Pixel Driving Circuit Threshold Voltage Compensation
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Solution Overview
Problem
High-resolution organic light emitting display devices face challenges in maintaining uniform brightness due to short charging times and increased data lines, which disrupt the voltage source and make it difficult to convert voltage signals into current signals within one frame period, leading to nonuniform brightness and potential instability.
Innovation Solution
A pixel driving circuit that includes multiple thin film transistors, a capacitor, and control signals to compensate for threshold voltage variations, allowing for stable and uniform current delivery to the organic light emitting diode, independent of the drive transistor's threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-resolution display is implemented with increased data lines, then display resolution is improved, but voltage source stability deteriorates and charging time becomes insufficient
Solution Approach 1:
The pixel circuit is segmented into multiple thin film transistors (switching TFT, drive TFT, compensation TFT) with dedicated functions. The compensation TFT specifically handles threshold voltage compensation, while the drive TFT controls current delivery. This segmentation allows each component to be optimized for its specific function, resolving the contradiction between high resolution and voltage stability.
Solution Approach 2:
The compensation TFT performs preliminary compensation of threshold voltage variations before the drive TFT delivers current to the OLED. By pre-compensating for threshold voltage shifts in the data storage node, the circuit ensures stable current delivery even when voltage source stability is compromised by high-resolution requirements.
2Measurement precision
If multiple data lines are used for high resolution, then display resolution is improved, but charging time becomes insufficient leading to nonuniform brightness
Solution Approach 1:
The pixel circuit uses multiple TFTs with specialized roles. The compensation TFT is dedicated to charging the data storage node and compensating for threshold voltage variations, separating the charging function from the current delivery function. This allows optimized charging timing independent of the drive TFT's current control requirements.
Solution Approach 2:
The compensation TFT maintains continuous charging of the data storage node throughout the frame period, ensuring the data voltage remains stable and uniform. This continuous action compensates for the reduced charging time caused by increased data lines in high-resolution displays.
3Device complexity
If conventional pixel circuit is used, then device simplicity is maintained, but brightness uniformity deteriorates due to threshold voltage variations
Solution Approach 1:
The pixel circuit is divided into functionally specialized TFTs: switching TFT for pixel selection, drive TFT for current control, and compensation TFT for threshold voltage compensation. This segmentation enables uniform brightness by compensating for threshold variations while maintaining reasonable circuit complexity through modular design.
Solution Approach 2:
The compensation TFT implements a feedback mechanism where the data storage node voltage is continuously adjusted based on threshold voltage variations. This feedback loop ensures that the current delivered to the OLED remains uniform across all pixels, compensating for manufacturing variations in TFT threshold voltages.
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
This solution prevents nonuniform brightness and extends the lifespan of the display by ensuring consistent current delivery, effectively addressing the issues of voltage stability and brightness uniformity in high-resolution organic light emitting display devices.
Implementation Method 1
The organic material may emit light when current passes therethrough
Data Source
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AI summary
The present disclosure provides a pixel driving circuit and a display device, the pixel driving circuit includes: a control unit (214, 314); a capacitor (234, 334); a first transistor (228, 328); a second transistor (226, 326); a third transistor (224, 324) and a fourth transistor (230, 330). The present disclosure can effectively compensate the variation of the threshold voltage of the drive thin film transistor by controlling the thin film transistors, thus prevent nonuniform brightness of a screen due to nonuniform current, and extend lifespan of the screen.