Adaptive Notch Filter for Variable Power Line 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 like ECG machines that encounter unknown and varying power line frequencies, leading to incomplete noise removal and potential distortion of clinical signals.
Innovation Solution
A frequency-adaptive notch filter with a state observer unit and parameter adaptation unit that automatically identifies and adapts to 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
Solution Approach 1:
The patent implements an adaptive notch filter where the notch frequency is dynamically adjustable rather than fixed. The system continuously estimates the noise frequency from the input signal and adapts the filter's notch frequency to track the noise, allowing the filter to remove noise at varying frequencies while preserving signal components at other frequencies.
Solution Approach 2:
The patent changes the parameter of the notch filter (notch frequency) based on the estimated noise frequency. By continuously updating the notch frequency parameter to match the detected noise frequency, the system effectively removes noise while minimizing loss of desired signal components that are not at the noise frequency.
2Object-affected harmful factors
If a serial notch filter is used in ECG applications, then noise at the notch frequency is removed, but ringing occurs in the ECG waveform causing incorrect interpretation
Solution Approach 1:
The adaptive notch filter dynamically adjusts its notch frequency to track power line interference frequencies (e.g., 50Hz or 60Hz variations). This dynamic adaptation allows effective power line noise removal while maintaining ECG waveform integrity by precisely targeting only the noise frequency components.
Solution Approach 2:
The patent replaces the traditional fixed mechanical notch filter with a digital adaptive filter that uses signal processing algorithms. This substitution allows for more precise and flexible noise removal without the rigid frequency constraints and waveform distortion issues of traditional analog notch filters.
3Device complexity
If the notch frequency is preset to a fixed value, then the filter structure is simple, but it cannot adapt to different power line frequencies in different regions
Solution Approach 1:
The adaptive notch filter is self-adjusting and automatically estimates the noise frequency from the input signal without requiring manual configuration or prior knowledge of the power line frequency. The system serves itself by continuously adapting to the actual noise conditions in different regions.
Solution Approach 2:
The patent creates a universal filter that can operate effectively across different regions with different power line frequencies (50Hz, 60Hz, or variations). The adaptive mechanism allows a single filter design to serve multiple frequency environments, eliminating the need for region-specific fixed frequency filters.
4Object-affected harmful factors
If adaptive noise cancellation with averaging is used, then noise is removed, but nonrepetitive signals bearing clinically relevant physiological dynamic information are distorted or removed
Solution Approach 1:
The adaptive notch filter provides dynamic noise removal that tracks the instantaneous noise frequency without requiring time-averaging of the signal. This dynamic approach preserves nonrepetitive physiological signals while removing noise, as it processes each signal component individually rather than averaging over time periods that may contain clinically relevant variations.
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.