Pixel Drive Transistor Control for Display Voltage Drop Reduction
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Solution Overview
Problem
Active matrix electroluminescent display devices face issues with voltage drops along long and narrow power supply lines, causing non-uniformity and cross talk between pixels, especially in larger displays, which affect the brightness and image quality.
Innovation Solution
The solution involves determining an overall brightness level for an image and controlling the drive transistors of each pixel based on this level, either by processing input signals or varying supply voltages, to limit maximum currents and reduce voltage drops, thereby minimizing cross talk and improving image uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If long and narrow power supply lines are used to supply current to pixels in large displays, then the display area is increased, but voltage drops occur causing non-uniformity and cross talk between pixels
Solution Approach 1:
The patent applies dynamics by making the drive transistor parameters adjustable rather than fixed. The transistor's drive current capability is dynamically modified by changing the transistor width parameter in response to detected image brightness conditions. This allows the system to adapt to varying current demands across different display regions and image content, compensating for voltage drops in long power supply lines and reducing cross-talk between pixels while maintaining image uniformity across large display areas.
2Illumination intensity
If higher drive currents are supplied to pixels to improve brightness, then image visibility is enhanced, but voltage drops along power supply lines increase causing cross talk
Solution Approach 1:
The patent applies parameter changes by modifying the transistor width parameter to optimize drive current delivery. When image brightness requires higher currents, the transistor width is increased to reduce on-resistance and enable higher current flow without excessive voltage drops. This dynamic parameter adjustment allows the system to achieve the necessary pixel brightness while minimizing the harmful cross-talk effect caused by voltage drops along the power supply lines.
3Power
If transistor size is increased to provide higher drive current, then current supply capability is improved, but pixel area and device complexity increase
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing optimal transistor width parameters for different drive current requirements. Before actual display operation, the system determines the appropriate transistor dimensions needed to achieve the desired drive current capability. This preliminary sizing allows the transistor to be optimally configured for high current delivery without requiring excessive device area or complex multi-transistor arrangements, thus improving power supply capability while controlling device complexity.
Data Source
AI summary
In an active matrix electroluminescent display device, an overall brightness level of an image to be displayed in a frame period is determined. A drive transistor of each pixel is controlled in dependence on an input drive signal for the pixel and on the overall brightness level, for example using a signal processor (30) to vary the pixel drive signals. This arrangement can control the pixels to limit the maximum currents drawn by the pixels, thereby limiting the cross talk effects resulting from voltage drops along row or column conductors. If an image is bright, the pixel drive levels across the image (or at least a part of the image) can be reduced, so that the maximum brightness is reduced.