Backlight PWM Phase Shifting for Peak Power Reduction
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Solution Overview
Problem
Dual-modulation displays with backlights comprising multiple light emitting devices face challenges in power supply requirements due to simultaneous switching of light emitters, leading to increased cost and complexity, particularly in high dynamic range displays that require significant electrical power.
Innovation Solution
Divide light emitters into groups and stagger the start times of PWM cycles, phase-shifting the PWM signals to reduce peak power demand and distribute power requirements more evenly, allowing for a lower maximum power requirement and reduced surge capacity in the power supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If all light emitters are switched on simultaneously during PWM cycles, then the backlight can achieve maximum brightness output, but the power supply must handle high peak power demands and require complex surge protection circuits
Solution Approach 1:
The patent divides the array of light emitters into multiple groups that are controlled independently. Each group is assigned a different phase offset within the PWM cycle, causing them to switch on at different times rather than simultaneously. This segmentation of the light emitter array into phased groups reduces the peak power demand on the power supply while maintaining the overall maximum brightness output when all groups are operating.
2Productivity
If all light emitters are switched on simultaneously, then maximum light output is achieved, but the power supply complexity and cost increase due to surge capacity requirements
Solution Approach 1:
The light emitter array is segmented into multiple groups with different phase offsets. This allows the system to maintain high light output efficiency while reducing power supply complexity by eliminating the need for high surge capacity and complex protection circuits.
Solution Approach 2:
The patent employs periodic PWM cycling with different phase offsets for different groups of light emitters. This periodic action with phase distribution maintains overall productivity while simplifying the power supply requirements by avoiding simultaneous switching surges.
3Power
If light emitters are phased across multiple PWM cycles, then peak power demand is reduced, but the implementation complexity of the control system increases
Solution Approach 1:
The control system manages complexity by segmenting the light emitter array into groups, each with a simple fixed phase offset. This segmentation approach reduces peak power demand while keeping the control logic relatively simple through systematic phase distribution.
Solution Approach 2:
The system uses dynamic PWM phase offset assignment to different light emitter groups. This dynamic control approach allows flexible power management while maintaining manageable control system complexity through structured phase distribution patterns.
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 by moderating power variations, enhancing efficiency and reliability, and reducing the need for complex surge protection circuits.
Implementation Method 1
the backlight includes multiple light emitting devices, such as LEDs, for illuminating regions of the spatial light modulator
Implementation Method 2
Some displays, such as liquid crystal displays (LCDs), comprise a spatial light modulator that is illuminated by a backlight
Implementation Method 3
The brightness of light emitters on a backlight may be controlled by a technique known as pulse width modulation (PWM)
Data Source
AI summary
A backlight for a display comprises a plurality of independently controllable groups of light emitters. The brightness levels of the groups of light emitters are controllable by pulse width modulation (PWM) signals generated by PWM driving circuits. The phases of PWM signals to different groups of light emitters are configured to be offset by different amounts, so as to stagger the start times of light emitters of different groups. Such phase-shifting of PWM signals may result in total power consumption that ramps up more gradually, is distributed more evenly over time, and is held to a lower maximum value than if the same PWM signals were not phase-shifted. The duration of a first PWM cycle of PWM signals for an image may also be made longer than subsequent PWM cycles for the image so as to extend the initial power ramp-up time.