Pixel Circuit With Series Capacitors for Stable Luminance
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Solution Overview
Problem
Display devices face issues in maintaining desired image luminance due to variations in voltage of the first driving power, leading to inconsistent image display.
Innovation Solution
The pixel design incorporates a series connection of a first capacitor and a second capacitor between the first node and the light emitting element's electrode, along with multiple transistors controlled by specific scan and emission control signals to stabilize the voltage of the second node, ensuring consistent luminance regardless of variations in driving power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel circuit is used, then the device complexity is low, but the luminance stability deteriorates due to voltage variation in first driving power
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks: a first transistor for current control, a second transistor for data signal input, a third transistor for initialization, a fourth transistor for emission control, and a capacitor for voltage storage. Each block performs a specific function to collectively stabilize luminance despite voltage variations in the first driving power.
Solution Approach 2:
A capacitor is introduced as an intermediary element between the first transistor and the light emitting element. This capacitor stores the voltage level and acts as a buffer, decoupling the luminance output from voltage fluctuations in the first driving power, thereby ensuring stable image display.
2Reliability
If multiple transistors and capacitors are added to stabilize voltage, then the luminance stability improves, but the device complexity increases
Solution Approach 1:
The first transistor serves multiple functions: it controls the current through the light emitting element based on the stored voltage, and its gate is connected to the capacitor to receive the stabilized voltage level. This multi-functionality reduces the need for additional dedicated components while maintaining voltage stability.
Solution Approach 2:
The capacitor is pre-charged to a specific voltage level corresponding to the desired luminance before the emission phase. This preliminary action ensures that when the light emitting element is activated, the correct voltage is already stored, enabling stable luminance output without requiring continuous voltage regulation during emission.
3Reliability
If the capacitor is connected directly between first node and light emitting element, then the voltage stability improves, but the manufacturing precision requirements increase
Solution Approach 1:
The capacitor is connected through intermediate nodes (first node and second node) and controlled by the second transistor, which acts as a switch. This intermediary connection method provides manufacturing tolerance, as the precise connection points are defined by the transistor gates and terminals rather than requiring direct capacitor-to-electrode alignment.
Solution Approach 2:
The capacitor is strategically positioned and connected only at specific critical nodes (first node and second node) within the pixel circuit, rather than requiring uniform precision across the entire pixel structure. This localized connection approach reduces overall manufacturing precision requirements while maintaining voltage stability where it matters most.
Data Source
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AI summary
A pixel includes a first transistor including a first electrode connected to a first power line, a first gate electrode connected to a first node, and a second electrode connected to a second node, a second transistor connected between a data line and the first node, and including a gate electrode connected to a first scan line, a light emitting element including a first electrode connected to the second electrode of the first transistor, and a second electrode connected to a second power line, and a first capacitor and a second capacitor connected in series between the first node and the first electrode of the light emitting element.