Behind Display Proximity Sensing Using Wavelength Tuning
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Solution Overview
Problem
Conventional optical proximity sensors located behind displays in electronic devices face challenges such as low Signal-to-Noise ratio (SNR) due to high reflectance and transmission issues, leading to display distortion and inability to determine absolute distance, as current mitigation strategies either increase power consumption or require larger sensor modules.
Innovation Solution
The optical sensor emits light at a wavelength greater than the point of 50% absorption of the display, typically above 1100 nm, to minimize absorption and maximize transmissivity, using self-mixing interference (SMI) sensors with electrical or optical detection methods to improve SNR and reduce display distortion, while maintaining compactness and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the proximity sensor is located behind the display, then the display can extend to the edges of the device, but the Signal-to-Noise ratio decreases due to low transmission and high reflectance of the display
Solution Approach 1:
The patent changes the operating wavelength parameter of the optical sensor to match the transmission peak of the display (around 1100nm). This parameter adjustment allows the sensor to operate at a wavelength where the display has maximum transmission and minimum absorption, thereby maintaining high Signal-to-Noise ratio while enabling the sensor to be positioned behind the display for edge-to-edge display design.
2Measurement precision
If the illumination power is increased to improve SNR, then the Signal-to-Noise ratio improves, but power consumption increases and display distortion worsens
Solution Approach 1:
The patent changes the wavelength parameter from conventional visible light ranges to the near-infrared range at 1100nm, where the display material exhibits peak transmission. This allows the optical sensor to achieve high Signal-to-Noise ratio with lower illumination power, avoiding the need to increase power consumption while maintaining accurate proximity detection.
3Measurement precision
If the separation between emitter and receiver is increased to reduce crosstalk, then crosstalk reduction improves, but the sensor module size increases
Solution Approach 1:
The patent replaces the mechanical solution of increasing physical separation with an optical solution using wavelength-specific filtering. By operating at 1100nm and using bandpass filters tuned to this wavelength, the system achieves effective crosstalk rejection without requiring increased separation distance, thereby maintaining compact sensor module dimensions.
4Object-affected harmful factors
If the illumination power is lowered or beam is widened to reduce display distortion, then display distortion decreases, but Signal-to-Noise ratio decreases
Solution Approach 1:
The patent changes the illumination wavelength to 1100nm where the display material has minimal absorption and optimal transmission. This allows the use of moderate illumination power with a focused beam to achieve both low display distortion (by avoiding excessive power density) and high Signal-to-Noise ratio (by operating at the transmission peak), eliminating the need to trade off between these two parameters.
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 Signal-to-Noise ratio, reduces display distortion, and allows for accurate distance and velocity measurements without increasing power consumption or sensor size, making it suitable for edge-to-edge display devices like smartphones and tablets.
Implementation Method 1
The emitter is configured to emit light at a second wavelength greater than the first wavelength
Implementation Method 2
The absorption of the display is wavelength dependent and the absorption of the display is 50% at a first wavelength
Implementation Method 3
Optical proximity detection typically measures the intensity of reflected light to determine the distance to an object
Implementation Method 4
a receiver for receiving light reflected back through the display
Implementation Method 5
using self-mixing interference (SMI) sensors with electrical or optical detection methods
Data Source
AI summary
An optical device includes a display and an optical sensor. The display includes display circuitry. The optical sensor is arranged behind the display. The optical sensor includes an emitter for emitting light through the display and a receiver for receiving light reflected back through the display. An absorption of the display is wavelength dependent and the absorption of the display is 50% at a first wavelength. The emitter is configured to emit light at a second wavelength greater than the first wavelength.