OLED Pixel Circuit with Storage Capacitor for Voltage Stabilization
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Solution Overview
Problem
Conventional organic light emitting displays using N-type transistors face challenges in accurately displaying desired gray levels due to voltage variations and high power consumption, especially in digital driving configurations, where high voltage data signals increase manufacturing costs and power usage.
Innovation Solution
A pixel configuration with an organic light emitting diode, first and second transistors, and a storage capacitor, along with a third transistor for initialization, allows for reduced data signal voltage by maintaining a constant voltage in the storage capacitor, enabling stable current supply and efficient operation in both analog and digital driving modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If N-type transistors are used instead of P-type transistors to reduce manufacturing costs, then manufacturing cost is reduced, but the ability to accurately display desired gray levels deteriorates due to voltage variations
Solution Approach 1:
The patent introduces a storage capacitor as an intermediary element between the N-type transistor and the organic light emitting diode. This capacitor mediates the voltage variations caused by the N-type transistor, storing the voltage signal and providing stable voltage to the OLED, thereby enabling accurate gray level display while using cost-effective N-type transistors
Solution Approach 2:
The patent changes the operating parameters of the N-type transistor by introducing a storage capacitor that maintains stable voltage levels. This parameter stabilization allows the N-type transistor to operate effectively in controlling the OLED, achieving both cost reduction and display accuracy
2Ease of operation
If high voltage data signals are used in digital driving configuration, then switching control is improved, but power consumption increases
Solution Approach 1:
The storage capacitor performs preliminary action by storing the voltage signal during the scanning period. This pre-stored voltage is then used during the emission period to control the OLED current, eliminating the need for continuous high voltage signaling and thereby reducing power consumption while maintaining effective switching control
Solution Approach 2:
The patent implements periodic action where the storage capacitor is charged during the scanning period and then discharges to control the OLED during the emission period. This periodic charge-discharge cycle enables effective switching control only when needed, significantly reducing overall power consumption compared to continuous high voltage signaling
3Device complexity
If voltage is not stabilized in the storage capacitor, then circuit complexity is reduced, but current supply stability deteriorates leading to inaccurate gray levels
Solution Approach 1:
The storage capacitor serves as a mediator that stabilizes the voltage signal without adding significant circuit complexity. By placing the capacitor between the N-type transistor and OLED, it filters out voltage fluctuations and provides stable voltage, ensuring accurate gray level display while maintaining a relatively simple circuit structure
Solution Approach 2:
The storage capacitor performs self-service by automatically stabilizing the voltage signal through its inherent charge-storage property. It charges when voltage is high and discharges when voltage drops, self-regulating the voltage supply to the OLED without requiring additional control circuits, thus achieving current stability with minimal added 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 ensures accurate display of desired gray levels with reduced power consumption and lower manufacturing costs by stabilizing the voltage supply to the organic light emitting diode, even in digital driving configurations, and allows for the use of existing data drivers designed for PMOS transistors.
Implementation Method 1
the organic light emitting display displays images using organic light emitting diodes (OLEDs) that emit light through the recombination of electrons and holes
Implementation Method 2
a storage capacitor Cst coupled between a gate electrode of the second transistor M2 and a first electrode of the second transistor M2
Data Source
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AI summary
A pixel and an organic light emitting display using the same are provided. The display displays an image having desired gray levels while allowing the voltage of data signals to be reduced. The pixel includes an organic light emitting diode; a driving transistor for supplying a current to the organic light emitting diode; a switching transistor configured to supply a data signal from a data line to a gate electrode of the driving transistor based on a scan signal from a scan line; a storage capacitor coupled between the gate electrode of the driving transistor and a source electrode of the driving transistor; and an initialization transistor coupled between the source electrode of the driving transistor and an initialization power voltage.