Backlight Driver Enhances Luminance Resolution via Optical Mixing
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Solution Overview
Problem
Current backlight units with LED light sources have limited luminance resolution due to the use of pulse-width modulation (PWM) signals with limited bit-resolution, resulting in perceivable transitions between brightness levels, which can be distracting and negatively impact the user experience.
Innovation Solution
The implementation of a backlight driver that provides enhanced luminance resolution through optical mixing of different PWM-controlled luminance values and the use of offset trim voltages to adjust the reference voltage, allowing for intermediate luminance levels between each PWM-controlled level, thereby increasing the overall luminance resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PWM signals with limited bit-resolution are used to control LED backlight, then power consumption is reduced and control is simplified, but luminance resolution is limited and transitions between brightness levels are noticeable
Solution Approach 1:
The backlight unit is divided into multiple independently controllable LED strings. Each string can be controlled by separate PWM signals, allowing the system to create intermediate luminance levels by combining different duty cycles across multiple strings. This segmentation enables higher effective luminance resolution without requiring higher bit-resolution PWM signals for each individual string.
Solution Approach 2:
The system uses multiple PWM signals with duty cycles that are intentionally designed to be slightly excessive or partial relative to the final desired luminance level. By combining these partial actions from multiple LED strings, the system achieves the target luminance with finer resolution than any single PWM signal could provide alone.
2Measurement precision
If higher bit-resolution PWM signals are used, then luminance resolution is improved, but power consumption increases and processing requirements increase
Solution Approach 1:
Instead of using a single high-bit-resolution PWM signal, the system segments the control into multiple lower-bit-resolution PWM signals applied to different LED strings. This segmentation maintains luminance resolution while reducing the processing power and energy consumption associated with generating and processing high-resolution PWM signals.
Solution Approach 2:
The system creates multiple copies of the backlight control function across different LED strings, each controlled by simpler PWM signals. These copies work together to produce the equivalent of a high-resolution control signal, achieving the same luminance resolution without the energy cost of actually generating high-resolution PWM signals.
3Measurement precision
If multiple LED strings are controlled with different duty cycles, then intermediate luminance levels are achieved through optical mixing, but control complexity increases
Solution Approach 1:
The human eye acts as an intermediary that performs the complex mixing operation. By controlling multiple LED strings with different duty cycles and relying on the eye's temporal integration, the system achieves intermediate luminance levels without requiring complex real-time control algorithms. The eye naturally averages the different luminance levels, simplifying the control task.
Solution Approach 2:
The system uses periodic PWM signals with different duty cycles applied to different LED strings. By timing these periodic actions appropriately and utilizing the persistence of vision, the system creates the perception of intermediate luminance levels. This periodic approach simplifies control compared to attempting to precisely regulate continuous luminance output.
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 achieves a finer luminance resolution, making transitions between brightness levels less noticeable to the human eye, thereby enhancing the user experience and providing a more aesthetically pleasing display.
Implementation Method 1
An optical diffuser is disposed within the display and is configured to diffuse the light provided by the light source
Data Source
AI summary
Disclosed embodiments relate to techniques for enhancing luminance resolution in a backlight unit. A backlight unit may have light-emitting diode (LED) light sources arranged in strings. In one embodiment, a backlight controller provides enhanced luminance resolution by drive each LED string at either first or second consecutive luminance values corresponding to first and second duty cycles of a pulse width modulation (PWM) signal. The outputs of the LED strings are optically mixed to achieve intermediate luminance values between the first and second luminance values. In another embodiment, a reference voltage is adjusted using slight voltage offsets to achieve intermediate luminance values between the first and second luminance values