A 26-GΩ Input-Impedance 112-dB Dynamic-Range Two-Step Direct-Conversion Front-End With Improved Δ-Modulation for Wearable Biopotential Acquisition

This article presents a high dynamic range (DR) direct conversion front-end (Direct-FE) IC enabling the wearable acquisition of weak bio-potentials superposed onto large motion artifacts (MAs). The prototype IC has been fabricated in a standard 0.18- $\mu $ m CMOS process. Benefiting from the proposed feedback (FB) two-step direct conversion architecture with an improved $\Delta $ -modulation, as well as a novel differential difference amplifier (DDA) and a dynamic-element-matching (DEM) technique, it achieves a peak input range of 3.56 VPP, an input-referred noise (IRN) of $2.2~{\mu }$ Vrms, an input impedance of 26 G $\Omega $ , and a ±1.8-V electrode dc offset (EDO) tolerance, while consuming only 63- $\mu $ W power. Compared with state-of-the-art Direct-FEs, the proposed work demonstrates an advanced DR (112 dB) and a competitive FOMDR (175 dB). The prototype IC has been validated based on in vivo experiments, demonstrating its capability for artifact-tolerant wearable bio-potential acquisition.