OLED Pixel Circuit Leakage Prevention via Storage Capacitor
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Solution Overview
Problem
In OLED display panels, oxide Thin Film Transistors (TFTs) experience electric leakage when a negative bias voltage is applied, leading to a negative shift in threshold voltage, which causes display issues due to incomplete switching during the light emitting phase.
Innovation Solution
A pixel circuit design incorporating a driving sub-circuit with a storage capacitor, a writing sub-circuit, a reset sub-circuit, and a light emitting sub-circuit, utilizing N-type etching stopper oxide TFTs to manage gate-source voltage and prevent electric leakage by maintaining the driving transistor turned on, thereby ensuring continuous light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a negative bias voltage is applied to the oxide TFT gate-source voltage, then the threshold voltage shifts negatively, but this causes electric leakage in the oxide TFT acting as a switch during the light emitting phase
Solution Approach 1:
The pixel circuit is divided into multiple functional sub-circuits: a writing sub-circuit (with first and second transistors) for data input, a driving sub-circuit (with driving transistor and first storage capacitor) for maintaining the on-state, and a reset sub-circuit (with fourth transistor) for initialization. This segmentation allows each transistor to operate in optimized conditions, preventing the electric leakage problem while maintaining reliable switching.
Solution Approach 2:
The writing sub-circuit writes the data voltage into the driving transistor in advance during the writing phase, and the first storage capacitor pre-charges to maintain the gate-source voltage. This preliminary action ensures the driving transistor remains in a stable on-state before the light emitting phase begins, preventing electric leakage caused by threshold voltage shifts.
2Use of energy by moving object
If the driving transistor is turned off to save power, then energy consumption decreases, but the light emitting phase cannot proceed properly
Solution Approach 1:
The first storage capacitor continuously maintains the gate-source voltage of the driving transistor in the on-state throughout the light emitting phase. This continuous action ensures uninterrupted light emission while the transistor remains conductive, resolving the contradiction between power saving and functional reliability.
3Ease of operation
If the threshold voltage shifts negatively, then the transistor conducts more easily, but electric leakage occurs during the light emitting phase
Solution Approach 1:
The first storage capacitor acts as an intermediary element that stabilizes the gate-source voltage of the driving transistor. It compensates for threshold voltage shifts by maintaining a constant voltage difference, allowing the transistor to conduct properly without experiencing electric leakage during the light emitting phase.
Data Source
AI summary
The embodiments of the present application provide a pixel circuit, a method for driving the same, and a display apparatus. A driving sub-circuit in the pixel circuit includes a driving transistor and a first storage capacitor. The first storage capacitor has a first terminal electrically coupled to a gate of the driving transistor, and a second terminal coupled to a second electrode of the driving transistor. A writing sub-circuit is coupled to a scanning signal line, a data line, and the gate of the driving transistor, and is configured to write a data voltage into the driving transistor and maintain the driving transistor to be turned on. A reset sub-circuit is configured to supply an initial voltage to the light emitting sub-circuit so as to reset the light emitting sub-circuit. The driving transistor is further coupled to the light emitting sub-circuit to drive the light emitting sub-circuit to emit light.