OLED Pixel Driving Circuit Brightness Evenness
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Solution Overview
Problem
The existing pixel driving circuits for OLED displays suffer from uneven brightness due to varying threshold voltages of the driving transistor and voltage drops along the power line, leading to poor brightness evenness across the display screen.
Innovation Solution
A pixel driving circuit is designed with a driving transistor, capacitors, and switch transistors that write reference and data levels during specific stages, isolating the driving current from threshold voltage and power supply voltage fluctuations, thereby stabilizing the brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional 2T1C pixel driving circuit is used, then the circuit structure is simple, but the brightness evenness is poor due to threshold voltage variations and power line voltage drops
Solution Approach 1:
The pixel driving circuit is segmented into multiple functional blocks: a driving transistor for current control, a first capacitor for threshold voltage compensation, a second capacitor for data level storage, and a write circuit for voltage writing. This segmentation allows each component to address specific issues (threshold voltage variation, voltage drop) independently, improving brightness evenness while maintaining reasonable overall complexity
Solution Approach 2:
The write circuit performs preliminary action by writing the voltage of the first voltage terminal and the threshold voltage of the driving transistor to the first capacitor before the display stage. This preliminary voltage writing compensates for threshold voltage variations and power line voltage drops in advance, ensuring stable driving current and improved brightness evenness during actual display
2Illumination intensity
If threshold voltage compensation is implemented, then brightness evenness improves, but device complexity increases due to additional capacitors and switch transistors
Solution Approach 1:
The first capacitor serves multiple functions: it stores the threshold voltage of the driving transistor for compensation, and it also stores the voltage of the first voltage terminal for power line voltage drop compensation. The write circuit similarly performs multiple writing operations. This multi-functionality reduces the need for separate dedicated components, improving brightness evenness while controlling the increase in device complexity
Data Source
AI summary
The present disclosure provides a pixel driving circuit, a display device, and a driving method. The pixel driving circuit comprises a driving transistor, a light emitting element, a first capacitor, a second capacitor, a write circuit, and a first switch transistor. The write circuit is configured to write a reference level to a second terminal of the first capacitor during a vertical blanking stage, and write a data level to a second terminal of the second capacitor during a effective display stage. The first switch transistor is configured to write a voltage of a first voltage terminal and a threshold voltage of the driving transistor to a first terminal of the first capacitor during the vertical blanking stage and is turned off during the effective display stage.