OLED Pixel Circuit Third Transistor Voltage Stress Relief
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Solution Overview
Problem
The degradation of driving transistors in organic light emitting display apparatuses due to continuous voltage stress leads to shifts in threshold voltage, affecting the brightness and longevity of OLEDs.
Innovation Solution
Incorporating a third transistor and a capacitor configuration that applies a second scan signal to discharge charges from the capacitor, thereby reducing voltage stress on the driving transistor, and including this configuration within the pixel area or non-pixel area to maintain constant brightness and extend the durability of the pixel circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a general 2-transistor 1-capacitor circuit is used to drive OLED pixels, then the device complexity is reduced, but the driving transistor degrades due to continuous voltage stress, causing threshold voltage shifts and brightness alteration
Solution Approach 1:
The pixel circuit is segmented into multiple functional blocks: a driving transistor for current control, a switching transistor for signal input, a capacitor for voltage storage, and a third transistor specifically for stress relief. This segmentation allows each component to have a specialized function, with the third transistor dedicated to preventing degradation of the driving transistor by periodically releasing accumulated voltage stress.
Solution Approach 2:
The third transistor is activated before the driving transistor accumulates excessive voltage stress. By applying a reset signal to the third transistor, the capacitor is pre-charged or discharged to prevent the driving transistor from experiencing harmful voltage levels, thereby proactively preventing degradation before it occurs.
2Illumination intensity
If continuous voltage is applied to the gate electrode of the driving transistor to maintain OLED brightness, then the OLED luminance is maintained, but the threshold voltage of the driving transistor shifts due to voltage stress
Solution Approach 1:
The circuit implements periodic action by using the third transistor to periodically release voltage stress from the driving transistor's gate electrode. While the driving transistor maintains continuous current flow to the OLED for stable brightness, the third transistor periodically activates to discharge the capacitor or adjust the gate voltage, thereby cyclically relieving stress and preventing threshold voltage drift.
Solution Approach 2:
The circuit dynamically changes the voltage parameter at the gate electrode of the driving transistor. By controlling the third transistor to periodically adjust the capacitor's charge state, the gate voltage is modulated to maintain the required drive current while periodically reducing the voltage stress level, thus changing the voltage parameter to balance brightness maintenance with transistor protection.
3Reliability
If the third transistor is included in the pixel area to reduce voltage stress, then the driving transistor durability is improved, but the aperture ratio may be compromised
Solution Approach 1:
The third transistor is implemented using thin-film transistor (TFT) technology, which allows for compact and flexible integration. The TFT structure enables the transistor to occupy minimal space while still providing the necessary electrical functions, thus reducing the impact on the pixel aperture ratio while maintaining driving transistor durability through stress relief.
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
Prevents the degradation of driving transistors, maintains constant brightness, and increases the durability of the pixel circuit by reducing voltage stress, while allowing for either front or bottom emission types without compromising the aperture ratio.
Implementation Method 1
organic light emitting diode generating light
Data Source
AI summary
An organic light emitting display apparatus capable of preventing degradation of a driving transistor includes a third transistor in the pixel circuit with the third transistor removing a voltage stress applied to a gate electrode of the driving transistor by applying a ground voltage to the gate electrode of the first transistor according to a second scan signal. The third transistor is different from the driving transistor and the switching transistor. A method of driving the organic light emitting display apparatus is also provided.