Polysilicon TFT Threshold Voltage Compensation for Display Uniformity
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Solution Overview
Problem
Organic light emitting devices with polysilicon TFTs face challenges in uniform semiconductor characteristic formation, leading to luminance deviations between pixels and picture quality degradation due to non-uniform current flow caused by varying threshold voltages, especially in hold-type displays where motion blurring occurs due to sustained afterimages.
Innovation Solution
A method of driving the display device using a sensing line, light-emitting element, and driving transistor, which involves connecting and disconnecting control and output terminals to ground voltage, sensing voltages, and calculating threshold voltages to compensate for mobility and luminance non-uniformity, ensuring uniform current flow and improved picture quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polysilicon TFT is used to achieve high electron mobility and low leakage current, then electron mobility and leakage current characteristics are improved, but uniformity of semiconductor characteristics across pixels deteriorates
Solution Approach 1:
The patent implements a feedback mechanism by sensing the threshold voltage of each pixel's driving TFT and using this information to adjust the data voltage applied to that pixel. The sensing circuit measures the actual threshold voltage, and this measured value feeds back to the data driver which compensates for deviations by adjusting the input voltage, thereby maintaining uniform luminance across all pixels despite manufacturing variations.
Solution Approach 2:
The patent changes the operating parameters of the TFT by applying different voltages to adjust the threshold voltage compensation. By varying the gate voltage and measuring the resulting drain current at different voltage levels, the system determines the actual threshold voltage and uses this information to adjust subsequent operating parameters for uniform display performance.
2Duration of action of stationary object
If hold type display is used to sustain image for one frame, then image persistence is improved, but motion blurring occurs due to discrete display of moving objects
Solution Approach 1:
The patent applies periodic action by using impulse driving where the organic light emitting element is driven in short pulses rather than continuous hold. The display updates luminance values periodically at specific time points within each frame, and the organic electroluminescent material's inherent persistence maintains the visual display between updates, thereby reducing motion blur while maintaining image continuity.
Solution Approach 2:
The patent maintains continuity of useful action by leveraging the persistent luminescence property of organic electroluminescent materials. Although the electrical driving is impulsive and discontinuous, the optical output remains continuous due to the material's ability to sustain light emission after the driving pulse ends, ensuring smooth visual display without noticeable interruptions or blurring.
3Duration of action of moving object
If threshold voltage of organic light emitting element degrades over time, then device aging occurs, but non-uniform current flow results in picture quality degradation
Solution Approach 1:
The patent uses feedback to continuously monitor and compensate for threshold voltage degradation. The sensing circuit periodically measures the threshold voltage of each pixel's driving TFT and the organic light emitting element, and this measured information feeds back to adjust the data voltage in real-time, compensating for aging effects and maintaining uniform picture quality throughout the device's operational lifetime.
Solution Approach 2:
The patent performs preliminary sensing and measurement of threshold voltages before the actual display operation. By measuring the threshold voltage early in the frame period or during initialization, the system prepares compensation values in advance that account for any degradation that has occurred, ensuring that uniform current flow is maintained from the start of each display cycle.
Data Source
AI summary
A method of driving a display device including a sensing line, a light-emitting element, a capacitor, and a driving transistor, the driving transistor comprising a control terminal that is connected to the capacitor, an input terminal, and an output terminal, the method including: connecting the control terminal and the output terminal; connecting the control terminal and the output terminal to a ground voltage and then disconnecting the control terminal and the output terminal from the ground voltage; sensing a first voltage of the control terminal through the sensing line; and calculating a threshold voltage of the driving transistor based on the first voltage.