A Noncontact ECG Sensing System With a Micropower, Ultrahigh Impedance Front-End, and BLE Connectivity

Capacitive noncontact electrodes offer a promising solution to improve comfort and unobtrusiveness in continuous monitoring ECG systems which are becoming more widespread in wearable devices. Most implementations based on off-the-shelf components require rather large electrodes and power budgets while custom application-specific integrated circuits (ASICs) face significantly higher adoption challenges. In this article, we present a novel micropower ultrahigh impedance front-end with an equivalent input capacitance of 70 fF in the ECG band, enabling contactless ECG acquisition with electrodes as small as 78.5 mm2 with a power consumption of only $15 \, \mu \text{W}$. The front-end implements a novel power supply bootstrapping architecture and is integrated in a full acquisition system which includes a 24-bit analog to digital converter (ADC) and a bluetooth low energy (BLE)-capable Cortex M4 processor, achieving up to ten days of continuous operation on a 600 mAh PR44 battery.