Display Driving Circuit for Grayscale-Dependent TFT Compensation
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Solution Overview
Problem
Existing display devices using thin film transistors face challenges in maintaining consistent luminance due to variations in threshold voltage and mobility, which affect the current flowing through driving transistors, especially at different grayscale levels.
Innovation Solution
A driving method that adjusts the correction term for the driving transistor's voltage based on the input video signal's potential, ensuring the current value remains stable across various grayscale levels by varying the initial correction potential applied to the transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed offset voltage is used to correct threshold voltage variations, then threshold voltage compensation is achieved, but mobility variations cause residual luminance inconsistencies
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed offset voltage to a dynamic correction voltage that changes based on the video signal level. The correction voltage is generated by multiplying the video signal by a correction coefficient, allowing the compensation to adapt to different grayscale levels and effectively address mobility variations across the entire luminance range.
Solution Approach 2:
The patent implements parameter changes by modifying the correction voltage parameter based on the video signal level. Instead of using a constant offset voltage, the system adjusts the correction voltage dynamically according to the input signal amplitude, thereby compensating for mobility variations that affect different grayscale levels differently.
2Ease of manufacture
If thin film transistors are used to reduce cost and thickness, then manufacturing cost and device thickness are reduced, but threshold voltage and mobility variations increase
Solution Approach 1:
The patent applies feedback by using the video signal itself as a reference to generate the correction voltage. The correction coefficient is determined based on the relationship between the video signal level and the required current compensation, creating a feedback mechanism that automatically adjusts for transistor characteristic variations without requiring additional sensing circuits.
Solution Approach 2:
The system performs self-service by using its own video signal input to generate the correction voltage needed for compensation. The correction circuit utilizes the existing video signal and a correction coefficient to automatically adjust the driving voltage, eliminating the need for external calibration or additional sensing components.
3Illumination intensity
If a correction coefficient based on maximum luminance is used, then high luminance levels are compensated, but low grayscale levels remain uncorrected
Solution Approach 1:
The patent applies local quality by using different correction coefficients for different grayscale levels. Instead of a single correction coefficient optimized for maximum luminance, the system employs multiple correction coefficients corresponding to different video signal levels, allowing each grayscale range to be compensated optimally according to its specific characteristics.
Data Source
AI summary
A display device in which not only a variation in a current value due to a threshold voltage but also a variation in a current value due to mobility are prevented from influencing luminance with respect to all the levels of grayscale to be displayed. After applying an initial potential for correction to a gate and a drain of a driving transistor, the gate and the drain of the driving transistor is kept connected in a floating state, and a voltage is held in a capacitor before a voltage between the gate and a source of the driving transistor becomes equal to a threshold voltage. When a voltage obtained by subtracting the voltage held in the capacitor from a voltage of a video signal is applied to the gate and the source of the driving transistor, a current is supplied to a light-emitting element. A value of an initial voltage for correction differs in accordance with the voltage of the video signal.