Two-Stage Mobility Correction for OLED Drive Transistors
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Solution Overview
Problem
Existing active-matrix display devices with organic EL elements face challenges in achieving uniform image quality due to variations in mobility and threshold voltage of drive transistors, leading to luminance inconsistencies across pixels.
Innovation Solution
A display device with a pixel array and drive part that includes a sampling transistor, drive transistor, hold capacitor, and light-emitting element, where the drive transistor's mobility is corrected using a two-stage potential switching system to optimize mobility correction and maintain uniformity, independent of signal line potential fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-stage potential switching system is used for mobility correction, then the circuit complexity is reduced, but the image quality uniformity deteriorates due to insufficient mobility correction and signal line potential fluctuations
Solution Approach 1:
The mobility correction process is segmented into two distinct stages: a first mobility correction stage and a second mobility correction stage. Each stage operates at different potentials and serves specific correction purposes, allowing comprehensive compensation for transistor mobility variations while maintaining image quality uniformity across the display panel
Solution Approach 2:
The first mobility correction stage is performed preliminarily before the second mobility correction stage. By conducting the first correction at an initial potential level and then performing a second correction at a different potential level, the system proactively compensates for mobility variations across different operating conditions, ensuring consistent image quality
2Ease of operation
If mobility correction is performed without two-stage potential switching, then the drive circuit operation is simplified, but luminance consistency deteriorates due to variations in drive transistor characteristics
Solution Approach 1:
The mobility correction system dynamically adapts to different potential conditions by implementing two distinct correction stages at different voltage levels. The first correction operates at an initial potential while the second correction operates at a different potential, allowing the circuit to dynamically compensate for mobility variations that occur under different operating conditions, thereby maintaining luminance consistency
Solution Approach 2:
The system changes the potential parameter between the two mobility correction stages. By performing the first correction at one potential level and the second correction at a different potential level, the system accounts for mobility variations that depend on the operating potential, ensuring consistent luminance output despite transistor characteristic variations
3Speed
If the sampling transistor is switched only once during the writing period, then the control signal frequency is reduced, but the correction accuracy for drive transistor mobility deteriorates
Solution Approach 1:
The sampling transistor is controlled to switch periodically twice during the writing period: once for the first mobility correction and again for the second mobility correction. This periodic dual switching enables the system to perform corrections at different potential stages, significantly improving the accuracy of mobility correction compared to a single switching event
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
The solution ensures uniform image quality by optimizing mobility correction, reducing streaks and unevenness, and maintaining consistent luminance despite variations in drive transistor characteristics.
Implementation Method 1
The organic EL device is based on a phenomenon that an organic thin film emits light in response to application of an electric field thereto
Data Source
AI summary
In an embodiment of the present invention, a signal driver employs a two-stage system in which the potential of a signal line (SL) is switched from a reference potential (Vofs) to an intermediate potential (Vofs2), and then switched to a signal potential (Vsig) of a video signal. A scanner supplies a first control pulse to a scan line (WS) when the signal line (SL) is at the intermediate potential (Vofs2), and then supplies a second control pulse to thereby turn on and off a sampling transistor T1 when the signal line (SL) is at the signal potential (Vsig). Based on this configuration, two times of mobility correction (μ correction) are carried out.