Biosignal Acquisition Circuit for HF Interference Isolation
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Solution Overview
Problem
Existing systems for monitoring electro-physiological signals, such as EEG, in harsh electrical environments like surgical settings are prone to high-frequency interference, leading to signal corruption and unreliable data, as they either fail to completely filter out or measure residual interferences, which is critical for real-time patient monitoring.
Innovation Solution
A biopotential data acquisition system using a combination of active filters, isolation barriers, and cross-barrier voltage measurement circuitry to reduce and measure high-frequency interference, allowing for accurate and reliable signal acquisition by isolating patient-side electronics from earth ground and using a front-end active filter to buffer instrumentation amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If passive and active input filters are used to block HF interference, then interference reduction is improved, but residual interference measurement capability deteriorates
Solution Approach 1:
The system divides the measurement function into two separate pathways: one pathway (through the active filter and instrumentation amplifier) processes the biosignal for clinical monitoring, while another pathway (through the measurement circuitry connected to the isolation barrier) specifically measures the cross-barrier voltage representing residual interference. This segmentation allows both interference reduction and interference measurement to occur simultaneously without mutual interference.
Solution Approach 2:
The isolation barrier serves as an intermediary element that enables the measurement of residual HF interference by creating a measurable voltage difference (cross-barrier voltage) between the patient side and earth ground side. This intermediary measurement mechanism allows the system to quantify residual interference without affecting the primary signal processing pathway.
2Reliability
If isolation barrier is used to isolate patient from earth ground, then patient safety is improved, but interference measurement capability deteriorates
Solution Approach 1:
The isolation barrier acts as an intermediary that both protects the patient and enables measurement. By measuring the voltage difference across this barrier (cross-barrier voltage), the system can quantify the level of HF interference present without compromising the isolation's safety function. The measurement circuitry taps into the barrier's electrical characteristics to derive interference information.
Solution Approach 2:
The isolation barrier performs multiple functions simultaneously: it provides galvanic isolation for patient safety, blocks HF interference pathways, and serves as a reference for measuring residual interference levels. This multi-functionality resolves the contradiction by making the barrier both a protective element and a measurement enabler.
3Reliability
If front-end active filter and isolation barrier are used, then signal acquisition reliability is improved, but system complexity deteriorates
Solution Approach 1:
The system architecture is segmented into functionally distinct modules: the active filter stage for interference attenuation, the isolation barrier for safety and reference, and the measurement circuitry for monitoring. This modular segmentation organizes the complexity into manageable, independent blocks that can be designed and tested separately, making the overall complex system more maintainable and understandable.
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 effectively filters out and measures high-frequency interference, enabling accurate real-time monitoring of patient states even in harsh environments, ensuring reliable data for anesthesia management during surgeries.
Implementation Method 1
a front-end active filter, used to block the transmission of HF interferences to the instrumentation amplifiers
Implementation Method 2
an isolation barrier interface which isolates the patient from earth ground
Implementation Method 3
This circuitry is used to measure the difference in potential between the two isolated sides of the isolation barrier. This so-called 'cross-barrier' voltage is directly representative of the interference level
Data Source
AI summary
The present invention, herein is a method and apparatus that significantly limits the effect of high frequency (“HF”) interferences on acquired electro-physiological signals, such as the EEG and EMG. Preferably, this method comprises of two separate electronic circuitries and steps or electronics for processing the signals. One circuit is used to block the transmission of HF interferences to the instrumentation amplifiers. It is comprised of a front-end active filter, a low frequency electromagnetic interference (“EMI”) shield, and an isolation barrier interface which isolates the patient from earth ground. The second circuit is used to measure the difference in potential between the two isolated sides of the isolation barrier. This so-called “cross-barrier” voltage is directly representative of the interference level that the instrumentation amplifier is subjected to. This circuit is used to confirm that the acquired signals are not corrupted by the interference.