Dual Transistor OLED Pixel Circuit for Lifetime Extension
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Solution Overview
Problem
Active matrix organic electroluminescent display devices face reduced transistor lifetime due to continuous current supply and voltage shifts, leading to brightness reduction and display quality degradation, particularly when using amorphous silicon thin film transistors.
Innovation Solution
The implementation of a dual thin film transistor structure with alternating input sequences of image and refresh data for each sub-pixel, where first and second driving transistors are connected in parallel, and switching transistors are controlled by separate gate lines to manage current flow and reduce stress, ensuring continuous light emission without continuous current flow through one transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single thin film transistor is used to drive the organic light emitting diode, then the device structure is simple, but continuous current supply causes threshold voltage shift and reduced transistor lifetime
Solution Approach 1:
The patent divides the single driving transistor into two separate thin film transistors (first and second driving transistors) that operate alternately. Each transistor handles half of the driving duty cycle, preventing continuous current flow through one transistor. This segmentation reduces threshold voltage shift and extends transistor lifetime while maintaining the overall display function.
2Reliability
If dual thin film transistors are used with alternating data input, then transistor lifetime is extended and stress is reduced, but screen flashing occurs and display quality degrades
Solution Approach 1:
The patent implements periodic alternation between two driving transistors, where each transistor is activated in alternating frames. The first driving transistor drives the OLED in odd frames while the second drives in even frames. This periodic action distributes the electrical stress evenly across both transistors, extending their lifetime without causing visible flashing to humans due to the persistence of vision.
Solution Approach 2:
The patent dynamically switches between two driving paths by controlling which transistor is active in each frame. The data selecting portion dynamically selects between first and second data based on the current frame number, enabling flexible alternation between transistors. This dynamic approach allows the system to maintain display quality while protecting transistor reliability.
3Illumination intensity
If continuous current is supplied to the organic light emitting diode, then light emission is maintained, but brightness reduces and display quality degrades over time
Solution Approach 1:
The patent uses periodic alternation of driving transistors to maintain continuous light emission while reducing cumulative stress. By switching between two transistors in alternating frames, the OLED receives continuous driving current for light emission, but each individual transistor experiences reduced stress duration. This extends the overall display lifetime while maintaining illumination quality.
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 extends the lifespan of thin film transistors, reduces stress, and improves display quality by reversing the input sequence of data per frame, thereby minimizing flash phenomena and enhancing overall display performance.
Implementation Method 1
emitting light from the organic light emitting diode
Data Source
AI summary
An organic electroluminescent display device includes: a plurality of sub-pixels in a matrix form along a plurality of row and column lines and each including a light emitting diode; first and second driving transistors in the sub-pixel, connected in parallel with each other, and connected to the organic light emitting diode; first and second switching transistors in the sub-pixel, and connected to the first and second driving transistors, respectively; first and second gate lines along the row line and connected to the first and second switching transistors, respectively; and a data selecting portion selecting a refresh data or an image data, wherein the data selecting portion selects one of the refresh data and the image data when the first switching transistor is turned on, and selects the other one of the refresh data and the image data when the second switching transistor is turned on, and wherein the plurality of sub-pixels include sub-pixels an input sequence of the refresh data and the image data to which is reversed for a frame.