Pixel Circuit Threshold Voltage Compensation for OLED Uniformity
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Solution Overview
Problem
Existing organic light emitting display devices face challenges in controlling threshold voltage variations across driving transistors, leading to uneven brightness and emission time differences among pixels.
Innovation Solution
The proposed solution involves a pixel structure and driving method that includes specific transistor configurations and timing control to store and compensate threshold voltages, using transistors connected between data and power supplies, capacitors, and initialization power supplies to ensure uniform voltage across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional pixel structures are used, then device complexity is reduced, but threshold voltage variations cause uneven brightness and emission time differences
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage compensation before the pixel operates normally. The compensation transistor and capacitor are configured to pre-adjust the threshold voltage of the driving transistor during an initialization period, ensuring that all pixels start with compensated threshold voltages. This preliminary compensation action eliminates subsequent brightness uniformity issues without requiring continuous complex control mechanisms during operation.
Solution Approach 2:
The patent introduces a compensation transistor and capacitor as intermediary elements between the power supply and the driving transistor. These intermediary components facilitate the threshold voltage compensation process by providing a controlled path to adjust and store the compensated voltage, thereby mediating the effect of threshold voltage variations on pixel uniformity without directly modifying the driving transistor structure.
2Manufacturing precision
If threshold voltage compensation is implemented, then brightness uniformity is improved, but the pixel structure becomes more complex
Solution Approach 1:
The patent applies segmentation by dividing the pixel circuit into distinct functional modules: a driving transistor for current control, a compensation transistor for threshold voltage adjustment, and a capacitor for voltage storage. This segmentation allows each component to perform its specific function efficiently, achieving precise threshold voltage control while maintaining a manageable structure through clear functional separation rather than a monolithic complex design.
3Duration of action of stationary object
If multiple transistors and capacitors are added for compensation, then emission time uniformity is improved, but device complexity increases
Solution Approach 1:
The patent implements periodic action by structuring the operation into distinct periods: an initialization period where the compensation transistor and capacitor adjust and store the compensated threshold voltage, and an emission period where the stored compensation is applied. This periodic structure ensures that threshold voltage compensation occurs systematically before each emission cycle, maintaining consistent emission timing across all pixels through regular, rhythmic compensation actions rather than continuous complex control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively compensates for threshold voltage variations, eliminating uneven brightness and emission time differences, thereby enhancing the uniformity and reliability of organic light emitting display devices.
Implementation Method 1
An organic light emitting device may display an image by using an organic light emitting diode that generates light by recombination of electrons and holes
Data Source
AI summary
A pixel includes a first transistor connected between a data line and a first node, a second transistor including a second electrode connected to a second node, and a gate electrode connected to the first node, a third transistor connected between a reference power supply and the first node, a fourth transistor including a first electrode connected to a first power supply, and a second electrode connected to a first electrode of the second transistor, a capacitor including a first electrode connected to the first node, and a second electrode connected to the second node, an organic light emitting diode connected between the second node and a second power supply, a fifth transistor connected to an anode of the organic light emitting diode, and a sixth transistor including a first electrode connected to the fifth transistor, and a second electrode connected to an initialization power supply.