Electro-optic displays and driving methods

Abstract

A method for driving an electrophoretic display having a plurality of display pixels, the method comprising dividing the plurality of display pixels into a plurality of groups, updating a group of display pixels from among the plurality of groups of display pixels, the group of display pixels comprising at least n adjacent display pixels updated simultaneously, wherein n is an integer greater than or equal to 2, and applying an edge clear waveform to no more than (n x 2) + 2 primary pixels in the group of display pixels.

Description

[0001] Citation of relevant applications

[0002] This application relates to U.S. Provisional Application 62 / 072,268, filed on August 31, 2020.

[0003] The full disclosure of the above application is incorporated herein by reference. Background Technology

[0004] This disclosure relates to electro-optic displays, such as bistable electro-optic displays, and methods for resetting display pixels of such bistable electro-optic displays. More specifically, the invention relates to a driving method that, when display pixels are reset, results in less flicker, less stress, and less power consumption in the display compared to other driving methods. Summary of the Invention

[0005] According to one aspect of the subject matter disclosed herein, a method for driving an electrophoretic display having a plurality of display pixels includes dividing the plurality of display pixels into a plurality of groups, updating a group of display pixels from the plurality of groups of display pixels, the group of display pixels including at least n adjacent display pixels updated simultaneously, wherein n is an integer greater than or equal to 2, and applying an edge-clearing waveform to no more than (n×2)+2 principal pixels in the group of display pixels.

[0006] In another aspect, a method for driving an electrophoretic display having a plurality of display pixels may include dividing the plurality of display pixels into a plurality of groups, applying a first waveform to a group of display pixels from the plurality of groups of display pixels, the group of display pixels including at least two adjacent display pixels that are updated simultaneously; and applying a second waveform to no more than six principal pixels in the group of display pixels. Attached Figure Description

[0007] Various aspects and embodiments of this application will be described with reference to the following accompanying drawings. It should be understood that the drawings are not necessarily drawn to scale. Items appearing in multiple figures are indicated by the same reference numerals in all the figures in which they appear.

[0008] Figure 1A An electro-optical display with multiple display pixels is shown, the multiple display pixels being numbered for use in updating or resetting;

[0009] Figure 1B This shows frames that have undergone multiple updates or resets. Figure 1A The display pixels of the electro-optical display;

[0010] Figures 2A to 2C Another driving method for updating a display with multiple display pixels is shown;

[0011] Figures 3A to 3J These are some exemplary configurations showing how pixels can be clustered for update or reset purposes;

[0012] Figure 4 A comparison of residual voltage accumulated across different driving methods is shown;

[0013] Figure 5 This is a circuit diagram representing an electrophoresis display; and

[0014] Figure 6 The circuit model of the electro-optic imaging layer is shown. Detailed Implementation

[0015] This invention relates to a method for driving an electro-optic display, particularly a bistable electro-optic display, in dark mode, and an apparatus for using this method. More specifically, the invention relates to a driving method that can allow for reduction of ghosting and edge artifacts and reduce flicker in such a display when displaying white text on a black background. 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.

[0016] The term "electro-optic," used here in the context of materials or displays, refers to a material having first and second display states, where at least one optical property differs, and the material is changed from its first display state to its second display state by applying an electric field. While the optical property is typically color perceptible to the human eye, it can be another optical property, such as light transmission, reflection, emission, or, in the case of displays used for machine reading, a pseudocolor in the sense of a change in reflectivity at electromagnetic wavelengths outside the visible light range.

[0017] The term "gray state" is used here in its conventional meaning in the imaging field, referring to a state between the two extreme optical states of a pixel, but not necessarily a black-and-white transition between those two extremes. For example, several patents and publications of IENK mentioned above describe electrophoretic displays where the extreme states are white and dark blue, making the intermediate "gray state" actually a light blue. In fact, as already mentioned, a change in optical state may not be a color change at all. The terms "black" and "white" may be used below to refer to the two extreme optical states of a display, and should be understood to generally include extreme optical states that are not strictly black and white, such as the white and dark blue states mentioned above. The term "monochrome" may be used below to refer to a driving scheme that drives pixels only to their two extreme optical states without an intermediate gray state.

[0018] The majority of the discussion below will focus on the method used to drive one or more pixels of an electro-optic display by transitioning from an initial gray level (or “grayscale”) to a final gray level (which may or may not differ from the initial gray level). The terms “gray state,” “gray level,” and “grayscale” are used interchangeably herein and include both extreme optical states and intermediate gray states. Due to limitations such as the frame rate of the display driver and the discreteness of the driving pulses imposed by temperature sensitivity, the number of possible gray levels in current systems is typically 2–16. For example, in a monochrome display with 16 gray levels, gray level 1 is typically black, and gray level 16 is white; however, the gray level designations for black and white can be reversed. Here, grayscale 1 will be used to represent black. As the grayscale progresses towards grayscale 16 (i.e., white), grayscale 2 will be a lighter black.

[0019] The terms “bistable” and “bistable” are used herein in their conventional sense in the art, referring to a display comprising display elements having first and second display states, at least one optical property of which differs such that, after any given element is driven to present its first or second display state using an addressing pulse of finite duration, the state will persist for at least several times (e.g., at least four times) the minimum duration of the addressing pulse required to change the state of the display element after the addressing pulse terminates. As shown in U.S. Patent No. 7,170,670, some particle-based electrophoretic displays supporting grayscale are stable not only in their extreme black and white states but also in intermediate gray states, as are some other types of electro-optical displays. This type of display is aptly referred to as “multistable” rather than bistable, but for convenience, the term “bistable” may be used herein to encompass both bistable and multistable displays.

[0020] The term "impulse" as used here conventionally means the integral of voltage with respect to time. However, some bistable electro-optic dielectrics are used as charge converters, and with such dielectrics, an alternative definition of impulse can be used: the integral of current with respect to time (equal to the total applied charge). The appropriate definition of impulse should be used depending on whether the dielectric is used as a voltage-time impulse converter or a charge-impulse converter.

[0021] As used herein, the term "residual voltage" refers to a persistent or decaying electric field that may remain in an electro-optic display after the termination of an addressing pulse (a voltage pulse used to change the optical state of an electro-optic medium). This residual voltage can adversely affect the image displayed on the electro-optic display, including but not limited to the so-called "ghosting" phenomenon, where traces of the previous image remain visible after the display has been rewritten. Application 2003 / 0137521 describes how a DC unbalanced waveform can lead to the generation of residual voltage, which can be determined by measuring the open-circuit electrochemical potential of the display pixel.

[0022] The term "waveform" will be used to refer to the entire voltage-time curve used to achieve a transition from a particular initial gray level to a particular final gray level. Typically, such a waveform will include multiple waveform elements; where these elements are substantially rectangular (i.e., where a given element involves the application of a constant voltage over a period of time); these 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 gray levels of a particular display. A display may use more than one drive scheme; for example, as taught in the aforementioned U.S. Patent No. 7,012,600, the drive scheme may need to be modified based on parameters such as the temperature of the display or the operating time of the display during its lifespan, thus a display may have multiple different drive schemes for use at different temperatures, etc. A set of drive schemes used in this way may be referred to as a "set of associated drive schemes." As described in the aforementioned MEDEOD applications, more than one drive scheme may also be used 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 synchronized drive schemes."

[0023] Several types of electro-optic displays are known. One type of electro-optic display is the rotating bicolor component 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 bicolor sphere" display, the term "rotating bicolor component" is preferred as it is more accurate because in some of the patents mentioned above, the rotating component is not spherical). This display uses a number of small bodies (typically spherical or cylindrical) and internal dipoles, said bodies comprising two or more parts with different optical properties. These bodies are suspended within liquid-filled bubble chambers within a matrix, the bubble chambers being filled with liquid to allow the bodies to rotate freely. The appearance of a display is altered by applying an electric field to the display, thereby rotating the subject to various positions and changing which part of the subject is visible through the viewing surface. This type of electro-optic medium is typically bistable.

[0024] Another type of electro-optic display uses electrochromic media, such as those in the form of nanochromic films, which include electrodes formed at least partially of semiconductor metal oxides and multiple dye molecules attached to the electrodes capable of reversing color changes; 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. This type of nanochromic film is 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.

[0025] Another type of electro-optic display is the electrowetting display developed by Philips, described in Hayes, RA et al., “Video-Speed ​​Electronic Paper Based on Electrowetting”, Nature, 425, 383-385 (2003). U.S. Patent No. 7,420,549 shows that such an electrowetting display can be manufactured in a bistable manner.

[0026] Electro-optic displays, a type of display that has been the subject of intensive research and development for many years, are particle-based electrophoretic displays, in which multiple charged particles move through a fluid under the influence of an electric field. Compared to liquid crystal displays (LCDs), electrophoretic displays can offer advantages such as good brightness and contrast, wide viewing angles, state bistability, and low power consumption. However, long-term image quality issues have hindered their widespread use. For example, the particles constituting an electrophoretic display are prone to settling, resulting in a short lifespan for these displays.

[0027] As mentioned above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, this fluid is a liquid, but electrophoretic media can be generated using a gaseous fluid; see, for example, Kitamura, T. et al., “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. Patent Nos. 7,321,459 and 7,236,291. When such gas-based electrophoretic media are used in a direction that allows particle settling, such as in signs where the media are arranged in a vertical plane, they are susceptible to the same type of problems as liquid-based electrophoretic media due to the same particle settling. In fact, particle sedimentation is more severe in gas-based electrophoretic media than in liquid-based electrophoretic media because the lower viscosity of gaseous suspensions allows electrophoretic particles to settle more quickly compared to liquids.

[0028] Numerous patents and applications transferred to or in the name of MIT and Einkel describe various techniques for encapsulating electrophoretic and other electro-optic media. These encapsulated media comprise a plurality of small capsules, each capsule comprising an inner phase and a capsule wall surrounding the inner phase, wherein the inner phase contains electrophoretically mobile particles in a fluid medium. Typically, the capsules themselves are held in a polymer binder to form a coherent layer located between two electrodes. The techniques described in these patents and applications include:

[0029] (a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814;

[0030] (b) Encapsulation, adhesives, and encapsulation processes; see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719;

[0031] (c) Thin films and sub-assemblies containing electro-optic materials; see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564;

[0032] (d) Backplanes, adhesive layers and other auxiliary layers in displays, and methods thereof; see, for example, U.S. Patent Nos. 7,116,318 and 7,535,624;

[0033] (e) Color formation and color adjustment; see, for example, U.S. Patent No. 7,075,502; and U.S. Patent Application Publication No. 2007 / 0109219;

[0034] (f) A method for driving a display; see the above MEDEOD application;

[0035] (g) Applications of displays; see, for example, U.S. Patent No. 7,312,784 and U.S. Patent Application Publication No. 2006 / 0279527; and

[0036] (h) Non-electrophoretic displays, as described in U.S. Patent Nos. 6,241,921; 6,950,220; and 7,420,549; and U.S. Patent Application Publication No. 2009 / 0046082.

[0037] (i) "MEDEOD" (Method for Driving an Electro-Optical Display) application. The entire contents of these patents and co-pending applications, and the entire contents of all other U.S. patents and published and co-pending applications mentioned below, are incorporated herein by reference: 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; 7,116,466; 7,119,772; 7,1 93,625;7,202,847;7,259,744;7,304,787;7,312,794;7,327,511;7,453,445;7,492,339;7,528,822;7,545,358;7,583,251;7,602,374;7,612,760;7,679,599;7,688,297;7,729,039;7,733,311;7,733,335;7,787,169;7,952,557;7,956,841;7 999,787; 8,077,141; and 8,558,783; U.S. Patent Application Publication Nos. 2003 / 0102858; 2005 / 0122284; 2005 / 0253777; 2006 / 0139308; 2007 / 0013683; 2007 / 0091418; 2007 / 0103427; 2007 / 0200874; 2008 / 0024429; 2008 / 0024482; 2008 / 0048969; 2008 / 0129667; 2008 / 013677 4; 2008 / 0150888; 2008 / 0291129; 2009 / 0174651; 2009 / 0179923; 2009 / 0195568; 2009 / 0256799; 2009 / 0322721; 2010 / 0045592; 2010 / 0220121; 2010 / 0220122; 2010 / 0265561; 2011 / 0285754; 2013 / 0194250, 2014 / 0292830 and 2016 / 0225322; PCT Publication No. WO 2015 / 017624; and U.S. Patent Application No. 15 / 014,236, filed February 3, 2016.

[0038] Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thereby producing a so-called polymer dispersion electrophoretic display, wherein the electrophoretic medium comprises a plurality of discrete droplets of electrophoretic fluid and a continuous phase of polymeric material, and the discrete droplets of electrophoretic fluid within such a polymer dispersion electrophoretic display can be considered as capsules or microcapsules, even if no discrete capsule membrane is associated with each individual droplet; see, for example, the aforementioned U.S. Patent No. 6,866,760. Therefore, for the purposes of this application, such polymer dispersion electrophoretic media are considered a subclass of encapsulated electrophoretic media.

[0039] One related type of electrophoretic display is the so-called "microcell electrophoretic display." In a microcell electrophoretic display, charged particles and fluid are not encapsulated within microcapsules, but rather held within multiple cavities formed within a carrier medium (typically a polymer film). See, for example, U.S. Patent Nos. 6,672,921 and 6,788,449, both assigned to Sipix Imaging.

[0040] While electrophoretic media are typically opaque (because, for example, in many electrophoretic media, particles essentially block visible light from passing through the display) and operate in reflective mode, some electrophoretic displays can be fabricated to operate in a so-called "shutter mode," in which one display state is substantially opaque and the other is transmissive. See, for example, U.S. Patent Nos. 5,872,552; 6,130,774; 6,144,361; 6,172,798; 6,271,823; 6,225,971; and 6,184,856. Dielectrophoretic displays, similar to electrophoretic displays but dependent on changes in electric field strength, can operate in a similar mode; see U.S. Patent No. 4,418,346. Other types of electro-optic displays are also capable of operating in shutter mode. In the multi-layered structure of a full-color display, an electro-optic medium operating in shutter mode may be useful; in such a structure, at least one layer adjacent to the viewing surface of the display operates in shutter mode to expose or hide a second layer further away from the viewing surface.

[0041] Encapsulated electrophoretic displays are generally unaffected by the clustering and sedimentation failure modes of conventional electrophoretic apparatus and offer more beneficial effects, such as the ability to print or coat displays on a variety of flexible and rigid substrates. (The term "printing" is used to include all forms of printing and coating, including but not limited to: pre-metering coating such as patch die coating, slot or extrusion coating, slide or stack coating, curtain coating; roller coating such as roller blade coating, forward and reverse roller coating; concave coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; screen printing; electrostatic printing; thermal printing; inkjet printing; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar techniques.) Therefore, the resulting displays can be flexible. Furthermore, because the display medium can be printed (using a variety of methods), the display itself can be manufactured inexpensively.

[0042] Other types of electro-optic media can also be used in the display of this invention.

[0043] The bistable or multistable behavior of particle-based electrophoretic displays, and other electro-optic displays exhibiting similar behavior (hereafter referred to as "impulse-driven displays" for convenience), contrasts sharply with conventional liquid crystal ("LC") displays. Twisted nematic liquid crystals are not bistable or multistable; instead, they act as voltage converters, so applying a given electric field to a pixel in such a display produces a specific gray level at that pixel, regardless of the gray level previously present at that pixel. Furthermore, liquid crystal displays are driven in only one direction (from nontransmissive or "dark" to transmissive or "bright"), and the reverse transition from a brighter state to a darker state is achieved by reducing or eliminating the electric field. Finally, the gray levels of pixels in an LC display are insensitive to the polarity of the electric field, only to its magnitude; in fact, for technical reasons, commercial LC displays often frequently reverse the polarity of the driving field. In contrast, bistable electro-optic displays act as impulse converters in a first-order approximation, so the final state of a pixel depends not only on the applied electric field and the time of application but also on the state of the pixel before the application of the electric field.

[0044] Regardless of whether the electro-optic medium used is bistable, to achieve a high-resolution display, the individual pixels of the display must be addressable without interference from adjacent pixels. One way to achieve this is to provide an array of nonlinear elements (such as transistors or diodes), with at least one nonlinear element associated with each pixel to produce an "active matrix" display. The addressing or pixel electrode of a pixel is connected to an appropriate voltage source via the associated nonlinear element. Typically, when the nonlinear element is a transistor, the pixel electrode is connected to the drain of the transistor, and this arrangement will be assumed in the following description, although it is essentially arbitrary and the pixel electrode can be connected to the source of the transistor. Typically, in a high-resolution array, pixels are arranged in a two-dimensional array of rows and columns such that any particular pixel is uniquely defined by the intersection of a specified row and a specified column. The sources of all transistors in each column are connected to a single column electrode, while the gates of all transistors in each row are connected to a single row electrode; again, the source-to-row and gate-to-column assignments are conventional but essentially arbitrary and can be reversed if desired. Row electrodes are connected to row drivers, which essentially ensures that only one row is selected at any given time. That is, a voltage is applied to the selected row electrode to ensure all transistors in the selected row are turned on, while voltages are applied to all other rows to ensure all transistors in these unselected rows remain off. Column electrodes are connected to column drivers, which apply voltages to the individual column electrodes selected to drive the pixels in the selected row to their desired optical state. (These voltages are relative to a common front electrode, which is typically located on the side of the electro-optical medium opposite the nonlinear array and extends across the entire display.) After a preselection interval known as the “line addressing time,” the selected row is deselected, the next row is selected, and the voltage on the column driver is changed to write the next row to the display. This process is repeated to write to the entire display row by row.

[0045] At first glance, the ideal approach to addressing such impulse-driven electro-optic displays might seem to be the so-called "general grayscale image stream," where the controller schedules each write of the image so that each pixel transitions directly from its initial grayscale level to its final grayscale level. However, writing images to impulse-driven displays inevitably introduces some errors. Some of these errors encountered in practice include:

[0046] (a) Previous state dependence; for at least some electro-optic media, the impulse required to switch a pixel to a new optical state depends not only on the current and desired optical state, but also on the previous optical state of the pixel.

[0047] (b) Dwell time dependence; for at least some electro-optic media, the impulse required to switch a pixel to a new optical state depends on the time the pixel spends in its various optical states. The exact nature of this dependence is not yet clear, but in general, the longer a pixel remains in its current optical state, the more impulse is required.

[0048] (c) Temperature dependence; the impulse required to switch a pixel to a new optical state depends largely on temperature.

[0049] (d) Humidity dependence; for at least some types of electro-optic media, the impulse required to switch a pixel to a new optical state depends on the ambient humidity.

[0050] (e) Mechanical uniformity; the impulse required to switch a pixel to a new optical state may be affected by mechanical variations in the display, such as thickness variations in the electro-optic medium or associated laminating adhesive. Other types of mechanical non-uniformity may be caused by unavoidable variations between different manufacturing batches of the medium, manufacturing tolerances, and material variations.

[0051] (f) Voltage error; The actual impulse applied to the pixel will inevitably differ slightly from the theoretically applied impulse because there is an unavoidable small error in the voltage provided by the driver.

[0052] Grayscale image streams generally suffer from an "error accumulation" phenomenon. For example, suppose temperature dependence causes an error of 0.2L* in the positive direction of each transition (where L* has the usual CIE definition:

[0053] L*=116(R / R0)1 / 3-16,

[0054] Where R is reflectance and R0 is the standard reflectance value. After fifty transitions, this error will accumulate to 10L*. Perhaps more realistically, assume the average error per transition (expressed as the difference between the display's theoretical and actual reflectance) is ±0.2L*. After 100 consecutive transitions, the pixel will show an average deviation of 2L* from its expected state; for some types of images, this deviation is noticeable to the average observer.

[0055] This error accumulation phenomenon applies not only to temperature-induced errors but also to all types of errors listed above. Such errors can be compensated for, but with limited accuracy, as described in the aforementioned U.S. Patent No. 7,012,600. For example, temperature errors can be compensated for using a temperature sensor and a lookup table, but the temperature sensor has limited resolution and may read a temperature slightly different from that of the electro-optic medium. Similarly, previous state dependencies can be compensated for by storing previous states and using a multidimensional transition matrix, but the controller memory limits the number of states that can be recorded and the size of the transition matrix that can be stored, thus limiting the accuracy of this compensation.

[0056] Therefore, general grayscale image streams require very precise control of the applied impulse to produce good results, and experience has shown that, given the current state of electro-optical display technology, general grayscale image streams are not feasible in commercial displays.

[0057] U.S. Patent Publication No. 2013 / 0194250, now U.S. Patent No. 10,672,350, the entire contents of which are incorporated herein by reference, describes a technique for reducing flicker and edge ghosting. One such technique, referred to as a “Selective General Update” or “SGU” method, involves driving an electro-optical display having multiple pixels using a first driving scheme and a second driving scheme, in which all pixels are driven at each transition, and in the second driving scheme, pixels undergoing certain transitions are not driven. During a first update of the display, the first driving scheme is applied to the non-zero minor portions of the pixels, while the second driving scheme is applied to the remaining pixels during the first update. During a second update following the first update, the first driving scheme is applied to different non-zero minor portions of the pixels, while the second driving scheme is applied to the remaining pixels during the second update. Typically, the SGU method is applied to refresh a white background around text or an image such that only a small subset of pixels in the white background are updated during any given display update, but all pixels of the background are updated gradually, thus preventing the white background from drifting to gray without any flicker updates. It is obvious to those skilled in the art of electro-optical displays that the application of the SGU method requires a special waveform (hereinafter referred to as the "F" waveform or "F-Transition") for each pixel (updated on each transition).

[0058] The aforementioned U.S. Patent Publication No. 2013 / 0194250 also describes a “Balanced Pulse Pair White / White Transition Driving Scheme” or “BPPWWTDS”, which involves applying one or more pairs of balanced pulses (a balanced pulse pair or “BPP” is a pair of driving pulses of opposite polarities such that the net impulse of the balanced pulse pair is substantially zero) during a white-to-white transition of a pixel, the pixel being identified as potentially causing edge artifacts and being in a spatiotemporal configuration such that the balanced pulse pair will effectively erase or reduce edge artifacts. Ideally, pixels to which BPPs are applied are selected such that the BPPs are masked by other updating activities. Note that applying one or more BPPs does not affect the ideal DC balance of the driving scheme because each BPP inherently has zero net impulse and therefore does not change the DC balance of the driving scheme. A second such technique, referred to as a “White / White Top-Off Pulse Driving Scheme” or “WWTOPDS”, involves applying a “top-off” pulse during a white-to-white transition of a pixel, the pixel being identified as potentially causing edge artifacts and being in a spatiotemporal configuration such that the top-off pulse will effectively erase or reduce edge artifacts. The application of BPPWWTDS or WWTOPDS again requires a special waveform (hereinafter referred to as the "T" waveform or "T-Transition") for each pixel (updated on each transition). The T and F waveforms are typically applied only to pixels undergoing a white-to-white transition. In a globally constrained drive scheme, the white-to-white waveform is empty (i.e., consists of a series of zero-voltage pulses), while all other waveforms are not empty. Therefore, when applicable, the non-empty T and F waveforms replace the empty white-to-white waveform in a globally constrained drive scheme.

[0059] In some cases, it may be desirable to use multiple driving schemes for a single display. For example, a display supporting more than two grayscale levels can use a grayscale driving scheme (“GSDS”) and a monochrome driving scheme (“MDS”). GSDS can handle transitions between all possible grayscale levels, while MDS handles transitions between only two grayscale levels, providing a faster display rewrite than GSDS. MDS is used when all pixels changed during a display rewrite only handle transitions between the two grayscale levels used by MDS. For example, U.S. Patent No. 7,119,772 describes a display in the form of an e-book or similar device capable of displaying grayscale images as well as a monochrome dialog box that allows the user to input text related to the displayed image. When the user inputs text, a fast MDS is used to quickly update the dialog box, providing the user with rapid confirmation of the input. On the other hand, a slower GSDS is used when the entire grayscale image displayed on the display changes.

[0060] Alternatively, the display can use both GSDS and a "direct update" driving scheme ("DUDS"). DUDS can have two or more gray levels, typically fewer than GSDS, but the most important feature of DUDS is that the transition from the initial gray level to the final gray level is handled by a simple unidirectional driver, rather than the "indirect" transition often used in GSDS, where, at least in some transitions, the pixel is driven from the initial gray level to an extreme optical state and then in the opposite direction to the final gray level; in some cases, the transition can be achieved by driving from the initial gray level to an extreme optical state, then to the opposite extreme optical state, and finally to the final extreme optical state, see, for example, the driving scheme shown in Figures 11A and 11B of U.S. Patent No. 7,012,600. Therefore, the update time of current electrophoretic displays in grayscale mode can be about two to three times the length of the saturation pulse (where the "length of the saturation pulse" is defined as the time period sufficient to drive the pixels of the display from one extreme optical state to another at a specific voltage) or about 700-900 milliseconds, while the maximum update time of DUDS is equal to the length of the saturation pulse, or about 200-300 milliseconds.

[0061] However, variations in driving schemes are not limited to differences in the number of gray levels used. For example, driving schemes can be categorized into global driving schemes and partial update driving schemes. In a global driving scheme, driving voltage is applied to every pixel (potentially the entire display or a defined portion thereof) in the area where a global update driving scheme (more accurately referred to as a “globally complete” or “GC” driving scheme) is applied. In a partial update driving scheme, driving voltage is applied only to pixels undergoing a non-zero transition (i.e., a transition where the initial and final gray levels differ from each other), but no driving voltage or zero voltage is applied during zero transitions or null transitions (where the initial and final gray levels are the same). As used herein, the terms “zero transition” and “null transition” are used interchangeably. An intermediate form of driving scheme (specified as a “globally restricted” or “GL” driving scheme) is similar to a GC driving scheme, except that no driving voltage is applied to pixels undergoing a zero, white-to-white transition. For example, in a monitor used as an e-book reader that displays black text on a white background, there are many white pixels, especially between page margins and text lines. These white pixels remain unchanged from one page of text to the next; therefore, not rewriting these white pixels greatly reduces the noticeable "flickering" of the monitor rewriting.

[0062] However, some problems still exist in this type of GL-driven scheme. First, as discussed in detail in some of the aforementioned MEDEOD applications, bistable electro-optic media are generally not perfectly bistable; pixels in an extreme optical state gradually drift towards intermediate gray levels over time periods ranging from minutes to hours. In particular, pixels driven as white slowly drift towards lighter gray. Therefore, if, in a GL-driven scheme, white pixels are allowed to remain undriven after multiple page turns while other white pixels (e.g., those that form parts of text characters) are driven, the newly updated white pixels will be slightly brighter than the undriven ones, and eventually, the difference will become noticeable even to untrained users.

[0063] Secondly, a phenomenon known as "blooming" occurs when an undriven pixel is adjacent to an updating pixel. The driving of the driven pixel causes a change in the optical state over a region slightly larger than the driven pixel, and this region encroaches on the areas of adjacent pixels. This blooming manifests as an edge effect along the edge of the undriven pixel adjacent to the driven pixel. A similar edge effect occurs when using region updates (where only a specific area of ​​the display is updated, such as to display an image), except that with region updates, the edge effect occurs at the boundary of the area being updated. Over time, this edge effect becomes visually distracting and must be eliminated. To date, such edge effects (along with the color drift effect of undriven white pixels) have generally been eliminated by using GC updates periodically. Unfortunately, using such occasional GC updates reintroduces the problem of "flickering" updates; in fact, since flickering updates only occur over very long intervals, the flickering of updates can be exacerbated.

[0064] Some aspects of the present invention relate to reducing or eliminating the problems discussed above while still avoiding flicker updates as much as possible. However, an additional complexity arises in attempting to address these problems: the need for overall DC balancing. As discussed in many of the aforementioned MEDEOD applications, if the driving scheme used is not substantially DC balanced (i.e., if the algebraic sum of the impulses applied to the pixels does not approach zero during any series of transitions starting and ending at the same gray level), it can adversely affect the electro-optical characteristics and operational lifetime of the display. See in particular U.S. Patent No. 7,453,445, which discusses the DC balancing problem in a so-called “heterogeneous loop” involving transitions performed using more than one driving scheme. A DC-balanced driving scheme ensures that the total net impulse bias is bounded (for a finite number of gray states) at any given time. In a DC-balanced driving scheme, each optical state of the display is assigned an impulse potential (IP), and the individual transitions between optical states are defined such that the net impulse of the transition is equal to the difference in impulse potentials between the initial and final states of the transition. In a DC-balanced driving scheme, it is required that any round-trip net impulse is substantially zero.

[0065] In one aspect, the present invention provides a method for driving an electro-optic display having multiple pixels to display white text on a black background (“dark mode”, also referred to herein as “black mode”) while reducing edge artifacts, ghosting, and flickering updates. Furthermore, if the text is anti-aliased, the white text may include pixels with intermediate gray levels. Displaying black text on a light or white background is referred to herein as “light mode” or “white mode”. Typically, when displaying white text on a black background, white edges or edge artifacts may accumulate after multiple updates (similar to dark edges in light mode). This edge accumulation is particularly noticeable when background pixels (i.e., pixels in the margins and line spacing between text lines) do not flicker during updates (i.e., background pixels that remain in a black extreme optical state through repeated updates, undergoing repeated black-to-black zero transitions during which no driving voltage is applied to the pixels, and they do not flicker). A dark mode in which no driving voltage is applied during black-to-black transitions may be referred to as a “dark GL mode”; this is essentially the opposite of a light GL mode, in which no driving voltage is applied to background pixels undergoing white-to-white zero transitions. Dark GL mode can be implemented by simply defining a zero transition from black to black pixels, but it can also be implemented by the controller in some other way (such as partial updates).

[0066] Figure 5A schematic diagram of a pixel 500 of an electrophoretic display according to the subject matter submitted herein is shown. Pixel 500 may include an imaging film 510. In some embodiments, the imaging film 510 may be bistable. In some embodiments, the imaging film 510 may include, but is not limited to, an encapsulated electrophoretic imaging film, which may include, for example, charged pigment particles.

[0067] An imaging film 510 may be disposed between the front electrode 502 and the rear electrode 504. The front electrode 502 may be formed between the imaging film and the front portion of the display. In some embodiments, the front electrode 502 may be transparent. In some embodiments, the front electrode 502 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 to the front electrode 502. In some embodiments, a parasitic capacitance (not shown) may be formed between the front electrode 502 and the rear electrode 504.

[0068] Pixel 500 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 specified row and a specified column. In some embodiments, the pixel matrix can be an “active matrix” in which each pixel is associated with at least one nonlinear circuit element 520. The nonlinear circuit element 520 can be coupled between a backplane electrode 504 and an addressing electrode 508. In some embodiments, the nonlinear element 520 can include diodes and / or transistors, including but not limited to MOSFETs. The drain (or source) of the MOSFET can be coupled to the backplane electrode 504, the source (or drain) of the MOSFET can be coupled to the addressing electrode 508, and the gate of the MOSFET can be coupled to a driver electrode 506 configured to control the activation and deactivation of the MOSFET. (For simplicity, the terminal of the MOSFET coupled to the backplane electrode 504 will be referred to as the drain of the MOSFET, and the terminal of the MOSFET coupled to the addressing electrode 508 will be referred to as the source of the MOSFET. However, those skilled in the art will recognize that in some embodiments, the source and drain of the MOSFET can be interchanged.)

[0069] In some embodiments of the active matrix, the addressing electrodes 508 of all pixels in each column may be connected to the same column electrode, and the driver electrodes 506 of all pixels in each row may be connected to the same row electrode. The row electrodes may be connected to a row driver, which can select one or more rows of pixels by applying a voltage to the selected row electrode sufficient to activate a nonlinear element 520 of all pixels 500 in the selected row. The column electrodes may be connected to a column driver, which can apply a voltage suitable for driving the pixel to a desired optical state to the addressing electrodes 506 of the selected (activated) pixel. The voltage applied to the addressing electrodes 508 may be related to the voltage applied to the front panel electrode 502 of the pixel (e.g., approximately zero volts). In some embodiments, the front panel electrodes 502 of all pixels in the active matrix may be coupled to a common electrode.

[0070] In some embodiments, pixels 500 of the active matrix can be written row by row. For example, a row of pixels can be selected by a row driver, and a voltage corresponding to the desired optical state of that row of pixels can be applied to the pixels by a column driver. After a preselection interval known as “line addressing time”, the selected row can be deselected, another row can be selected, and the voltage on the column driver can be changed to write another row of the display.

[0071] Figure 6 A circuit model of an electro-optic imaging layer 510 disposed between a front electrode 502 and a rear electrode 504, according to the subject matter presented herein, is shown. Resistor 602 and capacitor 604 may represent the resistance and capacitance of the electro-optic imaging layer 510, the front electrode 502, and the rear electrode 504 (including any adhesive layers). Resistor 612 and capacitor 614 may represent the resistance and capacitance of the laminated adhesive layer. Capacitor 616 may represent the capacitance that may form, for example, interlayer interface contact regions between the front electrode 502 and the rear electrode 504 (e.g., the interface between the imaging layer and the laminated adhesive layer and / or the interface between the laminated adhesive layer and the backplane electrode). The voltage Vi across the imaging film 510 of the pixel may include the residual voltage of the pixel.

[0072] Figure 1A A pixel clearing method according to the subject matter presented herein is illustrated. In this method, the pixels of a display can be divided into different parts, wherein each display pixel is assigned a numerical tag (e.g., 1, 2, 3, 4, 5, 6, 7, 8, etc.), and the assignment of tags can be periodic or random. When the display is reset, display pixels with the same numerical tag are reset together. For example, as... Figure 1BAs shown, frame 1 of the driving method can update or reset all display pixels specified or marked as the number 1. Subsequently, in the next frame, in frame 2 or the second frame, all display pixels specified as the number 2 can be updated or reset. Similarly, as... Figure 1B As shown, frame 3 or the third frame will update or reset all display pixels designated as the number 3; the next frame (i.e., frame 4 or the fourth frame) will update or reset all display pixels designated as the number 4; the next frame (i.e., frame 5 or the fifth frame) will update or reset all display pixels designated as the number 5; the next frame (i.e., frame 6 or the sixth frame) will update or reset all display pixels designated as the number 6; the next frame (i.e., frame 7 or the seventh frame) will update or reset all display pixels designated as the number 7; similarly, the next frame (i.e., frame 8 or the eighth frame) will update or reset all display pixels designated as the number 8. In this configuration, this driving method updates or resets a portion of the display at a time (i.e., one-eighth of all pixels at a time), thereby reducing flicker caused by updates or resets.

[0073] Alternatively, pixels can be clustered for use in updating or resetting, such as Figures 2A to 2C As shown in the image. This is in contrast to situations where no two major or adjacent pixels are updated or reset during the same frame. Figure 1A compared to, Figures 2A to 2C The driving method shown causes two or more primary or adjacent display pixels to be updated or reset together. Now refer to... Figure 2A When display pixels are specified using numbers, adjacent or dominant pixels can be specified with the same number, meaning they can be updated or reset together or within the same frame. For example, see reference... Figure 2A The first two rows of the display pixels shown can have the same number. Thus, during an update or reset, these two pixels can be updated or reset simultaneously or within the same frame (e.g., two pixels from the first two rows designated as the number 1 can be reset together during frame 1; similarly, two pixels from the first two rows designated as the number 6 can be reset together during frame 6). In short, at least two adjacent display pixels designated as the same group of numbers can be driven together with a first waveform, which can be an update waveform or a reset waveform. Adjacent terms here refer to display pixels that share a common vertex or a common edge. Now refer to... Figure 2B It can be used Figure 2AThe methods outlined herein are for updating or resetting a display 210 with a dark background. For example, pixels 212a and 212b designated for updating or resetting can be reset using a black-to-black clear waveform. However, such a black-to-black clear waveform may cause edge artifacts in adjacent or principal pixels 214a, 214b, 214c, 214d, 214e, and 214f. In this case, to remove these edge artifacts, these principal pixels 214a, 214b, 214c, 214d, 214e, and 214f ​​will be applied a black-to-black edge clear waveform, while the remaining pixels (e.g., pixels 216a and 216b) will be applied a standard black-to-black waveform. In some embodiments, this black-to-black edge clear waveform may be DC unbalanced, in which case residual charge may accumulate within the display medium due to this DC imbalance. Similarly, as Figure 2C As shown, it can be used Figure 2A The method outlined herein is for updating or resetting a display 220 with a white background. Pixels 222a and 222b specified for updating or resetting can be reset using a white-to-white clearing waveform. Similarly, this white-to-white clearing waveform may also cause edge artifacts in the primary pixels 224a, 224b, 224c, 224d, 224e, and 224f, and these edge artifacts can be removed by applying a white-to-white edge clearing waveform, while a standard white-to-white waveform can be applied to the remainder of pixels 226a and 226b. Furthermore, as... Figure 2B As shown in the display 210 with a dark background, these white-to-white edge clearing waveforms may be DC unbalanced and may cause residual charge to accumulate in the display medium, which can stress the display and negatively affect display performance.

[0074] In comparison, with Figure 1A and 1B Compared to the driving method shown, Figures 2A to 2C The driving method shown produces less residual charge on the display. This is at least in part due to the fact that by clustering the reset pixels, compared to... Figure 1A and 1B Compared to the method outlined in [the document], fewer principal pixels (e.g., pixels 214a, 214b, 214c, 214d, 214e, and 214f; pixels 224a, 224b, 224c, 224d, 224e, and 224f) will require edge cleanup. Specifically, in [the document]... Figure 1A and 1B In this approach, each reset pixel will require at least four major pixels to drive the DC-unbalanced edge clearing waveform. In contrast, in... Figures 2A to 2C In the method shown, only 3 such primary pixels will be driven by a DC unbalanced edge-clearing waveform. Figure 4 This illustrates a comparison of the residual charge accumulated between the two methods described above. Curve 412 is obtained using... Figures 2A to 2C The residual charge accumulated by the method shown is represented by curve 410. Figure 1A and 1B The method shown illustrates the residual charge accumulation. It clearly demonstrates that clustering reset pixels effectively reduces residual charge accumulation in the display. Furthermore, as residual charge accumulation decreases, the stress on the display caused by residual charge also decreases, thereby improving the display's durability and performance. Moreover, by clustering display pixels for reset, this drive configuration, particularly for high-resolution displays, improves reset or update efficiency and reduces power consumption. In this configuration, the number of primary display pixels requiring a second waveform (e.g., an edge-clearing waveform) will not exceed (n×2)+2, where n is the number of display pixels driven together with the first waveform, specified by the same number. For example, when two display pixels are driven together with the first waveform, no more than six primary display pixels will be driven with the edge-clearing waveform; when three display pixels are driven together with the first waveform, no more than eight primary display pixels will be driven with the edge-clearing waveform.

[0075] In practice, the clustering of display pixels to be cleared or reset can take various forms and methods to further improve driving efficiency and reduce residual charge accumulation. Figure 3A-3J Some exemplary configurations that can be used are shown. For example, Figure 3A and 3C It is shown that two display pixels are driven together, therefore, no more than six main pixels surrounding these two pixels need to be driven with an edge-cleared waveform; Figure 3B and 3D The diagram shows that three display pixels are driven together, therefore, no more than eight main pixels surrounding these three pixels need to be driven with an edge-clearing waveform. Figure 3E , 3F And 3G shows that three display pixels are driven together, and because they are not like Figure 3B and 3D The configurations shown are positioned linearly, so these configurations only require applying the edge-sweeping waveform to just seven main display pixels. Furthermore, Figure 3H and 3J Two configurations are shown, in which four display pixels are driven together in a clustered manner, resulting in no more than eight major pixels requiring edge-clearing waveforms. Figure 3I In another embodiment presented, five display pixels are arranged such that one pixel is centered in the middle and surrounded by four other pixels. In this configuration, only eight primary pixels require edge-clearing waveforms.

[0076] It will be apparent to those skilled in the art that various changes and modifications can be made to the specific embodiments of the present invention described above without departing from the scope of the invention. Therefore, the entire foregoing description should be interpreted as illustrative rather than restrictive.

Claims

1. A method for driving an electrophoretic display having a plurality of display pixels, the method comprising: Divide the plurality of display pixels into multiple groups; During the first frame, a set of display pixels from a plurality of sets of display pixels is updated, wherein display pixels not in said set of display pixels are not updated during the first frame, said set of display pixels comprising n adjacent display pixels that are updated simultaneously, where n is an integer greater than or equal to 2; and The DC unbalanced edge clearing waveform is applied to no more than (n×2)+2 major pixels surrounding the n adjacent display pixels in the set of display pixels.

2. The method according to claim 1, wherein, Updating one set of display pixels from multiple sets of display pixels also includes updating pixels from all sets of said multiple sets of display pixels in a predetermined order.

3. The method according to claim 1, wherein, Updating one set of display pixels from multiple sets of display pixels also includes updating pixels from all sets of display pixels in a random order.

4. The method according to claim 1, wherein, The electrophoretic display also includes an electrophoretic dielectric layer.

5. The method according to claim 4, wherein, The electrophoretic dielectric layer is an encapsulated electrophoretic display medium.

6. The method according to claim 5, wherein, The encapsulated electrophoretic display medium includes an electrophoretic medium comprising a liquid and at least one particle disposed within the liquid and capable of moving through it when an electric field is applied to the medium.

7. The method according to claim 1, wherein, The set of display pixels includes three adjacent display pixels that are updated simultaneously, and the step of applying the DC unbalanced edge clearing waveform includes applying the DC unbalanced edge clearing waveform to no more than eight major pixels surrounding the three adjacent display pixels.

8. The method according to claim 1, wherein, The set of display pixels includes four adjacent display pixels that are updated simultaneously, and the step of applying the DC unbalanced edge clearing waveform includes applying the DC unbalanced edge clearing waveform to no more than ten major pixels surrounding the four adjacent display pixels.

9. The method according to claim 1, wherein, The set of display pixels includes five adjacent display pixels that are updated simultaneously, and the step of applying the DC unbalanced edge clearing waveform includes applying the DC unbalanced edge clearing waveform to no more than twelve major pixels surrounding the five adjacent display pixels.

10. The method according to claim 1, wherein, The set of display pixels includes three adjacent display pixels that are updated simultaneously, and the step of applying the DC unbalanced edge clearing waveform includes applying the DC unbalanced edge clearing waveform to no more than seven major pixels surrounding the three adjacent display pixels.

11. The method according to claim 1, wherein, The set of display pixels includes four adjacent display pixels that are updated simultaneously, and the step of applying the DC unbalanced edge clearing waveform includes applying the DC unbalanced edge clearing waveform to no more than eight major pixels surrounding the four adjacent display pixels.

12. The method according to claim 1, wherein, The set of display pixels includes four adjacent display pixels that are updated simultaneously, and the step of applying the DC unbalanced edge clearing waveform includes applying the DC unbalanced edge clearing waveform to no more than nine major pixels surrounding the four adjacent display pixels.

13. The method according to claim 1, wherein, The set of display pixels includes five adjacent display pixels that are updated simultaneously, and the step of applying the DC unbalanced edge clearing waveform includes applying the DC unbalanced edge clearing waveform to no more than nine major pixels surrounding the five adjacent display pixels.

14. The method according to claim 1, wherein, The set of display pixels includes five adjacent display pixels that are updated simultaneously, and the step of applying the DC unbalanced edge clearing waveform includes applying the DC unbalanced edge clearing waveform to no more than ten major pixels surrounding the five adjacent display pixels.

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