Active Matrix Display Pixel Compensation Using Calibration Lookup Tables
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Solution Overview
Problem
Active matrix displays, such as AMOLEDs, face non-uniform output due to variations in threshold voltage and manufacturing differences between pixels, limiting resolution and requiring additional transistors for compensation.
Innovation Solution
A method to determine a compensated voltage for each pixel, accounting for differences in the relation between applied voltage and threshold voltage, using individual calibration values to ensure uniform light intensity across the display, which can be stored in a look-up table or calculated using constants, and updating these values periodically to account for threshold voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If compensation circuits for handling threshold voltage variations are used, then uniform display output is improved, but device complexity increases due to larger number of transistors needed within each pixel
Solution Approach 1:
The patent changes the compensation approach from circuit-based (adding transistors) to parameter-based (storing calibration values). Each pixel's drive transistor characteristics are characterized during manufacturing and stored as calibration values in a lookup table. During operation, these calibration values are used to adjust drive voltages to compensate for threshold voltage variations, achieving uniform display output without adding transistors to each pixel.
2Device complexity
If a common relation is used to determine compensated voltage for all pixels, then device complexity is reduced, but manufacturing precision deteriorates due to geometric variations between pixels
Solution Approach 1:
The patent applies local quality by assigning individual calibration values to each pixel based on its specific characteristics. During manufacturing, each pixel's drive transistor is characterized and stored with unique calibration data in a lookup table. This allows each pixel to be compensated according to its local geometric variations and manufacturing tolerances, rather than applying a uniform compensation scheme to all pixels.
3Manufacturing precision
If individual calibration values are stored for each pixel to compensate for manufacturing variations, then manufacturing precision is improved, but memory usage increases
Solution Approach 1:
The patent extracts the compensation function from the pixel circuitry and places it in an external lookup table stored in memory. Instead of implementing compensation circuits within each pixel, the calibration data is extracted and stored separately, allowing the display controller to perform compensation calculations externally. This reduces the memory requirement compared to storing full compensation circuits while still achieving pixel-to-pixel uniformity.
Data Source
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AI summary
A method for driving an active matrix display comprising a plurality of pixels (110), wherein each pixel (110) comprises a drive transistor (120) having a driver gate (122) and a calibration gate (129), is disclosed. The method comprises: receiving information of a desired image to be displayed; determining a compensated voltage for the driver gate (122) for each pixel (110) based on calibration data; and outputting the compensated voltage for the driver gate for each of the pixels. The calibration data comprises a set of individual calibration values applying to different pixels (110), wherein said compensated voltage compensates for differences between pixels affecting a relation of an intensity of light output by the pixel (110) as function of a difference between the voltage applied to the driver gate (122) and a threshold voltage of the drive transistor (120).