Abstract
This paper addresses the design of the low-frequency response of a multi-stage bioelectric amplifier intended for use in the measurement of the human electrocardiogram (ECG) using high-impedance un-gelled electrodes. The response is optimised to meet the International Electrotechnical Commission 60601 standards [1, 2] for electrocardiograph recorders in both the time and frequency domains. The optimum design for a three stage amplifier, having two differential stages and a differential-to-single-ended conversion stage was established in the context of low-power ambulatory ECG monitoring. The optimum configuration was found to be two differential stages with a gain of 20dB each and a differential-to single-ended output stage with unity gain. The −3dB pole is placed at 0.013Hz and a zero at 0.0013Hz in the first and second stages to give an overall −3dB low cut-off frequency of 0.02Hz. In addition, the pole of the input ac coupling network was placed at 0.0013Hz in order to cancel the zero in the non-inverting front-end stage. This ensured that undershoot and recovery slope performance requirements in response to a narrow pulse of 3mV amplitude and 100ms duration were met.
Highlights
The nature of the low-frequency response of bioelectric amplifiers intended for use in recording the human electrocardiogram (ECG) is of the utmost importance because of the clinical significance of these recordings
This paper investigates the issues in the design of the low-frequency response of bioelectric amplifiers intended for ECG recording using un-gelled or dry electrodes
Standards for the performance requirements of ECG recorders have been developed in the US by the American National Standards Institute (ANSI) with recommendations made by the American Heart Association (AHA)
Summary
The nature of the low-frequency response of bioelectric amplifiers intended for use in recording the human electrocardiogram (ECG) is of the utmost importance because of the clinical significance of these recordings. Miniaturisation and portability has meant that the use of ECG recorders has extended beyond the hospital clinics and wards to non-clinical scenarios such as general practice, sports medicine, physiology and even the factory floor. This increase in low-power, battery-operated equipment has meant corresponding changes in electronic instrumentation and circuit design. Lower power supply voltages have tended to make amplifier front-end stages ac coupled rather than dc coupled as in the past. Recent trends towards un-gelled electrodes have increased the magnitude of these polarisation voltages
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