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-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>m CMOS process. Benefiting from the proposed feedback (FB) two-step direct conversion architecture with an improved <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta $ </tex-math></inline-formula>-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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.2~{\mu }$ </tex-math></inline-formula>Vrms, an input impedance of 26 G<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula>, and a ±1.8-V electrode dc offset (EDO) tolerance, while consuming only 63-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>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.