Electro-optical display and method for driving the same

Abstract

A method for driving an electro-optical display having a plurality of display pixels is provided, the method comprising: applying a first waveform selected from a first set of waveforms for black-to-white transitions and white-to-white transitions if the pixel is determined to display color; and applying a second waveform selected from a second set of waveforms for black-to-white transitions and white-to-white transitions if the pixel is determined to display a grayscale image.

Description

[0001] Citation of Related Applications

[0002] This application is related to and claims priority from U.S. Provisional Application No. 63 / 038,014, filed on June 11, 2020.

[0003] The entire disclosure of the above application is incorporated herein by reference. Technical Field

[0004] The present invention relates to a method for driving an electro-optic display. More particularly, the present invention relates to a driving method for reducing pixel edge artifacts and / or image sticking in an electro-optic display. Background Art

[0005] Electro-optic displays typically have a backplane provided with a plurality of pixel electrodes, each defining a pixel of the display; conventionally, a single common electrode extends over a large number of pixels, and typically the entire display is provided on opposite sides of the electro-optic medium. The individual pixel electrodes can be driven directly (i.e., a separate conductor can be provided to each pixel electrode), or they can be driven in an active matrix manner familiar to those skilled in the art of backplane technology. Since adjacent pixel electrodes will typically be at different voltages, they must be separated by inter-pixel gaps of finite width to avoid electrical shorting between the electrodes. Although at first glance it might appear that the electro-optic medium overlying these gaps will not switch when a drive voltage is applied to the pixel electrodes (and, in fact, this is often the case for certain non-bistable electro-optic media (e.g., liquid crystals), where a black mask is typically provided to hide these non-switching gaps), in the case of many bistable electro-optic media, the medium overlying the gaps does switch due to a phenomenon known as "blooming."

[0006] Dispersion refers to the tendency of the optical state of the electro-optical medium to change over an area larger than the physical size of the pixel electrode due to the application of a drive voltage to the pixel electrode. Although excessive dispersion should be avoided (e.g., in a high-resolution active matrix display, it is undesirable to apply a drive voltage to a single pixel to cause switching over an area covering several adjacent pixels because this would reduce the effective resolution of the display), a controlled amount of dispersion is generally useful. For example, consider an electro-optical display with black text on a white background, which displays numbers using a seven-segment array of seven conventional directly driven pixel electrodes for each digit. For example, when displaying 0, six segments turn black. In the absence of dispersion, six inter-pixel gaps would be visible. However, by providing a controlled amount of dispersion, such as described in U.S. Patent No. 7,602,374 (the entire contents of which are incorporated herein), the inter-pixel gaps can be made black, making the digits more aesthetically pleasing. However, dispersion can lead to a problem known as "edge ghosting."

[0007] The diffused areas are not uniformly white or black, but are generally transition areas, where the color of the medium changes from white through various shades of gray to black as one moves across the diffused area. Thus, edge ghosting will generally be areas of varying gray shades, rather than uniform gray areas, but can still be visible and objectionable, particularly because the human eye is well-equipped to detect gray areas in monochrome images (where each pixel should be pure black or pure white). In some cases, asymmetric diffusion can cause edge ghosting. "Asymmetric diffusion" refers to the phenomenon that in certain electro-optical media (such as the copper chromite / titanium dioxide encapsulated electrophoretic media described in U.S. Patent No. 7,002,728, the entire contents of which are incorporated herein), the diffusion is "asymmetric" in the sense that more diffusion occurs during a transition from one extreme optical state of a pixel to the other extreme optical state than during a transition in the opposite direction; in the media described in this patent, the diffusion is generally greater during a black to white transition than during a white to black transition.

[0008] Thus, there is a need for a driving method that also reduces ghosting or blooming effects. Summary of the Invention

[0009] Thus, in one aspect, the subject matter presented herein provides a method for driving an electro-optical display having a plurality of display pixels, which may include applying a first waveform selected from a first set of waveforms for black-to-white transitions and white-to-white transitions if the pixel is determined to display color; and applying a second waveform selected from a second set of waveforms for black-to-white transitions and white-to-white transitions if the pixel is determined to display a grayscale image.

[0010] In some embodiments, the claimed method may further include applying a third waveform selected from a third set of waveforms for black to white transitions and white to white transitions if the pixel is determined to display black text on a white background.

[0011] In some other embodiments, the method may further include applying a fourth waveform selected from a fourth set of waveforms for black to white transitions and white to white transitions if an algorithm is required to perform edge artifact cleaning on the pixel.

[0012] In another embodiment, the first set of waveforms is configured for a first drive mode, and the first drive mode is configured for displaying color on the display.

[0013] In yet another embodiment, the second set of waveforms is configured for a second drive mode, and the second drive mode is configured for displaying a grayscale image on the display.

[0014] In some other embodiments, the third set of waveforms is configured for a third drive mode, where the third drive mode is configured for displaying black text on a white background on a display.

[0015] Another aspect of the subject matter disclosed herein provides a display controller capable of controlling the operation of a bi-stable electro-optical display, the controller being configured to perform a driving method for operating the display, and the method may include: applying a first waveform selected from a first set of waveforms for black to white transitions and white to white transitions if the pixel is determined to display color; and applying a second waveform selected from a second set of waveforms for black to white transitions and white to white transitions if the pixel is determined to display a grayscale image.

[0016] In another embodiment, the driving method may further include applying a third waveform selected from a third group of waveforms for black to white transition and white to white transition if the pixel is determined to display black text on a white background.

[0017] In yet another embodiment, the driving method may further include applying a fourth waveform selected from a fourth set of waveforms for black to white transition and white to white transition if an algorithm is required to perform edge artifact cleaning on the pixel. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a circuit diagram showing an electrophoretic display;

[0019] Figure 2 A circuit model of the electro-optical imaging layer is shown;

[0020] Figure 3 shows a cross-sectional view of an electro-optical display having a color filter array;

[0021] Figure 4 A comparison of different waveforms for different driving schemes or modes is shown;

[0022] Figure 5 shows exemplary waveforms according to the subject matter disclosed herein;

[0023] Figure 6 A table showing selection of different modes and waveforms for different display applications;

[0024] Figure 7A Another table showing one drive mode for selecting waveforms according to a display application is shown;

[0025] Figure 7B A flow chart showing one driving mode for selecting a waveform based on a display application is shown;

[0026] Figure 8 A controller or control device for controlling the operation of the electro-optical device is shown;

[0027] Figure 9 A flow chart showing another driving mode for selecting a waveform based on a display application is shown; and

[0028] Figure 10 An exemplary rotation waveform is shown. DETAILED DESCRIPTION

[0029] The present invention relates to a method for driving an electro-optical display, in particular a bistable electro-optical display, and to an apparatus for use with such a method. More particularly, the invention relates to a driving method which can allow for reduced "ghosting" and edge effects and reduced flashing in such displays. The invention is particularly, but not exclusively, intended for use with particle-based electrophoretic displays, in which one or more types of charged particles are present in a fluid and move through the fluid under the influence of an electric field to alter the appearance of the display.

[0030] The term "electro-optical," as applied to a material or display, is used herein in its conventional sense in the field of imaging, to refer to a material having first and second display states that differ in at least one optical property, the material being caused to change from its first display state to its second display state by application of an electric field to the material. While the optical property is typically color perceptible to the human eye, it may be another optical property, such as light transmission, reflection, luminescence, or, in the case of displays intended for machine reading, false color in the sense of a change in reflectivity at electromagnetic wavelengths outside the visible range.

[0031] The term "gray state" is used herein in its conventional sense in the field of imaging, referring to a state between the two extreme optical states of a pixel, but does not necessarily mean a black and white transition between the two extreme states. For example, several patents and published applications of Iink Corporation referred to below describe electrophoretic displays in which the extreme states are white and dark blue, so that the intermediate "gray state" is actually light blue. In fact, as already mentioned, the 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 the 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. The term "monochromatic" may be used below to refer to a drive scheme in which pixels are driven only to their two extreme optical states without an intermediate gray state.

[0032] Certain electro-optic materials are solid in the sense that they have a solid outer surface, although they may, and often do, have internal spaces filled with liquid or gas. For convenience, displays using such solid-state electro-optic materials may be referred to hereinafter as "solid-state electro-optic displays." Thus, the term "solid-state electro-optic display" includes rotating two-color component displays, packaged electrophoretic displays, microcell electrophoretic displays, and packaged liquid crystal displays.

[0033] The terms "bistable" and "bistability" are used herein in their conventional sense in the art to refer to a display comprising a display element having first and second display states, wherein the first and second display states differ in at least one optical property such that after any given element is driven to assume its first or second display state by an addressing pulse of finite duration, that state persists after termination of the addressing pulse for a time that is 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 can be stable not only in their extreme black and white states, but also in intermediate gray states, as can some other types of electro-optical displays. Such displays are properly referred to as "multistable" rather than bistable, but for convenience, the term "bistable" will be used herein to cover both bistable and multistable displays.

[0034] The term "impulse" is used here in its conventional sense, namely, the integral of voltage with respect to time. However, some bistable electro-optical media act as charge converters, and for such media, another definition of impulse may be used, namely, the integral of current with respect to time (which is equal to the total applied charge). Depending on whether the medium acts as a voltage-to-time impulse converter or a charge-to-impulse converter, the appropriate definition of impulse should be used.

[0035] Much of the following discussion will focus on methods for driving one or more pixels of an electro-optical display from an initial grayscale to a final grayscale (which may be different from or the same as the initial grayscale). The term "waveform" will be used to refer to the overall voltage versus time curve used to achieve the transition from a particular initial grayscale to a particular final grayscale. Typically, such a waveform will include multiple waveform elements; where these elements are substantially rectangular (i.e., a given element includes applying a constant voltage for a period of time); the elements may be referred to as "pulses" or "drive pulses." The term "drive scheme" refers to a set of waveforms sufficient to achieve all possible transitions between grayscales for a particular display. A display may utilize more than one drive scheme; for example, the aforementioned U.S. Patent No. 7,012,600 teaches that the drive scheme may need to be modified based on parameters such as the temperature of the display or the amount of time it has been in operation during its lifetime, and thus a display may be provided with multiple different drive schemes for use at different temperatures, etc. A set of drive schemes used in this manner may be referred to as a "set of related drive schemes." As described in several of the aforementioned MEDEOD applications, it is also possible to use more than one drive scheme simultaneously in different areas of the same display, and a set of drive schemes used in this way may be referred to as a "set of simultaneous drive schemes".

[0036] Several types of electro-optical displays are known. One type of electro-optical display is the rotating dichromatic element type, as described, for example, in U.S. Patent Nos. 5,808,783; 5,777,782; 5,760,761; 6,054,071; 6,055,091; 6,097,531; 6,128,124; 6,137,467; and 6,147,791 (although this type of display is often referred to as a "rotating dichromatic sphere" display, the term "rotating dichromatic element" is preferred for greater accuracy because, in some of the aforementioned patents, the rotating element is not spherical). This display uses many small bodies (usually spherical or cylindrical) and internal dipoles, with the body consisting of two or more parts with different optical properties. These bodies are suspended within a liquid-filled vacuole within a matrix, which is filled with liquid to allow the body to rotate freely. The appearance of the display is changed by applying an electric field to the display, thereby rotating the body to various positions and changing which part of the body is seen through the viewing surface. This type of electro-optic medium is typically bistable.

[0037] Another type of electro-optical display uses an electrochromic medium, for example in the form of a nanochromic film comprising an electrode formed at least in part from a semiconducting metal oxide and a plurality of dye molecules attached to the electrode that are capable of reversible color change; see, for example, O'Regan, B. et al., Nature 1991, 353, 737; and Wood, D., Information Display, 18(3), 24 (March 2002). See also Bach, U. et al., Adv. Mater., 2002, 14(11), 845. Nanochromic films of this type are also described, for example, in U.S. Patent Nos. 6,301,038; 6,870,657; and 6,950,220. This type of medium is also typically bistable.

[0038] Another type of electro-optical display is the electrowetting display developed by Philips and described in Hayes, RA et al., "Video-Speed ​​Electronic Paper Based on Electrowetting", Nature, 425, 383-385 (2003). It is shown in US Pat. No. 7,420,549 that such an electrowetting display can be made bistable.

[0039] One type of electro-optical display that has been the subject of intensive research and development for many years is the particle-based electrophoretic display (EPD), in which multiple charged particles move through a fluid under the influence of an electric field. Compared to liquid crystal displays (LCDs), EPDs can offer good brightness and contrast, wide viewing angles, state bistability, and low power consumption. However, issues with the long-term image quality of these displays have hindered their widespread adoption. For example, the particles that make up EPDs are prone to sedimentation, resulting in a short lifespan for these displays.

[0040] As mentioned above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, the fluid is a liquid, but electrophoretic media can be generated using a gaseous fluid; see, for example, Kitamura, T. et al., "Electronic toner movement for electronic paper-like display", IDW Japan, 2001, Paper HCS 1-1, and Yamaguchi, Y. et al., "Toner display using insulative particles charged triboelectrically", IDW Japan, 2001, Paper AMD4-4. See also U.S. Patents No. 7,321,459 and 7,236,291. When such gas-based electrophoretic media are used in a direction that allows particle sedimentation, such as in signs where the media is arranged in a vertical plane, such gas-based electrophoretic media are susceptible to the same type of problems caused by particle sedimentation as liquid-based electrophoretic media. In fact, the particle sedimentation problem is more severe in gas-based electrophoretic media than in liquid-based electrophoretic media, because the lower viscosity of the gaseous suspending fluid allows for faster sedimentation of the electrophoretic particles compared to the liquid suspending fluid.

[0041] Numerous patents and applications assigned to or in the names of the Massachusetts Institute of Technology (MIT) and Iink Corporation describe various techniques for encapsulated electrophoretic and other electro-optical media. These encapsulated media comprise a plurality of small capsules, each of which itself comprises an inner phase containing electrophoretically mobile particles in a fluid medium and a capsule wall surrounding the inner phase. Typically, the capsules themselves are held in a polymer binder to form a coherent layer positioned between two electrodes. The techniques described in these patents and applications include:

[0042] (a) electrophoretic particles, fluids, and fluid additives; see, e.g., U.S. Patent Nos. 7,002,728 and 7,679,814;

[0043] (b) capsules, adhesives, and encapsulation processes; see, e.g., U.S. Patent Nos. 6,922,276 and 7,411,719;

[0044] (c) microcell structures, wall materials, and methods of forming microcells; see, e.g., U.S. Patent Nos. 7,072,095 and 9,279,906;

[0045] (d) Methods for filling and sealing microlocations; see, e.g., U.S. Patent Nos. 7,144,942 and 7,715,088;

[0046] (e) Films and subassemblies containing electro-optical materials; see, e.g., U.S. Patent Nos. 6,982,178 and 7,839,564;

[0047] (f) Backsheets, adhesive layers and other auxiliary layers and methods for use in displays; see, e.g., U.S. Patent Nos. 7,116,318 and 7,535,624;

[0048] (g) color formation and color adjustment; see, e.g., U.S. Patent Nos. 7,075,502 and 7,839,564;

[0049] (h) Display applications; see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348;

[0050] (i) non-electrophoretic displays, such as those described in U.S. Patent No. 6,241,921 and U.S. Patent Application Publication No. 2015 / 0277160; and applications of packaging and microcell technology other than displays; see, for example, U.S. Patent Application Publication Nos. 2015 / 0005720 and 2016 / 0012710; and

[0051] (j) Methods for driving displays; see, e.g., U.S. Patent Nos. 5,930,026; 6,445,489; 6,504,524; 6,512,354; 6,531,997; 6,753,999; 6,825,970; 6,900,851; 6,995,550; 7,012,600; 7,023,420; 7,034,783; 7,061,166; 7,061,662; 7,116,466; 7,119,772; 7,177,066; 7,193,625; 7,202,847; 7,242,514; 7,259,744; 7,304,787; 7, 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, 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 No.2003 / 0102858; 2004 / 0246562; 2005 / 0253777; 2007 / 0070032; 2007 / 0076289; 2007 / 0091418; 2007 / 0103427; 2007 / 0176912; 2007 / 0296452; 2008 / 0024429; 2008 / 0024482; 2008 / 0136774; 2008 / 0169821; 2008 / 0218471; 2008 / 02911 29;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 / 02 21740; 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; 2016 / 0071465; 2016 / 0078820; 2016 / 0093253; 2016 / 0140910; and 2016 / 0180777.

[0052] Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in encapsulated electrophoretic media can be replaced by a continuous phase, thereby creating 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 that the discrete droplets of electrophoretic fluid within such polymer-dispersed electrophoretic displays can be considered to be capsules or microcapsules, even though no discrete capsule membrane is associated with each individual droplet; see, for example, the aforementioned 2002 / 0131147. Therefore, for the purposes of this application, such polymer-dispersed electrophoretic media are considered to be a subclass of encapsulated electrophoretic media.

[0053] A related type of electrophoretic display is the so-called "microcell electrophoretic display." In a microcell electrophoretic display, the charged particles and the suspended fluid are not encapsulated in microcapsules, but rather are held in a plurality of cavities formed within a carrier medium (e.g., a polymer film). See, for example, International Application Publication No. WO 02 / 01281 and Published U.S. Application No. 2002 / 0075556, both assigned to Sipix Imaging, Inc.

[0054] Many of the aforementioned Iink and MIT patents and applications also contemplate microcell EPDs and polymer dispersed EPDs. The term "encapsulated EPD" may refer to all such display types, which may also be collectively referred to as "microcavity EPDs" to encompass the overall wall morphology.

[0055] Another type of electro-optical display is the electrowetting display developed by Philips and described in Hayes, RA et al., "Video-Speed ​​Electronic Paper Based on Electrowetting," Nature, 425, 383-385 (2003). In co-pending application serial No. 10 / 711,802 filed on October 6, 2004, it is shown that such an electrowetting display can be made bi-stable.

[0056] Other types of electro-optical materials may also be used. Of particular interest, bistable ferroelectric liquid crystal displays (FLC) are known in the art and exhibit residual voltage behavior.

[0057] Although electrophoretic media can be opaque (because, for example, in many electrophoretic media, the particles substantially block visible light from being transmitted through the display) and operated in a reflective mode, some electrophoretic displays can be made to operate in a so-called "shutter mode," in which one display state is substantially opaque and one display state is light-transmissive. See, for example, U.S. Patents Nos. 6,130,774 and 6,172,798 and 5,872,552, 6,144,361, 6,271,823, 6,225,971, and 6,184,856. Dielectrophoretic displays, which are similar to electrophoretic displays but rely on changes in electric field strength, can operate in a similar mode; see U.S. Patent No. 4,418,346. Other types of electro-optical displays can also operate in a shutter mode.

[0058] A high-resolution display may include individual pixels that are addressable and uninterrupted by neighboring pixels. One way to achieve such pixels is to provide an array of nonlinear elements (e.g., transistors or diodes), with at least one nonlinear element associated with each pixel to produce an "active matrix" display. The addressing or pixel electrode used to address a pixel is connected to an appropriate voltage source through the associated nonlinear element. When the nonlinear element is a transistor, the pixel electrode may be connected to the drain of the transistor, and this arrangement will be used in the following description, but it is essentially arbitrary and the pixel electrode may be connected to the source of the transistor. In a high-resolution array, the pixels may be arranged in a two-dimensional array of rows and columns, such that any particular pixel is uniquely defined by the intersection of a designated row and a designated column. The sources of all transistors in each column may be connected to a single column electrode, while the gates of all transistors in each row may be connected to a single row electrode; again, the source-to-row and gate-to-column arrangements may be reversed as desired.

[0059] The display can be written to in a row-by-row manner. The row electrodes are connected to a row driver, which can apply a voltage to the selected row electrode, for example to ensure that all transistors in the selected row are conductive, while applying a voltage to all other rows, for example to ensure that all transistors in these unselected rows remain non-conductive. The column electrodes are connected to a column driver, which applies a voltage on each column electrode, the voltage being selected to drive the pixels in the selected row to their desired optical state. (The aforementioned voltages are relative to a common front electrode, which can be located on the side of the electro-optical medium opposite the non-linear array and extending across the entire display. As is known in the art, voltage is relative and is a measure of the difference in charge between two points. One voltage value is relative to another voltage value. For example, zero voltage ("0V") means there is no voltage difference relative to another voltage.) After a pre-selection interval called the "line address time", the selected row is deselected, the next row is selected, and the voltage on the column driver is changed to cause the next line of the display to be written.

[0060] However, in use, certain waveforms may produce a residual voltage to the pixels of the electro-optic display, and as will be apparent from the above discussion, this residual voltage produces several unwanted optical effects and is generally undesirable.

[0061] As described herein, a "shift" of the optical state associated with an addressing pulse refers to a situation where a particular addressing pulse is first applied to an electro-optical display resulting in a first optical state (e.g., a first gray tone), and a subsequent application of the same addressing pulse to the electro-optical display results in a second optical state (e.g., a second gray tone). Because the voltage applied to a pixel of the electro-optical display during application of the addressing pulse includes the sum of a residual voltage and the voltage of the addressing pulse, the residual voltage may cause the shift in the optical state.

[0062] "Drift" of the optical state of a display over time refers to the situation where the optical state of an electro-optical display changes while the display is stationary (e.g., during a period when addressing pulses are not applied to the display). Because the optical state of a pixel can depend on a residual voltage of the pixel, and the residual voltage of the pixel can decay over time, the residual voltage can cause the optical state to drift.

[0063] As mentioned above, "ghosting" refers to the situation where traces of a previous image remain visible after an electro-optical display is rewritten. Residual voltage can cause "edge ghosting," a type of ghosting where the outline (edge) of a portion of the previous image remains visible.

[0064] Exemplary EPD

[0065] Figure 1 A schematic diagram of a pixel 100 of an electro-optical display according to the subject matter presented herein is shown. Pixel 100 may include an imaging film 110. In some embodiments, imaging film 110 may be bi-stable. In some embodiments, imaging film 110 may include, but is not limited to, an encapsulated electrophoretic imaging film, which may include, for example, charged pigment particles.

[0066] The imaging film 110 may be disposed between the front electrode 102 and the rear electrode 104. The front electrode 102 may be formed between the imaging film and the front surface of the display. In some embodiments, the front electrode 102 may be transparent. In some embodiments, the front electrode 102 may be formed of any suitable transparent material, including but not limited to indium tin oxide (ITO). The rear electrode 104 may be formed opposite the front electrode 102. In some embodiments, parasitic capacitance (not shown) may be formed between the front electrode 102 and the rear electrode 104.

[0067] Pixel 100 can be one of a plurality of pixels. The plurality of pixels can be arranged in a two-dimensional array of rows and columns to form a matrix, such that any particular pixel is uniquely defined by the intersection of a designated row and a designated column. In some embodiments, the matrix of pixels can be an "active matrix," wherein each pixel is associated with at least one nonlinear circuit element 120. Nonlinear circuit element 120 can be coupled between backplate electrode 104 and addressing electrode 108. In some embodiments, nonlinear element 120 can include a diode and / or a transistor, including but not limited to a metal oxide semiconductor field effect transistor (MOSFET). The drain (or source) of the MOSFET can be coupled to backplate electrode 104, the source (or drain) of the MOSFET can be coupled to addressing electrode 108, and the gate of the MOSFET can be coupled to driver electrode 106, which is configured to control activation and deactivation of the MOSFET. (For simplicity, the terminal of the MOSFET coupled to the backplate electrode 104 will be referred to as the drain of the MOSFET, and the terminal of the MOSFET coupled to the addressing electrode 108 will be referred to as the source of the MOSFET. However, one of ordinary skill in the art will recognize that in some embodiments, the source and drain of the MOSFET may be interchanged).

[0068] In some embodiments of an active matrix, the addressing electrodes 108 of all pixels in each column can be connected to the same column electrode, and the driver electrodes 106 of all pixels in each row can be connected to the same row electrode. The row electrodes can be connected to a row driver that can select one or more rows of pixels by applying a voltage to the selected row electrodes that is sufficient to activate the nonlinear elements 120 of all pixels 100 in the selected row. The column electrodes can be connected to a column driver that can apply a voltage to the addressing electrodes 106 of the selected (activated) pixels that is suitable for driving the pixels to a desired optical state. The voltage applied to the addressing electrodes 108 can be relative to the voltage applied to the frontplate electrodes 102 of the pixels (e.g., a voltage of approximately zero volts). In some embodiments, the frontplate electrodes 102 of all pixels in the active matrix can be coupled to a common electrode.

[0069] In some embodiments, the pixels 100 of the active matrix can be written in a row-by-row manner. For example, a row driver can select a row of pixels, and a column driver can apply a voltage to the pixels corresponding to the desired optical state of the row of pixels. After a preselection interval known as a "line address time," the selected row can be deselected, another row can be selected, and the voltage on the column driver can be changed to cause another line of the display to be written.

[0070] Figure 2 104 ). A circuit model of an electro-optic imaging layer 110 according to the subject matter presented herein is shown, the electro-optic imaging layer 110 being disposed between the front electrode 102 and the back electrode 104. Resistor 202 and capacitor 204 can represent the resistance and capacitance of the electro-optic imaging layer 110, including any adhesive layers, the front electrode 102, and the back electrode 104. Resistor 212 and capacitor 214 can represent the resistance and capacitance of the laminating adhesive layer. Capacitor 216 can represent the capacitance that can be formed between the front electrode 102 and the back electrode 104 (e.g., at an interfacial contact area between the layers, such as between the imaging layer and the laminating adhesive layer and / or between the laminating adhesive layer and the backplane electrode). The voltage Vi across the imaging film 110 of a pixel can include the residual voltage of the pixel.

[0071] In use, expect Figure 1 and Figure 2The electro-optic display shown updates to subsequent images without flickering the display background. However, a straightforward approach using idle transitions in image updates for background color to background color (e.g., white to white, or black to black) waveforms can result in the accumulation of edge artifacts (e.g., blooming). In black and white electro-optic displays, edge artifacts can be reduced by top-offing the waveform. However, in electro-optic displays, such as electrophoretic displays (EPDs) having colors generated using color filter arrays (CFAs), maintaining color quality and contrast can sometimes be challenging.

[0072] Figure 3 1 shows a cross-sectional view of a CFA-based color EPD according to the subject matter disclosed herein. Figure 3 As shown, a color electrophoretic display (generally designated 300) includes a backplane 302 carrying a plurality of pixel electrodes 304. The backplane 302 may be laminated with an inverted front plane laminate that may include a monochrome electrophoretic medium layer 306 having black and white extreme optical states, an adhesive layer 308, a color filter array 310 having red, green, and blue regions aligned with the pixel electrodes 304, a substantially transparent conductive layer 312 (typically formed of indium tin oxide), and a front protective layer 314.

[0073] In use, in a CFA-based color EPD, any color region in the image will result in modulation of the pixels behind each CFA element. For example, optimal red is achieved when the red CFA pixel is turned on (e.g., white) and the green and blue CFA pixels are turned off (e.g., black). Any blooming in the white pixels can result in a reduction in the chromaticity and brightness of the red. Algorithms are explained in more detail below, in which these edge artifacts (e.g., blooming) can be identified and reduced without sacrificing color saturation.

[0074] EPD drive solution

[0075] However, variations in drive schemes are not limited to differences in the number of grayscales used. For example, drive schemes can be divided into global drive schemes, in which a drive voltage is applied to every pixel in the region (which can be the entire display or some defined portion thereof) where a global update drive scheme (more accurately referred to as a "global full" or "GC" drive scheme) is being applied; and partial update drive schemes, in which a drive voltage is applied only to pixels undergoing non-zero transitions (i.e., transitions where the initial grayscale and the final grayscale are different from each other), but no drive voltage is applied during zero transitions (where the initial grayscale and the final grayscale are the same). An intermediate form of drive scheme (referred to as a "global limited" or "GL" drive scheme) is similar to the GC drive scheme, except that no drive voltage is applied to pixels undergoing zero transitions from white to white. In displays used, for example, as e-book readers (which display black text on a white background), there are many white pixels, particularly in the margins and between lines of text, which remain unchanged from one page of text to the next; therefore, not rewriting these white pixels significantly reduces the noticeable "flicker" of the display rewriting. However, there are still some problems with this type of GL drive scheme. First, as discussed in detail in some of the aforementioned MEDEOD applications, bistable electro-optical media are generally not completely bistable, and pixels in one extreme optical state will gradually drift toward an intermediate grayscale over a period of minutes to hours. In particular, white-driven pixels will slowly drift toward a light gray. Therefore, if a white pixel is allowed to remain undriven after several page turns in the GL drive scheme, during which time other white pixels (e.g., those forming part of text characters) are driven, the newly updated white pixel will be slightly brighter than the undriven white pixel, and eventually the difference will become noticeable even to an untrained user.

[0076] Secondly, when an undriven pixel is adjacent to a pixel being updated, a phenomenon known as "blooming" occurs, in which the driving of the driven pixel causes an optical state change in an area slightly larger than the area of ​​the driven pixel, and the area invades the area of ​​the adjacent pixel. This blooming manifests itself as an edge effect along the edge of the undriven pixel adjacent to the driven pixel. Similar edge effects occur when using regional updating (wherein only specific areas of the display are updated, such as areas for displaying an image), except that the edge effects of regional updating occur at the boundaries of the area being updated. Over time, such edge effects become visually distracting and must be removed. So far, such edge effects (and the effect of color drift in undriven white pixels) are typically removed by using a single GC update at intervals. Unfortunately, using such random GC updates reintroduces the problem of "flickering" updates, and in fact, the flickering nature of the updates may be enhanced by the fact that flickering updates only occur at long intervals.

[0077] Reduced ghosting and / or smearing

[0078] Figure 4 Some driving modes or schemes that may be used to drive an electro-optical display (eg, an electrophoretic display or EPD) having a CFA are shown. Figure 4 Shown is a comparison between a first GC drive mode variant (i.e., GC16) and a second GC drive mode variant (i.e., GCC16). In some embodiments, the GC16 drive mode includes a waveform best suited for black and white display applications, where the white to white transition (i.e., W→W) waveform can have two full long pulses designed to drive the display pixel to black and / or white. For example, a first portion 502 having a duration of 18 frames and an amplitude of 15 volts, configured to drive the display pixel to black, is followed by a second portion 504 having a duration of 18 frames and an amplitude of negative 15 volts, configured to drive the display pixel to white. (See Figure 5 ) while the black to white transition (i.e. B→W) waveform can include a single, complete, long pulse designed to drive the pixel to white. In some cases, the GCC16 drive mode may be more suitable for color applications because it can reduce differential blotting effects. Differential blotting can occur when the fringe field of a switching pixel affects the optical state of its neighboring pixels. In the rendered image, there can be pixel-sized patterns where pixels go into different optical states. Or the pixels can go from different initial optical states to the same optical state using different waveforms, with the result that the pixels experience different blotting artifacts and they end up with slightly different brightnesses. All of these blotting artifacts result in differential blotting ghosting. In some embodiments, the GCC16 drive mode can have a longer update time compared to GC16. For example, Figure 4As shown, the GCC16 black to white transition (i.e., B→W) waveform may be longer than the black to white transition waveform of the GC16 driving scheme. The GCC16 B→W waveform may include a pre-pulse 402 portion, a mid-pulse portion 404, and a setup pulse portion, each of which may be adjusted to achieve optimal viewing appearance.

[0079] In another variation of the GC drive mode, the GL16 mode is similar to the GC16 mode, but drives white-to-white transitions with a null waveform (e.g., no voltage is applied to the pixel) to reduce screen flicker during page updates. For example, when displaying black text on a white background, the electro-optical display screen does not appear to flicker excessively due to background pixels undergoing white-to-white transitions when the text is updated.

[0080] Now refer to Figure 6 , where Table 1 shows an overview of the GL, GC16, and GCC16 drive modes. As shown in the figure, GL or GL16 mode can provide the best performance for displaying text, GC16 mode can provide the best performance for grayscale images, and GCC16 mode may be best suited for color images. And these three modes provide different waveforms for different optical state transitions. For example, for white to white or W→W transition, GL16 mode will use the empty transition waveform, while GC16 and GCC16 will both use Figure 4 GC16 W→W waveform shown; for B→W transitions, both GL16 and GC16 modes will use Figure 4 GC16 B→W waveform shown; however, GCC16 mode will use Figure 4 The GCC16 B→W waveform is shown; for all other transitions, GL16 and GC16 will use the GC16 transition waveform, but GCC16 mode will use the GCC16 transition waveform.

[0081] In some embodiments, a single mode can be configured to include all different waveforms from different drive modes, and waveforms are selected and applied based on a specific display application. For example, a display controller or control device associated with an electro-optical display (e.g., a bistable display with a CFA) and capable of controlling the operation of the bistable electro-optical display can be configured to store all transition waveforms from the GL16 / GC16 / GCC16 drive modes. Moreover, the display can also be programmed with an algorithm to select the best waveform for a specific transition based on the specific display application for which the display is used. For example, as shown in Table 2 shown in Figure 7, a controller or control device can run a specific drive mode, such as GCC16, but the controller or control device is also configured to store all waveforms from the GL16 / GC16 / GCC16 mode, and for white to white or W→W transitions, if the display is updating text, the controller or control device can select a blank waveform, or alternatively, if the display is updating with a grayscale image or a color image, the controller or control device can select a GC16W→W transition. Similarly, if the display is being updated with text or a grayscale image, the controller or control device may select the GC16 B→W transition waveform, but if the display is being updated with a color image, the controller or control device may alternatively select the GCC16 B→W transition waveform. In this way, the controller or control device is configured to select and apply the waveform that provides the best image quality on the display based on the specific type of image being updated on the display. In some embodiments, for this new mode, which now includes all transition waveforms from various drive modes, GC16 B→W can be placed in an empty slot in the 5-bit waveform structure (e.g., slot 1→32) and an empty slot can be reserved for an empty W→W transition (e.g., 32→32). Based on the content of the current image and the next image, the algorithm can assign waveform state numbers.

[0082] Figure 7B A block diagram outlining the above process is shown. In step 702, it is determined whether the image to be displayed on the display is a color image. If the image is a color image, the GCC16 B→W transition waveform and the GCC16 / GC16 W→W transition waveform are used; otherwise, if the image is not a color image, the GC16 B→W transition waveform and the Blank W→W transition waveform are used.

[0083] In yet another embodiment, the GL mode can be further modified to include an algorithm configured to clean up edge ghosting or blooming artifacts (e.g., a Regal algorithm), such as those described in U.S. Patent No. 11,030,936 and U.S. Patent Application No. 17 / 334,751, the entire contents of which are incorporated herein. These algorithms can be configured to apply correction pulses to pixels that experience blooming from neighboring pixels. This new drive mode (e.g., GLR16) can act to reduce flicker when updating a white background and minimize text residue caused by blooming.

[0084] In another embodiment, a new mode (e.g., GLRC16 mode) can be constructed to include the characteristics of the GCC16 and GLR16 modes, where low-difference diffuse ghosting in color areas and no flickering background in text areas are achieved by integrating the different modes into one mode and using an algorithm to determine the best waveform to use based on the content of each pixel.

[0085] Figure 8 A block diagram showing an electro-optical display such as EPD 800 in accordance with the subject matter disclosed herein is shown. Referring now to Figure 8 , EPD 800 may include a display portion 802, a controller 804, a central processing unit (CPU) 806, a video RAM (VRAM) 808, and a random access memory (RAM) 810 and a ROM 812. These portions are interconnected via a bus. Controller 804 corresponds to the control means of EPD 800. It should be understood that in some embodiments, a portion including the combination of controller 804 and CPU 806 may be defined as the control means of EPD 800. Alternatively, the entirety of controller 804, CPU 806, VRAM 808, RAM 810, and ROM 812 may be defined as the control means of EPD 800.

[0086] In some embodiments, the controller 804 outputs an image signal indicating an image to be displayed on the display portion 802 and various other signals (clock signal, etc.). The CPU 806 is a processor that controls the operation of the EPD 800, and in particular, controls the storage of image data to be displayed on the display portion 802 in the VRAM 808. The VRAM 808 can be used as a frame buffer and stores image data to be displayed on the display portion 802 based on the control of the CPU 806.

[0087] In some embodiments, on an EPD screen that displays different content simultaneously (e.g., black and white text and a color image), in the color area, GCC or other drive schemes or modes optimized for color content can be used, while in the black and white area, other drive modes can be used to optimize image quality. Moreover, a unified update time across different modes can be achieved. For example, the faster GLR mode can be modified to include an additional null or zero volt drive to match the slower GCC mode in terms of update time. In some embodiments, this can be implemented by filling the GCC-based transitions between the 16 gray tones in the even states of the 5-bit waveform, and using the odd states (e.g., faster GLR-based transitions) for the black and white mode.

[0088] In some embodiments, an algorithm may be used to select the best waveform to apply based on the display application. For example:

[0089] For all pixels in any order:

[0090] If the pixel is a color display pixel, a GCC16 B->W shift and a GCC16 or GC16 W->W shift are applied;

[0091] otherwise

[0092] If the pixel is displaying a grayscale image, a GC16 B->W shift and a GCC16 or GC16 W->W shift are applied;

[0093] otherwise

[0094] If it is determined that the pixel requires edge artifact removal, the GC16 B->W transition and T

[0095] W->W transition;

[0096] otherwise

[0097] Apply GC16 B->W transition and empty W->W transition;

[0098] Finish

[0099] Now refer to Figure 9, shows a flow chart outlining an algorithm for selecting a waveform according to the subject matter disclosed herein. A controller or control for controlling the operation of an EPD may run one mode but have all waveforms available from other drive schemes or modes and be configured to select the waveform that best suits a particular display application. For example, in step 902, is the pixel determined to be a color image pixel? If so, the controller or control device selects the GCC16 B→W waveform for the B→W transition and the GCC16 / GC16 W→W waveform for the W→W transition (see step 904); otherwise, if not, the controller or control device continues to determine whether the pixel is being updated to display a grayscale image (see step 906). If so, the controller or control device selects the GC16 B→W waveform for the B→W transition and the GCC16 / GC16 W→W waveform for the W→W transition (see step 908); if not, the controller or control device continues to step 910 and determines whether an edge cleaning algorithm (e.g., Regal) is required for cleaning edge artifacts (e.g., ghosting). If so, the controller or control device selects the GC16 B→W waveform for the B→W transition and the TW→W waveform for the W→W transition (see step 912); otherwise, if not, at step 914, the controller or control device selects the GC16 The B→W waveform is used for B→W transitions, and the Null waveform is selected for W→W transitions.

[0100] Figure 10 An exemplary TW→W transition waveform 1000 is shown. The TW→W transition waveform 1000 may include a variable number of rotating pulses (twiddle pulses) 1010 having variable positions within the waveform 1000, and a variable number of top cutoff pulses 1008 having variable positions within the waveform 1000 relative to the rotating pulses 1010. In some embodiments, a single top cutoff pulse 1008 corresponds to one frame of driving white with an amplitude of negative 15 volts, where the rotating pulses 1010 may include one frame of driving to black at 15 volts and one frame of driving to white at negative 15 volts. Figure 4 As shown in FIG. 8B , the spinning pulse 1010 may repeat itself multiple times, and the top cut pulse 1008 may be located before the spinning pulse 1010 , after the spinning pulse 1010 , and / or between the spinning pulses 1010 .

[0101] It will be apparent to those skilled in the art that many changes and modifications may be made to the specific embodiments of the present invention described above without departing from the scope of the present invention. Therefore, the foregoing description is to be interpreted as illustrative rather than restrictive in nature.

Claims

1. A method for driving an electro-optical display having a plurality of display pixels, the method comprising: applying a first waveform selected from a first set of waveforms for a black-to-white transition and a white-to-white transition if the pixel is determined to display color; as well as applying a second waveform selected from a second set of waveforms for black-to-white transitions and white-to-white transitions if the pixel is determined to display a grayscale image; wherein the first set of waveforms includes a black-to-white transition waveform comprising a pre-pulse, an intermediate pulse, and a setup pulse, and the black-to-white transition waveform is configured to reduce a differential blooming effect of pixels displaying color, and The duration of the black-to-white transition waveforms in the first group of waveforms is longer than the duration of the black-to-white transition waveforms in the second group of waveforms.

2. The method according to claim 1, further comprising: If the pixel is determined to display black text on a white background, a third waveform selected from a third set of waveforms is applied for black to white transitions and white to white transitions.

3. The method according to claim 1, further comprising: If an algorithm is required to perform edge artifact cleaning on the pixel, a fourth waveform selected from a fourth set of waveforms is applied for black to white transitions and white to white transitions.

4. The method according to claim 1, wherein The first set of waveforms is configured for a first drive mode.

5. The method according to claim 4, wherein The first drive mode is configured for displaying color on the display.

6. The method according to claim 1, wherein The second set of waveforms is configured for a second drive mode.

7. The method according to claim 6, wherein: The second drive mode is configured for displaying a grayscale image on the display.

8. The method according to claim 2, wherein: The third set of waveforms is configured for a third drive mode.

9. The method according to claim 8, wherein The third drive mode is configured to display black text on a white background on the display.

10. An electro-optic display configured to perform the method of claim 1, the electro-optic display further comprising a color filter array.

11. A display according to claim 10 comprising a rotating dichroic member, an electrochromic or an electrowetting material.

12. An electro-optic display according to claim 10, comprising an electrophoretic material comprising a plurality of charged particles disposed in a fluid and capable of moving through the fluid under the influence of an electric field.

13. The electro-optical display according to claim 12, wherein The charged particles and the fluid are confined within a plurality of capsules or microcells.

14. The electro-optical display of claim 12, wherein: The charged particles and the fluid exist as a plurality of discrete droplets surrounded by a continuous phase comprising a polymer material.

15. A display controller capable of controlling the operation of a bi-stable electro-optical display, the controller being configured to perform a driving method for operating the display, the method comprising: applying a first waveform selected from a first set of waveforms for a black-to-white transition and a white-to-white transition if the pixel is determined to display color; as well as applying a second waveform selected from a second set of waveforms for black-to-white transitions and white-to-white transitions if the pixel is determined to display a grayscale image; wherein the first set of waveforms includes a black-to-white transition waveform comprising a pre-pulse, an intermediate pulse, and a setup pulse, and the black-to-white transition waveform is configured to reduce a differential blooming effect of pixels displaying color, and The duration of the black-to-white transition waveforms in the first group of waveforms is longer than the duration of the black-to-white transition waveforms in the second group of waveforms.

16. The controller according to claim 15, wherein: The driving method further includes applying a third waveform selected from a third group of waveforms for black-to-white transitions and white-to-white transitions if the pixel is determined to display black text on a white background.

17. The controller according to claim 15, wherein: The driving method further includes applying a fourth waveform selected from a fourth set of waveforms for black-to-white transitions and white-to-white transitions if an algorithm is required to perform edge artifact cleaning on the pixel.

Images