Biopotential Acquisition System Using Capacitive ETI Coupling
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Solution Overview
Problem
Conventional portable medical devices using smaller dry electrodes face detection errors in ECG signals due to high electrode impedance and motion artifacts, which are exacerbated by current injection methods that introduce noise and narrow the input range of ECG signals.
Innovation Solution
A biopotential acquisition system with a circuitry comprising an input node, an ETI transmitter, and capacitors coupled between the input node and the ETI transmitter, which generates a transmitter signal to measure electrode-tissue impedance (ETI) without inducing noise, using a digital-to-analog converter (DAC) to produce a filtered signal that is processed by a low-noise amplifier and analog-to-digital converter to maintain accurate ECG signal measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current injection method is used to measure ETI, then ETI can be detected to reduce motion artifact, but additional noise is induced to electrodes causing detection error of ECG signals
Solution Approach 1:
A capacitor is introduced as an intermediary component between the ETI transmitter and the electrode. The capacitor blocks the direct path for noise-induced current while allowing the ETI measurement signal to pass through, thereby separating the ETI measurement function from the ECG signal path and preventing noise contamination of the ECG measurement.
Solution Approach 2:
The measurement circuit is segmented into separate functional paths: one for ETI measurement and another for ECG signal acquisition. By using the capacitor to couple these paths, the system allows independent optimization of each measurement function while preventing interference between them, thus eliminating the trade-off between ETI measurement capability and ECG signal quality.
2Adaptability or versatility
If current generator with lower impedance is connected to electrodes, then ETI measurement is enabled, but strength of ECG signals is influenced and input range becomes narrow
Solution Approach 1:
The capacitor serves as a frequency-dependent intermediary that presents different impedance characteristics at different frequencies. At the frequency of the ETI measurement signal, it allows efficient signal transmission, while at the frequency of ECG signals, it maintains the high input impedance necessary for accurate ECG measurement, thus preserving both measurement capabilities without compromising ECG input range.
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
The system accurately measures ECG signals and ETI simultaneously, reducing detection errors and maintaining a wide input range for ECG signals by minimizing noise interference and maintaining high input impedance, thus improving the reliability of physiological signal acquisition.
Implementation Method 1
A capacitor is coupled between the ETI transmitter and the input node
Data Source
AI summary
The present invention provides a circuitry of a biopotential acquisition system, where the circuitry includes an input node, an ETI transmitter, a capacitor and an ETI receiver. The input node is configured to receive an input signal from an electrode of the biopotential acquisition system. The ETI transmitter is configured to generate a transmitter signal. A first node of the capacitor is coupled to the ETI transmitter, and a second node of the capacitor is coupled to the input node. The ETI receiver is coupled to the input node, and is configured to receive the transmitter signal via the capacitor to generate an ETI.