Design of an ECG measuring system by the coupling capacitance amplifier between the human body

Abstract

This paper proposes an electrocardiogram (ECG) measuring system which simultaneously enables the reduction of input impedance and low-frequency cutoff through virtual amplification of the coupling capacitance formed by body capacitance and ECG electrode. This virtual amplification of the coupling capacitance is realized by the additional circuit which controls the inflow of external current to create the situation as if the time constant of the capacitance has increased. Moreover, not only this additional function but the amplification circuits commonly used in ECG measuring system has also been perfectly tuned-up. Here, instead of using the MOS-FET which shows bad noise characteristics, the combinations of J-FET differential amplifier and current feedback circuit have been used for stable amplification. In addition, coupling capacitors of the system are removed due to the DC-Coupling enabled by using single operational amplifiers instead of instrumentation operational amplifiers.

Keywords

• ecg
• coupling capacitance
• time constant
• instrumentation operational amplifiers