PWM Control Circuit for HMD Display Illumination Flicker Reduction
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Solution Overview
Problem
Conventional display illumination systems using LEDs face challenges in maintaining color stability and reducing flicker when changing brightness, particularly in head-mounted display units that require high-quality augmented-reality images without distortions.
Innovation Solution
A display illumination system employing pulse width modulation (PWM) control circuits to generate multiple PWM control signals for subframes of an image frame, adjusting duty cycles to maintain constant LED emission time and reduce flicker, while aligning with the liquid crystal's transitional effects to minimize color and image cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional LED control methods are used to change brightness, then brightness adjustment is achieved, but color stability deteriorates and flicker increases
Solution Approach 1:
The patent applies pulse width modulation (PWM) to control LED brightness by periodically switching the LED on and off at different duty cycles. Multiple PWM control signals are generated within each subframe, creating periodic action that maintains color stability while adjusting brightness. The periodic switching avoids the color drift issues of conventional dimming methods.
Solution Approach 2:
The patent segments each subframe into multiple PWM control signal periods, generating multiple control signals within a single subframe. This segmentation allows for more precise control of LED emission timing and duration, maintaining consistent color characteristics while achieving brightness adjustment through duty cycle variation.
2Illumination intensity
If conventional LED control methods are used to change brightness, then brightness adjustment is achieved, but perceived flicker increases
Solution Approach 1:
By implementing multiple PWM control signals within each subframe at a high frequency, the patent creates periodic illumination that is above the human flicker fusion threshold. This high-frequency periodic action eliminates perceived flicker while still allowing brightness control through duty cycle adjustment.
Solution Approach 2:
The patent maintains continuous LED emission within each PWM period by ensuring the emission time spans the entire subframe duration. This continuity of useful action prevents gaps in illumination that would cause flicker perception, while duty cycle variation across multiple periods achieves brightness control.
3Stability of the object's composition
If PWM control signals are generated for subframes, then color stability and flicker reduction are achieved, but device complexity increases
Solution Approach 1:
The PWM control circuit is designed to generate multiple control signals for different light sources (red, green, blue LEDs) using a unified control architecture. This multi-functional approach allows the same control circuit to manage multiple LED types and subframes, reducing overall system complexity despite the increased control signal requirements.
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
The system effectively maintains color stability and reduces perceived flicker during brightness changes, enhancing the user experience in head-mounted displays by providing stable and high-quality augmented-reality images.
Implementation Method 1
The PWM control circuit operates using a duty cycle of the PWM control circuit. In operation, the PWM control circuit drives the plurality of light sources based on generating control signals for two or more subframes of an image frame.
Implementation Method 2
Light emitting diodes (LEDs) can be used in a variety of lighting applications. LEDs are useful in a number of lighting applications including light for liquid crystal display (LCD) based monitors and television.
Implementation Method 3
aligning with the liquid crystal's transitional effects to minimize color and image cross-talk
Data Source
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AI summary
In various embodiments, methods and systems for controlling display illumination is provided. A display illumination system supports maintaining color stability and reducing perceived flicker while changing the brightness of a display. The display illumination system supports light emitting diode (LED) sequencing using a pulse width modulation (PWM) control circuit for controlling the brightness and dimness of LEDs. In operation, the PWM control circuit drives the plurality of LEDs based on generating control signals for two or more subframes of an image frame. Specifically, within each subframe, at least two control signals are generated therien. In one embodiment, the display illumination system supports a display of an optical see-through head mounted display (HMD) device. In particular, the HMD device includes LEDs that allow a user to observe their physical surroundings, while LEDs and other optical elements add light into a visual path of a user to provide an augmented reality image.