OLED Pixel Circuit Brightness Uniformity via Reference Signal
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Solution Overview
Problem
In OLED display devices, the non-uniformity of transistor structures, electrical properties, and stability leads to variations in threshold voltages, causing uneven current flow and brightness across the display, especially as the devices age and signal line loads increase, resulting in non-uniform image brightness.
Innovation Solution
A pixel circuit comprising a light emitting device, a capacitor, a driving control sub-module, a charging and resetting sub-module, and a light emitting control sub-module is designed, where the current for the light emitting device is controlled independently of the driving transistor's threshold voltage by using a reference signal, ensuring consistent brightness across the display.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional pixel circuits are used to drive OLEDs, then the circuit structure is simple, but the threshold voltage variations of transistors cause non-uniform current flow and brightness across the display
Solution Approach 1:
The patent introduces a reference voltage terminal and reference signal as an intermediary element. The reference voltage terminal provides a stable reference potential that is independent of transistor threshold voltage variations. By comparing the driving signal against this reference, the circuit compensates for transistor parameter deviations, ensuring uniform current flow and brightness across different pixel locations without requiring complex circuit structures.
Solution Approach 2:
The patent changes the operating parameters of the pixel circuit by introducing a reference voltage level that shifts the operating point of the driving transistor. This parameter change allows the circuit to operate in a region where threshold voltage variations have minimal impact on the output current, thereby achieving brightness uniformity while maintaining circuit simplicity.
2Duration of action of moving object
If transistors are turned on for a long period to maintain display operation, then the display can be viewed continuously, but the stability of transistors decreases leading to threshold voltage shifts
Solution Approach 1:
The patent implements a feedback mechanism where the reference voltage terminal continuously monitors and compensates for threshold voltage drift in the driving transistor during prolonged operation. The reference signal provides a stable baseline that enables the circuit to detect and correct for transistor degradation over time, maintaining consistent display performance during continuous operation.
3Area of stationary object
If OLEDs are increased by size during development, then the display area is enlarged, but the loads on signal lines become large resulting in voltage attenuation and operation voltage changes
Solution Approach 1:
The patent applies the equipotentiality principle by providing a reference voltage terminal that establishes a stable reference potential across the entire enlarged display area. This reference voltage compensates for voltage drops in signal lines, ensuring that all pixel circuits operate at the correct voltage levels regardless of their distance from the signal source, thereby maintaining voltage stability in large-sized displays.
Data Source
AI summary
A pixel circuit, an organic electroluminescent display panels and a display device is configured to improve image brightness uniformity in the displaying region of the display device. The pixel circuit comprises a capacitor (CST), a light emitting device (D1), a driving control sub-module (1), a charging and resetting sub-module (2), and a light-emitting control sub-module (3). A first terminal of the capacitor (CST) serves as a first node (A), and a second terminal of the capacitor (CST) servers as a second node (B). A first terminal (x) of the light emitting device (D1) is connected to a fifth terminal (e′) of the light emitting control sub-module (3), and a second terminal (y) of the light emitting device is connected to a second reference signal terminal (Vref2). When the charging and resetting sub-module (2) is turned on, the data signal is written to the first node (A), and the first terminal and third terminal of the driving control sub-module (2) are shorted, which can reset the voltage of the second node (B) and charge the capacitor (CST). When the light emitting control sub-module (3) is turned on, the driving control sub-module (1) and the light emitting device (D1) are connected and the light emitting device (D1) is driven to emit light.