OLED Display Driving Circuit Threshold Voltage Sampling
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Solution Overview
Problem
High-resolution OLED displays face challenges in maintaining image quality due to reduced sampling periods for threshold voltage variations in driving TFTs, leading to inadequate compensation and brightness distortion.
Innovation Solution
The OLED display employs a driving circuit that samples threshold voltages in one horizontal period and initializes gate voltages in another, ensuring a sufficient sampling period to compensate for threshold voltage variations, while also using a double-gate structure for transistors connected to storage capacitors to reduce leakage currents and prevent brightness distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the sampling period is reduced to accommodate high-resolution displays, then the display resolution is improved, but the threshold voltage compensation capability deteriorates
Solution Approach 1:
The patent performs threshold voltage sampling in advance during the (j-1)-th horizontal period before the actual data writing in the j-th horizontal period. By preparing the sampled threshold voltage values beforehand, the system ensures accurate compensation without extending the critical sampling period during high-resolution display operations.
Solution Approach 2:
The patent separates the sampling operation from the data writing operation by using different pixel rows at different time periods. The (j-1)-th pixel row is used for sampling while the j-th pixel row is used for data writing, effectively utilizing the row dimension to resolve the time conflict between sampling and display resolution requirements.
2Productivity
If the sampling period is reduced for high-resolution displays, then the display refresh rate is improved, but the image quality deteriorates
Solution Approach 1:
The system performs threshold voltage sampling in advance during the (j-1)-th horizontal period, preparing compensation data before the actual display refresh operation. This preliminary sampling ensures that image quality is maintained through accurate threshold voltage compensation without compromising the display refresh rate.
Solution Approach 2:
The patent divides the pixel array into multiple rows and assigns different functions to different rows at different time periods. By segmenting the display into (j-1)-th pixel rows for sampling and j-th pixel rows for data writing, the system can maintain both high refresh rate and image quality simultaneously.
3Device complexity
If transistors with single-gate structure are used, then the device complexity is reduced, but leakage currents increase causing brightness distortion
Solution Approach 1:
The patent uses a double-gate transistor structure where two gates control the same channel. This composite transistor structure with dual gate control provides better electrostatic control and reduces leakage currents that cause brightness distortion, while the overall pixel circuit design keeps the system complexity manageable.
Solution Approach 2:
The double-gate structure is applied specifically to transistors connected to storage capacitors where leakage control is most critical. This localized enhancement of transistor structure provides targeted leakage reduction without unnecessarily increasing the complexity of all transistors in the pixel circuit.
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
This approach effectively compensates for threshold voltage variations, maintaining image quality and reducing brightness distortion, even in high-resolution displays with shorter sampling periods.
Implementation Method 1
When a driving voltage is applied to the anode electrode and the cathode electrode, a hole passing through the HIL and an electron passing through the ETL move to the EML to form an exciton, and thus, the EML emits a visible light
Data Source
AI summary
Provided is an organic light emitting diode (OLED) display which includes a driving circuit and pixels arranged on pixel rows. In a (j−1)-th horizontal period, the driving circuit samples a threshold voltage of a driving Transistor (DT) of each pixel arranged on the (j−1)-th pixel row, and initializes a voltage of a gate electrode of a driving TFT of each pixel arranged on the j-th pixel row. In addition, in a j-th horizontal period, the driving circuit samples a threshold voltage of the driving TFT of each pixel arranged on the j-th pixel row.