A 255nW ultra-high input impedance analog front-end for non-contact ECG monitoring

Abstract

This paper presents a high-input impedance analog front-end (AFE) for low-power bio-potential acquisition. In order to boost input impedance, parasitic capacitance from PCB, pad, and amplifier gate input were cancelled using shielding buffer and positive feedback. To maximize the amount of positive feedback while guaranteeing stability, a self-calibration scheme is proposed for the positive feedback. A prototype IC fabricated in 0.18μm CMOS consumes 255nW from 0.8V supply. Measured input impedance with the proposed calibration is 50GΩ at 50Hz which is equivalent to an input capacitance of 60fF. It is also verified that the proposed scheme is resilient to supply and temperature variations and applicable to non-contact ECG monitoring.