OLED Luminance Compensation via Reverse Bias Control
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Solution Overview
Problem
Conventional pixel circuits for organic EL display devices fail to adequately mitigate the decrease in luminance due to deterioration over time, leading to screen burn-in and inefficient light emission.
Innovation Solution
An active matrix display device with reverse bias control lines and a compensation unit that supplies a compensation signal based on reverse direction current to the driving unit, allowing for luminance compensation during non-light emitting periods, thereby extending the lifespan of organic EL elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional pixel circuits are used without reverse bias control, then the device structure is simple, but luminance decreases due to organic EL element deterioration over time
Solution Approach 1:
The patent applies preliminary anti-action by implementing reverse bias control that actively counteracts the deterioration effects of organic EL elements before significant luminance loss occurs. The reverse bias control unit applies a reverse voltage during non-light emitting periods to prevent cumulative degradation, thereby maintaining luminance output over extended operational periods and resolving the contradiction between sustained illumination intensity and operational life.
Solution Approach 2:
The patent implements preliminary action by performing compensation operations during non-light emitting periods (such as black screen intervals) before the next light emission cycle begins. The reverse bias control unit utilizes these idle periods to reset and compensate for deterioration effects, ensuring that the organic EL elements are restored to optimal condition before subsequent luminance-critical operations, thus maintaining both luminance quality and extending operational lifespan.
2Illumination intensity
If reverse bias control is implemented to compensate for deterioration, then luminance stability is improved, but device complexity increases due to additional control lines and circuits
Solution Approach 1:
The patent applies universality by designing the reverse bias control unit to perform multiple functions: it provides reverse bias control during non-light emitting periods, supplies compensation signals to counteract deterioration, and integrates with existing pixel circuit structures. This multi-functional approach achieves luminance stability improvement without proportionally increasing device complexity, as the same control infrastructure serves both compensation and normal driving functions.
Solution Approach 2:
The patent implements self-service by enabling the pixel circuit to automatically perform compensation operations using its own internal resources and timing structures. The reverse bias control unit leverages existing non-light emitting periods (such as black screen intervals that already exist in normal display operation) to execute compensation without requiring additional dedicated time slots or external intervention, thereby achieving luminance stability with minimal added complexity.
3Speed
If compensation operations are performed during light emitting periods, then response time is reduced, but light emission quality deteriorates due to interference
Solution Approach 1:
The patent applies periodic action by scheduling compensation operations to occur during regular non-light emitting periods (such as black screen intervals) in a cyclic manner synchronized with the display refresh rate. This periodic timing ensures that compensation is performed at predictable intervals without interfering with light emission quality, while maintaining adequate response speed through consistent, rhythmic compensation cycles that prevent deterioration accumulation.
Solution Approach 2:
The patent implements preliminary action by completing all compensation operations before the next light emission cycle begins. The reverse bias control unit finishes its compensation tasks during the non-light emitting period, ensuring that the organic EL elements are fully restored and stabilized before luminance-critical operations start, thereby eliminating any potential interference between compensation and light emission while maintaining rapid response through advance preparation.
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
The solution effectively mitigates luminance decrease and extends the operational life of organic EL elements by compensating for deterioration through reverse biasing and compensation signals, reducing screen burn-in and maintaining image quality.
Implementation Method 1
an organic EL element which is a light-emitting electrooptical element driven by current
Implementation Method 2
causing the electrooptical element to be reverse biased between the second power source line and the reverse bias control line during the first prescribed period
Data Source
AI summary
In a pixel circuit, during a period during which an organic EL element is not emitting light, transistors are in an “on” state and the organic EL element (OLED) is reversed-biased by a low-level power-supply potential and a reverse-biasing power-supply potential. A reverse-direction voltage determined by a reverse-direction current that depends on the degree to which degradation of the organic EL element has progressed is thus written to a capacitor. A data voltage is then supplied to the capacitor via another capacitor, bringing the drive voltage of a transistor (T2) that controls the current that drives the organic EL element to Vsig+Voledr. This makes it possible to minimize decreases in the emission luminance of an electrooptical element such as an organic EL element due to degradation thereof over time.