OLED Pixel Circuit Reducing Gate Leakage Current
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Solution Overview
Problem
Organic light emitting display devices face issues with leakage current at the gate electrode of the driving transistor when using a low frequency driving method, leading to voltage drops and defects like flicker due to the high number of transistors coupled to the gate electrode.
Innovation Solution
The pixel design includes first and second initialization transistors coupled in series, which are turned on to provide an initialization signal to the organic light emitting diode and the driving transistor, reducing the number of transistors connected to the gate electrode, thereby decreasing leakage current and improving initialization efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple transistors are coupled to the gate electrode of the driving transistor, then the initialization and control functions are comprehensive, but the leakage current increases and voltage drops occur
Solution Approach 1:
The patent divides the initialization function into two separate transistors (first initialization transistor TI1 and second initialization transistor TI2) that operate at different stages. TI1 performs initial initialization of the OLED anode, while TI2 performs initialization of the driving transistor gate electrode. This segmentation reduces the number of transistors simultaneously connected to the gate electrode, thereby reducing leakage current and voltage drops while maintaining comprehensive initialization coverage.
2Use of energy by moving object
If low frequency driving method is used, then power consumption is decreased, but leakage current at the gate electrode increases causing flicker defects
Solution Approach 1:
The patent applies preliminary initialization actions before the low frequency driving period begins. The first initialization transistor TI1 initializes the OLED anode electrode in advance, and the second initialization transistor TI2 initializes the driving transistor gate electrode in advance. By performing these initialization actions beforehand, the patent prevents voltage drops and flicker defects that would otherwise occur during low frequency driving, while still maintaining the power consumption benefits of the low frequency method.
3Loss of energy
If series coupling of initialization transistors is implemented, then leakage current is reduced, but the circuit complexity increases
Solution Approach 1:
The second initialization transistor TI2 serves multiple functions: it initializes the driving transistor gate electrode, acts as a switching element for the data signal path, and works in conjunction with the storage capacitor to maintain the data signal. By making TI2 multi-functional, the patent reduces the need for additional dedicated transistors, thereby limiting the increase in circuit complexity despite the series coupling configuration.
Data Source
AI summary
A pixel of an organic light emitting display device and an organic light emitting display device having the same includes an organic light emitting diode, a first switching transistor configured to transfer a data signal, a storage capacitor configured to store the data signal, a driving transistor configured to generate a driving current of the organic light emitting diode, a first initialization transistor and a second initialization transistor configured to simultaneously provide an initialization signal to the organic light emitting diode and the driving transistor, a second switching transistor configured to be turned on in response to a second scan signal and transfer the data signal or the initialization signal, a first emission control transistor configured to transfer a high power voltage to the driving transistor, and a second emission control transistor configured to transfer the driving current to the organic light emitting diode.