Staggered PWM Backlight Control for HDR Display Power Management
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Solution Overview
Problem
High Dynamic Range (HDR) display systems face challenges in reducing overall and instantaneous power demands due to the simultaneous activation of multiple light emitters, leading to increased cost and complexity of the power supply, especially when displaying very bright images.
Innovation Solution
The implementation of staggered PWM cycles for groups of light emitters, where each group's start time is offset by a phase shift, reducing the peak power requirement and distributing the power ramp-up more gradually, allowing for a lower maximum power value and reduced power surges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If multiple light emitters are activated simultaneously to achieve high brightness levels, then the brightness and image quality are improved, but the instantaneous power demand and power supply complexity increase
Solution Approach 1:
The backlight is divided into multiple independently controllable segments or zones, allowing different portions of the display to be illuminated at different times. This segmentation enables the system to achieve high brightness in specific areas without requiring all light emitters to operate simultaneously, thereby reducing peak power demands and simplifying power supply requirements.
Solution Approach 2:
The system employs periodic activation of light emitter groups through techniques such as temporal dithering and frame sequential backlight scanning. By cycling through different groups of light emitters across multiple frames or time intervals, the system achieves the perception of full-screen high brightness while actually activating only a subset of emitters at any given moment, reducing instantaneous power requirements.
2Illumination intensity
If all light emitters are activated simultaneously to display very bright images, then the image quality is improved, but the instantaneous power surge increases
Solution Approach 1:
The backlight array is divided into multiple independently controllable segments that can be activated in different time intervals. This allows the system to distribute the power demand across multiple time slots rather than requiring all segments to draw power simultaneously, thereby maintaining high overall brightness while reducing peak instantaneous power surges.
Solution Approach 2:
The system uses periodic activation patterns where different groups of light emitters are turned on and off in sequence across multiple frames or time intervals. This temporal distribution of activation ensures that the total light output over time achieves the desired brightness level while the instantaneous power demand at any moment remains within manageable limits.
3Use of energy by moving object
If the update rate of the backlight is reduced to gain additional resolution, then the power consumption is decreased, but the temporal resolution may be affected
Solution Approach 1:
The system employs periodic backlight activation with variable update rates, allowing the backlight to be updated at lower frequencies when full temporal resolution is not required. This periodic operation enables the system to reduce average power consumption by keeping the backlight off during intervals between updates, while still maintaining acceptable visual performance for static or slowly changing content.
Solution Approach 2:
The backlight update rate is made dynamic and adaptable based on content requirements. The system can adjust the update frequency and activation patterns according to whether the displayed content is static, slowly changing, or rapidly changing, thereby optimizing the balance between power consumption and temporal resolution for different usage scenarios.
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 decreases the complexity and cost of the power supply, improves efficiency and reliability, and allows for more moderate surge capacity, load regulation, and transient response, while maintaining the brightness levels and image quality.
Implementation Method 1
The implementation of staggered PWM cycles for groups of light emitters, where each group's start time is offset by a phase shift, reducing the peak power requirement and distributing the power ramp-up more gradually
Data Source
Figure 1A~1B
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AI summary
Techniques are provided to provide various pulse width modulation (PWM) schemes to embodiments of dual modulator display systems that may comprise a backlight of individually addressable and controllable light emitters. The backlight provides illumination to a light modulator for further conditioning of the light to be presented to a viewer. The backlight may be striped and each stripe is assigned a PWM scheme that effectively increases the bit depth of the controller for each stripe. The display system may allow a better matching of PWM periods to LCD frame rates to reduce visual artifacts. In another embodiment, the display system may detect a small bright feature to be rendered in the image data and, with a pre-assignment of light emitters to different partitions, the backlight controller may drive a subset of the light emitters according to the partitions.