Electrophoretic Display Driving Method for Bright Color States
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Solution Overview
Problem
Conventional color display methods using color filters result in a dim white state due to sub-pixel reflectance limitations, leading to unsatisfactory brightness and color saturation, especially in applications requiring high readability like e-readers.
Innovation Solution
A driving method for electrophoretic displays using a fluid with three types of pigment particles of differing optical characteristics, where two types carry opposite charge polarities and the third type has the same polarity but lower zeta potential, allowing for controlled voltage applications to enhance color display brightness and purity.
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 (white level becomes substantially less than half of black and white display)
Solution Approach 1:
The invention segments the display into dedicated color sub-pixels (red, green, blue) and dedicated black/white sub-pixels. Each sub-pixel type is optimized for its specific function: color sub-pixels use color filters for saturated color display, while black/white sub-pixels provide high brightness white and deep black states without color filter losses. This segmentation resolves the contradiction by allowing color display capability to be improved through color sub-pixels while maintaining high white state brightness through dedicated black/white sub-pixels that don't suffer from the 1/3 reflectance limitation of conventional approaches.
2Illumination intensity
If a fourth white pixel is added to double the white level, then white state brightness is improved, but color saturation deteriorates (colors become very light and unsaturated)
Solution Approach 1:
The invention separates the display function into dedicated color sub-pixels and dedicated black/white sub-pixels. The black/white sub-pixels provide high brightness white states without compromising color saturation, because they are not used for color display. Instead, color saturation is achieved through the dedicated color sub-pixels that use color filters. This resolves the contradiction by allowing white level to be doubled through additional black/white sub-pixels while color saturation is maintained through the separate color sub-pixel system.
Solution Approach 2:
The invention adds a fourth dimension to the color space by introducing dedicated black/white sub-pixels that operate independently from the RGB color sub-pixels. This creates a new dimension for brightness control that doesn't interfere with color saturation. The black/white sub-pixels provide an additional brightness channel that can be combined with color sub-pixels to achieve high brightness white states while maintaining saturated colors when needed.
3Illumination intensity
If color saturation of three sub-pixels is reduced to achieve brighter colors, then color brightness is improved, but color saturation deteriorates
Solution Approach 1:
The invention segments color display and brightness functions into separate sub-pixel types. Color sub-pixels are optimized for saturation with color filters, while black/white sub-pixels provide brightness. This allows color brightness to be improved by using the black/white sub-pixels to provide backlight or ambient light, while the color sub-pixels maintain their saturation through color filters. The contradiction is resolved because the brightness enhancement doesn't come from reducing color saturation, but from adding a separate brightness channel.
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
The method significantly improves color brightness and purity by effectively separating pigment particles, resulting in better color separation and display quality, particularly in achieving vibrant and readable white and black states.
Implementation Method 1
an electrophoretic fluid which comprises a first type of pigment particles, a second type of pigment particles and a third type of pigment particles, all of which are dispersed in a liquid, wherein the first type of pigment particles and the second type of pigment particles carry opposite charge polarities
Implementation Method 2
applying a first driving voltage to a pixel in the electrophoretic display for a first period of time, the first driving voltage having a polarity driving the first type of pigment particles towards the first surface
Data Source
AI summary
The present invention is directed to driving methods for a color display device which can display high quality color states. The display device utilizes an electrophoretic fluid which comprises three types of pigment particles having different optical characteristics, and provides for displaying at a viewing surface not only the colors of the three types of particles but also the colors of binary mixtures thereof.