Abstract
Non-contact capacitive electrodes are a suitable choice for unobtrusive and long-term ECG/heart-rate monitoring applications, but require a front-end amplifier with large input impedance, low noise, and motion artifact (MA) reduction methods. This paper proposes a front-end amplifier structure with a fast reset scheme. It enables MA recovery prior to saturation and therefore avoids a long recovery process which may take up to several seconds and results in signal loss in typical capacitive sensing systems. A reconstruction algorithm restores the waveform and hence extends the dynamic range beyond the original saturation level. The proposed fast-reset amplifier and a conventional pseudo-resistor biased amplifier were fabricated in an 180nm CMOS technology. The electrical characterization results s how that the fast-reset version is superior to the conventional structure, by achieving an input resistance of 1.8 TΩ, a 3-100Hz 2.3 μV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> integrated noise level with a 10 pF source impedance, and the ability to deal with MA saturation. Finally a 4-channel system employing the proposed amplifiers was built. It can successfully measure ECG R-peaks through clothes, while the fast reset scheme enables continuous detection in the presence of MAs.
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