5T1C Pixel Circuit for OLED Threshold Voltage Compensation
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Solution Overview
Problem
In active matrix OLED displays, the pixel current must be compensated due to threshold voltage shifts and material degradation, leading to potential abnormal displays and compensation invalidation, which existing pixel circuit designs and driving methods fail to effectively address.
Innovation Solution
A pixel circuit with a 5T1C structure, including specific configurations of N-channel and P-channel switching transistors, and a pixel driving method that involves distinct phases for scanning signals and voltage supply stages to ensure proper discharge and communication of voltages across storage capacitors, preventing abnormal displays and compensation issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional 2T1C pixel circuit structure is used, then the device complexity is low, but the reliability is poor due to threshold voltage shift and material degradation causing compensation invalidation
Solution Approach 1:
The pixel circuit is divided into multiple functional modules with specialized transistors: driving transistor M1 for OLED control, switching transistors M2-M5 for signal routing, and capacitor M6 for storage. This segmentation allows each component to perform its specific function optimally, improving overall reliability while maintaining manageable complexity through modular design
Solution Approach 2:
Storage capacitor Cst acts as an intermediary between the data line and the driving transistor gate, maintaining the data voltage during the holding period. This intermediary component ensures stable pixel current by preserving the threshold voltage setting despite threshold voltage shifts and material degradation, thereby improving compensation reliability
2Stability of the object's composition
If data voltage is continuously supplied to compensate for threshold voltage shift, then the brightness stability improves, but abnormal display occurs due to voltage leakage and interference
Solution Approach 1:
The pixel circuit operates in periodic cycles with distinct phases: programming phase when data voltage is applied through switching transistor M2, and holding phase when storage capacitor Cst maintains the voltage through transistor M6. This periodic operation allows voltage compensation while preventing continuous leakage and interference that cause abnormal display
Solution Approach 2:
The harmful effect of voltage leakage is isolated by extracting the data voltage storage function from the driving transistor gate and placing it in a dedicated storage capacitor Cst. This separation allows the gate voltage to be stable during holding phase while the storage capacitor absorbs leakage effects, preventing abnormal display
3Ease of operation
If switching transistors are controlled by single scanning line, then the ease of operation is high, but compensation invalidation occurs due to simultaneous switching conflicts
Solution Approach 1:
The switching control is segmented into multiple scanning lines: first scanning line SCAN1 controls transistors M2 and M4, while second scanning line SCAN2 controls transistors M3 and M5. This segmentation prevents simultaneous switching conflicts and ensures proper timing for voltage programming and holding, maintaining compensation validity while keeping the control structure organized and manageable
Data Source
AI summary
An exemplary pixel circuit includes an OLED, a storage capacitor, a driving transistor and first through fourth switching transistors. The driving transistor is for driving the OLED at a predetermined brightness. The first source/drain electrode of the driving transistor is coupled to a terminal of the storage capacitor, the second source/drain electrode is coupled to the OLED, and the gate electrode is coupled to receive a data voltage through the first switching transistor. Gate-on voltages of the first and second switching transistors are in opposite phases to each other, and the first and second switching transistors are controlled by the same control signal. Likewise, gate-on voltages of the third and fourth switching transistors are in opposite phases to each other, and the third and fourth switching transistors are controlled by the same control signal. A pixel driving method is also disclosed.