Pulse Oximetry Phase Division Multiplexing Noise Reduction
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Solution Overview
Problem
Pulse oximetry measurements are noise-sensitive due to ambient light interference and flickering noise sources, leading to biased and inaccurate readings, especially when multiple light sources are used simultaneously.
Innovation Solution
A pulse oximetry measurement system employing phase division multiplexing (PDM) with a pseudo-random noise generator using a maximum length sequence, which allows simultaneous measurement of multiple light sources by phase-shifting the sequence for each source, reducing noise interference and enabling effective subtraction of ambient light noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple light sources are used simultaneously for pulse oximetry measurements, then measurement completeness is improved, but noise interference from ambient light and flickering sources increases
Solution Approach 1:
The patent applies periodic action by modulating multiple light sources with distinct periodic patterns (different frequencies or phase relationships). Each light source is turned on and off in a periodic manner, allowing the detector to receive modulated signals that can be separated through frequency or phase analysis. This periodic modulation enables the system to distinguish between signals from different light sources and reject ambient light noise that does not follow these specific periodic patterns.
Solution Approach 2:
The patent employs parameter changes by varying temporal characteristics (timing patterns, duty cycles, frequencies) of the light sources. Each light source operates with unique temporal parameters, creating distinguishable signal signatures. The system changes these temporal parameters dynamically to encode information from each light source, allowing the detector to differentiate between multiple sources and extract meaningful measurements while rejecting noise.
2Measurement precision
If light intensity is increased to improve signal detection, then signal-to-noise ratio improves, but risk of tissue damage and patient discomfort increases
Solution Approach 1:
The patent uses periodic action by implementing pulsed light emission instead of continuous illumination. Light sources are activated in periodic pulses with controlled duty cycles, allowing the tissue to recover between pulses. This periodic illumination maintains sufficient signal intensity during active periods while reducing overall energy exposure to the tissue, thereby improving signal detection capability without proportionally increasing tissue damage risk.
Solution Approach 2:
The patent applies dynamics by making the light emission temporal characteristics adjustable and adaptive. The system dynamically controls the timing, duration, and intensity of light pulses based on measurement requirements and tissue response. This dynamic adjustment allows optimization of signal strength during active measurement while minimizing overall exposure, balancing signal detection capability with patient safety.
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 significantly reduces noise interference, allowing for accurate and simultaneous measurement of multiple light sources without bias, improving the precision of oxygen saturation and heartbeat detection in pulse oximetry.
Implementation Method 1
at least one light sensor adapted for detecting light amplitudes
Implementation Method 2
phase division multiplexing (PDM) with a pseudo-random noise generator using a maximum length sequence, which allows simultaneous measurement of multiple light sources by phase-shifting the sequence for each source
Implementation Method 3
HbO2 absorbs more infrared light and allows more red light to pass through. On the other hand, Hb absorbs more red light and allows more infrared light to pass through
Data Source
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AI summary
A pulse oximetry measurement system uses a pseudo-random noise generator to stimulate one or more light emitting diodes (LEDs). The light amplitudes from these LEDs, after passing through a part of a body, are detected by a phototransistor or photodiode and digitized with an analog-to-digital converter (ADC). The digitized ADC light amplitude values are re-correlated with the outgoing pseudo-random noise stimulus. Spread spectrum techniques are known for their noise mitigation properties, and ability to pass multiple signals through the same medium without interference. Thus, these measurements can be performed substantially simultaneously with minimal interference from each other. The pulse oximetry measurement system correlates the measured light intensities using pseudo-random noise generation and phase division multiplexing, and computes the measured and correlated peak- to-peak detected light amplitudes to obtain a ratio between these light amplitudes for determining oxygen saturation in the blood, and may also be used for heart rate monitoring.