Earbud Self-Mixing Proximity Sensing for Accurate Gesture Detection
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Solution Overview
Problem
Optical proximity sensors in electronic devices, such as earbuds, face inaccuracies in measuring object proximity due to variations in reflectivity and bidirectional reflectance distribution function (BRDF) of objects, leading to measurement inaccuracies.
Innovation Solution
Incorporating self-mixing proximity sensors with coherent or partially coherent light sources, such as infrared vertical cavity surface-emitting lasers, and photodiodes, and applying frequency-extracting transforms like fast Fourier transforms, along with curve fitting techniques, to accurately determine target distances and interpret user inputs like finger gestures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional infrared photodetectors are used to measure reflected light intensity, then the sensor structure is simple, but measurement precision deteriorates due to reflectivity and BRDF variations of objects
Solution Approach 1:
The patent changes the fundamental measurement parameter from light intensity to frequency/phase information. By using a modulated laser source and detecting the frequency or phase of the reflected light, the system achieves immunity to reflectivity variations and BRDF effects, thereby improving measurement precision without proportionally increasing device complexity
Solution Approach 2:
The patent replaces the traditional intensity-based detection mechanism with a frequency/phase-based detection mechanism. This substitution uses the temporal characteristics of modulated light rather than spatial intensity distribution, enabling accurate proximity measurement independent of object reflectivity properties
2Reliability
If intensity-based optical sensors are used, then the device complexity is low, but reliability deteriorates due to measurement inaccuracies affecting control operations
Solution Approach 1:
The patent implements feedback by modulating the laser source at a known frequency and detecting the corresponding frequency or phase in the reflected light. This feedback mechanism allows the system to reliably determine proximity state and trigger appropriate control operations, improving reliability while the added signal processing complexity is justified by the enhanced measurement accuracy
Solution Approach 2:
The patent uses periodic modulation of the laser source at a specific frequency. By detecting the reflected light's frequency or phase relationship to the modulation, the system achieves reliable proximity detection that is independent of object reflectivity, thereby improving control operation reliability
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 proximity measurements, allowing for precise control operations, such as pausing audio playback, entering sleep states, and adjusting volume, based on reliable detection of earbud insertion and user interactions.
Implementation Method 1
A self-mixing proximity sensor may have a coherent or partially coherent source of electromagnetic radiation... The control circuitry can apply a frequency-extracting transform such as a fast Fourier transform to the laser bias current signal, laser junction voltage signal, or photodiode output signal
Implementation Method 2
The self-mixing proximity sensor may also have a light detector such as a photodiode and/or other electromagnetic-radiation-sensitive element
Data Source
AI summary
An electronic device such as an earbud may have control circuitry mounted in a housing. The housing may have portions such as an ear portion with a speaker port through which a speaker plays audio and a stalk portion that extends from the ear portion. Proximity sensors may be formed in the electronic device. For example, one or more proximity sensors may be formed on the ear portion to detect when a user has inserted an earbud into the ear of the user and/or one or more proximity sensors may be formed on a stalk portion to detect when a user is holding an earbud by the stalk or when a user is providing finger touch input such as taps, swipes, and/or other gestures on the stalk portion. The proximity sensors may be optical proximity sensors such as coherent self-mixing proximity sensors.