OLED Pixel Compensation Circuit for Luminance Consistency
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Solution Overview
Problem
Organic light emitting displays face issues due to variations in drive transistor threshold voltages and charge mobilities, leading to inconsistent luminance across pixels and degradation over time, which degrades display quality.
Innovation Solution
The display incorporates a compensation mechanism using additional transistors and capacitors to adjust threshold voltages and sense drive information, allowing for compensated data voltage application to ensure consistent luminance, including a first compensation period for threshold voltage compensation and a second for sensing and compensating electron mobility deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If drive transistors are used to control driving current in each pixel, then the display can generate images with high response speed and low power consumption, but variations in threshold voltages and charge mobilities cause inconsistent luminance across pixels
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage compensation before the display image is displayed. A compensation image with inverted grayscale values is displayed first, causing the OLEDs to undergo reverse aging that compensates for the forward aging effects. This preliminary compensation action ensures that when the actual display image is shown, the luminance consistency is maintained despite variations in transistor characteristics and OLED deterioration.
Solution Approach 2:
The patent implements feedback by measuring the actual luminance output of each pixel and using this information to adjust the driving current for subsequent frames. The compensation image technique creates a feedback mechanism where the display system learns from previous frame performance and automatically adjusts to maintain consistent luminance across all pixels, counteracting the effects of transistor variations and OLED aging.
2Manufacturing precision
If additional compensation circuits are added to compensate for threshold voltage variations, then luminance consistency improves, but device complexity increases
Solution Approach 1:
The patent applies universality by making the existing drive transistors perform multiple functions. The same transistors that control the driving current for display images are also used to control the compensation current during the compensation phase. This multi-functionality eliminates the need for separate compensation transistors and circuits, maintaining luminance consistency without increasing device complexity.
Solution Approach 2:
The patent merges the compensation function with the existing pixel circuit structure. The compensation image display utilizes the same OLEDs, transistors, and control lines that are already present in the display pixel. By combining the compensation operation with the normal display operation using shared components, the patent achieves threshold voltage compensation without adding extra circuitry.
3Manufacturing precision
If compensation operations are performed for each frame, then luminance consistency is maintained, but response time and frame rate are reduced
Solution Approach 1:
The patent applies periodic action by performing compensation operations at specific intervals rather than continuously for every frame. The compensation image is displayed periodically (e.g., once per frame or at predetermined intervals), and during normal display operation, the compensation effects are maintained. This periodic approach balances luminance consistency with response speed, as the compensation is performed only when needed rather than on every single frame.
Solution Approach 2:
The patent performs compensation as a preliminary action before the main display image is shown. By displaying the compensation image first and then immediately showing the actual display image in the same frame period, the system achieves compensation without adding extra frame time. The preliminary compensation action is integrated into the frame structure itself, maintaining high response speed while ensuring luminance consistency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures consistent drive current and luminance across pixels, reducing deviations and improving display quality by compensating for transistor variations and organic light emitting element deterioration.
Implementation Method 1
An organic light emitting display generates images using organic light emitting elements that generate light based on a recombination of electrons and holes in an emission layer
Data Source
AI summary
A pixel of an organic light emitting display includes first through fourth transistors and a capacitor. The first transistor operates based on a scan signal and is connected between a data line and a first node. The capacitor is connected between the first node and a second node. The second transistor operates based on a gate signal and is connected between a first power voltage and a third node. The third transistor operates based on compensation control line signal and is connected between the second node and the third node. The fourth transistor operates based on sensing control line signal and is connected between the data line and the third node. The organic light emitting element is connected between the third node and a second power voltage.