4T2C Pixel Circuit With Global Compensation for Narrow-Pitch Displays
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Solution Overview
Problem
Display devices, particularly those used in virtual and augmented reality, face challenges with reduced pixel circuit area and high integration due to narrowed pitch, leading to restrictions on the number of transistors and signals, which affects emission reliability and integration.
Innovation Solution
A pixel circuit with a 4T2C structure, including a first transistor, second to fourth transistors, and two capacitors, where the threshold voltage of the driving transistor is compensated through a compensation transistor, improving driving and emission reliability, and allowing for high integration by using global signals for compensation and initialization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the pitch of the pixel circuit is narrowed to achieve small area and high integration, then the area of the pixel circuit is reduced, but the number of transistors and signals that can be applied to the pixel circuit is restricted
Solution Approach 1:
The patent merges the compensation transistor and initialization transistor into a single integrated structure that performs both threshold voltage compensation and initialization functions. This consolidation reduces the total number of transistors required in the pixel circuit while maintaining the necessary functionality for reliable operation at narrowed pitches
Solution Approach 2:
The compensation transistor is designed to serve multiple functions: it compensates for threshold voltage shifts, provides initialization voltage, and can be configured to work with global signals that apply to multiple pixel rows simultaneously. This multi-functionality reduces the overall component count and signal requirements
2Device complexity
If the number of transistors in the pixel circuit is reduced to improve integration, then the area is reduced, but the emission reliability may be compromised
Solution Approach 1:
The compensation transistor performs preliminary threshold voltage compensation during the initialization phase before the light emitting element is activated. This advance compensation ensures that the driving transistor operates with accurate threshold voltage, maintaining emission reliability even with fewer transistors in the circuit
Solution Approach 2:
The circuit incorporates feedback mechanisms where the compensation transistor monitors and adjusts the threshold voltage of the driving transistor based on observed shifts. This feedback loop ensures stable emission characteristics are maintained despite the reduced transistor count
3Device complexity
If global signals are used for compensation and initialization, then the integration is improved by eliminating additional drivers, but the signals must be applied simultaneously to multiple pixel-rows
Solution Approach 1:
The global compensation and initialization signals are applied in periodic cycles that synchronize across multiple pixel rows. This periodic application allows the circuit to maintain integration benefits while managing the timing requirements through systematic, repeating cycles of compensation and initialization
Data Source
AI summary
A display device includes a display panel including pixel circuits and a display panel driver. The pixel circuit includes a first transistor including a control electrode connected to a first node, a first electrode receiving a first driving voltage and as second electrode connected to a second node, a second transistor applying a data voltage to a third node in response to a write gate signal, a third transistor connecting the first node and the second node in response to a compensation gate signal, a first capacitor and a light emitting element including a first electrode connected to the second node and a second electrode receiving a second driving voltage. The first driving voltage has a driving-high voltage or a driving-low voltage, and the second driving voltage has the driving-high voltage and the driving-low voltage. The compensation gate signal may be globally applied.