A 0.5-mΩ/√Hz Dry-Electrode Bioimpedance Interface With Current Mismatch Cancellation and Input Impedance of 100 MΩ at 50 kHz

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- <tex-math notation="LaTeX">μ m </tex-math> CMOS process, the BioZ prototype IC occupies an area of 0.4 mm2 while consuming 15.8- and 14.4–128.4- <tex-math notation="LaTeX">μ W </tex-math> current, respectively, from the amplifier and the excitation current generator (CG). With these proposed techniques, this IC achieves a high input impedance of 100 <tex-math notation="LaTeX">MΩ </tex-math> at 50 kHz, 0.5- <tex-math notation="LaTeX">mΩ / </tex-math> 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.