OLED Pixel Circuit Voltage Prewriting for Grayscale Uniformity
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Solution Overview
Problem
OLED displays experience non-uniformity in displayed images due to voltage drops across metal VDD wires during light emission, affecting grayscale consistency across the screen.
Innovation Solution
A pixel circuit design incorporating a driver transistor, data writing sub-circuit, initializing sub-circuit, voltage prewriting sub-circuit, threshold compensating sub-circuit, first and second light-emission control sub-circuits, and a capacitor, where the voltage prewriting sub-circuit stores light-emission supply voltage in the capacitor, independent of the first voltage source, ensuring stable voltage for light emission and reducing voltage drop effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional pixel circuit is used with metal VDD wires for power supply, then the circuit structure is simple, but voltage drops occur during light emission causing non-uniform grayscale across the display screen
Solution Approach 1:
The patent introduces a voltage prewriting sub-circuit that performs preliminary voltage storage in a capacitor before the light emission phase. This preliminary action ensures that the driver transistor receives a stable reference voltage (VSEL) independent of the metal VDD wire voltage drops, thereby maintaining grayscale consistency without requiring complete circuit redesign
Solution Approach 2:
The patent introduces a capacitor as an intermediary element between the voltage prewriting sub-circuit and the driver transistor. This capacitor stores the prewritten voltage and provides it to the driver transistor during light emission, acting as a buffer that isolates the driver from voltage fluctuations in the metal VDD wire, thus ensuring uniform grayscale output
2Reliability
If the light-emission current depends on the metal VDD wire voltage, then the circuit operation is straightforward, but voltage drops cause non-uniformity in displayed images
Solution Approach 1:
The patent extracts the voltage reference function from the metal VDD wire by introducing a separate voltage prewriting sub-circuit. This sub-circuit writes the light-emission supply voltage (VSEL) to a capacitor independently of the metal VDD wire, thereby separating the voltage reference path from the power supply path and eliminating the impact of voltage drops on image uniformity
Solution Approach 2:
The patent changes the voltage parameter source for the driver transistor from the metal VDD wire voltage to a capacitor-stored voltage that was prewritten from VSEL. This parameter change ensures that the light-emission current depends on the stable VSEL voltage rather than the fluctuating metal VDD wire voltage, thereby improving image uniformity
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 enhances image uniformity by making light-emission current dependent on the stored light-emission supply voltage, independent of the first voltage source, thereby improving grayscale consistency across the OLED display screen.
Implementation Method 1
a capacitor, and configured to be charged or discharged according to the potential at the gate of the driver transistor, and the potential at the first node
Data Source
AI summary
A pixel circuit, a method for driving the same, a display panel and a display device are provided. The pixel circuit includes a driver transistor, a data writing sub-circuit, an initializing sub-circuit, a voltage prewriting sub-circuit, a threshold compensating sub-circuit, a first light-emission control sub-circuit, a second light-emission control sub-circuit, a capacitor, and a light-emitting element. The voltage prewriting sub-circuit pre-stores voltage of a light-emission supply voltage terminal into the capacitor before the light-emitting element emits light, the magnitude of light-emission current is dependent upon the voltage of the light-emission supply voltage terminal, and independent of the voltage of the first voltage source.