面向脉冲量子级联激光器气体检测的锁相放大器

Lock-in Amplifier for Pulse-Driven Quantum Cascade Lasers Gas Detection System

为了在基于脉冲式中红外量子级联激光器的气体检测系统中,精确提取窄脉冲传感信号的幅度,设计并实现了一种微秒级窄脉冲锁相放大器.根据微秒级窄脉冲的特点,窄脉冲信号经过窄带通滤波电路,得到基频正弦波信号,再经过主放大、移相、相敏检波电路,得到与脉冲幅值有关的直流信号.利用信号发生器产生的幅度、频率、相位可调的窄脉冲待测信号,对锁相放大器进行功能验证实验.结果表明,锁相放大器输出直流信号与输入信号的幅度呈良好的线性关系,线性拟合度约为98.043%;信号幅值的相对测量误差不超过3%;在1 h的测试时间内,信号波动范围在1‰以内.利用配备的不同浓度的一氧化碳样品及研制的锁相放大器,开展了一氧化碳气体检测实验.在0~180 ppm范围内,随着一氧化碳浓度的增加,锁相放大器的输出电压值与一氧化碳浓度呈现良好的e指数关系.根据A11an方差预测的系统检测下限为0.4123ppm.与商用锁相放大器相比,该放大器具有体积小、成本低、易于集成等特点,在基于脉冲式中红外量子级联激光器的气体检测中具有较好的应用前景.

For the gas detection system based on pulse-type infrared quantum cascade lasers,a μs-level narrow-pulse lock-in amplifier was designed and achieved to accurately extract the amplitude of the narrow pulse sensing signal.According to the characteristics of the microsecond narrow pulse signal,the narrow pulse signal passed through a narrow bandpass filter and a fundamental sine-wave signal was obtained.Then,the sine-wave signal passed through a preamplifier,a phase-shifter and a phase-sensitive detection circuit,so that a direct current signal related to the pulse amplitude was obtained.As a testing signal,the narrow pulse whose amplitude,frequency and phase were adjustable was produced by a signal generator,the detailed functional verification experiments were carried out to validate the performance of the proposed lock-in amplifier.The results show that,a good linear relationship is found between the output direct current voltage and the amplitude of the standard input pulse signal：the fitness of the system is about 98.043%：the relative detection error of its output voltage is less than 3%;within one hour s test,the fluctuation range of the measured signal is less than 1‰.The detailed gas detection experiments were carried out using prepared carbon monoxide（CO） samples with different concentrations and the lock-in amplifier.Within the CO concentration range of 0~180 parts per million（ppm）.the output voltage from the lock-in amplifier reveals an exponential relationship with CO concentration,which also proves the normal function of this device.The limit of detection predicted from the Allan variance is 0.412 3 ppm.Compared with commercial lock-in amplifiers,this amplifier has special characteristics including small volume,low cost,ease of integration,and so it has a good application prospect for mid-infrared gas detection based on quantum cascade lasers.