KR100885140B1 - Methods and apparatus for driving electro-optic displays - Google Patents

Abstract

The waveform driving the electro-optic display, in particular the bistable electro-optical display, includes the insertion of one or more balanced pulses into the base waveform; Deletion from the base waveform of one or more balanced pulses; And insertion into one or more zero voltage periods into the base waveform. This modification allows fine control of the gray level.

Electro-optical display, transition, gray level

Description

METHODS AND APPARATUS FOR DRIVING ELECTRO-OPTIC DISPLAYS}

The present invention relates to a method for driving an electro-optical display, in particular a bistable electro-optical display, and to an apparatus (controller) for use in such a method. More specifically, the present invention relates to a driving method which is intended to enable more precise control of the gray state of pixels of an electro-optical display. The invention also allows the drive scheme used to drive the display to remain DC balanced, while allowing such a display to compensate for the "dwell time" while the pixel stays in a particular optical state before the transition. It relates to a driving method which is intended to be driven. The present invention is used in particle-based electrophoretic displays in which, but not exclusively, one or more types of electrically charged particles are suspended in the liquid and moved through the liquid under the influence of electromagnetic fields to change the appearance of the display. Intended to.

The present application discloses International Application Publication No. WO 2005/054933, which the reader refers to as background information on the state of the art of driving electro-optic displays; WO 2005/006290; WO 2004/090857; WO 03/107315; And WO 03/044765. The following description is for convenience hereinafter "MEDEOD" (Electro-optical method for driving a display; ME thods for D riving E lectro- O ptic isplays D) may be referred to as a batch application, this assumption the read of the application in something to do.

Electro-optical displays in which the method of the present invention is used may be electro-optical materials that are solid in that the material may have a space filled with an internal liquid or gas and, nevertheless, the electro-optical material has a solid outer surface. Often includes. Such displays using solid electro-optic materials may be referred to hereinafter as "solid electro-optical displays" for convenience.

When applied to a material or display, the term “electro-optical” is used herein in its conventional sense in the image art to have a different first and second display state in one or more optical properties, which material It refers to a material that changes from its first to second display state by applying an electric field. Although optical properties are typically visually identifiable with color, in the case of displays intended for optical transmission, reflectance, cold light or machine reading, pseudo-color and The same may be other optical properties.

The term "gray state" is used herein in its conventional sense in the art to refer to a state in the middle of two extreme optical states of a pixel and does not necessarily mean a black-white transition between these two extreme states. . For example, several patents and published applications mentioned below describe electrophoretic displays in which the extreme states are white and indigo so that the intermediate "gray state" is actually light blue. Indeed, as already mentioned, the transition between two extreme states may be without color change at all. The term "gray level" is used herein to indicate a possible optical state of a pixel, including two extreme optical states.

The terms "bistable" and "bistable" are used herein in their conventional meaning in the art to include display elements having different first and second display states in one or more optical properties and having a constant duration. After any given element has been driven to take one of its first or second display states by means of addressing a pulse of C), after the end of the step of addressing the pulses, the state is indicative of the state of the display element. It refers to a display that will last for at least several times, for example, four or more times the minimum duration of the addressing pulse required to change. In published US patent application 2002/0180687, any gray-scale particle-based electrophoretic display is stable not only in its extreme black and white states, but also in its intermediate gray state, It is disclosed that the same is true for any other type of electro-optical display. The term "bistable" may be used herein to encompass both bistable and multi-stable displays for convenience, but this type of display is suitably referred to as "multi-stable" rather than bistable.

The term "impulse" is used herein in the conventional sense of the integration of voltage over time. However, some bistable electro-optical media behave as charge transducers, in which case an alternative definition of impulse, i.e., integration of current over time (same as the total applied charge) may be used. Depending on whether the medium acts as a voltage-time impulse converter or as a charge impulse converter, the appropriate definition of impulse should be used.

Much of the discussion below will focus on how to drive one or more pixels of an electro-optical display through transition from initial gray level to final gray level (which may or may not be different from the initial gray level). The term "waveform" will be used to denote the total voltage over a time curve used to cause a transition from one particular initial gray level to a particular final gray level. Typically, as illustrated below, this waveform will comprise a plurality of waveform elements, where such elements are necessarily rectangular (ie, the element given therein includes the application of a constant voltage for a period of time), and this element May be referred to as a "voltage pulse" or a "drive pulse". The term "drive scheme" denotes a set of waveforms sufficient to cause all possible transitions between gray levels for a particular display.

Several forms of electro-optic displays are known. One type of electro-optic display is described, for example, in US Pat. No. 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 a rotating bichromal member type as described in US Pat. No. 6,147,791 (although this type of display is often referred to as a "rotating bichromal ball" display, but in some of the patents described above it is a rotating member). The term "rotary dichroic member" is preferred because it is not spherical). This display uses a plurality of (usually spherical or cylindrical) small bodies with two or more compartments and different dipoles with different optical properties. These bodies are suspended in a liquid-filled vacuole in the matrix, which is charged with liquid so that the bodies are free to rotate. The appearance of the display is changed by applying an electric field to it, rotating the bodies to various positions, and changing which of the sections of the body are visible through the display surface. This type of electro-optic medium is typically bistable.

Another type of electro-optic display is an electrochromic medium, for example an electrode formed at least partially of a semiconductor metal oxide and a plurality of dyes attached to the electrode and capable of reversible color change. Using an electrochromic medium in the form of a nanochromic film containing molecules, see, for example, O'Regan, B., et al., 1991 Nature 353, 737 and Wood, D., Information Display. , 18 (3), 24 (March 2002). In addition, Bach, U., et al., Adv. See Mater., 2002, 14 (11), 845. Also, for example, US Pat. No. 6,301,038 and International Application Publication No. WO 01/27690, and US Patent Application No. 2003/0214695 disclose nanochromic films of this type. Also, this type of media is typically bistable.

Another type of electro-optic display, which has been the subject of intensive research and development for many years, is a particle-based electrophoretic display in which a plurality of charged particles move through a fluid under the influence of an electric field. Electrophoretic displays can have characteristics of excellent brightness and contrast, wide viewing angle, state bistable, and low power consumption when compared to liquid crystal displays. Nevertheless, the problem of long-term image quality of such displays has hindered its widespread use. For example, the particles that make up an electrophoretic display tend to settle, resulting in inadequate service-life for these displays.

As mentioned above, the electrophoretic medium requires the presence of a fluid. In most prior art electrophoretic media, this fluid is a liquid, but electrophoretic media can be produced using gas fluids, see, for example, Kitamura, T., et al., 2001 IDW Japan, Paper HCS1-1. See " Electric Toner Transfer for Electric Paper-Like Displays " and " Toner Display Using Nonconductive Particles Charged by Friction Electric ", 2001 IDW Japan, Paper AMD4-4 Yamaguchi, Y., et al. European Patent Application 1,429,178; 1,462,847; 1,482,354; And 1,484,625 and in international application WO 2004/090626; WO 2004/079442; WO 2004/077140; WO 2004/059379; WO 2004/055586; WO 2004/008239; WO 2004/006006; WO 2004/001498; WO 03/091799; And also WO 03/088495. When the medium is used in an orientation that allows for this precipitation, for example in a signal in which the medium is placed in a vertical plane, such gas-based electrophoretic medium is of the same type due to particle precipitation, such as liquid-based electrophoretic medium. It appears to be sensitive to the problem. Indeed, particle precipitation appears to be a more serious problem in gas-based electrophoretic media than liquid-based electrophoretic media, as the lower viscosity of the gas fluid causes electrophoretic particles to settle faster than in the case of liquid fluids. .

Numerous patents and applications assigned to the Massachusetts Institute of Technology (MIT) and to E INK disclose encapsulated electrophoretic media. This encapsulated medium comprises a number of small capsules, each of which includes an inner phase comprising electrophoretic-moving particles suspended in the fluid and includes a capsule wall surrounding the inner phase. Typically, the capsules are themselves fixed in a polymeric binder to form a coherent layer located between two electrodes. Encapsulated media of this type are described, for example, in US Pat. No. 5,930,026; 5,961,804; 6,017,584; 6,067,185; 6,118,426; 6,120,588; 6,120,839; 6,124,851; 6,130,773; 6,130,774; 6,172,798; 6,177,921; 6,232,950; 6,249,271; 6,252,564; 6,262,706; 6,262,833; 6,300,932; 6,312,304; 6,312,971; 6,323,989; 6,327,072; 6,376,828; 6,377,387; 6,392,785; 6,392,786; 6,413,790; 6,422,687; 6,445,374; 6,445,489; 6,459,418; 6,473,072; 6,480,182; 6,498,114; 6,504,524; 6,506,438; 6,512,354; 6,515,649; 6,518,949; 6,521,489; 6,531,997; 6,535,197; 6,538,801; 6,545,291; 6,580,545; 6,639,578; 6,652,075; 6,657,772; 6,664,944; 6,680,725; 6,683,333; 6,704,133; 6,710,540; 6,721,083; 6,724,519; 6,727,881; 6,738,050; 6,750,473; 6,753,999; 6,816,147; 6,819,471; 6,822,782; 6,825,068; 6,825,829; 6,825,970; 6,831,769; 6,839,158; 6,842,167; 6,842,279; 6,842,657; 6,864,875; 6,865,010; 6,866,760; 6,870,661; 6,900,851; And 6,922,276 and US Patent Application Publication No. 2002/0060321; 2002/0063661; 2002/0090980; 2002/0113770; 2002/0130832; 2002/0180687; 2003/0011560; 2003/0020844; 2003/0025855; 2003/0102858; 2003/0132908; 2003/0137521; 2003/0214695; 2003/0222315; 2004/0012839; 2004/0014265; 2004/0027327; 2004/0075634; 2004/0094422; 2004/0105036; 2004/0112750; 2004/0119681; 2004/0136048; 2004/0155857; 2004/0180476; 2004/0190114; 2004/0196215; 2004/0226820; 2004/0239614; 2004/0252360; 2004/0257635; 2004/0263947; 2005/0000813 2005/0001812; 2005/0007336; 2005/0007653; 2005/0012980; 2005/0017944; 2005/0018273; 2005/0024353; 2005/0035941; 2005/0041004; 2005/0062714; 2005/0067656; 2005/0078099; 2005/0105159; 2005/0122284; 2005/0122306; 2005/0122563; 2005/0122564; 2005/0122565; 2005/0151709; And 2005/0152022 and International Patent Application Publication No. WO 99/67678; WO 00/05704; WO 00/38000; WO 00/36560; WO 00/67110; WO 00/67327; WO 01/07961; And WO 03 / 107,315.

Many of the patents and applications described above allow the walls surrounding individual microcapsules in an encapsulated electrophoretic medium to be replaced by a continuous phase, so that the electrophoretic medium may contain a plurality of individual droplets of the electrophoretic fluid and a polymeric material. Produces a so-called "polymer-dispersed electrophoretic display" comprising a continuous phase, in which individual droplets of electrophoretic fluid in such a polymer-disperse electrophoretic display are separated from each individual capsule membrane. It is recognized that even if not associated with, it may also be considered as a capsule or microcapsules, see for example 2002/0131147, supra. Thus, for the purposes of the present application, such polymer-disperse electrophoretic media are considered as sub-species of encapsulated electrophoretic media.

Encapsulated electrophoretic displays typically do not suffer from the clustering and settling failure modes of conventional electrophoretic devices, such as the ability to print or coat a display on a variety of flexible or rigid substrates. It offers many advantages. (The use of the word "printing" is, without limitation, pre-metered such as patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating. Coating; roll coating such as knife over roll coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus Coatings including meniscus coating; spin coating; brush coating; air knife coating; silk screen printing process; electrostatic printing process; thermal printing process; inkjet printing process; and other similar techniques It is intended to include all forms of coating.) Thus, the resulting display is flexible. In addition, since the display medium can be printed (using various methods), the display itself can be manufactured at low cost.

A related type of electrophoretic display is the so-called "microcell electrophoretic display". In microcell electrophoretic displays, charged particles and fluids are not encapsulated inside the capsule, but instead remain in a plurality of cavities formed in a carrier medium, typically a polymeric membrane. See, eg, International Application Publication No. WO 02/01281 and US Patent Application Publication No. 2002/0075556, all assigned to Sipix Image, Inc.

Other types of electro-optical media may also be used in the displays of the present invention.

Electrophoretic media often operate in an opaque and reflective mode (eg, in many electrophoretic media, since the particles substantially prevent the transmission of visible light through the display), but many electrophoretic displays operate in one display state. Can be manufactured to operate in a so-called "shutter mode" which is substantially opaque and one is light-transmissive. See, for example, US Pat. Nos. 6,130,774 and 6,172,798 and US Pat. Nos. 5,872,552; 6,144,361; 6,271,823; 6,225,971; See 6,184,856. Dielectrophoretic displays, which are similar to electrophoretic displays but rely on electric field intensity variations, can operate in a similar mode, see US Pat. No. 4,418,346.

The bistable or multistable properties of particle-based electrophoretic displays and other electro-optical displays that display in a similar manner (such displays may be referred to herein for convenience as "impulse driven displays") are known in the art of conventional liquid crystal ("LC" ) It is significantly different than the display. Twisted nematic liquid crystals are not bistable or multistable, but behave like voltage converters, so that the application of a given electric field to a pixel of such a display is at that pixel, regardless of the gray level previously present at that pixel. Generate a specific gray level. In addition, the LC display is driven in only one direction (from non-transmissive or "dark" to transmissive or "bright"), and the reverse transition from the brighter to the darker state is caused by the reduction or elimination of the electric field. As a result, the gray level of the pixels of the LC display is not sensitive to the polarity of the electric field, but only to the magnitude of the electric field, and as a practical technical factor, commercial LC displays generally reverse the polarity of the driving field at frequent intervals. In contrast, the bistable electro-optic display operates in an first approximation, as an impulse converter, so that the final state of the pixel depends not only on the applied electric field and the time the field is applied, but also on the state of the pixel before application of the electric field.

An ideal way of addressing such an impulse-driven electro-optic display is a so-called "general gray scale," in which the controller arranges each write of an image such that each pixel directly transitions from its initial gray level to its final gray level. Image flow ". Inevitably, however, there are some errors in writing images to the impulse-driven display. Some of those errors that you actually face include:

(a) previous state dependence; In at least some electro-optical media, the impulse needed to switch a pixel to a new optical state does not only depend on the current and desired optical state, but also on the previous optical state of that pixel.

(b) residence time dependence; In at least some electro-optical media, the impulse needed to switch a pixel to a new optical state depends on the time the pixel spent in its various optical states. The exact nature of this dependency is not known, but in general, the longer a pixel is in its current optical state, the more impulses are required.

(c) temperature dependence; The impulse needed to switch the pixel to a new optical state is strongly dependent on temperature.

(d) humidity dependence; In at least some types of electro-optic media, the impulse needed to switch the pixel to a new optical state depends on the ambient humidity.

(e) mechanical uniformity; The impulse needed to switch the pixel to a new optical state may be affected by mechanical changes in the display, for example by changing the thickness of the electro-optic medium or associated lamination adhesive. Other types of mechanical non-uniformity may arise from the inevitable differences between different batches of manufacturing of media, manufacturing tolerances, and material diversity.

(f) voltage error; Because of the inevitable small error in the voltage delivered by the driver, the actual impulse applied to the pixel is necessarily slightly different from that applied in theory.

Typical grayscale image flows suffer from "accumulation of errors." For example, temperature dependence is 0.2 L * in the positive direction for each transition, where L * has a normal CIE definition:

L * = 116 (R / R ₀ ) ^1/3 -16,

Where R is the reflectivity and R ₀ is the standard reflectance value. After 50 transitions, this error will accumulate to 10 L *. Perhaps more practically, assume that the mean error for each transition, expressed as the difference between the theoretical and actual reflectance of the display, is ± 0.2 L *. After 100 successive transitions, the pixels will display an average deviation of 2L * from their expected state, which deviation is identified to the average observer of some type of image.

This accumulation of error phenomena applies not only to errors due to temperature, but also to all types of errors listed above. As described in the above-mentioned US Patent Publication 2003/0137521, compensation for such errors is possible, but only to a limited degree of accuracy. For example, the temperature error may be compensated for using a temperature sensor and lookup table, but the temperature sensor may have a limited resolution and read a temperature slightly different from the temperature of the electro-optic medium. Similarly, the previous state dependence can be compensated for storing the previous state and using a multidimensional transition matrix, but the controller memory limits the number of states that can be written and the size of the transition matrix that can be stored, which is such a compensation. Limit the type precision.

Thus, a typical grayscale image flow requires very precise control of the applied impulse to provide good results, and empirically it has been found that in the current state of electro-optic display technology, the typical grayscale image flow is not feasible in commercial displays. .

Almost all electro-optical media have their extreme (typically black and white) optical states acting as built-in resetting (error limiting) mechanisms, ie "optical rails". After a particular impulse is applied to a pixel of an electro-optic display, that pixel cannot get more white (or black). For example, in an encapsulated electrophoretic display, after a particular impulse is applied, all the electrophoretic particles are forced to each other or to the capsule wall and can no longer move, thus limiting the limited optical state or optical rail. Create Because of the distribution of electrophoretic particle size and charge in such media, some particles hit the rails before other particles, causing a "soft rail" phenomenon, whereby the final optical state of the transition is its extreme black and white When the state is reached, the required impulse accuracy is reduced, while the optical accuracy required at transitions ending near the center of the pixel's optical range is significantly increased.

Various types of drive schemes for electro-optic displays using optical rails are known. For example, the relevant descriptions in FIGS. 9 and 10 and paragraphs [0177] through [0180] of 2003/0137521 described above are “slides” in which the entire display is driven with one or more optical rails before any new image is written. Show "drive method. Clearly, a pure general grayscale image flow driving scheme cannot rely on the use of optical rails to prevent errors in gray levels, where any given pixel is gray level without touching either optical rail. Because they can go through an infinite number of changes.

Before moving on, it is desirable to define the slideshow driving method more accurately. The basic slideshow driving scheme is that the transition from the initial optical state (gray level) to the final (desired) optical state (gray level) is achieved by causing a transition from a finite number of intermediate states, where the minimum number of intermediate states Is one. Preferably, the intermediate state is at or near the extreme state of the electro-optical medium used. The transition will be different pixel by pixel in the display since the transition depends on the initial and final optical state. The waveform for a particular transition at a given pixel in the display is

R _2- > Goal _1- > Goal _2- >...-> Goal _n- > R ₁ (Method 1)

Or one or more intermediate or target states exist between the initial state R ₂ and the final state R ₁ . The target state is generally a function of the initial and final optical states. Currently the number of preferred intermediate states is two, but more or less intermediate states may be used. Each individual transition within the entire transition is achieved using a waveform element (typically a voltage pulse) sufficient to drive the pixel from one state of the sequence to the next. For example, in the waveforms symbolically indicated above, the transition from R ₂ to target ₁ is typically accomplished with waveform elements or voltage pulses. This waveform element may be a single voltage (ie, a single voltage pulse) for a finite time, or may include various voltages such that an accurate target ₁ state is achieved. This waveform element precedes the second waveform element for achieving a transition from target ₁ to target ₂ . If only two target states are used, the second waveform element precedes the third waveform element driving the pixel from the target _two state to the final optical state R ₁ . The target state may be independent of both R ₂ and R ₁ , or may depend on one or both.

The present invention seeks to provide an improved slide show driving scheme for electro-optical displays that achieves improved control of gray levels. The invention is in particular, but not exclusively, a pulse width adjusted drive scheme where the voltage applied to any given pixel of the display at any given moment can be only -V, 0 or + V, where V is any voltage. It is intended for use in More specifically, the present invention provides two distinct types of improvements in the slide show drive scheme, namely (a) the insertion of any modification element into the base waveform for this drive scheme; And (b) defining the drive scheme such that at least some gray level is accessed from the optical rail from the desired gray level.

In another aspect, the invention relates to residence time compensation in a drive scheme for an electro-optical display. As discussed in the MEDEOD application, for at least many particle-based electro-optic displays, the impulse required to change a given pixel through the same change in the gray level (as determined by the naked eye or standard optics) must be It has been found that it is not constant and is not necessarily a substitute. For example, consider a display where each pixel can display gray levels of 0 (white), 1, 2, or 3 (black) that are beneficially spaced apart from each other. (The spacing between levels may be linear at percent reflectance as measured by the naked eye or instrument, but other spacing may be used. For example, the spacing may be linear at L * or to provide a particular gamma. A gamma of 2.2 may often be chosen for monitors, and when electro-optical displays are used as a replacement for the monitor, the use of similar gamma may be desirable.) Change pixel from level 0 to level 1 (after It has been found that the impulse required to conveniently refer to "0-1 transition" is often not the same as that required for 1-2 transition or 2-3 transition. Also, the impulse required for a 1-0 transition is not necessarily the same as the inverse of that required for a 0-1 transition. In addition, some systems have been shown to display a "memory" effect (say) that the impulse needed for a 0-1 transition is somewhat dependent on whether a particular pixel undergoes a 0-0-1, 1-0-1 or 3-0-1 transition. Change depending on (In the "xyz" notation, x, y, z are all optical states, and 0, 1, 2, 3 represent a sequence of optical states that undergo successively from beginning to later with time.) These problems are necessary While driving or reducing all pixels of the display to one of the extreme states for quite some time before driving the pixels to another state, the resulting “flash” of solid color is often unacceptable, for example For example, an ebook reader may wish to scroll down the screen of a book's text, and if the display needs to flash solid black or white frequently, the reader will be disturbed or lost where he reads. In addition, the flash of such a display increases energy consumption and decreases the operating lifetime of the display. As a result, in at least constant cases, it has been found that the impulse required for a particular transition is affected by the temperature and the total operating time of the display, and that compensation for these factors is desirable to ensure accurate gray scale rendition. .

As briefly described above, it has been found that, at least in certain cases, the impulse required for a given transition in a bistable electro-optic display varies with the residence time of a pixel in its optical state, and in some prior art documents Although "stay time sensitivity" was used, this phenomenon is hereinafter referred to as "stay time dependent" or "DTD". Thus, it is desirable to change the applied impulse for a given transition as a function of the residence time of the pixel in its initial optical state and in some cases may actually be necessary.

The residence time dependence phenomenon will be described in detail with reference to FIG. 1 of the accompanying drawings, showing that the reflectance of the pixel is a function of time for the sequence of transitions represented by R ₃ → R ₂ → R ₁ , where each R _k term (generalizing the name used above) represents the gray level in the sequence of gray levels, where R of the large index value occurs before R of the small index value. R ₃ and R ₂ Transition between R ₂ And R ₁ Degree of transition between Also Is displayed. DTD is the change in the final optical state R ₁ caused by the change in time spent in the optical state R ₂ called retention time. The DTD is compensated for by selecting different waveforms for different residence times or different ranges of residence times in the previous optical state. This compensation method is called "retention-time compensation", "DTC" or simply "time compensation".

However, this DTC may conflict with other desirable properties of the drive scheme. In particular, for reasons discussed in detail in MEDEOD applications, in any transitional series where the driving scheme used for many electro-optical displays starts and ends in the same optical state, the applied impulse (ie, applied over time) In the sense that the integral of the voltage) is zero, it is very desirable to make the DC balance. This ensures that the total impulse experienced by a pixel of the display (also called "DC imbalance") is limited by known values regardless of the exact series of transitions experienced by that pixel. For example, a 15 V, 300 msec pulse may be used to drive the pixel from white to black. After this transition, the pixel experienced 4.5 V sec of DC unbalanced impulse. If a -15 V, 300 msec pulse is used to drive the pixel back to white, then the pixel is DC balanced for the entire application from white to black and back to white. This DC balance must be maintained for all possible appeasements of the series of optical states that are the same or different from the original optical state in one original optical state but return back to the original optical state.

The drive scheme may be voltage retention-time-compensated by adding to or removing from or from the base drive scheme. For example, we can start with a drive scheme for two optical state (black and white) displays, which drive includes four waveforms:

Table 1

This drive scheme is DC balanced because any series of transitions that brings a pixel into its initial optical state is DC balanced, i.e., the total area under the voltage profile for the entire series of transitions is zero.

Optical errors can arise from the DTD of the display. For example, a pixel can start in a white state, be driven to a black state, stay briefly, and then return to a white state again. The final white state reflectance is a function of the time spent in the black state.

It is desirable to have a very small DTD. If this is not possible in certain electro-optical displays, in accordance with one aspect of the invention, it is desirable to compensate the DTD by selecting different waveforms for different ranges of residence time in the previous optical state. For example, the final white state in the example just given may be found to be brighter after a short residence time in the previous black state than after a long residence time in the previous black state. One dwell-time-compensation scheme is to modify the duration of the pulse that brings the pixel layer from black to white to offset this DTD of the final optical state. For example, it is possible to shorten the pulse length in the transition from black to white when the dwell time in the previous black state is short, and to keep the pulse longer for long dwell times in the previous black state. This tends to produce darker white states for shorter pre-state dwell times, and offsets the effects of DTD. For example, according to Table 2 below, it is possible to select a waveform from black to white that varies with residence time in a black state.

TABLE 2

The problem with this approach to the DTC of the drive scheme is that the drive scheme as a whole is no longer DC balanced. Since the impulse for the transition from black to white is a function of the time spent in the black state, and similarly the impulse for the transition from white to black may be a function of the residence time in the white state, from black to white back to black The total impulse for the sequence of is, in general, not DC balanced. For example, -15 V = -4.2 V sec impulse for 280 msec preceding a transition from white to black using a voltage pulse of 15 V for 400 msec for an impulse of 6 V sec after a long residence time in the white state Assume this sequence is performed with a transition from black to white after a short residence time in black using a voltage pulse of. The total impulse in this sequence (black-white-black loop) is -4.2 V sec + 6 V sec = 1.8 V sec. Repeating this loop results in the establishment of DC imbalance, which can interfere with the performance of the display.

Accordingly, this aspect of the present invention provides a method for the retention time compensation of a DC balanced waveform or a drive scheme that preserves the DC balance of the waveform or drive scheme.

Another aspect of the invention is directed to a method and apparatus for driving an electro-optical display that allows for quick response to user input. The MEDEOD application described above describes some methods and controllers for driving electro-optical displays. Most of these methods and controllers are memory having two image buffers, the first storing the first or initial image (present on the display at the beginning of the transition or rewriting of the display) and the second on the display after rewriting. Use a memory with a buffer to store the final image you want to place. The controller compares the initial and final images, and if they are different, the drive voltage of the display causing the pixels to undergo a change in optical state such that the final image is formed on the display at the end of the rewrite (also called update). Applies to several pixels.

However, in most of the methods and controllers described above, the updating operation is "atomic" in the sense that once the update has started, the memory will not accept any new image data until the update is complete. This causes difficulties when it is desirable to use a display for an application that accepts user input, for example, via a keyboard or similar data input device because the controller does not respond to user input during the update. In electrophoretic media, where the transition between two extreme optical states may take several hundred milliseconds, this nonconforming period may vary from about 800 to about 1800 milliseconds, most of which is due to electro-optic material This is due to the update cycle required. The duration of the nonconforming period may be reduced by eliminating some of the performance artifacts that increase the update time and improving the response speed of the electro-optic material, but this technique alone would be difficult to reduce the nonconforming period to less than about 500 milliseconds. will be. This is still longer than desired for interactive applications such as electronic dictionaries where the user expects a quick response to user input. Therefore, there is a need for an image updating method and controller with reduced dead time.

This aspect of the present invention utilizes the concept of asynchronous image updating (see Zhou et al. "Active Matrix Electrophoretic Display" in the procedure of SIDA 2004) to significantly reduce the duration of non-conforming periods. The method described in this paper has only a slight increase in controller complexity and memory requirements, and uses an already developed structure for gray scale image display to reduce dead periods by 65 percent compared to conventional methods and controllers.

As a result, the present invention relates to a method and apparatus for driving an electro-optical display in which data used to define the drive scheme is compressed in a particular way. The MEDEOD application described above describes a method and apparatus for driving an electro-optical display in which data defining the driving scheme used is stored in one or more look-up tables (“LUT's”). Such LUTs must of course contain data defining the waveforms for each waveform of its drive or each drive, and a single waveform typically requires multiple bytes. As described in the MEDEOD application, the LUT must consider two or more optical states with adjustments to factors such as temperature, humidity, media operating time, and so on. Therefore, the amount of memory required to hold waveform information is important. It is desirable to reduce the amount of memory allocated to waveform information to reduce the cost of the display controller. A simple compression scheme that can be practically adapted to the display controller or host computer will help to reduce the display controller cost. The present invention relates to a simple compression scheme which is particularly advantageous for electro-optical displays.

Thus, one aspect of the present invention provides a method of driving an electro-optical display having one or more pixels capable of achieving three or more different gray levels comprising two extreme optical states. The method comprises one or more reset pulses sufficient to drive a pixel to or near one of the extreme optical states on the pixel, followed by one or more set pulses sufficient to drive the pixel at a gray level different from the one extreme optical state. And applying a base waveform including the above reset pulse. However, the base waveform is modified by one or more of the following:

(a) insertion of one or more balanced pulse pairs into the base waveform;

(b) deletion of one or more balanced pulse pairs from the base waveform; And

(c) the insertion of one or more periods of zero voltage into the base waveform,

Here a "balanced pulse pair" indicates a sequence of two pulses of opposite poles such that the total impulse of the balance pulse is necessarily zero.

Hereinafter, for convenience, this method of the present invention may be referred to as the "balanced pulse pair slide show" or "BPPSS" method of the present invention. If this method involves modification of the base waveform by insertion or deletion of one or more balanced pulse pairs (“BPP”), the two pulses of the balanced pulse pair may each be constant voltage but of opposite polarity and may be the same length. If the modification of the base waveform includes the deletion of one or more BPPs, the period of the base waveform occupied by the deleted BPP or each thereof may be replaced by a period of zero voltage, and alternatively, other elements of the base waveform It may be shifted in time to occupy a period previously occupied by the deleted BPP or each thereof, and a period of zero voltage may be inserted at a point in time that differs from that occupied by the deleted BPP or each thereof. .

In a preferred form of the BPPSS method of the present invention, the basis waveform is continuously, at or near the first reset pulse, its other extreme optical state, sufficient to drive the pixel to or near its extreme optical state. A second reset pulse sufficient to drive the signal, and one or more set pulses.

The BPPSS method may be performed using a drive circuit capable of voltage regulation, pulse width adjustment, or both. However, this is found to be particularly useful in a three-level driving scheme where a voltage of 0, + V or -V is applied to the pixel when V is a predetermined drive voltage at some point in time.

For reasons detailed in the following, in the BPPSS method, it is desirable to limit the total number of modifications to the base waveform (ie, the total number of inserted or deleted balanced pulse pairs and zero voltage inserted periods). In general, the total number of such modifications will not exceed 6, hopefully not more than 4 and preferably not more than 2.

As discussed above in the MEDEOD application and below, the BPPSS method of the present invention is preferably DC balanced, and if possible, it is also preferred that each individual waveform of the drive scheme used is DC balanced.

The BPPSS method of the present invention may be used with any type of electro-optical display discussed above. Thus, for example, the display may comprise a rotating dichroic member or an electrochromic medium. Alternatively, the display may include an electrophoretic electro-optical medium comprising a plurality of electrically charged particles that can move through the fluid within the fluid and upon application of an electric field to the fluid. In this type of display, the fluid may be a gas or a liquid. Charged particles and fluids may be localized in a plurality of capsules or microcells.

The present invention extends to a display controller, application specific integrated circuit or software code configured to perform the BPPSS of the present invention.

In another aspect, the present invention provides a method of driving an electro-optical display having a plurality of pixels, each pixel capable of achieving at least four different gray levels comprising two extreme optical states, the method Applies to each pixel a waveform comprising a reset pulse sufficient to drive the pixel to or near its extreme optical state and a set pulse sufficient to drive the pixel following it to a final gray level different from the one extreme optical state. Wherein the reset pulse is selected such that the image on the display immediately before the set pulse is substantially the inverse of the monochrome projection of the final image following the set pulse.

In the following, for convenience, this method of the present invention may be referred to as the "reverse monochrome projection" or "IMP" method of the present invention. As described in more detail below, the monochrome projection of a gray scale image is a gray in one extreme optical state or in a gray state (eg, white and light gray pixels) closer to one extreme optical state than a predetermined threshold. Every pixel in the scale image is a projection that changes to or near the extreme optical state (e.g. white), while the gray state (e.g., closer to the opposite extreme optical state than the opposite extreme optical state or threshold). For example, pixels of black and dark grey) change to opposite extreme optical states (eg black) or near thereto. Inverse monochrome projection is the inverse of monochrome projection.

In a preferred form of the IMP method of the invention, a first reset pulse sufficient to drive each pixel to or near its extreme optical state, a second enough to drive each pixel to or near its other extreme optical state A waveform comprising a reset pulse and a set pulse is applied to each pixel, and the first reset pulse is selected such that the image on the display immediately before the second reset pulse is substantially a monochrome projection of the final image following the set pulse. .

In the IMP method, the waveform may be modified by:

(a) inserting one or more balanced pulse pairs into a waveform;

(b) deletion of one or more balanced pulse pairs from the waveform; And

(c) the insertion of one or more periods of zero voltage into the waveform,

"Balanced pulse pair" is defined as above. In this modified waveform, the two pulses of the balanced pulse pair may each be constant voltage but of opposite polarity and the same length. When the modification of the base waveform includes the deletion of one or more BPPs, the period of the base waveform occupied by the deleted BPP or each thereof may be replaced by a period of zero voltage, and alternatively, other elements of the base waveform It may be shifted in time to occupy a period previously occupied by the deleted BPP or each thereof, and a period of zero voltage may be inserted at a point in time that differs from that occupied by the deleted BPP or each thereof. .

In addition to the BPPSS method, the IMP method of the present invention may be performed using a drive circuit capable of voltage regulation, pulse width adjustment, or both. However, the IMP method is found to be particularly useful for a three-level driving scheme where a voltage of 0, + V or -V is applied to a pixel at some point in time when V is a predetermined drive voltage. In addition to the BPPSS method, the IMP method may also be used with any type of electro-optical display discussed above. Thus, for example, the display may comprise a rotating dichroic member or an electrochromic medium. Alternatively, the display may include an electrophoretic electro-optical medium comprising a plurality of electrically charged particles that can move through the fluid within the fluid and upon application of an electric field to the fluid. In this type of display, the fluid may be a gas or a liquid. The charged particles and fluid may be trapped into a plurality of capsules or microcells.

The present invention extends to a display controller, application specific integrated circuit or software code configured to perform the IMP method of the present invention.

In another aspect, the present invention provides a method of driving an electro-optical display having one or more pixels capable of achieving two or more different gray levels, wherein the two or more different waveforms are pixels in the state where the transition begins. The two waveforms differ from each other by one or more of the following, depending on the duration of the residence time of:

(a) Insertion of one or more balanced pulse pairs

(b) deletion of one or more balanced pulse pairs; And

(c) inserting one or more periods of zero voltage,

"Balanced pulse pair" is defined as above.

Hereinafter, for convenience, this method of the present invention may be referred to as the "retention time compensated balanced pulse pair" or "DTCBPP" method of the present invention. In this way, the overall drive scheme is very hopefully DC balanced, and preferably all waveforms are themselves DC balanced. If this method involves modification of the base waveform by insertion and deletion of one or more BPPs, the two pulses of the balanced pulse pair are each of constant voltage but of opposite polarity and may be the same length. If the modification of the base waveform includes the deletion of one or more BPPs, the period of the base waveform occupied by the deleted BPP or each thereof may be replaced by a period of zero voltage, and alternatively, other elements of the base waveform It may be shifted in time to occupy a period previously occupied by the deleted BPP or each thereof, and a period of zero voltage may be inserted at a point in time that differs from that occupied by the deleted BPP or each thereof. .

In addition to the BPPSS method and the IMP method, the DTCBPP method of the present invention may be performed using a driving circuit capable of voltage regulation, pulse width adjustment, or both. However, the DTCBPP method is found to be particularly useful for a three-level drive scheme where a voltage of 0, + V or -V is applied to a pixel at some point in time when V is a predetermined drive voltage. For reasons detailed in the following, in the DTCBPP method, it is desirable to limit the total number of modifications to the base waveform (ie, the total number of inserted or deleted balanced pulse pairs and zero voltage inserted periods). In general, the total number of such modifications will not exceed 6, hopefully not more than 4 and preferably not more than 2.

In addition to the BPPSS and IMP methods, the DTCBPP method of the present invention may be used with any type of electro-optical display discussed above. Thus, for example, the display may comprise a rotating dichroic member or an electrochromic medium. Alternatively, the display may include an electrophoretic electro-optical medium comprising a plurality of electrically charged particles that can move through the fluid within the fluid and upon application of an electric field to the fluid. In this type of display, the fluid may be a gas or a liquid. The charged particles and fluid may be trapped into a plurality of capsules or microcells.

The present invention extends to a display controller, application specific integrated circuit or software code configured to perform the DTCBPP method of the present invention.

In another aspect, the present invention provides two related methods of reducing the dead period when the electro-optical display is updated. The first of such methods is to use to drive an electro-optic display with a plurality of pixels, where each pixel can achieve two or more different gray levels, the method being:

(a) providing a final data buffer arranged to receive data defining a desired final state of each pixel of the display;

(b) providing an initial data buffer arranged to store data defining an initial state of each pixel of the display;

(c) providing a target data buffer arranged to store data defining a target state of each pixel of the display;

(d) determining when the data in the initial and final data buffers differ and when such differences are found; (i) when the initial and final data buffers contain the same value for a particular pixel, Set to this value (ii) when the initial data buffer contains a larger value than the final data buffer for a particular pixel, set the target data buffer to the value of the sum of the initial data buffer and the increment; And (iii) updating the value of the target data buffer by setting the target data buffer to an initial data buffer and the value of the incremental subtraction when the initial data buffer includes a smaller value than the final data buffer for a particular pixel. ;

(e) updating the image on the display using the data of the initial data buffer and the target data buffer as the initial and final states of each pixel, respectively;

(f) after step (e), copying data from the target data buffer to the initial data buffer; And

(g) repeating steps (d) to (f) until the initial and final data buffers contain the same data.

The second of these two methods is to use to drive an electro-optic display with a plurality of pixels, where each pixel can achieve three or more different gray levels, the method being:

(a) providing a final data buffer arranged to receive data defining a desired final state of each pixel of the display;

(b) providing an initial data buffer arranged to store data defining an initial state of each pixel of the display;

(c) providing a target data buffer arranged to store data defining a target state of each pixel of the display;

(d) providing an array of polarity bits arranged for storing polarity for each pixel of the display;

(e) determining when the data in the initial and final data buffers differ and, when such differences are found, (i) the values for the particular pixel of the initial and final data buffer and the value of the initial data buffer are extremes of the pixel. When indicating the optical state, set the polarity bit for the pixel to a value that indicates the transition to the opposite extreme optical state. (Ii) When the value for a particular pixel in the initial and final data buffers is different, Updating the values of the polarity bit array and the target data buffer by setting the target data buffer to the value of the sum or subtraction of the initial data buffer and the increment according to the associated value;

(f) updating the image on the display using the data of the initial data buffer and the target data buffer as the initial and final states of each pixel, respectively;

(g) after step (f), copying data from the target data buffer to the initial data buffer; And

(h) repeating steps (e) to (g) until the initial and final data buffers contain the same data.

In the following, these two related methods may be referred to as "target buffer" or "TB" methods of the present invention for convenience. When it is desirable to distinguish between the two methods, the former may be referred to as the "non-polar target buffer" or "NPTB" method, and the latter may be referred to as the "polar target buffer" or "PTB". The invention extends to a display controller, application specific integrated circuit or software code configured to perform the TB method of the invention.

As a result, the present invention provides a method of reducing the amount of data that needs to be stored to drive an electro-optical display. Accordingly, the present invention provides a method of driving an electro-optical display having a plurality of pixels, wherein each pixel can achieve two or more different gray levels, the method comprising:

Storing a base waveform that determines a sequence of voltages to be applied during a particular transition by a pixel between gray levels;

Storing the multiplication factor; And

Causing said particular transition by applying said sequence of voltages to said pixel for a period of time dependent on said multiplication factor.

In the following, for convenience, this method may be referred to as the "waveform compression" or "WC" method of the present invention.

As already mentioned above, Figure 1 of the accompanying drawings shows the reflectance of a pixel of an electro-optical display as a function of time and illustrates the phenomenon of residence time dependence.

2A and 2B illustrate waveforms for two different transitions in the prior art three reset pulse slide show drive scheme of the type described in the aforementioned MEDEOD application.

2C and 2D illustrate the variation in time of reflectance of two pixels of an electro-optical display to which the waveforms of FIGS. 2A and 2B are applied, respectively.

3A and 3B illustrate waveforms for two different transitions in the prior art two reset pulse slide show drive scheme of the type described in the aforementioned MEDEOD application.

4A, 4B and 4C illustrate balanced pulse pairs that may be used to modify prior art slide show waveforms as shown in FIGS. 2A, 2B, 3A and 3B, in accordance with the BPPSS method of the present invention.

5A illustrates a waveform of a prior art two reset pulse slide show drive scheme.

5B-5D illustrate the BPPSS waveform of the present invention generated by modifying the waveform of FIG. 5A.

FIG. 6A illustrates the same prior art basis waveform as FIG. 5A.

6B-6D illustrate the BPPSS waveform of the present invention generated by the deletion of the balanced pulse pair from the base waveform of FIG. 6A.

7A illustrates the BPPSS waveform of the present invention generated by inserting a balanced pulse pair between two base waveform elements of the base waveform.

FIG. 7B illustrates the BPPSS waveform of the present invention generated by inserting the same balanced pulse pair as in FIG. 7A within a single base waveform element of the same base waveform as in FIG. 7A.

FIG. 8A illustrates the same conventional basis waveform as FIGS. 5A and 6A.

8B-8D illustrate the BPPSS waveform of the present invention generated by inserting a period of zero voltage at different positions in the base waveform of FIG. 8A.

9A and 9B illustrate prior art base waveforms that may be modified to generate the BPPSS waveform of the present invention.

FIG. 9C illustrates the BPPSS waveform of the present invention generated by inserting two balanced pulse pairs into the base waveform of FIG. 9B.

FIG. 9D illustrates the BPPSS waveform of the present invention generated by inserting a balanced pulse pair and a period of zero voltage into the base waveform of FIG. 9B.

10A-10C and 11A-11C illustrate the BPPSS waveform of the present invention generated by modifying the base waveforms of FIGS. 9A and 9B.

12 is a symbolic representation of the reverse monochrome projection method of the present invention.

FIG. 13 illustrates how the gray levels of a gray scale image are mapped to the monochrome projection of the image, as may occur in the preferred reverse monochrome projection of the present invention.

14 and 15 show selected waveforms used during the first reverse monochrome projection method of the present invention.

16 is a symbolic representation similar to the symbolic representation of FIG. 12 of the reverse monochrome projection method of the present invention.

FIG. 17 illustrates a modification of one of the IMP waveforms shown in FIG. 14 through insertion of a balanced pulse pair into the waveform.

FIG. 18 illustrates a modification of one of the IMP waveforms shown in FIG. 14 through deletion of a balance pulse pair from the waveform.

19 illustrates a modification of one of the IMP waveforms shown in FIG. 17 by a change in the position of insertion of a balanced pulse pair.

20 illustrates a modification of one of the IMP waveforms shown in FIG. 18 by a change in the position at which the balanced pulse pair is deleted.

21 illustrates a waveform of the IMP drive scheme of the present invention in a very schematic manner.

FIG. 22 is a graph showing gray levels generated by the driving scheme shown in FIG. 21.

FIG. 23 illustrates a modified form of the IMP driving scheme shown in FIG. 21 in the same manner as in FIG. 21.

FIG. 24 is a graph showing gray levels generated by the modified driving scheme shown in FIG.

25A-25E illustrate a set of dwell time compensated waveforms used in the first dwell time compensated balanced pulse pair drive scheme of the present invention.

26A-C illustrate a set of dwell time compensated waveforms used in the second dwell time compensated balanced pulse pair drive scheme of the present invention.

From the foregoing summary, it will be seen that the present invention provides a number of different methods of driving an electro-optic display, in particular a bistable electro-optical display, and the equipment and software code configured to perform such a method. While the various methods of the present invention are primarily described separately below, it should be understood that a single electro-optical display or component thereof may utilize one or more aspects of the present invention. For example, a single electro-optical display may utilize the BPPSS, IMP, and DTCBPP aspects of the present invention. Preferred forms of balanced pulse pairs are patterns that utilize such pulse pairs, such as adjusting the desired limits on the size of such pulse pairs and the length of the waveform to accommodate insertion or deletion of periods of such pairs and / or zero voltages. It should also be noted that common to all aspects of the invention. As a result, the above-described MEDEOD application and as discussed below, the desired DC balanced drive scheme and DC balanced waveform are also common to all aspects of the present invention.

Section A: Balanced Pulse Pair Slideshow Method and Device

As already mentioned, the BPPSS method of the present invention is a method of driving an electro-optical display having one or more pixels capable of achieving three or more different gray levels comprising two extreme optical states. The method is one or more reset pulses sufficient to drive a pixel to or near one of the extreme optical states, followed by one or more set pulses sufficient to drive the pixel to a different gray level than one subsequent optical state. Applying a base waveform to the pixel comprising a reset pulse, the base waveform being modified by one or more of the following:

(a) insertion of one or more balanced pulse pairs into the base waveform;

(b) deletion of one or more balanced pulse pairs from the base waveform; And

(c) the insertion of one or more periods of zero voltage into the base waveform,

Also, as already mentioned, "balanced pulse pair" denotes a sequence of two pulses of opposite polarity such that the total impulse of the balanced pulse pair is necessarily zero. In a preferred form of the BPPSS method, the two pulses of the balanced pulse pair are each of constant voltage but of opposite polarity and may be the same length. The term “base waveform element” or “BWE” may be used below to refer to the reset or set pulse of any base waveform. Insertion of a balanced pulse pair and / or zero voltage period (hereinafter referred to as “gap”) may occur within a single base waveform element or between two consecutive waveform elements. All these modifications have the property that y does not affect the total impulse of the waveform, while the total impulse is an integral of the waveform voltage curve integrated over time for the duration of the waveform. Balanced pulse pairs and zero voltage interruptions as well as zero total impulses. Typically the pulses of BPP will be inserted in close proximity to each other, but this is not necessary and the two pulses may be inserted in separate positions.

Where the modification of the base waveform consistent with the BPPSS method involves the deletion of one or more BPPs, the period previously occupied by the deleted BPP or each thereof may remain as a period of zero voltage. Alternatively, this period may be " closed " by moving some or all of the waveform elements later in time, but this would be standard since it would be standard to ensure that all pixels of the display are driven with waveforms of the same length. In any case at some later stage of the waveform, typically at the end of it, it would be standard to insert a period of zero voltage to ensure that the entire length of the waveform is maintained. Alternatively, of course, this period may be closed by moving some or all of the earlier waveform element later in time, at the earlier stages of the waveform, typically with the insertion of a period of zero voltage at its initial stage.

As already pointed out, the BPPSS waveform of the present invention is a modification of the underlying slide show waveform described in the MEDEOD application described above. As discussed above, the slide show waveform includes one or more reset pulses that cause the pixel to move to or at least close to one extreme optical state (optical rail); If the waveform contains two or more reset pulses, each reset pulse after the first will cause the pixel to move to the opposite extreme optical state, thus significantly passing its entire optical range. (For example, if the display uses an electro-optical medium with a range of 4 to 40 percent reflectance, each reset pulse after the first may pass through 8 to 35 percent reflectivity of the pixel.) If more than one reset pulse is used, the successive reset pulses must of course be of alternating polarity.

The slide show waveform further includes a set pulse that drives the pixel from the extreme optical state in which it was left by the pixel's desired last reset pulse to the final gray level. Note that this desired final gray level is one of the extreme optical states, and when the last reset pulse leaves the pixel in this desired extreme optical state, the set pulse may be zero duration. Similarly, the initial state of the pixel before the application of the slide show waveform is in one of the extreme optical states, and the first reset pulse may be zero duration.

By way of example only, preferred BPPSS waveforms of the present invention will now be described with reference to the accompanying drawings.

2A and 2B of the accompanying drawings illustrate waveforms used for two different transitions in the prior art (base) slide show driving scheme of the type described in the aforementioned MEDEOD application. This slide show drive scheme uses three reset pulses for each transition. 2C and 2D show corresponding variations with respect to time in the optical state (reflectance) of the pixel to which the waveforms of FIGS. 2A and 2B are applied, respectively. Consistent with the conventions used in the MEDEOD application described above, FIGS. 2C and 2D are drawn such that the lower horizontal line represents a black extreme optical state, the upper horizontal line represents a white extreme optical state, and the level between represents a gray state. The beginning and end of the reset and set pulses of the waveform are indicated in Figures 2A and 2B by vertical dashed lines, and in general the BWE may be of a more arbitrary length, but the various BWE (ie, reset and set pulses) If shown as including the same length pulses and consist of a series of same length pulses, more than ten such pulses will be used for the maximum length BWE as standard.

The base waveforms (generally designated 100) shown in FIGS. 2A and 2C cause a transition from white to white (ie, “transition” where both the initial and final states of the pixel are white extreme optical states). Waveform 100 includes a first negative (ie, black-going) reset pulse 102 that drives a pixel to its black extreme optical state, a first to drive the pixel to its white extreme optical state. Two positive (white-going) reset pulses 104, a third negative (black-going) reset pulse 106 that drives the pixel to its black extreme optical state, and a pixel to its white extreme A set pulse 108 that drives to an optical state. Each of the four pulses 102, 104, 106 and 108 has a maximum 10-unit duration. (To avoid the inconvenience of continuing reference to "units of duration", such units may be referred to hereinafter as "time units" or "TU's."

2B and 2D illustrate the waveform for the transition from dark gray to light gray using the same three reset pulse drive schemes as in FIGS. 2A and 2C. Waveform 150 includes a first reset pulse 152 that is negative and black-going, such as first reset pulse 102 of waveform 100. However, the transition where waveform 152 is used is that since after starting from the dark gray level, the duration of the first reset pulse 152 (illustrated as 4 TU) is shorter than the duration of the reset pulse 102, which is more This is because a short first reset pulse is needed to bring the pixel to its black extreme optical state at the end of the first reset pulse. For the remaining 6 TUs of the first reset pulse 152, a zero voltage is applied to the pixel. (FIGS. 2B and 2D illustrate a first reset pulse 152 with 4 TUs of negative voltage at the end of the period involved, but this is arbitrary and the periods of negative and zero voltage may be arranged as desired.

The second and third reset pulses 104 and 106 of waveform 150 are the same as the corresponding pulses of waveform 100. Set pulse 158 of waveform 150 is positive and white-going, like set pulse 108 of waveform 100. However, since the transition where waveform 150 is used ends at a light gray level, the duration of set pulse 158 (illustrated as 7 TU) is shorter than the duration of set pulse 108, which is a shorter set. This is because a pulse is needed to drive the pixel to its final light gray level. For the remaining 3 TUs of set pulse 158, a zero voltage is applied to the pixel. (Again, the distribution of the periods of the positive and zero voltages in set pulse 158 is arbitrary and the periods may be arranged as desired.)

From the foregoing, in the prior art slide show driving scheme shown in Figs. 2A to 2D, the durations of the first reset pulse and the set pulse vary depending on each of the initial and final states of the pixel, and in some cases one or more of these pulses. All may be zero duration. For example, in the driving scheme of FIGS. 2A-2D, a first reset pulse of zero duration transitioning from black to black (a pixel is reached at the end of the first reset pulses 102 and 152) and zero duration Has a set pulse (because at the end of the third reset pulse 106 the pixel is already in the desired extreme black optical state.)

In general, it is desirable for the user to prefer a display that displays new images quickly, and to keep the overall duration of the waveform as short as possible so that the display can be rewritten quickly. Since each reset pulse occupies a significant period of time, it is desirable to reduce the number of reset pulses to a minimum consistent with acceptable gray scale performance by the display, and generally one or two reset pulse slide show drive schemes are preferred. do. 3A and 3B of the accompanying drawings illustrate waveforms for two different transitions in a two reset prior art slide show drive scheme of the type described in the aforementioned MEDEOD application.

FIG. 3A is in white including a reset pulse 202 driving a pixel from its initial white state to black and a set pulse 208 (same as pulse 158 in FIG. 2B) driving the pixel from black to light gray. An example of a single reset pulse waveform (typically designated 200) in light gray is illustrated. Although waveform 200 uses only a single reset pulse, as indicated by the period of zero voltage on the left side of FIG. 3A, it actually drives two reset pulse slideshows with a first reset pulse of zero duration. It will be understood that they are part of.

FIG. 3B illustrates a first reset pulse 252 which drives the pixel from its initial black state to white, a second reset pulse 254 that drives the pixel from white to black, and FIG. 3A which drives the pixel from black to light gray. Two reset pulse waveforms (generally designated 250) from black to light gray that include the same set pulse 208 as the reset pulse of.

As already mentioned, the BPPSS waveform of the present invention can be obtained by inserting one or more balanced pulse pairs into the base waveform, deleting one or more balanced pulse pairs from the base waveform, or inserting one or more periods of zero voltage into the base waveform. It is derived from the base slide show waveform as illustrated in Figures 2A, 2B, 3A and 3B. In the case of deletion of BPP, the resulting gap may be closed or left as a period of zero voltage. Combinations of these modifications may be used.

4A-4C illustrate preferred balanced pulse pairs for use in the BPPSS waveform of the present invention. The BPP (generally designated 300) shown in FIG. 4A includes a positive pulse 304 of the same duration and voltage but opposite polarity as the negative pulse 302 of constant voltage and the pulse 302 immediately following it. . It will be apparent to apply an impulse of BPP 300 total zero to the pixel. The BPP (generally designated 310) shown in FIG. 4B is identical except that the order of the pulses is inverse to BPP 300. The BPP (generally designated 320) shown in FIG. 4C is derived from the BPP 310 by introducing a period 322 of zero voltage between the positive and negative pulses 304 and 302, respectively.

5A-5D illustrate modification of a base two reset pulse slide show waveform by BPP consistent with the present invention. 5A illustrates the basis waveform (generally designated 400) used for the transition from white to light gray. Waveform 400 is generally similar except that waveform 250 illustrated in FIG. 3B is in reverse order of two reset pulses. Thus, waveform 400 is a 16-TU negative black-going first reset pulse 402 (which drives a pixel from its original white state to its black extreme optical state), (which causes the pixel to have its black extreme optical state). 16-TU positive white-going second reset pulse 404 to drive its white extreme optical state, and 3-TU negative black- to drive the pixel from its white extreme optical state to the desired final light gray state. And going set pulse 408.

FIG. 5B illustrates the BPPSS waveform (generally designated 420) of the present invention generated by inserting the BPP of FIG. 4B into the waveform 400 of FIG. 5A between the second reset pulse 404 and its set pulse. . As seen from FIG. 5B, the negative pulse 302 of BPP increases the set pulse 408 to 4 TU, while the effect of this insertion is that the positive pulse 304 of BPP causes the second reset pulse 404 to be 17. Is to increase to TU.

5C illustrates the inventive BPPSS waveform (generally designated 440) generated by inserting the BPP of FIG. 4C after its set pulse 408 into the waveform 400 of FIG. 5A.

5D illustrates the BPPSS waveform (generally designated 460) of the present invention generated by further modifying waveform 420 shown in FIG. 5B. Waveform 460 has a second BPP 304 ', 302' inserted between its first and second reset pulses 402 and 404, respectively, which second BPP is pulsed with BPP 304, 302. All are similar except that the duration is doubled.

As already mentioned and illustrated in FIG. 5D, the BPPSS waveforms of the present invention are a plurality of BPP's, erases, pauses, and combinations thereof (hereinafter collectively referred to as “additional waveform elements” or “AWE's”). It may also include. However, it is generally desirable to use the minimum number of AWE in accordance with the desired degree of precise control of the final gray level produced by the waveform. Both BPP and interruption increase the waveform, and the integration of some of these BPPs and / or interruptions may require an undesired increase in the time period required to rewrite the display. For example, while waveform 460 of FIG. 5D uses only a short 3-TU set pulse 408, waveform 460 occupies all of the update period of the display (period between dashed vertical lines in FIG. 5D) and However, the introduction of any BPP or discontinuation may require an extension of this period. Thus, the total length of the modified waveform of the present invention preferably does not exceed the length of the corresponding base waveform sufficient for the duration of the set pulse to drive the pixel from one extreme optical state to the other extreme optical state. In many cases good control of gray levels (of course depending on the exact electro-optical medium and other characteristics of the driving electrical element used in the display) can be achieved with waveforms comprising AWE of 2 or less, in other cases 4 or less Or, typically, up to 6 AWE may be required, but it has been found that any increase in AWE is generally undesirable.

6A-6D illustrate modification of the base 2 reset pulse waveform by deletion of BPP in accordance with the present invention. For purposes of comparison, FIG. 6A illustrates the same waveform 400 as FIG. 5A. Since FIG. 6A assumes that 10 TU of the applied voltage is required to fully drive a pixel between its extreme optical states, as in FIGS. 2A, 2B, 3A-3B, waveform 400 is set pulse 408. Note that it will be necessary to increase the set pulse 408 to a maximum of 10 TUs at other waveforms of the same drive scheme, considering the terminating 7 TU after the end of. FIG. 6B deletes from the waveform 400 a BPP that includes the last two TUs of the first reset pulse 402 and the first two TUs of the second reset pulse 404, so that a 4-TU interrupt where zero voltage is applied to the pixel. Modified BPPSS waveform of the present invention (generally designated as 520) generated by leaving a 14-TU first reset pulse 402 'and a modified 14-TU second reset pulse 404' separated by 522. Exemplarily).

FIG. 6C illustrates the BPPSS waveform of the present invention (generally designated 540) generated by alternative modification of waveform 400 of FIG. 6A. Waveform 540 deletes BPP from waveform 400, which includes the last TU of second reset pulse 404 and the first TU of set pulse 408, and determines the period of time desired occupied by the deleted BPP. Generated by moving the second reset pulse later in time by 2 TUs to " close ". Thus, waveform 540 includes 2-TU interrupt 544, 16-TU first reset pulse 402, 15-TU second reset pulse 404 ″ and 2-TU set pulse 408 ′. Note that the set pulse 408 ′ ends at exactly the same time as the set pulse 408 of the base waveform 400, 7 TU before the end of the waveform.

6D illustrates the BPPSS waveform of the present invention (generally designated 560) generated by modification of waveform 400 of FIG. 6A. Waveform 560 deletes BPP from waveform 400, which includes the last two TUs of first reset pulse 402 and the first two TUs of second reset pulse 404, and is originally occupied by the deleted BPP. Is generated by "closing" the second reset pulse and the set pulse earlier by 4 TU in time. Thus, waveform 560 generates a 14-TU first reset pulse 402 ′ (same as that of FIG. 5), (same as that of FIG. 5B except for time), and 3-TU set pulse 408. Include. Because of the movement of the second reset pulse 404 ′ and the set pulse 408, the final period 562 of the zero voltage (following the set pulse 408) extends from 7 to 11 TU.

Preferred BPPSS waveform modifications discussed so far have included the insertion or deletion of BPP between successive base waveform elements or at the end of the base waveform. However, the BPPSS aspect of the present invention is not limited to this modification and extends to the modification in which the BPP is inserted into a single BWE as will now be illustrated with reference to FIGS. 7A and 7B. FIG. 7A is a diagram showing the relationship between the first reset pulse 420 and the second reset pulse 404 of the BPP 302 ′, 304 ′ similarly to that shown in FIG. 5D except that the order of the positive and negative pulses is reversed. Illustrate the BPPSS waveform 620 of the present invention generated by modifying the base waveform 400 with insertion. FIG. 7B corrects the base waveform 400 with the insertion of BPPs 302 ′, 304 ′, but inserts BPP 302 ′, 304 ′ at the mid-point of the second reset pulse 404 in waveform 640. Thus illustrating the BPPSS waveform 640 of the present invention, which is also generated by dividing this pulse into two separate compartments 404a and 404b. Thus, waveform 640 is continuously, 16-TU first reset pulse 402 (same as that of waveform 400), 8-TU pulse 404A, the first division of the second reset pulse, BPP ( 302 ', 304'), an 8-TU pulse 404B, a second section of the second reset pulse, and a 3-TU reset pulse 408 (same as that of waveform 400).

As described above, the BPPSS aspect of the present invention includes not only the insertion or deletion of BPP from the base waveform, but also the insertion of an interruption (period of zero voltage) into the base waveform, and the insertion of this interruption now shows FIGS. 8A-8D. Will be illustrated as a reference. For purposes of comparison, FIG. 8A illustrates the same base waveform 400 as in FIGS. 5A and 6A. FIG. 8B is a modified BPPSS waveform of the present invention (generally at 720) generated by introducing a 2-TU interrupt 722 between the second reset pulse 404 and the set pulse 408 of the base waveform 400. Is designated). It should be noted that the insertion of the interruption 722 necessarily reduces the length of the period of zero voltage following the set pulse 408 from 7 TU to 5 TU. 8C shows a waveform except that a 2-TU interrupt is inserted after the first 12 TU of the second reset pulse 404, thus separating this second reset pulse into a first compartment 404C and a second compartment 404D. Another BPPSS waveform of the present invention (generally designated 740), which is generally similar to 720, is illustrated. Thus, waveform 740 is in succession: 16-TU first reset pulse 402 (same as that of waveform 400), 12-TU pulse 404C, first division of second reset pulse, 2- TU interrupt 722 ', a 4-TU pulse 404D, a second partition of the second reset pulse, and a 3-TU reset pulse 408 (same as that of waveform 400).

8D illustrates the BPPSS waveform of the present invention (generally designated 760) that is regenerated by inserting a 2-TU break into the base waveform 400. However, at waveform 760, interrupt 722 ″ is inserted just before the first reset pulse 402. Accordingly, waveform 760 includes, in succession, interruption 722 ″, first reset pulse 402, second reset pulse 404, and set pulse 404, wherein the last three elements are all Same as the corresponding element of the base waveform 400.

As already indicated, the BPPSS waveform provided by the present invention is useful for improving gray level performance of electro-optic displays, in particular bistable electro-optic displays. The BPPSS waveform of the present invention can achieve this improved gray level performance while still preserving the long-term DC balance of the display. For reasons discussed in detail in the aforementioned MEDEOD application, the driving scheme used to drive at least some electro-optical displays requires that the integration of the applied voltage over time at a given pixel be limited, regardless of the series of optical states in which the pixel is driven. In this sense, it is important to be DC balanced. In accordance with the BPPSS aspect of the present invention, it has been found that the final gray level of a pixel can be adjusted by the insertion or deletion and / or insertion of interruption of the BPP. It has also been found that the final gray level of the pixel is affected by the location where insertion or deletion of BPP and / or insertion of interruption takes place. In general, good control of the final gray level can occur by inserting BPP between adjacent BWEs, while BPP is inserted into a single BWE to change the degree of “harmonicity” of the final gray level, as illustrated in FIG. 7B. For example, if the BPP added between two reset pulses does not provide sufficiently fine harmony of the final gray level, moving the BPP to a position in the middle of the BWE provides finer control over the final gray level. can do.

For example, the pulse 302 will effectively increase the set pulse 408 so that the final level will go somewhat higher (ie, slightly darker in color) from the white extreme optical state, but not in the BPP 304, 302. The pulse 304 has a slight or no effect on the gray level of the pixel because the gray level of the pixel will already be in the white extreme optical state at the end of the second reset pulse 404, and thus the waveform 420 of FIG. 5B. ) Will normally produce a gray level slightly darker than the gray level produced by the corresponding basis waveform 400 of FIG. 5A. On the other hand, the waveform 540 shown in FIG. 6C will typically produce a gray level slightly brighter than the gray level produced by the corresponding base waveform 400 of FIG. 6A. Since FIGS. 5A, 6A and 6C are based on the assumption that a pixel can be moved by application (as described above) for 10 TUs of the illustrated voltage between its extreme optical state, 16 of the base waveform 400 -TU second reset pulse 404 causes a significant "over-driving" of the pixel to the white optical rail (white extreme optical state), i.e. the second reset pulse 404 the pixel is already in its extreme white optical state. After reaching, it continues for a considerable period of time. Thus, generating the 15-TU second reset pulse 404 '' of the waveform 540 by shortening the 16-TU second reset pulse 404 by 1 TU results in the end of the second reset pulse 404 ''. There will be little or no effect on the gray level at. On the other hand, shortening the 3-TU set pulse of waveform 400 by 1 TU to produce the 2-TU set pulse 408 'of waveform 540 exists at the end of the second reset pulse 404' '. This significantly reduces the degree to which the white extreme optical state is driven to black so that the final gray level at the end of waveform 540 will be significantly darker than at the end of base waveform 400.

As already pointed out, it has also been found that interruption (period of zero voltage) can be used to adjust the final gray level. For example, adding a break between the last reset pulse and the set pulse affects the final gray level. Moving the interruption to the earlier point of the last reset pulse also causes some change in the final gray level. Thus, the stop position may be used to adjust the final gray level produced by the BPPSS waveform. In general, interruptions can be added at any point in the waveform. It may also be advantageous to move all BWEs in the waveform earlier or slower in time within the update time interval allotted for complete rewriting of the display, thereby initializing the relative temporary positioning of the various transitions occurring within the entire transition. To move to the final state. This temporary shift reduces the diversity between pixels that are intended to be at the same gray level for several reasons, for example, reducing the undesired temporary state of the display during transition, or to a more satisfactory final image. It may be advantageous for the reason of being led.

More preferred BPPSS waveforms and driving schemes of the present invention will now be described with reference to FIGS. 9A-9D, 10A-10C and 11A-11C of the accompanying drawings. 9A and 9B illustrate two basis waveforms of a prior art two reset pulse slide show drive scheme in which the first and second reset pulses and set pulses may occupy up to 12 TUs. 9A causes a transition from white to black, a 12-TU black-going first reset pulse 802, a 12-TU second white-going reset pulse 804, and a 12-TU black-going set pulse ( Illustrates a waveform 800 that includes 808. As described above with reference to FIGS. 2A and 2B, when the initial and final states of the pixel are intermediate gray levels that lie between the black and white extreme optical states of the pixel, the first reset and set pulses need to be adjusted in length and 9B shows a 7-TU first reset pulse 812, a 12-TU second reset pulse 804 (same as the corresponding pulse of waveform 800), and a 6-TU set pulse 818. . In order to “pad” waveform 810 to 36-TU length as waveform 800, 5-TU period 822 of zero voltage precedes first reset pulse 812 and 6 of zero voltage. -TU period 824 follows set pulse 824.

FIG. 9C shows the BPPSS waveform of the present invention (generally designated 840) generated by modification of waveform 810 shown in FIG. 9B. In particular, waveform 840 includes a first BPP and second pulse immediately after set pulse 818 that includes positive 1-TU pulse 842 and similar negative pulse 844 immediately before first reset pulse 812. It is derived from waveform 810 by inserting similar BPPs 846 and 848. Pulses 812, 804, and 818 remain unchanged, but the initial period 822 'of zero voltage is reduced to 3 TU to accommodate BPP while maintaining the overall length of waveform 840, and the final period of zero voltage ( 824 ') is reduced to 4 TUs.

The use of two BPPs in the manner illustrated in FIG. 9C allows for more accurate control of the gray levels that can be achieved with a single BPP, at least in some cases. The BPP placed after the set pulse (such as BPP 846 and 848 of waveform 840) can cause a significant change in the final gray level, with the driver used only relative to the duration of each half of the BPP. If only coarse adjustments are possible (eg, if the duration can only be adjusted in increments of 1 TU in FIG. 9C), the difference between the gray levels available by changing the duration of each half of the BPP by a minimum increment May be unacceptably large. The BPP inserted at a much earlier point in the waveform (such as the BPP 842, 844 of the waveform 840) has a much less effect than the BPP inserted after the set pulse at the final gray level, and thus the finer of the final gray level. Allow change. Thus, waveform 840 allows adjustment of a significant range of final gray levels by controlling the duration of BPP 846 and 848, resulting in coarse adjustment to the final gray level, and controlling the duration of BPP 842 and 844. This causes fine adjustment of this gray level.

9D illustrates the BPPSS waveform of the present invention (generally designated 860) generated by an alternative modification of waveform 910. Like waveform 840, waveform 860 includes BPPs 846 and 848 following set pulse 818. However, waveform 860 does not include the earlier second BPP of the waveform, but instead includes a 4-TU interrupt 850 between the second reset pulse 804 and the set pulse 818. The effect of the break tends to be smaller than the same length of BPP at the same point of the waveform, and the break 850 is accompanied by a change in the length of the break's BPP 842,844 to cause fine adjustment of the final gray level. Works in a similar way. The final period 824 'of zero voltage in waveform 860 is the same 4-TU length as in waveform 840, but the duration of the initial period 822' 'of zero voltage is the total 36-TU of the waveform. Note that it is reduced to 1 TU to accommodate the 4-TU interrupt 850 while maintaining the length.

10A-10C show three BPPSS waveforms of the present invention generated by various modifications of waveform 810 of FIG. 9B. The waveform of FIG. 10A (generally designated 920) is formed by adding BPPs 846 ′ and 848 ′ after the set pulse 818 of waveform 810, and each pulse 846 ′ and 848 of BPP. ') Is 2 TU in length. The final period 824 '' of zero voltage is reduced to 2 TUs to accommodate the 4-TU length of BPP.

As described above with reference to FIG. 9C, changing the length of the BPP following the set pulse may not provide sufficient fine adjustment of the final gray level, and FIG. 920 illustrates a waveform generated by modifying 920 (generally designated 940). Waveform 940 integrates second BPP 842 ′, 844 ′ between second reset pulse 804 and set pulse 818. The effect on the final gray level of the change in the length of the BPP 842 ', 844' is less than the corresponding change in the length of the BPP 846 ', 848', so that the BPP 842 ', 844' is the final gray level. It can be used to fine control of.

Although the effect of the change in the length of the BPP 842 ', 844' is less than the corresponding change in the length of the BPP 846 ', 848', this is a much earlier insertion of the waveform, e.g. 842, 844) much larger than the effect of the change in length. If the BPPs 842 ', 844' of the waveform 940 do not provide enough fine adjustment of the final gray level, a second BPP may be inserted when it reaches the waveform, and generally, earlier in the waveform The more BPP is inserted, the smaller the change in the final gray level produced by a given change in the length of the BPP. For example, FIG. 10C shows waveforms except that BPPs 842 ′, 844 ′ are replaced by BPPs 962, 964 disposed between the first reset pulse 812 and the second reset pulse 804. Illustrates a BPPSS waveform of the present invention similar to 940 (generally designated 960). (BPP 962, 964 is the opposite polarity to BPP 842 ', 844' in the sense that negative pulse 962 precedes positive pulse 964, and of course the effect of BPP's polarity on the final gray level. BPP of either polarity may be used anywhere in the waveform.)

As a result, FIGS. 11A-11C illustrate modification of the base waveform through introducing both BPP and interruption into the base waveform. 11A shows BPPs 842 ', 844' between the final second reset pulse 804 and the set pulse 818, with corresponding reductions up to 4 TUs of the length of the final period 824 'of zero voltage. Illustrates a waveform (generally designated 1020) generated by inserting and modifying the base waveform 810. For the reasons described above, variations in the length of the BPPs 842 'and 844' may not provide enough fine adjustment of the final gray level, and FIG. 11B shows in particular the introduction of the 2-TU interrupt 1042 in the second reset pulse. Shows a BPPSS waveform (generally designated 1040) generated by modifying waveform 1020 and thus dividing this pulse into first compartment 804A and second compartment 804B. To accommodate the interruption 1042, the length of the initial period 822 ′ of zero voltage is reduced to 3 TU, and the length of the final period 824 ′ of zero voltage remains 5 TU.

The stop 1042 is used for fine adjustment of the final gray level. Such fine adjustment may be made by changing the duration 1042 and / or its location of the interruption in the second reset pulses 804A, 804B. Like BPP, the effect of interruption on the final gray level depends not only on its length but also its position within the waveform. The BPPSS aspect of the present invention is of course not limited to the use of a single interruption, for example, interruption 1042 may be replaced by two separate interrupts, each of 1 TU duration, so that the second reset pulse is two Rather than being divided into three compartments.

As mentioned, if the waveform does not occupy the entire period available for updating the display (eg, a period of at least 36 TU is needed to update the display to accommodate longer waveforms 800 of the same drive scheme). In contrast, it may be advantageous to move the waveform 810 of FIG. 9B, which occupies only 25 TUs, the entire waveform within the update period, for example, to reduce temporary visual effects during the update. FIG. 11C moves the entire waveform 1040 of FIG. 11B earlier by 2 TU in time (as indicated by FIG. 11C, in effect by inserting a 2 TU gap immediately after the set pulse 818), thus reducing the zero voltage. The initial period 822 ″ decreases to 1 TU, and the length of the final period 824a of zero voltage increases to 6 TU, illustrating the waveform (generally designated 1060) generated.

Section B: Inverse Monochrome Projection Method and Apparatus

As already mentioned, the second aspect of the present invention provides a method of driving an electro-optical display having a plurality of pixels, each of which can achieve four or more different gray levels, including two extreme optical states. This method is a reset pulse sufficient to drive a pixel to or near one of its extreme optical states, with a reset pulse sufficient to drive the pixel from one subsequent optical state to a different final gray level. And applying a waveform including each pixel to each pixel. The reset pulse is selected such that the image on the display immediately before the set pulse is substantially the reverse monochrome projection of the final image following the set pulse. This process is referred to herein as the "inverse monochrome projection" or "IMP" method.

Using the name "target state" used in scheme 1 above, the IMP method may be defined such that the final target state is approximately the reverse monochrome projection of the desired final state R ₁ of the display. In a preferred form of the IMP method, the target state immediately before the final target state (target _n- 1 in the name of scheme 1) is approximately the reverse monochrome projection of the desired final state (R ₁ ) of the display. This preferred IMP process may be represented symbolically, as in the manner 2 shown in FIG. 12 where R _{1 , m} indicates a monochrome projection of R ₁ and the upper line indicates image reversal.

The monochrome projection of an optical state is one that maps to one of the two extreme optical states (for reasons described below) or one of the extreme optical states of each pixel of every possible gray level in the image. For this purpose, the gray levels may be represented as 1, 2, 3, ..., N, where N is the number of gray levels, and the gray level (usually black) with the smallest reflectance is represented by 1 and Next, the gray level having the smallest reflectance is 2, and the gray level (usually white) having the largest reflectance is represented by N. The monochrome projection of the gray scale image is such that gray levels below the threshold map to gray level 1 or near and gray levels above the threshold map to gray level N or near. The threshold is most preferably N / 2, but may actually be usefully set anywhere in the middle half of the range from 1 to N, ie the threshold is at least N / 4 at most 3N / 4.

An example of monochrome projection is shown in FIG. 13. In this example, the gray scale image (illustrated in a symbolic manner on the left side of FIG. 13) contains eight gray levels and is labeled 1 to 8. Gray levels 1 to 3 map to gray level 1 and gray levels 4 to 8 map to gray level 8 in the monochrome projection symbolically shown on the right side of the figure. Reverse monochrome projection is of course generated by simply reversing the two states used in monochrome projection.

Such projections, which include an optical state "close to" one of the preceding reference and extreme optical states of the IMP method "substantially" produce reverse monochrome projections, require explanation. In principle, monochrome projection and reverse monochrome projection require projection to one of the extreme optical states. However, the driving scheme and waveforms that actually drive the electro-optical display are defined as voltage pulses or other waveform elements applied to individual pixels of the display, and the application of defined voltage pulses or other waveform elements (although the two are closely related). It is not defined as the exact optical state that generates the signal. As described in detail in the MEDEOD application described above, the response to a given waveform or waveform element of at least some bistable electro-optical media may be determined by the pixel's initial optical state and the exact waveform or waveform element, as well as any previous optical state of the pixel and It depends on factors such as how long the pixel has stayed in the same optical state before the waveform or waveform element is applied (the dwell time dependent problem described above). Because slide show waveforms do not typically account for all of these related factors, the actual optical state achieved by the various pixels in monochrome or reverse monochrome projection may differ slightly from the extreme optical states theoretically achieved in such projection. .

The deviation from the extreme optical state of the actual optical state of the pixel is from black (gray level 1) to white (gray level 4) using a +15 V 200 msec pulse and white (grey) using a -15 V 200 msec pulse. Figure 4 shows the waveforms used for any selected transition in the two reset pulse slide show IMP method of the present invention using four gray level electro-optical media that can be driven from level 4) to black (gray level 1). It may be illustrated with reference to 14 and 15. The first waveform shown in FIG. 14 (generally designated 1420) is a transition from black (gray level 1) to white (gray level 4), the first reset pulse 1422 driving the pixel from black to white, A second reset pulse 1424 driving the pixel from white to black, and a set pulse 1426 driving the pixel from black to white. 14 also shows a waveform 1440 for the transition from gray level 2 (dark grey) to gray level 4 (white), which is in the case of the reset pulse 1422 of waveform 1420. And has a first reset pulse 1428 that is 140 msec in length rather than 200 msec. The second reset pulse 1424 and set pulse 1426 of waveform 1440 are the same as that of waveform 1420. As a result, FIG. 14 also shows a waveform 1460 for the transition from gray level 4 (white) to gray level 4, in which case the first reset pulse is zero duration (ie, simply at the beginning of the waveform). There is a period of zero voltage of 200 msec.) The second reset pulse 1424 and the set pulse 1426 of the waveform 1460 are identical to that of the waveform 1420.

FIG. 15 shows additional waveforms from the same drive scheme as in FIG. 14. The first waveform shown in FIG. 15 (generally designated 1480) is for the transition from gray level 1 (black) to gray level 1 and is necessarily the inverse of the waveform 1460 shown in FIG. 14. Waveform 1480 includes a first reset pulse of zero duration (ie, there is simply a period of zero voltage of 200 msec at the beginning of the waveform), a second reset pulse 1462 driving the pixel from black to white, and Has a set pulse 1484 that drives the pixel from white to black. 15 also illustrates the waveform 1500 used for the transition from gray level 1 (black) to gray level 3 (light grey). This waveform 1500 is the same as the waveform 1420 shown in FIG. 14 and has a first reset pulse 1422 that drives the pixel from black to white. Waveform 1500 also has a second reset pulse 1502 that drives the pixel from white to black, and a 130 msec set pulse 1504 that drives the pixel from black to gray level 3 (light gray). As a result, for the sake of completeness, FIG. 15 repeats the white to black (gray level 1 to gray level 4) waveform from FIG.

14 and 15, the illustrated driving scheme shows that the image on the display immediately before the set pulse is the inverse monochrome of the final image after the set pulse, as indicated by the upper line R _{1 , m} immediately before the set pulse in the various waveforms. IMP driven in terms of projection, and more specifically, in all transitions ending at gray level 1 or 2, the pixel is white just before the set pulse, whereas in all transitions ending at gray level 3 or 4, Is black just before the set pulse. In addition, in accordance with the preferred variant of the IMP method, the image on the display immediately before the second reset pulse is the monochrome of the final image after the set pulse, as indicated by R _{1 , m} just before the second reset pulse in the various waveforms. In all transitions that are projection and more specifically terminate at gray level 1 or 2, the pixel is black just before the second reset pulse, whereas at all transitions that end at gray level 3 or 4, the pixel is the second reset pulse. Just before white.

However, suppose that the difference between pixels at the same gray level is assumed to be relatively small relative to the total dynamic range of the display (the difference between the reflectances of the two extreme optical states), but of a given gray level achieved at various points of various waveforms. It is inferred from FIGS. 14 and 15 that the reflectance is not necessarily exactly the same. For example, immediately before the second reset pulse, the pixels undergoing waveforms 1420 and 1460 of FIG. 14 should all be at gray level 4 (white). However, a pixel undergoing waveform 1420 may remain in the white state for some time (as discussed in some of the MEDEOD applications described above) and the optical state of the bistable electro-optic medium While there is a tendency to "drift" (ie, change over time) while they are not driven, there will only be a transition from complete black to white at this point. Thus, the actual white state of the pixel undergoing waveform 1460 may be slightly different than that of the newly re-written pixel undergoing waveform 1420. As discussed below, modifications to the IMP driving scheme may modify the reflectances achieved at various target states and other points of the waveform, so that the reflectances of various targets and other states may be achieved at target states that could be achieved without such modifications. It can deviate significantly from the reflectance.

Although the IMP driving scheme illustrated in FIGS. 14 and 15 uses only two reset pulses and two target states, the IMP aspect of the present invention is of course not limited to a particular number of reset pulses and target states, for example, FIG. 16 symbolically illustrates the IMP driving scheme including the intermediate black (B) and white (W) states before the monochrome projection and reverse monochrome projection target states, in the same manner as in FIG. 12.

Not all pixels of the display necessarily reach the same point in time for a given target state (eg, reverse monochrome projection target state) during the rewriting of the display from the initial image to the desired final image. The time point at which the target state is reached is a function of the initial and desired final gray levels, R ₂ and R ₁ , respectively. Ideally (and as standardly illustrated here), the time points for R ₂ and R ₁ match, the entire display is driven through various target states, which are reached simultaneously by all pixels. However, it is often desirable to shift the relative time of the various waves of the drive scheme. The time shift of the waveform may be done to improve aesthetic reasons, for example, the appearance of the transition or the appearance of the resulting image. In addition, modifications as discussed below can shift the relative time position of the target state such that, for various combinations of R ₁ and R ₂ , the target state is reached at a different time during the transition.

It is possible to give an alternative definition of the IMP driving scheme without explicit reference to inverse monochrome projection. The IMP driving scheme is that the various gray levels of the display can be divided by the threshold such that one extreme optical state and one or more non-extreme optical states are on each side of the threshold, and the set pulse of the slide show driving scheme is respectively A set pulse of is defined as causing a transition above a threshold. As this definition makes clear, in an IMP drive scheme, the final set pulse of each waveform drives the pixel from the extreme optical state further away from the desired final gray level, where "farther" is simply It is used to indicate "on the opposite side of the threshold" rather than calculating the number of gray level differences between the desired final gray level and the two extreme optical states.

It has been found that the IMP drive scheme enables precise control of the final gray level and provides a wide temperature range. This advantage is believed to be linked to the relatively long set pulses used to drive from the "farther" extreme optical state to the final gray level and the resulting relatively constant power leakage on the drive electrical elements during display updates (the present invention contemplates this But not limited to).

The basic IMP drive scheme described above can be usefully modified in several different ways to make small adjustments in the final gray level achieved to change the appearance of the display during transition and to achieve the desired image quality.

Modifications of the first type of IMP drive scheme, as discussed in section A above, insert or delete balanced pulse pairs and / or insert zero voltage periods into the waveform, in a manner similar to that performed with the BPPSS drive scheme. to be. The balanced pulse pair used may have any form, for example, shown in FIGS. 4A-4C. Modification of the basic IMP waveform by inserting or deleting the BPP, or inserting a period of zero voltage (interruption) may be made in any manner previously described. The BPP may be inserted between two consecutive base waveform elements or within a single base waveform element. In many cases, this has the effect of increasing the pulse length to and from a particular target state. The deleted BPP may be replaced by a period of zero voltage or another base waveform element may be shifted in time to "close" the period previously occupied by the deleted BPP, and the period of zero voltage may be moved to another point in the waveform. It can also be inserted from. As with the BPPSS driving scheme, the final gray level achieved is sensitive not only to the presence of BPP and interruption in the waveform, but also to their positioning within the waveform, and the general rule is that the earlier the BPP is inserted or deleted in the waveform, or the interrupt is inserted. The smaller the effect of the change on the final gray level.

This waveform modification will affect the intermediate target state as well as the reflectance of the final optical state (ie, the final gray level). The target state of the basic IMP waveform is generally close to one of the extreme optical states (optical rails), by definition, close to the optical rail for the last target state, or close to the last two target states in the preferred form of the IMP drive scheme. When the above-described modification can move the reflectance from the optical rail in the target state. Giving less control in the final optical state (gray level) is a change in the degree of drive to the optical rail.

It has been found desirable to maintain an impulse of each of the voltage pulses comprising relatively small BPP. The magnitude of BPP may be defined by parameter d, an absolute value indicating the length of each of the two voltage pulses of BPP and a sine indicating the second sine of the two pulses. For example, the BPP shown in FIGS. 4A and 4B (although the BPP in FIG. 4C is assigned a d value −1 with a gap correction inserted between two pulses, in accordance with the scheme), has the d value +1 and Can be assigned to -1 respectively. In a preferred embodiment of the IMP drive scheme, all BPPs used have d values whose size is smaller than PL and preferably smaller than PL / 2, where PL (the same unit used to measure BPP) is driven. In the driving voltage characteristic of, it is defined as the average value of this voltage pulse whose length is not equal to the length of the voltage required to drive the pixel from one extreme optical state to another or the transition in two directions. In the example just given, d is expressed in units of display scan frame, and the BPPs of FIGS. 4A and 4B each have a voltage pulse that is one scan frame in length. In this case, PL will also be defined as a scan frame. All amounts can of course alternatively be expressed in time units such as seconds or milliseconds.

FIG. 17 of the accompanying drawings illustrates three waveforms generated by modifying the IMP waveform 1440 shown in FIG. 14 with the insertion of BPP. The first waveform shown in FIG. 17 (generally designated 1700) is a waveform except that a BPP 1702 including a -15 V 10 msec pulse preceding the +15 V 10 msec pulse is inserted at the end of the waveform. Same as (1440). The second waveform shown in FIG. 17 (generally designated 1720) is the same as the BPP 1702 but inserts a BPP 1722 inserted between the second reset pulse and the set pulse of the waveform, and inserts the BPP 1722. To accommodate, two reset pulses are moved by 20 msec earlier in time with a corresponding decrease in the duration of zero voltage at the beginning of the waveform. The third waveform (generally designated 1740) shown in FIG. 17 has a BPP 1742 inserted between the first and second reset pulses of the waveform, and the BPP 1742 has changed its pulse order to the BPP 1702. And 1722 inversely compared with each pulse having a length of 20 msec. To accommodate the BPP 1742, the first reset pulse is moved earlier by 40 msec in time with a corresponding decrease in the duration of zero voltage at the beginning of the waveform.

18 of the accompanying drawings illustrates three waveforms generated by modifying the IMP waveform 1440 shown in FIG. 14 by deleting BPP therefrom. The first waveform shown in FIG. 18 (generally designated 1760) deletes the BPP 1762 from waveform 1440, which includes the last 10 msec of the second reset pulse and the first scan frame of the set pulse, from waveform 1440. Created by no change in elements. The second waveform shown in FIG. 18 (generally designated 1780) may include a BPP 1782 that includes the last two scan frames of the first reset pulse and the first two scan frames of the second reset pulse. There is no change in the waveform element remaining after deleting from and similarly created by leaving a period of zero voltage of 40 msec at the point occupied by the deleted BPP. As a result, the third waveform shown in FIG. 18 (generally designated 1800) deletes from the waveform 1440 a BPP that includes the last scan frame of the first reset pulse and the first scan frame of the second reset pulse. By moving the remaining scan frame of the first reset pulse after 20 msec in time to close the resulting gap, it is created with a corresponding increase in the duration of zero voltage at the beginning of the waveform.

FIG. 19 of the accompanying drawings illustrates possible modifications of the waveform 1720 shown in FIG. 17. The upper portion of FIG. 19 includes the BPP 1722, repeating the fundamental waveform 1720 from FIG. 17. FIG. 19 also illustrates a modified waveform (generally designated 1920) that includes a BPP 1922 similar to BPP 1722 but inserted 40 msec earlier in time, prior to the last 4 scan frames of the second reset pulse. . 19 also shows a second modified waveform (generally designated 1940), which is similar to BPP 1722 but includes BPP 1942 being inserted 130 msec earlier in time before the last 13 scan frames of the second reset pulse. To illustrate. As already pointed out, the final gray level achieved by the waveform as shown in FIG. 19 is a function of the position of the insertion of the balance pulse pair, and the correction as shown in FIG. 19 can be used for fine adjustment of the final gray level. Can be.

20 of the accompanying drawings illustrates a modified IMP waveform generated by inserting a period of zero voltage (interrupt) into the basic IMP waveform 1440 shown in FIG. The first waveform shown in FIG. 20 (generally designated 2000) is the second reset pulse of the waveform, with two reset pulses moving 20 msec earlier in time and a corresponding decrease in the duration of zero voltage at the beginning of the waveform. And a 20 msec interrupt (designated 2002) between the set pulses. The second waveform shown in FIG. 20 (generally designated 2020) is generally similar to waveform 2000, but waveform 2020 is inserted after the first four scan frames of the set pulse, 40 msec after interrupt 2002. Has its interruption (designated 2022). The third waveform shown in FIG. 20 (generally designated 2040) is also generally similar to waveform 2000 but waveform 2040 is inserted after the first 13 scan frames of the set pulse, 130 msec after interrupt 2002. Has its interruption (designated 2042). In both waveforms 2020 and 2040, the scan frame of the set pulse preceding each of the breaks 2022 or 2042 is shifted 20 msec earlier in time compared to the waveform 2000 to accommodate the break. As already mentioned, the final gray level achieved by the waveform is sensitive to both the presence and location of the interruption, and the modification of the base waveform as shown in FIG. 20 is used to finely adjust the final gray level produced by the waveform. Can be used.

As already pointed out, the IMP driving scheme is DC balanced in the sense that the algebraic sum of the impulses applied to the pixels for any gray level loop (i.e. any sequence of gray levels starting and ending at the same gray level) is zero. Is preferably. An example of a gray level loop is

1-> 1

2-> 3-> 2

4-> 4-> 3-> 2-> 4.

A gray level loop that cannot be reduced begins at the first gray level, passes through zero or more gray levels, ends at the first gray level, and visits one or more gray levels at least once, except for the final gray level that has already been indicated to be the same. Can be defined as a gray level sequence that does not. Obviously, at any gray scale, there is a finite number of loops that cannot be reduced. Also, any gray level, e.g., complex sequence

1-> 4-> 3-> 2-> 3-> 2-> 3-> 2-> 1-> 2-> 1

It can be seen that can be reduced to a sequence of non-reducible loops and to an non-reducible loop put in an unreducible loop. For example, the sequence consists of a finite set of non-reducible loops, that is, two consecutive 2-> 3-> 2 loops followed by 1-> 4-> 3-> 2-> 1 loops followed by It can be decomposed into 1-> 2-> 1.

If all non-reducible loops are DC balanced, all possible sequences that start and end at the same gray level are DC balanced. A preferred embodiment of the IMP drive scheme is that the total voltage impulse of all non-reducible loops is zero, ie the waveform is DC balanced.

It is absolutely necessary to balance the IMP waveform with DC. While large DC imbalances result in poor display image performance, small amounts of DC imbalance can be tolerated. If it is not possible to achieve full DC balance, the IMP driving scheme is such that the total impulse of any non-reducible loop divided by the number of transitions in the loop is less than Q and is preferably controlled, where Q is the two of the pixels. One quarter of the smaller of the absolute value of the total impulse for transition between extreme optical states, where the impulse is determined using the characteristic voltage of the drive scheme. The total impulse required to drive the image film from one extreme optical state to another indicates the characteristic impulse of the medium and some DC imbalance should be measured relative to this characteristic impulse.

It is often desirable for an IMP drive to be of the "picket fence" type. As described in the MEDEOD application described above, it is often necessary or desirable to drive an electro-optical display using a drive circuit capable of supplying only two drive voltages. Since bi-safety electro-optical media are normally required to be driven in both directions between their extreme optical states, at least three drive voltages, i.e., V must be 0, + V,-when necessarily at any drive voltage. It may appear that V may be required so that one electrode for a particular pixel (typically a common front electrode in a conventional active matrix display) is the other electrode (usually a pixel electrode for that pixel) to which the pixel should be driven. Depending on the direction, it can be kept at + V or -V, while it can be kept at zero. When a two-voltage drive circuit is used, each waveform of the drive scheme is divided into time segments, which typically are but are not necessarily the same duration. In a non-picket fence drive scheme, a positive, zero or negative drive voltage may be applied to any particular pixel in any time segment. For example, while the individual pixel electrodes are kept at + V, 0 or -V, in three drive voltage systems, the common front electrode may be kept at zero. In the picket fence driving scheme, each time segment is actually divided into two, and in one of the two resulting segments, only the positive or zero driving voltage may be applied to any particular pixel in the other resulting segment, Only negative or zero driving voltages may be applied to any particular pixel. For example, consider driving voltages V and v where V> v. At the first of each pair of segments, the common front electrode is set to V and the pixel electrode is set to V (zero drive voltage) or v (negative drive voltage). In the second of each pair of segments, the common front electrode is set to v and the pixel electrode is set to v (zero drive voltage) or V (positive drive voltage). The resulting waveform is twice the length of the corresponding non-picket fence waveform.

It is often also desirable for an IMP drive scheme to be able to update locally. As described in the MEDEOD application described above, it is often desirable to drive an electro-optical display in such a way as to locally update a particular area of the display that is undergoing change while the rest of the display does not change. It may be desirable to update the dialog box to write text without updating the background image on the display. Locally updated versions of some IMP drive schemes can be made by removing all non-zero voltages from the waveform for zero transitions (ie, transitions from one gray level to the same gray level). For example, a waveform from gray level 2 to gray level 2 is typically made up of a series of voltage pulses. Removing a nonzero voltage from this waveform and doing so for all other zero transitions will result in a locally updated version of the IMP waveform. This local update version is beneficial when required to minimize extraneous flashing during the transition.

The following experiment illustrates the use of the modifications discussed above in the fine control of gray levels produced by the IMP drive scheme.

An encapsulated electrophoretic medium comprising polymer-coated titania and polymer-coated carbon black particles in a hydrocarbon liquid encapsulated in a gelatin / acacia capsule and comprising an internal phase is prepared and incorporated into an experimental single-pixel display. Substantially all are described in Paragraphs [0069] to [0076] of the aforementioned US Patent Publication 2002/0180687. This experimental display was then driven using four gray level IMP drive schemes. The display can be driven by +15 V, 500 msec pulses from gray level 4 (white) to gray level 1 (black), the opposite transition occurs by -15 V, 500 msec, and the default two reset pulse IMP The drive scheme was thus constructed. 21 of the accompanying drawings shows all 16 waveforms of this basic IMP drive scheme, labeled [R ₁ R ₂ ], in a highly schematic manner, so that the first given number indicates the final gray state. For example, the [1 4] waveform shown in the upper right corner of FIG. 21 causes a first +15 V 500 transition in gray level 4 (white) to gray level 1 (black) and driving the pixel to black. an msec reset pulse, a second -15 V 500 msec reset pulse that drives the pixel to white, and a +15 V 500 msec set pulse that drives the pixel to black.

The experimental display was driven using this basic IMP driving scheme through the varying sequence of gray levels and the reflectance of the display measured at the end of each sequence, and the results are shown in FIG. 22. Each point in FIG. 22 represents a reflectance following a different sequence of gray levels before reaching the final gray level shown on the abscissa. It will be seen from FIG. 22 that the reflectivity achieved at the same nominal gray level varies considerably, which is of course undesirable because it adversely affects the quality of the image produced by the multi-pixel display. In particular, the human eye is very sensitive to minor variations in gray levels that occur within blocks of pixels that must be at the same gray level and FIG. 22 indicates that such variations can be expected as a result of differences in the previous gray levels of the pixels. do.

The IMP drive scheme uses zero voltages at the beginning and end of various waveforms, with insertion and deletion of balanced pulse pairs (with closure of the resulting gap in the case of deletion) to achieve inconsistent gray levels after various gray level sequences. Modified in the manner described above by the insertion or removal of the period, to achieve the modified IMP drive scheme shown in FIG. FIG. 24 shows the gray level generated by the modified IMP driving scheme of FIG. 23 using the same gray level sequence as in FIG. It will be seen from FIG. 24 that the modified IMP drive scheme of FIG. 24 produces much more inconsistent gray levels than the unmodified drive scheme of FIG. 21.

Section C: Balanced Pulse Pair Retention Time Compensation Method and Apparatus

As already mentioned, in a third aspect, the present invention provides a method of driving an electro-optical display having one or more pixels capable of achieving two or more different gray levels. In this method, two or more different waveforms are used for the same transition between specific gray levels, depending on the duration of the pixel's dwell time at the beginning of the transition, and these two waveforms are used to insert one or more pairs of one or more balanced pulse pairs and And / or differ from one another by the deletion, or the insertion of one or more periods of zero voltage, where a "balanced pulse pair" has a previously defined meaning. In this way the drive scheme is very preferably the term DC balance as defined above.

In this balanced pulse pair dwell time compensation (BPPDTC) method (as in the previously described BPPSS and IMP methods), insertion or deletion of the balanced pulse pair and / or zero voltage period (interruption) is performed within a single waveform element or in two consecutive It may occur between waveform elements. The two waveforms used for the same transition following the different dwell time in the initial state at which the transition begins may be referred to as "alternative dwell time" or "ADT" waveforms below.

This movement of a BPP or interruption is a combination of the deletion of a BPP or interruption at one location and the insertion of a BPP or interruption at a different location, or the deletion of a BPP or interruption at one location and a different BPP at the same location or ( The ADT waveforms may differ from one another by the position and / or duration of the BPP or the interruptions in the waveform (eg, in the case of a change in duration at the same location) as a combination of insertions of interruptions. , See discussion of FIGS. 25B-25E below).

In the BPPDTC driving scheme, the insertion or deletion of BPP and / or interruption causes the same problem and may be treated in the same way, as in the BPPSS and modified IMP driving schemes described in Sections A and B above. Thus, if the difference between ADT waveforms consistent with the BPPDTC aspect of the present invention includes the deletion of one or more BPPs, the period previously occupied by the deleted BPP or each thereof may be left as a period of zero voltage. Alternatively, this period may be followed by the insertion of some or all of the waveform elements, typically at some later stage of the waveform, typically at the end thereof, with the insertion of a period of zero voltage so that the entire length of the waveform is maintained. It may be "sealed" by moving earlier in time. (In a practical display that will typically have more than a few thousand pixels, if one or more pixels undergoing all possible transitions will normally exist at any transition, and the waveforms for all pixels are not the same length, the controller logic is extremely Alternatively, of course, the period of time may be a part or all of the earlier waveform elements, later in time, with the insertion of a period of zero voltage, at any earlier stage of the waveform, typically at its beginning. It may be "sealed" by moving.

Similarly, BPP insertion adds the total duration of the waveform unless the existing period of zero voltage can be removed at the same time. Since all waveforms of the drive scheme have very preferably the same total length, in order to compensate for the increase in the overall waveform length caused by the insertion of the BPP, if one waveform of the drive scheme has an inserted BPP, the drive scheme All other waveforms of must have a period of zero voltage added to them, or any other modification made. For example, if a 40 msec BPP is inserted into the black to white waveform shown in Table 1 above (with a waveform length of 420 msec), the 40 msec interruption is shown in Table 1 so that all waveforms have a length of 460 msec. May be added to the remaining three waveforms. Obviously, if appropriate, BPP may be added to the other three waveforms rather than interruption, or any combination of BPP and interruption in total of 40 msec may be used.

Preferred driving schemes and waveforms of the BPPDTC aspect of the present invention will now be described by way of example only. The balance pulse pair and waveform used in this driving scheme may be of any type described above, for example, the type of BPP shown in FIGS. 4A-4C may be used.

25A-25E illustrate alternative residence time waveforms that may be used for a single transition in accordance with the BPPDTC aspect of the present invention. 25A illustrates the black to white waveforms mentioned in the third row of Table 1 and the last row of Table 2. FIG. Since this is a waveform that is suitable for the transition from black to white after a long residence time in the black state, to generate a waveform that is suitable for transition from black to white after a shorter residence time in the black state, It may be considered a waveform from base black to white that is modified in accordance with the BPPDTC aspect. As already pointed out, the base waveform of FIG. 25A consists of -15 V, 400 msec pulses followed by 0 V for 20 msec.

FIG. 25B illustrates the modification of the base waveform of FIG. 25A found to be effective in reducing the reflectivity of the final white state when a transition from black to white occurs after a short dwell time that does not exceed 0.3 seconds in the initial black state. . The waveform of FIG. 25B is generated by inserting a similar BPP to the BPP 300 shown in FIG. 4A at the end of the -15 V, 400 msec pulse of the waveform of FIG. 25A, the waveform of FIG. 25B being a +15 V, 20 msec pulse. And a -15 V, 420 msec pulse preceding 0 V for 20 msec.

25C and 25D illustrate two ADT waveforms for a transition from black to white that are the same as the waveforms of FIGS. 25A and 25B. The waveforms of FIGS. 25C and 25D were found to be effective in normalizing the reflectance of the final white state when the transition from black to white occurred after 0.3 to 1 second and 1 to 3 seconds, respectively, in the black state. The waveforms of FIGS. 25C and 25D are generated by inserting the same BPP as in FIG. 2B into the waveform of FIG. 25A at a different position from the position used in FIG. 25B. As pointed out above, it has been found that the location at which BPP is inserted into (or deleted from) the base waveform has a significant effect on the final optical state following the transition, and therefore, the location of the insertion of BPP with the base waveform. Moving is an effective means of compensating the waveform for variations in the residence time of the pixel in the initial optical state.

FIG. 25E is a preferred replacement for the waveform of FIG. 25A resulting in a transition from black to white after a long residence time (more than 3 seconds) in the black state. The waveform of FIG. 25E is generally similar to that of FIGS. 25B-25D in that it is generated by inserting the same BPP into the waveform of FIG. 25A. However, in FIG. 25E, it was found that BPP is inserted at the beginning of the waveform, and it is desirable to make a pulse of BPP 40 msec rather than 20 msec in duration. Because this makes the overall duration of the waveform 500 msec, when the waveform of Fig. 25E is used in combination with the waveforms of Figs. 25B-25D, the waveform of Figs. 25B-25D is added with an additional 40 msec 0 V at the end of the waveform. Pad ". Thus, a preferred set of ADT waveforms for the transition from black to white is shown in Table 3 below:

TABLE 3

Note that the impulse for the transition from black to white is -15 V * 400 msec or 6 seconds for all ADT waveforms in Table 3, so the drive scheme is DC balanced at all initial state residence times.

As already mentioned, DTC can also occur by BPP deletion from the base waveform. For example, consider the driving scheme shown in Table 4 below:

Table 4

In this drive scheme, all waveforms that are not just full drive schemes are "internally" DC balanced, and the desirability of such internal DC balance is discussed in detail in the aforementioned WO 2004/090857. Again, it should be understood that the DTC from white to black can occur in a similar manner, but the method for DTC will be discussed with reference to the black to white transition.

In this case, the DTC of the transition from black to white deletes BPP, ie one voltage of one polarity and one duration, simultaneously removing similar portions of one voltage pulse of opposite polarity and the same duration. This occurs by removing part of the pulse. To replace a pulse segment that was deleted with a period of zero voltage or the remainder of the waveform can be shifted in time to occupy a period previously occupied by the erased pulse pair, to maintain the total update time, Zero voltage segments matching the duration of the deleted pair may be added elsewhere, typically at the beginning or end of the waveform.

26A, 26B and 26C diagrammatically illustrate the process for modification of the waveform from black to white listed in the third column of Table 4 above for DTC at short dwell times of less than 0.3 seconds in the black state. 26A illustrates the base waveforms from Table 4. FIG. FIG. 26B shows that the resulting gap is removed by moving the negative pulse forward in time, as indicated by the arrow in FIG. 26B, and the last 80 msec portion of the positive voltage pulse and the first 80 msec of the negative voltage pulse from the waveform of FIG. 26A. The schematic of the deletion of the BPP formed by the part is shown. The resulting dwell time compensation waveform comprising the 320 msec positive pulse, the 320 msec negative pulse and the 180 msec zero voltage duration is shown in FIG. 26C.

In this case, it was found that DTC for all dwell times can occur simply by changing the length of the deleted BPP and that the FIG. 26A base waveform for longer dwell times of 3 seconds or more in the black state was satisfactory. Thus, in this case a complete list of ADT waveforms for the transition from black to white is shown in Table 5 below:

Table 5

As already mentioned, when the BPP is deleted from the base waveform in the manner shown in Fig. 26B, it is not necessary for the remaining components to be moved in time, and the deleted BPP can be replaced simply by a period of zero voltage. . Table 6 below shows a modified set of ADT waveforms similar to that of Table 5 but with deleted BPP replaced by a period of zero voltage:

Table 6

Although the BPPDTC of the present invention has been described above mainly with reference to a display having only two gray levels, it is not so limited and may be applied to a display having a larger number of gray levels. Also, in the particular waveform illustrated in the figure, the insertion or deletion of two elements of BPP occurred at a single point in the waveform, but the present invention is not limited to waveforms where insertion or deletion of BPP occurs at a single point, and BPP The two elements of may be inserted or deleted at different points, ie the two pulses making up the BPP need not be immediately contiguous and may be separated by time intervals. In addition, one or all pulses of the BPP can be subdivided into compartments, which can be deleted or inserted into the waveform for the DTC. For example, BPP may consist of a +15 V, 60 msec pulse and a -15 V, 60 msec pulse. This BPP can be divided into two components, e.g., +15 V, 60 msec pulses, and -15 V, 40 msec pulses immediately preceding -15 V, 20 msec pulses, and these two components are DTC Are simultaneously deleted from or inserted into the waveform to achieve it.

It has been found that the insertion or deletion of zero voltage segments from the waveform affects the final gray level after the transition, thus the insertion or deletion of such zero voltage segments provides a second method of adjusting the final gray level to achieve DTC. . Insertion or deletion of these zero voltage segments may be used alone or in combination with insertion or deletion of BPP.

Although the BPPDTC of the present invention has been described above with the primary reference to a pulse width adjustment waveform in which the voltage applied to a pixel at a given time may be only -V, 0, + V, the present invention is directed to the use of such a pulse width adjustment waveform. It is not limited and may be used with voltage regulating waveforms or waveforms using pulse and voltage regulation. The above definition of a balanced pulse pair can be satisfied by two pulses of opposite polarity with a total impulse of zero, and do not require the two pulses to be the same voltage or duration. For example, in the voltage regulation driving scheme, the BPP may be configured with a +15 V, 20 msec pulse preceding the -5 V, 20 msec pulse.

From the foregoing, it will be seen that the BPPDTC aspect of the present invention allows for the retention time compensation of the drive scheme while maintaining the DC balance of the drive scheme. This DTC will reduce the level of ghosting in the electro-optical display.

Section D: Target Buffer Methods and Devices

As already mentioned, the present invention provides two different methods of using a target buffer to drive an electro-optical display having a plurality of pixels, each of which can achieve two or more different gray levels. The first of these two methods, the non-polar target buffer method, comprises providing an initial, final and target data buffer; Determining when data in the initial and final data buffers are to be different; And when such a difference is found, (i) if the initial and final data buffer contain the same value for a particular pixel, set the target data buffer to this value; (ii) if the initial data buffer contains a larger value than the final data buffer for a particular pixel, setting the target data buffer to the value of the sum of the initial data buffer and the increment; (iii) if the initial data buffer contains a smaller value than the final data buffer for a particular pixel, updating the value of the target data buffer by setting the target data buffer to the initial data buffer and the value of the incremental subtraction. ; Updating the image on the display using the data of the initial data buffer and the target data buffer as the initial and final states of each pixel, respectively; Next, copying data from the target data buffer to the initial data buffer.

In the polar target buffer method, which is the second of these two methods, the final, initial and target data buffers are provided again with an array of polarity bits arranged to store polarity bits for each pixel of the display. The data of the initial and final data buffers are compared, and if they are different, the values of the polarity bit array and the target data buffer are (i) different for the particular pixel of the initial and final data buffer, and the value of the initial data buffer is extreme of the pixel. When indicating an optical state, setting the polarity bit for the pixel to a value indicating transition to the opposite extreme optical state; And in accordance with the associated value of the polarity bit array, the values of the polarity bit array and the target data buffer are updated in a manner that sets the target data buffer to the value of the sum or subtraction of the initial data buffer and the increment. The image on the display is then updated in the same manner as the first method, after which the data from the target data buffer is copied into the initial data buffer. This step is repeated until the initial and final data buffers contain the same data.

Prior art controllers for bistable electro-optical displays typically use logic similar to that shown in the following listing 1 (all listings are in pseudocode).

Listing  One

With a controller operating in this manner, the display waits to receive new image information, and then, when such new image information is received, performs a complete update before sending new information to the display, ie If one new image is accepted by the display, the display cannot accept the second new image until the display has completed rewriting of the display necessary to display the first new image, and in some cases such a rewrite procedure May take hundreds of milliseconds, and for reference some of the driving schemes are disclosed in sections A to C above. Thus, as the user scrolls or types, the display appears to be unresponsive to user input during this complete update (rewrite) time.

On the other hand, the controller causing the non-polar target buffer method of the present invention operates by the logic illustrated by the following Listing 2 (this type of controller may be referred to herein as "listing 2 controller" for convenience).

Listing  2

In this modified controller logic for the NPTB method, there are three image buffers. The initial and final buffers are the same as in the prior art controllers, and the new third buffer is the "target" buffer. This display controller can accept new images into the final buffer at any time. If the controller finds that the data in the last buffer is no longer the same as the data in the initial buffer (i.e. rewriting of the image is required), the new target data set is between the relevant values of the initial and final buffer. Depending on the difference, it is constructed by increasing or decreasing the values of the initial buffers by one (or not changing them). The controller then performs the display update in the conventional manner using the values from the initial and target buffers. When this update is complete, the controller copies the value from the target buffer to the initial buffer and then repeats the operation of calculating the difference between the initial and final buffer to create a new target buffer. The full update is complete when the initial and final buffers have the same data set.

Thus, in the NPTB method, a full update occurs as a series of subupdate operations, and one such subupdate operation occurs when the image is updated using the initial and target buffers. The term "meso-frame" will be used below for the period required for each such sub-update operation, and this meso-frame as well as a single scan frame of the display (see MEDEOD application described above) And a period between what is required for the superframe or a period required to complete the full update.

The NPTB method of the present invention improves interactive performance in two ways. Firstly, in the prior art method, the final data buffer is used by the controller during the update process so that no new data can be written to this final data buffer while the update is being performed, so that the display is the entire period required for the update. Cannot respond to new inputs while In the NPTB method of the present invention, the final data buffer is used only for the calculation of the data set of the target data buffer, and this calculation, which is simply a computer calculation, can be made much faster than the update operation requiring a physical response from the electro-optical material. Once the calculation of the data set in the target data buffer is complete, the update does not require any further access to the final data buffer, so that the final data buffer can accept new data.

For reasons discussed in the MEDEOD application described above and discussed further below with respect to waveforms, if a pixel is driven by a voltage pulse of one polarity from one extreme optical state, until the pixel reaches its other extreme optical state In the sense that no opposite polarity voltage pulse is applied to the pixel, it is often preferred that the pixel is driven in a cyclic manner, see, for example, FIGS. 11A and 11B and the related description of 2003/0137521 described above. This limitation may be referred to as a controller operating with the logic illustrated by Listing 3 (this type of controller may hereinafter be referred to as "listing 3 controller" for convenience, and those skilled in the art will understand the pseudocode of the operation with different numbers of gray levels). Although easily modified, this listing is satisfied by the PTB method of the present invention, which may use black gray levels with black levels numbered from black 1 to white).

Listing  3

This PTB method requires four image buffers, the fourth being a "polar" buffer with a single bit for each pixel of the display, which single bit indicates the current direction of transition of the associated pixel, i.e. the pixel. Indicates whether this is currently transitioning from white to black (0) or black to white (1). If the pixel concerned is not currently undergoing a transition, the polarity bit retains its value from the previous transition, for example, a pixel that is stable in the light gray state and was previously white will have a polarity bit of zero.

In the PTB method, the polarity bit array is considered when a new target buffer data set is constructed. If the pixel is currently black or white and a transition to the opposite state is required, the value of the polarity bit will be set accordingly and the target value will be set to a gray level close to black or white respectively. Alternatively, if the initial state of the pixel is an intermediate (gray) state, the target value is calculated by increasing or decreasing by 1, depending on the value of the polarity bit (+1 if polar = 1, -1 if polar = 0).

In this driving scheme, the state of the pixel in the intermediate state is independent of the current value of the final state for that pixel. The pixels that start the transition from black to white or white to black continue in the same direction until it reaches the opposite optical rail (extreme optical state, typically black or white). If the desired image and thus the target state changes during the transition, then the pixels will return in the opposite direction.

Preferred waveforms for use in the TB method of the present invention will now be discussed. Table 7 below illustrates one possible transition matrix that can be used for 1-bit (monochrome) operation with the NPTB and PTB methods of the present invention, which uses two intermediate states.

TABLE 7

The structure of this transition matrix with black, white, and two intermediate gray states looks very similar to that used in prior art two-bit drive schemes, such as those described in MEDEOD applications. However, in the TB method of the present invention, this intermediate state does not correspond to a stable gray state, but only a transition state that exists only between the completion of one meso-frame and the beginning of the next. In addition, there is no limitation on the uniformity of the reflecting force in this intermediate state.

Note that in the transition matrix shown in Table 7, multiple elements (indicated by dashes) are not allowed. The controller causes each transition to change the gray level by 1 unit in each direction, so that transitions involving multiple changes in gray level, for example direct 1-4 black to white transitions, are prohibited. The elements of the leading diagonal of the transition matrix (corresponding to zero transition) were prohibited for the intermediate state, and these leading diagonal elements are not recommended in the white and black states, but are strictly prohibited, as indicated by the asterisks in Table 7 It is not.

In the monochrome NPTB method, the update sequence appears as a series of states starting and ending in the extreme optical state (optical rail) with a sequence of intermediate gray states separated by zero residence time. For example, a simple transition from black to white

It may appear as 1-> 2-> 3-> 4.

On the other hand, if the final state of the display changes during the update, this transition

It can also be 1-> 2-> 3-> 2-> 1.

In the final state, multiple changes

It is also possible to produce transitions such as 1-> 2-> 3-> 2-> 3-> 4.

More generally, there are four possible types of transitions between extreme black and white optical states,

1-> 2-> 3 (-> 2-> 3)-> 4

1-> 2 (-> 3-> 2)-> 1

4-> 3-> 2 (-> 3-> 2)-> 1

4-> 3 (-> 2-> 3)-> 4

Where parenthesis means zero or more repetitions of the sequence in parentheses within parentheses.

The optimization ("adjustment") of this class of NPTB-driven schemes is a transition matrix to ensure non-consistent reflectivity values for the 1 (black) and 4 (white) states, independent of the number of iterations of the parenthesis sequence. Requires adjustment of a nonzero element of. The waveform operates for any dwell time in the black and white extreme optical states, but the dwell time in the intermediate state is always zero, so as mentioned above, the reflectivity of the transition state is not critical.

In general, the time required for any single meso-frame update is equal to the length of the longest element in the transition matrix. Thus, the total update time is three times the length of this longest element. In the best case, the black-to-white and white-to-black (1-> 4 and 4-> 1) waveforms can be divided into three equal-length portions, which approach maintains the same duration for the total update, We will reduce the update wait time to one third of the total update time. The longer the length of the meso-frame update, which may be the result of optimizing the waveform, the less important the benefit. For example, if one element is twice the length, the latency will increase to two thirds of the simple update time, and a full transition will require twice the length previously. It is possible to test to find the longest element present in a given meso-frame, and dynamically adjust the update time to that length, but this extra computational benefit will not matter.

It should be taken into account which electro-optical properties of the medium cause the display to use a medium suitable for using this type of NPTB drive. First, because this waveform combines a potentially much longer dwell time between transitions and a series of dwell times close to zero between meso-frames, the dwell time dependence of the medium is zero (ideally, or at least very Should be low). Second, because the direction of the transition may change in the mid-stream, for example, a 2-> 1 transition may follow a transition of either 1-> 2 or 3-> 2, the medium is in the initial state of the particular transition. It should be very insensitive or unaffected by the preceding optical state. As a result, the electro-optical medium must be symmetrical in its reaction, in particular close to the black and white state, 1-> 2-> 1 or 4-> 3-> reaching the same black or white state respectively. It is difficult to generate a DC balanced waveform that can perform four transitions.

For the reasons mentioned above, "intermediate reversal" in the NPTB driving scheme makes it very difficult to develop an optimized waveform. On the other hand, the PTB drive scheme significantly reduces the need for electro-optical media, and therefore must significantly mitigate the difficulty in optimizing the NTPB drive scheme while still providing improved performance.

While the configuration of the transition matrix for the PTB driving scheme should be the same as that for the NPTB driving scheme, the PTB driving scheme allows only two black to white and white to black transitions, i.e.

1-> 2-> 3-> 4; And

Only 4-> 3-> 2-> 1 is allowed.

In practice, these two transitions may be identical to the standard 1-> 4 and 4-> 1 transitions with transitions divided into three equal parts. Some slight return may be desirable to account for some delay between meso-frames, but adjustment is easy. For a simple typing input, this drive scheme should produce a two thirds decrease in latency.

There are also some disadvantages to the PTB method. Since extra memory is required for the polar bit array, and considering the direction of the transition in each pixel requires extra data (polar bits) to be considered in addition to the initial and final states for the transition. The controller operates this simpler drive. In addition, while the PTB method reduces the wait time to start the update, the controller must wait until the update is complete before reversing the transition. This limitation is apparent when the user types a character and immediately deletes it, and the delay before the character is deleted is equal to the total update time. This limits the usefulness of the PTB method for cursor tracking or scroll ring.

Although the NPTB and PTB methods are mainly described above for the monochrome driving scheme, they are compatible with the gray scale driving scheme. The NPTB method is inherently fully gray scale compatible, and the gray scale compatibility of the PTB method is discussed below.

From a driving scheme point of view, in the gray scale driving scheme, the intermediate states correspond to the actual gray levels, and therefore the optical values of these intermediate states are limited, so creating a workable gray scale driving scheme for NPTB is better than the corresponding monochrome scheme. Obviously it will be more difficult. It is also very difficult to create a gray scale drive scheme for the PTB method. In order to reduce latency, the meso-frame transition must be clearly shortened. For example, a 2-> 3 transition may be an independently manipulated transition, the last stage of a 1-> 2-> 3 transition, or the first of a 2-> 3-> 4 transition. Thus, there is a competitive demand to make this transition short (to achieve a shorter overall update) and exactly (if the transition stops at gray level 3).

The gray scale PTB method may be modified by introducing multiple gray level steps (ie, re-inserting more than one element of one step removed from the leading diagonal of the associated transition matrix, as shown in Table 7). Corresponding to, by allowing the gray level to change by more than one unit during each meso-frame), thus eliminating the degeneration of the meso-frame step described in the preceding paragraph. This modification may occur by replacing the polarity bit matrix with a counter array that, for each pixel of the display, contains more than one bit, up to the number of bits required for the full gray scale image representation. The waveform may include up to a total N × N transition matrix, with each waveform divided evenly into four (or other arbitrary number of meso frames).

The particular TB method described above is a 2-bit gray scale method, with two intermediate gray levels, but the TB method can of course be used for any number of gray levels. However, the incremental benefit of reduced latency will tend to decrease as the number of gray levels increases.

Thus, the present invention provides two types of TB methods that provide a significant reduction in update latency in monochrome mode, while minimizing the complexity of the controller algorithm. This method is particularly useful for interactive 1-bit (monochrome) applications, for example, handheld terminals and electronic dictionaries, where rapid response to user input is most important.

Section E: Waveform Compression Methods and Devices

As already mentioned, the last major aspect of the invention relates to a method of reducing the amount of waveform data that must be stored for driving a bistable electro-optical display. More specifically, this aspect of the present invention provides a "waveform compression" or "WC" method for driving an electro-optical display having a plurality of pixels, each of which can achieve two or more different gray levels. The method includes: storing a base waveform that defines a sequence of voltages to be applied during a particular transition by a pixel between gray levels; Storing a multiplication factor for a particular transition; And causing a specific transition by applying a sequence of voltages to the pixel for a period of time according to the multiplication factor.

When an impulse-driven electro-optic display is driven, each pixel of the display is associated with a voltage pulse (ie associated with that pixel) to cause a transition from one optical state of the pixel to another, typically between gray levels. Voltage difference between two electrodes) or a transient series of voltage pulses (ie, waveforms). Although the data may alternatively be stored on a host computer or other auxiliary device, the data needed to define a set of waveforms for each transition (forming a complete drive scheme) is generally stored in memory on the display controller. do. The drive scheme may comprise a number of waveforms (as described in the MEDEOD applicator described above), environmental parameters such as temperature and humidity, and non-environmental fluctuations, eg, operating life of an electro-optic medium It may be necessary to store multiple sets of waveform data to account for variations in. Thus, the amount of memory required to hold the waveform data can be significant. It is desirable to reduce the amount of memory to reduce the cost of the display controller. Simple compression schemes that can actually be accommodated in a display controller or host computer can be beneficial in reducing the amount of memory needed for waveform data and thus reducing display controller cost. The waveform compression method of the present invention provides a simple compression scheme that is particularly beneficial for electrophoretic displays and other known bistable displays.

The uncompressed waveform for a particular transition is stored as a series of bit sets in which each bit set specifies a particular voltage to be applied at a particular point in the waveform. By way of example, a pixel is driven to black using a positive voltage (+10 V in this example), to white using a negative voltage (-10 V), and maintained at its current optical state at zero voltage. Consider the level voltage driving scheme. The voltage for a given time element (scan frame for active matrix display) can be encoded using 2 bits, for example, as shown in Table 8 below:

Table 8

Using this binary representation, a waveform containing +10 V pulses lasting for five scan frames preceding two scan frames of zero voltage and used to drive an active matrix,

01 01 01 01 01 00 00 Waveforms containing multiple time segments require storage of a set of bits of multiple waveform data.

In accordance with the WC method of the present invention, the waveform data is stored as a base waveform (such as the binary representation described above) and as a multiplication factor. The display controller (or other suitable hardware) applies a sequence of voltages defined by the base waveform to the pixels for a period of time according to the multiplication factor. In a preferred form of this WC method, a bit set (as given above) is used to represent the base waveform, but the voltage defined by each bit set is applied to the pixel for n time segments, where n is applied to the waveform. The associated multiplication factor. The multiplication factor must be a natural number. For multiplication factor 1, the applied waveform does not change from the base waveform. For more than one multiplication factor, the representation of the voltage series is compressed for at least some waveforms, i.e. fewer bits are needed than needed if the data was stored in uncompressed form to represent such a waveform.

For example, using the three voltage level binary representations of Table 8, +10 V preceding 9 scan frames of -10 V preceding 6 scan frames of +10 V followed by 3 scan frames of 0 V Consider a waveform that requires 12 scan frames. This waveform is

01 01 01 01 01 01 01 01 01 01 01 01 10 10 10 10 10 10 10 10 10 01 01 01 01 01 01 00 00 00, which are expressed in uncompressed form, in compressed form,

Multi-application factor: 3

The base waveform is represented by 01 01 01 01 10 10 10 01 01 00.

The length of the voltage sequence that should be assigned for each waveform is determined by the longest waveform. For encapsulated electrophoresis and many other electro-optic displays, the longest waveforms are typically required at the lowest temperatures at which the electro-optic medium responds slowly to the applied field. At the same time, the resolution needed to achieve a successful transition is reduced when the response is slow, so that there is little loss in the accuracy of the optical state by grouping successive scan frames through the WC method of the present invention. Using this compression method, multiple scan frames (or generally time segments) suitable for waveforms at mild and high temperatures with short update times can be assigned to each waveform. At low temperatures where the number of scan frames required may exceed memory allocation, a multiplication factor larger than one unit may be used to generate long waveforms. This finally results in reduced memory requirements and costs.

The WC method of the present invention is in principle equivalent to simply changing the frame time of an active matrix display at various temperatures. For example, the display can be driven at room temperature, 50 Hz, and can be driven at 0 ° C., 25 Hz to extend the acceptable waveform time. However, the WC method is excellent because the backplane is designed to minimize the effects of capacitive and resistive voltage artifacts at a given scan rate. As one deviates significantly from this optimal scan rate in either direction, at least one type of artifact occurs. Therefore, it is better to keep the actual scan rate constant while grouping the scan frames using the WC method, which actually provides a way to achieve a virtual change in the scan rate without actually changing the physical scan rate.

Claims (48)

A method of driving an electro-optical display having one or more pixels capable of achieving three or more different gray levels comprising two extreme optical states, The method includes one or more reset pulses sufficient to drive the pixel to or near one of the extreme optical states, followed by one or more set pulses sufficient to drive the pixel to a different gray level than the one extreme optical state. Applying to the pixel a base waveform comprising the one or more reset pulses, The method is: (a) inserting one or more balanced pulse pairs into the basis waveform; (b) deleting one or more balanced pulse pairs from the base waveform; And (c) inserting one or more zero voltage periods into the basis waveform, Characterized in that the basis waveform is modified by one or more of A "balanced pulse pair" is a sequence of two pulses of opposite polarity such that the total impulse of the balanced pulse pair is essentially zero. The method of claim 1, Wherein the basis waveform is modified by insertion of one or more balance pulse pairs or deletion of one or more balance pulse pairs. The method of claim 2, Wherein the two pulses of the balanced pulse pair are each of constant voltage but of opposite polarity and of equal length. The method of claim 2, And said period of said base waveform occupied by said deleted pair of balanced pulses or each of which is replaced by a zero voltage period. The method of claim 2, One or more balanced pulse pairs are deleted from the base waveform, another element of the base waveform is time shifted to occupy the period previously occupied by the deleted balanced pulse pair or each, and the deleted balanced pulse pair or A zero voltage period is inserted at a point in time that is different from the point occupied by each. The method of claim 1, The basis waveform may be continuously: a first reset pulse sufficient to drive the pixel to or near one of the extreme optical states, a second reset pulse sufficient to drive the pixel to or near another extreme optical state, And the one or more set pulses. The method of claim 1, At any point in time, a voltage of 0, + V, or -V is applied to the pixel, and V is a predetermined drive voltage. The method of claim 1, The total number of balanced pulse pairs inserted, balanced pulse pairs deleted, and zero voltage periods inserted does not exceed six. The method of claim 8, The total number of balanced pulse pairs inserted, balanced pulse pairs deleted, and zero voltage periods inserted does not exceed four. The method of claim 9, The total number of balanced pulse pairs inserted, balanced pulse pairs deleted and zero voltage periods inserted does not exceed two. The method of claim 1, The method is DC balanced, electro-optic display driving method. The method of claim 1, And the display comprises a rotating bichromal member or an electrochromic medium. The method of claim 1, And wherein the display comprises an electrophoretic electro-optic medium comprising a plurality of electrically charged particles that can move through the fluid upon application of an electric field to the fluid within the fluid. The method of claim 13, And the fluid is a gas. The method of claim 13, Wherein the charged particles and the fluid are encased in a plurality of capsules or microcells. A display controller configured to perform the method according to claim 1. A method of driving an electro-optical display having a plurality of pixels, each of which can achieve four or more different gray levels comprising two extreme optical states, The method includes a reset pulse sufficient to drive the pixel to or near one of the extreme optical states of the pixel, preceded by a set pulse sufficient to drive the pixel from the one extreme optical state to a different final gray level. Applying to each pixel a waveform comprising a reset pulse, And the reset pulse is selected such that the image on the display immediately before the set pulse is substantially the reverse monochrome projection of the final image following the set pulse. The method of claim 17, A waveform comprising a first reset pulse sufficient to drive each pixel to or near one of the extreme optical states of each pixel, and a second reset pulse sufficient to drive each pixel to or near another extreme optical state; Applied to each pixel, And wherein the first reset pulse is selected such that the image on the display immediately before the second reset pulse is a monochrome projection of the final image substantially following the set pulse. The method of claim 17, The waveform is, (a) inserting one or more balanced pulse pairs into the waveform; (b) deleting one or more balanced pulse pairs from the waveform; And (c) inserting one or more zero voltage periods into the waveform, Is modified by one or more of A "balanced pulse pair" is a sequence of two pulses of opposite polarity such that the total impulse of the balanced pulse pair is essentially zero. The method of claim 19, Wherein the two pulses of the balanced pulse pair are each of constant voltage but of opposite polarity and of equal length. The method of claim 19, And said period of said waveform occupied by said deleted pair of balanced pulses or each thereof is replaced by a zero voltage period. The method of claim 19, One or more balanced pulse pairs are deleted from the waveform, other elements of the waveform are time shifted to occupy the period previously occupied by the deleted balanced pulse pair or each thereof, and the deleted balanced pulse pairs or each thereof A zero voltage period is inserted at a point in time different from the point occupied by the electro-optic display driving method. The method of claim 17, At any point in time, a voltage of 0, + V, or -V is applied to the pixel, and V is a predetermined drive voltage. The method of claim 17, And the display comprises a rotating dichroic member or an electrochromic medium. The method of claim 17, And wherein the display comprises an electrophoretic electro-optic medium comprising a plurality of electrically charged particles that can move through the fluid upon application of an electric field to the fluid within the fluid. The method of claim 25, And the fluid is a gas. The method of claim 25, Wherein the charged particles and the fluid are encased in a plurality of capsules or microcells. A display controller configured to perform the method according to claim 17. A method of driving an electro-optical display having one or more pixels capable of achieving two or more different gray levels, Two or more different waveforms are used for the same transition between specific gray levels, depending on the duration of the residence time of the pixel in the state where the transition begins, These two waveforms are (a) inserting one or more balanced pulse pairs; (b) deletion of one or more balanced pulse pairs; And (c) inserting one or more zero voltage periods, Different from each other by one or more of A "balanced pulse pair" is a sequence of two pulses of opposite polarity such that the total impulse of the balanced pulse pair is essentially zero. The method of claim 29, The method is DC balanced, electro-optic display driving method. The method of claim 29, All waveforms are DC balanced, how to drive an electro-optical display. The method of claim 29, Wherein the waveforms are different from each other by insertion of one or more balance pulse pairs or deletion of one or more balance pulse pairs. The method of claim 32, Wherein the two pulses of the balanced pulse pair are each of constant voltage but of opposite polarity and of equal length. The method of claim 32, And said period occupied by said erased balanced pulse pair or each is replaced by a zero voltage period. The method of claim 32, One or more balanced pulse pairs are deleted, other elements of the waveform are time shifted to occupy the period previously occupied by the deleted balanced pulse pairs or each, and occupied by the deleted balanced pulse pairs or each thereof And a zero voltage period is inserted at a point in time different from the point at which the point is made. The method of claim 29, At any point in time, a voltage of 0, + V, or -V is applied to the pixel, and V is a predetermined drive voltage. The method of claim 29, The total number of balanced pulse pairs inserted, balanced pulse pairs deleted, and zero voltage periods inserted does not exceed six. The method of claim 37, wherein The total number of balanced pulse pairs inserted, balanced pulse pairs deleted, and zero voltage periods inserted does not exceed four. The method of claim 38, The total number of balanced pulse pairs inserted, balanced pulse pairs deleted and zero voltage periods inserted does not exceed two. The method of claim 29, And the display comprises a rotating dichroic member or an electrochromic medium. The method of claim 29, And wherein the display comprises an electrophoretic electro-optic medium comprising a plurality of electrically charged particles that can move through the fluid upon application of an electric field to the fluid within the fluid. 42. The method of claim 41 wherein And the fluid is a gas. 42. The method of claim 41 wherein Wherein the charged particles and the fluid are encased in a plurality of capsules or microcells. A display controller configured to perform the method according to claim 29. A method of driving an electro-optical display having a plurality of pixels, each of which can achieve two or more different gray levels, The method, (a) providing a final data buffer arranged to receive data defining a desired final state of each pixel of the display; (b) providing an initial data buffer arranged to store data defining an initial state of each pixel of the display; (c) providing a target data buffer arranged to store data defining a target state of each pixel of the display; (d) determining when the data in the initial and final data buffers are to be different, where such differences are found; (i) when the initial and final data buffers contain the same value for a particular pixel. Setting the target data buffer to this value; (ii) if the initial data buffer includes a value greater than the final data buffer for a particular pixel, setting the target data buffer to the sum of the initial data buffer and the increment; (iii) if the initial data buffer contains a smaller value than the final data buffer for a particular pixel, set the value of the target data buffer by setting the target data buffer to the value obtained by subtracting the increment from the initial data buffer. Determining, updating; (e) updating an image on the display using the initial data buffer and the data of the target data buffer as the initial and final states of each pixel, respectively; (f) after step (e), copying data from the target data buffer into the initial data buffer; And (g) repeating steps (d) to (f) until the initial and final data buffers contain the same data. A method of driving an electro-optical display having a plurality of pixels, each of which can achieve three or more different gray levels, The method, (a) providing a final data buffer arranged to receive data defining a desired final state of each pixel of the display; (b) providing an initial data buffer arranged to store data defining an initial state of each pixel of the display; (c) providing a target data buffer arranged to store data defining a target state of each pixel of the display; (d) providing an array of polarity bits arranged to store polarity bits for each pixel of the display; (d) determining when the data of the initial and final data buffers are different, where such differences are found; (i) the values for particular pixels of the initial and final data buffers are different and the initial If the value of the data buffer indicates an extreme optical state of the pixel, setting the polarity bit for the pixel to a value indicating transition to an opposite extreme optical state; And (ii) if the value for a particular pixel of the initial and final data buffers is different, depending on the associated value of the polarity bit array, the target data buffer is incremented or subtracted with the initial data buffer incrementally; Determining a value of the polarity bit array and a target data buffer by setting; (e) updating an image on the display using the initial data buffer and the data of the target data buffer as the initial and final states of each pixel, respectively; (f) after step (f), copying data from the target data buffer into the initial data buffer; And (g) repeating steps (e) to (g) until the initial and final data buffers contain the same data. 30. A computer-readable medium having software code, when executed by a processor, that causes the processor to perform the method of any one of claims 1, 17 or 29. 30. An application specific integrated circuit configured to perform the method of any one of claims 1, 17 or 29.

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