Switch Transistor Isolates Organic EL From Reverse Bias
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Solution Overview
Problem
In active matrix image display devices using organic EL elements, the variation in threshold voltage of driving transistors can lead to degradation in image quality, and maintaining the organic EL elements in a reverse-biased state during non-emission periods risks their destruction.
Innovation Solution
An image display device with a switch transistor between the driving transistor and the light emitting element, where the switch transistor is set to an off state during non-emission periods, allowing for correction of threshold voltage variations without applying a reverse bias to the organic EL element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the organic EL element is maintained in a reverse-biased state during non-emission periods to correct threshold voltage variations, then the threshold voltage correction is achieved, but the organic EL element may be destroyed due to reverse bias
Solution Approach 1:
A switch transistor is introduced as an intermediary component between the driving transistor and the organic EL element. During non-emission periods, the switch transistor is turned off to isolate the organic EL element from reverse bias while allowing the driving transistor to undergo threshold voltage correction. This mediator protects the organic EL element from harmful reverse bias conditions while enabling necessary electrical adjustments to the driving transistor.
2Reliability
If a switch transistor is added to protect the organic EL element during non-emission periods, then the organic EL element is protected from reverse bias, but the device complexity increases
Solution Approach 1:
The switch transistor serves multiple functions: it protects the organic EL element from reverse bias during non-emission periods, enables threshold voltage correction of the driving transistor, and can be integrated into existing pixel circuit architectures. By making this single component multi-functional, the patent reduces the need for additional separate protection circuits, thereby limiting the increase in overall device complexity.
Data Source
AI summary
An image display device and method of driving an image display device with alternative repeating of an emission period during which the light emitting element is made to emit light and a non-emission period during which light emission of the light emitting element is stopped. The terminal voltage of a storage capacitor is set to the voltage of a signal line, whereby light emission luminance of the light emitting element in a next emission period is set.