Optical sensor system of a wearable device, a method for controlling operation of an optical sensor system and corresponding computer program product
Inventors
Koskela, Markku • Vallius, Tero
Assignees
Publication Number
US-11980439-B2
Publication Date
2024-05-14
Expiration Date
2039-05-27
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Abstract
The invention relates to an optical sensor system of a wearable device. The system comprises: at least two photo transmitters, a photoreceiver, receiving electronics, and a microcontroller. The microcontroller is configured to: set measurement conditions of the system; control taking at least one main sample from the received signal at one receiver channel; analyze the at least one main sample; control taking at least one test sample with at least one changed measurement condition at the same receiver channel; analyze the at least one test sample separately; compare at least one characteristic of the at least one test sample signal to the corresponding at least one characteristic of the at least one main sample signal; and change the measurement conditions to correspond to the measurement conditions used for the at least one test sample, if at least one characteristic of at least one test sample signal is better than corresponding at least one characteristic of the at least one main sample signal. The invention relates also to a method for controlling operation of an optical sensor system and a corresponding computer program product.
Core Innovation
The invention provides an optical sensor system of a wearable device comprising at least two photo transmitters, a photoreceiver, receiving electronics, and a microcontroller configured to control operation of the sensor system. The microcontroller sets measurement conditions, controls the taking of a main sample from the received signal, analyzes the sample for characteristics, takes test samples with changed measurement conditions, separately analyzes the test samples, and compares their characteristics to those of the main samples. If the test sample characteristics are better, the microcontroller changes the measurement conditions of the system accordingly.
The problem addressed relates to the challenges in optical heart rate measurement in wearable devices. These challenges include low power consumption requirements, variation in signal offset and amplitude due to skin and tissue optical properties, blood absorption, and measurement range limitations leading to signal saturation or weak pulse detection. The heart rate signals are slow and low frequency, so pulsing optical components is used to save power. Existing solutions either consume more power or have multiple channels and components, making them unsuitable for small, low power wearable devices.
The invention solves these problems by optimizing the selection of measurement conditions such as gain, offset, and light source using a single receiver channel. It introduces taking test samples with varied measurement conditions interleaved with main samples, analyzing and comparing these to adaptively select optimal conditions. This approach minimizes component count and power consumption while maintaining reliable and continuous heart rate detection. It also enables quick adaptation to signal variations to prevent saturation or loss of measurements, thereby improving reliability of heart rate monitoring in small wearable devices.
Claims Coverage
The claims include three independent claims covering an optical sensor system, a method for controlling it, and a computer program product embodying the control method. Four main inventive features emerge from the claims.
Adaptive measurement conditions control based on test and main sample comparison
The microcontroller sets measurement conditions, takes main samples from the photoreceiver signal, takes test samples with changed measurement conditions at the same receiver channel, analyzes both samples separately, compares their characteristics, and changes the measurement conditions of the sensor system to those used for the test samples if the main sample is out of measurable voltage range or the test samples are better.
Timing and replacement of test samples in main sample stream
Test samples are taken at time points where a main sample would otherwise be taken, and the microcontroller replaces these test samples in the main sample stream with a replacement sample calculated from other samples taken with unchanged measurement conditions to maintain signal processing consistency.
Signal event-based test sampling and heart pulse amplitude evaluation
The microcontroller analyzes the received signal to detect minimum and maximum amplitudes in a selected time window, takes test samples shortly after these extrema, uses two test samples with changed measurement conditions taken near the maxima and minima to define heart pulse amplitude, compares this amplitude with that defined from main samples, and changes measurement conditions if the test samples produce better heart pulse amplitude definition.
Measurement conditions and signal characteristics defined and used in control
Measurement conditions include gain of receiving electronics, gain of photoreceiver, offset of receiving electronics, and selection of light source. Signal characteristics include amplitude, offset, heart pulse, and heart rate. The receiving electronics comprise an amplifier, an analog-to-digital converter, and a digital-to-analog converter.
The claims collectively disclose a system, method, and software that dynamically and adaptively control measurement conditions of an optical sensor system in a wearable device by analyzing and comparing main and test samples to maintain optimal measurement range and signal quality with minimal component count and power consumption.
Stated Advantages
Reduces power consumption by using a single channel approach and pulsing photo transmitters and photoreceiver instead of continuous measurement.
Improves reliability of heart rate measurement by adaptively optimizing gain, offset, and light source selection to keep signals within measurable range and avoid saturation or low amplitude issues.
Enables quick adaptation to varying signal conditions, preventing loss of pulse detection and missed samples.
Minimizes number of components required in the sensor system, allowing very small and thin wearable device designs.
Allows measurement conditions to be changed rapidly using test sampling without interrupting main sampling data processing by replacing test samples with interpolated data.
Documented Applications
Wearable devices arranged to be attached to a user's skin such as rings or wrist devices for measuring optical properties of skin and tissue.
Monitoring of heart pulse, heart rate, heart rate variability, user activity, sleep, and recovery using photoplethysmography methods.
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