Bio-Sensing Light Timing for Ambient Flicker Cancellation
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Solution Overview
Problem
Optical bio-sensing devices, such as wrist-worn heart rate monitors, face challenges in accurately measuring biophysical parameters like heart rate due to ambient light flicker, which can introduce noise and reduce signal-to-noise ratio when light source and ambient sense phases are not aligned with the periodicity of ambient light signals.
Innovation Solution
The device employs a controller to iteratively adjust the timing between ambient sense phases to determine the periodicity of ambient light, ensuring that the ambient sense phase is aligned with either the period or an integer multiple of the ambient light signal, allowing for effective subtraction of ambient light from light source measurements, thereby improving the accuracy of biophysical parameter computation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ambient sense phase is performed immediately after light source sense phase, then device bandwidth requirement is reduced, but ambient light cancellation accuracy deteriorates due to non-alignment with ambient light periodicity
Solution Approach 1:
The patent performs preliminary ambient light measurements at multiple time intervals before the actual measurement to determine the ambient light periodicity. This preliminary action allows the system to characterize the ambient light signal in advance, enabling accurate cancellation during the subsequent measurement phase without requiring high bandwidth.
Solution Approach 2:
The patent utilizes the periodic nature of ambient light flicker by measuring at intervals that are integer multiples of the ambient light period. By synchronizing the ambient sense phase with the ambient light periodicity, the system achieves consistent cancellation accuracy while maintaining efficient bandwidth usage.
2Measurement precision
If ambient sense phase is spaced further from light source sense phase, then ambient light periodicity can be determined more accurately, but signal bandwidth requirement increases leading to higher noise
Solution Approach 1:
The system performs preliminary ambient light characterization measurements at multiple time intervals before the actual biophysical parameter measurement. This preliminary action determines the ambient light periodicity without requiring the main measurement to be spaced far from the light source phase, thus avoiding increased noise bandwidth.
Solution Approach 2:
The measurement process is segmented into distinct phases: preliminary ambient light characterization phase and main biophysical parameter measurement phase. This segmentation allows the system to determine ambient periodicity separately, then apply that knowledge to optimize the main measurement timing without compromising signal quality.
3Ease of operation
If light source and ambient sense phases are not aligned with ambient light periodicity, then device operation is simpler, but measurement accuracy deteriorates due to ambient light flicker noise
Solution Approach 1:
The system automatically determines the ambient light periodicity through preliminary measurements and autonomously adjusts its sensing phases to align with this periodicity. This self-service approach eliminates the need for manual configuration or complex external synchronization, maintaining ease of operation while achieving high measurement accuracy.
Solution Approach 2:
The system dynamically changes the timing parameters of its sense phases based on the detected ambient light periodicity. By adjusting the phase timing to be integer multiples of the ambient period, the system optimizes measurement accuracy without requiring complex hardware modifications or manual intervention.
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 enhances the accuracy of biophysical parameter measurements by ensuring equal ambient light strength in both sense phases, reducing noise and improving the signal-to-noise ratio, leading to more reliable heart rate and other biometric calculations.
Implementation Method 1
a photo diode that generates light and a photo detector that senses the light reflected off a person's body
Data Source
AI summary
A bio-sensing device (and method) calibrates a time period used to make bio-physical measurements. The device initiates a light source sense phase followed by a first ambient sense phase and a second ambient sense phase. In the light source sense phase, the device is configured to receive a digital value indicative of current through a photodetector while the light source circuit is enabled and in each of the first and second ambient sense phases, the device is configured to receive digital values while the light source circuit is disabled. The device iteratively varies the time period between the phases until the digital value received during the first ambient sense phase is within a threshold of the digital value received during the second ambient sense phase. It then applies the same time separation between the light source sense phase and the ambient phase thereby equalizing the magnitude of the ambient light in the two phases.