Electrophoretic Display Pixel Leakage Control
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Solution Overview
Problem
Electrophoretic display devices face issues with leakage current between adjacent pixels, leading to increased power consumption and potential electrochemical reactions that deteriorate pixel electrode reliability, especially when using high-voltage memory circuits.
Innovation Solution
The implementation of a configuration where the first and second control lines connected to the pixel electrode form a leakage path only during signal input, and are otherwise set to a high impedance state, along with the use of a 'common oscillation driving' method and switch circuits with transfer gates or transistors to control electric potential and reduce leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high voltage (10V or above) is applied to the memory circuit to drive the electrophoretic element, then the display function is achieved, but a leakage current flows between adjacent pixel electrodes through the adhesive, increasing power consumption
Solution Approach 1:
The pixel electrode is divided into multiple segments (first pixel electrode and second pixel electrode) that can be independently controlled. By segmenting the electrode structure and applying different voltages to different segments, the patent enables selective activation of adjacent pixels, preventing continuous leakage current while maintaining display functionality.
Solution Approach 2:
The patent employs dynamic voltage control where the voltage applied to pixel electrodes changes over time based on display requirements. During non-display periods, voltages are reduced or equalized to minimize potential differences and leakage current, while during display periods, sufficient voltage difference is applied to activate the electrophoretic elements.
2Illumination intensity
If a large difference in electric potential is applied between adjacent pixel electrodes to display different colors, then the display contrast is improved, but a leakage current flows between adjacent pixels through the adhesive
Solution Approach 1:
The patent applies different voltage levels to different local regions (pixel electrodes) based on display requirements. By controlling the voltage of each pixel electrode independently and locally adjusting the potential difference, the patent achieves high display contrast where needed while minimizing leakage current in regions where contrast is not required.
Solution Approach 2:
The voltage difference between adjacent pixel electrodes is dynamically adjusted based on the display content. When adjacent pixels need to display different colors, sufficient voltage difference is applied; when they display the same color or during non-display periods, the voltage difference is reduced or eliminated to prevent leakage current.
3Reliability
If a pre-display operation (all white display, all black display, or inverted image display) is executed to prevent after-image, then the display quality is improved, but data must be transferred to all pixels causing increased power consumption
Solution Approach 1:
Instead of applying pre-display operations to all pixels, the patent applies them only to specific pixels that require it. By selectively identifying and treating only the necessary pixels for pre-display operations, the patent maintains display quality while significantly reducing the power consumption associated with full-screen pre-display sequences.
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 approach effectively suppresses leakage current between adjacent pixels, enhances power saving, and improves the reliability of the electrophoretic display device by reducing power consumption and preventing electrochemical reactions.
Implementation Method 1
an electrophoretic element is driven to be able to display an image
Implementation Method 2
the first and second control lines connected to the pixel electrode form a leakage path only during signal input, and are otherwise set to a high impedance state
Data Source
Figure 1
Figure 2~4
Figure 5A~5B
AI summary
An electrophoretic display device includes a pair of substrates, an electrophoretic element that includes electrophoretic particles and that are held between the pair of substrates, and a display portion formed of a plurality of pixels. The display portion includes pixel electrodes, an opposite electrode, a first control line and a second control line. Each of the pixel electrodes is formed in each of the pixels. The opposite electrode is opposed to the plurality of pixel electrodes through the electrophoretic element. The first control line and the second control line are connected to each of the pixels. Each of the pixels includes a pixel switching element, a memory circuit, and a switch circuit. The memory circuit is connected to the pixel switching element. Switching of the switch circuit is performed by an output signal of the memory circuit to switch between a connected state where the pixel electrode is connected to the first control line and a connected state where the pixel electrode is connected to the second control line.