Compressive Sampling PPG Circuit for Motion Artifact Reduction
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Solution Overview
Problem
Current biosignal acquisition systems, particularly those using photoplethysmogram (PPG) sensors for heart rate detection, face significant challenges in motion artifact reduction, especially in continuous or ambulatory modes, which affect measurement accuracy due to body movement.
Innovation Solution
A low-power, robust random subsampling PPG readout circuit employing compressive sampling (CS) and digital motion artifact reduction techniques, including a Lomb-Scargle periodogram for direct feature extraction, reduces LED driver power consumption and enhances measurement robustness by normalizing and subtracting motion signal power spectral density from PPG signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If compressive sampling is used to reduce LED driver power consumption, then energy efficiency is improved, but measurement precision deteriorates due to reduced sampling rate
Solution Approach 1:
The patent changes the sampling parameter from uniform high-rate sampling to non-uniform compressive sampling below the Nyquist rate. This parameter change reduces the LED driver power consumption while the Lomb-Scargle periodogram algorithm compensates for the reduced sampling rate by providing accurate frequency estimation from irregularly spaced samples, thus maintaining measurement precision.
Solution Approach 2:
The patent replaces the traditional mechanical sampling approach (uniform high-rate sampling) with a computational approach (compressive sampling combined with Lomb-Scargle periodogram analysis). This substitution allows for lower power consumption during the sampling phase while achieving equivalent or superior measurement precision through advanced signal processing.
2Reliability
If motion artifact reduction techniques are applied to improve measurement robustness, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent extracts and removes the motion artifact component from the PPG signal by calculating the power spectral density of the motion signal and subtracting it from the PPG signal's power spectral density. This extraction approach improves measurement robustness by eliminating motion-related interference while maintaining relatively simple processing through spectral analysis.
Solution Approach 2:
The patent introduces the power spectral density calculation as an intermediary step between the raw PPG signal and the final heart rate measurement. This intermediary transformation to the frequency domain facilitates motion artifact reduction by enabling the subtraction of motion signal components, improving reliability without requiring complex time-domain filtering.
3Productivity
If Lomb-Scargle periodogram is used for direct feature extraction from compressed samples, then processing speed is improved, but measurement precision may deteriorate
Solution Approach 1:
The patent performs preliminary transformation of the compressively sampled PPG signal into the frequency domain using the Lomb-Scargle periodogram before heart rate detection. This preliminary action enables direct frequency estimation from the compressed samples without requiring full signal reconstruction, thus improving processing speed while maintaining measurement precision through the robustness of the Lomb-Scargle method for irregularly spaced data.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate and efficient heart rate detection with reduced power consumption, improved robustness against motion artifacts, and increased patient comfort through non-contact, single-point biosignal measurement, making it suitable for wearable medical devices.
Implementation Method 1
a light emitting diode (LED) and a photodiode (PD)
Data Source
AI summary
Example embodiments relate to systems and methods for heart rate detection with motion artifact reduction. One embodiment includes an electronic system for heart rate detection. The electronic system includes a random sampling sensor module. The random sampling sensor module includes a first sensor circuit configured to provide nonuniform random samples below a Nyquist rate of a photoplethysmographic signal. The random sample sensor module also includes a second sensor circuit configured to provided nonuniform random samples below a Nyquist rate of a motion signal. The motion signal and the photoplethysmographic signals are sampled with an equivalent pattern. The electronic system also includes a heart rate detection module. The heart rate detection module is configured to calculate a heart rave value based on frequencies corresponding to peak powers of calculated power spectral density value sets corresponding to the photoplethysmographic signals in a frequency range of interest.