Development of Near-infrared Spectroscopy Signal Collecting System Based on Digital Demodulation

Achieving demodulation for near-infrared spectroscopy signal with digital envelope demodulation technique. A near-infrared spectroscopy signal collecting system with simple and flexible signal processing are designed and implemented. Altera Corporation's CPLD EPM240TIOOC5N, which has enough I/O ports for the system expansion, was selected to generate sequence pulse for ADS8505; STC89LE54RD+ was used used as microcontroller. Quartus II development environment was used to design internal procedure of CPLD. Experiments on effect of total sampling periodical number on SNR (single-to-noise ratio) and effect of single periodical sampling number on SNR were designed to implement system detection and verification. Compared with the phase-sensitive detection circuit, the digital signal processing is simple and flexible, and simplifies circuit and reduces the debugging steps.