Adaptive Digital Filter for ECG Power Line Interference
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Solution Overview
Problem
Existing noise reduction techniques for ECG signals, such as line frequency filters and notch filters, are ineffective in addressing power line interference variations, leading to loss of clinically relevant information and potential misinterpretation of ECG waveforms due to ringing effects.
Innovation Solution
A dynamically configurable adaptive digital filter that identifies the current power line frequency using a lookup table and adjusts its coefficients in real-time to effectively filter out power line interference from ECG signals without removing the 50/60 Hz component, ensuring accurate signal interpretation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a line frequency filter is used to eliminate power line interference, then the power line noise is removed effectively, but the filter becomes ineffective when the power line frequency varies by more than ±0.5 Hz
Solution Approach 1:
The patent implements a dynamic filter frequency adjustment mechanism that continuously tracks the actual power line frequency and updates the filter parameters in real-time. This allows the filter to maintain effectiveness despite frequency variations, resolving the contradiction between reliable noise removal and adaptability to frequency changes.
Solution Approach 2:
The system employs feedback mechanisms to detect the actual power line frequency and use this information to adjust the filter characteristics. This closed-loop approach ensures the filter remains tuned to the correct frequency even when power line conditions change, maintaining both reliability and adaptability.
2Reliability
If a notch filter at 50 Hz/60 Hz is used to eliminate power line interference, then the power line noise is removed, but the 50 Hz/60 Hz component present in the ECG signal is also removed and ringing occurs
Solution Approach 1:
The patent applies localized filtering by targeting only the specific frequency components corresponding to the detected power line interference, rather than applying a broad notch filter. This selective approach removes the interference while preserving adjacent ECG signal components, reducing information loss and avoiding ringing effects.
Solution Approach 2:
The system dynamically adjusts filter parameters such as center frequency and bandwidth based on the detected power line frequency and characteristics. By adapting these parameters in real-time, the filter effectively removes interference while minimizing impact on the ECG signal, preventing both information loss and ringing artifacts.
3Reliability
If band limiting the signal to below the powerline frequency using low pass filters is used, then power line interference is eliminated, but all frequencies above 50/60 Hz are attenuated resulting in loss of information
Solution Approach 1:
The patent replaces the fixed cutoff frequency approach of low-pass filters with a dynamic parameter adjustment mechanism. The filter characteristics are adapted in real-time based on the detected power line frequency, allowing the system to remove interference while preserving high-frequency ECG components that would otherwise be attenuated.
Data Source
AI summary
A method and system for correcting power line interferences in an ElectroCardioGram (ECG) signal is disclosed. The method comprises: providing an input signal having ECG signal along with interference signals to a digital filter capable of filtering at a preset frequency and identifying current power line frequency, if any, from the filtered input signal. The method further includes providing a look up table with index number for a set of frequency levels and corresponding filter coefficients, the set of frequency includes incremental steps in the range of possible variations on the power line frequency. The filter coefficient corresponding to current power line frequency is identified from the look up table. The digital filter is configured using the identified filter coefficient and the input signal is filtered using the re-configured digital filter.