Five-Transistor Pixel Circuit for Compact VR/AR Displays
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Solution Overview
Problem
Display devices, particularly those used in VR and AR, face limitations due to the small pixel area which restricts the number of transistors and signal lines, impacting display quality.
Innovation Solution
A pixel design incorporating multiple transistors and capacitors with alternating voltage levels and a light-emitting element, allowing for improved display quality by optimizing transistor operation and reducing the need for additional signal lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the pixel area is reduced to increase PPI for VR/AR applications, then the display resolution and pixel density are improved, but the number of transistors and signal lines that can be accommodated is restricted
Solution Approach 1:
The patent combines multiple functions into fewer transistors. Specifically, the first transistor serves dual purposes: it acts as a driving transistor during the emission period and as a compensation transistor during the compensation period. This merging of functions reduces the total transistor count from the conventional 6-8 transistors to just 5 transistors, thereby accommodating the reduced pixel area while maintaining necessary display functions
Solution Approach 2:
The first transistor is designed with multi-functionality, serving as both a driving transistor and a compensation transistor depending on the operational period. This universal design allows the pixel circuit to perform multiple functions with fewer components, directly addressing the constraint of reduced pixel area while maintaining display quality
2Area of stationary object
If the number of transistors is reduced to accommodate smaller pixel area, then the pixel area is improved, but the display quality and transistor operation control may be compromised
Solution Approach 1:
The patent employs periodic action by dividing the operation into distinct periods: a compensation period where the first transistor compensates for threshold voltage, and an emission period where it drives the light emitting element. The power voltage alternates between first and second voltage levels in different periods, enabling the first transistor to perform different functions at different times. This periodic operation ensures that despite having fewer transistors, the display quality is maintained through proper timing and voltage control
Solution Approach 2:
The patent introduces dynamic voltage control where the power voltage alternates between first and second voltage levels based on the operational period. This dynamic adjustment allows the first transistor to be properly biased for compensation during the compensation period and for driving during the emission period, ensuring reliable operation and maintaining display quality despite the reduced transistor count
3Loss of energy
If conventional pixel circuits are used with alternating voltage levels, then leakage currents occur during voltage transitions, but using optimized transistor control prevents leakage currents
Solution Approach 1:
The patent applies preliminary action by performing compensation for the first transistor's threshold voltage during the compensation period before the emission period begins. The storage capacitor stores the compensated voltage, ensuring that when the emission period starts and voltage levels alternate, the transistor is already properly biased and leakage currents are minimized. This preliminary compensation action prevents leakage issues that would otherwise occur during voltage transitions
Data Source
AI summary
A pixel includes a first transistor including a gate electrode connected to a first node and connected between a second node and a third node, a second transistor including a gate electrode receiving a first power voltage, a first electrode receiving a second power voltage, and a second electrode connected to the third node, a third transistor including a gate electrode receiving a gate signal and connected between a data line and the first node, a fourth transistor including a gate electrode receiving a first emission signal and connected between the gate electrode of the second transistor and the second node, a fifth transistor including a gate electrode receiving a second emission signal and a first electrode connected to the third node, and a light emitting element including an anode electrode connected to the second electrode of the fifth transistor and a cathode electrode receiving a third power voltage.