OLED Pixel Current Mirror Transistor Saturation Stability
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Solution Overview
Problem
Existing organic light emitting displays face challenges in maintaining display quality due to rapid degradation and luminance reduction, particularly when driving transistors operate in linear regions, leading to inefficient current supply and voltage application.
Innovation Solution
The implementation of a pixel structure with transistors driven in saturation regions, including a current source transistor and a switch transistor, along with a storage capacitor, to control current flow and voltage application to the organic light emitting diode, minimizing degradation and improving luminance control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If transistors are driven in linear regions to control current flow, then switching speed is improved, but current supply stability deteriorates and degradation increases
Solution Approach 1:
The transistor is divided into two distinct functional regions: a saturation region for stable current supply (first transistor) and a linear region for switching control (second transistor). This segmentation allows each region to optimize its specific function without compromising the other, resolving the contradiction between stability and speed.
Solution Approach 2:
Different regions of the transistor circuit are assigned different operational characteristics: the current supply path operates in saturation mode for stability, while the switching path operates in linear mode for speed. This local differentiation of operational quality enables simultaneous optimization of both stability and switching performance.
2Reliability
If transistors operate in saturation regions to ensure stable current supply, then current stability is improved, but switching speed deteriorates
Solution Approach 1:
The transistor circuit is segmented into two functional units: a saturation-mode transistor for stable current supply and a linear-mode transistor for rapid switching. This segmentation resolves the speed-stability tradeoff by assigning each transistor to optimize for its specific function.
Solution Approach 2:
The second transistor operating in linear mode serves as an intermediary switching element that controls the current flow from the first transistor (operating in saturation mode). This intermediary enables fast switching without compromising the stable current supply characteristics of the first transistor.
3Illumination intensity
If voltage is applied directly to organic light emitting diode to improve luminance, then luminance intensity is improved, but degradation accelerates
Solution Approach 1:
A transistor current mirror circuit is introduced as an intermediary between the voltage source and the organic light emitting diode. This intermediary converts voltage control into precise current control, enabling luminance adjustment through current modulation rather than direct voltage application, thereby reducing degradation.
Solution Approach 2:
The control parameter for luminance is changed from voltage to current. By using current as the primary control parameter through the transistor current mirror, the system achieves luminance control while operating conditions that minimize degradation are maintained.
4Illumination intensity
If current is increased to improve luminance output, then luminance is improved, but transistor degradation increases
Solution Approach 1:
The harmful effect of high current on transistor durability is extracted and isolated by using the second transistor as a switching element that operates in linear mode. This allows the first transistor to supply stable current at optimized levels while the second transistor handles the switching function, separating the luminance control from the potentially harmful high-current operation.
Solution Approach 2:
The operating parameters of the transistors are optimized by operating one transistor in saturation mode for stable current supply and another in linear mode for switching. This parameter optimization enables efficient current control that maintains luminance while minimizing transistor stress and degradation.
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 ensures a constant current supply to the organic light emitting diode, reducing degradation and enhancing display quality by adjusting the channel/length ratio of transistors, thereby improving the lifespan and luminance consistency.
Implementation Method 1
the OLED has a fast response speed and is driven with low power consumption. The OLED displays images by using organic light emitting diodes that emit light through recombination of electrons and holes
Data Source
AI summary
An organic light emitting display includes: pixels respectively positioned in areas defined by scan lines and data lines; and a data driver configured to supply a data signal to the data lines, the data signal includes a first data signal corresponding to an emission of the pixels and a second data signal corresponding to a non-emission of the pixels, wherein each pixel includes: an organic light emitting diode; a first transistor coupled to the organic light emitting diode, the first transistor configured to be a current source driven in a saturation region; a second transistor coupled as a current mirror to the first transistor, the second transistor configured to control an amount of a current flowing in the first transistor; and a third transistor coupled to the second transistor, the third transistor configured to be a switch driven in a linear region, according to the data signal.