An Ultra-High Input Impedance Analog Front End Using Self-Calibrated Positive Feedback

作者：Jinseok Lee, Geon-Hwi Lee, Hyojun Kim, SeongHwan Cho · 发表于：IEEE Journal of Solid-State Circuits · 年份：2018 · DOI：10.1109/jssc.2018.2831231 · 被引用次数：79 · 研究领域：Analog and Mixed-Signal Circuit Design、Neuroscience and Neural Engineering、Electrical and Bioimpedance Tomography

This paper presents circuit techniques for ultra-high input impedance analog front end (AFE). In order to boost input impedance, various on- and off-chip parasitic capacitances are cancelled using an active shield and negative capacitance technique. To maximize the cancellation, a self-calibration scheme with active shield replica is proposed for positive feedback-based negative capacitance, which settles at the boundary between stable and unstable states in calibration mode. A prototype IC fabricated in 0.18-$\mu \text{m}$CMOS achieves an input impedance of 50$\text{G}\Omega$at 50 Hz, equivalent to 60-fF capacitance, while consuming 289 nW from 0.8-V supply. The proposed AFE is applied to heart-rate monitoring using 1-cm2dry electrodes over clothes without any straps.