Transient Response of Low-Power ECG Recoding Amplifiers for Use with Un-gelled Electrodes

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