Simultaneous Impedance and Biopotential Signal Measurement
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Solution Overview
Problem
Existing methods for continuously measuring impedance and biopotential signals face challenges in power efficiency and motion artifact reduction, particularly due to high power consumption and interference from electrode and skin-related motion artifacts.
Innovation Solution
A method and device that simultaneously measure impedance and biopotential signals using a predetermined alternating current with a chosen frequency, allowing for the separation of signals through chopper modulation and demodulation, reducing the need for active bandpass filters and enabling low-power processing, and using low-pass filters to extract both signals as baseband signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sinusoidal current sources and analog multipliers are used to continuously monitor electrode impedance, then impedance measurement accuracy is improved, but power consumption increases
Solution Approach 1:
The patent changes the frequency parameter of the excitation current to be significantly higher than the biopotential signal frequencies. This parameter change enables frequency-based signal separation, allowing impedance measurement without requiring complex analog multiplication circuits, thereby reducing power consumption while maintaining measurement accuracy
Solution Approach 2:
The patent replaces the mechanical/analog multiplication operation with a frequency-based separation approach. By using high-frequency excitation current and subsequent filtering, the system eliminates the need for power-consuming analog multipliers while achieving the same impedance measurement function
2Measurement precision
If high sampling rate is used in ADC for impedance measurement, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent changes the frequency parameter of the excitation current to be significantly higher than the biopotential signal frequencies. This parameter change enables frequency-based signal separation, allowing impedance measurement without requiring complex analog multiplication circuits, thereby reducing power consumption while maintaining measurement accuracy
Solution Approach 2:
The patent uses periodic high-frequency excitation current to modulate the impedance measurement signal. This periodic action at a known frequency allows for efficient signal extraction through synchronous detection or filtering, enabling accurate impedance measurement at lower ADC sampling rates and thus reducing ADC power consumption
3Measurement precision
If motion artifacts are reduced through design, then signal quality is improved, but device complexity increases
Solution Approach 1:
The patent extracts motion artifact information through separate impedance measurement channels. By measuring electrode-tissue impedance independently from the biopotential signal, the system can identify and compensate for motion artifacts without adding complex filtering or processing to the main signal path
Solution Approach 2:
The patent introduces impedance measurement as an intermediary mechanism to detect motion artifacts. The impedance signal serves as a mediator that correlates with motion artifacts, allowing the system to compensate for these artifacts in the biopotential signal without directly processing the complex artifact patterns
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 reduces power consumption and effectively differentiates between biopotential and impedance signals, allowing for accurate measurement and compensation of motion artifacts, enhancing the robustness of signal acquisition while minimizing the impact on biopotential signal quality.
Implementation Method 1
applying a predetermined alternating current having a first frequency to the output electrodes for creating an alternating voltage signal over the input electrodes
Implementation Method 2
a first amplifier connected to the input terminals for amplifying the input signal
Implementation Method 3
The alternating voltage signal is extracted by amplifying and demodulating the input signal using a control signal having a frequency equal to the first frequency of the applied alternating current
Data Source
Figure 1~2
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AI summary
A method and device for continuously and simultaneously measuring an impedance signal and a biopotential signal on a biological subject's skin. The method comprises the steps of: attaching input and output electrodes to the biological subject's skin; applying a predetermined alternating current having a first frequency to the output electrodes for creating an alternating voltage signal over the input electrodes, the first frequency being above a predetermined minimum frequency; measuring an input signal from the input electrodes, the input signal comprising a biopotential signal and the alternating voltage signal; extracting from said input signal the biopotential signal; extracting from said input signal the alternating voltage signal and determining the impedance signal from the alternating voltage signal. The alternating voltage signal is extracted by amplifying and demodulating the input signal using a control signal having a frequency equal to the first frequency of the applied alternating current.