Voltage Compensation Pixel Circuit for OLED Electron Mobility
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Solution Overview
Problem
Conventional voltage driving compensation circuits in active matrix OLED display devices fail to compensate for the difference in electron mobility caused by continuous gate bias, leading to reduced opening ratio and increased charging time, especially in high-resolution and large-sized panels, and require additional signal lines and TFT units, which increase costs.
Innovation Solution
A voltage compensation pixel circuit that includes a driving TFT, multiple switching TFTs, and a storage capacitor, allowing for the adjustment and compensation of critical voltage by charging and discharging voltages through specific TFT operations, enabling electron mobility compensation and stable OLED current supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional signal lines and TFT units are added to compensate for critical voltage changes, then voltage compensation is improved, but pixel area and opening ratio are greatly decreased
Solution Approach 1:
The patent combines the critical voltage compensation function with the existing switching TFTs in the pixel circuit. Specifically, the switching TFTs that are already present for signal routing are made to perform dual functions: signal switching and critical voltage compensation. This merging eliminates the need for separate dedicated compensation TFTs and signal lines, thereby maintaining voltage compensation capability while preserving pixel area and opening ratio.
Solution Approach 2:
The patent makes the switching TFTs universal by enabling them to perform multiple functions. During different time periods, the same switching TFTs are used for signal transmission and for compensating critical voltage changes. The gate electrodes of these switching TFTs are connected to receive compensation signals, allowing them to adjust their threshold voltages to compensate for critical voltage drift without requiring additional dedicated compensation circuitry.
2Speed
If voltage driving compensation is used for fast pixel operating speed, then pixel operating speed is improved, but electron mobility difference is not compensated
Solution Approach 1:
The patent implements a feedback mechanism where compensation signals are generated based on the actual critical voltage changes in the pixel circuit. These compensation signals are fed back to the gate electrodes of the switching TFTs, which then adjust their operating characteristics to compensate for electron mobility differences. This feedback loop enables the voltage driving compensation circuit to dynamically adapt to and correct for TFT parameter variations, achieving both fast operation and mobility compensation.
Solution Approach 2:
The patent changes the electrical parameters (threshold voltage) of the switching TFTs dynamically through applied compensation signals. By adjusting the gate voltage of switching TFTs based on detected critical voltage changes, the circuit compensates for electron mobility differences in real-time, allowing the voltage driving mode to achieve both speed and accuracy.
3Reliability
If storage capacitor is charged by data current in current driving mode, then electron mobility compensation is improved, but charging time is greatly increased
Solution Approach 1:
The patent performs preliminary charging of the storage capacitor using voltage from signal lines before the data current charging phase. By pre-charging the capacitor to a significant portion of the required voltage level, the subsequent charging time when data current flows is greatly reduced. This preliminary action addresses the time loss issue while maintaining the electron mobility compensation capability of the current driving mode.
4Manufacturing precision
If amorphous silicon TFT is used for large sized substrate, then manufacturing uniformity is improved, but electric stability is poor
Solution Approach 1:
The patent uses feedback compensation signals to counteract the electric instability of amorphous silicon TFTs. By continuously monitoring critical voltage changes and applying compensating voltages to the gate electrodes, the system corrects for the threshold voltage drift that occurs in amorphous silicon TFTs under continuous gate bias, thereby maintaining stable operation despite the inherent material limitations.
Solution Approach 2:
The patent dynamically changes the gate voltage parameters of the amorphous silicon TFTs to compensate for their instability. By adjusting the operating point of these TFTs through applied compensation signals, the circuit maintains consistent electrical characteristics despite the material's tendency toward threshold voltage drift, effectively stabilizing the electric properties of amorphous silicon TFTs on large substrates.
Data Source
AI summary
A voltage compensation pixel circuit includes a driving transistor coupled to the light emitting element between a high potential power line and a low potential power line to drive the light emitting element in response to a predetermined voltage applied to a gate, switching transistor including a first switching transistor being switched in response to a voltage of a first gate signal, a second switching transistor and a third switching transistor being switched in response to a voltage of a third gate signal, and a fourth switching transistor being switched in response to a voltage of a second gate signal, a storage capacitor coupled between a first node and a second node, and a setup transistor coupled between the light emitting element and the driving transistor and operated by the driving transistor. The first node is coupled to the driving transistor. The second node is coupled between the second switching transistor and the fourth switching transistor.