OLED Drive TFT Gate Potential Reset for Luminance Control
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Solution Overview
Problem
Conventional organic EL display devices face challenges in achieving precise gradation display due to variations in threshold voltage of TFTs, leading to uneven luminance, particularly in high luminance modes, and require longer reset times that limit data write time and affect image quality.
Innovation Solution
The solution involves a driving method that changes the drive control signal based on luminance modes, using a polysilicon TFT on a transparent substrate, with a precharge control line and switch means to adjust the gate potential of the OLED drive TFT, allowing for reduced reset time in standard mode and ensuring accurate gradation display in high luminance mode, while also enabling measurement of current-to-voltage characteristics for feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the reset time is increased to compensate for TFT threshold voltage variation, then gradation display precision is improved, but data write time is reduced and overall productivity deteriorates
Solution Approach 1:
The patent applies preliminary action by performing the reset operation before the data write operation. The reset TFT switch is turned on in advance to reset the gate potential of the OLED drive TFT, ensuring that the threshold voltage variation is compensated before data is written. This preliminary reset action enables subsequent fast data writing without compromising gradation precision.
Solution Approach 2:
The patent segments the driving waveform into distinct time periods: a reset period where the reset TFT switch is on to compensate for threshold voltage, and a data write period where data is rapidly written. This temporal segmentation allows the reset operation to be performed separately and quickly, preventing it from bottlenecking the data write speed while still ensuring precision.
2Illumination intensity
If the supply voltage is increased to achieve high luminance mode, then outdoor visibility is improved, but power consumption increases
Solution Approach 1:
The patent implements dynamic voltage adjustment by switching between a first supply voltage (lower) for standard indoor viewing conditions and a second supply voltage (higher) for outdoor high luminance requirements. The voltage is dynamically changed based on the display mode, allowing the system to optimize between luminance and power consumption depending on environmental conditions.
Solution Approach 2:
The patent changes the electrical parameter (supply voltage) to control luminance output. By adjusting the supply voltage level, the system can achieve different luminance modes - lower voltage for power saving in indoor use, and higher voltage for maximum luminance in outdoor use - thus adapting power consumption to actual display requirements.
3Manufacturing precision
If the reset TFT switch remains on during data writing, then threshold voltage compensation is maintained, but data write precision deteriorates due to continuous resetting
Solution Approach 1:
The reset operation is performed as a preliminary action before data writing begins. The reset TFT switch is turned on during the reset period to compensate for threshold voltage, then turned off before data writing starts. This ensures threshold voltage compensation is established beforehand without interfering with the precision of subsequent data writing operations.
Solution Approach 2:
The reset TFT switch operates periodically - on during the reset period to provide threshold voltage compensation, then off during the data write period to allow precise data writing. This periodic switching ensures that compensation is applied when needed while preventing interference during critical data writing operations.
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 reduces reset time in standard mode, prevents uneven luminance in high luminance mode, and allows for effective inspection of OLED elements, improving gradation display precision and luminance adjustment.
Implementation Method 1
a display apparatus (hereinafter referred to as 'organic EL display apparatus (OLED)') using organic electro luminescence
Implementation Method 2
a display apparatus (FED display apparatus) in which electron sources using field emission are arranged in a matrix, and illuminate phosphors that are arranged on anodes to form an image
Data Source
AI summary
When an organic EL display apparatus enables display of a standard luminance mode and a high luminance mode, it takes long time to reset the gate potential of the OLED drive TFT to a given value in a standard mode. In the reset operation of the gate potential of an OLED drive TFT at the time of writing an image signal, in a standard mode, a precharge current is allowed to flow in the OLED element for a short period before the reset operation to set an initial value of the gate potential of the OLED drive TFT to be close to a supply potential or a reference potential. With the above operation, the variation of the OLED drive TFT gate potential after resetting is reduced. As a result, the light emitting period during one frame can be extended. Also, since a blanking period can be extended, it is possible to measure the characteristic of the OLED element by using the blanking period.