Design And Implementation Of Multichannel Lock-In Amplifier Based On DSP

As a kind of important instrument in the field of weak signal detection,lock-in amplifier plays an important role in scientific research and engineering practice in recent years.The lock-in amplifier has excellent noise immunity and can recover effective signals from strong background noise.With the deepening of human exploration of nature,in the fields of biological science,intelligent sensing,basic materials,etc.,the ability to synchronously collect and detect different types of weak signals is put forward,and the use of traditional single channel/single-phase lock-in amplifiers is increasingly limited.Therefore,it is imperative to carry out research work on multi-channel lock-in amplifiers.Based on the in-depth research on the existing lock-in amplifier algorithm and design principle,this paper proposes a multi-channel lock-in amplifier design.The main research contents are as follows:(1)Starting from the time domain and frequency domain behavior of lock-in amplifier,the similarities and differences between the traditional orthogonal lock-in algorithm and the discrete Fourier transform algorithm are analyzed,An improved Goertzel algorithm is proposed to optimize the digital lock-in algorithm.By introducing an iterative phase correction factor,the theoretical detection frequency range of the algorithm is extended to any frequency,and the signal phase can be accurately tracked.Then,based on the analysis of the frequency response of the Goertzel algorithm,the narrow-band low-pass filter is implemented by using the interpolation FIR filter to complete the extraction of the weak signal.The Matlab simulation proves that the algorithm can effectively detect the weak signal buried deep in the noise.While reducing the large amount of calculation,the performance is equivalent to the traditional lock-in algorithm.(2)Using the 8-channel synchronous sampling analog-to-digital converter AD7768 to design the hardware part of the multi-channel lock-in amplifier for the core device.The design concept of circuit system for weak signal acquisition of modern ?-? ADC is expounded,and the specific scheme of preamplifier and anti-aliasing filter design is proposed.(3)Using AM5728 multi-core heterogeneous DSP platform,complete the software part of multi-channel lock-in amplifier in Linux environment,and use OpenCL to complete data synchronization and algorithm acceleration between ARM and DSP,so that the system is more suitable for modern DSP processor architecture and Software system.And through the software test analysis combined with the DSP running characteristics under the OpenCL architecture,the DSP-side algorithm is optimized.Through the hardware and software measurement,it is verified that the system has the ability to simultaneously detect multiple weak signals.The simulation and experimental data analysis show that the multi-channel lock-in amplifier based on DSP has strong research and engineering value.