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

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
$\mu \text{m}$
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.