OLED Scan Driver Timing for Fast Data-Line Charging and Gray Scale
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Solution Overview
Problem
Conventional OLED display driving methods face challenges in expressing high gray scales due to deviations in threshold voltage and mobility of TFTs, leading to non-uniform current and voltage supply, which affects image quality and increases charging time for data lines.
Innovation Solution
A scan driver is designed to generate secondary signals by delaying a primary signal and inverting them, allowing for efficient control of light emission duration in organic light emitting devices, reducing the time required to charge data lines while maintaining image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If voltage-programming method is used to drive OLED, then the display can operate with conventional TFT structures, but high gray scales cannot be expressed due to threshold voltage deviation and mobility variation
Solution Approach 1:
The patent changes the driving parameter from voltage to current. By using current-programming method where the OLED current is directly controlled by a data current source, the system becomes insensitive to TFT threshold voltage deviation and mobility variation. The current relationship IOLED=IDATA eliminates the need for precise voltage control, thereby achieving high gray scale precision without compromising ease of manufacture.
2Manufacturing precision
If current-programming method is used to drive OLED, then panel uniformity can be achieved, but data line charging time becomes excessively long
Solution Approach 1:
The patent segments the scanning process into two distinct phases: a precharge period where data lines are rapidly charged to the data voltage level, and a display period where the OLEDs are driven by the stored voltage. This segmentation allows the system to benefit from current-programming precision during display while using voltage-programming for rapid line charging, thereby reducing overall charging time without compromising panel uniformity.
Solution Approach 2:
The patent implements a precharge operation before the actual data display. During this preliminary phase, the data lines are charged to the required voltage level using a precharge transistor. This preliminary action prepares the data lines in advance, so that when the display period begins, the lines are already charged and ready for immediate OLED driving, significantly reducing the effective charging time during normal operation.
3Productivity
If high current is applied to charge data lines rapidly, then charging time is reduced, but brightness of all pixels increases and image quality deteriorates
Solution Approach 1:
The patent divides the driving cycle into distinct precharge and display periods. During the precharge period, high current is applied to rapidly charge data lines without affecting OLED brightness. During the display period, the precharge transistor is turned off and OLEDs are driven by the stored voltage at controlled current levels. This temporal segmentation allows rapid charging without compromising image quality, as the high current is applied only when OLEDs are not being driven.
Solution Approach 2:
The patent implements periodic precharge pulses at the beginning of each horizontal scanning line. These periodic precharge actions occur only during the precharge period of each line scan, providing rapid charging when needed, while the display period maintains stable, controlled current for consistent image quality. This periodic application of high current solves the contradiction between charging speed and image quality.
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 enables rapid charging of data lines without compromising image quality, stabilizing the operation of organic light emitting displays by controlling the duration of light emission and reducing the time needed for data line charging.
Implementation Method 1
an organic light emitting display device... electrically excites phosphorus organic components, and visualizes an image by voltage-programming or current-programming M, X, and N numbers of organic light emitting cells
Implementation Method 2
The organic thin film layer has a multi-layered structure including an emission layer, an electro transport layer (ETL), and a hole transport layer (HTL) so as to balance electrons and holes and thereby enhancing efficiency of light emission
Data Source
AI summary
A light emission device according to the present invention includes a plurality of pixel circuits in a matrix. A plurality of first scan lines transmits a selection signal to select the pixel circuits. A plurality of second scan lines transmits an emission signal to control the duration of light emission of the pixel circuits. A scan driver sequentially delays a primary signal having a first-level pulse about a first period for generating a plurality of secondary signals, inverting the plurality of secondary signals for outputting the emission signal, and generating a signal having a second-level pulse when the secondary signal and the emission signal are in the first-level.