OLED Pixel Circuit Leakage Current Compensation
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Solution Overview
Problem
Organic light emitting diode (OLED) display devices experience image quality degradation due to leakage current distortion of data voltage at the gate node, particularly during low frequency operations, leading to undesired luminance and image quality issues.
Innovation Solution
Incorporating a compensating transistor with first and second sub-transistors coupled in series between the gate node and drain of the driving transistor, and a panel driver that calculates an average representative gray level to determine a node controlling voltage, which is applied to control the voltage between these sub-transistors, minimizing leakage current and optimizing image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a storage capacitor is used to store data voltage at the gate node, then the pixel can maintain the data voltage for image display, but leakage current distorts the stored voltage especially during low frequency operation, degrading image quality
Solution Approach 1:
The compensating transistor is divided into first and second sub-transistors connected in series between the gate node and drain. This segmentation allows independent control of voltage at the node between sub-transistors, enabling precise leakage current compensation while maintaining data voltage storage stability.
Solution Approach 2:
The panel driver dynamically adjusts the voltage level at the node between the first and second compensating sub-transistors based on average representative gray level calculations from input image data. This parameter change optimizes leakage current compensation across different display conditions and frequency operations.
2Use of energy by moving object
If the display panel operates at low frequency to reduce power consumption, then energy efficiency improves, but leakage current distortion intensifies causing image quality degradation
Solution Approach 1:
The system dynamically changes the voltage parameter at the compensating transistor node based on operating conditions. During low frequency operation, the adjusted voltage level compensates for increased leakage current effects, maintaining image quality while preserving energy efficiency benefits.
Solution Approach 2:
The panel driver calculates average representative gray level from input image data and uses this feedback to determine the appropriate voltage level for the compensating transistor node. This closed-loop control adapts leakage current compensation to actual display conditions and operating frequency.
3Object-affected harmful factors
If a compensating transistor is added to reduce leakage current, then image quality improves, but device complexity increases
Solution Approach 1:
The compensating transistor is segmented into two sub-transistors with a controllable node between them. This segmentation, while adding complexity, enables precise voltage control that effectively reduces leakage current, achieving better performance than a simple uncompensated structure.
Solution Approach 2:
The compensating transistor structure serves multiple functions: it compensates for leakage current, enables dynamic voltage adjustment based on image data, and maintains compatibility with standard OLED pixel architectures. The same structure adapts to different operating frequencies and display conditions.
Data Source
AI summary
An organic light emitting diode display device includes a display panel including a plurality of pixels, and a panel driver configured to drive the display panel. Each pixel includes a driving transistor, a compensating transistor including first and second compensating sub-transistors coupled in series between a gate node and a drain of the driving transistor, a storage capacitor, and an organic light emitting diode. The panel driver calculates an average representative gray level of input image data in a plurality of frame periods, determines a voltage level of a node controlling voltage based on the average representative gray level, and provides the node controlling voltage to each of the plurality of pixels to control a voltage of a node between the first and second compensating sub-transistors.