Variable Storage Capacitor for OLED Threshold Voltage Compensation
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Solution Overview
Problem
The existing OLED display devices face issues with non-uniform luminance and afterimages due to low threshold voltage compensation efficiency, primarily caused by slow charging rates of the storage capacitor, which are affected by parasitic capacitance and storage capacitance, leading to reduced sampling speed and increased error rates.
Innovation Solution
The OLED display device incorporates a variable storage capacitor with capacitance varying according to the applied voltage, connected in parallel to the gate electrode of the driving TFT, along with a fixed capacitor, to enhance the charging speed and rate of the data voltage, thereby improving threshold voltage compensation efficiency and addressing non-uniform luminance and afterimages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a storage capacitor is formed in the gate of the driving TFT for voltage compensation, then threshold voltage compensation is achieved, but the charging rate of the storage capacitor is slowed down due to large storage capacitance
Solution Approach 1:
The patent applies the dynamics principle by making the storage capacitance variable rather than fixed. The capacitance value changes dynamically based on the voltage applied to the gate electrode of the driving TFT. When voltage compensation is needed, the capacitance is larger to store sufficient charge. During high-speed driving when fast charging is needed, the capacitance reduces to allow faster charging rates, thus resolving the contradiction between compensation reliability and charging speed.
Solution Approach 2:
The patent implements parameter changes by varying the capacitance value of the storage capacitor according to the operating conditions. The capacitance parameter is adjusted based on the magnitude of the voltage applied to the gate electrode, allowing the system to optimize between storing enough charge for compensation and charging quickly for high-speed operation, thereby resolving the contradiction between compensation accuracy and charging rate.
2Productivity
If the sampling time is reduced for high-speed driving, then driving speed is improved, but the charging rate of the storage capacitor becomes insufficient leading to higher threshold voltage compensation error rate
Solution Approach 1:
The patent uses the dynamics principle to make the storage capacitance adaptable to different driving conditions. During high-speed driving with reduced sampling time, the capacitance automatically adjusts to a lower value enabling faster charging within the shortened sampling window. This dynamic adjustment allows the system to maintain both high driving speed and acceptable compensation accuracy by matching the capacitance to the available charging time.
Solution Approach 2:
The patent applies parameter changes by varying the capacitance value based on the sampling time and driving speed requirements. When sampling time is reduced for high-speed operation, the capacitance parameter decreases to allow sufficient charging within the shorter time window, thereby maintaining compensation precision despite faster driving speeds.
3Device complexity
If a fixed capacitance storage capacitor is used, then the structure is simple, but it cannot adapt to varying voltage magnitudes leading to non-uniform luminance and afterimages
Solution Approach 1:
The patent implements dynamics by transitioning from a fixed capacitance structure to a variable capacitance structure. The capacitance value changes dynamically according to the voltage magnitude applied to the gate electrode, allowing the system to adapt to different operating conditions. This resolves the contradiction by providing both luminance uniformity through adaptive capacitance and maintaining relatively simple implementation using standard capacitor structures with variable characteristics.
Solution Approach 2:
The patent applies parameter changes by making the capacitance value variable based on the voltage magnitude. Instead of using a fixed capacitance that cannot adapt to different voltage levels, the system varies the capacitance parameter to match the voltage conditions, ensuring consistent performance and eliminating luminance non-uniformity and afterimage effects while keeping the overall structure manageable.
Data Source
AI summary
An organic light emitting diode (OLED) display device includes a display panel including a plurality of OLED pixels arranged in a matrix form to display an image, and the plurality of OLED pixels each includes a switching thin film transistor (TFT) to switch a data voltage pass supplied from a data line in response to a scan signal input through a gate line, a driving TFT turned on in accordance with a magnitude of a data voltage supplied from the switching TFT to control an amount of light emitted from an OLED, and a variable storage capacitor connected in parallel to a gate electrode of the driving TFT and having a capacitance varying in accordance with a magnitude of a voltage applied to the gate electrode of the driving TFT may increase a charging speed and a charging rate of a data voltage of the OLED pixel. As a result, it is possible to improve threshold voltage compensation efficiency and solve a problem such as non-uniform luminance and an afterimage.