OLED Drive Transistor Threshold Correction via Acceleration Potential
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Solution Overview
Problem
Organic electroluminescence (EL) display devices face challenges in achieving high luminance, high definition, and high frame rates due to luminance unevenness across pixels, which is exacerbated by the difficulty in efficiently canceling threshold voltage variations in drive transistors, particularly at higher frequencies.
Innovation Solution
A display device with a pixel array featuring a drive transistor, storage capacitor, and threshold correction operation, where the gate potential is initially set to a correction acceleration potential higher than the reference potential during the first half of the threshold correction operations, then returned to the reference potential, to rapidly converge the voltage between the gate and source to the threshold value, thereby accelerating the threshold correction process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the threshold correction operation is performed multiple times with the gate potential fixed at the reference potential, then the threshold voltage is accurately corrected, but the correction time becomes too long to achieve high frame rates
Solution Approach 1:
The gate potential is preliminarily set to the correction acceleration potential (higher than reference potential) before the threshold correction operation begins. This preliminary action accelerates the convergence speed of the threshold correction by increasing the initial voltage difference, allowing the correction to complete faster while maintaining accuracy. After the accelerated correction, the gate potential is returned to the reference potential for normal operation.
2Productivity
If the frame rate is increased to achieve high definition display, then the response speed improves, but the threshold correction operation cannot be completed accurately within the shorter time period
Solution Approach 1:
The gate potential is dynamically adjusted during the threshold correction operation. It is temporarily raised to the correction acceleration potential during the correction phase to speed up convergence, then returned to the reference potential for normal display operation. This dynamic adjustment allows accurate threshold correction to be completed within the shorter time periods required for high frame rates.
3Speed
If the gate potential is continuously kept at the correction acceleration potential, then the threshold correction speed is maximized, but the power consumption increases and normal display operation is affected
Solution Approach 1:
The correction acceleration potential is applied periodically and temporarily only during the threshold correction operation, not continuously. The gate potential is switched between the correction acceleration potential (during correction) and the reference potential (during normal display). This periodic application achieves fast correction when needed while minimizing power consumption during normal operation.
Data Source
AI summary
A display device includes: a pixel array including pixel circuits arranged in a matrix, each pixel circuit having a light emitting element, a drive transistor, and a storage capacitor storing a threshold voltage of the transistor and an inputted signal value; and a threshold correction operation means for performing a threshold correction operation plural times, which allows the storage capacitor to store the threshold voltage by applying a drive voltage to the transistor in a state where a gate potential of the transistor is fixed in a reference potential before giving the signal value to the storage capacitor. The threshold correction operation is started in a state where the gate potential is made a correction acceleration potential higher than the reference potential only at the threshold correction operation of the first half in the plural threshold correction operations, then, returns the gate potential to the reference potential to be fixed.