Enhanced push-pull (EPP) waveforms for implementing a primary color set in a multicolor electrophoretic display

Abstract

Enhanced push-pull drive waveforms for driving a four-particle electrophoretic medium comprising four different types of particles, e.g., one set of scattering particles and three sets of subtractive particles. A method of identifying a preferred waveform for a target color state when using a voltage driver having at least five different voltage levels.

Description

[0001] Related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 108,521, filed November 2, 2020. All patents and publications disclosed herein are incorporated herein by reference in their entirety. Background Technology

[0003] Electrophoretic displays (EPDs) change color by modifying the position of charged colored particles relative to a light-transmitting viewing surface. These electrophoretic displays are often called "electronic paper" or "ePaper" because the resulting displays have high contrast and are readable in sunlight, much like ink on paper. Electrophoretic displays are used in e-readers such as... It is widely used because electrophoretic displays provide a book-like reading experience, consume little power, and allow users to carry libraries of hundreds of books in a lightweight handheld device.

[0004] For many years, electrophoretic displays have contained only two types of charged color particles: black and white. (To be sure, the term "color" as used here includes both black and white.) White particles are typically light-scattering and include, for example, titanium dioxide, while black particles are absorbent in the visible spectrum and can include carbon black, or absorbent metal oxides such as copper chromite. In its simplest sense, a monochrome electrophoretic display requires only a transparent electrode at the viewing surface, a back electrode, and an electrophoretic medium comprising white and black particles with opposite charges. When a voltage of one polarity is applied, the white particles move to the viewing surface, and when a voltage of the opposite polarity is applied, the black particles move to the viewing surface. If the back electrode comprises controllable regions (pixels)—an active matrix of segmented electrodes or pixel electrodes controlled by transistors—a pattern can appear electronically at the viewing surface. For example, the pattern could be the text of a book.

[0005] Recently, a variety of color options have become commercially available for electrophoretic displays, including tricolor displays (black, white, and red; black, white, and yellow) and quadricolor displays (black, white, red, and yellow). Similar to the operation of a black-and-white electrophoretic display, the operation of an electrophoretic display with three or four reflective pigments is similar to that of a simple black-and-white display because the desired color particles are driven onto the observation surface. The driving scheme is far more complex than that with only black and white, but ultimately, the optical function of the particles is the same.

[0006] Advanced Color Electronic Paper (ACeP) TMThis also includes four types of particles, but the cyan, yellow, and magenta particles are subtractive rather than reflective, thus allowing for thousands of colors to be produced at each pixel. The color process is functionally equivalent to the printing methods long used in offset and inkjet printing. A given color is produced by using the correct proportions of cyan, yellow, and magenta on a bright white paper background. In the case of ACeP, the relative positions of the cyan, yellow, magenta, and white particles relative to the viewing surface determine the color at each pixel. While this type of electrophoretic display allows for thousands of colors per pixel, careful control of the position of each pigment (50 to 500 nanometers in size) within a working space approximately 10 to 20 micrometers thick is crucial. Clearly, variations in pigment position will result in an incorrect color being displayed at a given pixel. Therefore, this system requires precise voltage control. Further details of the system are available in the following U.S. patents, all of which are incorporated herein by reference in their entirety: U.S. Patent Nos. 9,361,836, 9,921,451, 10,276,109, 10,353,266, 10,467,984, and 10,593,272.

[0007] This invention relates to waveforms for driving color electrophoretic displays, and more particularly, but not exclusively, to electrophoretic displays capable of displaying more than two colors using a single-layer electrophoretic material comprising multiple colored particles (e.g., white, cyan, yellow, and magenta particles). In some cases, two particles will be positively charged and two particles will be negatively charged. In some cases, one positively charged particle will have a thick polymer shell, and the other negatively charged particle will have a thick polymer shell.

[0008] The term "gray state" is used here in its conventional meaning in the imaging field, referring to a state between two extreme optical states of a pixel, but not necessarily a black-and-white transition between these two extremes. For example, several IENK patents and publications mentioned below describe electrophoretic displays where the extreme states are white and dark blue, making the intermediate gray state actually a pale blue. In fact, as already mentioned, a change in optical state may not be a color change at all. The terms "black" and "white" may be used below to refer to the two extreme optical states of a display, and should be understood to generally include extreme optical states that are not strictly black and white, such as the white and dark blue states mentioned above.

[0009] The terms “bistable” and “bistable” are used herein in their conventional sense in the art, referring to a display comprising display elements having first and second display states, at least one optical characteristic of which differs such that, after any given element is driven to present its first or second display state using an addressing pulse of finite duration, the state will persist for at least several times (e.g., at least four times) the minimum duration of the addressing pulse required to change the state of the display element after the addressing pulse terminates. As shown in U.S. Patent No. 7,170,670, some particle-based electrophoretic displays supporting grayscale are stable not only in their extreme black and white states but also in intermediate gray states, as are some other types of electro-optical displays. Such displays are aptly referred to as multistable rather than bistable; however, for convenience, the term “bistable” may be used herein to encompass both bistable and multistable displays.

[0010] The term "impulse," when used in connection with driving an electrophoretic display, refers herein to the integral of the voltage applied during driving the display with respect to time. The term "waveform," when used in connection with driving an electrophoretic display, describes a series or pattern of voltages supplied to the electrophoretic medium over a given time period (second, frame, etc.) to produce the desired optical effect in the electrophoretic medium.

[0011] Particles that absorb, scatter, or reflect broadband or selected wavelengths of light are referred to herein as colored or pigment particles. Various materials that absorb or reflect light (strictly speaking, this term refers to insoluble colored materials) other than pigments, such as dyes or photonic crystals, may also be used in the electrophoretic media and displays of the present invention.

[0012] For many years, particle-based electrophoretic displays have been a subject of intensive research and development. In such displays, multiple charged particles (sometimes called pigment particles) move through a fluid under the influence of an electric field. Compared to liquid crystal displays (LCDs), electrophoretic displays can offer advantages such as good brightness and contrast, wide viewing angles, state bistability, and low power consumption. However, long-term image quality issues have hindered their widespread use. For example, the particles constituting an electrophoretic display are prone to settling, resulting in a short lifespan for these displays.

[0013] As mentioned above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, this fluid is a liquid, but electrophoretic media can be generated using a gaseous fluid; see, for example, Kitamura, T., et al., Electrical toner movement for electronic paper-like display, IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y., et al., Toner display using insulative particles charged triboelectrically, IDW Japan, 2001, Paper AMD4-4). See also U.S. Patent Nos. 7,321,459 and 7,236,291. When such gas-based electrophoretic media are used in a direction that allows particle settling, such as in signs where the media are arranged in a vertical plane, they are susceptible to the same type of problems as liquid-based electrophoretic media due to the same particle settling. In fact, particle sedimentation is more severe in gas-based electrophoretic media than in liquid-based electrophoretic media because the lower viscosity of gaseous suspensions allows electrophoretic particles to settle more quickly compared to liquids.

[0014] Numerous patents and applications transferred to or in the name of MIT and Einkel describe various techniques for encapsulating electrophoretic and other electro-optic media. These encapsulated media comprise a plurality of small capsules, each capsule comprising an inner phase and a capsule wall surrounding the inner phase, wherein the inner phase contains electrophoretically movable particles in a fluid medium. Typically, the capsules themselves are held in a polymer binder to form a coherent layer located between two electrodes. The techniques described in these patents and applications include:

[0015] (a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814;

[0016] (b) Encapsulation, adhesives, and encapsulation processes; see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719;

[0017] (c) Microunit structures, wall materials, and methods of forming microunits; see, for example, U.S. Patent Nos. 7,072,095 and 9,279,906;

[0018] (d) Methods for filling and sealing microcells; see, for example, U.S. Patent Nos. 7,144,942 and 7,715,088;

[0019] (e) Thin films and sub-assemblies containing electro-optic materials; see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564;

[0020] (f) Backplanes, adhesive layers and other auxiliary layers in displays, and methods thereof; see, for example, U.S. Patent Nos. 7,116,318 and 7,535,624;

[0021] (g) Color formation and color adjustment; see, for example, U.S. Patent Nos. 6,017,584; 6,545,797; 6,664,944; 6,788,452; 6,864,875; 6,914,714; 6,972,893; 7,038,656; 7,038,670; 7,046,228; 7,052,571; 7,075,502; 7,167,155; 7,385,751; 7,492,505; 7,667,684; 7,684,108;7,791,789;7,800,813;7,821,702;7,839,564;7,910,175;7,952,790;7,956,841;7,982,941;8,040,594;8,054,526;8,098,418;8,159,636;8,213,076;8,363,299;8,422,116;8,441,714;8,441,716;8,466 852;8,503,063;8,576,470;8,576,475;8,593,721;8,605,354;8,649,084;8,670,174;8,704,756;8,717,664;8,786,935;8,797,634;8,810,899;8,830,559;8,873,129;8,902,153;8,902,491;8,917,439;8,964,282 ; 9,013,783; 9,116,412; 9,146,439; 9,164,207; 9,170,467; 9,170,468; 9,182,646; 9,195,111; 9,199,441; 9,268,191; 9,285,649; 9,293,511; 9,341,916; 9,360,733; 9,361,836; 9,383,623; and 9,423,666; and U.S. Patent Application Publication No.2008 / 0043318; 2008 / 0048970; 2009 / 0225398; 2010 / 0156780; 2011 / 0043543; 2012 / 0326957; 2013 / 0242378; 2013 / 0278995; 2014 / 0055840; 2014 / 0078576; 2014 / 0340430; 2014 / 0340736; 2014 / 0362213; 2 015 / 0103394; 2015 / 0118390; 2015 / 0124345; 2015 / 0198858; 2015 / 0234250; 2015 / 0268531; 2015 / 0301246; 2016 / 0011484; 2016 / 0026062; 2016 / 0048054; 2016 / 0116816; 2016 / 0116818; and 2016 / 0140909.

[0022] (h) A method for driving a display; see, for example, U.S. Patent Nos. 5,930,026; 6,445,489; 6,504,524; 6,512,354; 6,531,997; 6,753,999; 6,825,970; 6,900,851; 6,995,550; 7,012,600; 7,023,420; 7,034,783; 7,061,166; 7,061,662; 7,116,466; 7,119,772; 7,177,066; 7,193,625; 7,202,847; 7,242,514; 7,259,744; 7,304,787; 7,31 2,794; 7,327,511; 7,408,699; 7,453,445; 7,492,339; 7,528,822; 7,545,358; 7,583,251; 7,602,374; 7,612,760; 7,679,599; 7,679,813; 7,683,606 7,688,297; 7,729,039; 7,733,311; 7,733,335; 7,787,169; 7,859,742; 7,952,557; 7,956,841; 7,982,479; 7,999,787; 8,077,141; 8,125,501; 8,13 9,050; 8,174,490; 8,243,013; 8,274,472; 8,289,250; 8,300,006; 8,305,341; 8,314,784; 8,373,649; 8,384,658; 8,456,414; 8,462,102; 8,514,168 ; 8,537,105; 8,558,783; 8,558,785; 8,558,786; 8,558,855; 8,576,164; 8,576,259; 8,593,396; 8,605,032; 8,643,595; 8,665,206; 8,681,191; 8,73 0,153; 8,810,525; 8,928,562; 8,928,641; 8,976,444; 9,013,394; 9,019,197; 9,019,198; 9,019,318; 9,082,352; 9,171,508; 9,218,773; 9,224,338; 9,224,342; 9,224,344; 9,230,492; 9,251,736; 9,262,973; 9,269,311; 9,299,294; 9,373,289; 9,390,066; 9,390,661; and 9,412,314; and U.S. Patent Application Publication No.2003 / 0102858; 2004 / 0246562; 2005 / 0253777; 2007 / 0091418; 2007 / 0103427; 2007 / 0176912; 2008 / 0024429; 2008 / 0024482; 2008 / 0136774; 2008 / 0291129; 2008 / 0303780; 2009 / 0174651; 2009 / 0195568; 2009 / 0322721; 2010 / 01 94733; 2010 / 0194789; 2010 / 0220121; 2010 / 0265561; 2010 / 0283804; 2011 / 0063314; 2011 / 0175875; 2011 / 0193840; 2011 / 0193841; 2011 / 0199671; 2011 / 0221740; 2012 / 0001957; 2012 / 0098740; 2013 / 0063333; 2013 / 0194250; 2 013 / 0249782; 2013 / 0321278; 2014 / 0009817; 2014 / 0085355; 2014 / 0204012; 2014 / 0218277; 2014 / 0240210; 2014 / 0240373; 2014 / 0253425; 2014 / 0292830; 2014 / 0293398; 2014 / 0333685; 2014 / 0340734; 2015 / 0070744; 2015 / 009 7877; 2015 / 0109283; 2015 / 0213749; 2015 / 0213765; 2015 / 0221257; 2015 / 0262255; 2015 / 0262551; 2016 / 0071465; 2016 / 0078820; 2016 / 0093253; 2016 / 0140910; and 2016 / 0180777 (these patents and applications may be referred to hereinafter as MEDEOD (Method for Driving an Electro-Optical Display) applications).

[0023] (i) Applications of displays; see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348; and

[0024] (j) Non-electrophoretic displays, as described in U.S. Patent No. 6,241,921 and U.S. Patent Application Publication No. 2015 / 0277160, and U.S. Patent Application Publication Nos. 2015 / 0005720 and 2016 / 0012710.

[0025] Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thereby producing so-called polymer-dispersed electrophoretic displays, wherein the electrophoretic medium comprises a plurality of discrete droplets of electrophoretic fluid and a continuous phase of polymeric material, and the discrete droplets of electrophoretic fluid within such a polymer-dispersed electrophoretic display can be considered as capsules or microcapsules, even if no discrete capsule membrane is associated with each individual droplet; see, for example, U.S. Patent No. 6,866,760. Therefore, for the purposes of this application, such polymer-dispersed electrophoretic media are considered a subclass of encapsulated electrophoretic media.

[0026] One related type of electrophoretic display is the so-called microcell electrophoretic display. In a microcell electrophoretic display, charged particles and fluid are not encapsulated within microcapsules, but rather held within multiple cavities formed within a carrier medium (typically a polymer film). See, for example, U.S. Patent Nos. 6,672,921 and 6,788,449.

[0027] Although electrophoretic media are typically opaque (because, for example, in many electrophoretic media, particles essentially block visible light from passing through the display) and operate in reflective mode, many electrophoretic displays can be fabricated to operate in so-called shutter mode, in which one display state is substantially opaque and the other is transmissive. See, for example, U.S. Patent Nos. 5,872,552; 6,130,774; 6,144,361; 6,172,798; 6,271,823; 6,225,971; and 6,184,856. Dielectrophoretic displays, similar to electrophoretic displays but dependent on changes in electric field strength, can operate in a similar mode; see U.S. Patent No. 4,418,346. Other types of electro-optic displays are also capable of operating in shutter mode. Electro-optic media operating in shutter mode can be used in multilayer structures of full-color displays; in such structures, at least one layer adjacent to the viewing surface of the display operates in shutter mode to expose or hide a second layer further away from the viewing surface.

[0028] Encapsulated electrophoretic displays are generally free from the aggregation and sedimentation failure modes of conventional electrophoretic apparatus and offer more beneficial effects, such as the ability to print or coat displays on a variety of flexible and rigid substrates. (The term "printing" is used to include all forms of printing and coating, including but not limited to: pre-metering coating such as patch die coating, slot or extrusion coating, slide or stack coating, curtain coating; roller coating such as roller blade coating, forward and reverse roller coating; concave coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; screen printing; electrostatic printing; thermal printing; inkjet printing; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar techniques.) Therefore, the resulting displays can be flexible. Furthermore, because the display medium can be printed (using a variety of methods), the display itself can be manufactured inexpensively.

[0029] As described above, the simplest existing electrophoretic media essentially displays only two colors. This electrophoretic medium uses a single type of electrophoretic particles of a first color in a colored fluid of a second, different color (in this case, the first color is displayed when the particles are near the viewing surface of the display, and the second color is displayed when the particles are separated from the viewing surface), or first and second types of electrophoretic particles of different first and second colors in a colorless fluid (in this case, the first color is displayed when the first type of particles are near the viewing surface of the display, and the second color is displayed when the second type of particles are near the viewing surface). Typically, these two colors are black and white. If a full-color display is required, an array of color filters can be deposited on the viewing surface of a monochrome (black and white) display. Displays with color filter arrays rely on area sharing and color mixing to create color stimuli. Available display areas can be shared among three or four primary colors, such as red / green / blue (RGB) or red / green / blue / white (RGBW), and the filters can be arranged in a one-dimensional (stripes) or two-dimensional (2x2) repeating pattern. Other options of primary colors or more than three primary colors are also known in the art. Three (in the case of an RGB monitor) or four (in the case of an RGBW monitor) subpixels are chosen to be small enough that they visually blend together at the intended viewing distance to form a single pixel with uniform color stimulation (“color blending”). An inherent drawback of area sharing is that colorant is always present, and colors can only be modulated by switching the corresponding pixel of the underlying monochrome display to white or black (turning the corresponding primary color on or off). For example, in an ideal RGBW monitor, red, green, blue, and white primary colors each occupy a quarter of the display area (a quarter of the subpixels), white subpixels are as bright as the white of the underlying monochrome display, and each colored subpixel is no brighter than one-third of the white of the monochrome display. The brightness of white displayed by the monitor as a whole cannot exceed half the brightness of the white subpixels (the white area of ​​the monitor is generated by displaying one white subpixel out of every four white subpixels, plus the colored form of each colored subpixel being equivalent to one-third of the white subpixel, so the sum of the three colored subpixels does not exceed one white subpixel). The brightness and saturation of colors are reduced by sharing areas with color pixels switched to black. When mixing yellow, area sharing is particularly problematic because it is brighter than any other color of equal brightness, and saturated yellow is almost as bright as white. Switching the blue pixels (a quarter of the display area) to black makes the yellow too dark.

[0030] U.S. Patent Nos. 8,576,476 and 8,797,634 describe a multicolor electrophoretic display with a single backplane comprising independently addressable pixel electrodes and a common transparent front electrode. Multiple electrophoretic layers are disposed between the backplane and the front electrode. The displays described in these applications are capable of displaying any primary color (red, green, blue, cyan, magenta, yellow, white, and black) at any pixel location. However, using multiple electrophoretic layers located between a single set of addressable electrodes has drawbacks. The electric field experienced by particles in a particular layer is lower than that of a single electrophoretic layer addressed with the same voltage. Furthermore, optical losses in the electrophoretic layer closest to the observation surface (e.g., caused by light scattering or undesirable absorption) can affect the appearance of the image formed in the underlying electrophoretic layers.

[0031] Attempts have been made to provide full-color electrophoretic displays using a single electrophoretic layer. For example, U.S. Patent No. 8,917,439 describes a color display comprising an electrophoretic fluid comprising one or two types of pigment particles dispersed in a transparent and colorless or colored solvent, the electrophoretic fluid being disposed between a common electrode and a plurality of pixels or driving electrodes. The driving electrodes are arranged to expose a background layer. U.S. Patent No. 9,116,412 describes a method for driving a display unit filled with an electrophoretic fluid comprising two types of charged particles with opposite charge polarities and having two contrasting colors. The two types of pigment particles are dispersed in a colored solvent or in a solvent dispersed with uncharged or slightly charged colored particles. The method comprises driving the display unit to display the color of the solvent or the color of the uncharged or slightly charged colored particles by applying a driving voltage of about 1% to about 20% of the full driving voltage. U.S. Patent Nos. 8,717,664 and 8,964,282 describe an electrophoretic fluid and a method for driving an electrophoretic display. The fluid contains pigment particles of types one, two, and three, all dispersed in a solvent or solvent mixture. The first and second types of pigment particles have opposite charge polarities, and the third type of pigment particles has a charge level approximately 50% lower than that of the first or second types. The three types of pigment particles have different levels of threshold voltage, or different levels of mobility, or both. None of these patent applications disclose a full-color display in the sense of the terminology used below. Summary of the Invention

[0032] This paper discloses an improved method for driving a full-color electrophoretic display and a method for identifying waveforms for a full-color electrophoretic display using these driving methods. One aspect discloses a method for driving an electrophoretic display. This driving method includes providing an electrophoretic medium comprising four groups of particles, each group having different optical properties and different charge properties; disposing the electrophoretic medium between a first transparent electrode and a second electrode; providing a voltage driver configured to provide at least five voltage levels: high negative voltage, medium negative voltage, zero voltage, medium positive voltage, and high positive voltage; and driving the electrophoretic medium to a desired optical state by providing a push-pull waveform. This push-pull waveform includes a first positive portion consisting of a first pulse and a second pulse, the first pulse having a first positive amplitude and a first time width, and the second pulse having a second positive amplitude and a second time width. The push-pull waveform also includes a second negative portion consisting of a third pulse and a fourth pulse, the third pulse having a first negative amplitude and a third time width, and the fourth pulse having a second negative amplitude and a fourth time width. The first positive amplitude, the second positive amplitude, the first negative amplitude, and the second negative amplitude are all non-zero, and at least three of the first time width, the second time width, the third time width, and the fourth time width are non-zero. In one embodiment, the first group of particles is reflective, while the second, third, and fourth groups of particles are subtractive. In one embodiment, two groups of particles are positively charged, and two groups of particles are negatively charged. In one embodiment, one group of particles is positively charged, and three groups of particles are negatively charged. In one embodiment, three groups of particles are positively charged, and one group of particles is negatively charged. In one embodiment, the second electrode comprises a plurality of pixel electrodes arranged in an array. In one embodiment, the second electrode is transparent. In one embodiment, the high negative voltage is between -30V and -20V, the medium negative voltage is between -20V and -2V, the medium positive voltage is between 2V and 20V, and the high positive voltage is between 20V and 30V.

[0033] In another aspect, a method for identifying enhanced push-pull waveforms is provided. The method includes selecting a finite group of voltages to drive an electrophoretic display, wherein the group comprises at least five different voltage levels; selecting a finite time width for candidate waveforms; calculating all waveforms having a first positive portion and a second negative portion, the first positive portion consisting of a first pulse and a second pulse, wherein the first pulse has a first positive amplitude and a first time width, the second pulse has a second positive amplitude and a second time width, and the second negative portion consisting of a third pulse and a fourth pulse, the third pulse having a first negative amplitude and a third time width, and the fourth pulse having a second negative amplitude and a fourth time width. The first positive amplitude, second positive amplitude, first negative amplitude, and second negative amplitude each have values ​​from the finite group of voltages, and the sum of the first pulse width, second pulse width, third pulse width, and fourth pulse width equals the finite time width. A final step involves calculating the optical state generated by each candidate waveform using a model of an electrophoretic display having an electrophoretic medium comprising four groups of particles, each group of particles having different optical properties and different charge properties, and the electrophoretic medium being disposed between a first transparent electrode and a second electrode; and selecting a waveform to generate a target optical state. In one embodiment, selection includes comparing a target color with a predicted output color. In one embodiment, a selected waveform is input to a physical electrophoresis display comprising an electrophoretic medium containing four groups of particles, each group having different optical and charge properties, and the electrophoretic medium is disposed between a first transparent electrode and a second electrode. In one embodiment, the color output of the physical electrophoresis display is evaluated and compared to a target color. In one embodiment, the voltages of the finite groups include a high negative voltage between -30V and -20V, a medium negative voltage between -20V and -2V, a medium positive voltage between 2V and 20V, and a high positive voltage between 20V and 30V. In one embodiment, the voltages of the finite groups include -27V, 0V, and +27V. In one embodiment, the first group of particles is reflective, while the second, third, and fourth groups of particles are subtractive. In one embodiment, two groups of particles are positively charged, and two groups of particles are negatively charged. In one embodiment, one group of particles is positively charged, and three groups of particles are negatively charged. In one embodiment, three groups of particles are positively charged, and one group of particles is negatively charged. Attached Figure Description

[0034] Figure 1 This is a cross-sectional schematic diagram showing the positions of various colored particles in the electrophoretic medium of the present invention when displaying black, white, three subtractive primary colors, and three additive primary colors.

[0035] Figure 2AThe diagram illustrates four different types of pigment particles used in multi-particle electrophoresis media.

[0036] Figure 2B The diagram illustrates four different types of pigment particles used in multi-particle electrophoresis media.

[0037] Figure 2C The diagram illustrates four different types of pigment particles used in multi-particle electrophoresis media.

[0038] Figure 3 An exemplary equivalent circuit for a single pixel of an electrophoretic display is shown.

[0039] Figure 4 A layer of an exemplary electrophoretic color display is shown.

[0040] Figure 5 A simple push-pull waveform is shown that can be used to realize a set of primary colors in an optimization system, which includes a reflective (white) particle and three subtractive (cyan, yellow, magenta) particles.

[0041] Figure 6 A set of voltage pulses for a seven-stage driver that can be used in an electrophoretic display is shown. Each waveform that can be used to drive the electrophoretic medium is some combination of these voltage pulses.

[0042] Figure 7 An algorithm for identifying enhanced push-pull waveforms is shown.

[0043] Figure 8 An exemplary enhanced push-pull waveform is shown.

[0044] Figure 9 An exemplary enhanced push-pull waveform is shown.

[0045] Figure 10 The model using a metal oxide TFT backplane and a four-particle ACeP type electrophoretic medium is shown to achieve 10,000 final color states through an enhanced push-pull waveform.

[0046] Figure 11 A subset of DC-balanced EPP waveforms is shown for a model using a metal oxide TFT backplane and a four-particle ACeP-type electrophoretic dielectric.

[0047] Figure 12A and Figure 12B Comparison of calculated DC imbalance ( Figure 12A ) and DC balance ( Figure 12B The waveform is used to obtain a specific green color.

[0048] Figure 13A and Figure 13B Comparison of calculated DC imbalance ( Figure 13A ) and DC balance ( Figure 13B The waveform is used to obtain a specific green color. Detailed Implementation

[0049] This invention details a method for identifying enhanced push-pull waveforms used to drive multi-particle color electrophoretic media, for example, wherein at least two types of particles are colored and subtractive, and at least one particle is scattering. Typically, such a system includes white particles and subtractive primary color particles of cyan, yellow, and magenta. Such a system in… Figure 1 The image is schematically shown, and it can provide white, yellow, red, magenta, blue, cyan, green, and black at each pixel.

[0050] In the ACeP example, each of the eight primary colors (red, green, blue, cyan, magenta, yellow, black, and white) corresponds to a different arrangement of the four pigments, such that the observer can only see those colored pigments located on the observation side of the white pigment (i.e., the only pigment scattering light). It has been found that classifying the four pigments into appropriate configurations to produce the waveforms of these colors requires at least five voltage levels (high positive, low positive, zero, low negative, high negative). See also Figure 1 To achieve a wider color gamut, additional voltage levels must be used to better control the pigments, for example, seven voltage levels, or even nine voltage levels. This invention provides a method for identifying enhanced push-pull waveforms to drive such electrophoretic media, resulting in faster, less flickering pixel color refreshes and producing a more pleasing color spectrum for the observer.

[0051] The three particles providing the three subtractive primary colors (e.g., in an ACeP system) can be substantially non-scattering (“SNLS”). The use of SNLS particles allows for color mixing and provides more color results than could be achieved using the same number of scattering particles. These thresholds must be sufficiently separated relative to the voltage drive level to avoid crosstalk between particles, and this separation requires high addressing voltages for some colors. Furthermore, addressing the colored particle with the highest threshold also moves all other colored particles, and these other particles must then switch to their desired positions at lower voltages. This stepped color addressing scheme produces undesirable color flicker and longer transition times.

[0052] As mentioned earlier, in the attached diagram Figure 1 This is a cross-sectional schematic diagram showing the positions of various particles in an ACeP-type electrophoretic medium when displaying black, white, the three subtractive primary colors, and the three additive primary colors. Figure 1In this embodiment, it is assumed that the viewing surface of the display is at the top (as shown in the figure), i.e., the user views the display from this direction, and light is incident from this direction. As already noted, in the preferred embodiment, only one of the four particles used in the electrophoretic medium of the present invention substantially scatters light, and... Figure 1 In this context, the particle is assumed to be a white pigment. This light-scattering white particle forms a white reflector, through which any particle above the white particle (such as...) can reflect light. Figure 1 All of these particles (as shown) can be observed. Light entering the display's observation surface passes through these particles, is reflected by the white particles, passes through these particles again, returns, and exits from the display. Therefore, the particles above the white particles can absorb various colors, and the colors presented to the user are produced by the combination of particles above the white particles. Any particles located below the white particles (behind them from the user's perspective) are masked by the white particles and do not affect the displayed colors. Because the second, third, and fourth particles are essentially non-light-scattering, their order or arrangement relative to each other is not important; however, for the reasons already stated, their order or arrangement relative to the white (light-scattering) particles is crucial.

[0053] More specifically, when cyan, magenta, and yellow particles are located below white particles ( Figure 1 In case [A], there are no particles above the white particle and the pixel displays only white. When a single particle is above a white particle, the color of that single particle is... Figure 1 In cases [B], [D], and [F], the colors are yellow, magenta, and cyan, respectively. When two particles are positioned above a white particle, the displayed color is a combination of the colors of those two particles; Figure 1 In case [C], magenta and yellow particles appear red; in case [E], cyan and magenta particles appear blue; and in case [G], yellow and cyan particles appear green. Finally, when all three colored particles are above the white particle ( Figure 1 In the case of [H], all incident light is absorbed by the three subtractive primary color particles and the pixel displays black.

[0054] A subtractive primary color can be represented by a single type of light-scattering particle, so the display will contain two types of light-scattering particles, one white and one colored. However, in this case, the position of the light-scattering colored particles relative to other colored particles covering the white particles will be important. For example, when displaying black (when all three colored particles are above the white particles), the scattering colored particles cannot be above the non-scattering colored particles (otherwise they would be partially or completely hidden behind the scattering particles, and the color displayed would be the color of the scattering colored particles, not black).

[0055] If more than one type of colored particle scatters light, it is not easy to appear black.

[0056] Figure 1 An idealized scenario is illustrated where the color is uncontaminated (i.e., light-scattering white particles completely mask any particles located behind them). In reality, the masking of white particles may not be perfect, so particles that would ideally be completely masked may still have some light absorption. This contamination typically reduces the brightness and chromaticity of the resulting color. In the electrophoretic medium of this invention, this color contamination should be minimized to a degree that the resulting color is commensurate with industry standards for color reproduction. A particularly popular standard is SNAP (Newspaper Advertising Production Standard), which assigns L*, a*, and b* values ​​to each of the eight primary colors mentioned above. (Hereinafter, "primary color" will be used to refer to...) Figure 1 The eight colors shown are black, white, the three subtractive primary colors, and the three additive primary colors.

[0057] Figure 2A and 2B Cross-sectional schematic diagrams of four pigment types (1-4; 5-8) used in ACeP-type electrophoretic displays are shown. Figure 2A In this design, the polymer shell adsorbed onto the core pigment is represented by a dark shading, while the core pigment itself appears unshaded. Various forms can be used for the core pigment: spherical, needle-like, or other anisoaxial shapes; aggregates of smaller particles (i.e., “grape clusters”); composite particles containing small pigment particles or dyes dispersed in a binder; and so on, as is known in the art. The polymer shell can be a covalently bonded polymer prepared by grafting processes or chemisorption known in the art, or it can be physically adsorbed onto the particle surface. For example, the polymer can be a block copolymer containing both insoluble and soluble segments.

[0058] exist Figure 2A In the embodiments, the first and second particle types preferably have a more robust polymer shell than the third and fourth particle types. The light-scattering white particles belong to either the first or second type (negatively or positively charged). In the following discussion, it is assumed that the white particles are negatively charged (i.e., belonging to type 1), but those skilled in the art will understand that the general principles described will apply to a group of particles in which the white particles are positively charged.

[0059] In addition, such as Figure 2B As shown, compared to the third and fourth particle types, the first and second particle types do not require different polymer shells. Figure 2BAs shown, sufficient differential charges on the four particles will allow for electrophoretic control of the particles and the creation of the desired color at the observed surface. For example, particle 5 could have a much larger negative charge than particle 7, and particle 6 could have a much larger positive charge than particle 8. Other combinations of polymer functionality and charge (or particle size) can also be used; however, it must be that all four particles can be separated from each other in the presence of a suitable electric field, such as a low-voltage electric field that can be generated using commercial digital electronics.

[0060] exist Figure 2A In the system of the present invention, the electric field required to separate aggregates formed by a mixture of particles of types 3 and 4 in a suspension containing a charge control agent is greater than the electric field required to separate aggregates formed by any other combination of the two types of particles. On the other hand, the electric field required to separate aggregates formed between the first and second types of particles is less than the electric field required to separate aggregates formed between the first and fourth particles or between the second and third particles (and of course less than the electric field required to separate the third and fourth particles).

[0061] exist Figure 2A In this model, the core pigments containing the particles are shown to have approximately the same size, and the electromotive force of each particle (although not shown) is assumed to be approximately the same. The difference lies in the thickness of the polymer shell surrounding each core pigment. Figure 2A As shown, the polymer shells of particles of types 1 and 2 are thicker than those of particles of types 3 and 4.

[0062] In this invention, it is not necessary for all colored pigments to behave as described in the reference above. Figure 2A and 2B As described. Figure 2C As shown, the third particle can have a robust polymer shell and can possess a wide range of charges, including a weak positive charge. In this case, the surface chemistry of the third particle must differ from that of the first particle. For example, the first particle can have a covalently linked silane shell grafted with a polymer, which can be composed of preferably hydrophobic acrylic or styrene monomers. The third particle can comprise a non-covalently linked polymer shell deposited on the surface of the core particle through dispersion polymerization. In this case, the invention is not limited to the above references. Figure 2A and 2B The mechanism described.

[0063] To achieve a high-resolution display, each pixel of the display must be addressable without interference from adjacent pixels. One way to achieve this is by providing an array of nonlinear elements, such as transistors or diodes, with at least one nonlinear element associated with each pixel to produce an "active matrix" display. The addressing or pixel electrode of a pixel is connected to an appropriate voltage source via the associated nonlinear element. Typically, when the nonlinear element is a transistor, the pixel electrode is connected to the drain of the transistor, and this arrangement will be assumed in the following description, although it is essentially arbitrary and the pixel electrode can be connected to the source of the transistor. Typically, in a high-resolution array, pixels are arranged in a two-dimensional array of rows and columns such that any particular pixel is uniquely defined by the intersection of a specified row and a specified column. The sources of all transistors in each column are connected to a single column electrode, and the gates of all transistors in each row are connected to a single row electrode; again, the source-to-row and gate-to-column assignments are conventional but essentially arbitrary and can be reversed if desired. Row electrodes are connected to row drivers, which essentially ensures that only one row is selected at any given time. That is, a selection voltage is applied to the selected row electrode to ensure all transistors in the selected row are turned on, while a non-selection voltage is applied to all other rows to ensure all transistors in these unselected rows remain off. Column electrodes are connected to column drivers, which apply voltages to individual column electrodes. These voltages are selected to drive the pixels in the selected row to their desired optical state. (The voltages mentioned above are relative to a common front electrode, which is typically located on the side of the electro-optic medium opposite to the nonlinear array and extends across the entire display.) After a pre-selection interval called the “line addressing time,” the selected row is deselected, the next row is selected, and the voltage on the column driver is changed to write the next line of the display. This process is repeated to write the entire display line by line. The time between addressings in the display is called a “frame.” Therefore, a display updating at 60Hz has a 16-millisecond frame.

[0064] Traditionally, each pixel electrode has an associated capacitor electrode, such that the pixel electrode and the capacitor electrode form a capacitor; see, for example, International Patent Application WO 01 / 07961. In some embodiments, an N-type semiconductor (e.g., amorphous silicon) can be used to form a transistor, and the “select” and “non-select” voltages applied to the gate electrode can be positive and negative, respectively.

[0065] The attached diagram Figure 3An exemplary equivalent circuit for a single pixel of an electrophoretic display is depicted. As shown, the circuit includes a capacitor 10 formed between a pixel electrode and a capacitor electrode. The electrophoretic dielectric 20 is represented as a capacitor and a resistor connected in parallel. In some cases, the direct or indirect coupling capacitance 30 between the gate electrode of the transistor associated with the pixel and the pixel electrode (often referred to as "parasitic capacitance") can introduce unwanted noise into the display. Typically, the parasitic capacitance 30 is much smaller than the capacitance of the storage capacitor 10, and when a pixel row of the display is selected or deselected, the parasitic capacitance 30 can cause a small negative offset voltage, also referred to as "recoil voltage," to the pixel electrode, typically less than 2 volts. In some embodiments, to compensate for the unwanted "recoil voltage," a common potential V can be provided to the top plate electrode and the capacitor electrode associated with each pixel. com , so that when V com Set to equal to the recoil voltage (V) KB When the value is ), each voltage supplied to the display can be offset by the same amount, and no net DC imbalance is experienced.

[0066] U.S. Patent No. 9,921,451 describes a set of waveforms for driving a color electrophoretic display with four types of particles, which is incorporated herein by reference. In U.S. Patent No. 9,921,451, seven different voltages are applied to the pixel electrodes: three positive voltages, three negative voltages, and zero voltage. However, in some embodiments, the maximum voltage used in these waveforms is higher than the voltage that amorphous silicon thin-film transistors can handle. In this case, a suitable high voltage can be obtained by using top-plate switching. However, when using top-plate switching, using voltages related to V... com Setting up the same number of independent power supplies is both expensive and inconvenient. Furthermore, it is known that top-panel switching increases backlash, thereby reducing the stability of color states.

[0067] Methods for manufacturing ACeP-type electrophoretic displays have been discussed in the prior art. The electrophoretic fluid can be encapsulated in microcapsules or incorporated into a microcell structure subsequently sealed with a polymer layer. The microcapsules or microcell layers can be coated or imprinted onto a plastic substrate or film with a transparent conductive material coating. The assembly can be laminated to a backplane with pixel electrodes using a conductive adhesive. Alternatively, the electrophoretic fluid can be directly dispensed onto a thin, open-cell mesh already arranged on a backplane including an active matrix of pixel electrodes. The filled mesh can then be top-sealed with an integrated protective sheet / transparent electrode.

[0068] Figure 4A schematic cross-sectional view (not to scale) of a display structure 200 of an ACeP-type electrophoretic display is shown. In the display 200, the electrophoretic fluid is shown as confined within microcuplets, although an equivalent structure comprising microcapsules may also be used. A substrate 202, which may be glass or plastic, has pixel electrodes 204, which are individually addressed segments or associated with thin-film transistors in an active matrix arrangement. (The combination of substrate 202 and electrodes 204 is commonly referred to as the backplane of the display.) Layer 206 is an optional dielectric layer applied to the backplane according to the invention. (A method for depositing a suitable dielectric layer is described in U.S. Patent Application No. 16 / 862,750, incorporated by reference.) The front panel of the display includes a transparent substrate 222 with a transparent conductive coating 220. The electrode layer 220 is an optional dielectric layer 218. One layer (or layers) 216 is a polymer layer that may include a base layer for adhering the microcuplets to the transparent electrode layer 220 and some residual polymer forming the bottom of the microcuplets. The walls of the microcup 212 are used to contain the electrophoretic fluid 214. The microcup is sealed with layer 210, and the entire front panel structure is adhered to the back panel using a conductive adhesive layer 208. A process for forming the microcup is described in the prior art, for example, in U.S. Patent No. 6,930,818. In some cases, the depth of the microcup is less than 20 micrometers, for example, less than 15 micrometers, for example, less than 12 micrometers, for example, about 10 micrometers, for example, about 8 micrometers.

[0069] Due to the widespread availability of manufacturing facilities and the cost of various starting materials, most commercial electrophoretic displays use amorphous silicon-based thin-film transistors (TFTs) in the construction of the active matrix backplane (202 / 024). Unfortunately, amorphous silicon TFTs become unstable when provided with gate voltages that allow voltage switching above approximately + / -15V. Nevertheless, as described below, the performance of ACeP is improved when high amplitudes of positive and negative voltages exceeding + / -15V are allowed. Therefore, as previously disclosed, improved performance is achieved by additionally changing the bias voltage of the top transparent electrode relative to the bias voltage on the backplane pixel electrode, also known as top-plate switching. Thus, if a voltage of +30V (relative to the backplane) is required, the top plate can be switched to -15V while the appropriate backplane pixel is switched to +15V. A method for driving a four-particle electrophoretic system using top-plate switching is described in more detail, for example, in U.S. Patent No. 9,921,451.

[0070] The top-plate switching method has several drawbacks. First, when the top plate is not pixelated but is a single electrode extending across the entire surface of the display, its potential affects every pixel in the display. If it is set to match one of the largest voltage amplitudes available from the back plate (e.g., the largest positive voltage), there will be no net voltage on the ink when that voltage is applied to the back plate. When any other available voltage is supplied to the back plate, a negative voltage will always be supplied to any pixel in the display. Therefore, if a waveform requires a positive voltage, it cannot be supplied to any pixel until the top plate voltage is changed. A typical waveform for a multicolor display used in the third embodiment uses multiple pulses of both positive and negative polarities, and the lengths of these pulses differ from the lengths of the waveforms used to generate the different colors. Furthermore, the phases of the waveforms for different colors may differ: in other words, for some colors, the positive pulse may precede the negative pulse, while for others, the negative pulse may precede the positive pulse. To accommodate this, "pauses" (i.e., pauses) must be added to the waveform. In practice, this results in waveforms that are much longer (up to twice as long) than ideally needed.

[0071] Secondly, there are limitations on the selectable voltage levels during top plate switching. If the voltage applied to the top plate is expressed as V... t+ and V t- The voltages applied to the backplane are expressed as V. b+ and V b- In order to achieve a zero-volt condition in the electrophoretic fluid, it must be |V t+ |=|V b+ | and | V t- |=|V b- However, the amplitudes of positive and negative voltages do not have to be the same.

[0072] In previous embodiments of advanced color electronic paper (ACeP), waveforms (voltage versus time curves) of the pixel electrodes applied to the backplane of the display of the present invention were described and plotted, assuming the front electrode was grounded (i.e., at zero potential). The electric field experienced by the electrophoretic medium is, of course, determined by the potential difference between the backplane and the front electrode and the distance between them. Displays are typically observed through their front electrode, and thus it is the particles adjacent to the front electrode that control the color displayed by the pixels. It is sometimes easier to understand the optical transitions involved if the potential of the front electrode relative to the backplane is taken into account; this can be simply done by reversing the waveforms discussed below.

[0073] Figure 5 The diagram shows a typical waveform (simplified form) used to drive the aforementioned four-particle color electrophoretic display system. This waveform has a "push-pull" structure: that is, it consists of a dipole containing two pulses of opposite polarity. The amplitude and length of these pulses determine the resulting color. At least five such voltage levels are required. Figure 5 The display shows high and low positive and negative voltages, as well as zero volt. Generally, "low" (L) refers to a range of approximately 5–15V, while "high" (H) refers to a range of approximately 15–30V. Generally, the higher the amplitude of the "high" voltage, the better the color gamut achieved by the display. "Medium" (M) levels are typically around 15V; however, the value of M will depend to some extent on the composition of the particles and the environment of the electrophoretic medium. In some embodiments, high negative voltage is between -30V and -20V, medium negative voltage is between -20V and -2V, medium positive voltage is between 2V and 20V, and high positive voltage is between 20V and 30V. For example, high negative voltage is -27V, medium negative voltage is -15V, medium positive voltage is 15V, and high positive voltage is 27V. If only three voltages are available (i.e., +V...)... high 0 and -V high Then, by using a voltage of V high However, addressing with a pulse of 1 / n duty cycle achieves the same result as addressing at a lower voltage (e.g., V). high / n, where n is a positive integer greater than 1).

[0074] Enhanced push-pull (EPP) waveforms can be achieved with more drive levels. For example, a seven-level driver can provide seven different voltages (e.g., V) to the data lines during selected pixel updates of the display. H V H ',V H ”,0,V L ”,V L ',V L For example, +V H +V M +V L ,0,-V L ,-V M ,-V H The spacing between drive levels can be the same or different, depending on the formulation of the electrophoretic medium. For example, +V H =27V,+V M =15V,+V L =5V,0,-V L =-5V,-V M =-15V, -V H = -27V. For example, +V H =30V,+V M =20V,+V L =10V,0,-V L =-10V, -V M =-20V,-V H= -30V. However, when using a seven-level driver to drive an active matrix backplane with a single controller, the controller can only update one given pixel per frame at a time. Therefore, any enhanced push-pull waveform consists of a combination of pulses, each lasting one frame period, i.e., as shown... Figure 6 As shown. The resulting waveform used to achieve the desired optical state in the medium is... Figure 6 A certain combination of pulses constitutes the waveform, assuming such a waveform can exist without... Figure 6 Each pulse or having a certain number n Figure 6 Each pulse.

[0075] It is difficult to achieve a seven-level driver with sufficient voltage amplitude using standard amorphous silicon backplanes. It has been found that control transistors made from less common materials with higher electron mobility allow the transistors to switch larger control voltages, such as + / -30V, as needed to achieve seven-level drive. Newly developed active matrix backplanes can include thin-film transistors incorporating metal oxide materials, such as tungsten oxide, tin oxide, indium oxide, and zinc oxide. In these applications, this metal oxide material is used to form the channel formation region for each transistor, allowing for faster switching of higher voltages, for example, in the range of approximately -27V to +27V. Such transistors typically include a gate electrode, a gate insulating film (typically SiO2), a metal source electrode, a metal drain electrode, and a metal oxide semiconductor film above the gate insulating film, which at least partially overlaps with the gate, source, and drain electrodes. Such backplanes are available from manufacturers such as Sharp / Foxconn, LG, and BOE. A preferred metal oxide material for such applications is indium gallium zinc oxide (IGZO). The electron mobility of IGZO-TFTs is 20-50 times that of amorphous silicon. By using IGZOTFTs in an active matrix backplane, a voltage greater than 30V can be provided by a suitable display driver.

[0076] By using, for example, a seven-stage driver, enhanced push-pull (EPP) waveforms can achieve desired optical performance using a wider range of waveform shapes and durations. EPP waveforms are limited to consist of a finite number of positive or negative pulses, where N is... P These are easily processed numbers, where N is the number of possible voltage levels and P is the number of pulses. See also Figure 6 For example, if N = 7, then P < 5. Given a set of voltage level choices, a fixed waveform length, and a number of pulses, all possible waveforms can be enumerated. For each pulse, we can have each of N voltage levels, resulting in N... PA unique voltage arrangement (with substitutions) is given, where P is the number of pulses. The pulse lengths can be chosen based on the fact that the total waveform length M is fixed. If we consider the case of P pulses, then for P pulses we have N*(N-1) P A unique voltage level is chosen because adjacent pulses cannot have the same length (this would be P-1 pulses). We can then calculate the number of pulse lengths as... It is read as M-1 choosing P-1 (binomial coefficient). In summary:

[0077]

[0078] This formula describes the number of waveforms for a given multi-pulse structure. This also includes the variation in the test pulse length for each frame. Generally, by testing every D frames, the number of waveforms can be significantly reduced, which requires a substitution in the equation above: To calculate all possible unique pulse-based structures, where P ≤ the number of pulses, we express it using the formula...

[0079]

[0080] It was generated after simplification.

[0081]

[0082] Where 2F1 is a hypergeometric function.

[0083] Of course, identifying the “optimal” waveform is not a simple task. Given N=7, P=3, M=42, the total number of unique waveforms is 206,640. Each of these 206,640 waveforms needs to be tested against a given set of environmental conditions (e.g., light source and temperature) and prefixed with a waveform to provide appropriate cleansing (e.g., vibration pulses) so that the initial state of the medium matches the expected starting state of the waveform.

[0084] A more efficient method for identifying the preferred EPP waveform is to virtually execute each proposed EPP waveform in an alternative model representing the final display construction. A specific electrophoretic display construction can be represented by a transfer function. In its simplest form:

[0085] O(t) = f(V(t), (0))

[0086] Where O(t) is the optical state as a function of time, and f is the voltage applied to the display as a function of time, given an initial state of the system at t = 0 as (x(0)). Other inputs can be specified here, including but not limited to temperature, relative humidity, and incident spectrum. The function f can be estimated in various ways, such as an ab initio model built from component measurements, but the preferred embodiment described herein is one in which f is represented by a differentiable deep learning network based on a recurrent neural network architecture, hereinafter described as follows. Because the true value of f is approximated by deep learning-based modeling.

[0087] once Each enhanced push-pull (EPP) waveform can be evaluated on an alternative model to obtain the final optical state color value, intermediate states (optical tracking information), and subsequent computable quantities such as ghosting performance, voltage sensitivity, transition appearance (e.g., "flicker"), and temperature sensitivity. Any or all of these metrics can be combined into a total cost function to identify preferred EPP waveforms, which are then validated on a real electrophoresis display under test. These subsequent measurements on the real electrophoresis display can be fed back into a deep learning model to provide... Further improvements. This complete process is underway. Figure 7 It is described in block format. It should be recognized that... Figure 7 The method described is exhaustive in its parameterization, i.e., it searches for all possible permutations. Therefore, this method naturally overcomes a common challenge in parameterization: how to ensure that the optimization algorithm adequately samples the parameter space. The combination of an active matrix driver with a set clock period and a driver with finite voltage levels greatly reduces the parameter space, yet the output waveform is meaningful and can be immediately applied to the physical display. Therefore, the EPP tuning method is mathematically exhaustive, thus requiring no additional optimization when tuning the final waveform for the display.

[0088] like Figure 7As shown, the process begins with selecting the waveform length (710). As mentioned above, limitations such as frame width, client application, and power consumption may restrict this calculation. Nevertheless, the method can be used for various waveform lengths ranging from tens of milliseconds to several seconds. In steps (720) and (730), the number of pulses and the total voltage and voltage level are selected, respectively, which may again be limited by the cost and availability of waveform storage media and commercial production limitations such as the cost of multiple power supplies and the additional cost of variable power supplies. Once all these factors have been accumulated, a basic set of unique waveforms is generated in step (740), and each waveform is subsequently evaluated against a color target in step (750). For example, the color target may be the RGB color code or hexadecimal code of a digital image. Alternatively, the color target may be Pantone colors or the CMYK printing standard. In step (760), the waveform that achieves the result closest to the color target is output as a candidate waveform. This waveform can actually be fed to a real four-particle electrophoresis display corresponding to the modeled display, so that the results are measured with a calibrated optical bench and compared with the target. In some embodiments, these measurements are fed back to the model via step (770). For more detailed information on suitable calibration optical benches for evaluating the output of four-particle electrophoresis displays, see “Optical measurement standards for reflective e-paper to predict colors displayed in ambient illumination environments,” Color Research and Application, vol. 43, issue 6, pages 907-921 (2018), the entire contents of which are incorporated herein by reference.

[0089] By using the method described above, a faster and less flickering subset of color waveforms in the ACeP-type system is quickly isolated for further testing. This push-pull waveform can include dipoles that are essentially bifurcated (or trifurcated) into some combination of pulse height and relative polarity width. For example, as... Figure 8 and Figure 9 As shown, the enhanced push-pull waveform may include a V L The amplitude and first width t1 of the first part of the negative dipole, and having V L The second part of the negative dipole has an amplitude of 'VH' and a second width of t2. The positive part of the dipole can be a single pulse, for example, with an amplitude of VH and a third width of t3, or the positive part of the dipole can be determined according to the model. Bifurcation or trifurcation can be performed based on user update needs (e.g., speed, energy consumption, color specificity). Of course, such as... Figure 9The mirror-enhanced push-pull function shown can provide better waveforms for user needs.

[0090] Of course, achieving the desired color using push-pull drive pulses depends on the particles starting the process from a known state that is unlikely to be the last color displayed on the pixel. Therefore, a series of reset pulses precede the drive pulses, which increases the amount of time required to update the pixel from the first color to the second color. The reset pulses are described in more detail in U.S. Patent No. 10,593,272, which is incorporated by reference. The lengths of these pulses (refresh and address) and any pauses (i.e., the zero-voltage periods between them) can be selected such that the entire waveform (i.e., the integral of voltage over time over the entire waveform) is DC balanced (i.e., the integral of voltage over time is essentially zero). DC balance can be achieved by adjusting the lengths of the pulses and pauses in the reset phase such that the net impulse provided in the reset phase is equal in magnitude and opposite in sign to the net impulse provided in the addressing phase, during which the display is switched to a specific desired color.

[0091] The use of EPP waveforms is superior to completely unconstrained waveforms because the transition appearance is restricted to a set of abrupt color changes with a maximum value of P. While unconstrained waveforms can be designed to reduce the number of color changes or have a pleasing transition appearance, this is a technical challenge requiring more training data analysis and more computational power. This is much easier with the EPP waveforms chosen as described in this paper. Furthermore, this EPP tuning method allows for full enumeration of square pulse-based waveforms, which have historically offered a good trade-off between simple waveform structures with controlled transition appearances and optimization complexity. Preventing single-frame drive and numerous transients may also make the resulting EPP waveform more robust in other aspects (temperature sensitivity, voltage sensitivity, robustness to manufacturing variability).

[0092] Example

[0093] The above method was used to construct a model function describing a metal oxide AM-TFT backplane and a four-particle electrophoretic dielectric (including one reflective (white) particle and three subtractive particles (cyan, magenta, and yellow)). For 42 frames of waveforms at 85 Hz (0.5 s), each 3-pulse EPP waveform (a total of 206,640 unique waveforms) was tested. Eight color targets were selected, corresponding to black, white, magenta, blue, cyan, green, yellow, and red. 10,000 waveforms with a final color state closest to each of these eight targets were selected for further evaluation. These 10,000 final color state points were plotted on... Figure 10 On the a*-b* diagram.

[0094] Interestingly, the method presented in this paper provides deeper insights when searching for other salient features, such as ghosting or DC balance. Figure 11 As shown, many of the same color states can be achieved using either a DC balanced (triangle) or DC unbalanced (circular) waveform. Please note... Figure 11 The overlap between the DC unbalanced EPP waveform (circular) and the DC balanced EPP waveform (triangular) under representative color conditions is shown. However, observing the actual waveforms, it is noteworthy that in some cases, the shapes of the DC balanced and DC unbalanced waveforms are very similar. For example, a comparison is provided. Figure 12A and 12B (corresponding to) Figure 11 (the square in the middle) and Figure 13A and 13B (corresponding to) Figure 11 (The star shape in the middle). Figure 12A and 12B In the examples, the difference between DC balanced and DC unbalanced waveforms is very small, while Figure 13A and 13B In the DC balanced and DC unbalanced waveforms, the difference is very obvious.

[0095] exist Figure 10 and 11 It is worth noting that, in a given ACeP-type electrophoretic display construction, using an EPP waveform may not achieve the preferred target color. Figure 11 (The "X" in the image). This phenomenon is reproduced in physical displays.

[0096] Several aspects and embodiments of the technology described herein have been so described; it should be understood that various changes, modifications, and improvements will readily occur to those skilled in the art. Such changes, modifications, and improvements are intended to be within the spirit and scope of the technology described herein. For example, those skilled in the art will readily conceive of various other means and / or structures for performing functions and / or obtaining the results and / or one or more advantages described herein, and each of these variations and / or modifications is considered to be within the scope of the embodiments described herein. Those skilled in the art will recognize, or can determine, many equivalents of the particular embodiments described herein using only conventional experimentation. Therefore, it should be understood that the foregoing embodiments are presented by way of example only, and embodiments of the invention may be practiced in ways other than those specifically described within the scope of the appended claims and their equivalents. Furthermore, any combination of two or more features, systems, articles, materials, kits, and / or methods described herein (if such features, systems, articles, materials, kits, and / or methods are not inconsistent with each other) is included within the scope of this disclosure.

Claims

1. A method for driving an electrophoretic display, comprising: An electrophoretic medium comprising four groups of particles, each group having different optical properties and different charge properties, is provided. The electrophoretic medium is placed between the first transparent electrode and the second electrode; A voltage driver is provided, which is configured to provide at least five voltage levels: high negative voltage, medium negative voltage, zero voltage, medium positive voltage, and high positive voltage; as well as The electrophoretic medium is driven to a desired optical state by providing a push-pull waveform, the push-pull waveform having: The first positive portion consists of a first pulse and a second pulse that are adjacent to each other. The first pulse has a first positive amplitude and a first time width, and the second pulse has a second positive amplitude and a second time width. The second negative portion consists of a third pulse and a fourth pulse that are adjacent to each other. The third pulse has a first negative amplitude and a third time width, and the fourth pulse has a second negative amplitude and a fourth time width. The first positive amplitude, the second positive amplitude, the first negative amplitude, and the second negative amplitude are all non-zero, and at least three of the first time width, the second time width, the third time width, and the fourth time width are non-zero. The first positive amplitude, the second positive amplitude, the first negative amplitude, and the second negative amplitude each have a voltage level value provided by the voltage driver, and The sum of the first time width, the second time width, the third time width, and the fourth time width is equal to a finite time width, and the time widths of adjacent pulses are different.

2. The method according to claim 1, wherein, The first group of particles is reflective, while the second, third, and fourth groups of particles are subtractive.

3. The method according to claim 2, wherein, Two groups of the particles are positively charged, and two groups of the particles are negatively charged.

4. The method according to claim 2, wherein, One group of the particles is positively charged, and three groups of the particles are negatively charged.

5. The method according to claim 2, wherein, Three groups of the particles are positively charged, and one group of the particles is negatively charged.

6. The method according to claim 1, wherein, The second electrode includes a plurality of pixel electrodes arranged in an array.

7. The method according to claim 1, wherein, The second electrode is transparent to light.

8. The method according to claim 1, wherein, The high negative voltage is between -30V and -20V, the medium negative voltage is between -20V and -2V, the medium positive voltage is between 2V and 20V, and the high positive voltage is between 20V and 30V.

9. The method according to claim 1, wherein, The voltage driver is configured to provide seven voltage levels: high negative voltage, medium negative voltage, low negative voltage, zero voltage, low positive voltage, medium positive voltage, and high positive voltage.

10. A method for identifying enhanced push-pull waveforms, comprising: Selecting a finite group of voltages to drive the electrophoretic display, wherein the group includes at least five different voltage levels; Select a time with a finite time width for the candidate waveform; Calculate all candidate waveforms, each candidate waveform having a first positive portion and a second negative portion. The first positive portion consists of a first pulse and a second pulse that are adjacent to each other. The first pulse has a first positive amplitude and a first time width, and the second pulse has a second positive amplitude and a second time width. The second negative portion consists of a third pulse and a fourth pulse that are adjacent to each other. The third pulse has a first negative amplitude and a third time width, and the fourth pulse has a second negative amplitude and a fourth time width. Wherein the first positive amplitude, the second positive amplitude, the first negative amplitude, and the second negative amplitude each have a voltage value from the finite set, and The sum of the first pulse width, the second pulse width, the third pulse width, and the fourth pulse width is equal to the finite time width, and the time widths of adjacent pulses are different; The optical state generated by each candidate waveform is calculated using a model of an electrophoretic display having an electrophoretic medium comprising four groups of particles, wherein each group of particles has different optical properties and different charge properties, and the electrophoretic medium is disposed between a first transparent electrode and a second electrode; and The waveform with the optical state that is closest to the color target is selected from the candidate waveforms to generate the target optical state.

11. The method according to claim 10, wherein, The option includes comparing the target color with the predicted output color.

12. The method of claim 11, further comprising inputting the selected waveform into a physical electrophoresis display, the physical electrophoresis display comprising an electrophoretic medium containing four groups of particles, wherein each group of particles has different optical properties and different charge properties, and the electrophoretic medium is disposed between a first transparent electrode and a second electrode.

13. The method of claim 12, further comprising evaluating the color output of the physical electrophoresis display and comparing the color output with the target color.

14. The method according to claim 11, wherein, The voltages of the finite group include high negative voltages between -30V and -20V, medium negative voltages between -20V and -2V, medium positive voltages between 2V and 20V, and high positive voltages between 20V and 30V.

15. The method according to claim 10, wherein, The voltages of the finite group include -27V, 0V, and +27V.

16. The method of claim 10, wherein, The group includes seven voltage levels: high negative voltage, medium negative voltage, low negative voltage, zero voltage, low positive voltage, medium positive voltage, and high positive voltage.

17. The method according to claim 10, wherein, The first group of particles is reflective, while the second, third, and fourth groups of particles are subtractive.

18. The method according to claim 17, wherein, Two groups of the particles are positively charged, and two groups of the particles are negatively charged.

19. The method according to claim 17, wherein, One group of the particles is positively charged, and three groups of the particles are negatively charged.

20. The method of claim 17, wherein, Three groups of the particles are positively charged, and one group of the particles is negatively charged.

Images