OLED Pixel Circuit Threshold Voltage Compensation
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Solution Overview
Problem
As the resolution ratio of display screens increases, the area of individual pixels decreases, requiring more precise control of driving circuits in OLED displays to maintain current density, while also necessitating compensation for threshold voltage variations caused by production processes, which affects the output current and display quality.
Innovation Solution
A pixel circuit design incorporating a first and second switching transistor, a first and second capacitor, and a driving transistor, where the second capacitor has a greater capacitance value than the first, allowing for extended input range of data voltage and stable current output independent of threshold voltage, thereby improving precision and uniformity of the display.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the area of single pixel is reduced to increase resolution ratio, then the number of pixels per area increases, but the driving current must be reduced which requires higher precision control
Solution Approach 1:
The pixel circuit is segmented into multiple functional modules including switching transistors (T1-T4), capacitors (C1-C3), and a driving transistor, each performing specific functions. This segmentation allows precise control of different signal paths and current components, enabling high precision current control in reduced pixel areas.
Solution Approach 2:
The patent employs multiple capacitors with different capacitance values (C1, C2, C3) to store and regulate voltage signals. By carefully selecting capacitance parameters, the circuit maintains stable gate voltages for the driving transistor, ensuring precise current control even when pixel area is reduced and driving current is lowered.
2Productivity
If the area of single pixel is reduced to increase resolution ratio, then more pixels fit in the same area, but the device complexity increases
Solution Approach 1:
The switching transistors T1-T4 serve multiple functions: T1 and T2 are involved in both data writing and threshold voltage compensation, while T3 and T4 control the light emitting phase and maintain gate voltages. This multi-functionality reduces the need for additional dedicated transistors, managing circuit complexity while enabling advanced features.
Solution Approach 2:
The circuit performs threshold voltage compensation in advance during the compensation phase before the light emitting phase. By pre-adjusting the gate voltage of the driving transistor to compensate for Vth variations, the circuit eliminates the need for complex real-time adjustment mechanisms, simplifying the overall design.
3Reliability
If threshold voltage compensation function is added to the driving circuit, then the influence of Vth change on output current is reduced, but the device complexity increases
Solution Approach 1:
The circuit performs threshold voltage compensation in advance during the compensation phase before the light emitting phase. By pre-adjusting the gate voltage of the driving transistor to compensate for Vth variations, the circuit eliminates the need for complex real-time adjustment mechanisms, simplifying the overall design.
Solution Approach 2:
The pixel circuit uses its own internal transistors and capacitors to perform self-compensation for threshold voltage variations. The compensation is achieved through the interaction of existing circuit elements without requiring external compensation circuits, thereby maintaining simplicity while improving reliability.
Data Source
AI summary
The present disclosure discloses a pixel circuit, a method for driving the same, a display panel and a display device. The pixel circuit includes: a first switching transistor, a second switching transistor, a first capacitor, a second capacitor, a driving transistor, and a light emitting device; where a gate electrode of the first switching transistor is connected with a scanning signal end, a first electrode of the first switching transistor is connected with a reference signal end, and a second electrode of the first switching transistor is connected with a gate electrode of the driving transistor; and a gate electrode of the second switching transistor is connected with a light emitting control signal end, a first electrode of the second switching transistor is connected with a first power supply end, and a second electrode of the second switching transistor is connected with a first electrode of the driving transistor.