In this paper, the power line noise characteristics between conventional ECG measurement system using Ag/AgCl electrodes and capacitive-coupled ECG system using capacitive electrodes are compared by the concept of the effective coupling impedance. For this comparison, it is considered that both two systems include the negative feedback circuit, which is called Driven-Right-Leg in typical ECG system, to reduce the common mode noise. As the result, the negative feedback gain plays an important role in decreasing the effective coupling impedances and increasing the signal-to-noise ratios for the ECG signal and power line interferences to both two systems.
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