Bio-Sensing Photodetector Timing for Ambient Light Cancellation
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Solution Overview
Problem
Bio-sensing devices face challenges in accurately measuring biophysical parameters like heart rate due to high noise bandwidth and low signal-to-noise ratio caused by closely spaced light source and ambient sense phases, which fail to adequately account for periodic ambient light.
Innovation Solution
The device iteratively varies the timing between ambient sense phases to align with the periodicity of ambient light, ensuring equal ambient light magnitude in both phases, thereby improving signal accuracy by subtracting ambient light from light source measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the light source sense phase and ambient sense phase are closely spaced, then the measurement speed is improved, but the signal-to-noise ratio deteriorates due to high noise bandwidth and inadequate ambient light cancellation
Solution Approach 1:
The patent applies periodic action by iteratively varying the time separation between ambient sense phases to match the periodicity of ambient light. The system performs multiple ambient sense phases at different time intervals, identifies the periodicity where ambient light magnitudes are equal, and uses this periodic timing to optimize the separation between light source sense phase and ambient sense phase. This periodic approach enables both fast measurement and effective ambient light cancellation.
2Measurement precision
If the time separation between light source sense phase and ambient sense phase is increased, then ambient light cancellation accuracy is improved, but the measurement time increases
Solution Approach 1:
The patent applies preliminary action by performing iterative calibration of the time separation between ambient sense phases before conducting the actual biophysical measurement. The system pre-determines the optimal time separation that matches ambient light periodicity through multiple calibration phases, stores this calibrated timing information, and then uses it for subsequent measurements. This preliminary calibration enables accurate ambient light cancellation without requiring excessive time separation during actual measurements.
3Measurement precision
If iterative calibration of time separation is performed, then ambient light periodicity alignment is improved, but the device complexity increases
Solution Approach 1:
The patent applies self-service by enabling the device to automatically perform iterative calibration of its own timing parameters. The system uses its built-in photodetector and control logic to autonomously measure ambient light periodicity, calculate optimal time separation, and configure its measurement phases without external intervention. This self-calibrating capability achieves precise ambient light alignment while minimizing the need for external calibration equipment or complex manual configuration.
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 effectively canceling out ambient light, reducing noise and improving the signal-to-noise ratio, leading to more reliable data for parameters such as heart rate.
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
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AI summary
In described examples, a bio-sensing device (100) calibrates a time period used to make bio-physical measurements. The device (100) 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 (100) is configured to receive a digital value indicative of current through a photodetector (122) while a light source circuit (120) is enabled. In each of the first and second ambient sense phases, the device (100) is configured to receive digital values while the light source circuit (120) is disabled. The device (100) 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 to equalize the magnitude of the ambient light in the two phases.