Floating Front-End Amplifier for One-Wire Biopotential Sensing
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Solution Overview
Problem
Existing biopotential and impedance measurement systems face challenges in minimizing noise and motion artifacts, particularly in ambulatory settings, due to high impedance at the electrode-body interface and the need for multiple electrodes and cables, which can be uncomfortable and obtrusive.
Innovation Solution
A floating front-end amplifier with power supplies biased by a voltage source controlled by the output of a feedback filter, allowing for a one-wire connection and embedded electronics in measurement sites, reducing the need for additional electrodes and cables, and utilizing a guard electrode to minimize mains disturbances and stray capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple electrodes and cables are used for biopotential and impedance measurements, then measurement capability is improved, but device complexity and subject comfort deteriorate
Solution Approach 1:
The patent implements a universal electrode that can serve multiple functions: it can measure both biopotentials and impedance, and it can function as both a signal electrode and a guard electrode depending on the configuration. This multi-functionality eliminates the need for separate dedicated electrodes for different measurement types, thereby reducing the overall number of electrodes and cables required while maintaining comprehensive measurement capability.
Solution Approach 2:
The patent combines the signal electrode and guard electrode functions into a single physical electrode structure. By merging these previously separate components into one unified electrode, the system reduces cable count and simplifies the interface with the body, while the electronic circuitry maintains the functional separation needed for accurate measurements through software-controlled configuration.
2Object-affected harmful factors
If shielded cables with driven shields are used, then noise protection is improved, but device complexity and cabling requirements worsen
Solution Approach 1:
The patent extracts the shield function from the cable assembly and relocates it to the electrode itself. By making the electrode structure inherently shielded rather than relying on external cable shielding, the system eliminates the need for complex driven shield cables while maintaining effective noise protection. The electrode's own capacitance and geometry provide the shielding effect, simplifying the cabling requirements.
Solution Approach 2:
The patent introduces a virtual ground potential as an intermediary reference that eliminates the need for physical shield cables. By using the body's own potential as a reference and creating a virtual ground through electronic means, the system achieves noise rejection without requiring traditional shielded cable infrastructure, thereby simplifying the cabling system.
3Measurement precision
If follower operational amplifiers with unitary gain are used, then input impedance is improved, but common mode rejection deteriorates due to incomplete capacitance cancellation
Solution Approach 1:
The patent implements dynamic gain adjustment in the follower operational amplifier, allowing the gain to vary between exactly unity (for optimal input impedance) and slightly different from unity (for complete capacitance cancellation and improved common mode rejection). This dynamic capability enables the system to optimize performance for different operating conditions, resolving the contradiction between maintaining high input impedance and achieving complete parasitic capacitance compensation.
Solution Approach 2:
The patent changes the electrical parameter of amplifier gain from a fixed value to a variable parameter that can be precisely controlled. By allowing the gain to deviate slightly from unity when needed, the system achieves complete cancellation of parasitic capacitance and improved common mode rejection ratio, while still maintaining sufficiently high input impedance for accurate biopotential and impedance measurements.
Data Source
AI summary
A follower amplifier with power supply biased by a controlled voltage source such that the power supply potentials are, for the frequencies of interest, as close as possible to the potential of the follower output. There is proposed a front-end electronic circuit for biopotential and impedance measurements with outstanding performances (very high input impedance and gain very close to unity). Preferably, the explicit guard electrode and the explicit electronic unit at the belt are no longer necessary; all electronics is embedded in units placed directly at the measurement sites. Moreover, the proposed front-end electronic circuit allows a drastic simplification of the cabling and connectors since all units are connected to only one wire (the theoretical minimum) for potential reference and current return. Preferably, this wire does not even require an electrical isolation and can be easily embedded in the textile of a shirt, in a garment, mesh, belt, etc.