Pixel Circuit Threshold Voltage Compensation
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Solution Overview
Problem
Low temperature poly-silicon thin-film transistors in display panels exhibit varying threshold voltages due to unstable excimer laser annealing, leading to differences in grain size and number across regions, which complicates the circuit structure and reduces the aperture ratio of display panels.
Innovation Solution
A pixel circuit design that includes a light emitting element, two driver transistors, and a compensation capacitor, where the control terminal of the first driver transistor receives a data signal, and the voltage of a compensation node between the compensation capacitor and the second driver transistor is twice the voltage of the second driver transistor's control terminal, effectively simplifying the circuit architecture and compensating for threshold voltage variations without additional control signal lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If in-pixel compensation technique is used to compensate for threshold voltage variation, then the threshold voltage variation is compensated, but the circuit structure becomes complicated and aperture ratio decreases
Solution Approach 1:
The patent extracts the compensation function from a complex in-pixel compensation circuit and implements it through a simplified dual-transistor structure. By taking out only the essential compensation elements (two driver transistors and one compensation capacitor) and removing unnecessary circuit components, the design achieves threshold voltage compensation while maintaining a simple circuit structure that preserves aperture ratio.
Solution Approach 2:
The pixel circuit is segmented into two distinct driver transistors (first driver transistor and second driver transistor) with separate functions. The first driver transistor handles the data signal input, while the second driver transistor is specifically dedicated to compensation operations. This segmentation allows each transistor to be optimized for its specific function, achieving effective compensation without requiring a complex unified circuit structure.
2Measurement precision
If more control signal lines are added to achieve compensation, then the compensation precision is improved, but the circuit complexity increases
Solution Approach 1:
The control terminal of the first driver transistor serves multiple functions: it receives the data signal during the data input period and simultaneously functions as a compensation node during the compensation period. This multi-functionality eliminates the need for separate control signal lines for data input and compensation operations, achieving precise compensation while minimizing the number of control signal lines required.
Solution Approach 2:
The pixel circuit operates in periodic cycles, alternating between a data input period and a compensation period. During the data input period, the control terminal receives the data signal. During the compensation period, the same control terminal serves as the compensation node, and the voltage relationship (compensation node voltage being twice the second driver transistor control terminal voltage) establishes precise compensation. This periodic operation allows one control signal line to perform multiple functions without sacrificing compensation precision.
Data Source
AI summary
A pixel circuit includes a light emitting element, a first driver transistor, a second driver transistor, and a first compensation capacitor. A first terminal of the first driving transistor is configured to receive a power signal, and a second terminal of the first driving transistor is electrically coupled to the light emitting element. A first terminal of the second driving transistor receives the power signal, and a control terminal of the second driving transistor is electrically coupled to the light emitting element. The first compensation capacitance is electrically coupled to a control terminal of the first driving transistor and the second terminal of the second driving transistor, respectively.