Pixel Circuit with Threshold Voltage Compensation for AMOLED Displays
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Solution Overview
Problem
The drifting of threshold voltage in Thin Film Transistors within AMOLED display panels leads to non-uniform image quality and limited application scope, as existing pixel circuits with 3T1C structure are only suitable for Simultaneous Emission mode and not Progressive Emission mode.
Innovation Solution
A pixel circuit with a structure of five transistors and one capacitor, including PMOS type thin film transistors, where the fifth transistor compensates for the degradation of the OLED, allowing the circuit to be used in both SE and PE modes, and includes a method for compensating threshold voltage through a scanning signal and precharge voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a 3T1C pixel circuit structure is used, then threshold voltage compensation can be achieved, but the circuit can only be used in SE mode and not in PE mode
Solution Approach 1:
The pixel circuit is divided into distinct functional modules: a first transistor for data signal input, a second transistor for reference voltage input, a third transistor for driving the OLED, and a storage capacitor for voltage storage. This segmentation allows each component to perform its specific function independently, enabling the circuit to adapt to different driving modes (SE and PE) while maintaining manageable complexity.
Solution Approach 2:
The pixel circuit design achieves multi-functionality by incorporating both SE and PE mode compatibility within the same circuit structure. The circuit can operate in Simultaneous Emission mode where all pixels emit light at the same time, or in Progressive Emission mode where pixels are scanned and emit light sequentially, making it universally applicable to different display device types regardless of size.
2Productivity
If laser scanning is used for crystallization, then manufacturing efficiency is improved, but threshold voltage uniformity deteriorates due to unstable laser beam power
Solution Approach 1:
The pixel circuit incorporates a feedback mechanism through the storage capacitor that compensates for threshold voltage variations. The capacitor stores the voltage difference caused by threshold voltage drift, and this stored voltage is used to compensate for the non-uniformity in subsequent operations, thereby correcting the manufacturing precision issue while maintaining high productivity from laser scanning.
3Duration of action of stationary object
If Thin Film Transistor T2 is driven with positive bias for a long time, then continuous light emission is achieved, but threshold voltage drift occurs
Solution Approach 1:
The circuit performs preliminary action by storing the threshold voltage information in the storage capacitor before the drift becomes problematic. The capacitor captures the voltage state early in the operation, and this stored information is used to compensate for subsequent threshold voltage changes, allowing continuous light emission while maintaining reliability through proactive compensation.
Data Source
AI summary
The present disclosure discloses a pixel circuit, a display panel comprising the pixel circuit, and a display device comprising the pixel circuit. The pixel circuit comprises a first transistor, a second transistor, a third transistor, a fourth transistor, and a fifth transistor. The lifetime of the circuit can be prolonged by the pixel circuit with threshold voltage compensation function of the present disclosure. The pixel circuit can not only be used in large sized display device driven through SE mode, but also be used in medium or small sized display device driven through PE mode.