Pixel Circuit Voltage Range Expansion for High PPI Displays
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Solution Overview
Problem
High-density pixel displays for virtual and augmented reality require a narrower pixel pitch, limiting the number of transistors and signal application, which results in decreased luminance accuracy due to a reduced data voltage range as pixels per inch increase.
Innovation Solution
A pixel circuit design incorporating a light emitting element, multiple transistors, capacitors, and specific signal activation periods to expand data voltage range and minimize body effect, allowing for high ppi displays with a reduced number of transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the pixel pitch is narrowed to increase pixels per inch, then the display density is improved, but the data voltage range decreases resulting in reduced luminance accuracy
Solution Approach 1:
The pixel circuit is segmented into multiple functional blocks: a first transistor for driving current control, a second transistor for data voltage application, a first capacitor for voltage storage, and a second capacitor for reference voltage storage. This segmentation allows independent optimization of each function, enabling the circuit to maintain luminance accuracy through proper voltage management even when pixel pitch is narrowed
Solution Approach 2:
The patent employs parameter changes by utilizing multiple voltage levels (data voltage, reference voltage, and their differences) and configuring transistors with specific threshold voltages. The capacitors store voltages at different levels to expand the effective data range, allowing the circuit to overcome the limited voltage swing available in high-density displays and maintain sufficient luminance differentiation
2Device complexity
If the number of transistors is reduced to accommodate narrower pixel pitch, then the device complexity is reduced, but the ability to provide sufficient data voltage range is compromised
Solution Approach 1:
The capacitors in the circuit serve multiple functions: the first capacitor stores both data voltage and reference voltage at different times, while the second capacitor provides reference voltage for comparison. This multi-functionality allows the circuit to achieve sufficient voltage range control with minimal transistor count, as the capacitors compensate for the reduced transistor capability
Solution Approach 2:
The patent introduces a time dimension to the voltage control mechanism by sequentially applying data voltage and reference voltage to the capacitors during different time periods. This temporal dimension allows the circuit to achieve voltage range control that would otherwise require additional transistors operating in parallel, effectively trading time for device complexity
Data Source
AI summary
A pixel circuit includes a light emitting element, a first transistor that provides a driving current to the light emitting element, a first capacitor including a first electrode connected to a control electrode of the first transistor and a second electrode connected to a first electrode of the first transistor, a second capacitor including a first electrode directly connected to the control electrode of the first transistor and a second electrode, and a second transistor that provides a data voltage to the control electrode of the first transistor in response to a write gate signal.