OLED Pixel Circuit Carrier Discharge for Afterimage Inhibition
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Solution Overview
Problem
Existing display devices using organic EL elements suffer from afterimages due to carriers trapped in trap levels within the channel region of drive transistors, leading to variations in current flow and image luminance.
Innovation Solution
A display device configuration that includes a switching transistor connected to the channel region of the drive transistor, allowing carriers trapped in trap levels to be discharged to a constant voltage supply line during the emission period, thereby maintaining consistent current flow and inhibiting afterimages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a precharge transistor and hold capacitance line are used to extract trapped carriers, then afterimage occurrence is inhibited, but circuit configuration becomes complex
Solution Approach 1:
The patent extracts the carrier discharge function from a separate precharge transistor and hold capacitance line configuration, and integrates it directly into the drive transistor structure by forming a discharge electrode in the channel region. This extraction simplifies the circuit by eliminating redundant components while maintaining the carrier discharge capability that prevents afterimages.
Solution Approach 2:
The patent merges the carrier discharge function with the drive transistor by integrating a discharge electrode directly into the channel region of the drive transistor. This consolidation combines multiple functions (driving and carrier discharge) into a single transistor structure, reducing the overall circuit complexity while maintaining afterimage inhibition capability.
2Illumination intensity
If carriers are trapped in trap levels during white display, then threshold voltage varies, but current flow becomes inconsistent leading to afterimages
Solution Approach 1:
The patent converts the harmful effect of trapped carriers (which cause threshold voltage variation and current inconsistency) into a beneficial discharge mechanism. By providing a dedicated discharge electrode in the channel region, trapped carriers are actively removed and converted into a controlled discharge current, thereby stabilizing the threshold voltage and current flow while maintaining display luminance consistency.
Solution Approach 2:
The patent implements preliminary carrier discharge action during the emission period by maintaining the discharge electrode in a state that allows continuous or periodic removal of trapped carriers. This preliminary action prevents carrier accumulation before it can significantly affect threshold voltage and current stability, ensuring consistent display performance throughout the emission period.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed solution effectively inhibits the occurrence of afterimages by ensuring that the drive current flowing through the drive transistor is not affected by trapped carriers, maintaining the original image luminance.
Implementation Method 1
A display device configuration that includes a switching transistor connected to the channel region of the drive transistor, allowing carriers trapped in trap levels to be discharged to a constant voltage supply line during the emission period
Data Source
AI summary
In a display device including organic EL elements OLED, a p-channel switching transistor T8 is connected at a conductive terminal to a channel region of a p-channel drive transistor T4. When holes are trapped in trap levels within the channel region of the drive transistor T4 while the display device presents a white display image, this configuration enables the holes to be extracted through the switching transistor T8 to an initialization line Vini. Consequently, a drive current flows through the drive transistor T4 in accordance with a data voltage, resulting in no perceptible afterimage even when a gray display image is presented during an immediately subsequent frame.