A 26.6–119.3-μW 101.9-dB SNR Direct Digitization Bio-Impedance Readout IC
Tan‐Tan Zhang, Hyunwoo Son, Jianming Zhao, Chun-Huat Heng, Yuan Gao
Abstract
This article presents a direct digitization bio-impedance (BioZ) readout IC with high power-to-noise efficiency over a wide input impedance range. This design features a delta-sigma ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \Sigma$ </tex-math></inline-formula> )-based BioZ readout topology with the first-order noise shaping and a feedback current-steering digital-to-analog converter (IDAC) that minimizes the residual current to suppress the input-dependent noise modulation in current balancing instrumentation amplifier (CBIA). Furthermore, various dynamic element matching (DEM) techniques are applied to mitigate the impact of 1/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f$ </tex-math></inline-formula> noise and switching noise during analog to digital conversion. The proposed BioZ readout circuit was implemented in a standard 40-nm CMOS process. Measurement results showed 101.9-dB SNR within 4-Hz bandwidth with lower than 0.1-Hz 1/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f$ </tex-math></inline-formula> noise corner and 152.6-dB figure-of-merit (FoM) for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I$ </tex-math></inline-formula> path.