TFT Mobility Sensing for OLED Current Uniformity
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Solution Overview
Problem
Light emitting display devices face significant challenges in maintaining consistent current driving capability across pixels due to variations in threshold voltage of driving Thin Film Transistors (TFTs), leading to deviations in screen quality.
Innovation Solution
A method involving sensing the threshold voltage and mobility of each pixel's driving TFT using specific sensing voltages, correcting mobility errors, and compensating video data based on the threshold voltage and corrected mobility to ensure uniform current driving across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If driving TFTs are used as constant current elements in pixels, then the display device can operate with simple pixel structure, but threshold voltage variations cause significant deviation in current driving capability between pixels
Solution Approach 1:
The patent performs preliminary sensing of threshold voltage and mobility parameters before normal display operation. By measuring these parameters in advance and storing compensation values, the system prepares correction data that will be applied during video data compensation, thereby preventing current driving capability deviation before it affects display quality
Solution Approach 2:
The patent implements a feedback mechanism where the actual threshold voltage and mobility of each driving TFT are sensed and measured. These measured values are fed back to the timing controller, which then compensates video data based on the deviations detected, creating a closed-loop system that continuously corrects for parameter variations
2Reliability
If threshold voltage and mobility are sensed for each pixel, then current driving capability deviation can be corrected, but the sensing and compensation process increases system complexity
Solution Approach 1:
The patent uses existing data lines and power lines for dual purposes: both for normal pixel operation and for sensing threshold voltage and mobility parameters. The data driver and timing controller perform multiple functions including driving pixels, sensing parameters, storing compensation values, and compensating video data, thereby reducing the need for additional dedicated sensing circuits
Solution Approach 2:
The system uses its own existing infrastructure (data lines, power lines, driving TFTs) to perform the sensing and measurement functions. The driving TFTs themselves are utilized as the sensing elements, and the existing control circuits are made to perform the additional sensing and compensation tasks without requiring completely separate dedicated circuits
3Manufacturing precision
If mobility error is corrected through re-sensing, then current driving capability uniformity is improved, but additional sensing operations increase processing time
Solution Approach 1:
The patent performs mobility sensing and threshold voltage sensing in advance during initialization or dedicated sensing periods. By completing these measurements before normal display operation begins, the system establishes compensation values that will be used throughout subsequent operation, thereby minimizing the time impact on actual display performance
Solution Approach 2:
The sensing and compensation operations are performed periodically or at specific intervals rather than continuously. The system uses distinct sensing periods where sensing voltages are applied, followed by normal operation periods where the compensated values are used, thereby distributing the time cost of sensing across different operational phases
Data Source
AI summary
Disclosed is a light emitting display device capable of minimizing deviation of current driving capability between driving switching devices of respective pixels, thereby achieving enhanced screen quality. A method of driving the light emitting display device includes sensing the threshold voltage and mobility of driving Thin Film Transistor (TFT) of each pixel through each data line or each power line using a first sensing voltage; correcting an error of the mobility between the driving TFTs by again sensing the mobility of the driving TFT of each pixel through each data line or each power line using a second voltage; and compensating for video data to be displayed on a display panel using the threshold voltage and the corrected mobility.