Research on weak signal detection of integral average digital lock-in amplifier

Abstract

In the process of detecting the amplitude and phase of the weak signal based on digital lock-in amplifier (DLIA), a low-pass filter (LPF) with an extremely low cut-off frequency is required. Even so, the effect is often not good. The detection results of amplitude and phase of weak signal are distorted and fluctuate sharply. To eliminate the difficulty of LPF design, and to reduce the distortion and output fluctuation of detection results of DLIA, this paper proposes a weak signal detection method based on integral average digital lock-in amplifier (IADLIA), which can be used for weak signal detection under strong noise. This method optimizes the structure of the traditional DLIA based on the principle of cross-correlation detection. And then this paper analyzes the influence of the cut-off frequency and signal-to-noise ratio of the LPF on the detection accuracy and output stability of the weak signal amplitude and phase. Finally, the corresponding weak-signal amplitude at the bearing rotating frequency is accurately detected by the proposed method, and the accurate identification of bearing faults is realized. The experimental results show that the IADLIA is characterized by stable output, strong anti-interference ability and high output accuracy. The proposed method can accurately detect the amplitude and phase information of the weak signal in a strong noise environment, get rid of the structure of LPF, and the overall performance is better than the traditional DLIA.

A Software Digital Lock-In Amplifier Method with Automatic Frequency Estimation for Low SNR Multi-Frequency Signal

“…Therefore, a lowpass filter with a very narrow bandwidth is used to filter out the high-frequency component and noise. Typically, the integral average filter (IAF) [21] is used to realize the lowpass filter:…”

“…Stimpson et al [20] designed a high-speed digital LIA structure based on an FPGA. Xinda Chen et al [21] used the integral average filter as the lowpass filter to compress the filter bandwidth and improve the amplitude measurement accuracy of the DLIA. Alves et al [22] designed a microcontroller-based dual-channel DLIA which enhanced the frequency resolution of the reference signal.…”

“…Due to the analog LIA being easily affected by the temperature drift and time drift of the analog device, many researchers mainly focus on the specific digital LIA realized by a DSP, FPGA, MCU, and other digital chips, which is applied as a signal processing module in a dedicated research field or application [21]. One of the key factors affecting the amplitude measurement accuracy is the frequency error between the reference signal and the measured signal.…”

Square wave reference digital lock-in detection using non-orthogonal demodulation

“…Digital lock-in detection technique has been widely used in a variety of fields to measure weak signals [ [1] , [2] , [3] , [4] ]. It can measure a signal of interest frequency without being disturbed by noise of other frequencies.…”

Digital demodulation method based on multichannel combined acquisition for near-infrared spectrometer

“…Currently, Lock-in amplifier can be divided into two kinds on the basis of different phase sensitive detectors [7]: analog lock-in amplifier (ALIA) and digital lock-in amplifier (DLIA). Among them, DLIA can simplify circuits which makes it more reliable [8]. However, compared with ALIA, its SNR of DLIA is relatively low.…”