OLED Pixel Circuit with Segmented Power Sources
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Solution Overview
Problem
Conventional organic light emitting display devices face challenges in maintaining desired luminance due to variations in the voltage of the first power source across the display unit and threshold voltages of the driving transistors, leading to inconsistent image quality.
Innovation Solution
The proposed solution involves a pixel circuit with specific transistor configurations and capacitors that control current flow to an organic light emitting diode, using a second power source, initial power source, and reference power source to manage current flow independently of the first power source and threshold voltage, ensuring consistent luminance through voltage differences and emission control signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional pixel circuits are used with a single power source, then the device structure is simple, but the luminance consistency deteriorates due to voltage variations and transistor threshold voltage differences
Solution Approach 1:
The power supply system is segmented into multiple independent power sources (first power source ELVDD, second power source ELVSS, reference power source Vref, and initial power source Vint). Each power source serves a specific function in the pixel circuit, allowing independent control of current flow and voltage levels to compensate for variations in transistor threshold voltages and maintain consistent luminance across the display.
Solution Approach 2:
The invention changes the electrical parameters (voltage levels) of multiple power sources to achieve precise current control. By adjusting the voltage differences between power sources (e.g., ELVDD - Vref, Vint - ELVSS), the circuit compensates for threshold voltage variations in transistors, ensuring uniform luminance output despite parameter variations in individual components.
2Reliability
If multiple power sources and transistors are added to control current flow, then luminance consistency is improved, but the pixel circuit complexity increases
Solution Approach 1:
The pixel circuit uses multi-functional transistors and capacitors that serve multiple purposes. For example, the fourth transistor M4 controls current flow to the OLED while also being controlled by voltage differences from multiple power sources. The capacitors C1 and C2 are involved in both charge storage and voltage regulation functions, reducing the need for additional dedicated components.
Solution Approach 2:
The invention introduces intermediate control elements (capacitors C1 and C2, and transistor M5) that mediate between the multiple power sources and the OLED. These intermediaries regulate and coordinate the interactions between different power sources, enabling precise current control without requiring a complex direct connection structure between all power sources and the OLED.
3Stability of the object's composition
If current control is made independent of power source voltage variations, then luminance stability is improved, but the circuit requires additional components for voltage compensation
Solution Approach 1:
The pixel circuit implements a feedback mechanism where the voltage differences between multiple power sources (ELVDD, Vref, Vint, ELVSS) automatically compensate for threshold voltage variations in the transistors. The reference power source Vref and initial power source Vint provide stable reference levels that create compensating voltage differences, ensuring that current flow to the OLED remains stable despite variations in the main power source ELVDD or transistor characteristics.
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 allows for precise control of current to the organic light emitting diode, enabling the display of images with desired luminance regardless of variations in the first power source voltage and threshold voltages of the driving transistors, thus ensuring consistent image quality.
Implementation Method 1
the organic light emitting device displays an image by using organic light emitting diodes that emit light by recombining holes with electrons
Data Source
AI summary
A pixel and organic light emitting display device. The pixel includes an organic light emitting diode, first through fourth transistors, and a second capacitor. The fourth transistor is for controlling an amount of current flowing through the organic light emitting diode. A first transistor is coupled between a second terminal of the second capacitor and a data line and is configured to turn on in response to a scan signal supplied to an i-th scan line. A second transistor is coupled between a first terminal of the second capacitor and an initial power source and is configured to turn on in response to an other scan signal supplied to an (i−1)-th scan line. A third transistor is coupled between the second terminal of the second capacitor and a reference power source and is configured to turn off in response to an emission control signal supplied to an (i+1)-th emission control line.