Physiological Measurement Recording With Adaptive Common-Mode Filtering
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Solution Overview
Problem
Existing physiological measurement devices struggle with common-mode interference, which degrades the accuracy of electrophysiological recordings due to artifacts from both internal stimulation signals and external sources, particularly in devices with integrated stimulation and recording capabilities.
Innovation Solution
The device leverages the common-mode interference generated by the stimulation unit to update digital filter coefficients in real-time, using algorithms like least-mean-squares or recursive-least-squares, to improve common-mode rejection by enhancing the symmetry of input channels, thereby reducing artifacts in both internal and external interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If digital filters are used to reduce common mode interference, then measurement precision is improved, but device complexity increases due to the need for continuous filter coefficient adjustment during stimulation
Solution Approach 1:
The system uses the stimulation signal itself as the reference input to automatically adjust filter coefficients. The processing unit determines adjusted filter coefficients by comparing the stimulation signal with measurement signals during stimulation, allowing the system to self-calibrate without external intervention. This resolves the contradiction by making the complexity inherent to the solution rather than an added burden.
Solution Approach 2:
The system dynamically changes filter coefficients based on the stimulation signal characteristics. By continuously adjusting the filter parameters during stimulation using algorithms like least-mean-squares or recursive-least-squares, the system adapts to varying interference conditions, maintaining high measurement precision while managing complexity through parameter optimization.
2Object-affected harmful factors
If filter coefficients are adjusted during stimulation, then common mode interference is minimized, but processing time increases due to real-time coefficient determination
Solution Approach 1:
The filter coefficient adjustment occurs continuously during stimulation rather than in separate calibration phases. The processing unit determines adjusted coefficients in real-time using the ongoing stimulation signal, ensuring continuous interference minimization without interrupting the useful stimulation action. This resolves the time loss by making the calibration process concurrent with the primary function.
Solution Approach 2:
The system implements feedback by using the measurement signals acquired during stimulation to determine adjusted filter coefficients. The processing unit continuously compares the stimulation signal with the measured signals and adjusts coefficients accordingly, creating a closed-loop system that minimizes interference in real-time without significant processing delays.
3Reliability
If multiple input channels are used to calculate vector signals, then measurement reliability is improved, but susceptibility to common mode interference increases
Solution Approach 1:
The system applies channel-specific filter coefficients to each input channel individually before calculating vector signals. By tailoring the filter characteristics to each channel's specific interference characteristics while using the stimulation signal as reference, the system maintains reliability through multiple channels while minimizing common mode interference through localized filter adjustment.
Solution Approach 2:
The system introduces asymmetry in the filter coefficient adjustment process, where each channel's coefficients are independently determined based on its specific relationship with the stimulation signal. This asymmetric approach allows the system to exploit the known stimulation signal characteristics to cancel common mode interference while preserving the reliability benefits of multiple measurement channels.
Data Source
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AI summary
The present invention relates to a physiological measurement device, system and method. The device (11) comprises multiple input channels (15) configured to obtain multiple measurement signals (si) acquired from a subject; a recording unit (10) configured to filter the multiple measurement signals (si) by use of a digital filter and calculate multiple vector signals (yj) from the multiple filtered measurement signals; a stimulation unit (20) configured to generate one or more stimulation signals (wk) for electrically stimulating tissue of the subject; multiple output channels (22, 32) configured to output the multiple vector signals (yi) and the one or more stimulation signals (wk); and a processing unit (27) configured to determine adjusted filter coefficients of the digital filter during or after the generation and output of the one or more stimulation signals (wk) based on the current filter coefficients, the one or more stimulation signals (wk) and the multiple measurement signal (si) acquired while the one or more stimulation signals (wk) are outputted for stimulation.