MOS Transistor Sizing for LCD Color Cast Compensation
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Solution Overview
Problem
Liquid crystal display panels with narrow borders experience voltage latency issues due to uneven trace impedances, leading to color cast problems in color blending, particularly in grey frames, resulting in unsatisfactory brightness and color distortions like greenish or bluish hues.
Innovation Solution
A color cast compensation method that involves calculating trace impedances, obtaining correlation curves, adjusting the size of MOS transistor cross-sectional areas based on real driving force curves to ensure consistent pixel charging voltages across channels, thereby optimizing driving forces and reducing chip size and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the layout area for fan-out shape traces is limited in narrow border liquid crystal display panel, then the border width is reduced, but the impedance uniformity of traces deteriorates causing voltage latency
Solution Approach 1:
The patent applies local quality by making the cross-sectional area of MOS transistors channel-dependent. Different channels (left, center, right) have different trace impedances due to their positions, so the transistor cross-sectional areas are adjusted locally for each channel to compensate for impedance differences. This ensures uniform driving forces across all channels despite the limited layout area causing impedance variations.
2Power
If the cross-sectional area of MOS transistor is increased to compensate for trace impedance, then the driving force is improved, but the chip area is enlarged
Solution Approach 1:
Instead of uniformly increasing all transistor cross-sectional areas, the patent applies local quality by adjusting only the cross-sectional area of transistors in channels with insufficient driving force. Channels with longer traces (left and right) have larger cross-sectional areas, while the center channel uses a smaller cross-sectional area. This localized adjustment compensates for impedance differences without unnecessarily increasing the overall chip area.
Solution Approach 2:
The patent changes the physical parameter of cross-sectional area of MOS transistors based on channel position and trace impedance characteristics. By establishing a correspondence relationship between channel position and required driving force, the cross-sectional area is adjusted as a variable parameter rather than a fixed value, optimizing the balance between driving force and chip area.
3Device complexity
If uniform driving force is applied to all channels, then the transistor design is simplified, but color cast appears in color blending grey frame
Solution Approach 1:
The patent resolves this contradiction by applying local quality through channel-dependent cross-sectional area adjustment. The design becomes slightly more complex by introducing channel position considerations, but this complexity is necessary to eliminate color cast. The adjusted cross-sectional areas compensate for trace impedance differences, ensuring uniform voltage delivery to all pixels and preventing color cast in color blending grey frames.
Data Source
AI summary
The embodiments of the present invention publishes a color cast compensation method for liquid crystal display panel, which comprises the steps of obtaining a trace impedance of each trace of a plurality of traces in a fan-out-shape and obtaining a correlation curve showing the relationship between the trace impedance and a channel according to the trace impedance; obtaining a curve of a real driving force on an output terminal of the channel according to the correlation curve showing the relationship between the trace impedance and the channel; adjusting a size of a cross-sectional area of a MOS transistor on the output terminal of the channel according to the curve of the real driving force. The embodiment of the present invention further publishes another color cast compensation method for liquid crystal display panel and a color cast compensation system for liquid crystal display panel. The embodiments of the present invention solves the color cast problem appears in the liquid crystal display panel nowadays.