AMOLED Pixel Circuit Threshold Voltage Compensation
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Solution Overview
Problem
Active matrix organic light emitting displays (AMOLEDs) face challenges with display non-uniformity due to transistor threshold voltage deviations, which complicates manufacturing and hinders high-speed scan driving, increasing the complexity of the circuit and reducing the aperture ratio, making it difficult to implement high-speed scan driving and 3D display effectively.
Innovation Solution
The implementation of a pixel circuit with three transistors and two capacitors in each pixel, utilizing a simultaneous emission scheme where all pixels receive control signals and power voltages at different levels concurrently, allowing for threshold voltage compensation and high-speed driving, thereby reducing the number of transistors and signal lines, and enabling efficient 3D display performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a compensation circuit with additional transistors and capacitors is added to each pixel, then threshold voltage compensation is improved, but device complexity increases and aperture ratio is reduced
Solution Approach 1:
The patent combines the threshold voltage compensation function with the existing pixel circuit operations by utilizing the same transistors and capacitors during different time periods. The pixel circuit performs both data writing and threshold voltage compensation without requiring separate dedicated compensation components, thereby merging multiple functions into a unified circuit structure.
Solution Approach 2:
The existing pixel circuit components (transistors and capacitors) are designed to serve multiple functions: data writing, threshold voltage compensation, and display driving. The same hardware resources are reused across different operational phases, making the circuit universal and eliminating the need for additional specialized components.
2Manufacturing precision
If a compensation circuit with additional transistors and capacitors is added to each pixel, then threshold voltage compensation is improved, but aperture ratio is reduced
Solution Approach 1:
The patent merges the threshold voltage compensation function with the existing pixel circuit by using the same transistors and capacitors during different time periods. This eliminates the need for additional dedicated compensation components that would occupy extra area, thereby maintaining a high aperture ratio while achieving effective threshold voltage compensation.
3Speed
If scan driving speed is increased to reduce screen motion blur, then response speed is improved, but charging time per scan line is reduced
Solution Approach 1:
The patent performs threshold voltage compensation and data writing operations during the same time period through concurrent writing. By preparing and writing data to the pixel circuits simultaneously with compensation operations, the system ensures that pixel circuits are fully prepared before the emission period begins, enabling high-speed scan driving without sacrificing charging time.
Solution Approach 2:
The patent maintains continuous useful action by overlapping the data writing period with the threshold voltage compensation period. Both operations occur concurrently during the same time window, ensuring that no time is wasted and the pixel circuits are fully prepared before emission, thereby supporting high refresh rates.
4Manufacturing precision
If multiple transistors are added to each pixel for compensation, then threshold voltage compensation is improved, but the probability of defects increases
Solution Approach 1:
The patent merges the threshold voltage compensation function with the existing pixel circuit by using the same transistors and capacitors during different time periods. This eliminates the need for additional dedicated compensation components, thereby reducing the total number of components in each pixel and lowering the probability of manufacturing defects while achieving effective threshold voltage compensation.
Data Source
AI summary
An organic light emitting display includes a display unit that includes pixels coupled to scan lines, control lines, and data lines; a control line driver for providing control signals to the respective pixels through the control lines; a first power driver for applying a first power to the pixels of the display unit; and a second power driver for applying a second power to the pixels of the display unit, wherein the first power and/or the second power is applied to the pixels of the display unit, having voltage values at different levels, during periods of one frame, and the control signals and the first and second powers are concurrently provided to all of the pixels.