Biometric Sensor Noise Cancellation via Common-Mode Coupling
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Solution Overview
Problem
Biometric sensors in exercise equipment face interference from non-common-mode noise due to independent pickup of unwanted electrical signals by electrodes, which complicates the measurement of heart rate signals.
Innovation Solution
The use of a biometric sensor system with a pair of electrodes spatially separated on an exercise apparatus, where noise from one electrode is proximally coupled to the other electrode's line, creating a common-mode situation within the instrumentation amplifier to reject noise effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrodes are physically separated on the exercise apparatus, then the biometric sensor can detect heart rate signals, but non-common-mode noise is independently picked up by each electrode causing interference
Solution Approach 1:
The patent introduces a common reference line (third conductor) as an intermediary that couples both electrodes to a common ground reference point. This mediator creates a common-mode reference for both electrode inputs, allowing the instrumentation amplifier to reject non-common-mode noise while maintaining the spatial separation needed for biopotential detection.
Solution Approach 2:
The patent changes the electrical configuration parameter by adding a third conductor that provides a common reference potential. This parameter change transforms the noise rejection capability of the system, enabling the amplifier to distinguish between common-mode signals (including noise) and differential biopotential signals through the relationship Vout = (V2 - V1) / (2 * RCMRR) + (V1 + V2) / 2.
2Measurement precision
If high impedance, high gain amplifiers are used to measure small electrical potentials, then biopotential signals can be detected, but common-mode noise rejection becomes complicated when noise is not present on both inputs
Solution Approach 1:
The patent creates equipotential conditions by connecting both amplifier inputs to a common reference potential through the third conductor. This establishes a common-mode voltage reference that simplifies noise rejection, allowing the high-gain amplifier to operate effectively while maintaining common-mode rejection through the balanced configuration where both inputs share the same reference.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively reduces noise interference, enhancing the accuracy of heart rate signal detection by ensuring that noise sources affect both amplifier inputs equally, thereby isolating the signal of interest.
Implementation Method 1
When the heart or other muscles contract, the body generates a very low amplitude electrical signal known as a biopotential signal. Biopotential signals can be electrically detected on the surface of a person's skin.
Implementation Method 2
Since amplifiers do a good job of attenuating signals in common to both inputs, the difference does not contain the common noise. This is referred to as common-mode noise rejection.
Implementation Method 3
the noise on the first electrode is proximally coupled to the second line and the noise on the second electrode is also proximally coupled to the first line, thereby creating a common-mode situation between inputs of the amplifier
Data Source
AI summary
In a biometric sensor provided for use with an exercise apparatus and having a pair electrodes for sensing a biopotential signal, a common-mode rejection circuit can be used to cancel noise in the signal resulting from various sources including motion of the apparatus.