LCD Panel Drive Timing for Uniform Gray Shades
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Solution Overview
Problem
As liquid crystal display panels increase in size, write-in voltages experience attenuation and distortion, leading to uneven shades of gray across the screen due to the increased distance they must travel, and existing solutions face challenges in precision circuit adjustment.
Innovation Solution
A liquid crystal display apparatus and method that control the write-in period based on the geometric distance along column lines, using digital circuitry to vary the pulse duration and generate write-in voltages at end points of the column lines, allowing for precise adjustment and elimination of shade inconsistencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the screen size is increased to develop large sized high definition display panels, then the display area and resolution are improved, but the write-in voltages suffer from attenuation and distortion causing different shades of gray between top and bottom of the screen
Solution Approach 1:
The patent applies local quality by providing different write-in periods to different regions of the display panel. Specifically, liquid crystal cells at different distances from the column line endpoints receive different write-in periods - those farther away receive longer write-in periods to compensate for voltage attenuation, while those closer receive shorter periods. This localized adjustment ensures uniform gray shades across the entire large screen area.
2Manufacturing precision
If variable supplemental voltages are generated and combined with write-in voltages to compensate for attenuation, then the uniformity of gray shades is improved, but the complexity of circuit adjustment increases due to analog circuitry
Solution Approach 1:
The patent replaces the analog voltage adjustment system with a digital timing control system. Instead of using analog circuitry to generate variable supplemental voltages, the invention uses digital circuitry to control the duration of write-in voltage pulses. The write-in period is adjusted digitally based on the distance from column line endpoints, eliminating the need for complex analog circuit adjustment while achieving the same uniformity improvement.
3Ease of operation
If the write-in period is fixed for all row lines, then the circuit control is simple, but the write-in voltages suffer from distortion and attenuation over long column lines
Solution Approach 1:
The patent introduces dynamic control of the write-in period, making it variable rather than fixed. The write-in period is dynamically adjusted based on the distance from the column line endpoints - longer periods are applied to cells farther away where voltage attenuation occurs, and shorter periods to cells closer to the endpoints. This dynamic adjustment maintains reliable voltage delivery across the entire display while keeping the control mechanism digitally simple.
Data Source
AI summary
In a liquid crystal display apparatus, a set of write-in voltages are generated corresponding to a horizontal line signal of an input video frame so that they appear at end points of the column lines of a LCD panel. The row lines of the LCD panel are successively selected and the write-in voltages are supplied from the end points of the column lines to the liquid crystal cells of the selected row line for a variable write-in period. In order to compensate for shades-of-gray differences between the top and bottom of the LCD panel, the write-in period is increasingly varied as a function of the geometric distance from the selected row line to the end points of the column lines. The write-in period may be increasingly variable from a nominal value, or from a less-than-nominal value to the nominal value, or a combination of both.