OLED Driving Circuit with Storage Capacitor for Luminance Uniformity
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Solution Overview
Problem
Conventional active matrix organic light-emitting devices face non-uniformity in thin film transistor characteristics, leading to unstable power output and reduced ability to express low gray levels, especially in larger displays due to parasitic capacitance from data line loads.
Innovation Solution
The proposed organic light-emitting device incorporates a storage capacitor and multiple switching units connected to scan lines, allowing for efficient data and initialization voltage management, which compensates for variations in thin film transistor characteristics by using a combination of current and voltage driving methods to ensure uniform luminance and improved gray level expression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional current driving method is used to compensate for TFT non-uniformity, then luminance uniformity is improved, but the ability to express low gray levels deteriorates due to parasitic capacitance from data line loads
Solution Approach 1:
The patent divides the data signal into two separate signals: a data voltage signal and a data current signal. These are transmitted through separate data voltage line and data current line, respectively. The segmentation allows independent optimization of each signal path, enabling current driving for luminance uniformity while preserving voltage signal integrity for low gray level expression.
Solution Approach 2:
The patent introduces a current-to-voltage converter as an intermediary component that converts the data current signal into a voltage signal suitable for driving the OLED. This intermediary device bridges the gap between current driving benefits and voltage driving advantages, allowing the system to achieve both luminance uniformity and low gray level expression capability.
2Device complexity
If polysilicon TFTs are used for AMOLED manufacturing, then device integration is improved, but output current stability deteriorates due to non-uniform device characteristics
Solution Approach 1:
The patent employs a feedback mechanism where the data current signal is generated based on the OLED's actual characteristics and the data voltage signal. The current-to-voltage converter adjusts the converted voltage to compensate for TFT non-uniformity, creating a feedback loop that maintains output current stability despite variations in polysilicon TFT characteristics.
Solution Approach 2:
The patent changes the driving parameters by using both voltage and current signals instead of relying solely on voltage signaling. The data current signal's amplitude and duration are specifically optimized to compensate for TFT non-uniformity, while the data voltage signal maintains proper timing and level for low gray level expression.
3Area of stationary object
If data line load increases in larger displays, then display area is improved, but low gray level expression ability deteriorates due to increased parasitic capacitance
Solution Approach 1:
The patent segments the data transmission into separate voltage and current paths. The data current signal is transmitted through a dedicated data current line with controlled impedance, isolating it from the capacitive effects of the data voltage line. This segmentation allows the current signal to reach the converter accurately even in large displays with high parasitic capacitance.
Solution Approach 2:
The current-to-voltage converter acts as an intermediary that is positioned close to the OLED, minimizing the impact of parasitic capacitance from long data lines in large displays. The converter locally generates the precise voltage signal needed for low gray level expression, independent of the data voltage line's capacitive effects.
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 solution effectively compensates for non-uniform transistor characteristics, achieving uniform luminance and enhanced ability to display low gray levels by eliminating the impact of data line loads, thereby improving picture quality, especially in larger displays.
Implementation Method 1
An organic light-emitting diode (OLED) is an active light-emitting device in which light is emitted by recombination of electrons and holes and a phosphor is excited
Implementation Method 2
a storage capacitor for receiving a data voltage from a data line and storing the received data voltage
Data Source
AI summary
An organic light-emitting device and an organic light-emitting display having the same are provided. The organic light-emitting device comprises: an organic light-emitting diode emitting light using an output current; a storage capacitor for receiving a data voltage from a data line, and storing the received data voltage; a driving thin film transistor connected between a source voltage and the organic light-emitting diode and having a gate connected to one terminal of the storage capacitor; a first switching unit connected between the one terminal of the storage capacitor and the data line and having a gate connected with a first scan line; a second switching unit connected between the other terminal of the storage capacitor and an initialization voltage line and having a gate connected with the first scan line; and a third switching unit connected between the other terminal of the storage capacitor and the data line and having a gate connected with a second scan line.