Pixel Circuit Array for AMOLED Luminance Uniformity
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Solution Overview
Problem
Active matrix organic light emitting diode (AMOLED) display panels face issues with circuit instability and uneven OLED luminance due to non-uniform threshold voltages of TFTs and IR drops, leading to inefficiencies and increased power consumption.
Innovation Solution
A pixel circuit array with a precharge circuit, compensation circuit, holding circuit, and light emitting circuit, where the current delivered to the OLED is independent of the threshold voltage of TFTs and power supply voltage, using a specific transistor and capacitor configuration to maintain constant current and compensate for threshold voltage uniformity and IR drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a traditional passive matrix organic light emitting display (PMOLED) is used to increase display size, then the display size is increased, but the transient current must be increased and power consumption increases
Solution Approach 1:
The pixel circuit is divided into multiple functional modules: switching transistor T2 for signal input, driving transistor T1 for current control, compensation transistor T3 for threshold voltage compensation, and storage capacitor C1 for voltage holding. This segmentation allows each module to perform its specific function efficiently, enabling large display sizes without proportionally increasing power consumption.
2Power
If a large current is applied to increase transient current for larger displays, then the transient current is increased, but the voltage drop on the ITO line becomes extremely large and operation voltage becomes extremely high
Solution Approach 1:
The compensation transistor T3 and storage capacitor C1 perform preliminary compensation of the threshold voltage before the driving transistor T1 operates. This preliminary action ensures that the driving transistor operates at optimal conditions, reducing the need for excessive transient current and thereby reducing voltage drop on the ITO line.
3Device complexity
If the threshold voltage of TFTs is non-uniform, then the circuit operation is simple, but circuit instability and uneven OLED luminance occur
Solution Approach 1:
The compensation transistor T3 is configured to sense and compensate for threshold voltage variations of the driving transistor T1. During the compensation period, T3 adjusts the voltage on capacitor C1 to counteract threshold voltage deviations, providing negative feedback that stabilizes the circuit operation and ensures uniform OLED luminance despite TFT threshold voltage non-uniformity.
4Device complexity
If the threshold voltage of TFTs is non-uniform, then the circuit operation is simple, but uneven OLED luminance occurs
Solution Approach 1:
The compensation transistor T3 and storage capacitor C1 form a feedback mechanism that detects and corrects threshold voltage variations. This feedback ensures that the driving current to each OLED pixel remains consistent, thereby achieving uniform OLED luminance across the display panel despite variations in TFT threshold voltages.
5Speed
If a voltage signal representing gray scale is provided by an integrated driving chip and converted to current signal inside the pixel circuit, then the driving speed is fast and implementation is easy, but the current delivered to OLED depends on threshold voltage uniformity and power supply voltage
Solution Approach 1:
The compensation transistor T3 provides real-time feedback compensation for threshold voltage variations, ensuring that the converted current signal remains stable and accurate. This feedback mechanism maintains reliable current delivery to the OLED while preserving the fast driving speed and easy implementation characteristics of the voltage-type driving method.
Data Source
Figure 1~2A
Figure 2B~3B
Figure 4A~5
AI summary
The disclosed technology is related to a pixel unit circuit, a pixel array, a display panel and display panel driving method. The pixel circuit array includes pixel unit circuits, and each of the pixel unit circuit includes a precharge circuit, a compensation circuit, a holding circuit, a driving circuit, a light emitting circuit, a first power supply terminal, a second power supply terminal, a third power supply terminal, a scanning control terminal, a first control terminal and a second control terminal. With the pixel unit circuit, as long as the inputted direct-current reference voltage and the data voltage signal are not varied, the current delivered to an OLED remains constant, thus the uniformity of the OLED can be compensated for.