Ambient Light Cancellation Circuit for Wearable PPG Sensors
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Solution Overview
Problem
Wearable devices face accuracy issues in detecting physiological characteristics due to intense ambient light, which exceeds the tolerance range of their back-end circuits, affecting the reliability of health status monitoring.
Innovation Solution
An ambient light signal adjustment method that automatically determines whether to activate an ambient light cancellation circuit based on the intensity of the ambient light signal, dynamically adjusting the cancellation signal intensity to keep the adjusted light signal within a preset range, ensuring accurate detection of physiological characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If ambient light intensity is high, then the wearable device can operate in bright environments, but the received light signal exceeds the tolerance range of the back-end circuit, affecting detection accuracy
Solution Approach 1:
The patent converts the harmful ambient light signal into a beneficial component by using it to generate a cancellation signal. The ambient light signal is processed through a series of circuits (transimpedance amplifier, filter, variable gain amplifier) to create a cancellation signal that is subtracted from the PPG signal, thereby eliminating the ambient light interference and improving detection accuracy in bright environments.
Solution Approach 2:
The patent introduces an ambient light cancellation circuit as an intermediary between the light receiver and the back-end processing circuits. This intermediary circuit processes the ambient light signal separately and subtracts it from the total received signal, allowing the system to handle bright environments while maintaining detection accuracy within the tolerance range of the back-end circuits.
2Measurement precision
If an ambient light cancellation circuit is always on, then detection accuracy is maintained, but power consumption increases and new interference may be introduced
Solution Approach 1:
The patent implements dynamic control of the ambient light cancellation circuit by using an ambient light sensor to detect current light conditions and automatically enabling or disabling the cancellation circuit accordingly. The circuit is enabled when ambient light exceeds a threshold and disabled when it is below the threshold, optimizing power consumption while maintaining detection accuracy when needed.
Solution Approach 2:
The patent employs feedback control through an ambient light sensor that continuously monitors ambient light intensity and provides feedback to the control logic. Based on this feedback, the system automatically adjusts the state of the ambient light cancellation circuit, enabling it only when ambient light interference is present, thereby balancing power consumption and detection accuracy.
3Object-affected harmful factors
If the cancellation signal intensity is increased, then ambient light interference is reduced, but the signal may exceed the preset range and cause distortion
Solution Approach 1:
The patent uses a variable gain amplifier with dynamically adjustable gain controlled by a digital-to-analog converter. The gain is adjusted based on the intensity of the ambient light signal, allowing the cancellation signal intensity to match the ambient light interference level precisely. This dynamic adjustment ensures that the cancellation signal is strong enough to eliminate interference but not so strong as to cause signal distortion or exceed the preset range.
Solution Approach 2:
The patent implements feedback control where the intensity of the cancellation signal is continuously adjusted based on the detected ambient light signal intensity. The system monitors the combined signal and adjusts the cancellation signal gain to maintain the output within the preset range, preventing both insufficient cancellation and signal distortion.
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 method effectively adjusts ambient light signals to prevent interference, improving the accuracy and reliability of wearable devices in detecting physiological characteristics by maintaining the intensity of the light signal within a tolerable range, even in environments with varying light conditions.
Implementation Method 1
a sensor (e.g., a sensor disposed in proximity to the human body, above the human body, or close to an external body surface of the human body in other ways) in the smart device (e.g., a wearable device) can be used for detection
Implementation Method 2
if ambient light is too intense, a received light signal will exceed a tolerance range of a back-end circuit
Data Source
AI summary
An ambient light signal adjustment method, a chip and electronic equipment. The method includes: receiving a first ambient light signal which is an ambient light signal acquired by a photo plethysmor graph (PPG) sensor; then determining, according to an intensity of the first ambient light signal automatically, whether to turn on an ambient light cancellation circuit which is configured to adjust the first ambient light signal according to the intensity of the first ambient light signal; and if it is determined to turn on the ambient light cancellation circuit, then adjusting a cancellation signal intensity of the ambient light cancellation circuit automatically to enable an intensity of the adjusted first ambient light signal to be within a preset range. Adjustment of the ambient light signal acquired by the PPG sensor is realized, thereby ensuring accuracy of a wearable device to detect a physiological characteristic of a user.