Development And Application Of A Digital Lock-in Amplifier With High Performance

Lock-in amplifier is a weak signal detection and demodulation equipment.In recent years,the development of computer and embedded system has promoted the development of lock-in amplifier technology.In order to make the digital lock-in amplifier suitable for embedded applications,it is urgent to develop a digital lock-in amplifier module with high performance to meet the practical needs.The main work of this paper includes:Firstly,design and manufacture of a digital lock-in amplifier module with high performance.In this paper,the circuit and software of digital lock-in amplifier module were designed,including preamplifier circuit,high-order low-pass filter circuit and power tree.Four-channel phase sensitive detection was designed by field programmable gate array and microcontroller.A digital lock-in amplifier module with very low noise,wide band,small size,low power consumption was developed,and it can meet the needs of embedded applications.Secondly,the performance test and verification of the digital lock-in amplifier module with high performance.This paper built a test system,specifically tested the linearity,nonlinear distortion,AC transmission characteristics,stable voltage power supply quality and spontaneous heat situation of signal-input-channel;In the experiment of demodulating weak amplitude-modulation signal,the linearity,noise and SNR of demodulation result of self-made lock-in amplifier module were tested,and the influence on demodulation result of different time constants and orders were tested.In the application of TDLAS technology,the functions of waveform output and synchronous demodulation of primary and secondary harmonics were tested.The important performance indexes of the self-made lock-in amplifier module were tested.The noise influence on the demodulation results of the lock-in amplifier was analyzed,and its inherent output noise was traced to the source.Thirdly,the application of the digital lock-in amplifier module with high performance in the field of spectral analysis technology.The CO gas concentration detection experiment system was built,and the primary and secondary harmonics of the detector output signal were synchronously demodulated with the self-made lock-in amplifier module.The results of demodulation were calibrated,and the application effects of commercial lock-in amplifier and self-made lock-in amplifier module in spectral analysis were compared.The results show that the demodulation effect of the self-made lock-in amplifier module is not only better than the modular lock-in amplifier LIA-MVD-200,but also better than the desktop lock-in amplifier SR844.In this paper,the output noise density and the output dynamic range are used as the evaluation parameters of the lock-in amplifier.The self-made lock-in amplifier module can realize synchronous demodulation of primary and secondary harmonics,the output dynamic range is as high as 103.84 d B,the output noise density is as low as53.6 n V /?Hz,and the power consumption is only 1.87 W.It can meet the needs of embedded applications and spectral analysis while maintaining high performance.