OLED Data Driver Current Storing Module for Stable Gray-Scale Output
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Solution Overview
Problem
Existing OLED display data drivers face challenges in maintaining stable gray-scale current due to fluctuations in threshold potential levels and mobility of TFTs, leading to inconsistent brightness in large-sized and high dpi displays.
Innovation Solution
A data driver with a digital-to-analog current converter and a current storing/reproducing module, along with a control circuit, transforms digital signals into analog current signals and stores a predetermined voltage to generate a duplicate current signal that is almost equal to the original, ensuring stable gray-scale current output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a digital-to-analog current converter is used to transform digital signals into analog current signals, then the gray-scale current can be generated, but the output current becomes unstable due to TFT threshold potential fluctuations and mobility variations
Solution Approach 1:
The patent applies preliminary action by pre-storing the analog current signal in a current storage module before it is affected by TFT fluctuations. The stored current signal is then reproduced through the unstable TFTs without being further degraded, as the critical conversion has already been completed and stored. This resolves the contradiction by performing the precise digital-to-analog conversion before the signal passes through the unreliable TFT components.
2Adaptability or versatility
If TFTs with width-to-length ratio assigned as 1:2:4:8 are used to generate 16 current gray scales, then the digital-to-analog conversion can be achieved, but significant variation occurs due to threshold potential and mobility fluctuations
Solution Approach 1:
The patent applies copying by creating a stored copy of the analog current signal in the current storage module. Instead of repeatedly converting digital signals through unstable TFTs, the system creates one accurate analog copy and reproduces it multiple times. This stored copy serves as a stable reference that is insensitive to subsequent TFT parameter variations, thereby maintaining gray-scale accuracy while preserving the ability to drive multiple pixels.
3Device complexity
If the output impedance of the digital-to-analog current converter is not high enough, then the circuit can be simpler, but the output potential level is affected by current flow causing unstable output
Solution Approach 1:
The patent introduces an intermediary current storage module between the digital-to-analog converter and the output stage. This intermediary buffer isolates the converter from load variations and current flow effects. The storage module acts as a mediator that decouples the converter's output impedance limitations from the final output stability, allowing the use of simpler converter circuits while maintaining reliable output potential levels.
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 stable duplicate current signal that maintains consistent brightness across the display, improving the reliability and quality of large-sized and high dpi OLED displays by minimizing the impact of TFT fluctuations.
Implementation Method 1
the current storing/reproducing module is composed of a capacitor and a plurality of MOS transistors, wherein the capacitor is used to store a predetermined voltage required for conducting the analog current signal
Data Source
AI summary
A data driver used in a current-driving display device for receiving a digital signal and for outputting a gray-scaled current signal to a data line. The data driver includes a digital-to-analog current converter for transforming the digital signal into an analog current signal, a current-copying/reproducing module, and a control circuit. The current-copying/reproducing module is used to store a predetermined voltage for conducting the analog current signal in a transforming/storing status and to conduct a reproducing current signal to the data line in a reproducing/sustaining status. The control circuit is electrically connected between the digital-to-analog current converter and the current-copying/reproducing module for providing a switch between the transforming/storing status and the reproducing/sustaining status. The reproducing current signal is the gray-scaled current signal and is almost equivalent to the analog current signal.