OLED Pixel Compensation Circuit for Threshold Sensing and Flicker Control
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Solution Overview
Problem
Existing organic electroluminescent displays suffer from non-uniform luminance due to differences in the electric characteristics of driving elements among pixels, which can worsen over time, leading to flicker and reduced image quality.
Innovation Solution
A display device with an internal compensation circuit that samples and compensates for the threshold voltage of driving elements, separating the sensing and writing steps in time to ensure accurate compensation and minimize luminance differences, and using an anode reset voltage separate from the reference voltage to improve flicker performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an internal compensation circuit is added to compensate for driving element threshold voltage differences, then threshold voltage compensation is improved, but non-uniform luminance occurs at low luminance operation
Solution Approach 1:
The pixel circuit is divided into separate functional regions: a first capacitor dedicated to threshold voltage sensing and compensation, and a second capacitor for data voltage storage. This segmentation allows independent optimization of compensation accuracy and luminance uniformity without interference between functions.
Solution Approach 2:
Different capacitors are assigned to different functional requirements: the first capacitor is optimized for threshold voltage sensing with appropriate sizing and connection to the driving element gate, while the second capacitor is optimized for data voltage storage. This local optimization resolves the conflict between compensation precision and luminance uniformity.
2Productivity
If pixels are operated at high speed, then productivity is improved, but threshold voltage sensing time is insufficient leading to compensation errors
Solution Approach 1:
The threshold voltage sensing operation is performed in advance during a dedicated sensing period before the data writing phase. This preliminary action ensures that compensation is complete and accurate before high-speed pixel operation begins, resolving the conflict between speed and sensing accuracy.
Solution Approach 2:
The pixel circuit operates in periodic cycles: a sensing period for threshold voltage measurement and compensation, followed by a data writing period. This periodic structure allows sufficient time for accurate sensing while maintaining high overall productivity through efficient time division.
3Device complexity
If a single capacitor is used for both threshold voltage storage and data voltage storage, then device complexity is reduced, but error components are introduced due to charge separation issues
Solution Approach 1:
The single capacitor is segmented into two separate capacitors: a first capacitor for threshold voltage storage and a second capacitor for data voltage storage. This segmentation eliminates charge interference and error components while maintaining manageable circuit complexity through modular design.
Solution Approach 2:
Separate capacitors act as intermediaries between the driving element and the respective voltage sources (threshold voltage and data voltage). This intermediary structure prevents direct charge interference and ensures accurate voltage storage for each function independently.
Data Source
AI summary
A display device can include a display panel on which a plurality of data lines, a plurality of gate lines, a plurality of power lines, and a plurality of pixels are disposed on a substrate, a data driver configured to output a data voltage of pixel data to one of the data lines, and a gate driver configured to supply a gate signal to one of the gate lines sequentially. The pixel can include a light emitting element having a first electrode, a second electrode facing the first electrode, and a light emitting layer disposed between the first electrode and the second electrode, a driving element configured to control the light emitting element, and a plurality of switching elements configured to control the driving element. The driving element can include an oxide semiconductor layer.