Key result
An ultra-high input impedance buffer prototype for dry ECG electrodes achieved a 191 fF input capacitance at 50 Hz and a CMRR of 81.4 dB with zero mismatch.
Why the study?
Many health and wellness applications require non-intrusive ECG monitoring, driving the need for reduced input capacitance and enhanced acquisition with dry or non-contact capacitive electrodes.
The proposed ultra-high input impedance buffer provides a low-cost, robust solution for acquiring ECG signals using dry or capacitive electrodes.
May enable dry-electrode ECG systems; leaves open clinical validation before practice adoption.
A large number of health and wellness applications wish to monitor electrocardiogram signal (ECG) in the least intrusive way possible. The use of dry textile electrodes with high input impedance bio-amplifiers is a common technique. This paper presents a novel ultra-high input impedance buffer to obtain a reduced input capacitance and enhance the acquisition of results for dry or non-contact capacitive ECG electrodes. Based on different bootstrapping techniques, input stage biasing and unipolar power supply, an operational amplifier buffer is implemented on Printed Circuit Board (PCB) to provide a low cost solution. The solution considers the protections for electrostatic discharges (ESD) and filters for interferences, maintaining high input impedance design. A method to measure input impedances in the range of femtofarads is also proposed. This active electrode prototype presents a 191 fF input capacitance at 50 Hz. Different skin-electrode impedance cases are studied to obtain the Common Mode Rejection Ratio (CMRR). As a result, a value of 81.4 dB is obtained with zero mismatch and 76.1 dB at 50 Hz is obtained with a resistive mismatch of 1-2.2 MΩ. Moreover, ECG test is evaluated using a discrete back-end circuit, digital filtering and software display. Finally, the full ECG circuit has been simulated under an ESD transient of ±8 kV IEC 61000-4-2 waveform. This paper demonstrated that the proposed solution with standard discrete components fulfills the industry requirements for robust ultra-high impedance ECG sensor.
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Camós-Vidal et al. (2023) studied Electrocardiogram signal (ECG) monitoring. Ultra-high input impedance buffer for dry or capacitive ECG electrodes was evaluated on Input capacitance and Common Mode Rejection Ratio (CMRR). An ultra-high input impedance buffer prototype for dry ECG electrodes achieved a 191 fF input capacitance at 50 Hz and a CMRR of 81.4 dB with zero mismatch.
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