7T-1C Pixel Circuit for Leakage Control in OLED Displays
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Solution Overview
Problem
Leakage currents in pixel driving circuits of display devices lead to degradation of display quality by altering the current flow through light emitting elements, resulting in reduced image quality and potential afterimages.
Innovation Solution
A 7T-1C pixel structure is implemented, comprising specific transistors and capacitors connected in a manner that controls current flow, including a 7T-1C structure with transistors connected between nodes and power lines, and capacitors to stabilize voltage levels, minimizing leakage and improving display quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel driving circuit is used, then the device complexity is low, but leakage currents occur causing display quality degradation
Solution Approach 1:
The pixel driving circuit is segmented into multiple functional blocks: a driving transistor (T1) for current control, a switching transistor (T2) for signal input, a compensation transistor (T3) for threshold voltage compensation, an emission control transistor (T4) for light output timing, and additional transistors (T5-T7) for enhanced compensation. Each segment performs a specific function to collectively eliminate leakage currents and improve display quality.
Solution Approach 2:
The compensation transistor (T3) performs preliminary compensation for threshold voltage variations before the main driving operation. By pre-adjusting the gate voltage of the driving transistor based on compensation signals, the circuit eliminates leakage currents that would otherwise degrade display quality during subsequent operation.
2Reliability
If transistors and capacitors are added to reduce leakage currents, then display quality improves, but the area of the pixel increases
Solution Approach 1:
Multiple compensation functions are merged into a coordinated system of transistors T3, T5, T6, and T7 that share common nodes and control signals. The capacitors Cst and Chold are strategically placed to serve multiple purposes: stabilizing voltages at different nodes and providing compensation storage. This merging reduces the total area compared to separate independent compensation circuits.
Solution Approach 2:
The capacitors in the circuit serve multiple functions: Cst stabilizes the gate voltage of the driving transistor and provides threshold voltage compensation, while Chold maintains the compensation voltage during the emission period. The additional transistors T5-T7 participate in both compensation and emission control functions, maximizing the utility of each component to minimize pixel area.
3Reliability
If a 7T-1C structure is implemented, then leakage currents are reduced and display quality is enhanced, but the manufacturing process becomes more complex
Solution Approach 1:
The patent implements local quality enhancement by adding specific transistors and capacitors only where needed in the pixel circuit. The compensation transistor T3 and capacitor Cst are placed at the gate of the driving transistor to locally compensate for threshold voltage variations, while T5-T7 and Chold provide localized compensation at other critical nodes. This targeted approach improves display quality without requiring complete redesign of the entire manufacturing process.
Data Source
AI summary
A pixel includes a light emitting element connected between a first power line and a first node, a first transistor including a first electrode electrically connected to the first node, a second electrode electrically connected to a second node, and a gate electrode electrically connected to a third node, a second transistor including a first electrode electrically connected to a data line, a second electrode electrically connected to a fourth node, and a gate electrode to receive a scan signal, a third transistor including a first electrode connected to the first node, a second electrode connected to the third node, and a gate electrode to receive a compensation signal, a fourth transistor including a first electrode electrically connected to the third node, a second electrode electrically connected to the fourth node, and a gate electrode to receive a first light emitting signal, and a first capacitor.