Pixel Circuit Threshold Compensation for Uniform OLED Luminance
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Solution Overview
Problem
Existing display devices with light-emitting elements face issues of uneven luminance due to fluctuations in threshold voltage of driving transistors, leading to high power consumption and potential for screen burn-in, as well as low duty ratios in light-emitting periods.
Innovation Solution
A pixel structure incorporating a transistor, first and second storage capacitors, and switches to hold and divide potentials, allowing for stable current supply to light-emitting elements, reducing luminance deviations and enhancing power efficiency by suppressing current variations caused by threshold voltage fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transistor is used to control current supplied to a light-emitting element, then the light-emitting element can be driven with controlled current, but threshold voltage fluctuations cause ununiform luminance across different pixels
Solution Approach 1:
The patent measures and stores the threshold voltage of each transistor in advance before the light-emitting element is driven. This preliminary action allows the system to compensate for threshold voltage fluctuations by using the stored threshold voltage information to adjust the gate voltage, thereby ensuring uniform luminance across all pixels despite manufacturing variations.
Solution Approach 2:
The patent implements a feedback mechanism where the threshold voltage of the transistor is measured and stored, then used to adjust the gate voltage in subsequent operations. This feedback loop compensates for threshold voltage fluctuations by continuously adapting the control voltage based on the actual transistor characteristics, thereby maintaining uniform luminance output.
2Loss of energy
If conventional pixel structures are used, then the device can operate, but power consumption increases and screen burn-in becomes more likely
Solution Approach 1:
The patent dynamically adjusts the gate voltage of the transistor based on the actual threshold voltage measured during initialization. By making the gate voltage adaptive rather than fixed, the system optimizes current flow through the light-emitting element, reducing excessive power consumption and minimizing thermal stress that would otherwise lead to screen burn-in.
Solution Approach 2:
The patent changes the gate voltage parameter dynamically based on the measured threshold voltage. By adjusting this critical parameter to match the actual transistor characteristics, the system achieves optimal current control, thereby reducing power consumption and preventing conditions that would cause screen burn-in.
3Device complexity
If threshold voltage fluctuations are not compensated, then the device structure remains simple, but current variations cause luminance non-uniformity
Solution Approach 1:
The patent performs threshold voltage measurement and storage during an initialization phase before normal operation. This preliminary action adds minimal complexity to the overall device structure while enabling effective compensation for threshold voltage fluctuations, thereby achieving uniform luminance without requiring complex continuous adjustment mechanisms.
Solution Approach 2:
The patent introduces a storage capacitor as an intermediary element to hold the measured threshold voltage. This intermediary component allows the threshold voltage information to be retained and used during subsequent operations, effectively compensating for transistor variations without requiring complex real-time measurement and adjustment circuits.
4Productivity
If light-emitting elements are driven continuously, then display duty ratio increases, but power consumption and thermal stress increase
Solution Approach 1:
The patent dynamically optimizes the gate voltage based on the actual transistor threshold voltage, allowing the light-emitting element to be driven continuously with optimal current control. This dynamic adjustment ensures high duty ratio operation while minimizing power consumption by preventing excessive current flow and associated thermal stress.
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
The solution provides a display device with stable luminance and reduced power consumption, achieving high brightness with minimal luminance deviations and increased light-emitting period duty ratios, thereby improving the reliability and efficiency of the display.
Implementation Method 1
a first storage capacitor 115, a second storage capacitor 116... Voltage obtained by adding a potential in which the potential in accordance with the video signal and the first storage capacitor are capacitively divided to the threshold voltage
Data Source
AI summary
A pixel having a transistor which controls a current value supplied to a load, a first storage capacitor, a second storage capacitor, and first to fourth switches is included. After the threshold voltage of the transistor is held in the second storage capacitor, a potential in accordance with a video signal is input to the pixel. Voltage obtained by adding a potential in which the potential in accordance with the video signal and the first storage capacitor are capacitively divided to the threshold voltage is held in the second storage capacitor in this manner, so that variation of a current value caused by variations in the threshold voltage of the transistor is suppressed. Thus, desired current can be supplied to the load such as a light-emitting element. In addition, a display device with little deviation from luminance specified by the video signal can be provided.