Time-shifted waveform for multi-particle electrophoresis displays providing low-flash image updates

Abstract

An electrophoretic display having a multi-particle electrophoretic medium, and an improved method for driving such a multi-particle electrophoretic medium, particularly using an active matrix backplane and controller. A larger lookup table is used, containing multiple time-shifted waveforms for each color transition. Thus, the controller can easily cause a phase shift of color flashes across the display, which ultimately reduces or eliminates the perception that the device is "flashing" during the update from the first image to the second image. The method is generalizable to any electrophoretic display using waveforms and is particularly well suited to newer multi-particle electrophoretic displays capable of producing four or more colors at each pixel.

Description

Background Art

[0001] (Related Application) This application claims priority to U.S. Provisional Application No. 63 / 523,484, filed Jun. 27, 2023, which is incorporated herein by reference in its entirety. All patents and publications disclosed herein are incorporated herein by reference in their entirety.

[0002] An electrophoretic display (EPD) changes color by changing the position of one or more charged colored particles with respect to a light-transmissive viewing surface. Such electrophoretic displays are commonly referred to as "electronic paper" or "ePaper" because the resulting display has a high contrast like ink on paper and is readable even in sunlight. Electrophoretic displays are widely adopted in e-book readers because they provide a reading experience like a book, consume little power, and enable a user to carry a library of hundreds of books in a lightweight handheld device. Such devices are increasingly being adopted for displaying outdoor (OOH) digital content such as shelf labels, outdoor advertising, and traffic signs.

[0003] For many years, electrophoretic displays have contained only two types of charged color particles: black and white. (As used herein, “color” includes both black and white.) White particles are often light-scattering and include, for example, titanium dioxide, while black particles are absorbent across the entire visible spectrum and may include carbon black or absorbent metal oxides such as copper chromite. In its simplest sense, a monochrome electrophoretic display requires only a light-transmitting electrode on the viewing surface, a back electrode, and an electrophoretic medium containing positively and negatively charged white and black particles. 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 contains controllable regions (pixels) (either segmented electrodes or an active matrix of transistor-controlled pixel electrodes), a pattern can be electronically displayed on the viewing surface. The pattern could be, for example, text from a book.

[0004] Recently, a wide variety of color options have become commercially available for electrophoretic displays, including three-color displays (black, white, red; black, white, yellow) and four-color displays (black, white, red, yellow). Similar to the operation of a monochrome electrophoretic display, an electrophoretic display using three or four reflective pigments operates similarly to a simple monochrome display, as it drives particles of the desired color onto the viewing surface. Although the driving mechanism is far more complex than that of simple monochrome, the optical properties of the particles are ultimately the same.

[0005] Advanced Color Electronic Paper (ACeP) TMAlthough it also contains four particles, the cyan, yellow, and magenta particles are subtractive rather than reflective, making it possible to generate thousands of colors in each pixel. The color process is functionally equivalent to the printing methods that have been used for many years in offset printing and inkjet printers. A specific color is produced by using the appropriate ratio of cyan, yellow, and magenta on a bright white paper background. In the ACeP example, the relative positions of the cyan, yellow, magenta, and white particles to the viewing surface determine the color of each pixel. In this type of electrophoretic display, thousands of colors are envisioned in each pixel, but it is crucial to carefully control the position of each pigment (50-500 nanometers in size) within a working space of approximately 10-20 micrometers in thickness. Naturally, variations in the position of the pigments will cause the wrong color to be displayed in a particular pixel. Therefore, precise voltage control is required in such systems. Further details of this system are described in the following U.S. patents, all incorporated together by reference: U.S. Patents No. 9,361,836, No. 9,921,451, No. 10,276,109, No. 10,353,266, No. 10,467,984, No. 10,593,272, and No. 10,657,869.

[0006] As described in the aforementioned patent, the waveform (i.e., the electric field provided across the electrophoretic medium as a function of time) typically requires significant fluctuations in voltage polarity over short periods. This can cause, in some cases, color electrophoretic displays to "flicker," "blink," or "appear to flicker" when switching between color images. This drawback is particularly noticeable when full-color e-readers switch between full-color images at high speeds (i.e., less than a second). U.S. Patent No. 10,657,869 addresses a similar problem. However, the '869 patent does not suggest the use of a lookup table to store offset waveforms, as described below. Other patents held by E Ink Corporation (e.g., U.S. Patent No. 8,593,396) also offered solutions for shifting the start of the waveform or reducing (or expanding) the size of the waveform to improve grayscale control. However, these patents failed to recognize that such adjustments would reduce flickering when properly coordinated.

[0007] In particular, the present invention relates to a color electrophoretic display, and more particularly to an electrophoretic display capable of rendering more than two colors using a single layer of electrophoretic material containing, but not exclusively, multiple colored particles, for example, white, cyan, yellow, and magenta particles. In some examples, two of the particles are positively charged and one (or two) are negatively charged. In some examples, one of the particles is positively charged and three are negatively charged. In some examples, one of the particles is negatively charged and three are positively charged. The particles may also differ in the type of charge species on the particle surface and / or the type of polymer functionalized on the surface. The particles may contain organic or inorganic pigments or dyes.

[0008] The term "gray state" is used herein in its conventional sense in imaging techniques to refer to an intermediate state between two extreme optical states of a pixel, and does not necessarily mean a black-and-white transition between these two extreme optical states. For example, some of the E Ink patents and published applications cited below describe electrophoretic display devices where the extreme states are white and deep blue, so the intermediate gray state would actually be light blue. In fact, as already mentioned, a change in optical state may not be a change in color at all. The terms black and white may be used below to refer to two extreme optical states of a display device and should be understood to usually include extreme optical states that are not strictly black and white (e.g., the white and deep blue states mentioned above).

[0009] The terms bistable and bistable are used herein in their conventional sense in imaging skills to refer to a display device having a display element having a first and second display state, each having at least one different optical property, wherein after any given element is driven to take either the first or second display state using a finite-duration addressing pulse, the state persists for at least several times, e.g., at least four times, the minimum interval of addressing pulses required to change the state of the display element after the addressing pulse has ended. U.S. Patent No. 7,170,670 shows that several particle-based electrophoretic display devices capable of grayscale are stable not only in their extreme black and white states but also in their intermediate gray states, and the same is true for several other types of electro-optic displays. While this type of display device is more accurately called polystable rather than bistable, for convenience, the term bistable may be used herein to encompass both bistable and polystable displays.

[0010] When the term "impulse" refers to the driving of an electrophoretic display, it is used herein to refer to the integral of the applied voltage with respect to time during the period in which the display is driven.

[0011] Particles that absorb, scatter, or reflect light over a broadband or selected wavelength are referred to herein as colored particles or pigment particles. In the electrophoretic media and displays of the present invention, a variety of materials other than pigments (strictly speaking, meaning insoluble coloring materials), such as dyes and photonic crystals, may also be used to absorb or reflect light.

[0012] Particle-based electrophoretic displays have been the subject of intense 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 offer advantages such as better brightness and contrast, wide viewing angles, state bistability, and low power consumption. Nevertheless, problems with the long-term image quality of these displays have hindered their widespread use. For example, the particles that make up electrophoretic displays tend to settle, resulting in insufficient lifespan for these displays.

[0013] As described above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, this fluid is a liquid, but electrophoretic media can also be produced 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. Patents 7,321,459 and 7,236,291. Such gas-based electrophoretic media are considered susceptible to the same types of particle sedimentation problems as liquid-based electrophoretic media when the medium is used in a label where the medium is positioned in a vertical plane, for example, in an orientation that allows such sedimentation. In fact, particle sedimentation is considered a more serious problem in gas-based electrophoretic media than in liquid-based electrophoretic media, due to the lower viscosity of gaseous suspension fluids compared to the viscosity of liquids, which allows for faster sedimentation of electrophoretic particles.

[0014] Numerous patents and applications, assigned to or in the name of the Massachusetts Institute of Technology (MIT) and E Ink Corporation, describe various techniques used in encapsulated electrophoretic media and other electro-optical media. Such encapsulated media comprise numerous small capsules, each comprising an internal phase containing, in itself, particles movable by electrophoresis in a fluid medium, and a capsule wall surrounding the internal phase. Typically, the capsules themselves form a coherent layer, held within a polymer binder and positioned between two electrodes. The techniques described in these patents and applications include: (a) Electrophoretic particles, fluids, and fluid additives, see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814. (b) Capsules, binders, and encapsulation processes, see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719. (c) Microcell structures, wall materials, and methods for forming microcells, see, for example, U.S. Patent Nos. 7,072,095 and 9,279,906. (d) Methods for filling and sealing microcells, see, for example, U.S. Patent Nos. 7,144,942 and 7,715,088. (e) Films and subassemblies containing electro-optical materials, see, for example, U.S. Patents 6,982,178 and 7,839,564. (f) Backplanes, adhesive layers, other auxiliary layers, and methods used in displays, see, for example, U.S. Patents 7,116,318 and 7,535,624. (g) Color formation and color adjustment (e.g., U.S. Patent) [ka] and publication of U.S. patent applications [ka] [ka] See below. (h) A method for driving a display, e.g., a U.S. patent. [ka] and publication of U.S. patent applications [ka] See also. (These patents and applications may hereafter be referred to as MEDEOD (Method for Driving Electro-Optical Displays) applications.) (i) Application of displays (see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348) (j) Non - electrophoretic displays as described in U.S. Patent No. 6,241,921 and U.S. Patent Application Publication Nos. 2015 / 0277160, as well as U.S. Patent Application Publication Nos. 2015 / 0005720 and 2016 / 0012710.

[0015] Many of the aforementioned patents and applications recognize that the wall surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thus generating a so - called polymer - dispersed electrophoretic display, in which the electrophoretic medium comprises a plurality of discrete droplets of an electrophoretic fluid and a continuous phase of a polymeric material, and that the discrete droplets of the electrophoretic fluid within such a polymer - dispersed electrophoretic display can be regarded 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. Thus, for the purposes of this application, such a polymer - dispersed electrophoretic medium is regarded as a sub - species of an encapsulated electrophoretic medium.

[0016] A 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 instead are retained within a plurality of cavities formed within a carrier medium, usually a polymeric film. See, for example, U.S. Patent Nos. 6,672,921 and 6,788,449.

[0017] Electrophoretic media are often impermeable (for example, in many electrophoretic media, the particles substantially block the transmission of visible light through the display) and operate in reflective mode. However, many electrophoretic displays can be made to operate in a so-called shutter mode, where one display state is substantially impermeable and the other is light-transmitting. See, for example, U.S. Patents 5,872,552, 6,130,774, 6,144,361, 6,172,798, 6,271,823, 6,225,971, and 6,184,856. Dielectric displays, similar to electrophoretic displays but relying on variations in electric field strength, can operate in a similar mode. See, for example, U.S. Patent 4,418,346. Other types of electro-optical displays may also be able to operate in shutter mode. An electro-optical medium operating in shutter mode can be used in a multilayer structure for a full-color display, in which at least one layer adjacent to the viewing surface of the display operates in shutter mode, exposing or concealing a second layer further away from the viewing surface.

[0018] Encapsulated electrophoretic displays typically do not suffer from the clustering and sedimentation failure modes of conventional electrophoretic devices and offer additional advantages such as the ability to print or coat displays on a wide variety of flexible and rigid substrates. (The use of the term "print" is intended to include any form of printing and coating, including but not limited to pre-metered coatings such as patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating; roll coatings such as knife over roll coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; silk screen printing processes; electrostatic printing processes; thermal printing processes; inkjet printing processes; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar techniques.) Thus, the resulting display can be flexible. Additionally, since the display medium can be printed (using various methods), the display itself can be fabricated at a low cost.

[0019] As described above, the simplest prior art electrophoretic media essentially display only two colors. Such electrophoretic media use either a single type of electrophoretic particle having a first color in a colored fluid having a second distinct color (in which case the first color is displayed when the particle is adjacent to the viewing surface of the display, and the second color is displayed when the particle is separated from the viewing surface), or first and second types of electrophoretic particles having different first and second colors in an uncolored fluid (in which case the first color is displayed when the first type of particle is adjacent to the viewing surface of the display, and the second color is displayed when the second type of particle is adjacent to the viewing surface). Typically, the two colors are black and white. If a full-color display is desired, a color filter array may be deposited on the viewing surface of a monochrome (black and white) display. Displays with a color filter array rely on area sharing and color mixing to create color stimuli. The available display area is 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 (striped) or two-dimensional (2x2) repeating pattern. Other primary colors or selections of three or more primary colors are also known in the art. The three (for RGB displays) or four (for RGBW displays) subpixels are selected to be small enough that, at the intended viewing distance, they visually blend together into a single pixel with a uniform color stimulus ("color blending"). An inherent drawback of area sharing is that a colorant is always present, and color can only be modulated by switching the corresponding pixels of the underlying monochrome display to white or black (switching the corresponding primary color on or off). For example, in an ideal RGBW display, the primary colors red, green, blue, and white each occupy one-quarter of the display area (one subpixel out of four), the white subpixel is as bright as the white of the underlying monochromatic display, and each of the colored subpixels is no brighter than one-third of the white of the monochromatic display.The brightness of white displayed by the display cannot, as a whole, exceed half the brightness of the white subpixels (the white area of ​​the display is generated by displaying one of each of four white subpixels, and in addition, each colored subpixel in its colored form is equivalent to one-third of a white subpixel; therefore, three combined colored subpixels contribute to one or fewer white subpixels). The brightness and saturation of a color are reduced by sharing space with color pixels that have been switched to black. This sharing space is particularly problematic when mixing yellow, because yellow is brighter than any other color of equal brightness, and saturated yellow is almost as bright as white. Switching blue pixels (one-quarter of the display area) to black makes yellow too dark.

[0020] U.S. Patents 8,576,476 and 8,797,634 describe a multicolor electrophoretic display having a single backplane with independently addressable pixel electrodes and a common light-transmitting front electrode. Multiple electrophoretic layers are arranged between the backplane and the front electrode. The displays described in these applications can render any primary color (red, green, blue, cyan, magenta, yellow, white, and black) at any pixel position. However, the use of multiple electrophoretic layers located between a set of address electrodes has drawbacks. The electric field experienced by particles in a particular layer is lower than that of a single electrophoretic layer addressed at the same voltage. In addition, optical losses in the electrophoretic layer closest to the viewing surface (e.g., caused by light scattering or undesirable absorption) can affect the appearance of the image formed in the underlying electrophoretic layers.

[0021] 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 containing one or two types of pigment particles dispersed in a transparent and colorless or colored solvent, the electrophoretic fluid being positioned between a common electrode and a number of pixels or driving electrodes. The driving electrodes are positioned to expose the background layer. U.S. Patent No. 9,116,412 describes a method for driving a display cell filled with an electrophoretic fluid containing two types of charged particles having opposite charge polarities and two contrasting colors. The two types of pigment particles are dispersed in a colored solvent, or in a solvent having uncharged or slightly charged colored particles dispersed therein. The method comprises driving the display cell 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 total driving voltage. U.S. Patents No. 8,717,664 and 8,964,282 describe electrophoretic fluids and methods for driving electrophoretic displays. The fluids comprise first, second, and third types of pigment particles, all of which are 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 have a charge level less than approximately 50% of the charge level of the first or second type. The three types of pigment particles have different levels of threshold voltage, or different levels of mobility, or both.

[0022] Electrophoretic displays capable of rendering any color at any pixel location are described in U.S. Patents 10,475,399 and 10,678,111. Patent 10,678,111 describes a display in which a white (light-scattering) pigment moves in a first direction when addressed at a low applied voltage and in the opposite direction when addressed at a higher voltage. Patent 111 describes a full-color electrophoretic display in which four pigments are present, namely white, cyan, magenta, and yellow, with two of the pigments being positively charged and two being negatively charged. U.S. Patent Publication 2022 / 0082896 describes a full-color electrophoretic display in which four pigments are present, namely white, cyan, magenta, and yellow, with three colored pigments being positively charged and the white pigment being negatively charged. Embodiments of this type of invention are referred to as CMYW embodiments.

[0023] In addition, there are multi-particle display designs in which colored pigments scatter light (i.e., reflective colored particles). U.S. Patent No. 10,339,876 describes this type of display having black, white, and red particles capable of rendering three states. A similar display design containing four pigments can render four different colors (see, for example, U.S. Patent No. 9,922,603), or by using translucent colored particles, such a display can render six colors (see, for example, U.S. Patent No. 11,640,803). Many multi-particle display designs using light-scattering particles incorporate long, "flashing-like" updates that some observers find unappealing. The solutions described below can be used to reduce the "flashing" of updates in such displays and typically require little additional cost in terms of new controllers or drivers. [Prior art documents] [Patent Documents]

[0024] [Patent Document 1] U.S. Patent No. 9,361,836 [Non-patent literature]

[0025] [Non-Patent Document 1] Kitamura,T.,et al.,Electrical toner movement for electronic paper-like display, IDW Japan, 2001, Paper HCS1-1 [Overview of the Initiative] [Means for solving the problem]

[0026] Disclosed herein are improved methods for driving full-color electrophoretic displays and full-color electrophoretic displays using these driving methods. In one aspect, the present invention includes an electrophoretic display comprising: a light-transmitting electrode; an active matrix backplane having a plurality of rows of pixel electrodes, each pixel electrode being coupled to a thin-film transistor having a gate line and a source line; and an electrophoretic medium disposed between the light-transmitting electrode and the active matrix backplane, the electrophoretic medium comprising at least three different types of charged pigment particles. The electrophoretic display further comprises a controller coupled to a plurality of gate lines, each gate line coupled to a thin-film transistor of one row of a plurality of rows of pixel electrodes, the controller coupled to a plurality of source lines, and the controller further configured to address the pixel electrodes row by row by providing both a gate voltage and a source voltage to each thin-film transistor, and a non-temporary memory coupled to the controller and having a lookup table, for a transition between a first color and a second color, the lookup table includes a first waveform for transitioning the electrophoretic medium between the first color and the second color, and a second waveform for transitioning the electrophoretic medium between the first color and the second color, the first and second waveforms being identical in terms of the number of voltage pulses and the respective polarity and magnitude of the voltage pulses, but the first and second waveforms being time-shifted by at least 1 ms, e.g., 5 ms, e.g., 8 ms, e.g., 12 ms. In addition, when the controller updates the electrophoretic display between the first image and the second image, it performs the following steps: receiving a first waveform from a lookup table; providing the first waveform to the pixel electrodes of the first row; receiving a second waveform from a lookup table; and providing the second waveform to the pixel electrodes of the second row adjacent to the pixel electrodes of the first row.

[0027] In one embodiment, the lookup table further comprises a third waveform for transitioning the electrophoretic medium between a first color and a second color, wherein the first, second, and third waveforms are identical in terms of the number of voltage pulses and the respective polarities and magnitudes of the voltage pulses, but the first, second, and third waveforms are time-shifted by at least 5 ms from each other, and the controller further takes the step of receiving the third waveform from the lookup table and providing the third waveform to the pixel electrodes of the third row adjacent to the electrodes of the second row, the electrodes of the second row being located between the electrodes of the first row and the electrodes of the third row. In one embodiment, the lookup table further comprises a fourth waveform for transitioning the electrophoretic medium between a first color and a third color, wherein the third waveform is not identical to the first and second waveforms in terms of the number of voltage pulses and the respective polarities and magnitudes of the voltage pulses, but the first, second, and third waveforms are time-shifted by at least 1 ms from each other. In one embodiment, the first and second waveforms are time-shifted by at least 5 ms, optionally at least 10 ms, and optionally between 12 ms and 20 ms. In one embodiment, the first and second waveforms are time-shifted by a frame, where a frame is the time required to address all pixels in the active matrix backplane once when addressing the active matrix backplane row by row. In one embodiment, the magnitude of the voltage pulse is between -15V and +15V, or between -24V and +24V. In one embodiment, the electrophoretic medium includes reflective white particles and at least one subtractive color particle, or reflective white particles and at least one reflective color particle. In one embodiment, the electrophoretic medium includes a fourth type of electrophoretic particle. In one embodiment, two of the particle types are negatively charged and two of the particle types are positively charged, or one of the particle types is negatively charged and three of the particle types are positively charged, or three of the particle types are negatively charged and one of the particle types is positively charged.In one embodiment, the electrophoretic medium is encapsulated within a microcapsule or microcell. [Brief explanation of the drawing]

[0028] [Figure 1A] Figure 1A is a typical cross-sectional view of a four-particle electrophoresis display in which the electrophoretic medium is encapsulated within a capsule. The structure of Figure 1A can be used for multi-particle electrophoresis media having both reflective pigment particles and subtractive pigment particles.

[0029] [Figure 1B] Figure 1B is a typical cross-sectional view of a four-particle electrophoresis display in which the electrophoretic medium is encapsulated within a microcell. The structure of Figure 1B can be used for multi-particle electrophoresis media having both reflective and subtractive pigment particles.

[0030] [Figure 2] Figure 2 illustrates an exemplary equivalent circuit for a single pixel in an electrophoretic display using an active matrix backplane of pixel electrodes coupled to a storage capacitor.

[0031] [Figure 3] Figure 3 is a schematic diagram of an exemplary drive system for controlling the voltage supplied to the pixel electrodes in an active matrix device. The resulting drive voltage can be used to set the optical state of the multi-particle electrophoresis medium.

[0032] [Figure 4] Figure 4 illustrates an exemplary electrophoretic display including a display module. This electrophoretic display also includes a processor, non-temporary memory, one or more power supplies, and a controller. The electrophoretic display may also include sensors to allow the electrophoretic display to adjust its operating parameters based on ambient conditions such as temperature and lighting.

[0033] [Figure 5] Figure 5 illustrates the preferred positions of four sets of particles for generating eight standard colors in a white-cyan-magenta-yellow (WCMY) four-particle electrophoretic display, where white particles are reflective and cyan, magenta, and yellow particles are absorptive.

[0034] [Figure 6A] Figure 6A shows an exemplary push-pull drive scheme for addressing an electrophoretic medium containing three subtractive (cyan, yellow, and magenta) particles and a scattering (white) particle.

[0035] [Figure 6B] Figure 6B shows an exemplary push-pull drive scheme for addressing an electrophoretic medium containing one absorbent (black) particle, two reflective (red and yellow) particles, and a scattering (white) particle.

[0036] [Figure 7] Figure 7 depicts a "typical" drive waveform supplied to the pixel electrodes during a single update from the first color to the second color. In particular, the waveform includes a repetitive push-pull voltage.

[0037] [Figure 8] Figure 8 shows three identical push-pull waveforms that have been time-shifted by just one frame (approximately 12 ms) to reduce the flickering during the update from the first color to the second color.

[0038] [Figure 9] Figure 9 illustrates the display of the present invention, in which the same offset waveform is supplied to three adjacent rows of pixel electrodes that undergo the same color transition.

[0039] [Figure 10]Figure 10 illustrates an update pattern for a display according to the present invention, in which three different offset waveforms are supplied to various rows in a portion of the display that undergo the same transition from a first color to a second color. The same technique can also be used when more than one color transition is required in the portion of the display being updated.

[0040] [Figure 11A] Figure 11A illustrates the color transients (measured by reflectance in L*, a*, b* space) generated when an electrophoretic display containing white reflective particles and cyan, yellow, and magenta subtractive particles is addressed across the entire display using the repeating bipolar waveform of Figure 7, and when a time-shifted (interlaced) waveform is not used.

[0041] [Figure 11B] Figure 11B illustrates the color transients (measured by reflectivity in L*, a*, b* space) generated when odd and even pixel electrode rows receive time-shifted (interlaced) waveforms, with each even row receiving the same waveform, and each odd row receiving the same waveform, except the odd row is time-shifted by approximately 12 ms.

[0042] [Figure 11C] Figure 11C illustrates an electrophoretic display containing white reflective particles and cyan, yellow, and magenta subtractive particles, addressed across the entire display using the repeating bipolar waveforms of Figure 7, with three different time-shifted waveforms used. It illustrates the color transients (such as those measured by reflectance in L*, a*, b* space) generated when each time-shifted waveform is delivered to one-third of the row. Each subsequent row is shifted by only one frame (approximately 12 ms) until the time-shifted waveform is in phase with the previous waveform. [Modes for carrying out the invention]

[0043] The present invention includes an electrophoretic display having a multi-particle electrophoretic medium, and an improved method for driving such a multi-particle electrophoretic medium. The display of the present invention typically includes an active matrix backplane of pixel electrodes controlled by thin-film transistors. Typically, each pixel electrode is also coupled to a storage capacitor. The method of driving the display is generalizable to all different types of electrophoretic displays (segmented, direct-driven, indirectly-driven, active-matrix) and may be used with various waveforms, but the displays of the present invention are often used to drive more complex electrophoretic media that require simultaneous precise control of, for example, three, four, or more particles. In a preferred embodiment, the display of the present invention uses an active matrix backplane controlled by an array of thin-film transistors, and the driving waveform is of the iterative "push-pull" type. Using the techniques described herein, electrophoretic displays incorporating the disclosed driving scheme would typically appear less "flashing" compared to conventional row-by-row updating addressing using a single "best" waveform for specific color transitions, which has been state-of-the-art for some time. Such displays may include a plurality of subtractively colored electrophoretic particles and / or a plurality of reflectively colored electrophoretic particles. In a preferred embodiment, the electrophoretic medium includes white particles and subtractively mixed primary color particles of cyan, yellow, and magenta, i.e., a WCMY system.

[0044] Methods for creating electrophoretic displays containing four (or more) particles have been discussed in the prior art. The electrophoretic fluid may be encapsulated in microcapsules or incorporated into microcell structures, which are then sealed with a polymer layer. The microcapsules or microcell layers may be coated or laminated onto a plastic substrate or film having a transparent coating of conductive material. Alternatively, the microcapsules may be coated onto a light-transmitting substrate or other electrode material using spraying techniques (see U.S. Patent No. 9,835,925, incorporated herein by reference). The resulting assemblies may be laminated onto a backplane supporting pixel electrodes using a conductive adhesive. Alternatively, the assemblies may be attached to one or more segment electrodes on the backplane, which are directly driven.

[0045] The present invention provides, among other things, an architecture and method for addressing dipole electrophoretic displays using thin-film transistor arrays. A larger lookup table is used, containing multiple time-shifted waveforms for each color transition. Thus, the controller can easily induce a phase shift of color flashes across the display, which ultimately reduces or eliminates the perception that the device is "flashing" during the update from the first image to the second image. Thus, various multi-particle (color) electrophoretic displays can be addressed without visible flickering or blinking.

[0046] The electrophoretic media used herein include charged particles that differ in color, reflectance or absorption properties, charge density, and mobility in an electric field (measured as zeta potential). Particles that absorb, scatter, or reflect light in a broadband or selected wavelength are referred to herein as colored particles or pigment particles. In the electrophoretic media and displays of the present invention, various materials other than pigments that absorb or reflect light (in the strict sense of the term meaning insoluble coloring materials), such as dyes, photonic crystals, quantum dots, etc., may also be used. For example, the electrophoretic medium may include a fluid and a plurality of first particles and a plurality of second particles dispersed in the fluid, wherein the first and second particles carry opposite polarity charges, the first particles are light-scattering particles, and the second particles have one of the subtractive primary colors, and a plurality of third particles and a plurality of fourth particles dispersed in the fluid, wherein the third and fourth particles carry opposite polarity charges, and the third and fourth particles each have a different subtractive primary color from each other and from the second particles. Here, the electric field required to separate aggregates formed by the third and fourth particles is greater than the electric field required to separate aggregates formed from any two other types of particles.

[0047] The electrophoretic media of the present invention may contain any additives used in prior art electrophoretic media, such as those described in the above-mentioned E Ink and MIT patents and applications. For example, the electrophoretic media of the present invention typically contains at least one charge control agent to control the charge of various particles, and the fluid may dissolve or disperse a polymer having a number-average molecular weight greater than about 20,000 and being essentially non-absorbent to particles in the fluid to improve the bistability of the display, as described in U.S. Patent No. 7,170,670 above.

[0048] In one embodiment, the present invention uses typically white light-scattering particles and three substantially non-light-scattering particles. Naturally, there are no particles that are completely light-scattering or completely non-light-scattering, and the minimum light-scattering degree of the light-scattering particles and the maximum acceptable light-scattering degree of the substantially non-light-scattering particles used in the electrophoresis of the present invention can vary to some extent depending on factors such as the exact pigments used, their colors, and the user's ability to tolerate some deviation from the ideal desired color, or application factors. The scattering and absorption properties of the pigments can be evaluated by measuring the diffuse reflectance of samples of the pigments dispersed in a suitable matrix or liquid against white and dark backgrounds. Results from such measurements can be interpreted according to a number of models well known in the art, e.g., one-dimensional Kubelka-Munk treatment. In the present invention, it is preferable that the white pigment exhibits a diffuse reflectance of at least 5% at 550 nm, measured against a black background, when the pigment is distributed approximately isotropically at 15 volume% in a 1 μm thick layer containing the pigment and a liquid with a refractive index of less than 1.55. Yellow, magenta, and cyan pigments preferably exhibit a diffuse reflectance of less than 2.5% at 650, 650, and 450 nm, respectively, measured on a black background under the same conditions. (The wavelengths selected above for the measurement of yellow, magenta, and cyan pigments correspond to the spectral regions of minimum absorption by these pigments.) Coloring pigments that meet these criteria are hereafter referred to as “non-scattering” or “substantially non-light-scattering.” Specific examples of suitable particles are disclosed in U.S. Patent No. 9,921,451, which is incorporated herein by reference.

[0049] Alternative particle sets may also be used, including four sets of reflective particles, or one absorbing particle and three or four sets of different reflective particles, such as those described in U.S. Patents 9,922,603 ​​and 10,032,419, which are incorporated herein by reference. For example, white particles may be formed from inorganic pigments such as TiO2, ZrO2, ZnO, Al2O3, Sb2O3, BaSO4, and PbSO4, while black particles may be formed from CI Pigment Black 26 or 28 (e.g., manganese ferrite black spinel or copper chromite black spinel) or carbon black. Third / fourth / fifth types of particles may be colors such as red, green, blue, magenta, cyan, or yellow. Pigments for this type of particle may include, but are not limited to, CI pigments PR254, PR122, PR149, PG36, PG58, PG7, PB28, PB15:3, PY138, PY150, PY155, or PY20. Specific examples include Clariant Hostaperm Red D3G70-EDS, Hostaperm Pink E-EDS, PV fast red D3G, Hostaperm red D3G 70, Hostaperm Blue B2G-EDS, Hostaperm Yellow H4G-EDS, Hostaperm Green GNX, BASF Irgazine red L 3630, Cinquasia Red L 4100 HD, and Irgazin Red L 3660 HD; Sun Chemical phthalocyanine blue, phthalocyanine green, diallylid yellow, or diallylid AAOT yellow.

[0050] As shown in Figures 1A and 1B, an electrophoretic display (101, 102) typically comprises an upper transparent electrode 110, an electrophoretic medium 120, and a lower electrode 130, the lower electrode 130 being a pixel electrode of an active matrix of pixels, often controlled by thin-film transistors (TFTs). In the electrophoretic medium 120 described herein, there are four different types of particles 121, 122, 123, and 124, however, more (or fewer) sets of particles can be used with the methods and displays described herein. For example, the techniques of the present invention can be used with a set of three types of particles, e.g., white, black, and red, where one of the three different types of particles has a smaller charge magnitude than the other two types of particles. In some examples, two of the particles will be positively charged and one (or two) of the particles will be negatively charged. In some examples, one of the particles will be positively charged and three of the particles will be negatively charged. In some examples, one particle may be negatively charged and three particles positively charged. The electrophoretic medium 120 is typically partitioned by the walls of microcapsules 126 or microcells 127, etc. An optional adhesive layer 140 may be located adjacent to any of the layers, but is typically adjacent to the electrode layer (110 or 130). In a given electrophoretic display (105, 106), there may be more than one adhesive layer 140, but it is more common to have only one. The entire display stack is typically placed on a substrate 150, which may be rigid or flexible. The displays (101, 102) also typically include a protective layer 160, which may simply protect the upper electrode 110 from damage or enclose the entire display (101, 102) to prevent the ingress of water, etc. The electrophoretic displays (101, 102) may also include a sealing layer 180, if necessary. In some embodiments, the adhesive layer 140 may contain a primer component to improve adhesion to the electrode layer 110, or a separate primer layer (not shown in Figure 1B) may be used.The structure and components of electrophoretic displays, pigments, adhesives, electrode materials, etc., are described in numerous patents and patent applications published by E Ink Corporation, such as U.S. Patents 6,922,276, 7,002,728, 7,072,095, 7,116,318, 7,715,088, and 7,839,564, all of which are incorporated herein by reference in their entirety.

[0051] In some embodiments, as shown in Figure 1A, for example, an electrophoretic display may include a light-transmitting electrode, an electrophoretic medium, and a plurality of back-facing pixel electrodes. To produce a high-resolution display for displaying an image, for example, each pixel electrode 130 is individually addressable without interference from adjacent pixels, thereby faithfully reproducing the image file on the display. One way to achieve this objective is to provide an array of nonlinear elements, such as transistors and diodes, and associate at least one nonlinear element with each pixel to create an "active matrix" display (see Figure 2). The addressing or pixel electrode 130 that addresses a single pixel is connected to a suitable voltage source through 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 array will be assumed in the following description, but this is essentially arbitrary, and the pixel electrode may be connected to the source of the transistor.

[0052] Conventionally, in high-resolution arrays, pixels are arranged in a two-dimensional array of rows and columns such that any particular pixel is uniquely defined by the intersection of one designated row and one designated column (see Figure 3). 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. Again, the assignment of sources to rows and gates to columns is conventional but essentially arbitrary and can be reversed as desired. Row electrodes are typically connected to row drivers (gate drivers, gate controllers), which essentially ensure that at any given moment, only one row is selected, i.e., a selection voltage is applied to the selected row electrode such that all transistors in the selected row are conductive, while a deselection voltage is applied to all other rows such that all transistors in those unselected rows remain non-conductive. Column electrodes are typically connected to column drivers (source drivers, source controllers), which apply selected voltages to the various column electrodes to drive the pixels in the selected row to their desired optical states. (The aforementioned voltage is applied to a common front electrode that is conventionally supplied from the nonlinear array to the opposite side of the electro-optical medium and extends throughout the entire display.) After a predetermined interval known as the “line address time,” the selected row is deselected, the next row is selected, and the next row of the display is written by changing the column driver voltage. This process is repeated until the entire display is written row by row. The time between addresses in the display is known as a “frame.” Therefore, a display updated at 60 Hz has a frame of 16 milliseconds. A display updated at 85 Hz has a frame of 12 milliseconds. A display updated at 120 Hz has a frame of 8 milliseconds.

[0053] It should be noted that the magnitude of the voltage that can be provided in such row-column drives may be limited by nonlinear elements, such as the material from which the thin-film transistor is made. In many embodiments, the semiconductor material is silicon, particularly amorphous silicon, which can control the drive voltage on the order of ±15V. In other embodiments, the semiconductor of the thin-film transistor may be a metal oxide such as indium gallium zinc oxide (IGZO), which allows for a wider range of drive voltages, such as up to ±30V, as described, for example, in U.S. Patent Application Publication 2022 / 0084473. This design feature is particularly suitable when driving waveforms to separate pigments in multi-particle systems. In such systems, it is beneficial to provide at least five voltage levels (high positive, low positive, zero, low negative, high negative), with higher total voltages making it easier to separate particles. For further details, see U.S. Patent Publication 2021-0132459.

[0054] Figure 2 of the attached drawings depicts an exemplary equivalent circuit of a single pixel in an electrophoretic display. As shown, the circuit includes a storage capacitor 10 formed between the pixel electrode (element 130 in Figures 1A and 1B) and the capacitor electrode. The electrophoretic medium 20 is represented as a capacitor and resistor in parallel. In some examples, direct or indirect coupling capacitance 30 (usually referred to as “parasitic capacitance”) between the gate electrode of the transistor associated with the pixel and the pixel electrode can generate unwanted noise in 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 result in a small negative offset voltage to the pixel electrode, also known as the “kickback voltage,” which is typically less than 2 volts. [In some embodiments, to compensate for the unwanted “kickback voltage,” a common potential Vcom may be supplied to the upper planar electrode and capacitor electrode associated with each pixel, thus V com The kickback voltage (V KBWhen set to a value equal to ), all voltages supplied to the display may be offset by the same amount, and no net DC imbalance is incurred.

[0055] In conventional electrophoretic displays using an active matrix backplane, a capacitor electrode (storage capacitor) is associated with each pixel electrode, and the pixel electrode and the capacitor electrode form a capacitor. See, for example, international patent application WO01 / 07961. In some embodiments, an N-type semiconductor (e.g., amorphous silicon) may be used to form a transistor, and the “selective” and “deselective” voltages applied to the gate electrode may be positive and negative, respectively.

[0056] Additional details of row-column addressing used in "active matrix" displays are shown in Figure 3. Addressing electrodes, or pixel electrodes, that address a single pixel are fabricated on the substrate 402 and connected to appropriate voltage sources 404 and 406 via relevant nonlinear elements. It should be understood that the voltage sources 404 and 406 may originate from separate circuit elements, or the voltage may be delivered with the assistance of a single power supply and power management integrated circuit (PMIC). In some examples, an intervening source controller 420 is used to control the supplied voltage, while in other embodiments, a controller 460 is configured to control the entire addressing process, including tuning the gate and source lines. Also, although Figure 3 is a diagram of the layout of the active matrix backplane 400, it should be understood that in practice the active matrix has depth, and some elements, such as TFTs, may actually be directly below the pixel electrodes with vias providing electrical connections from the drain to the upper pixel electrodes.

[0057] Conventionally, in high-resolution arrays, pixels are arranged in a two-dimensional array of rows and columns such that any particular pixel is uniquely defined by the intersection of one specified row and one specified column. The sources of all transistors in each column are connected to a single column (scan) line 406, and the gates of all transistors in each row are connected to a single row (gate) line 408, although, as before, the assignment of sources to rows and gates to columns is essentially arbitrary and can be reversed as desired. The gate line 408 is optionally connected to a gate line driver 412, which essentially ensures that at any given moment only one row is selected, i.e., a selection voltage is applied to the electrodes of the selected row to ensure that all transistors in the selected row are conductive, while a deselection voltage is applied to all other rows to ensure that all transistors in those unselected rows remain nonconductive. The column scan lines 406 are optionally connected to a scan line driver 410, which applies a selected voltage to the various scan lines 406 to drive the pixels of the selected row to their desired optical state. (The aforementioned voltages are for a common upper electrode and are not shown in Figure 3.) In conventional driving, after a predetermined interval known as the “line address time,” the selected row is deselected, the next row is selected, and the next line of the display is written by changing the voltage of the column driver. This process is repeated linearly until the entire display is written line by line. As shown in Figure 3, the time intervals between gate voltage pulses in each frame are typically constant and represent the rhythm of line-by-line addressing. In particular, the present invention does not achieve uniform spacing between each gate voltage pulse for a given address row of the pixel electrodes.

[0058] The active matrix backplane described with respect to Figure 3 is coupled to an electro-optical medium, for example, as illustrated in Figures 1A and 1B, and is typically sealed to create a display module 55, as shown in Figure 4. Such a display module 55 is the focus of the electrophoretic display 40. The electrophoretic display 40 typically includes a processor 50, which coordinates many functions related to displaying content on the display module 55 and is configured to convert a “standard” image, such as an sRGB image, to a color regime that best replicates the image on the display module 55. Naturally, if the electrophoretic display is used as a sensor or counter, the content may be related to other inputs. The processor is typically a mobile processor chip, such as those made by Freescale or Qualcomm, but other manufacturers are also known. The processor frequently communicates with non-temporary memory 70, from which it retrieves image files and / or lookup tables to perform the color image conversions described below. The non-temporary memory 70 may also contain gate drive instructions to the extent that certain color transitions may require different gate drive patterns. The electrophoretic display 40 may have one or more non-temporary memory chips. The non-temporary memory 70 may be flash memory. In many embodiments, the non-temporary memory 70 is directly integrated into the end consumer device by integrating all the elements of Figure 4 into a circuit board or package. However, in some cases, such as when the display is external to an object like an automobile, the driving circuit is not directly integrated into the display.

[0059] The waveform (described below) is typically stored in non-temporary memory 70, but can also be incorporated into the controller 60 or processor 50, or stored in the cloud and downloaded via communication 85. To facilitate the method of the present invention, a number of lookup tables can be used, in particular to provide the time-shifted waveform to the controller 60 as appropriate. In particular, with respect to a given transition from a first color to a second color in an electrophoretic medium having eight primary colors, the lookup table may include instructions to update from color 1 to the subsequent color (without time offset) in lookup slots 1 to 8, instructions to update from color 1 to the subsequent color (with a first time offset) in lookup slots 9 to 16, instructions to update from color 1 to the subsequent color (with a second time offset) in lookup slots 17 to 24, and so on. Naturally, this type of lookup table can also be indexed for performance improvement, taking into account operating conditions such as device temperature, battery health, front light color, and front light intensity.

[0060] Once the desired image is converted for display on the display module 55, a specific image command is sent to the controller 60, which facilitates the transmission of a voltage sequence to each thin-film transistor (described above). Such voltages typically originate from one or more power supplies 80, which may include, for example, a power management integrated chip (PMIC). The electrophoretic display 40 may also include communication 85, which may be, for example, the WIFI protocol or BLUETOOTH®, enabling the electrophoretic display 40 to receive images and commands, which may also be stored in memory 70. The electrophoretic display 40 may also include one or more sensors 90, which may include a temperature sensor and / or a light sensor, and such information can be supplied to the processor 50, enabling the processor to select the optimal lookup table when a lookup table is indexed for ambient temperature or incident illumination intensity or spectrum. In some examples, multiple components of the electrophoretic display 40 can be embedded in a single integrated circuit. For example, a special integrated circuit may perform the functions of the processor 50 and the controller 60.

[0061] As shown in Figure 5, the ACEP (e.g., WCMY) system functions, in principle, similar to printing on bright white paper, in that the viewer only sees the colored pigment on the viewing side of the white pigment (i.e., the only pigment that scatters light). In Figure 5, we assume that the viewing surface of the display is located at the top (as shown in the figure), i.e., the user views the display device from this direction, and the illumination light also enters from this direction. In Figure 5, we assume that the light-scattering particles are white pigment. These light-scattering white particles form a white reflector, and any particles above the white particles (as illustrated in Figure 5) are visible relative to this reflector. Some of the incident light passes through the subtractive particles, is reflected by the white particles below the subtractive particles, returns through these particles, and exits the display. Different portions of the incident light are absorbed by the subtractive particles. Therefore, particles above the white particles can absorb various colors, and the colors seen by the user result from the combination of particles above the white particles. Any particle positioned below the white particle (behind it from the user's perspective) is masked by the white particle and does not affect the displayed color. The second, third, and fourth particles are substantially non-light-scattering, so their relative order or arrangement is not important; however, for the reasons mentioned above, their order or arrangement relative to the white (light-scattering) particle is significant.

[0062] More specifically, when cyan, magenta, and yellow particles are below the white particle (situation [A] in Figure 5), there are no particles above the white particle, and the pixel simply displays white. When a single particle is above the white particle, the color of that single particle is displayed as yellow, magenta, and cyan in situations [B], [D], and [F] in Figure 5, respectively. When two particles are above the white particle, the displayed color is a combination of the colors of these two particles, and in Figure 5, in situation [C], the magenta and yellow particles display red; in situation [E], the cyan and magenta particles display blue; and in situation [G], the yellow and cyan particles display green. Finally, when all three colored particles are above the white particle (situation [H] in Figure 5), all incident light is absorbed by the three subtractive primary colored particles, and the pixel displays black.

[0063] It is possible that a primary color of subtractive color mixing can be rendered by light-scattering particles, and therefore a display may have two types of light-scattering particles, one of which may be white and the other colored. However, in this case, the position of the light-scattering colored particles relative to the other colored particles that cover the white particles will be important. For example, when rendering a color as black (when all three colored particles are on top of the white particles), the scattering colored particles cannot be on top of the non-scattering colored particles (otherwise they will be partially or completely hidden behind the scattering particles, and the rendered color will be the color of the scattering colored particles, not black).

[0064] Figure 5 shows an ideal situation where the colors are not contaminated (i.e., the light-scattering white particles completely mask any particles behind them). In reality, the masking by the white particles is not perfect, so slight light absorption may occur by particles that should ideally be completely masked. Such contamination typically reduces both the brightness and saturation of the rendered color. In the electrophoretic medium of the present invention, such color contamination should be minimized to the extent that the formed color meets industry-standard color reproduction. A particularly preferred standard is SNAP (Standard for Newspaper Advertising Production), which has L for each of the eight primary colors mentioned above. * a * , b * The values ​​are defined. (Hereafter, "primary colors" will be used to refer to the eight colors shown in Figure 5: black, white, the three subtractive primary colors, and the three additive primary colors.)

[0065] Figure 6A shows (in a simplified form) the push-pull waveform used to drive the aforementioned four-particle WCMY electrophoresis display system. Such a waveform consists of a dipole with two pulses of opposite polarity. Typically, each dipole has a pulse of voltage V1 applied for time t1, followed by a pulse of voltage V2 applied for time t2. The dipole is impulse-equipped when V1t1 + V2t2 = 0. The magnitude and length of these pulses determine the resulting color. There should be at least five such voltage levels. Figure 6A shows positive and negative voltages for high and low voltages, as well as zero volts. Typically, "low" (L) refers to a range of approximately 5–15V, and "high" (H) refers to a range of approximately 15–30V. Generally, the greater the magnitude of the "high" voltage, the better the color gamut achieved by the display. In some examples, intermediate voltages are also included, especially when more colors are required. The "Medium" (M) level is typically around 15V, but the value of M will depend to some extent on the particle composition and the environment of the electrophoretic medium.

[0066] In particular, in the dipole waveform of Figure 6A, the dipoles used to provide magenta, yellow, green, and blue are at least nearly impulse-balanced. On the other hand, dipole addressing is not required to generate black and white. A simple monopole pulse in either direction will move the oppositely charged colored and white pigments toward and away from the viewing surface, and therefore the display will behave like a conventional display containing black and white pigments under these circumstances. Furthermore, since these monopole pulses are not DC-balanced, an additional charge-clearing pulse must be incorporated into the device drive protocol at the beginning or end of image updates, or at the end of extended unbalanced drive sequences, as can occur when scrolling. However, dipole addressing can break symmetry even when the waveform is impulse-balanced overall. For example, [ka] and [ka] This can be true. For example, see Dukhin AS, Dukhin SS, “Aperiodic capillary electrophoresis method using an alternating current electric field for separation of macromolecules.” Electrophoresis, 2005 Jun;26(11):2149-53. Then, insofar as the pigment mobility depends on the applied electric field, this type of waveform can result in overall pigment drift.

[0067] Figure 6B shows two typical push-pull waveforms used to make the colors of less charged particles appear on a viewing surface for a four-particle system including a scattering white particle, an absorbing black particle, and two colored scattering particles (yellow and red). See, for example, U.S. Patent No. 10,339,876. In the example depicted in Figure 6B, the yellow particle is highly charged with negative polarity, the white particle has a lower charge with negative polarity, the black particle is highly charged with positive polarity, and the red particle has a lower charge and positive polarity.

[0068] As seen in Figures 6A-6B, typically, one pulse within a dipole used to produce a particular color has a shorter duration than the other. Furthermore, while Figures 6A and 6B show the simplest push-pull waveforms (dipoles) required to form a color, it will be recognized that practical waveforms typically require multiple repetitions of these patterns, as shown in Figure 7. Repeating dipoles are the main cause of flicker in displays because the pigment is driven first in one direction and then in the other. If the frequency of this flicker is too low, the appearance of the transition from one color to another becomes unpleasant.

[0069] One way to reduce flickering for a given transition from a first color to a second color is to provide a time-offset (slightly) offset waveform for the same transition. Similar to noise-canceling headphones, by providing adjusted peaks when the dominant waveform has a trough, the viewer does not perceive large fluctuations between colors; i.e., the image is optically quieter. Methods for this improvement are illustrated in detail in Figures 8-10. In one embodiment, the first row of the display receives a "normal" waveform, and then subsequent rows receive time-shifted waveforms until the pattern begins to repeat again. For example, the waveform going to the second row of the display is shifted by one frame, the waveform going to the third row of the display is shifted by another frame from the waveform going to the second row, and so on. With respect to Figure 8, the first row may receive phase 2 (bottom), the second row may receive phase 1 (middle), the third row may receive phase 0 (top), or in any other order. Furthermore, it is understood that different rows may use waveforms that are shifted less (or more) than the frame, for example, shifted by approximately 10ms, or shifted by approximately 5ms.

[0070] Figure 9 illustrates the interaction of the same waveform, time-shifted in two forms and stored in a lookup table in non-temporary memory. For a first row of the active matrix backplane, a pixel undergoing a transition from color 1 to color 2 receives a first waveform, causing the desired change in the electrophoretic medium. Subsequent rows receive a waveform that is the same in terms of pulse count, pulse magnitude, and pulse polarity, but here the waveform is time-shifted by, for example, one frame, e.g., 5ms, e.g., 8ms, e.g., 12ms. This second waveform is stored in a different set of waveforms in the lookup table. The second waveform may belong to a set of time-shifted waveforms that are all assigned to every other row, every three rows, every four rows, etc. Subsequent rows then receive a third waveform that is the same in terms of pulse count, pulse magnitude, and pulse polarity, but further time-shifted. A wider raster pattern using the technique of Figure 9 is shown in Figure 10. Using this technique, the overall color update from color 1 to color 2 is only a few tens of milliseconds longer, but this color update is imperceptible to the human viewer compared to conventional driving methods where each line updating from color 1 to color 2 receives the same waveform within a single frame. Furthermore, since non-temporary memory is relatively inexpensive, there is little additional cost to provide a set of time-shifted waveforms for each possible color transition, for example, stored in one or more lookup tables. A further advantage of the interlaced time-shifted patterns in Figures 9 and 10 is that this technique equalizes the current draw of the gate drivers, especially when a large portion of the display is driven between the same colors during image updates. In normal driving, all gate lines in the update region draw current almost simultaneously as defined by the push-pull waveform, but interlaced and time-shifted driving results in fewer gate lines drawing the entire current simultaneously. In some cases, the reduction in current fluctuations would allow less expensive electrical components to be used in the device. In some cases, this current leveling results in less power drain, and therefore, battery charge will last longer for the same number of refreshes.In other embodiments, gate-line directional scanning with interlacing allows the current to be drawn in much the same way as with non-interlacing. When interlacing is used with a source driver (i.e., via the source line), the waveform mismatch with interlacing can result in a larger overhead of current consumption than usual, because even uniform color patches require voltage switching more frequently.

[0071] It should be noted that the techniques in Figures 8-10 are not limited to active matrix backplanes, because adjacent segmented displays can also utilize time-shifted waveforms to reduce flicker, especially when using repetitive push-pull waveforms to drive color transitions. Furthermore, the techniques are not limited to repetitive push-pull waveforms, because more complex waveforms that are not simple push-pull can be temporally offset to provide transitions with less flicker. In addition, for driving systems incorporating both push-pull and more complex waveforms, it is possible to "hide" the more complex waveforms within time-shifted interlaced push-pull waveforms using the methods described. For example, in the ACEP system with eight color waveforms shown in Figure 6A, when one of the waveforms is not push-pull (and is more complex) and the rest are push-pull, the multi-line interlacing of the push-pull waveforms hides the more complex transitions, resulting in an overall transition that is not "unpleasant" to the viewer. While all of the aforementioned techniques can be applied using extended lookup tables, it is also possible to program the controller (communicating with both gate and source lines) to provide a short pause before continuing with the next line update in order to achieve less flickering updates. In addition, this technique is not limited to every other line or every three lines interlacing. Interlacing does not have to be line by line and can include blocks of lines. For example, 4-frame single-pixel line interlacing for a 4-frame periodic push-pull waveform, or 3-frame double-pixel line interlacing for a 3-frame periodic push-pull waveform, or 6-frame single-line interlacing for a 3-frame periodic push-pull with the possibility of shifting 1 / 2 frames through changes to source / gate drives, etc.

[0072] (Examples) Figures 11A–11C illustrate the optical transients that occur when a repetitive push-pull waveform is used to update the display from color 1 to color 2, using various interlacing schemes facilitated by an extended lookup table. The optical transients in Figures 11A–11C show the reflectance measured at L*, a*, and b* for each color in cyan, magenta, and yellow media. In Figure 11A, the experimental display is driven using a three-frame repetitive push-pull waveform, similar to that in Figure 7, but with an intervening pause. The display starts in a white state, and all pixels of the display are addressed by a dipole sequence consisting of a first pulse of -24V and a duration of 12ms followed by a second pulse of +12V and a duration of 16ms. A 12ms 0V pause is inserted between the first and second pulses. (These remainders are not needed to form the color, but are needed to measure the optical density as the waveform progresses, due to the integration limitations of the spectrometer used.) In Figure 11A, all rows are addressed with typical row-by-row addressing, and there are no time-shifted waveforms. As can be seen, in Figure 11A, all three color pigments move in phase, resulting in large fluctuations back and forth in the measured reflectance of the color, which results in a “flickering” update.

[0073] Figure 11B shows reflectance measurements of the same display driven from a white state to a second color using the same waveform, but here the waveforms provided to every other row are time-shifted by only one frame (approximately 12 ms), i.e., interlaced every other row. Due to the interaction of reflectance peaks and troughs caused by the time-shifted waveforms, the overall effect is a smaller fluctuation in the overall reflectance, and as a result, the display update appears less flicker. This technique can be further extended to include three different time-shifted waveforms, each waveform supplied to one-third of the display in an interlaced manner. As seen in Figure 11C, in this example the reflectance fluctuations are almost eliminated, and the resulting transition from white display to the first color is gradual, taking only slightly more time than in the example in Figure 11A. Comparing Figures 11A-11C, the advantages of the present invention are quite clear.

[0074] The present invention enables non-flashing updates of multipigment color displays without requiring substantial modifications to the drive electronics. While several aspects and embodiments of the art of this application have been described in this manner, it should be recognized that various changes, modifications, and improvements will be readily conceivable to those skilled in the art. Such modifications, modifications, and improvements are intended to be within the spirit and scope of the art described herein. For example, those skilled in the art will readily conceive of various other means and / or structures for performing the functions described herein and / or obtaining one or more of the results and / or advantages, and each of such variations and / or modifications will be considered within the scope of the embodiments described herein. Those skilled in the art can recognize or confirm many equivalents to the particular embodiments described herein by means of routine experimentation alone. Thus, it should be understood that the embodiments described herein are presented only as examples, and that embodiments of the present invention may be carried out in ways other than those specifically described, within the scope of the appended claims and their equivalents. In addition, any combination of two or more features, systems, articles, materials, kits, and / or methods described herein is included in the scope of this disclosure, provided that such features, systems, articles, materials, kits, and / or methods are not inconsistent with each other.

Claims

1. Electrophoretic display, Light-transmitting electrodes and, An active matrix backplane having multiple rows of pixel electrodes, each pixel electrode being coupled to a thin-film transistor having a gate line and a source line, An electrophoretic medium disposed between the light-transmitting electrode and the active matrix backplane, wherein the electrophoretic medium comprises at least three different types of charged pigment particles. A controller coupled to multiple gate lines, each gate line coupled to the thin-film transistor of one row of the multiple rows of pixel electrodes, the controller coupled to multiple source lines, and the controller further configured to address the pixel electrodes row by row by providing both a gate voltage and a source voltage to each thin-film transistor, A non-temporary memory coupled to the controller and comprising a lookup table, wherein for a transition between a first color and a second color, the lookup table includes a first waveform for transitioning the electrophoretic medium between the first color and the second color, and a second waveform for transitioning the electrophoretic medium between the first color and the second color, wherein the first and second waveforms are identical in terms of the number of voltage pulses and the polarity and magnitude of each voltage pulse, but the first and second waveforms are time-shifted by at least 1 ms. Equipped with, When the controller updates the display between the first image and the second image, The steps include receiving the first waveform from the lookup table, The steps include providing the first waveform to the pixel electrodes of the first row, The steps include receiving the second waveform from the lookup table, The steps of providing the second waveform to the pixel electrodes of the second row adjacent to the pixel electrodes of the first row, and An electrophoretic display that performs electrophoresis.

2. The lookup table further comprises a third waveform for transitioning the electrophoretic medium between a first color and a second color, wherein the first, second, and third waveforms are identical in terms of the number of voltage pulses and the respective polarities and magnitudes of the voltage pulses, but the first, second, and third waveforms are time-shifted by at least 5 ms from each other, and the controller further takes the step of receiving the third waveform from the lookup table and providing the third waveform to a pixel electrode in a third row adjacent to the electrodes in the second row, wherein the electrodes in the second row are located between the electrodes in the first row and the electrodes in the third row, the electrophoretic display according to claim 1.

3. The electrophoretic display according to claim 1 or 2, wherein the lookup table further comprises a fourth waveform for transitioning the electrophoretic medium between a first color and a third color, the third waveform being not identical to the first and second waveforms in terms of the number of voltage pulses and the polarity and magnitude of each of the voltage pulses, but the first, second and third waveforms being time-shifted by at least 1 ms from each other.

4. The electrophoretic display according to any one of claims 1 to 3, wherein the first waveform and the second waveform are time-shifted by at least 5 ms, optionally at least 10 ms, and optionally between 12 ms and 20 ms.

5. The electrophoretic display according to any one of claims 1 to 3, wherein the first waveform and the second waveform are time-shifted by a frame, the frame being the time required to address all pixels in the active matrix backplane once when addressing the active matrix backplane row by row.

6. The electrophoretic display according to any one of the claims, wherein the magnitude of the voltage pulse is between -15V and +15V, or between -24V and +24V.

7. The electrophoretic display according to any one of the claims, wherein the electrophoretic medium comprises reflective white particles and at least one subtractive color particles, or reflective white particles and at least one reflective color particles.

8. The electrophoretic display according to any one of the claims, wherein the electrophoretic medium comprises a fourth type of electrophoretic particles.

9. The electrophoretic display according to claim 8, wherein two of the particle types are negatively charged and two of the particle types are positively charged, or one of the particle types is negatively charged and three of the particle types are positively charged, or three of the particle types are negatively charged and one of the particle types is positively charged.

10. The electrophoretic display according to any one of the claims, wherein the electrophoretic medium is encapsulated in a microcapsule or microcell.

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