OLED Pixel Driving Circuit Reverse Bias Reset
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Solution Overview
Problem
Active matrix driving OLEDs (AMOLEDs) face issues with brightness attenuation over time, leading to reduced user experience due to insufficient reverse bias reset in existing pixel driving circuits.
Innovation Solution
A pixel driving circuit comprising multiple thin film transistors and a capacitor that applies a reverse bias voltage to the OLED, increasing the reverse bias time and adjusting the voltage to enhance the light emitting lifetime of AMOLEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a typical pixel driving circuit is used with gate reset voltage Vi set to -3.5V, then data writing time is maintained, but reverse bias reset effect on OLED is insufficient
Solution Approach 1:
The patent divides the reset function into two separate stages: a first reset voltage Vi applied during data writing, and a second reset voltage Vr applied after data writing. This segmentation allows each voltage to be optimized for its specific function without compromising the other, resolving the contradiction between maintaining data writing timing and achieving sufficient reverse bias reset effect.
Solution Approach 2:
The patent applies a preliminary reset voltage Vi before data writing to prepare the OLED, then applies a second reset voltage Vr after data writing to complete the reverse bias reset. This preliminary action ensures that the OLED is properly reset without interfering with the data writing process, thereby maintaining both timing requirements and reset effectiveness.
2Reliability
If the gate reset voltage Vi is lowered to achieve reverse bias reset, then OLED reverse bias effect is improved, but data writing time increases
Solution Approach 1:
By separating the reset function into two distinct voltage stages with different timing, the patent allows the first voltage Vi to be optimized for speed (maintaining normal data writing timing) while the second voltage Vr is optimized for reset effectiveness. This eliminates the need to lower Vi, thus maintaining data writing speed while achieving proper reverse bias reset.
Solution Approach 2:
The patent dynamically adjusts the reset voltage level based on the timing phase: using a moderate voltage Vi during data writing and a stronger voltage Vr after data writing. This dynamic adjustment allows the system to achieve reverse bias reset effect without permanently compromising data writing speed, as the higher voltage is only applied when data writing is complete.
3Duration of action of moving object
If scan signal is kept low for longer duration to increase reverse bias time, then OLED reverse bias time is extended, but response speed decreases
Solution Approach 1:
The patent applies a preliminary reset voltage Vi that begins the reverse bias process early, then follows up with a second reset voltage Vr that extends the reverse bias duration. This preliminary action ensures that the OLED receives adequate reverse bias treatment over an extended period without requiring the scan signal to remain low for the entire duration, thus maintaining response speed while achieving sufficient reverse bias time.
Solution Approach 2:
The patent implements periodic reset actions with two distinct phases: the first reset voltage Vi applied during the data writing phase, and the second reset voltage Vr applied in the subsequent phase. This periodic application of reset voltages ensures the OLED receives adequate reverse bias treatment over an extended period without continuously holding the scan signal low, thereby maintaining response speed while achieving sufficient reverse bias duration.
Data Source
AI summary
A pixel driving circuit includes: a first thin film transistor, a second thin film transistor, a third thin film transistor, a fourth thin film transistor, a fifth thin film transistor, a sixth thin film transistor, a seventh thin film transistor, an eighth thin film transistor, a first capacitor, and an organic light emitting diode (OLED). Gates of the seventh thin film transistor and the eighth thin film transistor respectively input a first scanning signal and a second scanning signal, and when the first scanning signal is at a low level, a reverse bias reset can be performed on the OLED.