Adaptive Notch Filter for Variable-Frequency ECG Noise Removal
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Solution Overview
Problem
Existing methods for removing sinusoidal noise, such as notch filters and adaptive noise cancellation, are inadequate for systems with unknown and varying noise frequencies, leading to incomplete noise removal and potential distortion of clinical signals in medical devices like ECG machines.
Innovation Solution
A frequency-adaptive notch filter system that includes a state observer unit and parameter adaptation unit, capable of identifying and adapting to unknown and time-varying noise frequencies, allowing for effective subtraction of sinusoidal noise from electrical signals without prior knowledge of the noise frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a serial notch filter is used to eliminate noise at a specific frequency, then noise removal is improved, but the frequency component of the desired signal at the notch frequency is eliminated as well, causing loss of information
Solution Approach 1:
The patent uses parameter adaptation to dynamically adjust the notch filter frequency based on the detected noise frequency. Instead of using a fixed notch frequency, the system continuously estimates the noise frequency from the input signal and adapts the filter parameters accordingly. This allows the filter to target only the noise component while preserving the desired signal at other frequencies.
Solution Approach 2:
The patent implements a feedback mechanism where the output of the notch filter is fed back through an adaptive filter that estimates the noise component. This estimated noise is then subtracted from the input signal. The system continuously monitors the error signal and adjusts its parameters to minimize the noise component while preserving the desired signal, thereby preventing information loss.
2Object-affected harmful factors
If a serial notch filter is used to remove sinusoidal noise, then noise elimination is improved, but ringing artifacts are introduced in the ECG waveform, causing incorrect interpretation
Solution Approach 1:
The patent introduces an intermediate adaptive filtering stage between the noise detection and signal subtraction processes. The adaptive filter acts as a mediator that estimates the noise component in a way that minimizes transient effects and ringing artifacts. By using the error signal from the notch filter to drive the adaptive estimation, the system smoothly adapts to noise frequency changes without introducing harmful artifacts.
3Object-affected harmful factors
If Adaptive Noise Cancelling with averaging is used to remove noise, then noise cancellation is improved, but signal characteristics may be distorted or nonrepetitive signals removed, losing clinically relevant information
Solution Approach 1:
The patent employs dynamic parameter adaptation instead of static averaging. The notch filter frequency and the adaptive filter parameters are continuously adjusted based on the instantaneous noise frequency estimation. This dynamic approach allows the system to track time-varying noise frequencies without requiring long averaging windows, thereby preserving transient and nonrepetitive signal characteristics while effectively canceling noise.
4Device complexity
If the noise frequency is preset in the Internal Mode approach, then the filter implementation is simplified, but the system cannot adapt to unknown or varying noise frequencies, reducing versatility
Solution Approach 1:
The patent implements a self-adjusting system where the filter automatically detects and adapts to the noise frequency without requiring manual configuration or prior knowledge. The frequency estimation algorithm continuously monitors the input signal and self-adjusts the notch filter parameters to match the current noise frequency. This self-service capability maintains relatively simple implementation while achieving high adaptability to unknown and varying noise frequencies.
Data Source
AI summary
One apparatus includes a notch filter that has a state observer unit and a parameter adaptation unit. The state observer unit is configured to receive a sampled noisy electrical signal and a sampled filtered electrical signal, the state observer unit having an estimated noise signal output, the estimated noise signal output carrying an estimated noise signal to be subtracted from the sampled noisy electrical signal, resulting in the filtered electrical signal. The parameter adaptation unit is configured to receive the estimated noise signal and an error signal from the state observer unit. The parameter adaptation unit is also configured to determine, based on the estimated noise signal and the error signal, an updated estimated noise frequency, thereby causing the state observer unit to generate an updated estimated noise signal to be provided on the estimated noise signal output.