AUTHORS: M. J. Burke, O. Tuohy

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ABSTRACT: This paper investigates the low-frequency response of a multi-stage bioelectric amplifier intended for use in the measurement of the electrocardiogram (ECG) using dry contact electrodes. These electrodes have an impedance which is typically an order of magnitude greater than that of the standard disposable self-adhesive electrodes used in clinical ECG recording. The design was undertaken with the intention of exploiting micro-power CMOS operational amplifier technology to minimise power in ambulatory recording. The response is optimised to meet the transient response requirements of the International Electrotechnical Commission Standard 60601 applying to electrocardiographs [1,2]. The optimum configuration was established to be two differential stages with a gain of 20dB each and a differential-to-single-ended output stage having unity gain. The -3dB pole is placed at 0.013Hz in the first and second stages to give an overall -3dB low cut-off frequency of 0.02Hz. In addition, a zero at 0.0013Hz in the non-inverting front-end stage was cancelled by the pole of the input ac coupling network. This ensured that the maximum undershoot of 100μV and the maximum recovery slope of 300μVs-1 permitted in response to a narrow pulse of 3mV amplitude and 100ms duration were met.

KEYWORDS: ECG Recording, Bioelectric Amplifiers, Dry Electrodes, Un-gelled Electrodes

REFERENCES:

[1] International Electrotechnical Commission, Medical Electrical Equipment Std. 2-25. IEC 60601, 2011.

[2] International Electrotechnical Commission, Medical Electrical Equipment Std. 2-47. IEC 60601, 2012.

[3] A. S. Berson and H. V. Pipberger, The LowFrequency Response of Electrocardiographs: A Frequent Source of Recording Errors, American Heart Journal, Vol.71, 1966, pp. 779-789.

[4] D. Tayler and R. Vincent, Signal Distortion in the Electrocardiogram Due to Inadequate Phase Response, IEEE Transactions in Biomedical Engineering, Vol.30, 1983, pp. 352-356.

[5] M. J. Burke and M. Nasor, The Time Relationships of the Constituent Components of the Human Electrocardiogram, Journal of Medical Engineering & Technology, Vol.26, 1999, pp. 1-6.

[6] M. J. Burke and G. Shorten, A Time Domain Based Classifier for ECG Pattern Recognition, Proceedings of the 33rd IEEE Annual International Conference on Engineering in Medicine & Biology, EMBC, Boston, 2011, pp. 4980-4983.

[7] C. E. Kossmann et al., Recommendations for Standardization of Leads and of Specifications for Instruments in Electrocardiograpy and Vectorcardiography, Circulation, Vol.35, 1967, pp. 583–602.

[8] H. V. Pipberger et al., Recommendations for Standardization of Instruments in Electrocardiography and Vectorcardiograhy, IEEE Transactions in Biomedical Engineering, Vol.14, 1967, pp. 60-68.

[9] M. J. Burke and D. T. Gleeson, An Ultra-Low Power Pre-Amplifier for Pasteless Electrocardiograpy, Proceedings of the 6th IEEE International Conference on Electronics, Circuits & Systems, ICECS, Cyprus, 1999, pp. 615-619.

[10] Baba, A. and Burke, M. J., Measurement of the Electrical Properties of Un-Gelled ECG Electrodes, NAUN International Journal of Biological & Biomedical Engineering, Vol.2, 2008, pp. 89-97.

[11] M. J. Burke and M. V. Whelan, ‘Photoplethymography: Selecting OptoElectronic Components, Medical & Biological Engineering & Computing, Vol.24, 1986, pp. 647-650.