Motion Artifact Mitigation Using Negative Feedback in Capacitively-Coupled ECG

Abstract

The standard electrocardiogram (ECG) depends on wet electrodes which contain a conductive gel that may cause irritation and dry out during long term measurements leading to artifacts. Capacitively-Coupled ECG (ccECG) promises to allow physicians to perform ECG through clothing or unprepared skin, without conductive gel. However, as the patient moves, air gaps are created between electrodes and the skin. Thus, the total interface capacitance varies during ccECG measurements giving rise to motion artifacts (MA). To mitigate this issue, a circuit implementing negative feedback through the human body is proposed. The system relies on the principle that the coupling capacitance and input capacitance forms a gain stage which changes as motion happens. By adding the feedback stage, this gain is stabilized. When the coupling capacitance is swept from 100 nF to 1 pF in Spice simulation, within a frequency range of 500 mHz to 100 Hz, the system gain fluctuations are reduced from 12 dB (open-loop) down to 2 dB using the proposed technique. The proposed system can maintain the same bandwidth, similar settling time and does not present instability for the desired gain and frequency range.