Pixel Compensating Circuit for AMOLED Brightness Uniformity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In AMOLED display devices, the 2T1C pixel circuit is sensitive to threshold voltage and channel mobility of thin film transistors, leading to uneven brightness due to varying OLED light emission characteristics.
Innovation Solution
A pixel compensating circuit comprising specific thin film transistors and a storage capacitor, where the threshold voltage of the first thin film transistor is compensated by the second thin film transistor, allowing the current through the light emitting device to be independent of the threshold voltage, thereby ensuring uniform brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a 2T1C pixel circuit is used, then the device complexity is reduced, but the brightness uniformity deteriorates due to sensitivity to threshold voltage and channel mobility variations
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage compensation before the light emitting operation. The pixel circuit pre-calculates and stores the compensation value in a capacitor during a first period, then uses this pre-computed compensation to eliminate the threshold voltage impact during the actual light emitting phase, ensuring brightness uniformity without adding excessive complexity
Solution Approach 2:
The patent segments the pixel circuit operation into distinct time periods: a first period for threshold voltage compensation and a second period for light emitting. This temporal segmentation allows the circuit to perform compensation functions separately from the display function, enabling brightness uniformity while maintaining reasonable circuit complexity
2Illumination intensity
If a compensating circuit is added to reduce threshold voltage influence, then the brightness uniformity is improved, but the device complexity increases
Solution Approach 1:
The patent merges the threshold voltage compensation function with the existing pixel circuit structure. By integrating the compensation capability into the pixel circuit itself rather than adding a completely separate compensation circuit, the solution improves brightness uniformity while minimizing the increase in device complexity
Solution Approach 2:
The pixel circuit is designed to perform multiple functions: it serves as both the light emitting driver and the threshold voltage compensator. The same transistors and capacitors are used for both compensation and driving operations at different time periods, reducing the need for additional components and maintaining circuit simplicity
3Device complexity
If the threshold voltage drift is not compensated, then the device complexity remains low, but the manufacturing precision deteriorates due to uneven brightness
Solution Approach 1:
The pixel circuit performs self-compensation for threshold voltage drift by automatically detecting and correcting its own threshold voltage variations. Each pixel independently measures and compensates for its threshold voltage, eliminating the need for external compensation circuits and maintaining low device complexity while achieving high manufacturing precision
Data Source
AI summary
In the compensating circuit, a second thin film transistor (TFT) are connected to a gate and drain of a first TFT, and a source of the first TFT receives a constant DC voltage signal, and the second TFT receives a scan signal of nth stage; a third TFT is connected to the drain of the first TFT, is connected to a common ground through a light emitting device, and receives an enable signal; a fourth TFT receives a scan signal of n−1th stage, and is connected to a first end of a storage capacitor and the gate of the TFT, and a second end of the storage capacitor is connected to a fifth TFT and a sixth TFT; the fifth TFT receives a data signal and the scan signal of nth stage, respectively; the sixth TFT is connected to the common ground and receives the enable signal, respectively.