OLED Pixel Circuit Decoupling Power Supply from Data Signal
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Solution Overview
Problem
Display devices using light-emitting diodes face luminance non-uniformity due to voltage drops in power supply wiring and threshold voltage variations in transistors, increasing complexity and cost.
Innovation Solution
A pixel circuit with a specific configuration of transistors and a capacitor that includes a first transistor with a gate electrode receiving a light-emitting signal, a second transistor with a gate electrode receiving a scanning signal, and a light-emitting element connected to transistors receiving power supply voltages, along with a driving method that manages signal and voltage transfers to maintain uniform electric potentials across nodes, thereby compensating for voltage drops and threshold variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If power supply wiring is used to transfer power supply voltage to pixel circuits, then the display device can operate with proper power supply, but voltage drop occurs in the power supply voltage causing luminance non-uniformity across the display screen
Solution Approach 1:
The patent introduces a reference voltage wiring system as an intermediary to transfer reference voltage to each pixel circuit independently. This reference voltage wiring is designed with sufficient width to minimize voltage drop, and the reference voltage serves as a stable baseline for luminance calculation, compensating for power supply voltage variations and ensuring uniform luminance across the display screen.
Solution Approach 2:
The patent changes the approach from directly using power supply voltage for luminance determination to using a combination of reference voltage and stored voltage differences. By storing the difference between power supply voltage and reference voltage in a capacitor, and using this stored difference to adjust the drive signal, the system compensates for power supply voltage fluctuations and maintains uniform luminance.
2Illumination intensity
If threshold compensation is implemented to address transistor threshold voltage variations, then display uniformity is improved, but the complexity and cost of the pixel circuit increase
Solution Approach 1:
The transistor serving as a switch for the light-emitting element is given multiple functions: it not only controls the light-emitting element but also participates in threshold voltage compensation through its connection to the capacitor and reference voltage wiring. This multi-functional design eliminates the need for separate compensation transistors, reducing pixel circuit complexity while maintaining display uniformity.
Solution Approach 2:
The pixel circuit uses its own existing components (transistor, capacitor, wiring) to perform threshold compensation without requiring additional dedicated compensation components. The capacitor stores voltage information that automatically compensates for threshold variations, and the reference voltage wiring provides the necessary reference level, enabling the circuit to self-correct for threshold voltage differences.
Data Source
AI summary
A pixel circuit, a driving method of a pixel circuit and an organic light-emitting display device are provided. The pixel circuit includes a first transistor having a gate electrode receiving a first light-emitting signal, a first terminal receiving a first reference voltage, and a second terminal connected to a first node; a second transistor having a gate electrode receiving a first scanning signal, a first terminal receiving a second reference voltage, and a second terminal connected to a second node; a third transistor having a gate electrode connected to the second node, a first terminal connected to a third node and a second terminal connected to a fourth node; a fourth transistor having a gate electrode receiving a second scanning signal, a first terminal receiving a data signal, and a second terminal connected to the third node; a fifth transistor having a gate electrode receiving the second scanning signal, a first terminal connected to the fourth node, and a second terminal connected to the second node; a sixth transistor having a gate electrode receiving a second light-emitting signal, a first terminal receiving a first power supply voltage, and a second terminal connected to the third node; a seventh transistor having a gate electrode receiving the second light-emitting signal, a first terminal receiving the first power supply voltage, and a second terminal connected to the first node; an eighth transistor having a gate electrode receiving the second light-emitting signal and a first terminal connected to the fourth node; a light-emitting element having a first terminal connected to the second terminal of the eighth transistor and a second terminal receiving a second power supply voltage; and a first capacitor having a first terminal connected to the first node and a second terminal connected to the second node.