Pixel Circuit Driving Method for Threshold Voltage Compensation
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Solution Overview
Problem
High-refresh-rate and high-resolution applications using 7T1C internal compensation circuits in pixel circuits face issues with uneven brightness and image sticking due to insufficient threshold voltage compensation, primarily caused by short charging times.
Innovation Solution
A method is introduced to determine and apply compensation data voltages for the drive transistor at different gray levels by calculating the difference between theoretical and actual threshold voltages, ensuring adequate gate potential compensation, thereby overcoming current and brightness differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-refresh-rate and high-resolution applications are implemented using 7T1C internal compensation circuit, then display refresh rate and resolution are improved, but threshold voltage compensation becomes insufficient causing uneven brightness and image sticking
Solution Approach 1:
The patent applies preliminary action by measuring and storing the actual threshold voltage of the drive transistor before the display operation begins. The compensation data voltages are pre-calculated based on the difference between theoretical and actual threshold voltages at multiple gray levels. This allows the pixel circuit to use accurate compensation values during high-refresh-rate operation without requiring additional compensation time, thus resolving the contradiction between high refresh rate and compensation accuracy.
2Speed
If short charging time is used to achieve high refresh rate, then display refresh rate is improved, but threshold voltage compensation is insufficient leading to current and brightness differences
Solution Approach 1:
The patent performs threshold voltage measurement and compensation data calculation in advance, before the actual display rendering. By storing the measured actual threshold voltage and pre-calculating compensation values for all gray levels, the system eliminates the need for time-consuming compensation operations during each refresh cycle. This enables fast charging speeds while maintaining reliable brightness uniformity through accurate pre-computed compensation.
Solution Approach 2:
The patent implements feedback by measuring the actual threshold voltage of the drive transistor and using this measured value to calculate compensation data voltages. The compensation process forms a closed loop where the measured actual threshold voltage feeds back into the compensation calculation, ensuring that the compensation accurately reflects the real device characteristics. This feedback mechanism guarantees brightness uniformity even with short charging times.
3Device complexity
If theoretical threshold voltage is used for compensation, then compensation process is simplified, but actual threshold voltage variations at different gray levels are not compensated causing display defects
Solution Approach 1:
The patent applies parameter changes by measuring the actual threshold voltage at multiple different gray levels (not just a single theoretical value) and using these varied measurements to calculate gray-level-specific compensation data voltages. This approach accounts for the non-linear behavior of the drive transistor across different operating points, significantly improving display uniformity while the pre-calculation and storage mechanism keeps the overall process complexity manageable.
Data Source
AI summary
A method for driving a pixel circuit. The pixel circuit includes a drive transistor. The method includes: acquiring a theoretical threshold voltage of the drive transistor and actual threshold voltages of the drive transistor at a plurality of different gray levels; determining compensation data voltages of the drive transistor at the plurality of different gray levels according to the theoretical threshold voltage of the drive transistor and the actual threshold voltages of the drive transistor at the plurality of different gray levels; and driving the pixel circuit emit light according to the compensation data voltages of the drive transistor at the plurality of different gray levels.