JP2015111307A - Method for driving electro-optic display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for driving an electro-optic display.SOLUTION: An electro-optic display is driven by using a plurality of different drive schemes. Waveforms of the drive schemes are selected such that an absolute value of a net impulse applied to a pixel for all homogeneous and heterogeneous irreducible loops divided by the number of transitions in the loops is less than 20% of a characteristic impulse (i.e., the average of absolute values of impulses required to drive the pixel between its two extreme optical states). The plurality of different drive schemes include grayscale drive schemes and monochrome drive schemes.

Description

(Refer to related applications)
This application includes US Patent Application Publication No. 2006/0280626, US Patent No. 7,012,600, US Patent No. 6,531,997, US Patent No. 6,504,524, US Patent Application Publication No. 2005. Related to U.S. Patent Application Publication No. 2005/000153, US Patent Application Publication No. 2005/0024353, US Patent Application Publication No. 2005/0270261, US Patent Application Publication No. 2005/0179642, and US Patent Application Publication No.

(Technical field)
The present invention relates to a method for driving an electro-optic display, in particular a bistable electro-optic display, and to an apparatus used in such a method. More specifically, the present invention relates to a drive method that is intended to update an electro-optic display by allowing multiple drive schemes to be used simultaneously. The present invention is particularly, but not exclusively, by having one or more types of electrically charged particles suspended in a liquid and moving through the liquid under the influence of an electric field. Intended for use with particle-based electrophoretic displays that change the appearance of the display.

  The term “electro-optic” as applied to a material or display is used herein in the conventional sense in imaging technology and has first and second display states where the display states differ in at least one optical characteristic. Refers to a material that is changed from its first to second display state by the application of an electric field to the material. The optical property is usually a color that can be perceived by the naked eye, but can be another optical property such as optical transmission, reflectance, luminescence, or in the case of a display intended for machine reading, out of the visible range. It may be another optical characteristic such as a false color in the sense of a change in the reflectance of the electromagnetic wave length.

  The term “gray state” is used herein in the conventional sense in imaging technology and refers to a state intermediate between the two extreme optical states of a pixel, not necessarily a black and white transition between these two extreme states. Does not mean. For example, several patents and published applications referenced below describe electrophoretic displays in which the extreme states are white and indigo, resulting in an intermediate “gray state” "Becomes substantially light blue. Indeed, as already mentioned, the transition between two extreme states may not be a color change at all.

The terms “bistable” and “bistable” are used herein in the conventional sense in the art, and display elements having first and second display states, wherein the display states differ in at least one optical characteristic. And the addressing pulse is stopped after any given element is driven for either its first or second display state by a finite time addressing pulse. After that, it indicates that the state lasts for at least several times, for example at least four times, the minimum duration of the addressing pulse required to change the state of the display element. In the aforementioned US Patent Application Publication No. 2002/0180687, some particle-based electrophoretic displays with gray scale capability are stable not only in their extreme black and white state, but also in their intermediate gray state. It is shown that some other types of electro-optic displays are the same. This type of display is not bistable and is appropriately referred to as “multistable”, but for convenience, the term “bistable” is used herein to encompass both bistable and multistable displays. Can do.

  The term “impulse” is used herein in the conventional sense of the integration of voltage over time. However, some bistable electro-optic media function as charge converters, for which there is an alternative definition of impulse, ie the integration of current over time (equal to the total charge applied) Can be used. Depending on whether the medium functions as a voltage time impulse converter or a charge impulse converter, an appropriate definition of impulse should be used.

  Most of the discussion below will involve one or more pixels of an electro-optic display through a transition from an initial gray level to a final gray level (which may or may not be different from the initial gray level). Focus on how to drive. The term “waveform” is used to mean an overall voltage curve over time used to accomplish a transition from one particular initial gray level to a particular final gray level. In general, such a waveform includes a plurality of waveform elements, where these elements are essentially rectangular (ie, where a given element includes a constant voltage application in a time period) The element may be referred to as a “pulse” or “drive pulse”. The term “drive scheme” means a set of waveforms sufficient to accomplish all possible transitions between gray levels for a particular display.

  Several types of electro-optic displays are known. One type of electro-optic display is a rotating two-color member type, for example, US Pat. Nos. 5,808,783, 5,777,782, 5,760,761, 6,054,071. No. 6,055,091, No. 6,097,531, No. 6,128,124, No. 6,137,467, and No. 6,147,791 (of this kind The display is often referred to as a “rotating dichroic ball” display, but the term “rotating dichroic member” is preferred as being more accurate, because in some of the above patents, the rotating member is spherical Because it ’s not.) Such a display uses a large number of small bodies (usually spherical or cylindrical) that have two or more parts with different optical properties and an internal dipole. These bodies are suspended in a liquid-filled vacuole in the matrix, which is filled with liquid so that the body rotates freely. The appearance of the display changes with the application of an electric field thereto, thereby rotating the body to various positions and changing which part of the body can be seen through the display surface. This type of electro-optic medium is generally bistable.

  Another type of electro-optic display is an electrochromic medium, for example, an electrode formed at least in part from a semiconductor metal oxide and a plurality of dye molecules that allow a reversible color change attached to the electrode. An electrochromic medium in the form of a nanochromic film is used. See, for example, O'Regan, B et al., “Nature 1991”, 353, 737, and Wood, D. et al. See, “Information Display”, 18 (3), 24 (March 2002). Also, Bach, U.S. Et al., Adv. Mater., 2002, 14 (11), 845. This type of nanochromic film is also described, for example, in US Pat. Nos. 6,301,038 and 6,870,657, and US Patent Application Publication No. 2003/0214695. This type of medium is also generally bistable.

Another type of electro-optic display is an electrowetting display, which was developed by Philips and is entitled “Performing Pixels: Moving Images on Electronic Paper” in the magazine “Nature” published on 25 September 2003. Described, and Hayes, R .; A. Et al., “Video-Speed Electronic Paper Based on.
Electrifying ", Nature, 425, 2003, 383-385. US Patent Application Publication No. 2005/0151709 shows that such an electrowetting display can be made bistable.

  Another type of electro-optic display, which has been the subject of intense research and development over the years, is a particle-based electrophoretic display in which multiple charged particles are fluidized under the influence of an electric field. Move through. An electrophoretic display may have the characteristics of good brightness and contrast, wide viewing angle, state bistability, and low power consumption compared to a liquid crystal display. Nevertheless, the long-term image quality problems of these displays have prevented their widespread use. For example, the particles that make up electrophoretic displays tend to settle, resulting in poor service life for these displays.

  As mentioned above, the electrophoretic medium requires the presence of a fluid. In the state of the art of electrophoretic media, this fluid is a liquid, but electrophoretic media can be produced using a gaseous fluid, see, for example, Kitamura, T .; Et al., “Electrical toner movement for electronic paper-like display”, IDW Japan, 2002, Paper HCS1-1, and Yamaguchi, Y. et al. Et al., “Toner display using insulating particles charged trielectrically”, IDW Japan, 2001, Paper AMD4-4. Also, US Patent Application Publication No. 2005/0001810, European Patent Applications No. 1,462,847, No. 1,482,354, No. 1,484,635, No. 1,500,971, No. 1, No. 501,194, No. 1,536,271, No. 1,542,067, No. 1,577,702, No. 1,577,703, No. 1,598,694, and International Application No. See also WO 2004/090626, WO 2004/077942 and WO 2004/001498. When the electrophoretic medium is used in an orientation that allows such precipitation, for example in the case of signs where the medium is placed in a vertical plane, such a gas-based electrophoretic medium is a liquid-based electrophoretic medium. It seems likely to be affected by the same problem of particle precipitation as the medium. In fact, particle precipitation appears to be a more serious problem in gas-based electrophoretic media than in liquid-based media, which is lower for gaseous fluids compared to liquid viscosity. This is because the viscosity allows for faster precipitation of the electrophoretic particles.

  A large number of patents and applications assigned to or in the name of Massachusetts Institute of Technology (MIT) and E Ink Corporation describe recently-encapsulated electrophoretic media. Such an encapsulated medium contains a large number of small capsules, each of which itself contains an internal phase, which is suspended in a liquid in which the medium is suspended. Encapsulating particles, and the capsule wall surrounds the inner phase. Usually, the capsule itself is held in a polymer binder, forming a coherent layer located between the two electrodes. This type of encapsulated medium is, for example, U.S. Pat.

および、米国特許出願公開番号

And US Patent Application Publication Number

および、国際出願公開第ＷＯ００／３８０００号、第ＷＯ００／３６５６０号、第ＷＯ００／６７１１０号、および第ＷＯ０１／０７９６１号、ならびに欧州特許第１，０９９，２０７（Ｂ１）号、および第１，１４５，０７２（Ｂ１）号に記述される。

And International Patent Publication Nos. WO00 / 38000, WO00 / 36560, WO00 / 67110, and WO01 / 07961, and European Patent Nos. 1,099,207 (B1) and 1,145, 072 (B1).

In many of the aforementioned patents and applications, the walls surrounding the dispersed microcapsules in the encapsulated electrophoretic medium can be replaced by a continuous phase, thereby creating a so-called “polymer dispersed electrophoretic display”. In the display, the electrophoretic medium includes a plurality of separated droplets of the electrophoretic fluid and a continuous phase of the polymer, and the dispersed droplets of the electrophoretic fluid in such a polymer dispersed electrophoretic display includes: There is no dispersive capsule membrane associated with each individual droplet, but it can be considered as a capsule or microcapsule. See, for example, the aforementioned US Pat. No. 6,866,760. Thus, for the purposes of this application, such polymer dispersed electrophoretic media are considered as sub-species of encapsulated electrophoretic media.

  Encapsulated electrophoretic displays usually do not suffer from the failure modes of conventional electrophoretic media clustering and precipitation, eg the ability to print or coat the display on a wide variety of flexible and rigid materials. (The use of the term “printing” is intended to include all forms of printing and coating, such as pre-measured coatings such as patch die coatings, slot or extrusion coatings, slides, etc. Or cascade coating, curtain coating, roll coating (knife over roll coating, front and back roll coating, etc.), gravure coating, spray coating, meniscus coating Spin coating, brush coating, air knife coating, silk screen printing process, an electrostatic printing process, heat printing process, an inkjet printing process, and other, including similar techniques, but not limited to). Thus, the resulting display can be flexible. Further, since the display media can be printed (using a variety of methods), the display itself can be made inexpensively.

  A related type of electrophoretic display is the so-called “microcell electrophoretic display”. In microcell electrophoretic displays, charged particles and fluid are not encapsulated, but instead are held in a plurality of cavities formed in a carrier medium, typically a polymer film. For example, both are described in Sipix Imaging, Inc. See International Application Publication No. WO 02/01281 and US Patent Application Publication No. 2002/0075556, assigned to.

  Electrophoretic media are often opaque (eg, in many electrophoretic media, where the particles substantially block the transmission of visible light through the display) and operate in reflective mode, but many electrophoretic media The display can be made to operate in a so-called “shutter mode”, in which the state of one display is substantially opaque and one is transparent to light. For example, the aforementioned US Pat. Nos. 6,130,774 and 6,172,798, and US Pat. Nos. 5,872,552, 6,144,361, 6,271,823, See 6,225,971 and 6,184,856. A dielectrophoretic display is similar to an electrophoretic display, but depends on changes in electric field strength and can operate in a similar mode. See U.S. Pat. No. 4,418,346.

The bistable or multi-stable behavior of particle-based electrophoretic displays, and electro-optic displays that display similar behavior (such displays can be referred to as “impulse-driven displays” below for convenience) are similar to conventional liquid crystals ( “LC”) in marked contrast to display behavior. Twisted nematic liquid crystals are neither bistable nor multi-stable, but function as voltage converters, so that applying a given electric field to the pixels of such a display can result in gray levels previously present in the pixels. Regardless, it produces a specific gray level in the pixel. In addition, LC displays are driven in only one direction (non-transparent or “dark” to transmissive or “light.” Finally, the gray level of LC display pixels is not sensitive to the polarity of the electric field. Sensitive only to its amplitude, and for practical reasons, commercially available LC displays usually reverse the electrodes of the driving field at frequent intervals. The optical display functions as an impulse converter in the first approximation, so that the final state of the pixel is not only the applied electric field and the time when this field is applied, but also the pixel before the application of the electric field. Depends on the state.

  In order to obtain a high resolution display, whether the electro-optic medium used is bistable or not, individual pixels of the display must be addressable without interference from adjacent pixels. Don't be. One way to achieve this goal is to provide an array of nonlinear elements, such as transistors or diodes, with at least one nonlinear element associated with each pixel to create an “active matrix” display. An addressing or pixel electrode that addresses one pixel is connected to an appropriate voltage source via an associated non-linear element. Usually, when the non-linear element is a transistor, the pixel electrode is connected to the drain of the transistor and this arrangement is assumed in the following description, but this is essentially arbitrary and the pixel electrode May be connected to the source of the transistor. Traditionally, in a high resolution array, the pixels are arranged in a two-dimensional array of rows and columns, so that any particular pixel has one specified row and one specified column. It is uniquely defined by the intersection. The sources of all transistors in each column are connected to a single column electrode, while the gates of all transistors in each row are connected to a single row electrode. Again, the assignment of sources to rows and gates to columns is conventional, but essentially arbitrary and can be reversed if desired. The row electrodes are connected to a row driver, which ensures that only one row is selected at any given moment. That is, when a voltage is applied to the electrodes of a selected row, it ensures that all transistors in the selected row are conductive, while when a voltage is applied to all other rows, It ensures that all transistors in these unselected rows remain non-conductive. The column electrodes are connected to column drivers that apply selected voltages to the various column electrodes to drive selected rows of pixels to a desired optical state (described above). Is for a common front power supply, which is conventionally provided on the opposite side from a non-linear array of electro-optic media and spans the entire display). After a preselected interval, known as "line address time", the selected row is disconnected, the next row is selected, and the voltage on the column driver is changed, resulting in the display being The next line is written. This process is repeated so that the entire display is written line by line.

Initially, the ideal way to address such an impulse-driven electro-optic display is for the controller to place each writing of the image so that each pixel has its first gray level to the last gray level. It can be thought of as a so-called “general grayscale image flow” that transitions directly to the level. However, inevitably there are some errors in writing an image on an impulse driven display. Some of such errors that are actually encountered include:
(A) Pre-state dependence; for at least some electro-optic media, the impulse required to switch a pixel to a new optical state is not only in the current and desired optical state, but also in the previous optical state of the pixel Dependent.
(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 that the pixel has used in its various optical states. The exact nature of this dependence is not deeply understood, but in general, the longer the pixel is in the current optical state, the more impulse is required.
(C) Temperature dependence; the impulse required to switch a pixel to a new optical state is highly temperature dependent.
(D) Humidity dependence; the impulse required to switch a pixel to a new optical state depends on the ambient humidity for at least some types of electro-optic media.
(E) Mechanical uniformity; impulses required to switch a pixel to a new optical state can be affected by mechanical changes in the display, eg, changes in the thickness of the electro-optic media or associated lamination adhesive . Other types of mechanical inhomogeneities can result from inevitable differences between different production batches of media, manufacturing tolerances and material differences.
(F) Voltage error; the actual impulse applied to the pixel is inevitably slightly different from the logically applied impulse because of the inevitable slight errors in the voltage transmitted by the driver. Different.

General grayscale image flow suffers from the “error accumulation” phenomenon. For example, temperature dependence, 0.2 L ^{* (L *} is in the positive direction at each transition, the usual CIE definition,
L ^* = 116 (R / R ₀ ) ^1/3 −16
Where R is the reflectivity and R ₀ is the standard reflectivity value). After 50 transitions, this error accumulates to 10L ^* . Perhaps more realistically, the average error at each transition is assumed to be ± 0.2 L ^* in terms of the difference between the display's theoretical and actual reflectivity. To do. After 100 consecutive transitions, the pixels display an average deviation 2L ^* from their predicted state. Such a shift is evident for an average observer for a given type of image.

  This accumulation of error phenomena not only applies to errors due to temperature, but also applies to all the above errors. As described in the aforementioned US Pat. No. 7,012,600, such errors can be corrected, but to a limited degree of accuracy. For example, the temperature error can be corrected by using a temperature sensor and a look-up table, but the temperature sensor has a limited resolution and can read a temperature slightly different from the temperature of the electro-optic medium. Similarly, pre-state dependence can be corrected by storing the pre-state 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, The accuracy of this type of correction is limited.

  Hence, the general gray scale image flow requires very precise control of the applied impulses in order to give good results. Empirically, it has been found that in the current state of the art of electro-optic display, a general grayscale image flow is not feasible on a commercial display.

Under some circumstances, it may be desirable for a single display to utilize multiple drive schemes. For example, a display with more than two gray level capabilities may have a gray scale drive scheme (“GSDS”) that can accomplish a transition between all possible gray levels, and typically between each of two gray levels. A monochrome drive scheme ("MDS") that can only achieve a transition between the two extreme optical states of a pixel of interest, MDS provides faster display rewriting than GSDS. MDS is used when all pixels that are changed during display rewrite will only transition between the two gray levels used by MDS. For example, the aforementioned US Patent Application Publication No. 2005/0001812 is a monochrome dialog box that can display a grayscale image and that allows a user to enter text associated with the displayed image. Describe a display in the form of an electronic book or similar device capable of displaying When the user is entering text, high-speed MDS
Used for quick update of the dialog box, thereby providing the user with a quick confirmation of the text entered. On the other hand, a slower GSDS is used when the entire grayscale image shown on the display is changed.

  The display can usefully use more than two drive schemes. For example, the display may have one GSDS used for updating a small area of the display and a second GSDS used when all images on the display need to be changed or refreshed. For example, a user editing a small portion of the drawing shown on the display may view the editing results using a first GSDS (which does not require a blinking display), but a second “ The “clearing” GSDS can be used to show the final edited drawing more accurately, or a new drawing can be shown on the display. In such a scheme, the second GSDS may be referred to as a “grayscale clear” drive scheme or “GSCDS”.

  As discussed in detail in the aforementioned US Patent Application Publication No. 2005/0001812, for at least some types of electro-optic displays, it is desirable that the drive scheme used be DC balanced. This means that for any series of arbitrary transitions that begin and end at the same gray level, the algebraic sum of impulses applied during the series of transitions is bounded. A DC balanced drive scheme has been found to provide more stable display performance and reduced image artifacts. Desirably, all individual waveforms in the drive scheme are DC balanced, but in practice it is difficult to make all waveforms DC balanced, and as a result The drive scheme is generally DC balanced, but is usually a mixture of a DC balanced waveform and a non-DC balanced waveform.

The use of two drive schemes that are so DC balanced in the same display can result in an overall drive scheme that is not DC balanced due to the transition loop using transitions from both drive schemes. . For example, consider a display using MDS and GSDS, and a display using a white-black-white single transition loop. The GSDS may have a net impulse of I ₁ for white-black (W → B) transitions and a net impulse of −I ₁ for B → W transitions (because it is DC balanced). Can have. Similarly, an MDS may have a net impulse of I ₂ (not equal to I ₁ ) for a white-black (W → B) transition, since it is DC balanced (because it is DC balanced). It may have a net impulse -I ₂ against. If the image is driven from white to black using GSDS and then from black to white using MDS, the net impulse for the loop is I ₁ -I ₂ , which is zero and Not equal. Furthermore, since this same loop can be repeated indefinitely, the net impulses for the loops can accumulate, so that the net impulses are not bounded and the overall drive scheme is no longer DC balanced. Not.

  The present invention provides an electro-optic display and a method for operating such a display, wherein the two driving schemes are used simultaneously so that the overall driving scheme is DC balanced or DC Guarantees that it is very close to being in equilibrium.

The present invention provides a method for driving an electro-optic display using a plurality of different drive schemes, between all uniform and non-uniform irreducible loops divided by the number of transitions in the loop. The drive scheme waveform is selected such that the absolute value of the net impulse applied to the pixel is less than 20 percent of the characteristic impulse, and the uniform irreducible loop starts at the first gray level and is zero. A sequence of gray levels that pass through or beyond the gray level and end at the first gray level, where all transitions are accomplished using the same drive scheme, and the loop is No non-gray level visits any gray level more than once, and the non-uniform irreducible loop starts at the first gray level and starts at 1 A sequence of gray levels passing through and ending at the first gray level, the loop including transitions using at least two different drive schemes to fulfill the last transition of the loop The drive scheme used is the same as the drive scheme used to accomplish the transition to the first gray level just before the start of the loop, the loop being a shorter irreducible loop The characteristic impulse is the average of the absolute values of the impulse required to drive the pixel between two extreme optical states.

  Desirably, the net impulse applied to the pixel during all uniform and non-uniform irreducible loops divided by the number of transitions in the loop is the characteristic impulse (as defined below) Less than 10 percent and preferably less than 5 percent of the characteristic impulse. Most desirably, the net impulse between all uniform and non-uniform irreducible loops is essentially zero, i.e. all such loops are DC balanced.

  In the method, the plurality of drive schemes may include a grayscale drive scheme and a monochrome drive scheme, or two grayscale drive schemes and a monochrome drive scheme. In the latter case, one of the two gray scale drive schemes may use local update of the image and the other may use global update. Alternatively, one of the two gray scale drive schemes may provide a more accurate gray level than the other, but results in more display blinking.

  The present invention may utilize any type of electro-optic media discussed above. Thus, for example, an electro-optic display can include a rotating dichroic member, an electrochromic display medium, or an electrowetting display medium. Alternatively, the electro-optic display can include a particle-based electrophoretic medium, in which a plurality of charged particles move through the fluid under the influence of an electric field. Charged particles and fluids can be encapsulated in a plurality of capsules or microcells, or can exist as a plurality of dispersed droplets in a continuous phase containing a polymer binder. The fluid can be gaseous.

  The present invention includes a layer of an electro-optic medium, at least one electrode arranged to apply an electric field to the layer of the electro-optic medium, and the electric field applied to the electro-optic medium by the at least one electrode. Extending to an electro-optic display including a controller arranged to control, the controller being arranged to carry out the method of the invention.

The display of the present invention is essentially an electro-optic display previously used, such as an ebook reader, portable computer, tablet computer, mobile phone, smart card, sign, clock, shelf label, and flash drive. It can be used in any application.
For example, the present invention provides the following items.
(Item 1)
A method of driving an electro-optic display using a plurality of different drive schemes, the method applied to pixels during all uniform and non-uniform irreducible loops divided by the number of transitions in the loop Characterized in that the waveform of the drive scheme is selected such that the absolute value of the net impulse to be made is less than 20 percent of the characteristic impulse,
A uniform irreducible loop is a sequence of gray levels that starts at a first gray level, passes through zero or more gray levels and ends at the first gray level, and all transitions are identical Accomplished using a drive scheme, the loop does not visit any gray level other than the first gray level more than once,
A non-uniform irreducible loop is a sequence of gray levels that starts at a first gray level, passes through one or more gray levels, and ends at the first gray level, the loop comprising at least 2 The drive scheme used to fulfill the last transition of the loop, including a transition using two different drive schemes, to fulfill the transition to the first gray level immediately before the start of the loop Is identical to the drive scheme used in the above, and the loop does not include a shorter irreducible loop;
The characteristic impulse is the average of the absolute values of the impulse required to drive a pixel between two extreme optical states.
Method.
(Item 2)
The absolute value of the net impulse applied to pixels during all uniform and non-uniform irreducible loops divided by the number of transitions in the loop is less than 10 percent of the characteristic impulse. The method according to 1.
(Item 3)
The absolute value of the net impulse applied to pixels during all uniform and non-uniform irreducible loops divided by the number of transitions in the loop is less than 5 percent of the characteristic impulse. 2. The method according to 2.
(Item 4)
4. The method of item 3, wherein the absolute value of the net impulse applied to a pixel during all the uniform and non-uniform irreducible loops is essentially zero.
(Item 5)
Item 2. The method of item 1, wherein the drive scheme comprises a gray scale drive scheme and a monochrome drive scheme.
(Item 6)
Item 2. The method of item 1, wherein the driving scheme comprises two gray scale driving schemes and a monochrome driving scheme.
(Item 7)
Item 7. The method of item 6, wherein one of the two gray scale drive schemes uses a local update of the image and the other uses a global update.
(Item 8)
Item 7. The method of item 6, wherein one of the two grayscale drive schemes provides a more accurate gray level than the other, but causes more blinking of the display.
(Item 9)
The method of claim 1, wherein the electro-optic display comprises a rotating dichroic member, an electrochromic display medium, or an electrowetting display medium. (Item 10)
The method of claim 1, wherein the electro-optic display comprises a particle-based electrophoretic medium in which a plurality of charged particles move through a fluid under the influence of an electric field. (Item 11)
Item 11. The method of item 10, wherein the charged particles and the fluid are encapsulated in a plurality of capsules or microcells.
(Item 12)
Item 11. The method of item 10, wherein the charged particles and the fluid are present as a plurality of dispersed droplets in a continuous phase comprising a polymer binder.
(Item 13)
11. A method according to item 10, wherein the fluid is gaseous.
(Item 14)
A layer of electro-optic medium, at least one electrode arranged to apply an electric field to the layer of electro-optic medium, and to control the electric field applied to the electro-optic medium by the at least one electrode An electro-optic display comprising a disposed controller,
14. An electro-optic display, wherein the controller is arranged to perform the method of any one of items 1-13.
(Item 15)
Item 15. An electronic book reader, portable computer, tablet computer, mobile phone, smart card, sign, clock, shelf label, or flash drive comprising the display of item 14.

  As already mentioned, the present invention provides a method for driving an electro-optic display using a plurality of different drive schemes, all the uniform and non-uniform existing divided by the number of transitions in the loop. The waveform of the drive scheme is selected so that the absolute value of the net impulse applied to the pixel during the approximately loop is less than 20 percent of the characteristic impulse.

The present invention is based on the concept of uniform and non-uniform irreducible loops. For this purpose, the gray level loop is a sequence of gray levels where the first and last gray levels are identical. For example, assuming a gray scale of 4 gray levels (2 bits), such gray levels are displayed as 1, 2, 3, and 4 from darkest to brightest. An example of a loop is
1 → 1
2 → 3 → 2
1 → 4 → 3 → 2 → 1
It is.

A uniform irreducible loop is a sequence of gray levels that starts at the first gray level, passes through zero or more gray levels, and ends at the first gray level, and all transitions have the same drive scheme. (Usually a gray level driving scheme, or “GSDS”). In general, a gray level loop can visit any gray level multiple times, while a uniform irreducible loop does not visit any gray level more than once, except for the last gray level, The last gray level must be the same as the first gray level, as already noted. For example, assuming a gray scale with four identical gray levels (2 bits), the uniform irreducible loop is
1 → 1
2 → 2
1 → 2 → 1
3 → 2 → 1 → 3
1 → 2 → 3 → 4 → 1
It is. The first loop simply transitions from gray level 1 to gray level 1, and the second loop transitions from gray level 2 to gray level 2. The third embodiment starts at gray level 1, transitions to gray level 2, and then returns to gray level 1.

The gray level loop can be uniform (ie, accomplish all transitions using the same drive scheme), but not irreducible. An example of a non-irreducible uniform loop is
1 → 2 → 3 → 2 → 1
1 → 2 → 2 → 1
3 → 2 → 3 → 2 → 3
It is. All of these loops are not irreducible because they involve repeated visits to the same gray level other than the first and last gray level, and all can be reduced to multiple irreducible loops. .

  It is readily apparent that there is a finite number of uniform irreducible loops for any number of gray levels in the gray scale.

A non-uniform loop is similar to a uniform loop, except that the non-uniform loop includes transitions that use at least two different drive schemes. In a non-uniform loop, as in the uniform loop, the first and last gray levels must be the same. Also, in a non-uniform loop, the drive scheme used to fulfill the last transition of the loop must be the same as the drive scheme previously used to fulfill the transition to the first gray level. Don't be. As an example, consider the following symbolically represented transition from gray level 1 to gray level 4 using drive scheme A on the four gray level scale described above.
1 → (a) → 4
The reverse transition from gray level 4 to gray level 1 using drive scheme B is displayed symbolically below.
A 4 → (b) → 1 heterogeneous loop can be made from these two transitions, hence
1 → (a) → 4 → (b) → 1
And the original gray level 1 state was achieved using drive scheme B as shown at the end of the loop.

It will be readily apparent that various other non-uniform loops can each be created using multiple drive schemes. A non-uniform irreducible loop can be defined as having the following two characteristics.
(A) The first and last gray levels are the same, and the drive scheme used to achieve the last gray level is the same as that used to achieve the first gray level.
(B) The non-uniform loop itself does not include an irreducible loop.

An example of a non-uniform irreducible loop is:
1 → (a) → 4 → (b) → 1 → (b) → 2 → (a) → 1
1 → (a) → 4 → (b) → 1 → (c) → 4 → (d) → 1
Examples of non-irreducible non-uniform loops are:
1 → (a) → 4 → (a) → 1 → (b) → 4 → (a) → 1
1 → (a) → 2 → (b) → 3 → (b) → 2 → (a) → 1
Because these contain irreducible loops, the first loop contains two consecutive 1 → (a) → 4 → (a) → 1 irreducible loops, and the second loop has two Includes nested irreducible loops.

It is understood that a composite uniform loop can be “decomposed” in a similar manner into irreducible loops contained within a finite series of irreducible loops and other irreducible loops. Thus, for example, 1 → 4 → 3 → 2 → 3 → 2 → 3 → 2 → 1 → 2 → 1 of a uniform loop.
Is broken down into two consecutive 2 → 3 → 2 loops contained in 1 → 4 → 3 → 2 → 1 followed by a 1 → 2 → 1 loop.

Both uniform and non-uniform loops can be decomposed in this manner into a combination of irreducible loops, so that all possible loops (ie, if all irreducible loops are DC balanced) (ie, All possible sequences that start and end at the same gray level) are D
This means that C is balanced.

  As already mentioned, when a single display utilizes multiple drive schemes, the overall drive scheme and the individual drive schemes must be DC balanced (or less desirable). It is beneficial to be substantially DC balanced in the sense that the algebraic sum of the impulses in any given loop is small. In accordance with the present invention, a drive scheme is selected such that all uniform and non-uniform irreducible loops are DC balanced, or all uniform and non-uniform in the less preferred form of the present invention. The irreducible loop is substantially DC balanced. Substantial DC balance allows small DC imbalances in some or all uniform and non-uniform loops.

As already mentioned, one preferred form of the invention uses a monochrome drive scheme and at least one clay scale drive scheme as the plurality of drive schemes. As is well known to those skilled in the electro-optic display art, a gray scale drive scheme (GSDS) can be used to make a transition from any gray level to any other gray level in gray scale. An example of a gray level sequence achieved through the action of a GSDS grayscale update is
2 → (G) 3 → (G) 1 → (G) 4 → (G) 3 → (G) 1 → (G) 3 → (G) 3 → (G) 3 (G) → 2
“→ (G)” means that the associated transition is accomplished by GSDS. This embodiment assumes a gray scale of the above four gray levels (2 bits), with gray levels displayed as 1, 2, 3 and 4 from the darkest to the brightest.

A monochrome driving scheme (MDS) can be used to accomplish transitions between gray levels belonging to a monochrome subset of gray levels, the monochrome subset including two gray levels of the aforementioned gray scale. In this example, the monochrome subset is {1, 4}, the darkest gray level and the lightest gray level (usually black and white, respectively). In any given sequence of gray levels, some transitions can be accomplished by MDS and others can be accomplished by GSDS. For example, the gray level sequence is
2 → (G) 3 → (G) 1 → (M) 4 → (M) 1 → (M) 4 → (G) 3 → (G) 1 → (M) 4 → (G) 2
“(M)” means that the associated transition is accomplished by MDS. This sequence means non-uniform updates, ie updates using a combination of GSDS and MDS.

  A particularly preferred embodiment of the present invention uses three different drive schemes: a gray scale drive scheme, a gray scale clear drive scheme and a monochrome drive scheme. Grayscale drive schemes and grayscale clear drive schemes can differ in various ways, for example, grayscale drive schemes use local updates (ie, only pixels that need to be changed are rewritten). On the other hand, the grayscale clear drive scheme may use global updates (ie, all pixels are rewritten regardless of whether their gray level is changed). Alternatively, a grayscale clear drive scheme may provide a more accurate gray level than a grayscale drive scheme, but at the cost of more flashing during the transition.

In order to achieve substantial or complete DC balance of all irreducible uniform and non-uniform irreducible loops, adjustment of the individual waveforms of the drive scheme used in the present invention is referred to in the first paragraph of this application. It can also be accomplished by any of the techniques described in various patents and applications. These techniques change the waveform depending on various previous states of the display (as a result, for example, both uniform loops 1 → 2 → 1 and 1 → 3 → 2 → 1 are 2 → 1 The waveform used for this 2 → 1 transition may be different in the two cases), achieving a balanced pair of pulses and some change in gray level, Includes the insertion of other waveform elements that may have a net impulse of zero.

Claims (1)

Invention described in this specification.