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利用可调谐激光光谱技术并结合二次谐波检测的波长调制方法对气体浓度进行检测,大大提高了检测灵敏度.然而光的传输和电路自身延时都会产生未知的相位延时,含有气体浓度信息的被测信号和二倍频参考信号的相位差变化严重影响二次谐波信号测量结果.本文设计出一种4路乘法锁相解调电路,设计中分别用正弦信号和余弦信号对被测信号进行解调,经积分电路后得到两路分别与相位差的正弦值和余弦值相关的解调信号.将两路解调信号平方,再通过加法器相加后消除相位差,得到完全与相位差无关的幅值信号.实验证明当被测信号相位在0°—90°变化时,解调得到的二次谐波信号保持不变,很好地提高了系统检测结果的稳定性.
The use of tunable laser spectroscopy combined with the wavelength modulation method of second harmonic detection to detect the gas concentration greatly improves the detection sensitivity, however, the transmission of light and the delay of the circuit will produce unknown phase delay and contain gas concentration information Of the measured signal and twice the frequency reference signal phase difference seriously affect the second harmonic signal measurement results.This paper designed a 4-way multiplication PLL lock phase demodulation circuit, respectively, the design of sine and cosine signals were measured The signal is demodulated by the integrated circuit to get two respectively phase difference sine and cosine value of the demodulated signal will be two demodulated signal square, and then added by the adder to eliminate the phase difference, to be completely and Phase difference independent amplitude signal.Experiments show that when the measured signal phase changes from 0 ° to 90 °, the demodulated second harmonic signal remains unchanged, which improves the stability of the system test results.