One-Decade Frequency Range, In-Phase Auto-Aligned 1.8 V 2 mW Fully Analog CMOS Integrated Lock-In Amplifier for Small/Noisy Signal Detection

Abstract

In this paper, we present a new fully analog integrated lock-in amplifier (LIA) for the accurate detection and the measurement of small, slow, and noisy signals, typical of sensors. The proposed LIA, designed as an integrated circuit in a 0.35 µm standard CMOS technology with low-voltage (1.8 V) low-power (2 mW) characteristics, performs an automatic alignment (auto-calibration) of the relative phase between the input and reference signals, both at power-ON of the system and for any variation during its operating time. Even if these kinds of amplifiers work at a specific single operating frequency at time, the proposed LIA has been optimized to operate, through an automatic frequency tuning function, in one-decade frequency variation range, set to [2.5-25 Hz], particularly affected by flicker noise. On-chip measurements have confirmed the proper functionality of the system in the recovery and amplification of small and noisy signal amplitudes, in particular 714 times lower than the noise level (i.e., signal-to-noise ratio (SNR) of about −57 dB), obtaining an experimental best resolution of 12.5 nV with maximum a sensitivity of about 124 000 [V/V]. Moreover, by means of the employment of the proposed LIA, the experimental SNR and resolution improvements are of a factor of about 4000.Index Terms-Analog lock-in amplifier, CMOS integrated circuit, automatic circuit, low-voltage, low-power, phase autoalignment, signal-to-noise recovery system, high resolution, high sensitivity, high accuracy, frequency tuning.

Low Cost Autonomous Lock-In Amplifier for Resistance/Capacitance Sensor Measurements

“…Thus, it constitutes a more versatile, hardware efficient and power Finally, Table 4 presents a comparative of the proposed Lock-in Amplifier with other recent LIA solution. Even though special emphasis was made on searching solutions focused on a single phase LIA with phase alignment, only a few papers were found [50,51], implemented with discrete components or, as the proposed system, consisting of a mixed approach. However, it should be noted that in [50] and [51], three and four PSDs are required, respectively, for a single measurement output, while in the proposed LIA only two PSD are used, and it can be configured as a single or dual phase LIA.…”

Accuracy study for lock‐in amplifiers in a scanning near‐infrared spectrometer

“…Thus, the relative standard deviation of amplitude caused by the phase error was σA α = |δA α |/√2 = 1.57 × 10 −3 . The relative standard deviation of amplitude σA caused by the combination of frequency error and phase error was calculated with (12) σA = (σA f ) 2 + (σA α ) 2 = 1.62 × 10 −3 (12) The SNR of the amplitude demodulation results was SNR = 1/σA = 617. The theoretical analysis showed that: if the amplitude detection was initiated at the zero phase of the measured signal, the SNR was 2273, which was only influenced by the frequency error; if the amplitude detection was initiated at a non-specific phase of the measured signal, the SNR was 617, which was influenced by the frequency error and phase error.…”

“…According to the implementation of phase-sensitive detection, the lock-in amplifier can be divided into analogue lock-in amplifier and digital lock-in amplifier [11]. Analogue lock-in amplifiers are implemented by analogue circuits, which are a mature technology and have good performance [12][13][14][15]. In recent years, digital lock-in amplifiers have received more attention due to the advantages of high accuracy, strong flexibility, good stability and no interference of temperature drift [16][17][18][19].…”

A CMOS Low Pass Filter for SoC Lock-in-Based Measurement Devices

“…Different integrated LIAs have been recently proposed for smart instrumentation applications [13,19,20,21] to exploit the advantages that render CMOS compatibility in terms of miniaturization. However, these LIAs maintain the LPF external use of off-chip resistors and capacitors [19,20,21] or, for fully integrated LIA solutions [13], the active filter area is rather large (it is the dominant element of the 3.6 mm 2 area of the implemented chip) for frequencies ~300 Hz. In particular, a previous author’s proposal [21] achieves very competitive capabilities in terms of area, power, and signal recovery, but the LPF is also kept external.…”