JP2009538451A - Method for driving an electro-optic display - Google Patents

Abstract

A method is provided for driving a bistable electro-optic display having at least first and second pixels separated by an inter-pixel gap. In one method, a driving pulse for driving the pixel in one extreme optical state is applied to the first pixel, and a reinforcing pulse having the same polarity as the driving pulse is applied to the second pixel in the extreme optical state. Applied. In the second method, the drive pulse applied to the first pixel drives the pixel away from one extreme optical state, and a reverse reinforcement pulse of opposite polarity applied to the second pixel is driven. Applied to the pulse. The driving method reduces edge ghosting or blooming.

Description

This application
(A) US Pat. No. 7,193,625 (b) US Pat. No. 7,012,600 (c) US Pat. No. 6,531,997 (d) US Pat. No. 6,504,524 (e Related to US Pat. No. 7,170,670 and (f) US Patent Application Publication No. 2005/0024353.

  These patents and published applications may hereinafter be referred to as “related patents”.

  The present invention relates to a method of driving an electro-optic display, and more particularly to a bistable electro-optic display, which uses such a method. The methods and displays of the present invention are particularly but not exclusively intended for use in driving bistable electrophoretic displays.

  Background terms and state of the art for electro-optic displays are discussed in detail in the aforementioned US Pat. Therefore, this terminology and advanced technology are briefly summarized below.

  The term “electro-optic” as applied to a material or display, in its conventional sense in imaging technology, is a material having first and second display states that differ in at least one optical property, Is used herein to refer to a material that changes from its first display state to its second display state by the application of an electric field.

  The term “gray state” is used herein to refer to a state that is in the middle of two extreme optical states of a pixel in its traditional sense in imaging technology, and is not necessarily black- It does not always suggest a white transition. The terms “black” and “white” may be used hereinafter to refer to the two extreme optical states of the display and should be understood as usually including extreme optical states that are not strictly black and white. is there. The term “monochrome” may be used hereinafter to describe a driving mechanism that only drives a pixel to two extreme optical states with no intervening gray state.

  The terms “bistable” and “bistable”, in their conventional sense in the art, comprise a display element having first and second display states that differ in at least one optical property, so that they have a finite duration. After a given element is driven to its first or second display state using the addressing pulse, the state is at least several times after the addressing pulse ends, for example, the state of the display element Is used to refer to a display lasting at least 4 times, which is the minimum duration of an addressing pulse required to change.

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

Several types of electro-optic displays are known, for example
(A) rotating two-color member display (for example, see Patent Documents 2 to 10),
(B) Electrochromic displays (eg, O'Regan, B., et al, Nature 1991, 353, 737; Wood, D., Information Display, 18 (3), 24 (March 2002); Bach, U., et al., Adv. Mater., 2002, 14 (11), 845; and U.S. Patent Nos. 6,301,038, 6,870.657, and 6,950,220).
(C) Electrowetting display (Hayes, RA, et al., “Video-Speed Electronic Paper Based on Electricting”, Nature, 425, 383-385 (25 September 2003) and US Patent Application No. 200 / 0151709)),
(D) a particle-based electrophoretic display (US Pat. Nos. 5,930,026, 5,961,804, 6,017,584) in which a plurality of charged particles flow through a fluid under the influence of an electric field. 6,067,185, 6,118,426, 6,120,588, 6,120,839, 6,124,851, 6,130,773, and 6,130,774, United States Patent Application Publication Nos. 2002/0060321, 2002/0090980, 2003/0011560, 2003/0102858, 2003/0151702, 2003/0222315, 2004/0014265, 2004/0075634, 2004/0094422, 2004 / 0105036, 2005/0062714, and Patent Document 1 And WO 00/38000, WO 00/36560, WO 00/67110, and WO 01/07961, and European Patent No. 1,099,207 B1, and 1,145. , 072 B1, and other MIT and E Ink patents and application documents discussed in US Pat.

  There are several different variants of electrophoretic media. The electrophoretic medium can use a liquid or gaseous fluid. For gaseous fluids, see, for example, Kitamura, T .; , Et al, "Electrical toner movement for electronic paper-like display", IDW Japan, 2001, Paper HCCl-I, and Yamaguchi, Y. et al. , Et al. , "Toner display using insulating particles charged triboelectrically", IDW Japan, 2001, Paper AMD4-4, US Patent Application Publication No. 2005/0001810, European Patent Nos. 1,462,847, 1,435, 484,635, 1,500,971, 1,501,194, 1,536,271, 1,542,067, 1,577,702, 1,577,703, and 1, 598,694, and WO 2004/090626, WO 2004/077942, and WO 2004/001498. The medium may be enclosed in a capsule, comprising a number of small capsules, each of which contains an inner phase containing electrophoretic mobile particles suspended in a liquid suspending agent and a capsule surrounding the inner phase With walls. Typically, the capsule itself is held in a polymeric binder to form a coherent layer positioned between the two electrodes. See the aforementioned MIT and E Ink patents and application documents. Alternatively, the wall surrounding the discrete microcapsules in the encapsulated electrophoretic medium may be replaced with a continuous phase, so that the electrophoretic medium contains a plurality of discrete droplets of electrophoretic fluid and a continuous phase of polymeric material. A so-called polymer-dispersed electrophoretic display is provided. See, for example, US Pat. No. 6,866,760. For purposes of this application, such polymer dispersed electrophoretic media are considered subspecies of encapsulated electrophoretic media. Another variant is a so-called “microcell electrophoretic display” in which charged particles and fluid are held in a plurality of cavities formed in a carrier medium, typically a polymeric thin film. See, for example, US Pat. Nos. 6,672,921 and 6,788,449.

  The electrophoretic medium can operate in a “shutter mode” where one display state is substantially opaque and one is light transmissive. 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 And 6,184,856. The dielectrophoretic display can operate in a similar mode. See U.S. Pat. No. 4,418,346. Other types of electro-optic displays may also be capable of operating in shutter mode.

  Particle-based electrophoretic displays and many other electro-optic displays are bistable, significantly different from conventional liquid crystal (“LC”) displays. Although the action of twisted nematic liquid crystals is not bistable, it acts as a voltage converter, so the step of applying a voltage to a pixel in such a display is not possible at the pixel, regardless of the gray level previously present in the pixel. Generate a specific gray level. Still further, LC displays can only be driven in one direction (non-transparent or “dark” to transmissive or “bright”), reducing or eliminating the electric field from a brighter state to a darker state. A reverse transition results. Finally, the gray level of the pixels of the LC display is sensitive only to its magnitude, not the polarity of the electric field, and certainly for technical reasons, commercial LC displays usually have a driving field at frequent intervals. Reverse the polarity. In contrast, because the bistable electro-optic display acts as an impulse converter for the first approximation, the final state of the pixel is not only the applied electric field and the time that this field is applied, It also depends on the state of the pixel before application of the electric field.

  As already pointed out, electrophoresis and some other electro-optic displays are bistable, which is not infinite, and the image on the display slowly disappears over time. If maintained for a long time, the image may have to be periodically refreshed to restore the image to its optical state when it was first written.

  However, such a refresh of the image can create its own problems. As discussed in US Pat. Nos. 6,531,997 and 6,504,524, the method used to drive the display produces a zero or near zero net time average applied electric field across the electro-optic medium. If not, problems may be encountered and the useful life of the display may be reduced. A drive method that provides a zero net time average applied electric field across an electro-optic medium is conventionally referred to as a “DC balanced” or “DC balanced” drive method. If the image is maintained for a long time by refreshing the pulses, these pulses must have the same polarity as the addressing pulses originally used to drive the associated pixels of the display to the maintained optical state. Yes, this results in a DC unbalanced drive mechanism.

The aforesaid US Pat. No. 6,053,075 can refresh an image on a bistable electro-optic display while reducing the adverse effects associated with the DC imbalanced drive mechanism when refresh is achieved with short pulses. Explain that. This publication is a so-called “refresh pulse” method for dealing with bistable electro-optic displays having at least one pixel,
Applying an addressing pulse to drive the pixel to a first optical state;
Allowing the pixel to go into a second optical state different from the first optical state by leaving the pixel undriven for a period of time;
Applying to the pixel a refresh pulse that substantially restores the pixel to a first optical state, the refresh pulse being shorter than the addressing pulse.

In this refresh pulse method, the refresh pulse typically has an impulse that is no more than about 20 percent of the addressing pulse impulse, desirably no more than about 10 percent of this impulse, and preferably no more than about 5 percent of this impulse. . Typically, the difference between the first and second optical state does not exceed about 1 unit of L ^* (wherein, L ^* has the usual CIE definition,
L ^* = 116 (R / R ₀ ) ^1/3 -16,
Where R is the reflectance and R ₀ is the standard reflectance value). Preferably, this difference will not exceed about 0.5 units of ^{L *,} and preferably, no greater than about 0.2 units of ^{L *.} A plurality of refresh pulses may be applied to the pixels at regular intervals.

This refresh pulse method allows refreshing of the image on the bistable electro-optic display and thus improves the appearance of the image, but necessarily introduces some DC imbalance. The aforementioned patent document 11 also describes various methods for reducing the generated DC imbalance.
US Pat. No. 7,012,600 US Pat. No. 5,808,783 US Pat. No. 5,777,782 US Pat. No. 5,760,761 US Pat. No. 6,054,071 US Pat. No. 6,055,091 US Pat. No. 6,097,531 US Pat. No. 6,128,124 US Pat. No. 6,137,467 US Pat. No. 6,147,791 US Patent Application Publication No. 2005/0270261

  The present invention is described in the aforementioned 2005/0270261, which can provide a similar improvement in the appearance of a bistable electro-optic display, while at least in some cases reducing the DC imbalance introduced. An improved refresh pulse method is provided.

  The present invention also seeks to mitigate or eliminate another problem encountered in bistable electro-optic displays, the so-called “edge ghosting” problem, not discussed in the aforementioned 2005/0270261. An electro-optic display typically has a backplane with a plurality of pixel electrodes, each defining one pixel of the display, each defining one pixel of the display. Traditionally, a single common electrode spans multiple pixels, and typically the entire display is provided on the opposite side of the electro-optic medium. Individual pixel electrodes may be driven directly (ie, a separate conductor may be provided for each pixel electrode) or the pixel electrodes may be driven in an active matrix manner that is well known to those skilled in the backplane art. May be. Since adjacent pixel electrodes often have different voltages, they must be separated by a finite width inter-pixel gap to avoid electrical shorts between the electrodes. At first glance, the electro-optic medium that covers these gaps may not seem to switch when a drive voltage is applied to the pixel electrode (although this is true for some non-bistable electro-optics such as liquid crystals). Common to media, in which case a black mask is typically provided to hide these non-gaps), in the case of many bistable electro-optic media, a gap known as "blooming" The media that covers is not switched.

  Blooming refers to the tendency of applying a drive voltage to a pixel electrode that causes a change in the optical state of the electro-optic medium over a region that is larger than the physical size of the pixel electrode. Excessive blooming should be avoided (e.g., in high resolution active matrix displays, the application of drive voltage to a single pixel switches over an area that covers several adjacent pixels to reduce the effective resolution of the display. A controlled amount of blooming is often useful, not wanting to cause. For example, consider a black-on-white electro-optic display that displays a number using a conventional seven-segment array of seven directly driven pixel electrodes for each number. For example, if zero is displayed, the six sections will be black. When there is no blooming, six inter-pixel gaps become visible. However, as explained in the aforementioned 2005/0062714, for example, by providing a controlled amount of blooming, the inter-pixel gap can be made black and more visually pleasing. Bring numbers. However, blooming can lead to a problem referred to as “edge ghosting”.

  Consider the general situation of a layer of electro-optic medium placed between a continuous front electrode and an array of pixel electrodes disposed on a backplane. When the pixel electrode is held at a different voltage than the front electrode, an electric field is present in the electro-optic medium. This electric field is mainly directed perpendicular to the layers of the electro-optic medium and has a substantially uniform intensity (for the purpose of this, neglect the space charge distortion effect and the polarization of the electro-optic medium itself). However, near the edge of the pixel, fringe fields form, and these fringe fields extend into the inter-pixel region between the pixel receiving the electric field and the adjacent pixel. In the fringe field region, the electric field lines are curved from the pixel to the top or adjacent electrode. The electric field in this region is generally weaker than the center of the pixel.

  The waveform is typically designed to achieve the correct transition to the desired optical state, away from the central portion of the pixel, i.e. the pixel edge, and thus away from the fringe field. For example, an array of pixels that are in one extreme optical state (eg, black) and one pixel is driven to the opposite extreme optical state (white) by applying a drive voltage to that pixel over the drive time, and then Consider the situation where a pixel is driven to black by applying an opposite voltage to that pixel over the same drive period. A voltage and drive period are selected to achieve an appropriate black state at the center of the pixel after this pair transition. However, in the fringe field region, the electric field during the transition is weaker than the central part of the driven pixel. Thus, in this fringe field region, the first voltage pulse does not drive the electro-optic medium from black to white but instead drives from black to intermediate gray. Also, in the fringe field region, the second voltage pulse drives the electro-optic medium from this intermediate gray again to black. However, as discussed in some of the above related application documents, the response of many electro-optic media to an electric field is not necessarily linear with the magnitude of the applied field, and is not necessarily relative to the direction of the electric field. It is not symmetrical. As a result, after the two transitions described above, the inter-pixel region does not necessarily return exactly to its original black state. In general, the optical state of the fringe field region will be a slightly lighter black than the original state, i.e. a very dark gray rather than a true black, and thus a fringe field that is lighter in color than the black central part of the pixel. Leave the area. This is called an edge ghost, which is a class of edge artifact. Such edge ghosts, if large enough, are easily detected by the human eye and are very unpleasant.

(The above discussion has been simplified for illustrative purposes. The blooming region is not uniform white or black, but is typically a transition zone, and across the blooming region, the color of the medium is white. The edge ghost typically becomes a gray area of various shades rather than a uniform gray area, but in particular the human eye has each pixel (It is still visible and unpleasant because it is well equipped to detect gray areas in a monochrome image that should be pure black or pure white.)
In some cases, asymmetric blooming may contribute to edge ghosting. “Asymmetric blooming” has been found in some electro-optic media (eg, the copper chromite / titania encapsulated electrophoretic media described in US Pat. No. 7,002,728) than during reverse transitions. The medium described in this patent refers to the phenomenon that blooming is “asymmetric” in the sense that many bloomings occur during the transition from one extreme optical state to another of the pixel. So, typically, blooming during a black to white transition is greater than during a white to black transition.

  The present invention provides a method for driving a bistable electro-optic display that can reduce or eliminate edge ghosting.

  Another problem associated with blooming is that one pixel may effectively control the area of the display that is intended to be controlled by adjacent pixels. Ideally, it may be desired that blooming be controlled so that a fringe field from one pixel causes a change in the optical state across half the gap between it and an adjacent pixel. However, in practice, blooming depends on a number of factors, particularly including the temperature of the electro-optic medium, so it may not always be possible to control blooming to an optimum value. Still further, as already described, because of the fringe field that varies with distance, the blooming region does not have a sharp edge between the two extreme optical states, but rather a finite transition between the two optical states. There is a width area. Thus, for example, ensure that the white area of a white pixel spans half of the inter-pixel gap (so that two adjacent pixels are both driven white and the inter-pixel gap is the same white as the pixel itself). If one wishes to do so, it may be necessary to allow a gray area that spans more than half of the inter-pixel gap when one pixel is driven to white while the other is still black. However, the presence of such a gray region may be a problem depending on the situation. For example, if the display is a color display with a color filter array and the two pixels involved are the basis for different colored regions of the color filter array, the first pixel is white and the second pixel is black The presence of the gray area may result in a “stain” of the color of the first pixel with some second color, thus adversely affecting the color rendering of the display.

  The present invention may be regarded as including various improvements of the refresh pulse driving method of the aforementioned 2005/0270261. In this method, “refresh” pulses are not generated at arbitrary intervals, but are the source of transitions occurring in other pixels. Still further, in the present method, the refresh pulse may not be applied to all pixels or all pixels having a given optical state, but may be limited to certain pixels adjacent to the transitioning pixel. For convenience, the correction pulse applied in accordance with the method of the present invention is referred to as a “reinforcement pulse”, while the term “refresh pulse” is used to represent the pulse applied in the method of 2005/0270261 described above. Is done.

  Accordingly, the present invention is capable of displaying the first and second extreme optical states (the pixel may or may not have other intermediate optical states), respectively, at least the first and second A first method of driving a bistable electro-optic display having a second pixel and first and second pixels having adjacent edges separated by an inter-pixel gap is provided. A first method comprising: applying a driving pulse to the first pixel effective to change the optical state of the first pixel to one of its extreme optical states; A reinforcement pulse having the same polarity as the drive pulse and applied at the same time as the drive pulse or within a predetermined period after the end of the drive pulse is applied to the second pixel in the extreme optical state Including the step of.

  This first method of the present invention (hereinafter may be referred to as the “reinforcement pulse method”) is intended for each pixel to display only the first and second (typically white and black) optical states. Applied to a monochrome display. In such a monochrome display, the first pixel is transitioning from its first to its second optical state (eg, from white to black), while the second pixel is in its second optical state. When in the state (black) and staying in this second optical state, the first pixel is given a pulse of one polarity, resulting in the desired transition. During or immediately after this pulse, the second pixel is given a reinforcing pulse of the same polarity as the drive pulse given to the first pixel (ie a blackening pulse). Since the second pixel is already black, the reinforcement pulse does not cause a macroscopic change in the black of the second pixel. However, if the second pixel has been in its black state for some time, its color will be “pushed” from true black to dark gray, so the reinforcement pulse will cause the second pixel to go to true black. And thus avoid having a dark gray second pixel that is immediately adjacent to the true black first pixel, which is a situation readily apparent to the human eye. The reinforcement pulse also serves to reduce or eliminate edge ghosting in the interpixel gap between the first and second pixels.

  As discussed in the related patents and application documents above, the waveforms used to drive the pixels of an electro-optic display from one optical state to another can be quite complex and can be bipolar. A drive pulse may be included. Therefore, the “driving pulse” applied to the first pixel in the reinforcing pulse method of the present invention may actually be a composite waveform including a plurality of individual driving pulses, which may partially have opposite polarities. Good. For this purpose, the polarity of such a composite waveform may be defined as the polarity of a single drive pulse of constant magnitude that results in the same first pixel optical transition as the composite waveform.

  The “reinforcement pulse” used in the method may itself comprise more than a single pulse. In particular, there are two principle variants of the present reinforcement pulse method, which may be referred to as single or double reinforcement pulse variants. As the name suggests, the single reinforcement pulse method uses only one reinforcement pulse. The double reinforcement pulse method is more complex. Consider a situation where a display has first and second pixels that share a common edge, and the first pixel transitions from white to black while the second pixel remains in its black state. If a single reinforcement method is used, a single pulse of the same polarity as the pulse applied to the first pixel, i.e. a blackening pulse, is applied to the second pixel. In the double reinforcing pulse method, first, a pulse having a polarity opposite to that applied to the first pixel (that is, a whitening pulse) is applied to the second pixel, and then the first pixel is applied to the first pixel. A pulse having the same polarity as that applied to the pixel (that is, a blackening pulse) is applied. The two successive pulses applied to the second pixel may hereinafter be referred to as “reverse reinforcement pulse” and “forward reinforcement pulse”, respectively. There may or may not be an interruption (period of zero voltage) between the reverse and forward reinforcement pulses. As discussed in more detail below, the dual reinforcement pulse method has been found to typically match the color of the second pixel more accurately to the color of the first pixel.

As already described, in this method, the reinforcing pulse may be applied only to pixels that share an edge with the pixel being driven (hereinafter, for convenience, pixels having this relationship are referred to as “edge adjacent pixels”). They may be distinguished from “corner adjacent pixels” where only one corner is common). There are three main variants of the method, all of which may be applied to typical types of displays with a two-dimensional array of pixels arranged in rows or columns.
(A) A “edge-adjacent limited” variant in which a reinforcement pulse is applied only to neighboring pixels adjacent to the edge of each pixel being driven from one optical state to another. In the general case where the pixels of a display are arranged in a rectangular matrix, most pixels will of course have four neighboring edge neighboring pixels. Although it is not considered necessary to apply a reinforcement pulse to the pixels adjacent to the driven pixels, it is of course possible to do this if so desired.
(B) A “global” variant in which when one or more pixels are driven to one extreme optical state, a reinforcement pulse is applied to all pixels already in that one extreme optical state.
(C) When one or more pixels in an adjacency are driven to one extreme optical state, a reinforcement pulse is applied to all pixels in that adjacency that are already in that one extreme optical state. An intermediate “adjacent” variant, in which the reinforcement pulse is not applied to a pixel that is already in its one extreme optical state outside of the adjacent.

  Variant (c) may require further explanation. Consider the common situation of a series of images where a single subject or a small number of subjects are moving against an essentially stationary background. More specifically, consider a series of monochrome images of a black airplane moving against a white sky. In order to produce a transition between successive images, certain pixels around the plane must be rewritten. In order to avoid the visually distracting effect, the reinforcement pulse may be applied to the black pixel representing the airplane, but it may be preferable not to apply it to the black pixel representing the ground below. Similarly, if the display is configured as a series of essentially independent windows, it may be desirable to use a drive mechanism in which the “global” update method is applied independently to each window.

  As already mentioned, in the reinforcement pulse method, the reinforcement pulse is applied either simultaneously with the drive pulse or within a predetermined period after the end of the drive pulse. The reinforcement pulse is to be part of the same transition as the driven pixel, rather than to the display user, there appears to be a first transition of the driven pixel and a second transition of the reinforcement pulse. It is desirable to think. Typically, the reinforcement pulse should be applied either simultaneously with the drive pulse or within a subsequent period equal to the length of the drive pulse and preferably not exceeding about 400 milliseconds. In most cases, it is convenient to generate a reinforcement pulse simultaneously with the last part of the drive pulse (ie simultaneously with the end of the drive pulse).

  The impulse applied by the reinforcement pulse may, of course, vary over a wide range, depending on the particular electro-optic medium employed and other parameters of the particular display. In some cases, the reinforcement pulse may have the same impulse as the drive pulse (the drive pulse is required to drive the first pixel from its first to second extreme optical state). Usually, however, the impulse of the reinforcement pulse is smaller. Typically, the reinforcement pulse impulse is about 10 to about 70 percent, more usually about 20 to about 50 percent, of the drive pulse impulse. In many cases, a reinforcement pulse with an impulse of about 25 percent of the impulse of the drive pulse appears to produce good results. Even in the so-called single reinforcement pulse variant of the method, the reinforcement pulse need not be in the form of a single continuous pulse, but multiple discretes separated by one or more interruptions (ie, periods of zero applied voltage). It may be in the form of a subpulse. For example, if the reinforcement pulse has an impulse of 20 percent of the impulse of the drive pulse, the reinforcement pulse can be in the form of two discrete subpulses, each having an impulse of 10 percent of the impulse of the drive pulse, where one subpulse is the drive Simultaneously with the last part of the pulse, the second is applied 100 ms after the end of the drive pulse (for example), with a period of zero voltage between the two subpulses. The voltage of the reinforcement pulse may be the same as or different from that of the drive pulse, and in some cases it may be advantageous for the reinforcement pulse to be a lower voltage than the drive pulse.

The invention extends to a bistable electro-optic display, controller or application specific integrated circuit arranged to carry out the reinforcing pulse method of the invention. Specifically, the present invention is disposed adjacent to a layer of a bistable electro-optic medium capable of displaying the first and second extreme optical states, a layer of the bistable electro-optic medium, And first and second pixel electrodes capable of applying an electric field to the medium, the first and second pixel electrodes having adjacent edges separated by a gap between pixels, and the first and second pixels A control device for controlling the voltage applied to the pixel electrode,
Applying to the first pixel electrode a drive pulse effective to change the optical state of the electro-optic medium adjacent to the first pixel electrode to one of its extreme optical states;
While the electro-optic medium adjacent to the second pixel electrode is in the one extreme optical state, the second pixel electrode is supplied with a reinforcing pulse having the same polarity as the drive pulse and simultaneously with the drive pulse or the drive pulse. Applying a reinforcing pulse applied at any time within a predetermined period after the end of the step, the electro-optical display arranged to perform a driving method.

  The present invention also provides a second driving method which may hereinafter be referred to as the “reverse reinforcement pulse method” of the present invention. What is the first (reinforcement pulse) method described above that is applied when one of the edge adjacent pairs of pixels is transitioning to one optical state while the other of the pair remains in that optical state? In contrast, the reverse reinforcement pulse method of the present invention is applied when one of the edge-neighboring pairs of pixels is transitioning from its optical state while the other of the pair remains in its optical state. For example, the reverse reinforcement pulse method may be applied when the first pixel is transitioning from white to black while the adjacent pixel remains white. In the reverse reinforcement pulse method, a pulse having a polarity opposite to that applied to the transition pixel is given to the non-transition pixel, that is, in the above example, the whitening pulse is given to the adjacent pixel.

  Accordingly, the present invention is capable of displaying the first and second extreme optical states (the pixel may or may not have other intermediate optical states), respectively, at least the first and second A method of driving a bistable electro-optic display having a first pixel and a second pixel having a second pixel and adjacent edges separated by an inter-pixel gap is provided. The reverse reinforcement pulse method includes applying a driving pulse to the first pixel effective to change the optical state of the first pixel from one of its extreme optical states; A reverse reinforcement pulse of the opposite polarity to the drive pulse, applied either to the second pixel in one extreme optical state, either simultaneously with the drive pulse or within a predetermined period after the end of the drive pulse Applying a reinforcement pulse.

  The reverse reinforcement pulse method of the present invention can utilize any of the previously described variants of the main reinforcement pulse method, and thus, for example, the reverse reinforcement method is applied on the edge adjacency, adjacent, or global basis. Although typically, it is applied on an edge-adjacent basis. The reverse reinforcement pulse method may also comprise more than one pulse, and in particular may comprise two pulses of opposite polarity, as described for the first method of the invention.

  The reverse reinforcement pulse method of the present invention aims to reduce or eliminate the problems caused by excessive blooming as described above. In the situation described above, where the first pair of adjacent white pixels transitions from white to black while the second pixel remains white, the resulting black region is half the inter-pixel gap. There is a tendency of the drive pulse applied to the first pixel to cause the above problem. By applying a reverse reinforcement (whitening) pulse to the second pixel, excessive black blooming is reduced or eliminated.

The present invention extends to a bistable electro-optic display, display controller, or application specific integrated circuit (ASIC) arranged to perform the second method of the present invention. Specifically, the present invention is disposed adjacent to a layer of a bistable electro-optic medium capable of displaying the first and second extreme optical states, a layer of the bistable electro-optic medium, And first and second pixel electrodes capable of applying an electric field to the medium, the first and second pixel electrodes having adjacent edges separated by a gap between pixels, and the first and second pixels A control device for controlling the voltage applied to the pixel electrode,
Applying to the first pixel electrode a driving pulse effective to change the optical state of the first pixel from one of its extreme optical states;
A reverse reinforcement pulse having a polarity opposite to that of the drive pulse, applied to the second pixel electrode in one extreme optical state, either simultaneously with the drive pulse or within a predetermined period after the end of the drive pulse. Applying an inverse reinforcing pulse to an electro-optic display arranged to perform a driving method.

  The display of the present invention may utilize any of the above-described bistable electro-optic media. Thus, for example, the display of the present invention may comprise a rotating two-color member or an electrochromic medium. Alternatively, the display may comprise an electrophoretic medium comprising a plurality of charged particles disposed in the fluid and capable of moving through the fluid under the influence of an electric field. Charged particles and fluids may be confined within multiple capsules or microcells. Alternatively, the charged particles and fluid may exist as a plurality of discrete droplets surrounded by a continuous phase containing a polymeric material, so that the electrophoretic medium is a polymer dispersed type. The fluid may be liquid or gaseous.

  The display of the present invention may be used in any application where prior art electro-optic displays are used. Thus, for example, the display may be used in electronic book readers, portable computers, tablet computers, cellular phones, smart cards, signs, watches, shelf labels, and flash drives.

  As already pointed out, the first aspect of the present invention is that the reinforcement pulse, which does not cause a gross change in the optical state of the pixel, can be applied to another pixel with a drive pulse that changes the optical state of the pixel. It relates to a method of driving a bistable electro-optic display applied to one or more pixels during or immediately after. The reinforcement pulse functions to match the color of the pixel that receives the reinforcement pulse with the color of the pixel that receives the drive pulse, and if two pixels are adjacent to each other, edge ghosting between the two pixels is reduced. To do.

  Compared with the aforementioned 2005/0270261 refresh pulse driving method, the method may reduce the number of reinforcing pulses required because the reinforcing pulse is not applied unless the display is updated for a long time. (Of course, if any pixel has not received a drive pulse or reinforcement pulse for a long time, this method is combined with the refresh pulse method by ensuring that the pixel receives a refresh pulse at the end of the long time. It is also possible that reinforcing pulses need not be applied to all pixels of the display in a given extreme optical state, which further reduces the number of reinforcing pulses required. Thus, the present invention can reduce the amount of DC imbalance in the refresh pulse drive method while still avoiding undesirable visual artifacts.

  The DC imbalance introduced by this augmentation pulse method may be compensated for in a manner similar to that described in the aforementioned 2005/0270261, and the display controller tracks the DC imbalance of each pixel, The drive pulse or waveform impulse used to drive the pixel from one extreme optical state to the other to compensate for the accumulated DC imbalance of the pixel may be adjusted. If the drive mechanism employed utilizes a blanking pulse (ie, a pulse that drives all pixels in the display or that particular area to the same optical state), DC balancing occurs conveniently during the application of the blanking pulse. Be made.

  FIG. 1 of the accompanying drawings is a graph of the optical state of two pixels of a monochrome bistable electro-optic display drawn against time. As shown in FIG. 1, both pixels (designated pixel 1 and pixel 2) are initially in a dark extreme optical state. Pixel 2 receives a drive pulse that drives it to the white optical state (represented near the top of the reflectance (R) ordinate in FIG. 1). This white state then decays slowly, as shown by the gentle downward slope of the curve of pixel 2 in FIG. Although not shown in FIG. 1, the pixels that are driven back to their black optical state are also attenuated in a similar manner, so that after some time the black and white image written on the display is dark with a reduced contrast ratio. Gray and light gray images (the degree of attenuation is exaggerated in FIG. 1 for ease of explanation). The human eye is very tolerant of such slow and uniform changes in the image, and in practice, if no part of the image needs to be changed, the image on the bistable display will have a reduced contrast ratio. It can be left for a significant period of time (often a few hours depending on the particular electro-optic medium employed) before it is unpleasant for most viewers.

  However, some time after pixel 2 is driven to its white state, pixel 1 (assumed to be bordered by pixel 2 for this purpose) is driven to its white state in FIG. There is a significant difference between the white newly rewritten pixel 1 and the partially attenuated light gray pixel 2 as shown by the vertical spacing between the two curves of It also shows that the difference persists for some time as the optical state of both pixels gradually decays. The resulting color difference between adjacent pixels, of course, tends to be very apparent to the human eye, depending on the degree of attenuation of the white state. An exact similar situation occurs when pixel 1 and pixel 2 are driven back to their black optical state at different times.

  FIG. 2 shows the same sequence of events as FIG. 1, but with the addition of a reinforcing pulse in accordance with the present invention. As can be seen from FIG. 2, after the reinforcement pulse, both pixel 1 and pixel 2 are the same because the reinforcement pulse is applied to pixel 2 at essentially the same time that pixel 1 is driven to its white state. A newly written white state. Thereafter, the white state of pixels 1 and 2 both decay, so that pixels 1 and 2 maintain the same color at all the later times shown in FIG. As already described, the reinforcement pulse also serves to reduce or eliminate the effect of edge ghosting between edge adjacent pixels 1 and 2.

  In practice, as usual, the problem is not as simple as illustrated in the somewhat idealized diagram of FIG. As mentioned in the above related patents and application documents, the extreme optical state of many electro-optic media is not absolutely fixed, and there is a so-called “soft rail” phenomenon, so that the media is in its extreme optical state. When trying to drive, the exact optical state achieved is a number of drive pulses applied, including the length of the applied drive pulse, the previous optical state of the pixels, and the period during which the pixels stayed in those optical states. Depends on factors. Repeated application of a single reinforcement pulse to a single pixel can be achieved when the pixel is cycled between its two extreme optical states, such that it is swept towards the more extreme optical state It has been found that it is possible to interrupt a pixel. This is not a scenario that is unlikely to occur in practice, but occurs at an invariant pixel adjacent to a blinking pixel, eg, at regular intervals, eg as part of a time management device.

This situation is experimental using an encapsulated titania / copper chromite electrophoresis medium as illustrated in FIG. 3 of the accompanying drawings and described in Example 4 of US Pat. No. 7,002,728. Figure 3 shows data generated from a single pixel display. The dashed line in FIG. 3 is repeatedly cycled between its black and white extreme optical states using ± 10 V, 240 ms drive pulses, 3 seconds between each drive pulse, and finally Shows L ^* values obtained from a pixel that was able to rest for 6 seconds (see only part of this pixel's trace adjacent to the black extreme optical state due to the ordinate scale in FIG. 3) It is possible that the obvious spread of the trace during the rest period is due to detector noise). It can be seen from FIG. 3 that this pixel behavior is consistent throughout the cycle, with a final L ^* value of 26.52 (after minor variations in the first cycle).

The solid line in FIG. 3 is first driven to its black extreme optical state using a 10V, 240 millisecond pulse in the same manner as the first pixel, then 10V, 40 at 6 second intervals. Fig. 6 shows a trace obtained from a second pixel that receives a millisecond augmentation pulse, thus mimicking a pulse applied to a pixel adjacent to a flashing pixel and subject to the single augmentation pulse method of the present invention. From FIG. 3, the reinforcement pulse gradually drives the second pixel to a darker optical state, and after 5 reinforcement pulses and a final 6 second rest period, the pixel has an L ^* value of 23.67. You will understand. A difference of approximately 3 units between the final L ^* values of the two pixels is easily perceived by the human eye and results in an unpleasant ghost, ie the blinking pixel is dark gray next to the black invariant pixel. Thus, if both pixels should be in the same final black state, leave a pale “ghost” of the white flash image.

At first glance, this ghosting problem may seem to be overcome simply by increasing the length of the drive pulse applied to the first flushing pixel, but empirically this is the case. I know it ’s not. FIG. 4 of the accompanying drawings shows a trace similar to that of FIG. 3, except that the flushing pixel was driven with a drive pulse of 480 milliseconds. From FIG. 4, a longer drive pulse initially drives the flushing pixel to a lower L ^* value than the shorter drive pulse used in FIG. 3, but the L ^* value is significantly increased 1-2 seconds after the drive pulse. The final state of the flushing pixel in FIG. 4 is not significantly different from that in FIG. 3 because it also causes a large change (a phenomenon called “self-erasing” or “kickback” in the aforementioned E Ink patent and application documents). In addition, it can be seen that the final L ^* value of the flushing pixel of FIG. 4 is slightly larger than that of FIG. 3, ie, the flushing pixel is actually slightly lighter in color at the end. As in FIG. 3, the difference between the final states of the two pixels in FIG. 4 is easily perceptible to the human eye, resulting in an unpleasant ghost image.

Use a drive waveform with a first flushing pixel with a drive pulse of 240 seconds, a 1 second break when no voltage is applied, and a second drive pulse of 40 milliseconds, both drive pulses at 10V Another attempt was made to eliminate the difference between the final states of the two pixels. In practice, these experiments applied a 40 millisecond reinforcement pulse to both the flashing and unchanged pixels. The resulting trace is shown in FIG. 5 of the accompanying drawings. From this figure, it can be seen that the difference between the final states of the two pixels has been substantially reduced. The remaining approximately 1 L ^* units will not be readily apparent to most observers. However, the 1 second break between the two drive pulses applied to the flushing creates an unpleasant “flash-like” effect, and the observer viewing the two pixels actually has an initial ghost image that disappears after 1 second. Will see.

Finally, FIG. 6 is similar to that of FIGS. 3-5, but shows a trace in which the invariant pixel was driven according to the double reinforcement pulse method of the present invention, and applied to this invariant pixel at −10V, 15 milliseconds. (Whitening) reverse reinforcement pulse was applied, followed immediately by a + 10V, 25 ms (blackening) forward reinforcement pulse. From FIG. 6, this double reinforcement pulse method essentially eliminates the final optical state of the two pixels, the actual value being 26.61 for the flashing pixel and 26.52 for the invariant pixel. Yes, it will be appreciated that 0.09L ^* units are less likely to be noticed by a professional observer. When the nominally invariant pixel first becomes slightly white and then slightly dark, the double reinforcement pulse produces a slight flash, which is two seconds apart by 1 second, Not much more unpleasant than the flash generated in FIG. Still further, the slight flash experienced with the drive scheme of FIG. 6 can be minimized by careful selection when a reinforcement pulse is applied to the drive pulse applied to the flushing pixel. is there. If this is the timing that coincides with the last part of the much more prominent white-to-black transition of the flushing pixel, the eye is less sensitive to a slight flash of invariant pixels.

  The double reinforcement pulse method of FIG. 6 not only produces an exact match of the final state of the flushing and invariant pixels, but also the DC introduced by the reinforcement pulse by a factor of 4 than the single reinforcement pulse method of FIG. The unbalance amount is also reduced, and the algebraic sum of the forward and reverse reinforcement pulses in the method of FIG. 6 is 10V, 10 ms pulse compared to the 10V, 40 ms pulse used in the method of FIG. is there.

  The optimum length of the reverse and forward reinforcement pulses in the double reinforcement pulse method of the present invention is the specific electro-optic medium employed, its temperature, such as the display used in the experiments shown in FIGS. And depends on several factors including the conductivity of the laminating adhesive normally present between the electro-optic medium and one of the electrodes. In general, the higher the conductivity of the laminating adhesive, the shorter the length of the reinforcing pulse and the less perceived flash from these pulses. However, high conductivity laminate adhesives increase blooming. As a result, low conductivity laminate adhesives such as those typically used in high-resolution active matrix displays can be used to display the display without causing some degree of flashiness that can be unpleasant in the display. It may be more difficult to apply the method of the invention. It should also be noted that the length of the reinforcement pulse is not necessarily the same for the black and white states. For example, the 15/25 millisecond combination used in FIG. 6 has been found to be optimal for the transition of the media to the black extreme optical state. However, when similar experiments were performed on the transition to the white extreme optical state of the same medium at the same temperature, the 20/25 millisecond combination produced the best results.

  Both the reinforcing pulse method and the reverse reinforcing pulse method of the present invention can be used on the same display at the same time. However, because a pixel has multiple edge-neighboring neighboring pixels (eg, in a typical rectangular matrix display, most pixels have four edge-neighboring neighboring pixels), the requirements of the two methods conflict. In some cases, rules need to be devised that allow the two methods to coexist. For example, a single invariant black pixel may have one edge neighboring neighboring pixel changing from black to white (suggesting the use of the reverse reinforcement pulse method) and another changing from white to black. There may be neighboring pixels (indicating the use of the “normal” reinforcement pulse method), and the optimal reinforcement pulse length may not be the same in the two cases. In general, artifacts due to mismatches between the optical states of the entire pixel are more unpleasant than artifacts due to mismatches in the interpixel region. Therefore, if the requirement for the reinforcement pulse method conflicts with that of the reverse reinforcement pulse method, the former requirement should generally take precedence.

FIG. 1 is a graph showing a change in reflectance of two pixels over time during the refresh pulse method of the aforementioned 2005/0270261. FIG. 2 is a graph similar to FIG. 1 but showing the reflectance of two pixels during the first augmentation pulse method of the present invention. FIG. 3 is a graph showing the time course of reflectivity of a “flashing” pixel that is repeatedly cycled between its black and white extreme optical states and a second pixel that is subjected to the single reinforcement pulse method of the present invention. It is. FIG. 4 is a graph similar to FIG. 3 but showing the effect of driving the flushing pixel with a longer drive pulse. FIG. 5 is a graph similar to that of FIGS. 3 and 4, but illustrating the effect of using the modified waveform for the flushing pixel. FIG. 6 is a graph similar to that of FIGS. 3-5, but showing the effect of using the double reinforcement pulse method of the present invention in the second pixel.

Claims (26)

A method of driving a bistable electro-optic display having at least first and second pixels, each of the pixels being capable of displaying a first and second extreme optical state, wherein the first And the second pixel has adjacent edges separated by an inter-pixel gap, the method comprising:
Applying to the first pixel a driving pulse effective to change the optical state of the first pixel to one of its extreme optical states;
Applying a reinforcement pulse of the same polarity as the drive pulse to a second pixel in the one extreme optical state, the reinforcement pulse being simultaneously with the drive pulse or after the end of the drive pulse Applying for any of a predetermined period of time. A layer of a bistable electro-optic medium capable of displaying the first and second extreme optical states, and an electric field applied to the medium disposed adjacent to the layer of the bistable electro-optic medium First and second pixel electrodes capable of being applied to the first and second pixel electrodes, the first and second pixel electrodes having adjacent edges separated by an inter-pixel gap A control device for controlling the voltage,
The control device
Applying to the first pixel electrode a drive pulse effective to change the optical state of the electro-optic medium adjacent to the first pixel electrode to one of its extreme optical states; ,
While the electro-optic medium adjacent to the second pixel electrode is in the one extreme optical state, the second pixel electrode is supplied with a reinforcing pulse having the same polarity as the drive pulse, simultaneously with the drive pulse. Or applying a reinforcing pulse applied either within a predetermined period after the end of the drive pulse. An electro-optic display arranged to perform a drive method.   An electronic book reader, portable computer, tablet computer, cellular phone, smart card, sign, watch, shelf label, or flash drive comprising the display of claim 2. A method of driving a bistable electro-optic display having at least first and second pixels, each of the pixels being capable of displaying a first and second extreme optical state, wherein the first And the second pixel has adjacent edges separated by an inter-pixel gap, the method comprising:
Applying to the first pixel a driving pulse effective to change the optical state of the first pixel from one of its extreme optical states;
Applying a reverse reinforcement pulse of the opposite polarity to the drive pulse to a second pixel in the one extreme optical state, wherein the reverse reinforcement pulse is simultaneously with the drive pulse or of the drive pulse; Applying at any time within a predetermined period after termination.   The method according to claim 1 or 4, wherein the display is a monochrome display in which each pixel displays only the first and second optical states.   The method according to claim 1 or 4, wherein the reinforcing pulse includes only a single pulse having a polarity opposite to that of the driving pulse.   The reinforcing pulse includes a first pulse having the same polarity as the drive pulse, and a second pulse having an impulse opposite to the drive pulse and having a larger impulse than the first pulse. Or the method of 4.   The display includes a two-dimensional array of pixels, and the reinforcement pulse is applied only to pixels that are in the one extreme optical state and share a common edge with the pixel to which the drive pulse is applied. Item 5. The method according to Item 1 or 4.   The display comprises a two-dimensional array of pixels, and when one or more pixels are driven out of one extreme optical state, the reinforcement pulse is all pixels already in that one extreme optical state. The method according to claim 1, wherein the method is applied.   The display comprises a two-dimensional array of pixels, and when one or more pixels in an adjacent portion are driven out of one extreme optical state, the reinforcement pulse is already in one extreme optical state. 5. A method according to claim 1 or 4, wherein the pixel is applied to all pixels within its neighbor but the reinforcement pulse is not applied to a pixel that is in its one extreme optical state outside of the neighbor.   The method according to claim 1 or 4, wherein the reinforcing pulse is applied simultaneously with the drive pulse or within a subsequent period equal to the length of the drive pulse.   The method of claim 11, wherein the subsequent period has a duration that does not exceed about 400 milliseconds.   The method of claim 11, wherein the reinforcement pulse is applied simultaneously with a terminal portion of the drive pulse.   5. The method of claim 1 or 4, wherein the reinforcing pulse has an impulse of about 10 to about 70 percent of the impulse of the drive pulse.   The method of claim 14, wherein the reinforcement pulse has an impulse of about 20 to about 50 percent of the impulse of the drive pulse.   The method of claim 15, wherein the reinforcement pulse has an impulse of about 25 percent of the impulse of the drive pulse.   The method according to claim 1 or 4, wherein the reinforcing pulse comprises a plurality of discrete sub-pulses separated by at least one period of zero voltage.   The method according to claim 1 or 4, wherein the reinforcing pulse has a lower voltage than the drive pulse.   5. A method according to claim 1 or 4, wherein the display comprises a rotating dichroic member or an electrochromic medium.   5. A method according to claim 1 or 4, wherein the display comprises an electrophoretic medium comprising a plurality of charged particles arranged in a fluid and capable of moving through the fluid under the influence of an electric field. .   21. The method of claim 20, wherein the charged particles and the fluid are confined within a plurality of capsules or microcells.   21. The method of claim 20, wherein the charged particles and the fluid are present as a plurality of discrete droplets surrounded by a continuous phase comprising a polymeric material.   21. The method of claim 20, wherein the fluid is gaseous.   A bistable electro-optic display, a display controller, or an application specific integrated circuit arranged to perform the method of claim 1 or 4. A layer of a bistable electro-optic medium capable of displaying the first and second extreme optical states, and an electric field applied to the medium disposed adjacent to the layer of the bistable electro-optic medium First and second pixel electrodes capable of being applied to the first and second pixel electrodes, the first and second pixel electrodes having adjacent edges separated by an inter-pixel gap; A control device for controlling the voltage to be
The control device
Applying to the first pixel electrode a drive pulse effective to change the optical state of the first pixel from one of its extreme optical states;
Applying a reverse reinforcement pulse of a polarity opposite to the drive pulse to the second pixel electrode in the one extreme optical state, wherein the reverse reinforcement pulse is simultaneously with the drive pulse or the drive pulse An electro-optic display arranged to perform a driving method, comprising: applying at any time within a predetermined period after the end of.   An electronic book reader, portable computer, tablet computer, cellular phone, smart card, sign, watch, shelf label, or flash drive comprising the display of claim 25.

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