利用可调谐二极管激光吸收光谱技术检测气体浓度时，为了从红外传感信号中提取一次及二次谐波信号来表征气体浓度，研发了一种基于数字信号处理器的数字正交锁相放大器.介绍正交锁相放大原理，设计谐波提取算法，给出数字正交锁相放大器的软硬件实现方案.利用配备的浓度为1%~5%的甲烷样品以及研制的锁相放大器，开展气体实验.实验结果显示，当甲烷浓度为5%时，在二次谐波对应的频率点处，测得的系统信噪比为34 dB，表明设计的锁相放大器具有较好的性能；测得的二次与一次谐波信号峰峰值的比值与气体浓度成线性关系；考虑动态配气以及气体沿管道传输的时间，检测系统的响应时间约为96~98 s；气体浓度为20 000 ppm时，测试浓度波动范围为-92 ppm ~ +118 ppm；根据Allan方差预测的系统检测下限为29.52 ppm.与模拟锁相放大器以及商用锁相放大器相比，本文研制的数字正交锁相放大器硬件结构简单、体积小、成本低、易于集成，在红外气体检测领域具有很好的应用前景.

By using Digital Signal Processor (DSP), a digital lock-in amplifier was experimentally demonstrated for extracting 1f and 2f signals in gas detection based on Tunable Diode Laser Absorption Spectroscopy (TDLAS). The orthogonal lock-in amplifying theory was introduced, the algorithm for extracting harmonic signals was designed, and both hardware structure and DSP software were proposed. By using the prepared CH4 samples within the concentration range of 1%~5% and the developed lock-in amplifier, detailed experiments were carried out to derive the device′s performances. As shown by experimental results, the system′s signal-to-noise ratio at the frequency of 2f signal is 34 dB under the CH4 concentration of 5%, which indicates good functions of the lock-in amplifier. The amplitude ratio between 2f and 1f signals is linear to gas concentration. Considering gas preparation and diffusion time, the response time of the detection system is about 96 ~ 98 s. The concentration variation is -92 ppm~+118 ppm for the measured CH4 sample with a concentration of 20000 ppm. The limit of detection obtained from the Allan variance is 29.52 ppm. Compared with analog and commercial lock-in amplifiers, the self-developed device shows great applications in infrared gas detection because of its simple structure, small size, low cost and easy integration.