Fast-Recovery Capacitive ECG Front-End Based on Reverse-Connected Zener Diodes

Z. Sajadi, R. Rieger (Faculty of Engineering Christian-Albrechts-Universität zu Kiel Kiel, Germany, Germany)

Capacitive electrocardiogram (cECG) systems enable non-contact cardiac monitoring for wearable and long-term applications, offering improved comfort, hygiene, and electrode reusability compared to conventional wet electrodes. However, a significant challenge in these systems arises from motion artifacts and environmental interference, which can drive the front-end amplifier into saturation and lead to signal dropouts lasting from several seconds to over one minute in severe conditions. In this work, we present a low-complexity biasing technique integrated into the bootstrapping network, employing reverse connected Zener diodes to accelerate the discharge of accumulated charge while preserving high input impedance under small-signal operation. Unlike active fast-recovery circuits or reset-based architectures, the proposed approach relies solely on passive components, reducing circuit complexity, power consumption, and implementation cost. Our experimental results demonstrate that, while traditional designs require up to several seconds to regain signal integrity after motion stops, our design achieves recovery in less than one second, providing superior responsiveness and robustness for real-time ECG acquisition. This paper outlines the design, implementation, and performance of this novel input structure in a capacitive electrode system.