Overdriving Target Computation for MVA LCD Brightness Switching
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Solution Overview
Problem
MVA LCDs face issues with image washout at wide viewing angles due to unbalanced cell gaps, and the 2D1G technique, while improving display effects, lowers transmittance and causes color cast and squinty brightness, necessitating a method to compute an overdriving target based on subpixel signal for brightness switching.
Innovation Solution
A method involving dynamic switching of four frames with specific grayscale thresholds and noise smoothing to determine an overdriving target that matches target brightness and time response, ensuring swift switching between high and low grayscales without reducing transmittance, using a 17×17, 33×33, or 65×65 overdriving table and median filtering for noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the 2D1G technique is used to improve wide viewing angle display effects, then viewing angle performance is improved, but transmittance is reduced
Solution Approach 1:
The pixel is divided into a main pixel and a subpixel, with different data lines connected to each. The subpixel uses a dedicated data line to receive specific grayscale values, allowing independent control of brightness for different viewing angles. This segmentation enables the main pixel to optimize for transmittance while the subpixel compensates for wide viewing angle performance.
Solution Approach 2:
Different grayscale values are applied to the main pixel and subpixel based on their specific functions. The main pixel uses higher grayscale values to maintain transmittance, while the subpixel uses lower grayscale values to compensate for viewing angle effects. This local quality differentiation resolves the contradiction between transmittance and wide viewing angle performance.
2Illumination intensity
If the subpixel is switched from low grayscale to high grayscale, then brightness increases, but overshoot occurs when maximal brightness exceeds 110% of target brightness
Solution Approach 1:
The patent pre-calculates overdriving target values and stores them in an overdriving table before actual display operation. This preliminary action allows the system to determine the optimal driving voltage in advance, preventing overshoot when switching from low to high grayscale. The pre-computed values ensure that brightness increases to the target level without exceeding 110% of the target brightness.
Solution Approach 2:
The patent implements a feedback mechanism by comparing the actual brightness curve with the target brightness and adjusting the driving voltage accordingly. The overdriving target values are computed based on the relationship between driving voltage, grayscale transitions, and resulting brightness. This feedback ensures that when the subpixel switches from low to high grayscale, the maximal brightness remains controlled within 110% of the target brightness.
3Illumination intensity
If the subpixel is switched from high grayscale to low grayscale, then brightness decreases, but undershoot occurs when minimal brightness is less than 90% of target brightness
Solution Approach 1:
The patent pre-calculates overdriving target values for high-to-low grayscale transitions and stores them in the overdriving table. This preliminary computation determines the optimal driving voltage to achieve the target brightness without undershoot. By having the target values ready in advance, the system can smoothly transition from high to low grayscale while maintaining brightness above 90% of the target value.
Solution Approach 2:
The patent uses feedback control to monitor the brightness curve during high-to-low grayscale transitions and adjusts the driving voltage to prevent undershoot. The overdriving target values are computed based on the inverse relationship between driving voltage and brightness decay. This feedback mechanism ensures that the minimal brightness during transition remains above 90% of the target brightness.
4Device complexity
If overdriving target computation is performed without brightness switching consideration, then computation is simpler, but transmittance is reduced and color cast occurs
Solution Approach 1:
The patent segments the overdriving computation into separate handling for main pixels and subpixels. The subpixel overdriving computation specifically considers brightness switching patterns and applies different algorithms based on whether the transition is low-to-high or high-to-low grayscale. This segmented approach maintains transmittance by optimizing the computation specifically for subpixel characteristics rather than using a generic simplified algorithm.
Solution Approach 2:
The patent changes the computation parameters based on the subpixel's brightness switching state. Different overdriving algorithms are applied depending on the grayscale transition direction and magnitude. This parameter adaptation ensures accurate color rendering and maintains transmittance by adjusting the computation complexity only where necessary, rather than using a universally simplified approach.
Data Source
AI summary
A method of computing an overdriving target based on brightness switching on a subpixel signal includes: trying an overdriving target for obtaining a curve of R/G/B luminance and time response of the overdriving target, and determining if brightness of the curve of the R/G/B luminance and the time response of the overdriving target and the target brightness are matched. The rule for matching includes: when the subpixel is switched from low grayscale to high grayscale, the maximal brightness of the curve of the R/G/B luminance and the time response of the driving target being not more than 110% of the target brightness; otherwise, the minimal brightness of the curve of the R/G/B luminance and the time response is not less than 90% of the target brightness. By using the matching rule, swift switching of H/L switching between upper-intermediate grayscale and low grayscale is realized, and wide viewing angle and transmittance remain.