PPG Sensor Offset Calibration for Heart Rate Accuracy
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Solution Overview
Problem
Conventional photoplethysmography (PPG) sensing schemes are adversely affected by motion artifacts, optical sensing system imperfections, and external noises, leading to erroneous heart rate detection due to signal offsets.
Innovation Solution
An electronic apparatus and method that employs multiple light wavelengths, an image sensing circuit, and a processing circuit to emit light rays, sense physiological characteristics, perform offset calibration, and calculate calibrated signals to reduce direct-current offsets and improve heart rate detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional PPG sensing scheme employs multiple light wavelengths to detect heart rate, then the capability to detect physiological characteristics is improved, but the susceptibility to motion artifacts and external noises worsens
Solution Approach 1:
The patent applies preliminary action by performing offset calibration before heart rate detection. The processing circuit first calibrates the PPG signals to remove motion artifacts and external noise offsets, then proceeds with accurate heart rate measurement. This preliminary calibration step ensures that subsequent measurements are not affected by harmful factors.
Solution Approach 2:
The patent converts the harmful effect of motion artifacts and external noises into a beneficial calibration process. By intentionally introducing known offset conditions and measuring them, the system characterizes the harmful factors and then subtracts them from the actual measurements, turning the previously harmful offsets into useful calibration data.
2Reliability
If conventional scheme directly adopts PPG signals of two different light wavelengths to calculate ratio, then partial alleviation of impacts is achieved, but the insurmountable problems of motion artifacts and external noises remain
Solution Approach 1:
The patent performs preliminary offset calibration for each light wavelength separately before calculating the ratio. This ensures that the PPG signals from both wavelengths are free from motion artifact offsets and external noise contamination before the ratio calculation, fundamentally solving the reliability problem rather than partially alleviating it.
Solution Approach 2:
The patent segments the signal processing into distinct steps: first calibrate offset for first wavelength, then calibrate offset for second wavelength, and finally calculate the ratio. This segmentation ensures that each wavelength's signal is independently purified from harmful factors before combination, preventing the propagation of offset errors through the calculation.
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
The solution effectively mitigates the impact of motion artifacts and external noises, enhancing the accuracy of heart rate detection by calibrating PPG signals and reducing direct-current offsets, thereby improving the overall performance of PPG sensors.
Implementation Method 1
conventional photoplethysmography (PPG) sensing scheme may employ multiple light wavelengths to detect a user's heart rate
Data Source
AI summary
A method for measuring physiologically characteristics of user includes: using at least one light emitting unit to emit light ray including first light component corresponding to first wavelength and second light component corresponding to second wavelength different from the first wavelength; using an image sensing circuit to sense and generate at least one physiologically characteristics measurement signal in response to the light ray; performing an offset calibration operation upon the physiologically characteristics measurement signal to generate at least one calibrated measurement signal; and, calculating the calibrated measurement signal to estimate a physiologically characteristics result.