FIR Filter for Line-Frequency Noise in Biometric Signals
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Solution Overview
Problem
Biometric devices, particularly those measuring small electrical signals, face interference from line frequency noise, which distorts measurements and is difficult to filter effectively using existing notch filters or digital filters due to size, cost, or high power consumption.
Innovation Solution
Implementing a finite impulse response (FIR) filter with specific coefficients to attenuate line frequency interference by intentional aliasing and Nyquist factor, reducing noise while preserving battery power in low-power devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If analog notch filters are used to filter out electromagnetic interference at line frequency, then interference attenuation is improved, but device size and cost increase
Solution Approach 1:
The patent replaces the traditional analog notch filter (electromechanical system) with a digital FIR filter implemented through software algorithms on a processor. This substitution eliminates the need for large, expensive analog filter components while achieving equivalent or superior interference attenuation through digital signal processing.
Solution Approach 2:
The patent creates a digital copy of the filtering function through software implementation rather than using physical analog filter components. The FIR filter algorithm replicates the noise rejection functionality of analog filters but in a compact digital form that can be implemented with minimal hardware resources.
2Object-affected harmful factors
If digital low-pass filters are used to filter out interference, then interference attenuation is improved, but power consumption increases due to higher sampling rates
Solution Approach 1:
The patent optimizes the sampling rate parameter to the minimum necessary value (just above twice the highest signal frequency of interest) rather than using higher sampling rates. This parameter optimization reduces the computational load on the processor, thereby lowering power consumption while still enabling effective interference attenuation through the FIR filter.
Solution Approach 2:
The patent applies a partial sampling approach where only the minimum necessary sampling rate is used to capture the biometric signal, rather than oversampling. This partial action reduces the amount of data that needs to be processed by the FIR filter, consequently reducing power consumption while maintaining adequate signal fidelity and interference rejection.
3Measurement precision
If higher sampling rates are used to accurately represent the signal, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent sets the sampling rate parameter to the minimum value required by the Nyquist-Shannon theorem (twice the highest signal frequency) rather than using higher rates. This parameter change achieves adequate signal representation accuracy while minimizing the computational resources needed for processing, thereby reducing power consumption.
Solution Approach 2:
The patent uses a computationally efficient FIR filter algorithm that can be implemented with simple arithmetic operations rather than requiring complex processing. This approach treats the filtering function as a lightweight computational task that can be performed efficiently with minimal processor power, reducing overall energy consumption while maintaining measurement precision.
Data Source
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AI summary
Aspects of the present disclosure include a biometric device configured to receive biometric signals from sensors placed on a subject, and attenuate at frequencies causing noise in the biometric signals. Aspects are directed to a finite impulse response (FIR) filter configured to attenuate noise frequencies caused by line frequencies and/or flicker frequencies. Aspects of the FIR filter may be configured based on an analog-to-digital (ADC) sampling rate.