavity ring-down time of having no gas absorption in the cavity, and using these two kinds of cavity ring-down time to calculate the gas concentration in the cavity.Firstly in this paper, it introduces the basic theory of cavity ring-down signal and cavity ring-down system built in laboratory, and on this basedment gives the overall design scheme of the system. Secondly, it gives the design of the specific hardware circuit, including power supply circuit, FPGA peripheral circuit, analog signal conditioning circuit, high-speed AD interface circuit and USB2.0 interface circuit etc; Thirdly, it gives the introduction of the internal digital logic design of FPGA, and completes the design and simulate of the FPGA main program module based on FPGA design method and development process. Fourthly, it gives the design of the system software, including the development of the USB2.0 firmware, USB driver and PC application program etc. Finally, it tests the function and performance of the system by the software and hardware of system, and applies the data acquisition system to collect and process cavity ring-down signal generated by the cavity ring-down system, which is built in the laboratory.