Pixel Circuit Layout for High-PPI Luminance Accuracy
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Solution Overview
Problem
The increasing pixels per inch (PPI) in display devices for virtual and augmented reality applications narrows the pitch of pixel circuits, restricting the number of transistors and reducing the data voltage range, leading to decreased luminance accuracy.
Innovation Solution
A pixel circuit design incorporating a light-emitting element, transistors, and capacitors that compensate for threshold voltage variations and minimize body effects, allowing for expanded data voltage range and improved luminance accuracy through voltage distribution and threshold voltage compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the pitch occupied by a pixel circuit is narrowed to achieve low area and high PPI, then the pixel density increases, but the number of transistors that can be accommodated decreases and the data voltage range is restricted
Solution Approach 1:
The patent combines multiple functions into fewer transistors. Specifically, the third transistor serves dual purposes: acting as a switching transistor during the write period and as a current blocking transistor during the emission period. This merging of functions reduces the total transistor count from the conventional 6 transistors to 5 transistors, resolving the contradiction between high PPI and sufficient transistor availability.
Solution Approach 2:
The third transistor is designed to perform multiple roles within the pixel circuit. During the write period, it functions as a switching transistor to enable data voltage writing. During the emission period, it transitions to function as a current blocking transistor to prevent reverse current flow. This multi-functionality allows the pixel circuit to maintain proper operation with reduced transistor count, enabling higher PPI displays.
2Area of moving object
If the pitch occupied by a pixel circuit is narrowed to achieve low area and high PPI, then the pixel density increases, but the data voltage range decreases leading to reduced luminance accuracy
Solution Approach 1:
The patent changes the operational parameters of the third transistor to optimize performance in high PPI displays. By adjusting the width-to-length ratio (W/L) of the third transistor and controlling its threshold voltage, the circuit maintains adequate data voltage range despite the reduced pixel area. This parameter optimization ensures that luminance accuracy is preserved even with narrower pitch and fewer available transistors.
Data Source
AI summary
A pixel circuit comprises a light-emitting element, a first transistor which provides a driving current to the light-emitting element, a first capacitor including a first terminal connected to a first terminal of the first transistor and a second terminal connected to a gate terminal of the first transistor, a second capacitor including a first terminal connected to the gate terminal of the first transistor and a second terminal connected to a second terminal of the first transistor, a second transistor which provides a data voltage to the gate terminal of the first transistor in response to a write gate signal, and a third transistor which connects the second terminal of the first transistor and an anode terminal of the light-emitting element in response to a first emission signal.