OLED Pixel Circuit Parasitic Capacitance Compensation
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Solution Overview
Problem
Parasitic capacitance between electronic circuits in organic light emitting displays affects display performance by altering voltage levels, leading to inefficiencies in driving current output and image quality.
Innovation Solution
The organic light emitting display apparatus incorporates a specific pixel circuit design with overlapping anodes and gates of driving transistors, synchronized scan signals, and compensation transistors to manage parasitic capacitance, ensuring stable voltage levels and efficient driving current delivery to OLEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the anode of the second OLED overlaps the gate of the driving transistor of the first pixel circuit, then parasitic capacitance occurs between the anode and gate, but this parasitic capacitance can be utilized to compensate for voltage changes in the driving transistor gate
Solution Approach 1:
The patent converts the harmful parasitic capacitance between the anode of the second OLED and the gate of the driving transistor of the first pixel circuit into a beneficial compensation mechanism. By strategically positioning the anode to overlap with the gate, the parasitic capacitance is generated and then utilized to counteract voltage drops in the driving transistor gate during operation, thereby improving display performance rather than merely tolerating the parasitic effect.
Solution Approach 2:
The patent modifies the spatial parameter of the OLED anode positioning to achieve overlap with the driving transistor gate of the adjacent pixel circuit. This parameter change (from non-overlapping to overlapping positioning) transforms the parasitic capacitance from a harmful byproduct into a functional compensation element that stabilizes the driving voltage.
2Measurement precision
If scan signals are output in synchronization with horizontal synchronization signal, then scanning timing can be precisely controlled, but the scanning time of first scan signal must precede scanning time of second scan signal by a cycle
Solution Approach 1:
The patent implements preliminary action by causing the first scan signal to be output before the second scan signal, with the first scan signal's scanning time preceding the second scan signal's scanning time by one horizontal synchronization cycle. This timing arrangement ensures that pixel circuits are properly initialized and ready before subsequent operations, maintaining precise scanning timing while managing signal coordination complexity.
3Illumination intensity
If driving current is output to OLED anode, then light emission is achieved, but parasitic capacitance causes voltage level changes that affect driving current accuracy
Solution Approach 1:
The patent converts the harmful voltage fluctuations caused by parasitic capacitance during driving current output into a beneficial compensation mechanism. The parasitic capacitance between the OLED anode and the driving transistor gate is utilized to counteract voltage drops, thereby maintaining accurate driving current levels while ensuring proper light emission from the OLED.
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 design effectively compensates for parasitic capacitance-induced voltage changes, maintaining intended voltage levels and improving display performance by ensuring accurate driving current output to OLEDs, thereby enhancing image quality and stability.
Implementation Method 1
In operation, parasitic capacitance may occur between electronic circuits that are near each other. For example, parasitic capacitance may occur when the voltage level of an electrode of one or both circuits changes.
Implementation Method 2
Each of the first and second pixel circuits may include a switching transistor to transfer the data signal based on a respective one of the first or second scan signals; and a storage capacitor to charge a voltage corresponding to the transferred data signal, wherein the driving transistor is to output the driving current corresponding to the voltage charged in the storage capacitor
Data Source
AI summary
An organic light emitting display apparatus includes first and second pixels on a display region, first and second scan lines connected to the first and second pixels respectively, and a gate driver to output a first scan signal and a second scan signal to the first and second scan lines respectively. The first pixel includes a first pixel circuit and a first organic light emitting diode (OLED). The second pixel includes a second pixel circuit and a second OLED. Each of the first and second pixel circuits includes a driving transistor to output driving current to the anode of a respective one of the first and second OLEDs. The anode of the second OLED at least partially overlaps the gate of a driving transistor of the first pixel circuit.