OLED Pixel Circuit Leakage Control via Segmented Reference Voltages
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Solution Overview
Problem
Thin-film transistors in organic light-emitting diode displays experience current leakage, particularly at low temperatures, which affects luminance and leads to undesirable artifacts.
Innovation Solution
The implementation of a display pixel circuit with seven transistors, a capacitor, and separate reference voltage terminals for transistors T4 and T7, along with dynamic reference voltage control and a conductive mesh shorted to the ground power supply, to minimize leakage and maintain desired luminance without lowering the ground voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the ground voltage is lowered to increase current through the light-emitting diode at low temperatures, then luminance is improved, but transistor leakage increases
Solution Approach 1:
The invention divides the reference voltage supply into separate terminals for different transistor groups. Specifically, first reference voltage terminals are provided for first group transistors (including drive transistors) and second reference voltage terminals for second group transistors (including switching and emission enable transistors). This segmentation allows independent voltage control to minimize leakage in each transistor group while maintaining required luminance levels.
Solution Approach 2:
Different transistor groups are assigned different reference voltages tailored to their specific functional requirements. The first reference voltage is optimized for drive transistors controlling current through the light-emitting diode, while the second reference voltage is optimized for switching and emission enable transistors. This local optimization minimizes leakage in each group without compromising overall display performance.
2Reliability
If more transistors are added to each pixel to control leakage, then transistor leakage is reduced, but device complexity increases
Solution Approach 1:
Instead of adding more transistors to each pixel, the invention segments the reference voltage supply across multiple terminals. This approach controls leakage through electrical configuration rather than increasing transistor count, thereby maintaining pixel circuit simplicity while achieving leakage reduction.
Solution Approach 2:
The invention changes the electrical parameters (reference voltages) rather than the structural parameters (transistor count). By providing separate reference voltage terminals and optimizing voltage levels for different transistor groups, leakage is controlled through parameter optimization without increasing device complexity.
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 configuration reduces transistor leakage, maintaining consistent luminance and reducing visible artifacts by allowing independent control of reference voltages and voltage drops across transistors, thereby enhancing the performance of organic light-emitting diode displays.
Implementation Method 1
Each pixel includes a light-emitting diode and thin-film transistors for controlling application of a signal to the light-emitting diode to produce light
Implementation Method 2
a conductive mesh shorted to the ground power supply
Data Source
AI summary
An organic light-emitting diode display may contain an array of display pixels. Each display pixel may have a respective organic light-emitting diode that is controlled by a drive transistor. At low temperatures, it may be necessary to increase the amount of current through an organic light-emitting diode to achieve a desired luminance level. In order to increase the current through the light-emitting diode, the ground voltage level may be lowered. However, this may lead to thin-film transistors within the pixel leaking, which may result in undesirable display artifacts such as bright dots being displayed in a dark image. In order to prevent leakage in the transistors, the transistors may be coupled to separate reference voltage supplies or separate control lines. Additionally, the transistors may be positioned to minimize leakage even at low ground voltage levels.