Tandem OLED Pixel Circuit for Brightness Leakage Control
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Solution Overview
Problem
Display apparatuses using tandem light-emitting elements experience brightness changes due to current leakage phenomena, leading to inconsistent image quality.
Innovation Solution
A pixel design incorporating a tandem light-emitting element connected in series with a driving thin-film transistor, storage capacitor, and initialization thin-film transistor, where the initialization voltage is controlled to minimize brightness fluctuations by managing sub-turn-on voltages and threshold compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If tandem light-emitting elements are used to improve display performance, then brightness and image quality are enhanced, but brightness changes occur due to current leakage phenomena
Solution Approach 1:
The patent applies preliminary action by initializing the storage capacitor with a controlled voltage before the light-emitting element operates. The initialization thin-film transistor applies a predetermined initialization voltage to the storage capacitor in advance, ensuring that the driving thin-film transistor starts with a known gate voltage state. This prevents unpredictable brightness changes caused by current leakage during operation, while maintaining the high brightness performance of tandem light-emitting elements.
2Illumination intensity
If higher driving voltage is applied to increase brightness, then illumination intensity improves, but current leakage phenomenon worsens causing greater brightness variation
Solution Approach 1:
The patent implements feedback control through the storage capacitor that maintains a stable gate voltage for the driving thin-film transistor. The capacitor stores the initialized voltage and provides it continuously during operation, creating a feedback mechanism that compensates for voltage drops caused by current leakage. This allows the system to maintain stable brightness even when operating at higher driving voltages to achieve greater illumination intensity.
3Ease of operation
If initialization voltage magnitude is increased to compensate for threshold voltage, then transistor switching improves, but brightness stability deteriorates due to exceeding sub-turn-on voltage
Solution Approach 1:
The patent applies parameter changes by precisely controlling the initialization voltage to fall within a specific range: greater than or equal to the first sub turn-on voltage but less than or equal to the difference between the turn-on voltage and the second sub turn-on voltage. This optimized parameter range ensures that the driving thin-film transistor switches effectively (improving ease of operation) while preventing the light-emitting element from receiving excessive voltage that would cause brightness instability. The careful selection of this voltage window resolves the contradiction between switching performance and brightness consistency.
Data Source
AI summary
A pixel includes a tandem light-emitting element including a first light-emitting element and a second light-emitting element that are connected in series, a driving thin-film transistor electrically connected to the tandem light-emitting element, a storage capacitor electrically connected to a gate electrode of the driving thin-film transistor and the tandem light-emitting element, and an initialization thin-film transistor electrically connected to an electrode of the storage capacitor, an initialization voltage being applied to the electrode of the storage capacitor. The tandem light-emitting element emits light when a voltage equal to a turn-on voltage or more is supplied to the tandem light-emitting element.