基于FPGA的TDLAS-WMS信号控制系统设计及实现

Design and Implementation of a Field Programmable Gate Array-Based Signal Control System for Tunable Diode Laser Absorption Spectroscopy-Wavelength Modulation Spectroscopy

针对已有的可调谐二极管激光吸收光谱-波长调制光谱(TDLAS-WMS)中所需的谐波检测二倍频信号产生往往需要复杂的“倍频-比较-移相”电路,提出一种新型的TDLAS-WMS控制信号产生方法:利用现场可编程门阵列(FPGA)控制高速数字/模拟(D/A)产生锯齿波扫描信号和正弦波调制信号,叠加后控制激光器实现波长调制扫描;同时,FPGA依据相位信号同步输出一个正弦波调制信号的二倍频方波信号,加入延时补偿环节后,与探测器模块接收到的吸收信号中的正弦波调制信号的相位差为零,解调经过气体吸收后的调制扫描信号。设计了基于该方法的TDLAS-WMS系统方案、高速D/A转换电路、延时电路及FPGA控制流程,实验验证了正弦信号与其二倍频方波延时信号的同步性,将该方法用于某气体检测系统,成功地检出了与浓度相关的二倍频吸收信号,检出幅值得到一定提升,从而验证了该方法的有效性。

A complex“frequency-doubling-comparison-phase-shifting”circuit is often required for the generation of frequencydoubling signals for harmonic detection in the existing tunable diode laser absorption spectroscopywavelength modulation spectroscopy(TDLASWMS).Thus,an innovative signal generation method is proposed in this paper.In this method,a field programmable gate array(FPGA),as a main controller,controls a highspeed digitaltoanalog(D/A)converter to generate a sawtooth scanning signal and sine modulation signal,which are used to drive a laser for wavelength modulation scanning after the signals are combined.Simultaneously,a square signal,which is frequencymultiplying and strictly inphase with the sine wave,is also generated based on the phase information for demodulation of the gas absorption signal.Based on this method,the system scheme,highspeed D/A conversion circuit,and FPGA control flow are designed,and the generation of the sinusoidal signal and its frequencydoubled square wave signal with a delay is verified experimentally.When the system is applied to a gas detection,an absorption signal related to the concentration is successfully detected,and the detection amplitude is improved to some degree,which verifies the effectiveness of the proposed method.