OLED Display Compensation for Transistor Threshold Voltage Variations
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Solution Overview
Problem
Organic light-emitting diode (OLED) display pixels experience variations in transistor threshold voltages due to manufacturing and operating variations, leading to inconsistent light production and the need for compensation schemes that increase image display time.
Innovation Solution
Incorporation of compensation circuitry that measures and compensates for threshold voltage variations by sampling the voltage of current source transistors and generating offset data to adjust analog pixel signals, allowing for improved light emission uniformity across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If compensation schemes are used to compensate for transistor threshold voltage variations, then display uniformity is improved, but the time required to display images increases
Solution Approach 1:
The patent performs threshold voltage sampling and compensation data generation in advance during initialization phases, before actual image display operations. Compensation data is stored in memory and applied during normal display operations, separating the compensation process from the display process to avoid increasing display time.
Solution Approach 2:
The patent divides the compensation process into distinct phases: sampling phase for measuring threshold voltages, evaluation phase for generating compensation data, and display phase for showing images. This segmentation allows compensation operations to be performed separately from image display operations, preventing time penalties during actual display.
2Measurement precision
If threshold voltage sampling is performed during normal display operations, then compensation accuracy is improved, but display speed decreases
Solution Approach 1:
The patent performs threshold voltage sampling during initialization phases before normal display operations begin. The sampling, evaluation, and compensation data generation are all completed in advance, allowing high-precision measurements without impacting display speed during actual image rendering.
Solution Approach 2:
The patent implements compensation operations during specific periodic phases (initialization frames) separate from normal display frames. This periodic structure allows accurate threshold voltage measurement during dedicated sampling windows while maintaining high display speed during regular image display frames.
3Measurement precision
If compensation data is generated and stored for each pixel, then compensation precision is improved, but memory requirements and device complexity increase
Solution Approach 1:
The patent generates and stores individualized compensation data for each pixel based on its specific threshold voltage characteristics. This localized compensation approach ensures high precision for each pixel while the data is stored in on-chip memory structures integrated into the display driver, minimizing additional device complexity.
Solution Approach 2:
The patent integrates compensation memory structures within the existing display driver circuitry and pixel structures. Compensation data is stored in on-chip memory that is nested within or adjacent to the driver circuits, and compensation circuitry is embedded within pixel structures, reducing the need for separate external memory components and minimizing device complexity.
Data Source
AI summary
A display may include an array of organic light-emitting diode display pixels having transistors characterized by threshold voltages subject to transistor variations. Compensation circuitry may be used to measure at transistor threshold voltage for a pixel. The threshold voltage may be sampled by controlling the pixel to sample the threshold voltage onto a capacitor at the pixel. The compensation circuitry may include sense circuitry that may be operated in combination with the pixel to transfer charge from the capacitor to the sense circuitry such that the threshold voltage is produced at an output of the sense circuitry. The compensation circuitry may generate compensation data based on the measured threshold voltage. During display operations, data circuitry may receive digital image data and process the digital image data along with the compensation data to generate analog data signals for the pixel.