Enhanced push-pull (EPP) waveforms for achieving primary color sets in multi-color electrophoretic displays

Abstract

This application provides an enhanced push-pull (EPP) waveform for realizing a primary color set in a multicolor electrophoretic display. It also provides an enhanced push-pull drive waveform for driving a four-particle electrophoretic medium comprising, for example, a set of scattering particles and three sets of subtractive particles. A method for identifying the preferred waveform for a target color state when using a voltage driver with at least five different voltage levels is also provided.

Description

(19) State Intellectual Property Office (12) Invention Patent Application (10) Application Publication Number (43) Application Publication Date (21) Application Number 202610876865.7 (22) Application Date 2021.11.01 (30) Priority Data 63 / 108521 2020.11.02 US (62) Divisional Application Data 202180071682.3 2021.11.01 (71) Applicant Einker Company Address Massachusetts, USA (72) Inventor A. Dilivara (74) Patent Agency Beijing Panhua Weiye Intellectual Property Agency Co., Ltd. 11280 Patent Attorney Wang Bo (51) Int.Cl. G09G 3 / 34 (2006.01) G06N 3 / 044 (2023.01) G02F 1 / 1685 (2019.01) G02F 1 / 167(2019.01) G02F 1 / 1679(2019.01) G02F 1 / 1675(2019.01) G09G 3 / 20(2006.01) (54) Invention Title: Enhanced Push-Pull (EPP) Waveform for Realizing Primary Color Sets in Multicolor Electrophoretic Displays (57) Abstract: This application provides an enhanced push-pull (EPP) waveform for realizing primary color sets in multicolor electrophoretic displays. An enhanced push-pull drive waveform is provided for driving a four-particle electrophoretic medium comprising four different types of particles, such as a set of scattering particles and three sets of subtractive particles. A method for identifying a preferred waveform for a target color state when using a voltage driver with at least five different voltage levels. Claims 2 pages, Description 15 pages, Drawings 14 pages, CN 122551727 A 2026.08.11 CN 1 22 55 17 27 A 1. A method for determining a push-pull waveform for driving an electrophoretic display, comprising: determining a set of candidate waveforms for driving the electrophoretic display; estimating an optical state generated by each candidate waveform using a model representing the electrophoretic display, wherein the model includes a transfer function represented by: O(t) = f(V(t), x(0)) where t is time, O(t) is the optical state of the electrophoretic display as a function of t, V(t) is the voltage applied to the electrophoretic display as a function of t, x(0) is the initial optical state of the electrophoretic display at t = 0, and f is a function of V(t) and x(0); and identifying a push-pull waveform for generating a target optical state based on the estimated optical state generated by the candidate waveforms. 2. The method of claim 1, further comprising: using the push-pull waveform identified as being used to generate the target optical state to drive the electrophoretic display to generate color output.3. The method of claim 2, further comprising: evaluating the color output of the electrophoretic display and comparing the color output with a target color. 4. The method of claim 2, further comprising: using the color output and associated waveforms as training data for the model. 5. The method of claim 1, wherein determining the set of candidate waveforms comprises: selecting a finite group of at least five different voltage levels for waveforms used to drive the electrophoretic display; selecting a finite time width for the waveforms; and identifying a set of waveforms, each waveform having a positive portion and a negative portion, wherein the positive portion and the negative portion each include at least one pulse, and at least one of the positive portion and the negative portion includes two pulses with different voltage amplitudes, each voltage amplitude corresponding to one of the at least five different voltage levels, wherein the sum of the pulse widths of the positive portion and the negative portion is equal to the finite time width. 6. The method of claim 5, wherein selecting the finite time width comprises comparing the target color with a predicted output color. 7. The method of claim 5, wherein the finite group of at least five different voltage levels comprises: 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. 8. The method of claim 5, wherein the finite group of at least five different voltage levels comprises -27V, 0V, and +27V. 9. The method of claim 5, wherein the finite group of at least five different voltage levels comprises seven voltage levels: a high negative voltage, a medium negative voltage, a low negative voltage, a zero voltage, a low positive voltage, a medium positive voltage, and a high positive voltage. 10. The method of claim 1, wherein determining the set of candidate waveforms comprises: selecting a finite group of voltages for driving an electrophoretic display, wherein the set of voltages includes at least five different voltage levels; selecting a time with a finite time width for the candidate waveforms; and 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, the first pulse having a first positive amplitude and a first time width, the second pulse having a second positive amplitude and a second time width, 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, the fourth pulse having 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 value from the finite group of voltages, and wherein 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.11. The method of claim 1, wherein the electrophoretic display comprises an electrophoretic medium disposed between a first transparent electrode and a second electrode, the electrophoretic medium comprising four groups of particles, wherein each group of particles has different optical properties and different charge properties than other groups of particles in the electrophoretic medium. 12. The method of claim 11, wherein the four groups of particles comprise a first group of particles, a second group of particles, a third group of particles, and a fourth group of particles, wherein the first group of particles is reflective, while the second, third, and fourth groups of particles are subtractive. 13. The method of claim 12, wherein two groups of the four groups of particles are positively charged, and two groups of the four groups of particles are negatively charged. 14. The method of claim 12, wherein one group of the four groups of particles is positively charged, and three groups of the four groups of particles are negatively charged. 15. The method of claim 12, wherein three groups of the four groups of particles are positively charged, and one group of the four groups of particles is negatively charged. 16. The method of claim 1, wherein the model is a differentiable deep learning model based on a recurrent neural network architecture. Claims 2 / 2 Page 3 CN 122551727 A Enhanced Push-Pull (EPP) Waveform for Realizing Primary Color Sets in a Multicolor Electrophoretic Display

[0001] This application is a divisional application of application No. 202180071682.3, filed November 1, 2021, entitled "Enhanced Push-Pull (EPP) Waveform for Realizing Primary Color Sets in a Multicolor Electrophoretic Display". 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 Art

[0003] Electrophoretic displays (EPDs) change color by modifying the position of charged colored particles relative to a light-transmitting viewing surface. Such electrophoretic displays are often referred to as "electronic paper" or "ePaper" because the resulting display has high contrast and is readable in sunlight, much like ink on paper. Electrophoretic displays are widely used in e-readers such as the AMAZON KINDLE® because they provide a book-like reading experience, consume little power, and allow users to carry a library 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. (It is certain that the term "color" as used herein includes both black and white.) White particles are typically of the light-scattering type and include, for example, titanium dioxide, while black particles are absorbent in the visible spectrum and may include carbon black or absorbing metal oxides.Compounds, such as copper chromite. In its simplest sense, a black-and-white electrophoretic display only requires a light-transmitting electrode, a back electrode, and an electrophoretic medium consisting of white and black particles with opposite charges at the observation surface. When a voltage of one polarity is provided, the white particles move to the observation surface, and when a voltage of the opposite polarity is provided, the black particles move to the observation surface. If the back electrode includes controllable regions (pixels)—an active matrix of segmented electrodes or pixel electrodes controlled by transistors—a pattern can be made to appear electronically at the observation surface. For example, the pattern could be the text of a book.

[0005] Recently, a variety of color options have been commercially available for electrophoretic displays, including tricolor displays (black, white, red; black, white, yellow) and quadcolor displays (black, white, red, 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 to 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™) also includes four types of particles, but the cyan, yellow, and magenta particles are subtractive rather than reflective, thus allowing thousands of colors to be produced at each pixel. The color process is functionally equivalent to the printing methods long used in offset printing and inkjet printers. A given color is produced by using the correct proportions of cyan, yellow, and magenta on a bright white paper background. In the ACeP instance, the relative positions of the cyan, yellow, magenta, and white particles with respect to the viewing surface determine the color at each pixel. While this type of electrophoretic display allows thousands of colors at each 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. Obviously, variations in pigment position will result in an incorrect color being displayed at a given pixel. Therefore, such a 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. Specification 1 / 15 page 4 CN 122551727 A

[0007] The present invention relates to waveforms for driving color electrophoretic displays, and more particularly, but not exclusively, to electrophoretic displays capable of presenting more than two colors using a single-layer electrophoretic material comprising a variety of 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, while one 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 meaning 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. 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. This type of display is aptly referred to as multistable rather than bistable, but 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, is used herein to refer to the integral of the voltage applied during driving the display relative to time. The term "waveform," when used in relation to 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 a 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, the term refers to insoluble colored materials) other than pigments, such as dyes or photonic crystals, can also be used in the electrophoretic medium and display of the present invention.

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

[0013] As mentioned above, the electrophoretic medium requires the presence of a fluid. In most prior art electrophoretic media, this fluid is a liquid, but the electrophoretic medium 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, for example in signs where the media are arranged in a vertical plane, they are susceptible to the same type of problems as those described in the same specification 2 / 15 page 5 CN 122551727 A for liquid-based electrophoretic media. In fact, the particle settling problem is more severe in gas-based electrophoretic media than in liquid-based electrophoretic media because the lower viscosity of the gaseous suspension fluid allows electrophoretic particles to settling more quickly compared to liquids.

[0014] Numerous patents and applications assigned 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 number 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 technologies 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) capsules, binders, 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 subassemblies comprising 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 Nos. 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; 2015 / 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, Instruction Manual 3 / 15 Page 6 CN 122551727 A 177,066; 7,193,625; 7,202,847; 7,242,514; 7,259,744; 7,304,787; 7,312,794; 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; 8,139,050;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, 730,153; 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 Nos. 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 / 0194733; 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; 2013 / 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 / 0097877; 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-optic display) applications);

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

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

[0025] Many of the foregoing 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 polymer 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] A related type of electrophoretic display is the so-called microcell electrophoretic display. In a microcell electrophoretic display, charged particles and fluids are not encapsulated within microcapsules, but are held in a plurality of 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 in so-called shutter mode.Operating in a shutter mode, in which one display state is substantially opaque and the other display state is light-transmitting. 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 coatings such as patch die coating, slot or extrusion coating, slide or stack coating, curtain coating; roller coatings 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.) Thus, the resulting display can be flexible. In addition, because the display medium can be printed (using a variety of methods), the display itself can be manufactured inexpensively.

[0029] As mentioned above, the simplest prior art electrophoretic medium essentially displays only two colors. This electrophoretic medium uses a single type of electrophoretic particles of a first color in a colored fluid with 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 with 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, a color filter array 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 include, for example, red / ...Three or four primary colors, such as green / blue (RGB) or red / green / blue / white (RGBW), are shared, and the filters can be arranged in a one-dimensional (stripes) or two-dimensional (2x2) repeating pattern. Other choices of primary colors or more than three primary colors are also known in the art. Three (in the case of RGB displays) or four (in the case of RGBW displays) subpixels are chosen to be small enough that they visually blend together at the expected viewing distance to become a single pixel with uniform color stimulation ("color mixing"). An inherent drawback of area sharing is that the colorant is always present, and the color 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 display, the red, green, blue, and white primary colors each occupy a quarter of the display area (a quarter of the subpixels), the 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 entire display cannot exceed half the brightness of the white subpixel (the white area of ​​the display 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 contributes no more than one white subpixel). The brightness and saturation of a color are reduced by sharing the area with the color pixel switched to black. Area sharing is particularly problematic when mixing yellow, as it is brighter than any other color of equal brightness, and saturated yellow is almost as bright as white. Switching a blue pixel (one-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, there are drawbacks to using multiple electrophoretic layers located between a single set of addressing electrodes. 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 unwanted absorption) may affect the appearance of the image formed in the underlying electrophoretic layer.

[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 a dispersion of a transparent and colorless or colored layer.One or two types of pigment particles in a solvent, an electrophoretic fluid disposed between a common electrode and multiple 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 two contrasting colors. The two types of pigment particles are dispersed in a colored solvent or in a solvent containing uncharged or slightly charged colored particles. The method includes 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 first, second, and third types of pigment particles, 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 that is about 50% less than that of the first or second type of pigment particles. 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 document 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. In one aspect, a method for driving an electrophoretic display is disclosed. The driving method includes providing an electrophoretic medium comprising four groups of particles, each group of particles 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. Such a 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 another embodiment, one group of particles is positively charged, and three groups of particles are negatively charged.Negative charge. 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. The method for identifying enhanced push-pull waveforms 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, wherein the first positive portion consists 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 consists of a third pulse and a fourth pulse, wherein 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, 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. The final step is to calculate 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 to select waveforms to generate a target optical state. In one embodiment, selection includes comparing a target color with a predicted output color. In one embodiment, the 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 with 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 the particle group is positively charged, and three groups of the particle group are negatively charged. In another embodiment, three groups of the particle group are positively charged, and one group of the particle group is negatively charged.

[0034] FIG1 is a schematic cross-sectional view 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] FIG2A schematically shows four different types of pigment particles used in a multi-particle electrophoretic medium.

[0036] FIG2B schematically shows four different types of pigment particles used in a multi-particle electrophoretic medium.

[0037] FIG2C schematically shows four different types of pigment particles used in a multi-particle electrophoretic medium.

[0038] FIG3 shows an exemplary equivalent circuit of a single pixel of an electrophoretic display.

[0039] FIG4 shows a layer of an exemplary electrophoretic color display.

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

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

[0042] Figure 7 shows an algorithm for identifying enhanced push-pull waveforms.

[0043] Figure 8 shows an exemplary enhanced push-pull waveform.

[0044] Figure 9 shows an exemplary enhanced push-pull waveform.

[0045] Figure 10 shows 10,000 final color states achieved by an enhanced push-pull waveform for a model using a metal oxide TFT backplane and a four-particle ACeP type electrophoretic medium.

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

[0047] Figures 12A and 12B compare the calculated DC imbalance (Figure 12A) and DC balance (Figure 12B) waveforms to obtain a specific green color as per specification page 7 / 15, 10 CN 122551727 A.

[0048] Figures 13A and 13B compare the calculated DC imbalance (Figure 13A) and DC balance (Figure 13B) waveforms to obtain a specific green color. Detailed Description

[0049] The present invention details a method for identifying enhanced push-pull waveforms for driving multi-particle color electrophoretic media, for example, wherein at least two 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 is schematically shown in Figure 1, 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 four pigments so 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 waveforms of these colors requires at least five voltage levels (high positive, low positive, zero, low negative, high negative). See 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. The present invention provides a method for identifying enhanced push-pull waveforms to drive such an electrophoretic medium, 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., for the ACeP system) can be substantially non-light-scattering (“SNLS”). The use of SNLS particles allows for color mixing and provides more color results than can 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 previously mentioned, Figure 1 in the accompanying drawings is a schematic cross-sectional view 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. In Figure 1, it is assumed that the viewing surface of the display is at the top (as shown), i.e., the user observes the display from this direction, and light is incident from this direction. As already noted, in a preferred embodiment, only one of the four particles used in the electrophoretic medium of the present invention substantially scatters light, and in Figure 1, this particle is assumed to be white pigment. This light-scattering white particle forms a white reflector, by which any particle above the white particle (as shown in Figure 1) 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 color presented to the user is 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 color. 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 below white particles (case [A] in Figure 1), there are no particles above the white particles and the pixel displays only white. When a single particle is above a white particle, the color of that single particle is displayed as yellow, magenta, and cyan in cases [B], [D], and [F] of Figure 1, respectively. When two particles are above a white particle, the displayed color is a combination of the colors of the two particles; in Figure 1, in case [C], magenta and yellow particles display red; in case [E], cyan and magenta particles display blue; and in case [G], yellow and cyan particles display green. Finally, when all three colored particles are above white particles (case [H] in Figure 1), 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 presenting black (when all three types of 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 presented would be the color of the scattering colored particles, not black).

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

[0056] Figure 1 illustrates an idealized case where the color is not contaminated (i.e., the light-scattering white particles completely mask any particles located behind the white particles). In reality, the masking of white particles may not be perfect, so particles that would ideally be completely masked may have a small amount of light absorption. This contamination usually reduces the brightness and chromaticity of the presented color. In the electrophoretic medium of the present 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 Ad 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 the eight colors shown in Figure 1, namely black, white, the three subtractive primary colors, and the three additive primary colors.)

[0057] Figures 2A and 2B show cross-sectional schematic diagrams of four pigment types (1-4; 5-8) used in ACeP-type electrophoretic displays. In Figure 2A, the polymer shell adsorbed onto the core pigment is represented by a dark shading, while the core pigment itself is shown without shading. Multiple forms can be used for the core pigment: spherical, needle-like, or other anisoaxial aggregates of smaller particles (i.e., "grapes").Clusters), composite particles containing small pigment particles or dyes dispersed in a binder, etc., as is known in the art. The polymer shell can be a covalently bonded polymer made 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 insoluble and soluble segments.

[0058] In the embodiment of FIG. 2A, 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 the first or second type (negatively charged or positively charged). In the following discussion, it is assumed that the white particles are negatively charged (i.e., belong 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] Furthermore, as shown in FIG. 2B, the first and second particle types do not need to have different polymer shells compared to the third and fourth particle types. As shown in FIG. 2B, sufficient differential charge on the four particles will allow for electrophoretic control of the particles and the creation of the desired color at the observation surface. For example, particle 5 can have a much larger negative charge than particle 7, while particle 8 In comparison, particle 6 has a much larger positive charge. Other combinations of polymer functionality and charge (or particle size) can also be used; however, it must be such that all four types of 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 by commercial digital electronics.

[0060] In the system of FIG. 2A, the electric field required by the present invention 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 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] In FIG. 2A, 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 is the thickness of the polymer shell surrounding each core pigment. As shown in FIG. 2A, the polymer shells of the particles of types 1 and 2 are thicker than the polymer shells of the particles of types 3 and 4. Specification 9 / 15 pages 12 CN 122551727 A

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

[0063] To obtain a high-resolution display, the individual pixels of the display must be addressable without interference from adjacent pixels. One way to achieve this is to provide 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 inherently arbitrary and the pixel electrode may 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, while the gates of all transistors in each row are connected to a single row electrode; similarly, the source-to-row and gate-to-column assignments are conventional but largely arbitrary and can be reversed if needed. 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 that all transistors in the selected row are turned on, while a non-selection voltage is applied to all other rows to ensure that all transistors in these unselected rows remain off. Column electrodes are connected to column drivers, which apply voltages to the individual column electrodes, the voltages being selected to drive the pixels in the selected row to their desired optical state. (These voltages 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 that updates at 60Hz has a frame rate of 16 milliseconds.

[0064] Conventionally, 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) may be used to form a transistor, and the “select” and “non-select” voltages applied to the gate electrode may be positive and negative, respectively.

[0065] Figure 3 of the accompanying drawings depicts an exemplary equivalent circuit of a single pixel of an electrophoretic display. As shown, the circuit includesThis includes a capacitor 10 formed between the pixel electrode and the capacitor electrode. The electrophoretic dielectric 20 is represented as a capacitor and 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") may 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 may cause a small negative offset voltage, also referred to as "recoil voltage," typically less than 2 volts, to the pixel electrode. In some embodiments, to compensate for the unwanted "recoil voltage," a common potential Vcom may be provided to the top plate electrode and the capacitor electrode associated with each pixel such that when Vcom is set to a value equal to the recoil voltage (VKB), each voltage supplied to the display can be offset by the same amount and without experiencing a net DC imbalance.

[0066] A set of waveforms for driving a color electrophoretic display with four particles is described in U.S. Patent No. 9,921,451, 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 as many independent power supplies as Vcom settings is both expensive and inconvenient. Furthermore, top-plate switching is known to increase recoil, 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 component can be laminated to a backplate with pixel electrodes using a conductive adhesive. Alternatively, the electrophoretic fluid can be directly dispensed onto a thin, open mesh already arranged on a backplane of an active matrix including pixel electrodes. The filled mesh can then be top-sealed with an integrated protective sheet / transparent electrode.

[0068] Figure 4 shows a schematic cross-sectional view (not to scale) of a display structure 200 of an ACeP-type electrophoretic display. In the display 200, the electrophoretic fluid is shown as confined in microcuplets, although an equivalent structure containing 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 generally referred to as the backplane of the display.) Layer 206This is an optional dielectric layer applied to the backplane according to the present invention. (A method for depositing a suitable dielectric layer is described in U.S. Patent Application No. 16 / 862,750, which is incorporated by reference.) The front panel of the display includes a transparent substrate 222 with a transparent conductive coating 220. The overlay 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 microcup to the transparent electrode layer 220 and some residual polymer forming the bottom of the microcup. The walls of the microcup 212 are used to contain electrophoretic fluid 214. The microcup is sealed with layer 210, and the entire front panel structure is adhered to the backplane using a conductive adhesive layer 208. A process for forming 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 the amplitude of high positive and negative voltages exceeds + / -15V. Therefore, as previously disclosed, the improved performance is achieved by changing the bias voltage of the top transparent electrode by additionally changing the bias voltage relative to the bias voltage on the backplane pixel electrode, which is also referred to as top-plate switching. Thus, if a voltage of +30V (relative to the backplane) is required, the topplate 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 disadvantages. First, when the top plate is not pixelated but is a single electrode extending across the entire surface of the display, its potential affects each 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 other colors, the negative pulse may precede the positive pulse.For positive pulses. To accommodate this situation, a "pause" (i.e., a pause) must be added to the waveform. In practice, this results in the waveform specification 11 / 15 pages 14 CN 122551727 A being much longer (up to twice as long) than ideally required.

[0071] Secondly, there are limitations on the selectable voltage levels during top plate switching. If the voltages applied to the top plate are represented as Vt+ and Vt-, and the voltages applied to the back plate are represented as Vb+ and Vb-, respectively, in order to achieve a zero-volt condition in the electrophoretic fluid, then |Vt+| = |Vb+| and |Vt-| = |Vb-| must be. However, the amplitudes of the positive and negative voltages do not have to be the same.

[0072] In a previous embodiment of Advanced Color Electronic Paper (ACeP), waveforms (voltage versus time curves) of the pixel electrodes applied to the back plate of the display of the present invention were described and plotted, while assuming that 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 back plate and the front electrode and the distance between them. The display is typically observed through its front electrode, and thus it is the particles adjacent to the front electrode that control the color displayed by the pixels. The optical transformation involved is sometimes easier to understand if the potential of the front electrode relative to the back plate is considered; this can be done simply by reversing the waveforms discussed below.

[0073] Figure 5 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 color obtained. There should be at least five such voltage levels. Figure 5 shows high and low positive and negative voltages, as well as zero volt. Typically, “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. The “medium” (M) level is 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, 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. For example, the high negative voltage is -27V, the medium negative voltage is -15V, the medium positive voltage is 15V, and the high positive voltage is 27V. If only three voltages are available (i.e., +Vhigh, 0, and -Vhigh), the same result as addressing at lower voltages (e.g., Vhigh / n, where n is a positive integer greater than 1) can be achieved by using a pulse with voltage Vhigh but a duty cycle of 1 / n.

[0074] Enhanced push-pull (EPP) waveforms can be implemented with more drive levels. For example, a seven-level driver can be displayedDuring a selected pixel update of the display, seven different voltages are supplied to the data lines (e.g., VH, VH', VH'', 0, VL'', VL', VL; e.g., +VH, +VM, +VL, 0, -VL, -VM, -VH). The spacing between the drive levels can be the same or different, depending on the formulation of the electrophoretic medium. For example, +VH = 27V, +VM = 15V, +VL = 5V, 0, -VL = -5V, -VM = -15V, -VH = -27V. Alternatively, +VH = 30V, +VM = 20V, +VL = 10V, 0, -VL = -10V, -VM = -20V, -VH = -30V. Regardless, 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 in Figure 6. The resulting waveform used to achieve the desired optical state in the medium is composed of some combination of the pulses in Figure 6, assuming that such a waveform can exist without each pulse of Figure 6 or with a certain number n of each pulse of Figure 6.

[0075] It is difficult to achieve a seven-level driver with sufficient voltage amplitude using a standard amorphous silicon backplane. It has been found that using control transistors made of less common materials with higher electron mobility allows the transistors to switch larger control voltages as needed, such as + / -30V, to achieve a seven-level drive. The newly developed active matrix backplane may include thin-film transistors incorporating metal oxide materials, such as tungsten oxide, tin oxide, indium oxide, and zinc oxide. In these applications, such metal oxide materials are used to form the channel formation region for each transistor, thereby allowing for faster switching of higher voltages, for example, in the range of about -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 IGZO TFTs in an active matrix backplane, voltages greater than 30V can be provided by a suitable display driver.

[0076] By using, for example, a seven-stage driver, enhancement-mode push-pull (EPP) waveforms can use waveform shapes with greater space.The desired optical performance is achieved through duration. The EPP waveform is constrained to consist of a finite number of positive or negative pulses, where NP is a tractable number, where N is the number of possible voltage levels, and P is the number of pulses. See Figure 6. For example, if N = 7, then P < 5. For 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 NP unique voltage permutations (with substitutions), where P is the number of pulses. For the pulse length, we can choose these constrained by the total length M of the waveform being fixed. If we consider the case of P pulses, there is a unique voltage level choice for P pulses because adjacent pulses cannot have the same length (this would be 1 pulse). We can then calculate the number of pulse lengths as , where it is read as the choice (binomial coefficient). In summary:

[0077]

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

[0079] ,

[0080] which is simplified to produce,

[0081] ,

[0082] where 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 206640. Each of these 206640 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 clearance (e.g., vibration pulses) so that the initial state of the medium matches the expected starting state of the waveform.

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

[0085] O

[0086] where is the optical state as a function of time, f is the voltage applied to the display as a function of time, given an initial state of the system at t=0 as ( ). 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 an embodiment in which f is represented by a differentiable deep learning network based on a recurrent neural network architecture, hereinafter described as 13 / 15 pages 16 CN 122551727 A.Because the true f is approximated by deep learning-based modeling.

[0087] Once established, each enhanced push-pull (EPP) waveform can be evaluated on an alternative model to obtain the final optical state color value, as well as intermediate states (optical tracking information), and subsequent computable quantities such as ghosting performance, voltage sensitivity, transition appearance (e.g., “flickering”), 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 the actual electrophoretic display under test. These subsequent measurements on the actual electrophoretic display can be fed back into the deep learning model for further improvements. This complete process is described in block format in Figure 7. It should be recognized that the method described in Figure 7 is exhaustive in its parameterization, i.e., searching all possible permutations. Therefore, this method naturally overcomes the common challenge of parameterization, i.e., how to ensure that the optimization algorithm adequately samples the parameter space. The combination of an active matrix drive with a set clock period and a driver with finite voltage levels greatly reduces the parameter space, but the output waveform is meaningful and can be immediately applied to the physical display. Therefore, the EPP tuning method may be mathematically exhaustive, thus requiring no additional optimization when tuning the final waveform for the display.

[0088] As shown in Figure 7, 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 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, 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 set of basic 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 into 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). More details on suitable calibrated optical benches for evaluating the output of a four-particle electrophoresis display can be found in "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 above method, a faster and less flickering subset of color waveforms for ACeP-type systems is quickly isolated for further testing. Such push-pull waveforms may include dipoles that are actually bifurcated (or trifurcated) into some combination of pulse height and relative polarity width. For example, as shown in Figures 8 and 9, an enhanced push-pull waveform may include a first portion of a negative dipole with an amplitude of VL and a first width t1, and a second portion of a negative dipole with an amplitude of VL' and a second width t2. The positive portion of the dipole may be a single pulse, for example, with an amplitude of VH and a third width t3, or the positive portion of the dipole may be bifurcated or trifurcated depending on the needs of the model and user updates (e.g., speed, energy consumption, color specificity). Of course, the mirrored enhanced push-pull functionality shown in Figure 9 can provide a better waveform for the user's needs.

[0090] Of course, achieving the desired color using push-pull drive pulses depends on the particles starting the process from a known state, which 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 Specification No. 10,593,272, pages 14 / 15, 17 CN 122551727 A, 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 substantially 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 an EPP waveform is superior to a completely unconstrained waveform because the transition appearance is restricted to a set of values ​​with a maximum value of P. The sudden color change. 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 for 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 balance between simple waveform structures with controlled transition appearances and optimization complexity.A good trade-off is achieved. Preventing single-frame drive and a large number of 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 is used to construct a model function describing a metal oxide AM-TFT backplane and a four-particle electrophoretic medium (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 are plotted on the a*-b* plot in Figure 10.

[0094] Interestingly, the method in this paper provides deeper insights when searching for other salient features (e.g., ghosting or DC balance). As shown in Figure 11, many of the same color states can be achieved using either DC balanced (triangle) or DC unbalanced (circular) waveforms. Note the overlap between the DC unbalanced EPP waveform (circular) and the DC balanced EPP waveform (triangle) in the representative color states of Figure 11. 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. Compare, for example, Figures 12A and 12B (corresponding to the squares in Figure 11) with Figures 13A and 13B (corresponding to the stars in Figure 11). In the examples of Figures 12A and 12B, the difference between the DC balanced and DC unbalanced waveforms is very small, while in Figures 13A and 13B, the difference between the DC balanced and DC unbalanced waveforms is very significant.

[0095] It is noteworthy in Figures 10 and 11 that, in a given ACeP-type electrophoretic display construction, the preferred target color (“X” in Figure 11) may not be achieved using the EPP waveform. This phenomenon is reproduced in the physical display.

[0096] Several aspects and embodiments of the technology described herein have been so described, and 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 experiments. Therefore, it should be understood that the foregoing embodiments are presented by way of example only, and that various modifications may be made in ways other than those specifically described within the scope of the appended claims and their equivalents.This invention is practiced through embodiments thereof. 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. Instruction manual page 15 / 15, 18 CN 122551727 A, Figure 1; Instruction manual figure 1 / 14 page, 19 CN 122551727 A, Figure 2A; Instruction manual figure 2 / 14 page, 20 CN 122551727 A, Figure 2B; Instruction manual figure 3 / 14 page, 21 CN 122551727 A, Figure 2C; Instruction manual figure 4 / 14 page, 22 CN 122551727 A, Figure 3; Instruction manual figure 5 / 14 page, 23 CN 122551727 A, Figure 4; Instruction manual figure 6 / 14 page, 24 CN 122551727 A, Figure 5; Instruction manual figure 7 / 14 page, 25 CN 122551727 A, Figure 6; Instruction manual figure 8 / 14 page, 26 CN 122551727 A, Figure 7; Instruction manual figure 9 / 14 page, 27 CN 122551727 A, Figure 8 Figure 9, Figure 10 / 14, Page 28, CN 122551727 A; Figure 10, Figure 11, Figure 12 / 14, Page 30, CN 122551727 A; Figure 12A, Figure 12B, Figure 13A, Figure 13 / 14, Page 31, CN 122551727 A; Figure 13B, Figure 14 / 14, Page 32, CN 122551727 A. Abstract: The present invention provides enhanced push-pull (EPP) waveforms for achieving primary color sets in multi-color electrophoretic displays. Enhanced push-pull driving waveforms are used for driving a four-particle electrophoretic medium, including four different types of particles, for example, a set of scattering...particles and three sets of subtractive particles. Methods for identifying a preferred waveform for a target color state when using a voltage driver having at least five different voltage levels.

Claims

1. A method for determining a push-pull waveform for driving an electrophoretic display, comprising: Determine a set of candidate waveforms for driving the electrophoretic display; The optical states generated by each candidate waveform are estimated using a model representing the electrophoretic display, wherein the model includes a transfer function represented by the following equation: O(t) = f(V(t), x(0)) Where t is time, O(t) is the optical state of the electrophoretic display as a function of t, V(t) is the voltage applied to the electrophoretic display as a function of t, x(0) is the initial optical state of the electrophoretic display at t = 0, and f is a function of V(t) and x(0). as well as Based on the estimated optical state generated by the candidate waveforms, the push-pull waveform used to generate the target optical state is identified.

2. The method of claim 1, further comprising: The electrophoretic display is driven to produce color output using the push-pull waveform identified as being used to generate the target optical state.

3. The method of claim 2, further comprising: The color output of the electrophoresis display is evaluated and compared with the target color.

4. The method of claim 2, further comprising: The color output and associated waveform are used as training data for the model.

5. The method of claim 1, wherein, Determining the set of candidate waveforms includes: Select at least five finite groups of different voltage levels for the waveform used to drive the electrophoretic display; Select a finite time width for the waveform; and Identify a set of waveforms, each waveform having a positive portion and a negative portion, wherein the positive portion and the negative portion each include at least one pulse, and at least one of the positive portion and the negative portion includes two pulses with different voltage amplitudes, each voltage amplitude corresponding to one of the at least five different voltage levels, wherein the sum of the pulse widths of the positive portion and the negative portion is equal to the finite time width.

6. The method of claim 5, wherein, Choosing a finite time width involves comparing the target color with the predicted output color.

7. The method of claim 5, wherein, The finite group of at least five different voltage levels includes: 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.

8. The method of claim 5, wherein, The finite group of at least five different voltage levels includes -27V, 0V, and +27V.

9. The method of claim 5, wherein, The finite group of at least five different voltage levels 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.

10. The method of claim 1, wherein, Determining the set of candidate waveforms includes: Select a finite group of voltages for driving the electrophoretic display, wherein the group of voltages includes at least five different voltage levels; Selecting a time with a finite time width for the candidate waveform; and Calculate all waveforms having a first positive portion and a second negative portion. The first positive portion consists 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 second negative portion consists 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. 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.

11. The method of claim 1, wherein, The electrophoretic display includes an electrophoretic medium disposed between a first transparent electrode and a second electrode. The electrophoretic medium includes four groups of particles, each of which has different optical properties and different charge properties than the other groups of particles in the electrophoretic medium.

12. The method of claim 11, wherein, The four groups of particles include a first group of particles, a second group of particles, a third group of particles, and a fourth group of particles, wherein the first group of particles is reflective, while the second, third, and fourth groups of particles are subtractive.

13. The method of claim 12, wherein, Two of the four groups of particles are positively charged, and two of the four groups of particles are negatively charged.

14. The method of claim 12, wherein, One of the four groups of particles is positively charged, and three of the four groups of particles are negatively charged.

15. The method of claim 12, wherein, Three of the four groups of particles are positively charged, and one of the four groups of particles is negatively charged.

16. The method of claim 1, wherein, The model is a differentiable deep learning model based on a recurrent neural network architecture.

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