OLED Pixel Circuit Threshold Compensation via Drive Transistor Merging
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Solution Overview
Problem
Existing display apparatuses using organic light emitting diodes (OLEDs) face challenges in achieving a highly precise structure due to the need for a large number of transistors to compensate for the threshold voltage of drive transistors, which increases the pixel circuit area and complicates precise control.
Innovation Solution
A display apparatus comprising a light emitting element with a capacitor and a drive transistor that controls current flow, where the capacitor is connected to the first electrode to stop current supply to the light emitting element, allowing for precise control and reduced transistor count, thereby minimizing pixel circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large number of transistors are used to compensate the threshold voltage of the drive transistor, then the threshold compensation precision is improved, but the pixel circuit area is increased
Solution Approach 1:
The patent combines the threshold compensation function and light emission control function into a single drive transistor. The drive transistor's gate electrode receives both the data signal and feedback signal from the capacitor, allowing the transistor to simultaneously perform threshold compensation and control light emission. This merging eliminates the need for separate compensation transistors, reducing the pixel circuit area while maintaining compensation precision.
Solution Approach 2:
The drive transistor is designed to perform multiple functions: it acts as both the light emission control transistor and the threshold compensation transistor. By making the drive transistor universal, the patent eliminates redundant components and reduces the overall pixel circuit area while achieving high-precision threshold compensation through the capacitor feedback mechanism.
2Productivity
If the pixel circuit area is reduced, then the number of pixels per unit area is increased, but the complexity of achieving precise structure is increased
Solution Approach 1:
By merging the compensation and control functions into one transistor, the patent simplifies the overall structure despite reducing pixel area. This consolidation reduces the number of interconnections and components, making the precise structure easier to implement and manufacture while increasing pixel density.
Solution Approach 2:
The drive transistor serves itself by receiving feedback from the capacitor connected to its gate. The capacitor stores the threshold voltage information and feeds it back to the gate, allowing the transistor to automatically compensate for its own threshold variations without requiring external compensation circuits, thereby simplifying the structure.
3Measurement precision
If the capacitor is connected to the first electrode to stop current supply, then the control precision is improved, but the power consumption is increased
Solution Approach 1:
The capacitor is periodically connected to and disconnected from the first electrode in synchronization with the light emission control timing. During the light emission period, the capacitor is disconnected to allow current flow and light emission. During non-emission periods, the capacitor is connected to stop current supply and maintain precise control. This periodic action achieves precise control while minimizing power consumption by allowing current flow only when necessary.
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 configuration enables a highly precise structure with reduced pixel area, allowing for more pixels per unit area and improved precision in threshold voltage detection, while also reducing power consumption and preventing degradation in display quality.
Implementation Method 1
a light emitting element including a first electrode, a second electrode and an organic light emitting layer disposed between the first electrode and the second electrode
Data Source
AI summary
Provided is a display apparatus that compensates a drive transistor threshold to attain a highly precise structure. The display apparatus comprises a light emitting element including a first electrode, a second electrode and an organic light emitting layer disposed between the first electrode and the second electrode, and a pixel circuit including a capacitor and a drive transistor letting current according to voltage of the capacitor flow in the light emitting element. The pixel circuit stops supply of current to the light emitting element while connecting the capacitor to the first electrode.