OLED Pixel Circuit with Dual Power Drivers for Threshold Compensation
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Solution Overview
Problem
Active matrix organic light emitting display devices face non-uniformity in display due to threshold voltage differences between driving transistors, which is compensated by additional transistors and capacitors, reducing the aperture ratio and increasing defect possibilities.
Innovation Solution
The implementation of a pixel structure with two transistors and two capacitors, utilizing a concurrent emission method where a reset voltage is applied to initialize the anode electrode of the organic light emitting diode, and separate power drivers to manage voltage levels, allowing for simultaneous emission and compensation of threshold voltage differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a compensating circuit with additional transistors and capacitors is used to compensate for threshold voltage differences, then display uniformity is improved, but the aperture ratio is decreased and the possibility of defect increases
Solution Approach 1:
The patent applies preliminary action by initializing the anode electrode voltage to a predetermined level (lower than the first high level) during a reset period before the concurrent emission period. This preliminary initialization compensates for threshold voltage differences without requiring additional compensating circuitry, thereby maintaining display uniformity while preserving aperture ratio
Solution Approach 2:
The patent changes the parameter of anode electrode voltage by applying a reset voltage that is lower than the first high level during the reset period. This parameter change enables threshold voltage compensation through voltage level adjustment rather than through additional circuit components, resolving the contradiction between display uniformity and aperture ratio
2Manufacturing precision
If a compensating circuit with additional transistors and capacitors is used to compensate for threshold voltage differences, then display uniformity is improved, but the number of components and signal lines increases
Solution Approach 1:
The patent makes the existing transistor and capacitor structure multi-functional. The transistor that controls current to the organic light emitting diode also functions to compensate for threshold voltage differences when the anode electrode is initialized to a predetermined level. This eliminates the need for separate compensating circuitry while maintaining display uniformity
Solution Approach 2:
The pixel circuit performs self-compensation for threshold voltage differences by utilizing its existing components. The initializing transistor and capacitor work together with the driving transistor to automatically compensate for threshold voltage variations without requiring external compensating circuitry, achieving self-service functionality
3Device complexity
If conventional single power driver is used, then device complexity is reduced, but the ability to stabilize display against threshold voltage variations is limited
Solution Approach 1:
The patent segments the power supply function into two separate power drivers: a first power driver that supplies power at a first high level during the emission period, and a second power driver that supplies power at a second low level during the emission period. This segmentation enables independent control of voltage levels to stabilize display against threshold voltage variations while maintaining manageable device complexity
Solution Approach 2:
The patent introduces dynamic voltage level control by having the first power driver supply power at a first high level and the second power driver supply power at a second low level during the emission period. This dynamic adjustment of power levels enables the system to compensate for threshold voltage differences and stabilize display performance
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 approach stabilizes the display by compensating for threshold voltage variations, reducing the number of transistors and signal lines needed, and enables the display of 3D images with improved uniformity and reduced defects.
Implementation Method 1
displays an image using organic light emitting diodes that emit light by the recombination of electrons and holes
Data Source
AI summary
An organic light emitting display device operating in a concurrent (e.g., simultaneous) emission method, which includes a first power driver configured to apply first power, which changes between a first low level and a first high level, to pixels of the display unit, and a second power driver configured to apply second power, which changes between a second low level and a second high level, to the pixels, wherein each of the pixels includes an organic light emitting diode, a driving transistor configured to control an amount of current supplied to the organic light emitting diode, and an initializing transistor coupled to an anode electrode of the organic light emitting diode and configured to be turned on during a reset period in one frame to supply a reset voltage, which is lower than the first high level of the first power, to the anode electrode of the organic light emitting diode.