Pixel Circuit Sync Transistors for Dynamic Threshold Voltage Control
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Solution Overview
Problem
Conventional back-biasing technologies in organic light-emitting display devices cannot selectively shift the threshold voltage of driving transistors based on operating phases and conditions, limiting the device's ability to optimize performance such as reducing after-image or increasing luminance.
Innovation Solution
A pixel circuit design that includes a switching transistor, a storage capacitor, a driving transistor, an emission control transistor, and sync transistors (source sync, gate sync, and constant-voltage sync transistors) which can be turned on or off in response to specific control signals to selectively shift the threshold voltage of the driving transistor, allowing for dynamic adjustment of the threshold voltage based on operating phases and conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional back-biasing technology is used with a fixed bottom metal electrode connection, then the threshold voltage of the driving transistor can be shifted in one direction, but the device cannot selectively adjust the threshold voltage in different directions according to different operating phases and conditions
Solution Approach 1:
The bottom metal electrode connection is segmented into multiple independent sync transistors (first sync transistor connected to source electrode, second sync transistor connected to gate electrode). This segmentation allows independent control of threshold voltage shifts in different directions by selectively activating specific sync transistors based on operating phases and conditions.
Solution Approach 2:
The bottom metal electrode connection is transformed from a fixed structure to a dynamic one controlled by multiple sync transistors. The threshold voltage shift direction and magnitude can be dynamically adjusted by controlling which sync transistors are activated, enabling adaptive optimization for different operating phases (initializing, compensating, data writing, light-emitting) and conditions (after-image reduction, luminance enhancement).
2Adaptability or versatility
If the bottom metal electrode is connected to only one electrode (source or gate) of the driving transistor, then the threshold voltage can be shifted in a specific direction, but the device loses the ability to shift the threshold voltage in both positive and negative directions
Solution Approach 1:
The multiple sync transistors share the common bottom metal electrode and serve multiple functions: the first sync transistor enables negative direction threshold voltage shifts by connecting to the source electrode, the second sync transistor enables positive direction threshold voltage shifts by connecting to the gate electrode. This multi-functional design allows a single bottom metal electrode structure to achieve bidirectional threshold voltage control.
Solution Approach 2:
The bottom metal electrode acts as an intermediary element that mediates between the sync transistors and the driving transistor. By controlling which sync transistors connect to the bottom metal electrode, the system can indirectly control the threshold voltage shift direction of the driving transistor, enabling bidirectional adjustment without directly modifying the driving transistor structure.
Data Source
AI summary
A pixel circuit including an organic light-emitting element, a switching transistor, a storage capacitor that stores a data signal applied via a data line, a driving transistor that allows a driving current corresponding to the data signal to flow into the organic light-emitting element, an emission control transistor electrically connected to the organic light-emitting element and the driving transistor in series, and sync transistors electrically connected to a bottom metal electrode of the driving transistor. The sync transistors include a first sync transistor electrically connected to a first one selected from a source electrode of the driving transistor, a gate electrode of the driving transistor, the high power voltage, and the low power voltage and a second sync transistor electrically connected to a second one selected from the source electrode of the driving transistor, the gate electrode of the driving transistor, the high power voltage, and the low power voltage.