Ambient Light Sensing Behind Display Using Sub-Frame Modulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing light sensing technologies face challenges in accurately measuring ambient light levels behind displays, particularly in dark environments and with limited space for light sensors, due to interference from display-generated stray light and the need for proximity detection, leading to significant errors and design constraints.
Innovation Solution
A method that modulates the brightness of display sub-frames using pulse width modulation (PWM) or amplitude and duty cycle modulation, allowing for longer integration times and separation of ambient light contributions from display light, enabling reliable light sensing and display control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the light sensor is placed close to the display for proximity detection, then proximity detection function is improved, but stray light from the display interferes with ambient light measurement
Solution Approach 1:
The display brightness is modulated periodically by dividing the display frame into multiple sub-frames with different brightness levels. The light sensor measures ambient light during specific sub-frames when the display is at known brightness levels, allowing separation of ambient light signal from display stray light through temporal modulation and mathematical processing.
2Use of energy by moving object
If the display brightness is reduced to save power in dark environments, then power consumption is reduced, but ambient light measurement accuracy deteriorates due to insufficient light
Solution Approach 1:
The system performs preliminary measurements of ambient light during sub-frames when the display is at higher brightness levels before the main display operation. This preliminary action allows the system to capture sufficient ambient light signal even when the display will be dimmed for power saving, ensuring measurement accuracy is maintained while enabling power reduction.
3Measurement precision
If the light sensor integrates light for longer periods to improve measurement accuracy, then measurement precision is improved, but the system complexity increases
Solution Approach 1:
The display frame is segmented into multiple sub-frames with different brightness levels. The light sensor performs multiple short integration measurements during these sub-frames rather than one long integration. The results are combined mathematically to achieve high measurement precision, avoiding the need for complex long integration hardware while maintaining accuracy.
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 allows for accurate detection of ambient light levels behind displays, facilitating improved display control and user experience by separating ambient and display light information, enabling longer integration times and simpler chip integration without visible effects to the user.
Implementation Method 1
Light being incident on the display may traverse through the display and can be received and eventually detected by means of the light sensor arrangement
Implementation Method 2
Light may be detected by the light sensor arrangement and typically comprises contributions from at least two sources
Data Source
AI summary
A method is proposed for sensing light being incident on an electronic device. The electronic device comprises a display and a light sensor arrangement which is mounted behind the display such as to receive incident light through the display. The method comprises the step of repeatedly switching the display on and off depending on a modulation signal, wherein a sub-frame is defined by an on-state and a consecutive off-state of the display. The modulation signal depends on at least one modulation parameter. In a first sub-frame a display brightness is set to a first level depending on a first value of the at least one modulation parameter. Then a first frame count is determined by integrating the incident light by means of the light sensor arrangement during the first sub-frame. In a second sub-frame the display brightness is set to a second level depending on a second value of the at least one modulation parameter. Then a second frame count is generated by integrating the incident light by means of the light sensor arrangement during the second frame. Finally, an ambient light level is determined depending on the first frame count and the second frame count.