Electrophoretic Display Driving Method for Bright Color States
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Solution Overview
Problem
Conventional color display methods using sub-pixels to achieve white states result in dim and unsaturated colors due to reduced reflectance, making them unsuitable for applications requiring high readability and contrast, such as e-readers.
Innovation Solution
A method for driving an electrophoretic display using a fluid with four types of charged particles (high positive, high negative, low positive, and low negative) dispersed in a solvent, where specific electric fields and a shaking waveform are applied to achieve a range of color states, including white, red, green, blue, and black, by manipulating particle distribution across the display surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If color filters are added on top of black/white sub-pixels to achieve color display, then color display capability is improved, but white state brightness deteriorates
Solution Approach 1:
The invention segments the particle population into four distinct types with different charge characteristics (high positive, high negative, low positive, low negative), allowing independent control of color states. This segmentation enables each particle type to be selectively positioned to achieve desired color displays without compromising white state brightness, as the low-charge particles can be precisely controlled to maintain adequate white level contribution.
Solution Approach 2:
The invention changes the charge parameter of particles by introducing both high-charge and low-charge particle types. The low-charge particles respond to low electric fields and can be precisely controlled to achieve color states while maintaining adequate white state brightness. This parameter differentiation allows the display to overcome the brightness loss inherent in conventional sub-pixel approaches.
2Illumination intensity
If a fourth sub-pixel is added to double white level, then white state brightness is improved, but color saturation deteriorates
Solution Approach 1:
The invention merges the functions of multiple particle types into a single electrophoretic medium. The high-charge particles provide strong response to high electric fields for achieving saturated color states, while low-charge particles respond to low electric fields to maintain white state brightness. This merging of particle types with different charge characteristics into one system eliminates the need for separate sub-pixels while maintaining both white brightness and color saturation.
Solution Approach 2:
The electrophoretic medium is formulated as a composite containing four types of particles with different charge characteristics and optical properties. This composite material approach allows the display to achieve both high white state brightness and saturated colors by utilizing the complementary properties of different particle types within the same medium, avoiding the trade-off inherent in adding separate white sub-pixels.
3Illumination intensity
If light from white pixel is added to achieve brighter colors, then color brightness is improved, but color gamut deteriorates
Solution Approach 1:
The invention replaces the mechanical/optical approach of adding physical white sub-pixels and light mixing with an electrical field-based approach. By applying controlled electric fields to manipulate the position and orientation of charged particles, the system achieves both color brightness and color gamut simultaneously. The electrical field control allows precise positioning of particles to achieve saturated colors without diluting the color gamut through light mixing from white sub-pixels.
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 enables brighter, more saturated colors and improved contrast, effectively addressing the limitations of conventional methods by enhancing the display's ability to produce a full color gamut without compromising brightness.
Implementation Method 1
the electrophoretic fluid comprising four and not more than four types of charged particles, namely high positive particles having a first optical characteristic, high negative particles having a second optical characteristic, low positive particles having a third optical characteristic and low negative particles having a fourth optical characteristic
Implementation Method 2
applying a high electric field having a polarity which drives the high positive particles towards the first surface, thereby causing the first optical characteristic to be displayed at the first surface
Implementation Method 3
applying a low electric field having a polarity which drives the low negative particles towards the first surface but is not strong enough to overcome the attractive force between the high positive particles and the high negative particles but sufficient to overcome the attractive force between other oppositely charged particles
Implementation Method 4
not strong enough to overcome the attractive force between the high positive particles and the high negative particles but sufficient to overcome the attractive force between other oppositely charged particles
Implementation Method 5
applying a shaking waveform to cause a fifth optical characteristic different from the first, second, third and fourth optical characteristics to be displayed at the first surface
Data Source
Figure 1
Figure 2-1(a)~2-1(b)
Figure 2-2(a)~2-2(c)
AI summary
The present invention provides a full color display device in which each pixel can display multiple high-quality color states. More specifically, an electrophoretic fluid is provided which comprises four types of particles, dispersed in a solvent or solvent mixture and each pixel can display at least five different color states.