Variable-Coefficient FIR Filtering for QRS-Preserving Noise Removal
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Solution Overview
Problem
Existing technologies face challenges in effectively removing environmental noise, such as air-conditioning noise, from magnetocardiographic measurement results without attenuating the QRS-wave, due to overlapping frequency bands.
Innovation Solution
A filtering apparatus utilizing an FIR filter with variable tap coefficients that switch from a first tap coefficient to a second tap coefficient sequentially for input digital data, allowing the FIR filter to smoothly switch its cut-off frequency between 20 Hz and 50 Hz to effectively remove noise while preserving the QRS-wave.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a low-pass filter with cut-off frequency set at 20 Hz is used to remove environmental noise, then environmental noise removal is improved, but QRS-wave attenuation increases
Solution Approach 1:
The patent applies dynamics by making the filter characteristics changeable over time. The tap coefficients are dynamically adjusted based on the detected cardiac cycle phase, switching between first tap coefficients (for P-wave and T-wave filtering with 20 Hz cut-off) and second tap coefficients (for QRS-wave preservation with 50 Hz cut-off). This dynamic adaptation allows the filter to optimize noise removal while preserving signal integrity at different time points.
Solution Approach 2:
The patent changes the parameter of tap coefficients to resolve the contradiction. By detecting the input signal waveform to identify P-wave, QRS-wave, and T-wave regions, the system selectively applies different tap coefficient sets: first tap coefficients during P-wave and T-wave periods for aggressive noise filtering, and second tap coefficients during QRS-wave periods for gentle filtering that preserves the cardiac signal.
2Reliability
If the cut-off frequency is switched between 20 Hz and 50 Hz to preserve QRS-wave, then QRS-wave preservation is improved, but filter characteristic switching complexity increases
Solution Approach 1:
The patent implements self-service by enabling the filter to automatically detect its own operating conditions and adjust its parameters accordingly. The waveform detection unit continuously monitors the input signal to identify the current cardiac cycle phase (P-wave, QRS-wave, or T-wave region), and the control unit automatically selects the appropriate tap coefficients based on this detection, eliminating the need for external manual control or complex switching mechanisms.
Solution Approach 2:
The system employs feedback through continuous waveform detection and analysis. The detected input signal is fed back to the control unit, which uses this information to determine the current cardiac phase and accordingly select the appropriate tap coefficients. This closed-loop feedback mechanism ensures that the filter characteristics are always optimized for the current signal condition without requiring complex external control systems.
Data Source
AI summary
According to the present invention, a filtering apparatus includes an FIR filter that has multipliers arranged to multiply input digital data having their respective different input time points by respective variable tap coefficients. The variable tap coefficients are each switched from a first tap coefficient to a second tap coefficient sequentially for the input digital data from later to earlier input time points. The first tap coefficient is arranged to cause the FIR filter to serve as a low-pass filter with the cut-off frequency set at a first frequency. The second tap coefficient is arranged to cause the FIR filter to serve as a low-pass filter with the cut-off frequency set at a second frequency different from the first frequency.