Pixel Circuit for OLED Uniform Current Flow
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Solution Overview
Problem
Organic light emitting display devices face challenges in maintaining uniform electric current flow to pixels due to voltage drops, especially at high resolutions and frequencies, leading to deteriorated picture quality as the time for compensating threshold voltage is reduced.
Innovation Solution
The implementation of a pixel circuit with multiple transistors and capacitors that manage the flow of electric current from a first pixel power supply to a second pixel power supply, using compensation power supplies to maintain consistent current flow independent of threshold voltage variations, ensuring that the electric current corresponds to the data signal and power supply voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high resolution and high frequency are implemented, then display quality and speed are improved, but voltage drops increase and threshold voltage compensation time is reduced
Solution Approach 1:
The patent applies preliminary action by introducing compensation transistors and capacitors that pre-compensate for threshold voltage variations before they affect the OLED current. The compensation circuit is activated in advance during specific timing phases to adjust gate voltages, ensuring stable OLED current even at high frequencies where compensation time is limited.
Solution Approach 2:
The patent uses compensation transistors (T3, T4) and capacitors (Cst, Ccomp) as intermediary elements between the data signal path and the OLED. These intermediaries buffer and adjust voltage levels, isolating the OLED from voltage drops and threshold variations caused by high-frequency operation and high-resolution pixel density.
2Measurement precision
If high resolution is implemented, then picture detail is improved, but voltage drops across pixels increase
Solution Approach 1:
The patent applies local quality by implementing pixel-level compensation circuits with individual compensation transistors and capacitors for each pixel. This allows localized adjustment of threshold voltage and current for each pixel, compensating for local voltage drops that occur in high-resolution displays where pixels are densely packed and experience greater voltage variations.
Solution Approach 2:
Compensation transistors and capacitors serve as intermediary elements that buffer voltage drops between the power supply and individual OLEDs. These intermediaries maintain stable voltage levels at each pixel location despite increased voltage drops associated with high-resolution configurations.
3Reliability
If threshold voltage compensation is performed, then current uniformity is improved, but circuit complexity increases
Solution Approach 1:
The patent segments the pixel circuit into distinct functional blocks: data writing transistors (T1, T2), compensation transistors (T3, T4), storage capacitors (Cst, Ccomp), and the OLED. This segmentation allows independent optimization of each function and simplifies the design of compensation mechanisms without requiring complete circuit redesign.
Solution Approach 2:
The compensation transistors and capacitors serve multiple functions: they compensate for threshold voltage variations, store data signals, and maintain gate voltages during different operation phases. This multi-functionality reduces the need for additional dedicated components, thereby limiting the increase in circuit complexity while achieving current uniformity.
4Measurement precision
If compensation time is increased, then threshold voltage accuracy is improved, but display frequency is reduced
Solution Approach 1:
The patent uses periodic action by implementing compensation during specific timing phases (e.g., during horizontal or vertical blanking intervals) rather than continuously. The compensation transistors are activated periodically to adjust threshold voltages, and capacitors maintain these compensated values throughout the display refresh cycle, enabling accurate compensation without reducing display frequency.
Solution Approach 2:
Compensation is performed in advance during timing intervals before the actual display refresh. By completing threshold voltage compensation beforehand and storing the compensated values in capacitors, the system achieves accurate compensation without requiring extended compensation time during the active display period, thus maintaining high display frequencies.
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 solution ensures consistent electric current flow to organic light emitting diodes, independent of threshold voltage variations and voltage drops, thereby enhancing picture quality and preventing cross-talk, even at high resolutions and frequencies.
Implementation Method 1
The organic light emitting diodes used for the organic light emitting display devices include an anode electrode, a cathode electrode, and a light emitting layer formed therebetween. The organic light emitting diode emits light, when electric current flows from the anode electrode and the cathode electrode
Data Source
AI summary
A pixel circuit and an organic light emitting display using the pixel circuit are disclosed. The pixel circuit compensates for variation of the threshold voltage of a driving transistor and for variation in the power supply to the pixel.