Miniature Near-infrared Spectrometer Detection System Design And Research

With the development of the Near-infrared Spectroscopy, the Near-infrared spectrometers have been widely used in various fields of science, such as chemistry, medicine, geology, physics, astronomy,and so on. Because of the simple operation and high speed characteristics of Miniature near-infrared spectrometer prompt people to gradually promote Miniature near-infrared spectrometer for distributed physical on-site analysis. Detection system is the important part of the entire miniature Near-infrared spectrometer, and the pros or cons of it directly determine the good or bad for the entire spectrometer. As most domestic miniature Near-infrared spectrometers are still using expensive imported equipment, the design of a cost-effective miniature Near-infrared spectrometer is particularly necessary.This design focuses on the core data processing system of miniature near-infrared spectrometer. With the development of integrated silicon industry and the production process, the integration of the CCD detector is getting higher and higher while the price becomes lower and lower, and the research cost of the entire detection system have been greatly reduced when using a CCD detector in laboratory. Since the CCD detector receive the spectrum of different wavelengths by the dragonfly compound eye liked multi-channel array detector, thus avoiding the movement of the grating or single detector parts and realizing the fixed optical path. Stable performance, fast scanning speed, high resolution and high signal to noise ratio of near-infrared spectroscopy instruments using CCD detectors make it reach the operation standards of the micro-spectrometer.The CCD detectors first convert optical signals into electrical signals, and output the electrical signal in accordance with the spatial order. Then the analog to digital converter chip converts analog signals into digital signals as well as signal denoising and gain adjustment, and we choose the AD9822in this design. Each pixel of the analog signal is converted to12bits digital signal by AD9822, then the digital signal will be processed by the FPGA on the next step. As the key part of the entire detection system, FPGA not only supply the CCD and the AD9822with driver timing and processing of pixel data but also upload the data to a PC in accordance with the timing requirements of the USB controller. In this design, we choose the EP2C8Q208C8of Altera Corporation. The main focus of this design is the design of the internal FPGA logic code and the main features of the FPGA design have the following:making adjustments to the CCD drive timing and CCD exposure time; AD9822sampling timing and the AD9822internal register read and write control of;12pixel data storage and cumulative pretreatment; transmit pixel information to the USB controller in accordance with the read and write timing process of USB controller; receive and perform control commands from the USB.USB selected controller is Cypress’s CY7C68013A, which is the most common USB controller chip. It supports12Mb/s full-speed transmission and480Mb/s high-speed transmission and it can be used in four USB transfer mode. Because our detection system belongs to the secondary device, we choose the Slave FIFO mode.