Non-contact ECG Sensor with Active Gain Correction
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Solution Overview
Problem
Traditional adhesive ECG electrodes are unsuitable for long-term use due to discomfort and motion-related artifacts, while non-contact biosensors face challenges with AC power interference, static charge, source impedance changes, and electronic noise, which obscure ECG signals.
Innovation Solution
A monolithic, non-contact ECG sensor system with charge amplifier and secondary sensing circuit to continuously monitor the subject-to-electrode gap, correcting gain and removing interference, allowing for accurate ECG signal recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If non-contact biosensors are used for long-term monitoring, then comfort and suitability for long-term use are improved, but motion-related artifacts and common mode interference increase
Solution Approach 1:
The patent employs feedback mechanisms through driven right leg (DRL) connections that actively counteract common mode interference by feeding back an inverted version of the interference signal to cancel it out. Active shielding and guarding of cables also use feedback principles to maintain signal integrity despite motion artifacts.
Solution Approach 2:
The patent introduces intermediary elements such as driven right leg connections that act as mediators between the interference source and the measurement system. These intermediaries transform the harmful common mode interference into manageable signals that can be processed and cancelled.
2Measurement precision
If driven right leg connection and active shielding are employed to reduce interference, then common mode rejection ratio is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple functions into integrated circuits and combined sensor assemblies. The DRL connection, active shielding, and ECG sensing are combined into a unified system architecture, reducing the number of separate components and simplifying the overall device while maintaining high CMRR.
3Measurement precision
If charge amplifier design is used to achieve gain independence from input capacitance, then noise performance is improved, but gain dependence on source capacitance increases
Solution Approach 1:
The patent uses feedback mechanisms to monitor and compensate for source capacitance variations. By continuously measuring the actual capacitance and adjusting the gain accordingly through feedback control, the system maintains stable gain despite changes in source capacitance caused by relative motion between electrodes and subject.
4Measurement precision
If accelerometers are used for ECG data correction, then motion artifact correction is improved, but positioning precision and correlation effectiveness decrease
Solution Approach 1:
The patent segments the motion sensing function into multiple distributed accelerometers positioned at specific locations around the ECG electrodes. This segmentation allows each accelerometer to capture local motion characteristics, and through coordinated processing, reconstructs the overall motion artifacts affecting the ECG signal with higher precision.
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 provides a robust and convenient heart rate monitor by correcting gain dependence on source capacitance and removing additive interference, enabling accurate ECG signal measurement through clothing without the need for invasive attachments.
Implementation Method 1
non-contacting electrodes that may work through a subject's clothing
Implementation Method 2
charge amplifier based ECG sensor system
Implementation Method 3
the subject to electrode gap is continuously monitored by a secondary sensing circuit
Implementation Method 4
interference from AC power mains may corrupt electrocardiograph signals due to low common mode rejection ratio (CMRR) of the sensor system
Implementation Method 5
by employing a notch filter at the output
Implementation Method 6
triboelectrically generated static charge caused by rubbing between the electrodes and the subject's clothing
Implementation Method 7
providing a static charge discharge path at the electrode subject interface
Data Source
AI summary
A non-contact electrocardiogram (ECG) sensor having an ECG electrode and guard electrode coupled to an electronic circuit that actively gain-corrects the electrocardiogram signal based on fringe capacitance signal and filters the gain-corrected signal based on a static charge reference signal. The compensation system first makes a gain correction for the preamplifier to address ECG electrode-to-subject motion and then removes any additive static common mode interference from motion-induced static charge generation.