OLED Pixel Circuit Double Gate Transistor Voltage Compensation
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Solution Overview
Problem
OLED displays face display unevenness due to variations in the threshold voltage of driving transistors, leading to inconsistent current intensity and manufacturing process-related uniformity issues in pixel circuits with storage and compensation capacitors.
Innovation Solution
A pixel circuit with a driving transistor having a double gate structure, including a first gate electrode connected to a first node, a second gate electrode connected to a second node, and separate connections for storage and compensation capacitors, which allows for independent voltage compensation and data voltage application, reducing voltage deviations and manufacturing variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel circuit with storage and compensation capacitors is used, then threshold voltage compensation is achieved, but display unevenness occurs due to variations in transistor threshold voltage and capacitance ratios
Solution Approach 1:
The pixel circuit is segmented into multiple independent transistor units, each with its own switching transistor, storage capacitor, and compensation capacitor. This segmentation allows independent threshold voltage compensation for each transistor, eliminating display unevenness caused by manufacturing variations in a single shared transistor
Solution Approach 2:
The circuit uses multiple copies of the same transistor-capacitor unit structure. Each pixel contains replicated circuit elements (switching transistors, storage capacitors, compensation capacitors) that are independently configured, allowing the system to compensate for variations by having redundant, matched pairs of components with identical electrical characteristics
2Reliability
If storage and compensation capacitors are used in the pixel circuit, then voltage compensation is achieved, but display unevenness occurs due to capacitance ratio variations
Solution Approach 1:
The capacitor system is segmented into separate storage capacitors and compensation capacitors for each transistor unit, rather than sharing capacitors across multiple transistors. This segmentation ensures that the capacitance ratio is consistent within each independent unit, eliminating display unevenness caused by variations in shared capacitor ratios
Solution Approach 2:
The circuit employs replicated capacitor structures where each transistor unit has its own matched pair of storage and compensation capacitors. These copied capacitor units are designed with identical electrical characteristics, ensuring consistent capacitance ratios across all pixel circuits and eliminating display uniformity issues
3Device complexity
If a single gate structure is used in the driving transistor, then device complexity is reduced, but voltage deviation occurs due to threshold voltage variations
Solution Approach 1:
The transistor control structure is segmented into multiple independent switching transistors, each with its own gate electrode connected to separate control nodes. This segmentation allows independent voltage control and threshold compensation for each transistor, improving voltage stability without requiring complex multi-gate structures within a single transistor
Solution Approach 2:
The circuit uses multiple copies of simple single-gate transistor structures rather than one complex multi-gate transistor. Each copied transistor unit has identical simple structure but operates independently with its own control signals and compensation capacitors, achieving voltage stability through redundancy rather than structural complexity
Data Source
AI summary
A pixel circuit and an OLED display including the same are disclosed. The pixel circuit includes a driving transistor having a double gate structure, the driving transistor including a first gate electrode electrically connected to a first node, a second gate electrode electrically connected to a second node, a first electrode electrically connected to a first power supply voltage, and a second electrode electrically connected to the anode of the OLED. The pixel circuit also includes a switching transistor including a gate electrode configured to receive a scan signal, a first electrode configured to receive a data voltage, and a second electrode electrically connected to the first node. The pixel circuit further includes a storage capacitor and a compensation capacitor including a first electrode electrically connected to the second node and a second electrode electrically connected to the first electrode of the driving transistor.