Organic EL Pixel Initialization Circuit for Bright Dot Suppression
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Solution Overview
Problem
In organic EL display devices employing an internal compensation method, bright dot defects can occur due to voltage fluctuations and leakage currents, affecting image quality and contrast.
Innovation Solution
The display device incorporates a configuration with first and second initialization switching elements in each pixel circuit, where the control terminal of the drive transistor in one pixel circuit is connected to the display element of an adjacent pixel circuit, allowing for efficient initialization and reduced voltage fluctuations during light emission, thereby minimizing bright dot defects without increasing the pixel circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pixel circuit uses an internal compensation method with initialization switching elements, then image quality and contrast are improved by suppressing bright dot defects, but the device complexity increases due to additional switching elements and circuit configuration
Solution Approach 1:
The patent merges the initialization function into the existing pixel circuit by utilizing the drive transistor and adding only one initialization switching element. The initialization switching element is integrated with the drive transistor to form a combined structure that performs both driving and initialization functions, rather than adding completely separate initialization circuitry.
Solution Approach 2:
The drive transistor serves multiple functions: it acts as the primary driving transistor for controlling the display element, and simultaneously serves as part of the initialization path when the initialization switching element is activated. This multi-functional design allows the same transistor structure to perform different operations at different times without requiring separate dedicated components.
2Reliability
If the pixel circuit connects to adjacent pixel circuits for initialization, then voltage fluctuations are suppressed and bright dot defects are prevented, but the area of the pixel circuit increases
Solution Approach 1:
The pixel circuit performs initialization by utilizing its own drive transistor and the initialization switching element within its boundary. The initialization process is self-contained, using the pixel's own components rather than requiring external assistance from adjacent pixels, thereby avoiding area expansion while achieving voltage stabilization.
3Reliability
If the initialization switching element is added to the pixel circuit, then leakage currents are suppressed and bright dot defects are eliminated, but the manufacturing precision requirements increase
Solution Approach 1:
The initialization switching element is designed with specific local characteristics optimized for its initialization function. The switching element has tailored electrical properties (such as threshold voltage and on-resistance) that are specifically suited for controlling the initialization current path, allowing it to effectively suppress leakage currents while maintaining manufacturability through targeted local optimization rather than requiring high precision across the entire circuit.
Data Source
AI summary
The present disclosure discloses a current-driven display device that uses an internal compensation method and can display a good-quality image with no bright dots that are not included in intended display content. In a pixel circuit of an organic EL display device, a voltage of a gate terminal of a drive transistor is initialized before the voltage of a data signal line is written to a holding capacitor via the drive transistor in a diode-connected state. A drain terminal of a first initialization transistor is connected to an anode electrode of the organic EL element in another pixel circuit adjacent to the drain terminal in a scanning signal line extension direction. In a reset period, a path for applying an initialization voltage to the gate terminal is formed by a second initialization transistor of the other pixel circuit, an initialization connecting line, and the first initialization transistor of the pixel circuit.