Variable Loop Filter PLL for Artifact-Resistant Biometric Sensing
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Solution Overview
Problem
Biological information measurement apparatuses with phase synchronization circuits face challenges in distinguishing fluctuations in base frequency from those caused by artifacts, leading to increased lock-up time and susceptibility to noise, especially in applications like electrocardiographs and photoplethysmographs where frequency variations are significant and artifacts are common.
Innovation Solution
A biological information measurement apparatus that includes a phase/frequency comparator, a variable loop filter unit with adjustable cutoff frequency and phase margin, a voltage-controlled oscillator, and a biological signal analyzing unit that analyzes phase, frequency, and signal-to-noise ratio (SNR) to synchronize the PLL with the biological signal, reducing the influence of artifacts and minimizing lock-up time by dynamically adjusting the loop filter constants based on analysis results.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the cutoff frequency of the loop filter is lowered to suppress artifacts, then noise resistance is improved, but lock-up time increases
Solution Approach 1:
The patent implements dynamic adjustment of the loop filter's cutoff frequency based on the detected signal state. When artifacts are detected in the biological signal, the cutoff frequency is automatically lowered to suppress noise; when the signal is clean, the cutoff frequency is raised to reduce lock-up time. This dynamic adaptation resolves the contradiction by making the filter characteristics variable rather than fixed.
Solution Approach 2:
The invention changes the parameter (cutoff frequency) of the loop filter based on the analyzed state of the biological signal. By monitoring signal characteristics and adjusting the cutoff frequency accordingly, the system optimizes both artifact suppression and lock-up time performance under different operating conditions.
2Speed
If the cutoff frequency of the loop filter is raised to reduce lock-up time, then response speed is improved, but susceptibility to artifacts increases
Solution Approach 1:
The system dynamically adjusts the cutoff frequency based on real-time signal analysis. When the biological signal is clean and stable, the cutoff frequency is raised to minimize lock-up time and improve response speed. When artifacts are present, the cutoff frequency is lowered to filter out noise, thus resolving the contradiction between speed and noise susceptibility.
Solution Approach 2:
The patent employs a feedback mechanism where the output of the phase comparator is analyzed to detect artifacts, and this analysis feeds back to control the cutoff frequency of the loop filter. This closed-loop control ensures that the filter parameters are continuously optimized based on the actual signal quality, balancing lock-up time and artifact rejection.
3Device complexity
If a fixed loop filter is used to simplify the circuit, then device complexity is reduced, but performance adaptability deteriorates
Solution Approach 1:
The patent introduces dynamic adaptability to the loop filter by making the cutoff frequency variable rather than fixed. This is achieved through automatic control based on signal analysis, allowing the filter to adapt to different signal conditions without requiring multiple fixed filters or complex manual configuration, thus balancing complexity and adaptability.
Solution Approach 2:
The system performs self-adjustment of the loop filter parameters through automatic analysis of the biological signal. The circuit monitors its own input signal characteristics and autonomously adjusts the cutoff frequency to optimize performance, eliminating the need for external intervention or complex manual tuning while maintaining high adaptability.
Data Source
AI summary
A biological information measurement apparatus includes a phase/frequency comparison unit that outputs a deviation signal based on a phase difference between a biological signal and an oscillation signal; a variable loop filter that varies a cutoff frequency and a phase margin and that selectively blocks a signal of a predetermined frequency band contained in the deviation signal; and a voltage controlled oscillation unit that generates the oscillation signal in accordance with the deviation signal that has passed through the variable loop filter. The apparatus further includes a CPU that estimates a SN ratio of the biological signal and analyzes a phase difference/frequency difference between the biological signal outputted from the comparison unit and the oscillation signal. The CPU further changes a constant of the variable loop filter based on the SN ratio and the phase difference/frequency difference.