Signal detection technique utilising ‘lock-in’ architecture using 2 c harmonic frequency for portable sensors

Abstract-The phase-sensitive or "lock-in" amplifier is a fundamental tool in experimental physics, and is able to extract exceedingly small signals in the presence of noise. The lock-in operates on the principle of synchronous excitation of the system under test, which effectively moves the desired system response above the influence of 1/f noise. The purpose of the paper is twofold: (i) to investigate the numerical aspects of implementation of the lock-in signal processing, particularly for computationally resource-constrained environments; and (ii) to investigate the tradeoff between A/D resolution and oversampling rates in this particular application, where a synchronous reference signal is available. We conclude that the quantization, sampling rate, and numerical precision aspects are somewhat interrelated when the best possible performance in terms of noise rejection is required.

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“…As an alternative to lowpass filtering, [2] recently suggested filtering the second harmonic 2ω s using a bandpass filter. Fig.…”

Section: Signal Processing For Lock-in Detectionmentioning

confidence: 99%

“…PREVIOUS WORK Recently, Aguirre et al discussed a lock-in amplifier for portable sensing systems [1], and Son et al proposed the use of the second harmonic rather than the more usual lowpass filtering approach [2].…”

Section: Introductionmentioning

confidence: 99%

Sampling, quantization and computational aspects of the quadrature lock-in amplifier

Leis

Kelly

Buttsworth

2012

2012 6th International Conference on Signal Processing and Communication Systems

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“…To avoid the flicker noise effect, which is inversely proportional to the frequency, we utilize a harmonic signal at 2! c instead of DC signal [11]. Here, !…”

Section: Introductionmentioning

confidence: 99%

Significantly enhanced sensor signal detection method using harmonic frequency in lock-in amplifier

Jeon

Kim

et al. 2018

IEICE Electron. Express

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In this study, we present a significantly enhanced signal detection method using harmonic frequency in a lock-in amplifier (LIA). This method reduces the effect of flicker noise that limits the signal-to-noise ratio in a conventional DC-based LIA. Furthermore, it has a definite advantage that it is not necessary to match the phase between the input and the reference signals. To verify such merits, we constructed a hybrid LIA circuit and conducted experiments. The results demonstrated that the dynamic range improved by approximately 43 dB compared to a conventional DC-based LIA. Moreover, the harmonic LIA output is successfully obtained regardless of the phase difference.

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“…The output filter value is proportional to the amplitude of the input signal and depends on a phase delay. This phase delay between the input signal and the sine-wave reference signal results from frequency fluctuations [ 5 ]. In this context it is important to set the reference phase to the value of the input phase signal in order to correctly recover the amplitude [ 6 ].…”

Section: Introductionmentioning

confidence: 99%

Circular Regression in a Dual-Phase Lock-In Amplifier for Coherent Detection of Weak Signal

Wang

Reboul

Choquel

et al. 2017

Sensors

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Lock-in amplification (LIA) is an effective approach for recovery of weak signal buried in noise. Determination of the input signal amplitude in a classical dual-phase LIA is based on incoherent detection which leads to a biased estimation at low signal-to-noise ratio. This article presents, for the first time to our knowledge, a new architecture of LIA involving phase estimation with a linear-circular regression for coherent detection. The proposed phase delay estimate, between the input signal and a reference, is defined as the maximum-likelihood of a set of observations distributed according to a von Mises distribution. In our implementation this maximum is obtained with a Newton Raphson algorithm. We show that the proposed LIA architecture provides an unbiased estimate of the input signal amplitude. Theoretical simulations with synthetic data demonstrate that the classical LIA estimates are biased for SNR of the input signal lower than −20 dB, while the proposed LIA is able to accurately recover the weak signal amplitude. The novel approach is applied to an optical sensor for accurate measurement of NO2 concentrations at the sub-ppbv level in the atmosphere. Side-by-side intercomparison measurements with a commercial LIA (SR830, Stanford Research Inc., Sunnyvale, CA, USA ) demonstrate that the proposed LIA has an identical performance in terms of measurement accuracy and precision but with simplified hardware architecture.

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Signal detection technique utilising ‘lock-in’ architecture using 2 c harmonic frequency for portable sensors

Cited by 11 publications

References 3 publications

Sampling, quantization and computational aspects of the quadrature lock-in amplifier

Sampling, quantization and computational aspects of the quadrature lock-in amplifier

Significantly enhanced sensor signal detection method using harmonic frequency in lock-in amplifier

Circular Regression in a Dual-Phase Lock-In Amplifier for Coherent Detection of Weak Signal

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