Common-mode rejection in the measurement of wearable ECG with cooperative sensors

Abstract

Recently, telemonitoring of vital signs has gained a lot of research interest. Especially for electrocardiogram (ECG), which is among the most frequently measured vital sign. However, the integration of classical ECG Holter in wearables is problematic since shielded cables and gel electrodes are required to get ECG signals of highest quality. We have recently introduced a novel sensing architecture based on active electrodes (so-called cooperative sensors) that significantly reduces the cabling complexity of the monitoring device. After briefly recalling the principle of cooperative sensors this paper details how they address rejection of common-mode voltage induced by electromagnetic disturbances. The proposed approach uses an auto-identification technique based on a continuous-time calibration of the sensor system and a digital control loop. To demonstrate the reliability of the proposed approach, a 12-lead ECG monitoring system was implemented with the new common-mode rejection method. Measurements on four healthy volunteers showed that the signal quality obtained with the cooperative-sensor system (using dry electrodes) is equivalent to the one measured with a gold standard medical device (using gel electrodes) in exercise stress tests.

Remotely Powered Two-Wire Cooperative Sensors for Biopotential Imaging Wearables

“…Since the total gain of the acquisition chain (from the potential v i to the demodulated signal ) may be slightly different from sensor to sensor, the common-mode rejection when performing the difference might be insufficient. The problem can be neatly solved by the method described in [ 15 ], which relies on online identification of the transfer functions through an excitation common-mode voltage added to the voltage source driven by the G controller.…”

“…Buses with a small number of lines, such as one or two at most, are the most desirable, but more difficult because the bus must perform several functions (potential reference, current return, synchronization, communication, and power supply). Cooperative sensors [ 13 , 14 , 15 , 16 , 17 , 18 , 19 ], defined as active electrodes connected to a parallel bus of up to two wires, have been proposed to address these challenges, except for the power supply. Adding the power supply function—without interfering with the other functions and addressing the medical safety issue in wearables—is the main contribution of this paper.…”