OLED Pixel Circuit Parasitic Light Suppression
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Solution Overview
Problem
Organic light emitting displays (OLEDs) suffer from reduced contrast ratio due to unintended light emission at undesired times, which is caused by the emission control signal leading to increased voltage at the anode electrode of the OLED, resulting in parasitic light generation.
Innovation Solution
Incorporating a capacitor between the emission control line and the gate electrode of the second transistor, which transmits a voltage lower than the emission control signal, to reduce the voltage at the anode electrode and minimize parasitic light emission, along with a specific transistor configuration to control current flow through the OLED.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If emission control signals are supplied to control OLED emission timing, then light emission timing is controlled, but voltage increases at the anode electrode causing parasitic light generation
Solution Approach 1:
A capacitor is introduced as an intermediary component between the emission control line and the gate electrode of the second transistor. This capacitor couples the emission control signal while blocking direct voltage transmission, thereby preventing the voltage increase that causes parasitic light generation at the OLED anode electrode while still maintaining emission timing control
Solution Approach 2:
The invention uses a capacitor to create a coupled copy of the emission control signal voltage at the gate electrode of the second transistor, rather than directly applying the full emission control signal voltage. This copied voltage signal maintains the timing control function while reducing the harmful voltage effect on the OLED
2Use of energy by moving object
If OLED efficiency is increased to enable low current operation, then brightness and power consumption improve, but unintended light emission occurs at undesired times
Solution Approach 1:
The capacitor acts as a mediator that allows the emission control timing to be transmitted to the pixel circuit while blocking the direct transmission of high voltage that would cause unintended OLED activation. This enables the OLED to operate at low currents for energy efficiency while preventing parasitic emission through voltage isolation
3Object-generated harmful factors
If a capacitor is added between the emission control line and the gate electrode of the second transistor, then parasitic light emission is reduced, but device complexity increases
Solution Approach 1:
A single capacitor is added as a minimal intermediary component to resolve the parasitic light emission issue. This simple addition provides effective voltage isolation without requiring complex circuit modifications, maintaining relatively simple pixel circuit architecture while achieving the desired emission control
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 effectively reduces unintended light emission, thereby enhancing the contrast ratio and maintaining stable current flow during emission control signal cessation.
Implementation Method 1
a capacitor connected between the emission control line and the gate electrode of the second transistor
Data Source
AI summary
A pixel includes a first transistor, a second transistor, a third transistor, and a capacitor. The first transistor connects a first power source to a light emitter based on a first control signal. The second transistor connects a pixel circuit to the light emitter. The third transistor connects a second power source to the pixel circuit based on a second control signal. The capacitor is a MOS capacitor having a first electrode connected to receive the second control signal and a second electrode connected to the second transistor.