Pixel Circuit Overlapping Data Line for Brightness Uniformity
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Solution Overview
Problem
Existing organic EL display technologies face challenges in maintaining uniform emission brightness due to variations in threshold voltage (Vth) and mobility characteristics across pixels, leading to non-uniformity and reduced reliability.
Innovation Solution
A pixel circuit design featuring a first storage capacitor overlapping the data line, allowing for large capacitance storage and effective threshold voltage compensation, along with a control method to correct both threshold voltage and mobility variations, ensuring uniform brightness across a wide gradation range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the first storage capacitor Cc is made larger to maintain dynamic range of gradation signal voltage, then brightness uniformity is improved, but the surface area of the opening section increases making it difficult to ensure reliability
Solution Approach 1:
The first storage capacitor Cc is positioned to overlap with the data line in the vertical dimension rather than occupying horizontal pixel area. This spatial reconfiguration allows the capacitor to achieve large capacitance value without increasing the opening section surface area, thus maintaining brightness uniformity while preserving element reliability.
2Manufacturing precision
If Vth correction circuit is implemented to correct threshold voltage variations, then brightness uniformity is improved, but mobility variations cannot be corrected and wide gradation range brightness uniformity remains difficult to ensure
Solution Approach 1:
The circuit implements feedback mechanisms where the first storage capacitor Cc stores threshold voltage information and the second storage capacitor Cs stores mobility information. These stored values are fed back to compensate for transistor parameter variations, enabling correction of both Vth and mobility effects across wide gradation ranges.
Solution Approach 2:
The invention changes the operational parameters of the driving transistor by dynamically adjusting gate voltage based on stored Vth and mobility values. This allows the circuit to adapt to different transistor characteristics and maintain uniform brightness across wide gradation ranges despite manufacturing variations.
3Manufacturing precision
If the first storage capacitor Cc occupies large surface area to avoid dynamic range reduction, then brightness uniformity is improved, but the opening section area increases reducing current density control
Solution Approach 1:
By positioning the first storage capacitor Cc to overlap the data line vertically, the design achieves large capacitance without consuming horizontal pixel area. This maintains the opening section area and current density control while providing sufficient capacitance for Vth compensation and brightness uniformity.
Data Source
Figure 1
Figure 2A~2B
Figure 2C
AI summary
To efficiently execute threshold value compensation for a driving transistor for an electroluminescent element. A first storage capacitor has a first terminal connected to a data line. A first terminal of a switching transistor and a first terminal of a reset transistor are connected to a second terminal of the first storage capacitor. The first storage capacitor is formed overlapping a data line.