Pixel Circuit Transistor Initialization and Driving Control
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Solution Overview
Problem
Existing organic light emitting display technologies face challenges in maintaining consistent gray scale expression due to variations in the operating characteristics of driving transistors, which complicates pixel circuit design and increases the number of transistors required, making it difficult to reduce the scale of pixel circuits.
Innovation Solution
A display apparatus and method that utilize P-type and N-type transistors with control circuits to manage the current and voltage levels for light emitting diodes, including a capacitive element and control lines to supply initialization, gray scale, and compensation voltages, allowing for efficient control of light emission states and reducing the number of transistors in each pixel circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If techniques are used to suppress threshold voltage variation of driving transistors, then gray scale expression is improved, but the number of transistors in each pixel circuit increases
Solution Approach 1:
The patent merges the initialization function and the driving function into a single transistor structure. The initialization transistor serves dual purposes: initializing the pixel during non-light-emitting periods and driving the light emitting diode during light-emitting periods. This consolidation eliminates the need for separate initialization and driving transistors, thereby suppressing threshold voltage variation while maintaining a reduced transistor count in each pixel circuit.
Solution Approach 2:
The patent implements multi-functionality by designing the initialization transistor to perform multiple functions across different time periods. During non-light-emitting periods, it acts as an initialization transistor to reset the pixel state. During light-emitting periods, it transitions to functioning as a driving transistor to control current flow through the light emitting diode. This universal design allows one transistor to replace what would traditionally require multiple specialized transistors, improving gray scale expression without increasing device complexity.
2Device complexity
If the number of transistors in each pixel circuit is reduced, then layout flexibility is improved, but control of light emission becomes more complex
Solution Approach 1:
The patent employs periodic action by controlling the initialization transistor through time-varying voltage signals applied to its gate terminal. During non-light-emitting periods, an initialization voltage is applied to initialize the pixel. During light-emitting periods, a different voltage level is applied to enable the transistor to function as a driving transistor. This temporal separation of functions through periodic voltage control simplifies the transistor count while maintaining ease of operation through systematic voltage sequencing.
Solution Approach 2:
The patent implements dynamics by making the transistor's function change over time rather than being static. The initialization transistor dynamically switches between initialization mode and driving mode based on the operational phase of the display. This dynamic behavior is controlled by varying the gate voltage levels and timing, allowing a single transistor to adapt its function to meet different operational requirements without increasing circuit complexity.
3Device complexity
If threshold voltage variation is not suppressed, then device complexity is reduced, but gray scale expression deteriorates
Solution Approach 1:
The patent implements feedback by utilizing the threshold voltage characteristics of the initialization transistor in a compensatory manner. The transistor's threshold voltage variation is accounted for in the initialization process, and the same transistor's characteristics are leveraged during the driving phase. This feedback mechanism ensures that gray scale expression remains accurate despite threshold voltage variations, achieving precise gray scale control without requiring additional compensation circuits or increasing overall device complexity.
Data Source
AI summary
A display device includes a driving transistor in a pixel circuit. A signal line is connected to a source or drain of the driving transistor. The source or drain of the driving transistor receives a power source voltage, an initialization voltage, and a data voltage through the signal line during different periods of operation. The periods of operation include an emission and non-emission periods.