Low-Frequency Response of a Multi-Stage Dry-Electrode ECG Bioelectric Amplifier

This paper reports the optimisation of the low-frequency response of a multi-stage bioelectric amplifier intended for use in the measurement of the electrocardiogram (ECG) using un-gelled electrodes. The frequency response was optimised to meet the International Electrotechnical Commission 60601 performance standards for electrocardiographs [1,2]. The low frequency response of a multi-stage amplifier configuration was optimised to meet both time and frequency domain specifications. The optimum circuit 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 giving an overall -3dB bandwidth of 0.043Hz. 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 response to a narrow pulse. Key-Words: Electrode Impedance, Un-gelled electrodes, Heart rate monitoring, ECG amplifier.