Display PWM-Aligned Variable Refresh Rate to Mitigate Flicker
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Solution Overview
Problem
In video display systems with variable refresh rates, misalignment between frame rendering and PWM control signals leads to flicker due to changes in effective duty cycle, detracting from the viewing experience.
Innovation Solution
Implement a discrete variable refresh rate (VRR) scheme that aligns frame periods with PWM cycles, using frame insertion or stretch modes to compensate for rendering delays, ensuring consistent duty cycles across frames.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If variable refresh rate is used to reduce rendering delay, then productivity is improved, but illumination intensity becomes unstable causing flicker
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the frame period to be an integer multiple of the PWM period. This ensures that the PWM duty cycle remains consistent across frames even when refresh rate varies, thereby maintaining stable brightness perception while allowing flexible frame rendering speeds.
Solution Approach 2:
The patent utilizes periodic action by synchronizing frame display timing with the PWM signal period. By ensuring frame periods are integer multiples of PWM periods, the system creates a periodic alignment that prevents brightness flicker while maintaining variable refresh capabilities.
2Speed
If frame rate is increased to improve smoothness, then speed is improved, but alignment with PWM cycles becomes difficult causing flicker
Solution Approach 1:
The system dynamically selects frame rates from a set of supported rates where each rate's period is an integer multiple of the PWM period. This parameter selection ensures that even at higher refresh rates, the PWM duty cycle remains consistent, preventing flicker while maintaining smooth visual performance.
3Illumination intensity
If discrete frame rates aligned with PWM periods are used, then illumination intensity stability is improved, but adaptability to variable rendering speeds decreases
Solution Approach 1:
The patent implements a discrete variable refresh rate (VRR) scheme that dynamically selects from multiple pre-defined frame rates. Each frame rate in the set is specifically chosen so its period is an integer multiple of the PWM period, allowing the system to adapt to different rendering speeds while maintaining brightness stability through PWM alignment.
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
Mitigates flicker by maintaining consistent brightness levels across frames, providing a smoother viewing experience.
Implementation Method 1
A digital control signal that controls a backlight in a transmissive display panel or directly controls the pixel intensities in an emissive display panel is pulse width modulated such that resulting brightness of the display panel is proportional to the duty cycle of the resulting PWM signal
Data Source
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AI summary
PWM-frame rate misalignment is mitigated through implementation of a discrete variable refresh rate (VRR) scheme. A target frame rate is limited to a frame rate selected from only those frame rates that facilitate alignment of each frame period to a specified edge of a PWM cycle of a brightness control signal of a display panel. This alignment results in each frame period at the selected frame rate starting at a same point in a corresponding PWM cycle and ending at a same point in a corresponding PWM cycle to help ensure a constant effective duty cycle across each successive frame period, which in turn mitigates perception of flicker that otherwise would arise. Further, the discrete VRR scheme can employ a compensation mode for compensating for the delay in rendering or otherwise obtaining a frame for display so as to maintain a consistent duty cycle in the brightness control signal.