A 0.5-mΩ/√Hz Dry-Electrode Bioimpedance Interface With Current Mismatch Cancellation and Input Impedance of 100 MΩ at 50 kHz
Qinjing Pan, Tianxiang Qu, Biao Tang, Fei Shan, Zhiliang Hong, Jiawei Xu
Abstract
This article describes a high-input-impedance, low-noise bioimpedance (BioZ) sensor interface IC for small-area dry-electrode cardio-respiratory signals monitoring. To facilitate high-precision BioZ sensing with high-impedance dry electrodes, the IC utilizes three key techniques as follows: 1) a bias control loop (BCL) to eliminate the excitation current mismatch, reducing the voltage fluctuation on high-impedance input; 2) a quiet-chopping current feedback instrumentation amplifier (QC-CFIA) to mitigate the input-signal-dependent noise; and 3) a full pre-charge (FPC) technique to cancel the input parasitic capacitance for impedance boosting. Manufactured in a 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">$\mu \text{m}$ </tex-math></inline-formula> CMOS process, the BioZ prototype IC occupies an area of 0.4 mm2 while consuming 15.8- and 14.4–128.4- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> current, respectively, from the amplifier and the excitation current generator (CG). With these proposed techniques, this IC achieves a high input impedance of 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{M}\Omega $ </tex-math></inline-formula> at 50 kHz, 0.5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega /\surd $ </tex-math></inline-formula> Hz sensitivity at 1 Hz, and a 106-dB signal-to-noise ratio (SNR). A gel-free respiration and impedance cardiography (ICG) recording has been successfully demonstrated on the human body with four 0.45-cm2 dry electrodes.