Simplified Pixel Circuit for Organic EL Displays
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Solution Overview
Problem
Existing self-luminous flat display devices with organic EL elements face variations in transistor drive characteristics and organic EL element characteristics over time, leading to non-uniform light emission brightness, which complicates the pixel circuit configuration and hinders higher definition displays.
Innovation Solution
A simplified pixel circuit configuration using a P-channel transistor as the drive transistor, a sampling transistor, and a holding capacitor, which corrects threshold voltage and mobility variations, and maintains constant light emission brightness through bootstrapping, reducing the number of transistors and components needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If correction functions are added to each pixel to compensate for transistor and organic EL element characteristic changes, then light emission brightness uniformity is improved, but pixel circuit complexity increases
Solution Approach 1:
The patent merges the correction function and the light emission driving function into a single integrated pixel circuit structure. The sampling transistor Tr1, drive transistor Tr2, and holding capacitor Cs work together to simultaneously perform threshold voltage correction, mobility correction, and brightness control, eliminating the need for separate correction circuits and reducing overall circuit complexity while maintaining uniformity.
Solution Approach 2:
The drive transistor Tr2 serves multiple functions: it acts as both the light emission driving element and the correction element. By using a P-channel transistor with high mobility, the circuit achieves both correction of threshold voltage and mobility variations, and control of light emission brightness through a single component, thereby reducing the number of required transistors and simplifying the pixel circuit configuration.
2Reliability
If multiple transistors and components are used in each pixel for correction functions, then characteristic variations are compensated, but definition quality is reduced due to increased pixel size
Solution Approach 1:
The patent extracts and eliminates unnecessary components from the conventional pixel circuit. By removing redundant transistors and correction circuits, the design achieves characteristic compensation with minimal components - only one sampling transistor Tr1, one drive transistor Tr2, and one holding capacitor Cs are required, thereby reducing pixel area and improving definition quality.
Solution Approach 2:
The patent changes the parameter of transistor type from N-channel to P-channel for the drive transistor Tr2. This parameter change enables the transistor to have higher mobility and better suitability for correction functions, achieving effective characteristic compensation with a simpler circuit structure and fewer components, thus improving both reliability and definition quality.
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 configuration achieves higher definition displays by simplifying the pixel circuit, reducing pixel size, and maintaining uniform light emission brightness despite changes in transistor and organic EL element characteristics, with improved screen uniformity and reduced susceptibility to voltage variations.
Implementation Method 1
a holding capacitor connected between the source and gate of the drive transistor
Implementation Method 2
An organic EL element relies on light emission from an organic thin film when applied with an electric field
Data Source
AI summary
A display device includes: a pixel array section; and a drive section, the pixel array section including scan lines, signal lines, pixels, and power lines, the drive section including a main scanner, a drive scanner, and a signal selector, wherein each of the pixels includes a light-emitting element, sampling transistor, drive transistor, and holding capacitor.