Direct-Sampling ETI Circuit for Compact ECG Impedance Sensing
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Solution Overview
Problem
Conventional dry electrodes for portable medical devices suffer from poor electrode impedance, leading to detection errors in electrocardiography (ECG) signals, exacerbated by changes in electrode-tissue impedance due to contact factors or motion artifacts, and existing ETI receivers consume high power and occupy large chip areas with poor mixer harmonics.
Innovation Solution
A direct sampling ETI system utilizing a single analog front-end circuit to simultaneously sense ECG and ETI signals, employing digital mixing and filtering to reduce chip area and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If smaller dry electrodes are used in portable medical devices, then the device portability and wearability are improved, but the electrode impedance increases leading to worse signal detection quality
Solution Approach 1:
The patent replaces the conventional analog ETI receiver circuit with a digital signal processing system. A test signal is injected through the electrode, and the response is captured by the same analog front-end and processed digitally to calculate ETI. This substitution of analog measurement circuitry with digital processing resolves the contradiction by enabling accurate impedance measurement without requiring additional analog components, thereby maintaining signal detection quality while supporting smaller electrode designs.
2Measurement precision
If a conventional analog ETI receiver is used to measure electrode-tissue impedance, then the ETI measurement function is achieved, but the chip area increases and power consumption rises
Solution Approach 1:
The patent merges the ECG signal acquisition path and the ETI measurement path into a single shared analog front-end circuit. The same amplifier and ADC are used for both purposes by sequentially injecting a test signal for ETI measurement and then acquiring ECG signals. This merging eliminates the need for a separate analog ETI receiver circuit, significantly reducing chip area and power consumption while maintaining accurate ETI measurement capability.
Solution Approach 2:
The analog front-end circuit is designed to serve multiple functions: it acts as both the ECG signal amplifier and the ETI measurement interface. By making the analog front-end universal and capable of handling both biomedical signal amplification and impedance measurement tasks, the patent eliminates redundant circuitry and achieves both measurement precision with minimized hardware resources.
3Measurement precision
If a conventional analog ETI receiver with mixer is used, then the ETI signal processing is achieved, but the mixer harmonics performance deteriorates and power consumption increases
Solution Approach 1:
The patent substitutes the analog mixer with a digital mixing operation performed after ADC conversion. The test signal response is digitally mixed with the reference test signal to extract the ETI magnitude and phase information. This replacement of the analog mixer with digital signal processing eliminates the harmonic distortion issues inherent in analog mixers and reduces power consumption, as digital processing can be more efficiently implemented in modern CMOS technology.
4Measurement precision
If separate analog circuits are used for ECG and ETI measurement, then both measurement functions are achieved independently, but the device complexity and chip area increase
Solution Approach 1:
The patent combines the ECG and ETI measurement functions into a single integrated system sharing the analog front-end, amplifier, and ADC. The system alternates between ECG acquisition mode and ETI measurement mode, using the same hardware resources for both purposes. This merging approach maintains independent measurement capability for both functions while significantly reducing device complexity and chip area compared to using separate dedicated circuits for each measurement type.
Data Source
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AI summary
The present invention provides a circuitry of a biopotential acquisition system comprising an input node, an ETI transmitter and an ADC. The input node is coupled to an electrode of the biopotential acquisition system, and the electrode is used to be in contact with a human body. The ETI transmitter is configured to generate a transmitter signal to the input node. The ADC is coupled to the input node, and is configured to process an input signal from the input node to generate a digital signal, wherein each of the input signal and the digital signal comprises components of an ECG signal and an ETI signal.