OLED Pixel Circuit Capacitance Ratio Threshold Compensation
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Solution Overview
Problem
OLED display devices face issues with threshold voltage variation in driving transistors, leading to non-uniform brightness and increased power consumption due to the need for complex pixel circuits and different data voltages for various pixels.
Innovation Solution
The OLED display device incorporates a pixel circuit with a drive transistor, switching transistors, and capacitors with different capacitance ratios to apply a suitable drive current to organic light emitting diodes, allowing equal voltage data signals to be applied across pixels while minimizing threshold voltage variation and maintaining aperture ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a compensation circuit is added to compensate for threshold voltage variation, then brightness uniformity is improved, but device complexity increases and aperture ratio decreases
Solution Approach 1:
The patent extracts the threshold voltage compensation function from a separate compensation circuit and integrates it into the drive transistor itself through the dual-capacitor configuration. The first capacitor stores the threshold voltage of the drive transistor, and the second capacitor stores the threshold voltage of the switching transistor, allowing the circuit to compensate for threshold variations without requiring additional compensation circuitry, thus reducing device complexity while maintaining brightness uniformity
Solution Approach 2:
The drive transistor is given multiple functions: it serves as both the pixel drive transistor for controlling OLED brightness and as a threshold voltage compensation element through its connection to the first capacitor. This multi-functionality eliminates the need for separate compensation circuits, reducing the number of transistors required per pixel and thereby increasing the aperture ratio
2Reliability
If different data voltages are applied to respective pixels to compensate for efficiency differences, then brightness uniformity is improved, but device complexity increases and power consumption increases
Solution Approach 1:
The patent changes the electrical parameters (capacitance values) of the first and second capacitors to different values, creating different voltage division ratios that compensate for the different efficiencies of red, green, and blue OLED pixels. By storing different threshold voltages and creating different voltage drops across the capacitors, the circuit achieves uniform brightness across all pixel types while using a single data voltage signal, thereby reducing power consumption compared to approaches requiring multiple data driving units
Data Source
AI summary
An organic light emitting diode (OLED) display device minimizes a threshold voltage variation of a drive transistor in a pixel circuit, increases an aperture ratio, and minimizes power consumption by applying a same range of data voltages to respective pixels. The OLED display device includes a first capacitor electrically connected between a first node and a power supply line; and a second capacitor electrically connected between the first node and a second node, wherein capacitances of the first and second capacitors are different from each other and adjustable.