OLED Pixel Circuit Separating Initialization and Compensation
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Solution Overview
Problem
In organic light emitting displays, the variation in threshold voltages of driving transistors leads to non-uniform image brightness, and existing solutions that concurrently perform initialization and compensation for these voltages result in unwanted emission and degraded contrast ratio, particularly in larger displays.
Innovation Solution
A pixel circuit design that separates initialization and compensation processes, using a specific configuration of NMOS transistors and capacitors to manage scan and data signals, allowing for sequential initialization and compensation, thereby preventing unwanted emission and improving contrast ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If initialization and compensation are performed concurrently in existing pixel circuits, then the circuit structure is simplified, but unwanted emission occurs and contrast ratio is degraded
Solution Approach 1:
The patent divides the initialization and compensation processes into separate time periods by introducing multiple scan lines (first scan line for initialization, second scan line for compensation). This segmentation allows the pixel circuit to perform initialization and compensation sequentially rather than concurrently, preventing unwanted emission while maintaining image uniformity.
2Object-affected harmful factors
If initialization is performed before compensation in the proposed pixel circuit, then contrast ratio is improved, but the timing sequence becomes more complex
Solution Approach 1:
The patent applies preliminary action by performing initialization in advance before compensation. The first scan line activates the initialization transistor to reset the node voltage before the second scan line performs compensation. This preliminary initialization ensures that subsequent compensation operations start from a known state, improving contrast ratio while the timing complexity is managed through systematic scan line sequencing.
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 brightness by compensating for threshold voltage variations without concurrent initialization and compensation, reducing unwanted emission and improving contrast ratio, especially in larger displays.
Implementation Method 1
organic light emitting displays display images using organic light emitting diodes (OLEDs), which generate light via recombination of electrons and holes
Data Source
AI summary
Pixel circuits and an organic electroluminescent display including the same are provided. The pixel circuit includes: an organic light emitting diode; a fifth transistor coupled to a third scan line, a reference power source, and a first node; a first capacitor coupled between the first node and a second node; a second capacitor coupled between the first node and the organic light emitting diode; a fourth transistor coupled to a second scan line, a data line, and the first node; a sixth transistor coupled to a first scan line, a first power source, and the second node; a second transistor coupled to the second scan line, the second node, and a third node; a third transistor coupled to an emission control line, the first power source, and the third node; and a first transistor coupled to the second node, the third node, and the organic light emitting diode.