Dual-Gate Pixel Circuit for High-PPI Threshold Compensation
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Solution Overview
Problem
Display devices with high PPI (Pixels Per Inch) for VR or AR applications face challenges due to narrow pixel pitch and limited transistor count, leading to restrictions on signal application and visible artifacts from threshold voltage variations.
Innovation Solution
A pixel circuit design utilizing a minimal number of transistors, including a first transistor connected to a data line, a second transistor for compensation, and a third transistor for driving an emission element, with capacitors for threshold voltage compensation, allowing for a smaller area occupation and higher PPI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of transistors in each pixel circuit is reduced to accommodate narrow pitch for high PPI, then the pixel circuit area is reduced and PPI is increased, but threshold voltage variations cause visible artifacts
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage compensation before the pixel circuit operates. A compensation circuit is configured to measure and store the threshold voltage of the driving transistor in advance, then use this stored value to correct subsequent drive currents, preventing visible artifacts caused by threshold voltage variations.
Solution Approach 2:
The patent introduces an intermediary compensation circuit that acts as a mediator between the driving transistor and the light emitting element. This compensation circuit includes additional transistors and capacitors that measure, store, and apply correction signals to compensate for threshold voltage variations, thereby maintaining image quality despite reduced transistor count in the main pixel circuit.
2Reliability
If more transistors are added to each pixel circuit to compensate for threshold voltage variations, then image quality is improved, but the pixel circuit area increases and PPI decreases
Solution Approach 1:
The patent merges the compensation function with the existing pixel circuit structure by integrating compensation transistors and capacitors into the pixel circuit layout. The compensation circuit shares common nodes and signal lines with the main pixel circuit, allowing threshold voltage compensation to be achieved without adding excessive area overhead that would reduce PPI.
3Productivity
If the pixel pitch is narrowed to increase PPI, then the display device resolution is improved, but the number of transistors that can be fitted in each pixel circuit is limited
Solution Approach 1:
The patent segments the pixel circuit into functional modules: a driving transistor for current control, a compensation circuit for threshold voltage measurement and storage, and a light emitting element. This segmentation allows each module to be optimized independently and arranged efficiently in the narrow pitch, reducing overall area while maintaining necessary functionality.
Solution Approach 2:
The patent utilizes another dimension by implementing dual-gate transistors that can be controlled from both front and back gates. This allows the compensation circuit to control the driving transistor's threshold voltage through the back gate, enabling compensation functionality without requiring additional transistor instances that would consume valuable area in the narrow pitch configuration.
Data Source
AI summary
The present application provides a pixel circuit and a display device. The pixel circuit includes a first transistor including a first gate electrode connected to a first node, a first electrode receiving a first power supply voltage, a second electrode connected to a second node, and a second gate electrode connected to a third node, a second transistor configured to connect a data line and the first node in response to a data write gate signal, a third transistor configured to provide a reference voltage to the third node in response to a compensation gate signal, a first capacitor including a first electrode connected to the first node and a second electrode connected to the second node, a second capacitor including a first electrode connected to the second node and a second electrode connected to the third node, and a light emitting element including an anode connected to the second node and a cathode receiving a second power supply voltage.