Common-Mode Driven Shield Circuit for Capacitive Biosignal Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Indirect contact biosignal measurement devices face challenges in minimizing common mode noise, particularly when there is high electrical resistance between the human body and the ground, which limits the effectiveness of existing methods like the right-leg-driven ground method.
Innovation Solution
The implementation of a capacitive coupling active electrode (CCE) circuit with a common mode interacting unit that includes filters, a frequency band changing unit, and a driven gain applying unit to interact with a shield voltage, effectively compensating for frequency bands and adjusting gain and phase to reduce common mode noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a maximally wide ground plate is employed to increase electrical capacity between the human body and ground, then equivalent impedance is decreased, but device complexity and size increase
Solution Approach 1:
A shield electrode is introduced as an intermediary component between the human body and ground. The shield is driven by a common mode driven unit that generates a drive signal to actively control the electrical field distribution, thereby reducing equivalent impedance without requiring a large ground plate area
Solution Approach 2:
The system dynamically adjusts the drive signal parameters (amplitude and frequency) from the common mode driven unit to optimize the electrical characteristics between the human body and ground. By changing the drive signal parameters, the equivalent impedance can be controlled and reduced without increasing the physical size of the ground plate
2Device complexity
If the right-leg-driven ground method is used to reduce ground plate size, then device size decreases, but common mode noise compensation effectiveness is limited
Solution Approach 1:
The shield electrode serves as an intermediary that actively compensates for common mode noise. By positioning the shield between the capacitive coupling active electrode and the human body, and driving it with a specifically designed common mode driven unit, the system can more effectively cancel common mode noise compared to traditional right-leg-driven methods
Solution Approach 2:
The system combines multiple functional components (capacitive coupling active electrode, shield electrode, common mode driven unit with filter and amplifier) into a composite measurement system. This composite structure integrates both signal acquisition and common mode noise compensation functions, providing superior noise rejection while maintaining compact size
3Reliability
If common mode noise is decreased using traditional methods, then measurement reliability improves, but frequency band compensation is insufficient
Solution Approach 1:
The common mode driven unit incorporates a filter unit and amplifier that can dynamically adjust to different frequency characteristics. The system adapts its frequency response to compensate for the specific frequency band characteristics of the biosignal being measured, providing both noise reduction and frequency band compensation
Solution Approach 2:
The shield electrode and common mode driven unit serve multiple functions simultaneously: they act as a shield against external interference, provide active common mode noise cancellation, and compensate for frequency band characteristics. This multi-functional design improves measurement reliability across different biosignal types without requiring separate compensation mechanisms
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 approach significantly decreases common mode noise by increasing the input impedance of the electrode, allowing for more accurate biosignal measurement even with high resistance between the body and ground, as demonstrated by the application of a unit-gain common mode driven shield.
Implementation Method 1
capacitive coupling active electrode (CCE) circuit including an electrode face configured to sense a biosignal
Implementation Method 2
a common mode interacting unit configured to enable a common mode signal to interact with a shield voltage in order to compensate for a frequency band
Implementation Method 3
a preamplifier configured to amplify the shield voltage and the biosignal
Implementation Method 4
a differential amplifier configured to amplify a differential component of the biosignal measured by the CCE
Data Source
AI summary
An apparatus and method of removing common mode noise in the case of measuring a biosignal using a capacitive coupling active electrode (CCE) is provided. A frequency band of a common mode signal may interact with a shield voltage and thus, a frequency band of a biosignal may be compensated for.