A Micropower High-Performance ECG Recording Amplifier

Abstract

This work introduces a novel micropowered single supply low-noise ECG amplifier that can be used with dry fabric-based paste-less electrodes for ambulatory electrocardiogram monitoring. The study emphasizes the need to include realistic values of source impedance as high as 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{M}\Omega $ </tex-math></inline-formula> to assess amplifier performance parameters, such as magnitude response, time-domain response, common-mode input impedance, semiconductor noise, and common mode rejection ratio (CMRR). The effect on these parameters associated with high values of electrode impedance at different input frequencies has been extensively demonstrated in this work. The recommendations and standards published by the International Electrotechnical Commission (IEC) 60601 pertaining to electrocardiographic equipment have been used to evaluate the performance requirements of the amplifier to ensure minimal distortion of the ECG signal. The amplifier attains a minimum common-mode input impedance of 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{G}\Omega $ </tex-math></inline-formula> at the input within a frequency range of 0.1–150 Hz. This boosted input impedance is preserved by neutralizing amplifier input capacitance using power supply bootstrapping. The amplifier also maintains a differential gain of 41 dB, the CMRR was measured at 84 dB at mains frequency, and the input referred semiconductor noise was measured at 32- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{V}$ </tex-math></inline-formula> peak-to-peak ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> Vpp) in a bandwidth of 250 Hz. The power consumption of the amplifier was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$130 ~\mu \text{W}$ </tex-math></inline-formula> operating from 3.7-V lithium battery and is intended to provide for ECG signals having amplitudes in the range 0.1–10 mV. This small portable amplifier is intended for use in long-term ECG and heart-rate monitoring applications.