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BES-AFE-1: Analog Front-End Module for ECGs
A fully functional single lead electrocardiograph analog
front-end module designed for prototyping and integration
in user designs.
As Featured In
DesignSpark
"Designed to offer the user a low noise, low offset, and low power
solution in a compact easy-to-use form factor."
The BES-AFE-1 is a fully functional single lead electrocardiograph (ECG) analog front-end
module designed for prototyping or for integration in user designs. This module provides
an easy to use solution to the problem of acquiring electrical heart activity for those
wanting to incorporate heart monitoring functionality in their project or product. Typical
users include makers, hobbyists, students, teachers, and engineers who want to
concentrate on developing their project or product without having to deal with the
arduous task of developing, characterizing, and testing an ECG analog front-end. This
module has been designed to offer the user a low noise, low offset, and low power
solution in a compact easy-to-use form factor with the benefits of built-in right-leg drive,
baseline wander rejection, notch filtering, and anti-aliasing.
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What Does It Do?
The BES-AFE-1 takes care of the problem of designing analog circuitry needed to convert a
low level, variable impedance, and often noisy electrical signal from the heart into a more
usable form that can be directly fed into an analog to digital converter (ADC) of a
microcontroller or oscilloscope. Without such a front-end, it would be very hard for the
ADC to pick up the heart’s electrical activity because the signal itself is often on the order
of tenths of a millivolt on the surface of the body. In addition, noise and offset are big
concerns when attempting to amplify such signals because both line interference (from the
AC power in a building) and contact induced offset/baseline wander (from breathing) will
be many orders of magnitude larger than the signal itself. Attempts by other people to
build an EKG often results in poor acquisition secondary to not only persistent noise
despite filtering but waveform distortion as well to the point that the morphologies of
various key components of the EKG signal (such as QRS complex) are no longer
representative of the electrical activity of the heart. Therefore, under many applications
such as heart rate monitoring, the module can reduce or even remove the need for
filtering while avoiding unacceptable distortion from inadequately designed analog
circuitry.
Target Audience
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Makers and Hobbyists:
Use it to easily test ideas and rapidly develop projects
pertaining to fitness, biometrics, and electrophysiology applications
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Students
Use it to quickly develop and validate designs for use in various class
projects such as the Senior Design/Capstone Project
•
Teachers
Use it as a teaching aid in the lab and to demonstrate concepts in both
fields of biology and engineering in the classroom
•
Engineers
Use it to easily acquire authentic real-time data to help you further define,
develop, and test your next MVP or maturing product within the areas of fitness,
automotive, security, gaming, and medicine.
Features & Specifications
•
Voltage Supply:
Single and dual rail ranging from 1.8v (±0.90) to +5.5v (±2.75v)
•
Current consumption:
180µA to 290µA. Typical 220µA @ 3.3v
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•
Internal Reference:
(Vdd-Vss)/2 which can be easily overridden by the user with an
external reference
•
Bandwidth:
100Hz
•
Low-Pass:
First order at 0.8Hz
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Notch:
50Hz or 60Hz with >20dB Notch Depth
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High-Pass:
Fourth Order Bessel at 100Hz, First Order at 96.6Hz on secondary gain
stage
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Size:
2” by 0.6” (50.8mm by 15.24mm)
•
Design Criteria:
Module has been designed to preserve waveform morphology and
maximize noise immunity at the expense of bandwidth and absolute gain accuracy.
Performance Graphs
Simulated ECG with Noise Input [yellow] and Output from Module [green]
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ECG signal through various stages of the AFE module. Yellow trace is the input and pink
trace is the output.
AFE module output when connected to a human subject in Lead II configuration using the
modified Mason-Likar variant for electrode placement.
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Current consumption of a typical BES-AFE-1 Module with inputs shorted to right leg drive
and a 1MΩ load on the output
Typical frequency response of the BES-AFE-1-A module (60Hz Notch Option)
