Optimisation of the Low-Frequency Response of a Multi-stage Bioelectric Amplifier for Electrocardiogram (ECG) Recording

¹ Dept. of Electronic and Electrical Engineering, Trinity College, University of Dublin, College Green, Dublin 2, Ireland
² Dept. of Engineering and IT, Medical Engineering, Carinthia University of Applied Sciences, 9020 Klagenfurt, Austria

^a Corresponding author: mburke@tcd.ie

Abstract

This paper reports the optimisation 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 frequency response was optimised to meet international performance requirements for electrocardiographic recorders, in particular the International Electrotechnical Commission 60601 standards [1,2]. The pole and zero locations of a multi-stage amplifier configuration were optimised to meet both time and frequency domain specifications. The optimum assignment for a three stage amplifier, having two differential stages and a differential-to-single-ended conversion stage was established by evaluating the performance of a number of circuit configurations. 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 0.028Hz and a zero at 0.0028Hz in the first and second stages to give an overall -3dB bandwidth of 0.043Hz. In addition, the pole of the input ac coupling network was placed at 0.0028Hz in order to meet the undershoot and recovery slope requirements in the narrow pulse response.