LED Backlighting and Ambient Light Sensing via Reverse Bias
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Solution Overview
Problem
Conventional LCDs face high power consumption due to backlight LEDs being driven to compete with strong ambient light, and the addition of ambient light sensors increases cost and size without considering the display's own light contribution.
Innovation Solution
Implementing a backlight ambient light sensor that reuses LEDs for both backlighting and ambient light sensing, eliminating the need for a traditional ambient light sensor by forward biasing LEDs for lighting and reverse biasing them to sense ambient light, and adjusting the PWM duty cycle based on sensed conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If traditional ambient light sensors are added to estimate ambient light conditions, then power consumption can be improved by adjusting backlight brightness, but cost and device size increase
Solution Approach 1:
The patent makes the backlight LED perform dual functions: forward biasing for illumination and reverse biasing for ambient light sensing. This eliminates the need for separate ambient light sensors, reducing device complexity, cost, and size while maintaining the ability to adjust backlight brightness based on ambient conditions
Solution Approach 2:
The backlight LED serves itself by using its own reverse bias mode to sense ambient light conditions. The LED measures both external ambient light and the display's own light contribution, enabling autonomous brightness adjustment without external sensors
2Illumination intensity
If backlight LEDs are driven with high power to compete with strong ambient light, then display visibility is improved, but power consumption increases
Solution Approach 1:
The patent implements a feedback mechanism where the reverse-biased LED continuously measures ambient light conditions (including external light and display's own light contribution). This measurement feeds back to the control logic, which dynamically adjusts the backlight PWM duty cycle to maintain optimal display brightness while minimizing power consumption
Solution Approach 2:
The system dynamically adjusts backlight brightness based on real-time ambient light conditions measured by the reverse-biased LED. The PWM duty cycle is continuously optimized to provide sufficient display visibility only when necessary, rather than maintaining constant high power output
3Ease of operation
If ambient light sensors are used to estimate ambient light conditions, then backlight brightness can be adjusted, but the display's own light contribution is not considered leading to sub-optimal brightness settings
Solution Approach 1:
The reverse-biased LED measures both external ambient light and the display's own light contribution simultaneously. This self-measurement capability provides comprehensive ambient light information that includes the display's emitted light, enabling more accurate brightness control decisions
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 reduces power consumption by optimizing backlight brightness based on ambient light conditions without the added cost and size of traditional sensors, while considering the display's own light contribution for more accurate adjustments.
Implementation Method 1
The backlight in a transmissive display is typically constructed from white light-emitting diodes (LEDs)
Implementation Method 2
one or more of the light-emitting diodes (LEDs) in the LED array are forward biased to produce light
Implementation Method 3
the one or more of the light-emitting diodes (LEDs) in the LED array are reverse biased to function as an ambient light sensor
Data Source
AI summary
Embodiments of a backlight module for illuminating a liquid crystal display (LCD) and sensing ambient light are provided herein. The backlight module includes a light-emitting diode (LED) array and a backlight controller. The backlight controller is configured to forward bias the LED array to backlight the LCD and reverse bias the LED array to sense the ambient light level. The backlight controller is configured to adjust the brightness of the LED array based on the current ambient lighting conditions sensed.