JP2015099376A - Method for driving electro-optical display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which is suitable for addressing a bi-stable electro-optical display device.SOLUTION: Disclosed is a method of addressing a bi-stable electro-optical display device having at least one pixel, the method which including the following processes: a process of applying an addressing pulse to drive the pixel in a first optical state; and a process of putting the pixel in a second optical state which is different from the first optical state by not driving the pixel in a certain time. This method is characterized such that a refresh pulse for substantially returning the pixel to the first optical state is applied to the pixel, and that the refresh pulse is shorter than the addressing pulse.

Description

  The present invention relates to a method and apparatus for driving an electro-optic display device, and more particularly to a bistable electro-optic display device. The method and apparatus of the present invention are not particularly limited, but are used for driving bistable electrophoretic display devices.

  This application relates to US Pat. Nos. 6,504,524 and 6,531,997. This application also relates to a co-pending international application PCT / US02 / 10267 (published international application 02/0779869) PCT / US02 / 37241.

  The term “electro-optic” is used herein in its conventional sense in imaging technology, as applied to a material or display device, and has first and second display states that differ in at least one optical characteristic. Say the material. This material changes from the first display state to the second display state by applying an electric field to the material. The optical properties are usually colors that the human eye can perceive, but for example, other optical properties such as light transmission, reflection, luminescence, or in the case of display devices for machine reading, changes in the reflection of electromagnetic length outside the visible range. In this sense, it is a pseudo color.

  The term “tone state” is used herein in its conventional sense in image technology and refers to a state intermediate between the two extreme light states of a pixel. This does not necessarily mean a black-and-white transition between these two extremes. For example, some of the following patents and published applications relating to electrophoretic display devices state that the extreme state is white and dark blue, and the intermediate “gradation state” is actually light blue. . In fact, the transition between the two extreme states already mentioned is not a discoloration.

  The terms “bistable” and “bistable” are used herein in their conventional sense in imaging technology and display comprising a display element having first and second display states that differ in at least one optical characteristic. Refers to a device, and after any given element is driven to either the first display state or the second display state by a finite time addressing pulse, the addressing pulse is stopped. This state is maintained at least several times, for example at least four times. The minimum duration of the addressing pulse is necessary to change the display element state. In the aforementioned U.S. Patent Application Serial No. 10 / 063,236, the particle-based electrophoretic display device capable of density gradation is not only in the extreme black and white state but also in the intermediate gradation state. It is stable and shows that this is true for some other types of electro-optic displays. The term “bistable” is used here for convenience to include both bistable display devices and multistable display devices, but this type of display device is correctly referred to as “multistable” rather than bistable. Called.

  As used herein, the term “impulse” is used in the conventional sense of voltage integration over time. However, some bistable electro-optic media act as charge transducers, in which such an impulse is another definition, ie, current vs. time integration (which is equal to the total charge applied). Can be used. Depending on whether the medium acts as a voltage time impulse transducer or a charge impulse transducer, it is necessary to define and use the impulse appropriately.

  Several types of bistable electro-optic display devices are well known. One of the electro-optic display devices uses a rotating two-color member. For example, US Pat. Nos. 5,808,783, 5,777,782, 5,760,761, No. 054,071, No. 6,055,091, No. 6,097,531, No. 6,128,124, No. 6,137,467, No. 6,147,791 ( This type of display device is often referred to as a “rotating two-color ball” type display device, but in some of the above-mentioned patents, the rotating member is not spherical, so the term “rotating two-color member” is Preferred because it is more accurate). Such display devices use a large number of small objects (typically spherical or cylindrical) having two or more cross-sections with different light characteristics and an internal dipole. These objects are suspended in vacuoles filled with liquid in the matrix. These vacuoles are filled with liquid so that the object rotates freely. By applying an electric field, the appearance of the display device is changed, and thus the object is rotated to take various postures so that the cross section of the object can be seen from the screen.

  Another type of electro-optic medium uses an electrochromic medium. For example, an electrochromic medium in the form of a nanochromic thin film is used, which includes an electrode at least partially formed from a semiconductive metal oxide and a plurality of dye molecules that are reversibly discolored attached to the electrode. Prepare. For example, B.I. O'Regan et al., Nature 1991, 353, 737, and D.C. See Wood, Information Display, 18 (3), 24 (March 2002). In addition, U.S. Bach et al., Adv. See Mater, 2002, 14 (11), 845. This type of nanochromic thin film is described, for example, in US Pat. No. 6,301,038 and published International Application No. 01/27690.

  Another type of electro-optic display that has been the subject of extensive research and development over the years is a particle-based electrophoretic display in which a plurality of charged particles move through a suspended fluid under the influence of an electric field. The electrophoretic display device has favorable luminance and contrast characteristics, a wide viewing angle, state bistability, and low power consumption compared with a liquid crystal display device. However, when these display devices are used for a long period of time, there is a problem in image quality, which hinders popularization. For example, particles constituting the electrophoretic display device are easily precipitated, and the useful life of these display devices is shortened.

  Recently, a number of patents and applications have been published describing sealed electrophoretic media, assigned under the names of Massachusetts Institute of Technology (MIT) and E Ink Corporation. Such a sealing medium comprises a number of small capsules, each capsule itself having a dispersed phase containing electrophoretic particles suspended in a liquid suspending medium and a capsule wall surrounding the dispersed phase. Typically, the capsule itself is held in a polymer binder, forming a coherent layer located between the two electrodes. For this type of sealing media, for example, U.S. Pat. Nos. 5,930,026, 5,961,804, 6,017,584, 6,067,185, 6,118, No. 426, No. 6,120,588, No. 6,120,839, No. 6,124,851, No. 6,130,773, No. 6,130,774, No. 6,172,798 Nos. 6,177,921, 6,232,950, 6,249,721, 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 No. 6,413,790, No. 6,422,687, No. 6,445,374, No. 6,445,489, No. 6,459,418, No. 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, U.S. Patent Application Publication No. 2002/0019081, 2002/0021270, 2002/0053900, 2002/0060321, 2002/0063661, 2002/0063677, 2002/0090980, second No. 02/0108847, No. 2002/0113770, No. 2002/0130832, No. 2002/0131147, No. 2002/0145792, No. 2002/0154382, No. 2002/0171910, No. 2002/0180687, No. 2002 / No. 0180688, No. 2002/0185378, No. 2003/0011560, No. 2003/0011867, No. 2003/0011868, No. 2003/0020844, No. 2003/0025855, No. 2003/0034949, No. 2003/0038755 2003/0053189 and WO 99/67678, 00/05704, 00/20922, 00/26761, 00/38000, 00/3 No. 8001, No. 00/36560, No. 00/67110, No. 00/67327, No. 01/07961, No. 01/08241.

  Many of the aforementioned patents and applications recognize that the walls surrounding individual microcapsules in a sealed electrophoretic medium can be replaced with a continuous phase, thus forming a so-called polymer dispersed electrophoretic display. In this apparatus, the electrophoretic medium comprises a plurality of individual droplets of electrophoretic fluid and a continuous phase of a polymeric material. Individual droplets of electrophoretic fluid in such polymer dispersion electrophoretic displays recognize that individual capsule membranes are not associated with each individual droplet, but are considered as capsules or microcapsules. For example, see the aforementioned 2002/0131147. Accordingly, the purpose of this application is to consider such polymer dispersed electrophoretic media as a variant of encapsulated electrophoretic media.

  Sealed electrophoretic display devices typically do not have the clustering and precipitation obstacle states of conventional electrophoretic devices, and can be used, for example, to print display devices on various bendable and rigid substrates. There is an advantage such as the ability to apply. (The term “printing” is used to include all forms of printing and application, including but not limited to patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating, etc. -Metered coating, roll coating such as roll knife coating, normal reversal roll coating, gravure coating, dip coating, spray coating, meniscus coating, spin coating, brush coating, air knife coating, silk screen printing process, electrostatic printing process Including thermal printing processes, inkjet printing processes and other similar technologies.) It is to have a cormorant sex. Further, since the display medium can be printed (using various methods), the display device itself can be manufactured at low cost.

  A related type of electrophoretic display is the so-called “microcell electrophoretic display”. In microcell electrophoretic display devices, charged particles and suspended fluid are not sealed within microcapsules, but instead are typically held within a plurality of cavities formed in a polymeric thin film carrier medium. See, for example, International Publication No. 02/01281 and US Patent Application Publication No. 2002-0075556, assigned to Sipix Imaging Inc.

  Electrophoretic display devices are often opaque (because particles substantially block visible light from passing through the display device) and operate in a reflective mode. It can also be operated in a so-called “shutter mode”. The particles are arranged so as to move laterally in the display device so that the display device is on the one hand substantially non-translucent and on the other hand light-transmissive. For example, the aforementioned US Pat. Nos. 6,130,774, 6,172,798, US Pat. Nos. 5,872,552, 6,144,361, 6,271,823, , 225,971, 6,184,856. The dielectrophoretic display device is similar to the electrophoretic display device, but can operate in the same mode based on fluctuations in electric field strength. See U.S. Pat. No. 4,418,346.

  The bistable or multi-stable behavior of particle-based electrophoretic displays and electro-optic displays that exhibit similar behavior shows a marked contrast with the behavior of conventional liquid crystal ("LC") displays. Twisted nematic liquid crystals are neither bistable nor polystable and act as voltage transducers, so by applying an arbitrary electric field to a pixel in such a display device, the pixel is independent of the gray level that the pixel previously indicated. A specific gradation is generated. Further, the LC display device is driven only in one direction (non-transmission, that is, from “dark” to transmission, that is, “bright”). By lowering or removing the electric field, a transition is made from a brighter state to a darker state. Finally, the gray level of the pixel of the LC display device does not react to the polarity of the electric field, but reacts only to the magnitude of the electric field. In fact, for technical reasons, commercially available LC displays often have the drive field polarity reversed frequently. In contrast, a bistable electro-optic display acts as an impulse transducer as a first similarity, so that the final state of the pixel applies an electric field as well as the applied electric field and the time the electric field was applied. It also depends on the state of the previous pixel.

  As already indicated, some electrophoretic display devices and other electro-optic display devices exhibit bistability. This bistability is limited, and the image on the display will slowly disappear with time, so to maintain the image for a longer period of time, the image must be restored to the optical state in which it was originally written. It is necessary to refresh regularly.

  However, there is a problem in refreshing the image itself. As described in the aforementioned US Pat. Nos. 6,531,997 and 6,504,524, the net time average applied electric field applied to the electro-optic medium by the method used for driving the display device is zero, Or, if it is not close to zero, a problem occurs and the operating life of the display device is shortened. For convenience, a driving method in which the net time average applied electric field applied to the electro-optic medium is not zero is referred to as “DC balance”, that is, “DC balance”. If the image is maintained for a long time by applying refreshing pulses, these pulses have the same polarity as the addressing pulses originally used to drive the relevant pixels of the display and maintain the optical state. This must be a DC unbalanced drive method.

  According to one aspect of the present invention, it has been found that if refreshing with a short pulse, the image on the display device can be refreshed while reducing harmful effects associated with the DC imbalance driving method.

  Furthermore, one aspect of the present invention addresses the problem that the aforementioned driving requirements of a bistable electro-optic display become a conventional driving method used to drive LCDs that are not suitable for such a bistable electro-optic display. About. Further, as described in the aforementioned US Pat. Nos. 6,531,997 and 6,504,524, a net time average applied electric field applied to an electro-optic medium by a method used for driving a display device. If is not zero or close to zero, a problem occurs and the operating life of the display device is shortened. For the sake of convenience, the driving method in which the net time average applied electric field applied to the electro-optic medium does not become zero is called “DC balance”, that is, “DC balance”. A similar problem occurs in LCDs, but due to the insensitivity of such display devices to the polarity of the applied electric field and the resulting ability to freely reverse the polarity, it is a problem of DC balance, but not a major problem in LCDs. . However, the need for DC balance is an important point that must be considered in devising a method for driving a bistable electro-optic display that is sensitive to the polarity of the electric field applied by the electro-optic medium.

  Accordingly, a further aspect of the present invention relates to a method and apparatus for driving an electro-optic display that meets the specific requirements of the bistable display described above. Certain methods and apparatus of the present invention are specifically intended for the generation of accurate gray scale displays in bistable display devices.

  Accordingly, in one aspect, the present invention provides a method for addressing a bistable electro-optic display having at least one pixel. This method includes:

Applying an addressing pulse to drive the pixel to the first optical state;
By not driving the pixel for a period of time, the pixel is placed in a second optical state different from the first optical state,
A refresh pulse is applied to the pixel to substantially return the pixel to the first optical state, the refresh pulse being short compared to the addressing pulse.

  This aspect of the invention will hereinafter be referred to as the “refresh pulse” method of the invention for convenience of explanation.

  In this refresh pulse method, the refresh pulse is typically 20% or less of the impulse of the addressing pulse, desirably 10% or less of the impulse of the addressing pulse, preferably 5% or less of the impulse of the addressing pulse. It is. For reasons discussed below, typically the difference between the first and second optical states is less than about 1 unit of L * (L * is a normal CIE specification), preferably this difference is L Less than about 0.5 units of *, preferably less than about 0.2 units of L *. A plurality of refresh pulses can be applied to the pixels at regular intervals.

  In one form of the refresh pulse method, after applying the refresh pulse, the display device is applied with a second addressing pulse that drives the pixel to a third optical state different from the first and second optical states; The impulse applied by the second addressing pulse includes (a) an impulse required to drive the pixel from the first optical state to the third optical state, and (b) the first addressing pulse and the second addressing pulse. This is the total amount of impulses of the same magnitude but opposite in polarity with respect to the algebraic sum of the refresh pulses applied to the pixels between the addressing pulses. The second addressing pulse has a constant voltage, but the period can be variable. The display device may also comprise a plurality of pixels and a second addressing pulse including a blanking pulse that drives all the pixels of the display device to one extreme optical state. In a preferred form of such a “blanking pulse / refresh pulse” process, the display device comprises a plurality of pixels so as to drive a first group of white pixels and a second group of black pixels. Applying a first addressing pulse to each pixel, applying at least one refresh pulse to each pixel, and a first blanking pulse that makes all pixels black, and a second that drives all pixels to white Are applied to the display device, two blanking pulses are applied in either order, and an impulse applied to each pixel of the first group during the first blanking pulse is (a ) The impulse required to drive the pixel from white to black; and (b) the peak between the first addressing pulse and the first blanking pulse. Impulse applied to each pixel of the second group during the second blanking pulse is the total amount of the same magnitude and the opposite polarity of the algebraic sum of the refresh pulses applied to the cell. (C) Impulse required to drive the pixel from black to white, and (d) Polarity relative to the algebraic sum of refresh pulses applied to the pixel between the first addressing pulse and the first blanking pulse Is the total amount of impulses of the same magnitude.

  In the refresh pulse method of the present invention, any type of electro-optic medium described above can be used. Therefore, in this method, the display device can be a rotating heavy chromium material or an electrochromic display device, or an electrophoretic display device, preferably a sealed electrophoretic display device.

  In another aspect, the present invention provides a method for addressing a bistable electro-optic medium that includes applying an AC pulse having a DC offset to the medium.

  In another aspect, the invention includes applying an AC pulse to the medium and changing the optical state of the electro-optic medium by changing at least one of the duty cycle and frequency of the pulse following the AC pulse. A method for addressing a bistable electro-optic medium is provided.

  In another aspect, the present invention provides a plurality of pixels arranged in a plurality of rows and a plurality of columns, a plurality of row electrodes each associated with one of the plurality of rows, and one of each of the plurality of columns. In order to select a plurality of column electrodes associated with each row and each row electrode in order, and write a row of a desired image on the display device by addressing the pixel row associated with the selected row electrode. A method of addressing a bistable electro-optic display device having drive means configured to apply column electrodes while selecting any of the row electrode voltages is provided. The method includes:

Write the first image on the display device,
Receiving data indicating a second image to be written to the display device;
Comparing the first image with the second image, dividing the rows of the display device into a first set, wherein at least one pixel row is different between the first image and the second image, Set of pixels are the same between the first image and the second image,
Write the second image by sequentially selecting only the row electrodes associated with the first set of rows, and write only the first set of rows by applying a voltage to the column electrodes, A second image is formed on the display device.

  In another aspect, the present invention is an electro-optic display device having a plurality of pixels, wherein at least one pixel comprises a plurality of sub-pixels each having a different area, and the display device has an optical state of the sub-pixels relative to each other. An apparatus is provided comprising drive means configured to vary independently. In such a display device, it is desirable that at least two subpixels are substantially in multiples of 2 and have different regions.

As already indicated, the present invention provides a number of improvements in the method of addressing electro-optic media and display devices and the construction of such display devices. The various aspects of the present invention will be described sequentially, but one electro-optic medium or display device can utilize more than one aspect of the present invention. For example, one electro-optic display device can use AC pulses with DC offset drive, and can also use refresh pulses.
As described above, in one aspect, the present invention provides a method for refreshing an image on an electro-optic display device by applying a short refresh pulse to the display device. Therefore, in the method of the present invention, an addressing pulse sufficient to change the optical state of the pixel is first applied to the pixel of the bistable display device. After the display device is not driven for a certain period of time, a refresh pulse shorter than the addressing pulse is applied to the pixel. Typically, the impulse applied by the refresh pulse is about 20% or less (desirably 10% or less, preferably 5% or less) of the impulse applied by the addressing pulse. For example, if a pixel requires an address pulse of 15V for 500 milliseconds, the refresh pulse can be 10 milliseconds at 15V and 2% of the impulse of the addressing pulse.

  The timing of the refresh pulse in this method needs to take into account the sensitivity of the human eye to sudden changes in the optical state. Since the human eye is relatively tolerant to progressively fading images, for example, the bistability of an electro-optic medium (defined by the usual CIE regulations), often measured as the time required for lightness L * See, for example, RW Hunt, Measuring Color, 3rd Edition, Fountain Press, Kingston Upon Thames, England (1998) (ISBN 0 86343 387). 1)) varies by 2 units from the maximum of the white optical state observed from the end of the addressing pulse (or from the minimum of the black state). However, when a refresh pulse is applied to the display device, a rapid change occurs in the brightness of the corresponding pixel, and a sudden change substantially less than one unit of L * is easily recognized by the human eye. Depending on the interval between refresh pulses, image changes due to these pulses appear as “flicker” in the image, and such flicker is very unpleasant for the viewer. In order to avoid such noticeable flicker or other noticeable fluctuations in the image due to the refresh pulse, the interval between the addressing pulse and the first refresh pulse is such that each refresh pulse causes a minimal change in the image. Or an interval between successive refresh pulses. Thus, the change in L * due to one refresh pulse is less than about 1 unit of L *, desirably less than about 0.5 unit, preferably less than about 0.2 unit.

  By using the refresh pulse in this method, DC imbalance occurs to some extent in the driving method while the refresh pulse is applied, but the driving method does not include long-term DC balance. It has been found that what is very important in determining the operating life of an electro-optic display is long-term DC balance rather than short-term DC balance. In order to achieve such long-term DC balance, after applying one or more refresh pulses, the pixel to which the refresh pulse is applied is replaced with a “switching” addressing pulse or a second addressing pulse and vice versa. Drive to the state. The impulse applied with this switching addressing pulse can be adjusted to form a DC balance (or at least a minimum DC imbalance) over the entire period. The first addressing pulse is substantially the same magnitude and opposite in polarity to the refresh pulse algebraic sum applied to the pixel between the two addressing pulses, and the impulse of this second addressing pulse is This is because it has been adjusted. For example, consider a display device that can be switched between a white optical state and a black optical state by applying an impulse of ± 15 V for 500 milliseconds. The pixel of this display device is first switched from black to white by applying an impulse of +15 V for 500 milliseconds, and then the white state of the pixel is changed to 10 refreshing pulses of +15 V for each 10 milliseconds. It is assumed that it is maintained by applying. It is desirable to return the pixel to the black optical state after 10 refresh pulses have been applied. This can be achieved by applying a -15V addressing pulse for 600 milliseconds (as opposed to 500 milliseconds), thus achieving an overall DC balance while the pixel transitions from all black to white to black. can do.

  This adjustment of the switching addressing pulse can be done when it is necessary to change the optical state of a pixel by writing a new image to the display. On the other hand, this adjustment can also be performed while the “blanking pulse” is applied to the display device. As described in the aforementioned PCT / US02 / 37241, it is often necessary or desirable to apply so-called “blanking pulses” to the electro-optic display device at regular intervals. Such a blanking pulse first drives all pixels of the display device to one extreme optical state (eg, white state), then puts all pixels into the opposite optical state (eg, black), and Writing a desired image is included. Making adjustments during the blanking pulse using the techniques already described in detail has the advantage that DC balance can be achieved substantially simultaneously for all pixels. The DC balance of the pixels where the previous image was black during the blanking pulse that drives all the pixels to white (the image displayed just before applying the blanking pulse) can be balanced, making all the pixels black During the driving blanking pulse, the DC balance of the pixels where the previous image was white can be achieved. Further, by adjusting during the blanking pulse, it is not necessary to find out how many times the refresh pulse has been applied to each pixel from the previous addressing pulse. Assuming that black and white pixels are refreshed at the same interval (as is often the case) and that a blanking pulse is inserted as each image transitions, each pixel between blanking pulses It is necessary to make the same adjustments (except for polarity). This adjustment is determined by the number of refresh pulses applied to the display device from the previous blanking pulse. Further, the present invention provides a method of applying the refresh pulse method to an electro-optic display device having three or more gradations by taking DC balance between blanking pulses. This is because, in such a display device, an unnecessary error occurs in the gradation by clearly adjusting the impulse applied during the gradation-to-gradation transition.

The refresh pulse method of the present invention can be used in addition or in combination as an alternative or in combination to increase the bistability of the electro-optic medium. For example, the present invention can be used with the electrophoretic medium described in the aforementioned 2002/0180687. The medium has a suspension in which the polymer is dissolved or dispersed, which increases the bistability of the medium.
(Item 1)
A method of addressing a bistable electro-optic display device having at least one pixel, the method comprising:
Applying an addressing pulse to drive the pixel to a first optical state; and not driving the pixel for a period of time to place the pixel in a second optical state different from the first optical state. This method involves
Applying a refresh pulse to the pixel to substantially return the pixel to a first optical state, the refresh pulse being short compared to the addressing pulse.
(Item 2)
2. The method according to item 1, wherein the refresh pulse is an impulse of 20% or less of the impulse of the addressing pulse.
(Item 3)
3. The method according to item 2, wherein the refresh pulse is an impulse of 10% or less of an impulse of the addressing pulse.
(Item 4)
4. The method according to item 3, wherein the refresh pulse is an impulse of 5% or less of the impulse of the addressing pulse.
(Item 5)
5. A method according to any one of items 1 to 4, wherein the difference between the first and second optical states is less than 1 unit of L *.
(Item 6)
6. The method of item 5, wherein the difference between the first and second optical states is less than 0.5 units of L *.
(Item 7)
Item 7. The method of item 6, wherein the difference between the first and second optical states is less than 0.2 units of L *.
(Item 8)
8. The method according to any one of items 1 to 7, wherein a plurality of refresh pulses are applied to the pixel at regular intervals.
(Item 9)
After applying the refresh pulse, the display device is applied with a second addressing pulse that drives the pixel to a third optical state different from the first and second optical states, and the second addressing pulse is applied. The impulse (a) the impulse required to drive the pixel from the first optical state to the third optical state;
(B) An item that is the total amount of impulses having opposite polarities and the same magnitude as the algebraic sum of refresh pulses applied to pixels between the first addressing pulse and the second addressing pulse. The method according to any one of 1 to 8.
(Item 10)
10. The method according to item 9, wherein the second addressing pulse is a constant voltage but the period is variable.
(Item 11)
Item 11 or 10 wherein the display device comprises a plurality of pixels and a second addressing pulse including a blanking pulse that drives all pixels of the display device to one extreme optical state. Method.
(Item 12)
A first addressing pulse is applied to each pixel so that the display device comprises a plurality of pixels and drives a first group of white pixels and a second group of black pixels, and at least one refresh pulse is applied. A first blanking pulse is applied to each pixel, and all pixels are black, and a second blanking pulse that drives all pixels to white is applied to the display device. The impulses applied to each pixel of the first group during the first blanking pulse are: (a) the impulse required to drive the pixel from white to black; and (b) Impuls with opposite polarity and the same magnitude as the algebraic sum of refresh pulses applied to the pixel between the first addressing pulse and the first blanking pulse Wherein the impulse applied to each pixel of the second group during the second blanking pulse is (c) the impulse required to drive the pixel from black to white, and (d) Items 1 to 3, characterized in that the total amount of impulses having the same polarity and opposite polarity with respect to the algebraic sum of refresh pulses applied to the pixels between the first addressing pulse and the first blanking pulse. 11. The method according to any one of 11 above.
(Item 13)
13. The method according to any one of items 1 to 12, wherein the display device is a rotating heavy chromium material or an electrochromic display device.
(Item 14)
13. The method according to items 1 to 12, wherein the display device is an electrophoretic display device.
(Item 15)
Item 15. The method according to Item 14, wherein the display device is a sealed electrophoretic display device.
(Item 16)
A method of addressing a bistable electro-optic medium, wherein an AC pulse having a DC offset is applied to the medium.
(Item 17)
Addressing a bistable electro-optic medium characterized by applying an ac pulse to the medium and changing the optical state of the electro-optic medium by altering at least one of the duty cycle and frequency of the pulse following the ac pulse how to.
(Item 18)
Multiple pixels arranged in multiple rows and multiple columns, multiple row electrodes each associated with one of the multiple rows, and multiple column electrodes each associated with one of the multiple columns And select any row electrode voltage to select each row electrode in turn and address one pixel row associated with the selected row electrode to write one row of the desired image on the display device A method of addressing a bistable electro-optic display device having drive means configured to apply column electrodes during the process, characterized in that:
Write the first image on the display device,
Receiving data indicating a second image to be written to the display device;
Comparing the first image with the second image, dividing the rows of the display device into a first set, wherein at least one pixel row is different between the first image and the second image, Set of pixels are the same between the first image and the second image,
Write the second image by sequentially selecting only the row electrodes associated with the first set of rows, and write only the first set of rows by applying a voltage to the column electrodes, A second image is formed on the display device.
(Item 19)
An electro-optic display device having a plurality of pixels, wherein at least one pixel comprises a plurality of sub-pixels each having a different area, and the display device is configured such that the optical state of the sub-pixels changes independently of each other. A device characterized by comprising a driving means.
(Item 20)
Item 20. The electro-optic display device according to item 19, wherein at least two subpixels are substantially a multiple of 2 and have different areas.

FIG. 1 is a graph showing that the gradation changes with time in a display device addressed using a DC pulse by pulse width modulation. FIG. 2 is a graph showing the same thing as FIG. 1 in a display device addressed using DC pulses with pulse height modulation. FIG. 3 is a graph showing the same thing as FIG. 1 in a display device addressed using an AC pulse with a DC offset according to the present invention. FIG. 4 is a graph showing the same thing as FIG. 1 in a display device using an AC pulse addressed by duty cycle modulation according to the present invention. FIG. 5 is a graph showing that gradation changes with time in a display device addressed using a double prepulse side show waveform. FIG. 6 is a graph showing that the gradation varies with time in a display device addressed using a single prepulse side show waveform. FIG. 7A and FIG. 7B show possible sub-pixel configurations in one pixel of the display device of the present invention. FIG. 7A and FIG. 7B show possible sub-pixel configurations in one pixel of the display device of the present invention.

The following examples illustrate one embodiment of the refresh pulse method of the present invention, but are for illustrative purposes only.
Example 1
In this example, a display device is used that includes an oppositely charged encapsulated two-particle medium comprising titanium dioxide white particles polymer coated in colorless suspension and polymer coated black particles. The display device is generally prepared by “Method B” described in paragraphs [0061] to [0068] of the aforementioned 2002/0180687.

  In the display device prepared as described above including a plurality of pixels, an addressing pulse of ± 15 V was applied for 500 milliseconds to switch between the black optical state and the white optical state. This display device has limited bistability. The time required to change the white optical state by 2 L * units was only about 15 seconds at room temperature. However, experience has shown that the white optical state and the black optical state can be maintained indefinitely by applying a short refresh pulse of ± 15 V at a duty cycle of approximately 6.7% at 4 seconds / minute. Judgment. To perform realistic tests and avoid flicker in the standard images used in these experiments (including both black and white areas), first apply a 500 millisecond addressing pulse, then ± 15V refresh pulse Was applied to the black and white pixels of the display at intervals of approximately 7 milliseconds, approximately 100 milliseconds.

In order to determine the DC unbalanced driving method in the display device in various periods, the four driving methods were examined separately.
480 minutes method The display was addressed with a standard image and this image was maintained using the refresh pulse described above for 480 minutes. Next, a series of blanking pulses were applied, and the cycle of the addressing pulse and the refresh pulse was repeated. No DC balance pulse was applied. After 83 hours of operation, a series of blanking pulses were applied and examined on separate areas of the display that were white and black, respectively, in the standard image. In the following table, the area of the display device that displayed white during the examination period is indicated as “480 W”, and the area that displayed black as “480 D”. Each inspected area was driven to the white optical state with a standard 500 millisecond addressing pulse to measure the percent reflection value. This value is shown in the table as “w%”. Next, the refresh pulse was not applied to each of the inspected regions for 15 seconds, and after 15 seconds, the change in L * was measured. The resulting change in L *, known as “difference in brightness”, is shown in the table as “bhdl”. After applying a further blanking pulse, each inspected area was driven to the black optical state by applying a standard 500 millisecond addressing pulse and the percent reflection value was measured. This value is shown in the table as “d%”. Next, a refresh pulse was not applied to each of the inspected regions for 15 seconds, and after a second 15 seconds, the change in L * was measured. The resulting change in L * known as “Darkness Difference” is shown in the table as “dhdl”.
60 minutes method This method is the same as the 480 minutes method, except that the image was maintained for 60 minutes before applying the blanking pulse. The area of the display device that presented white during the inspection period is shown in the following table as “60 W”, and the area that presented black as “60D”.
Ten-minute method In this method, the image was written in the same manner as the 480-minute method and maintained for 10 minutes using the same refresh pulse as the 480-minute method. Next, a reverse polarity pulse was applied for 40 seconds to balance the DC of the display, and the image was rewritten to repeat this cycle. The area of the display device that presented white during the inspection period is shown in the following table as “10W”, and the area that presented black is shown as “10D”.
1-minute method This method is the same as the 10-minute method, except that the image is maintained for 1 minute, then the second DC balance pulse is applied for 4 seconds and this cycle is repeated. The area of the display device that presented white during the examination period is shown in the following table as “1W”, and the area that presented black as “1D”.

  The results obtained from these experiments are shown in Table 1 below.

  (Table 1)

  From the data in Table 1, in the very unbalanced 480 minutes method, the reflection of the white state is greatly different in the area of the display device that presents white and black during the examination period, and the difference in darkness retention is also You can see that it was very different. Therefore, this very unbalanced driving method causes a considerable change in the optical state of the display device that is very far from other effects, such as damaging the electrodes. This can occur with such an unbalanced driving method. In addition, as can be seen from the difference seen in the difference between maintaining brightness and darkness, it means that white tends to remain in the area that has been white for a long time, while black tends to remain in the area that has been black for a long time. Thus, a “bias” is generated in the display device by an unbalanced driving method. The results obtained from the unbalanced 60-minute method showed what was expected, but to a lesser extent the same. In contrast, there was essentially no difference between the white and black areas in both the DC balance 10 min and 1 min methods.

  Therefore, from these experiments, if a long-term DC balance is generated by a blanking pulse having an interval, a temporary DC imbalance generated by using a short refresh pulse adversely affects the characteristics of the display device. It turns out that was not given.

The electrophoretic medium used in the refresh pulse method of the present invention can use the same components and manufacturing techniques as the aforementioned Eink and MIT patents and patent applications, which the reader is referred to for further information.
Basic elements of gradation drive waveform (including use of AC pulse)
As described in the aforementioned US Pat. Nos. 6,531,997 and 6,504,524, many display devices currently apply voltage pulses for a sufficient period of time to saturate electro-optic media. To switch from one extreme optical state to the other (eg, from black to white, or vice versa). For example, in a particle-based electrophoretic medium, charged particles are moved across the entire front or back electrode. With the conventional requirement of addressing electro-optic media until the optical state is saturated, a halftone state is not possible. An electro-optic display device that achieves gradation provides significant advantages in graphic performance and image quality.

  For convenience, a voltage waveform or a driving method for realizing gradation in a bistable electro-optical display device is hereinafter referred to as “gradation waveform” or “gradation driving method”, respectively. There are five basic gradation waveform elements used in such a gradation waveform or driving method. The term “gradation waveform element” means a voltage pulse, ie, a series of voltage pulses, and means to produce a change in the optical state of the electro-optic display. The gradation waveform elements themselves can generate gradations, and one or more gradation waveform elements arranged in a specific sequence together form a gradation drive waveform. The gradation drive waveform can switch the pixel of the display device from one gradation state to another. A sequence of one or more driving waveforms constitutes a driving method, whereby an arbitrary series of gradation images can be displayed on the display device.

  Drive waveform elements fall into two basic categories. That is, a direct current (DC) voltage pulse and an alternating current (AC) voltage pulse. In either case, the variable parameters of the pulse are the pulse height and the pulse length.

  Generating a gradation optical state in an electro-optic medium is very dependent on the way in which a voltage is applied to the medium, but the ability of the medium to maintain this gradation optical state when no voltage is applied. It is equally important in the gradation addressing method, and this ability depends on the nature of the medium. In fact, it depends on all the gradation switching characteristics. In this application, the gradation addressing method is mainly described with reference to the encapsulated particle-based electrophoretic medium, but such a method is necessary to enable the characteristics of other types of bistable electro-optic media. It will be readily apparent to those skilled in the art of such media.

The basic elements of the gradation drive waveform are as follows.
DC Pulse with Pulse Width Modulation The simplest way to achieve the desired gradation state is to stop pixel addressing during the transition from one extreme optical state to the other. In FIG. 1 of the accompanying drawings, the inset shows the DC pulse length modulation waveform element used to generate a tone transition in the encapsulated electrophoretic medium shown in the main figure. (The display device used in this experiment described below and the subsequent experiment is generally based on “Method B” described in paragraphs [0061] to [0068] of the aforementioned 2002/0180687.) Each of the three pulses used applied 15 V for 200 milliseconds, 400 milliseconds, and 600 milliseconds, and the generated three curves were displayed accordingly. Note that the time scale of the inset is not the same as the time scale of the main diagram. Therefore, the pulse height is constant, but the pulse time is different because the reflectivity varies separately. In FIG. 1, the reflectance of a pixel whose reflection state has changed from black to gray with a different level when these voltage pulses are applied is plotted against time. It can be seen that the change in reflectance increases as the pulse length increases.

  The tested display device responded immediately to the end of the applied voltage pulse and ended up in high optical state. At the microscopic level, it is presumed that the electrophoretic particles immediately stop when moving from one electrode to the other and are suspended at an intermediate position inside the capsule.

The advantage of a DC gray level drive pulse using pulse width modulation is the speed at which the desired gray level state is achieved.
DC pulse with pulse height modulation Another approach to achieving the desired gray scale state is to bring the pixel at a voltage lower than that required to completely switch from one extreme optical state of the pixel to the other. It is to address. In FIG. 2 of the accompanying drawings, a DC pulse high modulation waveform element that produces a gradation transition in the encapsulated electrophoretic medium shown in the main figure is shown in the inset. The voltage pulse length is fixed for the length of time required to completely switch the medium at the maximum voltage level. The three pulses used were applied at 5 V, 10 V, and 15 V for 500 milliseconds, and the three generated curves are displayed accordingly. Note that the time scale of the inset is not the same as the time scale of the main diagram. Therefore, although the pulse length is constant, the pulse high pulse time is different because the reflectivity changes separately. In FIG. 2, when these voltage pulses are applied, the reflectance of the pixel whose reflection state has changed from black to a different level of gradation is plotted against time. It can be seen that the change in reflectivity increases as the pulse height increases.

  If the driving voltage is stopped while the driving voltage is applied, it is presumed that the electrophoretic particles move the suspension at a slower speed at a lower voltage and remain suspended.

The advantage of a DC gray level drive pulse using pulse height modulation is that the achieved gray level is accurately controlled.
AC pulse using DC offset modulation The gradation driving of the above-described sealed electrophoretic medium is performed by an oscillation (AC) electric field. Such a switching mechanism using an AC electric field is considered to be completely different from DC driving of the same medium described above. In FIG. 3 of the accompanying drawings, the inset shows an AC pulse using a DC offset modulation waveform element that is used to generate a gradation transition in the encapsulated electrophoretic medium shown in the main figure. In either case, the frequency of the AC component (approximately 10 Hz) was set to a value that allows the particles to respond to the oscillating electric field, but the magnitude and direction of the DC offset (as shown in the three curves in FIG. 3). To 0V, -1V or -2.5V) as a result, the gradation state of the pixel is determined. As in the previous drawing, the time scale of the inset is not the same as the time scale of the main diagram. In FIG. 3, when these voltage pulses are applied, the reflectance of a pixel whose reflection state has changed from black to a different gradation level is plotted against time. It can be seen that the change in reflectivity increases as the DC offset increases.

  When an AC electric field is applied, the electrophoretic particles oscillate in the suspension. As can be easily seen from the left side of FIG. Observed. There is no net effect on reflectivity until a DC offset is applied. After applying a waveform for a certain time under the influence of DC offset, the reflectance approaches a certain value. There appears to be a restoring force opposite to the force on the particles due to the DC offset voltage. Otherwise, the particles will continue to flow into the capsule wall. This restoring force is due to the movement of the liquid between the capsule wall and the particles and / or the particles directly interacting with the capsule wall. The stability of the optical state after releasing the voltage is consistent with the other waveform elements.

The advantage of an AC waveform element is the ability to enter a particular reflectivity state by specifying the waveform element parameters, but the DC waveform element can only change with reflectivity. An advantage of an AC waveform element using a DC offset relative to other AC waveform elements is that it is not necessary to accurately tune the addressing pulse.
AC Pulse with Duty Cycle Modulation Another way to induce a DC bias using an oscillating electric field is to modulate the duty cycle. In FIG. 4 of the accompanying drawings, the inset shows an AC pulse using duty cycle modulation that produces the tone transition shown in the main diagram. In each pulse, the voltage is set to the maximum value, and the reflectance is determined by the duty cycle (the percentage of time in which the voltage is positive or negative). As shown in FIG. 4, the three duty cycles used were 50%, 47% and 40%. As in the previous drawing, the time scale of the inset is not the same as the time scale of the main diagram. In this figure, when these voltage pulses are applied, the reflectance of a pixel whose reflection state has changed from black to a gradation having a different level is plotted with respect to time.

  It can be seen from FIG. 4 that the curve shown in FIG. 4 approaches a certain value after applying a pulse for a certain time, as the curve shown in FIG. 3 is generated using an AC / DC offset pulse. Therefore, when duty cycle modulation is used, such as AC / DC offset, there appears to be a restoring force that forces particles away from the capsule wall and maintains a constant tone state. The physical mechanism of the restoring force is probably the same as described above. Further, when the application of the pulse is stopped, the change of the gradation state is stopped immediately.

An advantage of an AC waveform using duty cycle modulation is that it does not require voltage modulation.
AC Pulse with Frequency Modulation Another approach to switching AC gray levels is to apply an AC electric field to the electro-optic medium, which generates and oscillates the optical state of the medium and achieves the desired reflectivity. The AC electric field is stopped halfway through the cycle. This voltage is set to the maximum value and the AC frequency is changed in order to achieve a larger or smaller reflectance range. The magnitude of the oscillation of the reflectance is determined based on the frequency.

  When applied to a sealed particle-based electrophoretic medium with such an approach, the electrophoretic particles react to an AC electric field by oscillating around their initial position. The reflectivity typically does not result in either the black or white optical state at the counter electrode, so interaction with the capsule wall is minimized and the reflectivity response is relative to the applied voltage. It is relatively linear.

  An advantage of AC pulses using frequency modulation is that no voltage modulation is required.

  By combining the above types of pulses, the size of the waveform element can be developed. Since each has a unique switching mechanism, it is possible to provide a wide application method for driving different electro-optic media having different switching characteristics.

  When the principle of the driving method described above is applied to a specific example, by using pulse width modulation and an AC pulse, an electro-optical display device that can realize only a black state and a white state if not used is applied to an intermediate gradation. The state can be realized.

  For the reasons already mentioned, the ability to achieve gradation is highly desirable in electro-optic display devices. However, a large number of tones are composed of a high frame rate driver (high frame rate is necessary to “slice” the pulse width into multiple intervals, which allows for pulse width, A pulse width modulation using either a driver capable of controlling gradation very accurately) or a voltage-modulable driver is required. Both types of drivers are substantially more expensive than simple three-stage drivers. The three-stage driver can set each pixel of the display device to only + V, −V, and 0 potential with respect to the potential of the common front electrode (V is an arbitrary operating potential), and can perform only the black state and the white state. It is commonly used for display devices.

  The present invention provides a driving method that allows a gray level intermediate between a black level and a white level of a bistable electro-optical display device to be generated by a three-stage driver. This driving method can be easily understood from Table 2 below. 6 is a table showing voltages applied during successive frames of various types of transitions in the display device of the present invention.

  (Table 2)

  As can be seen from Table 2 above, the transition from black to white, or vice versa, is similar to a binary (black / white only) display. On the other hand, the transition to gradation has two parts. The first part is a square wave pulse (ie, multiple frames at the same potential) with the appropriate polarity and length to bring the reflectivity of the electro-optic medium as close as possible to the desired halftone brightness. The accuracy possible with this step is limited by the frame rate of the display device. The second part of the addressing pulse is composed of positive and negative voltage pulses of the same number in each frame. Applying an AC square wave to the encapsulated particle-based electrophoretic medium, as described above with reference to FIGS. 3 and 4, can bring the medium into a “relieved” “half-tone” state. Already shown. Thus, this second part of the pulse brings all pixels to the same uniform halftone state, regardless of the previous pulse history. Addressing out from the grayscale state to black or white is achieved with a short pulse of appropriate polarity.

  More generally, the AC portion of the pulse need not switch polarity every frame, but every other frame (frequency = frame rate / 4), or more generally every nth frame (frequency = Frame rate / 2n) Switch alternately with a lower frequency voltage.

  Accordingly, the present invention provides a method for generating a gray scale in another binary electro-optic display device using only a simple three-stage driver without using a complicated and expensive voltage modulation driver.

  Applying the above driving method principle to a second specific example, the present invention provides for collecting a two-dimensional transition matrix. Each element of the matrix is extracted from how the initial optical state (obviously, assigning the initial optical state to a row is optional, but here shown as the “row index”), and the final optical Specifies whether the target state (indicated here as “column index”) is reached. Each element of this matrix is composed of a series of waveform elements (as defined above), and generally an n-bit gray scale display device contains 2 (2N) elements of this matrix. The matrix of the present invention takes into account the need for DC balance in the drive method (as described above) and minimizes the “memory” effect in certain electro-optic media (ie, applying a particular pulse to the pixel). The resulting action depends not only on the current state of the pixel but also on the previous state), thereby generating a uniform optical state and maximizing the switching speed of the display, while also driving the active matrix It will work within the constraints of the method. The present invention also provides a method for determining the optimum value of the duration of elements in such a matrix for any particular electro-optic medium. In addition, the reader is referred to the aforementioned PCT / US02 / 37241 for a description of such matrices and their use in driving electro-optic displays.

  The presently preferred waveform of the present invention is described below for pulse width modulation (PWM) as described above. However, the same or similar results can be achieved using pulse height modulation or various combinations of the above-described AC modulation. Various other types of modulation are used in one waveform, for example, pulse width modulation is applied to all pulses except the last part of the pulse, and then voltage modulation is applied to the last part of the pulse.

  The first two waveforms of the present invention described below are "slideshow" waveforms. This is to return from a certain gradation state to a black state before addressing out to the next gradation state. Such waveforms are often compatible with updating methods of display devices that immediately turn off the entire screen, such as a slide projector.

Double Prepulse Slideshow Waveform In this waveform, a preferred form of waveform is shown in FIG. 5 of the accompanying drawings. The pixel of the electro-optic medium is first driven from black (denoted 100) to an initial (first) gray scale state using partial pulses. To change a pixel from this initial tone state to another desired (second) tone state, the pixel is first driven from the first tone state (102) to white and then white ( 104) to black. Finally, an appropriate pulse that results in the second gray scale state is applied to 106. To ensure that this type of waveform is maintained throughout the DC balance, the total amount of addressing pulse length at 106 and white pulse length at 102 must be equal to the white black pulse length at 104. is there. This waveform is required to switch between a black optical state and a white optical state up to three times the media switching time in order to transition between two arbitrary gray levels. Since it is necessary (and vice versa), it is called a triple waveform.

Single Prepulse Slideshow Waveform In this waveform, a preferred form of waveform is shown in FIG. 6 of the accompanying drawings. In the same manner as in section 6 of the double pre-pulse waveform, the pixel of the electro-optic medium is first driven from black (denoted 110) to the initial (first) tone state using partial pulses. To change the pixel from this initial tone state to another desired (second) tone state, the pixel is first driven from the first tone state (112) to black and then the second tone state. Appropriate pulses to 114 are applied to the second gray level. Obviously, the pixel returns to black again at 116, before the second transition. This type of waveform maintains DC balance across the waveform because the impulses applied at 112 and 116 are equal to the impulses applied at 110 and 114 (except for polarity), respectively. This waveform is referred to as a double waveform because it requires up to twice the media switching time to transition between two arbitrary gray levels.

Gradation vs Gradation Waveform Instead of using the slide show waveform described above, the display device is updated by directly addressing from one gradation state to another without passing through the black or white state. Since there are no obvious artifacts associated with such transitions (ie, black and / or white “flashing”), this is referred to as “tone versus tone” addressing. There are two main forms of gradation versus gradation waveforms. That is, DC balance and DC unbalance.

  In a DC balanced tone versus tone waveform, the transition between two arbitrary tone states is made by applying the exact modulation pulse length necessary to shift between the two states. The electro-optic medium does not transmit in the intermediate black state or white state. Since the maximum pulse length is the same as the ink addressing time, such a waveform is called a 1 × waveform. To maintain DC balance, there are n-1 free parameters that can be used to optimize the transition matrix associated with any particular waveform in a display device in n gray levels. This results in a system that is significantly over-constrained. For example, on the contrary, all transitions require the same and opposite impulses (ie, 2-3 is the same as 3-2 except for polarity).

The DC unbalanced gradation versus gradation waveform is basically the same as the DC balance gradation versus gradation waveform, except that the pulse length is not constrained by the DC balance limitation. Thus, each 2 ^(2N) entry in the migration matrix can be changed independently.

The above-described various waveforms enable gradation addressing in an active matrix display device, which is important when an electro-optic medium is applied to a personal digital assistant (PDA) or an electronic book. These waveforms minimize the memory effects of the electro-optic medium. Such a memory causes an image ghost. By selecting an optimal pulse length and sequence, a desired gradation optical state can be realized with a minimum number of pulses.
Selective Row Driving Another aspect of the present invention relates to improving the performance of an active matrix bistable electro-optic display by selectively driving the rows of the display.

As already mentioned and as described in more detail in the aforementioned patents and patent applications, the entire image area must be continuously refreshed to maintain the desired image on a conventional LCD. This is because the liquid crystal is typically not bistable and the image on the LCD fades in a very short time unless refreshing. As is well known to those skilled in the art of active matrix LCDs, such a display device continuously refreshes by turning on the gates of the transistors associated with one row pixel of the display device using a row driver. By applying to the column driver (connected to the source electrode of the transistor in each column of the display device) the potential necessary to write the pixels of the selected row that will be the relevant part of the desired image on the display device Write to the selected line on the display device. The row driver then selects the next row of the display device and repeats this process so that the row is refreshed periodically. (Assigning the row driver to the gate electrode and assigning the column driver to the source electrode is basically arbitrary, but can be reversed if desired.)
Since LCD requires continuous image refreshing, changing only a fraction of the displayed image is treated as part of the overall refreshing procedure. In the continuous refreshing display device, it is not necessary to prepare a portion for updating the image. Since a new image is made by writing the display device several times per second (in the case of LCD), any changes in the image portion that have disappeared on the display device are automatically transferred to the display device at short intervals. Will appear. As a result, conventional circuits developed to be used in LCDs cannot update only a portion of an image.

  In contrast, bistable electro-optic display devices do not require continuous refreshing. In fact, such continuous refreshing is not desirable because the energy consumption of the display device increases more than necessary. Also, during such refreshing, a capacitance voltage spike is applied to the pixel electrode by the gate (row) line, and some driver voltage error or an uncompensated gate-through bias error accumulates. All of these factors cause unnecessary shifts in the optical state of the pixels of the display device. Therefore, it is desirable that the bistable electro-optical display device includes a means for updating a part of the image without rewriting the entire image on the display device. One aspect of the invention relates to a bistable electro-optic display comprising such a “partially updated” means. According to the present invention, this is done by comparing successive images written to the display device, identifying different rows in the two images, and addressing only the rows thus identified.

In this method, only the rows of the display device that contain pixels that change the optical state are identified for a partial update on the display device. In a preferred form of this method, each line of the display device is examined by the display controller (see PCT / US02 / 37241 mentioned above) for all desired pixel electrode output voltages. If the output voltages on that line are all equal to the common display front electrode potential _Vcom (i.e., it is not necessary to rewrite the pixels in that row at all), then the controller outputs a _sync ( _Vsync ) pulse. It does not load data values into the column driver and does not issue a corresponding output enable (OE) command. The net effect is to pass the line driver token bit to the next line on the display without activating the current line. For rows where at least one pixel needs to be rewritten, data is loaded only into the column driver and only output enable is asserted.

There are two distinct types of advantages of the present invention. First, many power supplies of pseudo voltages for pixels that do not need to be rewritten have been removed. There are no capacitive gate spikes for these pixels, and errors in the column driver voltage are not transmitted to the unaddressed frame pixels. In many electro-optic media compared to liquid crystals, especially in electrophoretic media, the resistivity is relatively lower, so the pixel electrodes tend to relax with respect to the actual front voltage, thus maintaining the holding state of the electro-optic media. Can do. Second, the power consumption of the display device is minimized. There is no need to charge the corresponding gate line for all rows that do not need to be rewritten. Also, if the data is not loaded into the display device column driver, the extra power consumption that moves this data to the display device interface can also be eliminated.
Spatial Domain Dithering The aspects of the present invention described above relate to waveforms used in drive electro-optic display devices. However, the behavior of such a display device can also be changed by changing the structure of the backplane. This aspect of the invention relates to dividing one or more pixels of a display device, preferably each pixel, into a plurality of sub-pixels having separate regions.

  As already mentioned, it is highly desirable to form gradations with an electro-optic display device. This gray level is realized by driving the pixels of the display device to one of two extreme gray levels. However, if the media cannot achieve the desired number of intermediate states, or if the display device is driven by a driver that is not capable of forming the desired number of intermediate states, other methods may be used. It is necessary to realize the desired number of states. This aspect of the invention relates to spatial dithering for this purpose.

  The display device is divided into a plurality of “logic” pixels. Each logical pixel can display a desired number of gray levels or other optical states. However, obviously two or more physically separated areas can be displayed with logical pixels. In fact, this is common to color display devices that utilize "full color" logic pixels. Each logical pixel is composed of three sub-pixels of primary colors. For example, red, green and blue. For example, see the aforementioned 2002/0180688. Similarly, gradation can be realized by using a set of subpixels as logical pixels. Each subpixel could only perform binary switching. For example, a 2-bit gray scale could be formed using a logic pixel comprising four sub-pixels that can be controlled separately in the same region. However, in the 1-bit or 2-bit gradation, the number of subpixels is preferably large because the number of subpixels required doubles for every 1-bit increase in gradation.

  The present invention provides an electro-optic display device having at least one pixel comprising a plurality of sub-pixels. These subpixels have different areas. In a preferred embodiment of the invention, the at least two subpixels differ in area by a factor of substantially two. Thus, for example, assume that a logical pixel has subpixels in the 1 ×, 2 ×, 4 × region. X is an arbitrary area. This type of logical pixel is schematically illustrated in FIG. 7A of the accompanying drawings. This logical pixel uses only three electrodes to achieve a 3-bit gray level, but to achieve the same 3-bit gray level using subpixels in the same region requires eight subpixels.

  When driven, each subpixel reflects or transmits part of the incident light. A small amount is processed in the sub-pixel area. When reflection / transmission is averaged in the area of logical pixels, the gradation is spatially dithered by performing binary weighting of the driving area next.

  The subpixel area is arbitrary. The one shown in FIG. 7A is weighted by reflection. If the subpixel uses non-linear weighting (as appropriate for the same step in L * or the same step in gamma correction tone spacing), the region will be changed accordingly.

  Subpixel shapes need to be fully considered, and their relative areas must also be fully considered. As shown in FIG. 7A, a simple large block allows the subpixel array to be formed in a simple pattern, but under certain conditions, the subpixel may appear to be decomposed to the viewer. In addition, when displaying a wide area (over a large number of logical pixels) with an intermediate level of gradation (for example, only the area 4 in FIG. 7A is driven by each logical pixel), the viewer is Lines and grid patterns due to the pattern can be seen.

  Increasing the resolution of logical pixels reduces these problems, but requires a larger number of pixels. However, the number of pixels increases with the square of the resolution. Instead, subpixel visibility and / or visible pattern problems can be reduced by fitting the subpixels, for example, as shown in FIG. 7B. Note that this figure is for illustration only and does not accurately represent the relative area of the subpixels. The image quality can be improved using many fitting patterns similar to FIG. 7B.

  Another approach to deal with subpixel visibility and / or visible pattern issues is to orient the subpixels randomly. For example, in the pixel array having the sub-pixel configuration shown in FIG. 7A, the orientation of the configuration shown in FIG. 7A can be randomly selected for each pixel. By “randomizing” the sub-pixels in this way, the pattern is decomposed so that it is not unsightly for the viewer.

  In the embodiment of the present invention shown in FIGS. 7A and 7B, a 3-bit gradation is generated. However, it is understood that a gradation having an arbitrary number of bits can be generated in the present invention by adding more subpixels. Will.

  The advantages in this aspect of the invention are as follows.

  (A) The electro-optic medium itself does not need to realize gradation. Basically, the display device can be a black / white display device, and the sub-pixels are turned on and off to generate gradation. The scanned array can be implemented as a color subpixel array by further controlling the subpixels as needed and further providing column drivers for the same number of rows. This reduces the demand for the electro-optic medium to be used. For example, there is no need to worry about the possibility that the gradation of the medium will shift due to the operating life time.

  (B) No need for complex column drivers. The present invention can be easily interchanged using binary level drivers often used in conventional display devices. Therefore, various general-purpose electro-optic media and inexpensive “general-purpose components” can be easily used. Some methods for generating gradations require a voltage modulation driver for the column electrode. Such drivers are not widely marketed and are more expensive / harder to configure than binary level drivers.

(C) Thin film transistors (TFTs) designed for the active matrix array used in the present invention are not at all difficult than those required for full color. There are three subpixels (eg, RGB) per pixel, and the amount of data that must be supplied to the various components is small. Therefore, an active matrix backplane can be realized with the present invention without requiring any new technology development.
Various Technologies In many of the conventional active matrix driving methods of electro-optic display devices, a desired voltage is applied to the pixels by sequentially changing the voltage of the pixel electrodes on the backplane of the display device. The top surface is typically held at a specific voltage that may be advantageous for addressing the pixels. For example, when changing between zero volts and the voltage V ₀ of the voltage of the data line is supplied to the pixel electrode, to hold the top in V _0/2, V sequentially in both directions by lowering the voltage across the pixels ₀ / The size is 2.

According to one aspect of the present invention, it is possible to improve the addressing of the electro-optic medium by changing the voltage of the upper surface. For example, the upper surface voltage may be maintained at zero volts, and all pixel voltages may be decreased in order (upper surface minus pixel voltage), and may be reduced to −V ₀ . It is also possible to raise the top surface to V ₀ and reduce the pixel voltage to V ₀ . These large voltage drops can make the electro-optic medium addressing faster.

More generally, there is an advantage that the upper surface voltage can be set not only to zero voltage or V ₀ but also to other voltages. For example, there is the advantage of applying a full-time variable voltage to the electro-optic medium, consistent with the pixel-to-pixel voltage applied by the backplane.

  It is also well known that an electro-optical display device includes a capacitor between an electrode formed by extending a selection line so as to apply the same voltage as the selection line and a pixel electrode. As described in the above-mentioned International Publication No. WO 01/07961, by providing such a capacitor, the speed at which the electric field of the corresponding pixel is attenuated after the drive voltage is removed is reduced. In another aspect, the present invention provides an electro-optical display device having a storage capacitor formed between a (second) electrode having a variable voltage separately from a selection line of the display device and a pixel electrode. In a preferred embodiment, the second electrode tracks the top voltage. That is, the voltage differs from the top by a time dependent constant. By providing this type of capacitor, the capacitance voltage received by the pixel compared to the storage capacitor formed by overlapping between the select line that controls the adjacent (previous) row of the display device and the pixel electrode Significantly reduce spikes.

  Another aspect of the present invention relates to reducing or eliminating unnecessary switching of electro-optic media due to selection lines and data lines.

  As described above, the selection line and the data line are indispensable elements in the active matrix panel in that a voltage necessary for applying the pixel electrode to a desired value is supplied. However, the selection line and the data line have an unnecessary effect of switching the electro-optic medium adjacent to the data line. Unnecessary optical artifacts resulting from such switching can be removed by hiding the areas switched by the data lines and / or selection lines from the viewer using a black mask. However, providing such a black mask requires that the front surface of the display device be positioned with the backplane, reducing the portion of the electro-optic medium that is directed to the viewer. As a result, the display device becomes darker and the contrast becomes lower than the display device without the black mask.

  In another aspect of the present invention, during normal display device operation, the need for a black mask is achieved by extending the data lines in one direction small and laterally so as not to noticeably address adjacent electro-optic media. Avoid sex. This eliminates the need for a black mask.

  The aspect related to the present invention relates to the use of the passivation electrode and the change of the driving method used for driving the electro-optic medium. An impulse-driven electro-optic medium can be electronically addressed if it takes the form of a thin film between two electrodes. In general, the electrode is in contact with the electro-optic medium. However, if a dielectric material with a long electron relaxation time is present between one or two electrodes and the medium, the medium can be addressed. Passivation of one or two electrodes is desirable to avoid adversely affecting the backplane or front surface of the display device due to chemical or electrochemical interactions. See International Publication No. WO 00/38001 mentioned above. The presence of the dielectric layer greatly reduces the ability to maintain the voltage across the electro-optic medium, but if the voltage impulse can still be applied to the medium and the dielectric layer operates properly, these voltage impulses can be reduced. Through which the medium can be addressed.

  Of course, the optical state of the electro-optic medium is realized by changing the voltage of the pixel electrode. Due to this voltage change, the voltage applied to the electro-optic medium is attenuated as the charge leaks through the medium. If the outer dielectric layer (ie, the dielectric layer between the medium and one electrode) is thin enough and the electro-optic medium is sufficiently resistive, the voltage impulse applied to the medium will cause the medium to optical state. A sufficient desired shift will be generated. It is therefore possible to electronically address the electro-optic medium via the dielectric layer. However, the addressing method is different from addressing an electro-optic medium with an electrode in direct contact with the medium. In the latter case, the medium is addressed by applying a voltage to the pixel. However, in the former case, the addressing is realized by changing the pixel voltage. Each time it changes, a voltage impulse is applied to the electro-optic medium.

  Finally, the present invention provides a driving method for reducing crosstalk of an active matrix electro-optic display device.

  Inter-pixel crosstalk, which affects the optical state of other pixels by addressing one pixel, is unnecessary, but there are various causes. One of the causes is a finite current flowing through the off-state transistor. When a voltage for charging one pixel is applied to the data line, a transistor in an unselected row is charged due to current leakage in an off state. This is solved by using a low off-state current for the transistor.

  Another cause of crosstalk is current leakage between adjacent pixels. Current leaks through the elements of the backplane or through the electro-optic medium in contact with the backplane. In order to eliminate such crosstalk, the backplane is designed to have a large insulating gap between the pixel electrodes. The larger the gap, the smaller the leakage current.

  As already indicated, the preferred type of electro-optic medium used in the present invention is a sealed particle-based electrophoretic medium. Such electrophoretic media used in the method and apparatus of the present invention may use the same components and manufacturing techniques as described in the aforementioned E-ink and MIT patents and patent applications. Readers should refer to these for further information.

  Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, which are for illustrative purposes only.

Claims (1)

The invention described herein.

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