A 36.8-μW 66 nV/√Hz 85.7 dB-System-SNDR Reconfigurable Single-Channel ExG Acquisition System for Bio-Sensor Modules

Abstract

This paper presents a fully integrated reconfigurable single-channel IC with high energy efficiency for bio-signal acquisition in Internet-of-Medical Things (IoMT) systems. The overall signal chain consists of a capacitively-coupled instrumentation amplifier (CCIA) and a 16-bit delta-sigma ( $\Delta $ $\Sigma $ ) ADC. The ADC is directly driven by the CCIA without a traditional driver stage. The folded path of the first stage in CCIA is sliced for reconfigurable noise levels. In addition, a single-stage floating inverter amplifier (FIA) assisted by the correlated-level-shifting (CLS) technique is employed in the switched-capacitor (SC) $\Delta $ $\Sigma $ modulator for fully dynamic operation with sufficient DC gain. Fabricated in 180-nm CMOS, the CCIA achieves an input-referred noise level ranging from 35.8 to 67 nV/ $\surd $ Hz with a best noise-efficiency factor (NEF) of 5.54. It corresponds to an integrated noise ranging from 0.63 to 1.16 $\mu $ $\text {V}_{\text {rms}}$ (0.5-100 Hz) and 1.93 to 3.51 $\mu $ $\text {V}_{\text {rms}}$ (0.1-3 kHz), respectively. The ADC achieves a peak SNDR of 92.6 dB for a 2.3- $\text {V}_{\text {pp}}$ differential input and can support 16 $\times $ power/BW reconfigurability with ENOB>15 bit. The complete system occupies an active area of 0.56 mm2 and achieves 85.7-dB system SNDR over a 500 Hz BW with an OSR of 128. It consumes 36.8 $\mu $ W from a 1.8-V supply, corresponding to an SNDR-based Schreier FoM of 157 dB. Biological measurement is demonstrated successfully, and the results verify that the proposed IC is applicable to high-quality ExG signal acquisition.