Organic EL Display Drive Blocks for Luminance Uniformity
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Solution Overview
Problem
Conventional active-matrix organic electroluminescence (EL) display devices face issues with luminance unevenness due to variations in drive transistor characteristics, leading to increased drive circuit output load and limited high-precision threshold voltage correction, especially as display area increases.
Innovation Solution
The display device is organized into drive blocks with two signal lines per pixel column, incorporating switching transistors and capacitors to uniformly correct threshold voltage within each block, reducing signal switching frequency and output load on drive circuits, and allowing a longer threshold voltage correction period without compromising luminescence duty.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If active-matrix organic EL display device is used to enable continuous photon generation and low voltage operation, then power consumption is reduced and luminance stability is improved, but luminance unevenness occurs due to variation in drive transistor characteristics
Solution Approach 1:
The display device is divided into multiple drive blocks, where each block contains multiple pixels that share common control lines. This segmentation allows independent threshold voltage correction for each block while maintaining overall display functionality. The patent applies this by organizing pixels into drive blocks with shared scanning lines, control lines, and signal lines, enabling localized compensation for transistor characteristic variations.
Solution Approach 2:
The patent implements preliminary threshold voltage correction before normal operation by applying a reference voltage to the control line during a correction period. This preliminary action compensates for transistor threshold voltage variations before the actual image display begins, ensuring uniform luminance output. The correction is performed in advance using the holding capacitor to store the corrected voltage level.
2Manufacturing precision
If threshold voltage correction is performed for each pixel row to compensate for transistor variation, then luminance unevenness is reduced, but drive circuit output load increases and correction precision is limited
Solution Approach 1:
Multiple pixels are merged into drive blocks that share common control lines and correction mechanisms. Instead of independently correcting each pixel row, the patent combines multiple pixels into blocks that undergo synchronized threshold voltage correction through shared scanning lines and control lines. This merging reduces the number of separate correction operations and lowers drive circuit output load.
Solution Approach 2:
The control lines and scanning lines serve multiple functions: they are used for both threshold voltage correction and normal image display operation. The same control lines that apply reference voltage during correction also serve as signal lines during operation. This multi-functionality reduces the overall number of lines needed and decreases drive circuit complexity.
3Area of stationary object
If display area is increased to provide larger screen, then display capability is improved, but drive circuit output load increases and threshold voltage correction precision decreases
Solution Approach 1:
The display is segmented into multiple drive blocks that can be corrected independently. This segmentation allows the patent to maintain correction precision even for large display areas by dividing the correction task into manageable units. Each drive block receives synchronized correction signals, ensuring uniform compensation across the entire display regardless of size.
Solution Approach 2:
Threshold voltage correction is performed as a preliminary action before normal display operation begins. By applying the reference voltage and storing the corrected level in the holding capacitor before image display starts, the system ensures that accurate corrected voltages are available for all pixels in the drive block. This preliminary correction maintains precision even as display area increases.
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 improves image display quality by ensuring precise drive current flow to luminescence elements, reducing drive circuit load, and maintaining high luminescence duty even with increased display area, thereby enhancing overall display performance.
Implementation Method 1
Display devices using organic electroluminescence (EL) elements are well-known as display devices using current-driven luminescence elements
Data Source
AI summary
The display device including pixels has formed therein at least two drive blocks each made up of pixel rows. Each of the pixels includes: a drive transistor; a first capacitor element, a luminescence element; a first switching transistor which causes conduction between the drive transistor and the first capacitor element; and a second switching transistor which applies power supply voltage to the drive transistor. Each of the pixels further includes: a third switching transistor connecting a pixel in a k-th drive block and a first signal line; or a fourth switching transistor connecting a pixel in a (k+1)-th drive block and a second signal line. A first control line for controlling conduction of the first switching transistor and a third control line for establishing a source potential of the drive transistor are connected to each of the pixels in a same one of the drive blocks.