OLED Pixel Circuit Anode Voltage Compensation
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Solution Overview
Problem
Organic light-emitting display apparatuses face issues with non-uniformity of threshold voltages and electron mobility, leading to inconsistent image brightness due to variations in transistor threshold voltages and anode voltage control.
Innovation Solution
The apparatus includes a pixel circuit with transistors and a storage capacitor that adjusts the anode voltage of an organic light-emitting diode by using a combination of auxiliary, low, and data voltages, along with a compensation voltage generated from a power source, to ensure consistent brightness across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional pixel circuits are used with fixed power source voltages, then the circuit structure is simple, but the image brightness uniformity deteriorates due to threshold voltage variations and electron mobility changes
Solution Approach 1:
The power supply unit dynamically adjusts the power source voltages (ELVDD and ELVSS) during the frame period based on the scanning line being driven. Different voltage levels are applied to different scan lines to compensate for threshold voltage variations and electron mobility changes in transistors, thereby achieving uniform image brightness across the display without requiring complex per-pixel compensation circuits
Solution Approach 2:
The invention changes the voltage parameters of the power source connected to the pixel circuits. By varying the ELVDD and ELVSS levels according to the scan line position and transistor characteristics, the system compensates for manufacturing variations in threshold voltage and electron mobility, improving brightness uniformity while maintaining a relatively simple pixel circuit structure
2Manufacturing precision
If power source voltages are changed during frame period, then the brightness uniformity is improved, but the power supply control complexity increases
Solution Approach 1:
The power supply control is segmented by scan lines. The power supply unit applies different voltage levels to different scan lines during the frame period, with each scan line receiving optimized voltages based on its position and associated transistor characteristics. This segmentation allows systematic compensation for variations while keeping the control logic organized and manageable through sequential scanning
3Manufacturing precision
If anode voltage is increased during scan period, then the brightness uniformity improves, but the transistor threshold voltage variations cause instability
Solution Approach 1:
The pixel circuit includes a feedback mechanism where the anode voltage of the OLED is adjusted based on the data voltage and transistor threshold voltage characteristics. The circuit automatically compensates for threshold voltage variations by adjusting the anode voltage level, ensuring stable and uniform brightness output despite variations in transistor parameters
Solution Approach 2:
The pixel circuit performs preliminary voltage adjustment during the scan period before the actual emission period. By increasing the anode voltage during the scan period when data is being written, the circuit pre-compensates for threshold voltage variations, ensuring that the OLED operates at the correct brightness level during the subsequent emission period
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 solution enables the organic light-emitting display apparatus to achieve desired brightness levels by compensating for threshold voltage and mobility variations, resulting in improved image uniformity and stability.
Implementation Method 1
organic light-emitting display apparatuses, display an image via an organic light-emitting diode that emits light due to a recombination of electrons and holes
Data Source
AI summary
An organic light-emitting display apparatus includes: a pixel coupled to a scan line, a data line, a control line, and a power line, the pixel comprising an organic light-emitting diode configured to emit light in response to a data voltage; and a power supply unit configured to apply power source voltages of different levels during one frame period, wherein the pixel is configured to increase an anode voltage of the organic light-emitting diode in a scan period when the data voltage is inputted.