HK1180099B - Electro-optic display, display module driver device and display assembly - Google Patents

Description

Electro-optic display, display module driver device and display assembly

The present application is a divisional application of patent divisional applications with an application date of 2004, 26/11, and an application number of 201110104145.2 entitled "electro-optic display and driving method".

Technical Field

The present invention relates to electro-optic displays and methods of driving such displays. More particularly, the invention relates to large area electro-optic displays, drivers for such large area displays, and driving schemes and controllers aimed at reducing power consumption in active matrix electro-optic displays. The invention has particular, but not exclusive, application in electrophoretic displays.

Background

An electro-optic display comprises a layer of electro-optic material, the term "electro-optic material" being used herein in its conventional sense in the imaging art to mean a material comprising at least first and second display states differing in optical properties which can be changed from the first to the second display state by application of an electric field to the material. Although the human eye is generally able to perceive this optical property in color, this optical property may be another optical property, such as optical transmittance, reflectance, luminescence, or (in the case of a display for machine reading) a false color in the sense that the reflectance of electromagnetic waves outside the visible range changes.

In the displays of the invention, the electro-optic medium is typically solid in the sense that it has a solid exterior surface (hereinafter such displays will be referred to as "solid electro-optic displays" for convenience), although such media may have, and typically do have, an internal liquid or gas-filled space. Thus, the term "solid electro-optic display" includes encapsulated electrophoretic displays, encapsulated liquid crystal displays, and other types of displays described below.

The term "grey state" is used herein, which is conventionally meant in the imaging art to refer to a state between the two extreme optical states of a pixel, but does not necessarily imply a black-and-white transition between the two extreme states. For example, the patents and published applications referenced below describe electrophoretic displays in which the extreme states are white and deep blue, so that the intermediate "grey state" is effectively pale blue. In fact, as already described, it is possible that the transition between the two extreme states is not a color change at all.

The terms "bistable" and "bistability" are used herein and are conventionally used in the imaging arts to refer to displays comprising display elements having first and second display states differing in at least one optical property such that, after any particular element has been driven by an addressing pulse of finite duration to assume either its first or second display state, that state will persist for a time at least several times, for example at least four times, the minimum duration of the addressing pulse required to change the state of the display element after the addressing pulse has terminated. Published U.S. patent application No.2002/0180687 shows that some particle-based electrophoretic displays capable of displaying gray scale can be stabilized not only in their extreme black and white states, but also in their intermediate gray states, as can some other types of electro-optic displays. This type of display may be referred to as being "multi-stable" rather than bi-stable, although for convenience the term "bi-stable" is used herein to cover both bi-and multi-stable displays.

The term "pulse" is used herein, which is conventionally meant in the imaging art to refer to the integral of voltage over time. However, some bistable electro-optic media act as charge converters, so an alternative definition of pulses, i.e. the integral of current over time (equal to the total charge applied), can be employed for these media. The proper definition of pulses should be used depending on whether the medium is used as a voltage-to-time pulse converter or as a charge pulse converter.

Several types of electro-optic displays are known. One type of electro-optic display is a rotating two-color component of the type described in, for example, U.S. patent nos. 5808783, 5777782, 5760761, 6054071, 6055091, 6097531, 6128124, 6137467, and 6147791 (although this type of display is often referred to as a "rotating two-color ball display", the more definite term "rotating two-color component" is preferably used because the rotating component is not spherical in some of the above-mentioned patents). Such displays use many small bodies (typically spherical or cylindrical) having two or more portions with different optical properties and an internal dipole. The small objects are suspended in a liquid-filled vacuole in the matrix, which vacuole is filled with liquid so that the small objects can rotate freely. The appearance of the display is changed by applying an electric field to the display, thereby rotating the small object to various positions and changing the portion of the small object that is visible through the viewing surface. This type of electro-optic medium is generally bistable.

Another type of electro-optic display uses an electrochromic medium, such as in the form of a nano-chromic film that includes an electrode made at least in part of a semiconductive metal oxide and a plurality of dye molecules capable of reversible color change bonded to the electrode; for example, reference may be made to O' Regan, b.et al, Nature1991, 353, 737 and Wood, d., information display, 18(3), 24(March 2002). Reference may also be made to Bach, u., et al, adv. Nanochromic films of this type are also described, for example, in U.S. Pat. No.6301038, International patent application No. WO01/27690, and U.S. Pat. application 2003/0214695. This type of media is also generally bistable.

Another electro-optic display that has been the subject of extensive research and development for many years is a particle-based electrophoretic display in which a plurality of charged particles move through a suspension under the influence of an electric field. Electrophoretic displays have the advantages of good brightness and contrast, wide viewing angles, bistability of states, and low power consumption compared to liquid crystal displays. However, problems associated with long-term image quality of these displays have prevented their widespread use. For example, the particles that make up electrophoretic displays tend to settle, resulting in insufficient lifetime of these displays.

As previously mentioned, electrophoretic media require the presence of a suspension. In most prior art electrophoretic media, the suspension is a liquid, but gaseous suspensions can be used to make the electrophoretic media; for example, refer to Kitamura, T.et., "Electrical analysis for electronic paper-like display", IDWJapan, 2001, paperHCS1-1 and Yamaguchi, Y.et., "Tonerdisplayinginsulating scientific storage battery", IDWJapan, 2001, paperAMD 4-4). Reference may also be made to European patent applications 1429178, 1462847, 1482354, and 1484625, and international applications WO2004/090626, WO2004/079442, WO2004/077140, WO2004/059379, WO2004/055586, WO2004/008239, WO2004/006006, WO2004/001498, WO03/091799, and WO 03/088495. Such gas-based electrophoretic media appear to suffer from the same types of problems as liquid-based electrophoretic media when the media is used in an orientation that allows such precipitation, for example for the case of placing the media in a vertical plane, due to particle precipitation. In fact, particle settling in gas-based electrophoretic media appears to be more severe than in liquid-based electrophoretic media, because the lower viscosity of gas suspensions, compared to liquid suspensions, causes the electrophoretic particles to settle more quickly.

A number of patents and applications describing encapsulated electrophoretic media have recently been published, which were assigned to or filed in the name of the Massachusetts Institute of Technology (MIT) and EInk companies. Such an encapsulation medium comprises a plurality of small capsules, each of which itself comprises an internal phase containing electrophoretically mobile particles suspended in a liquid suspending medium, and a capsule surrounding the internal phase. Typically, the capsule itself is held within a polymeric binder, thereby forming a coherent layer disposed between two electrodes. Encapsulated media of this type are described, for example, in the following patents and applications: U.S. patent nos. 5930026, 5961804, 6017584, 6067185, 6118426, 6120588, 6120839, 6124851, 6130773, 6130774, 6172798, 6177921, 6232950, 6249721, 6252564, 6262706, 6262833, 6300932, 6312304, 6377387, 6312304, 2003/0214697, 2003/0222315, 2004/0008398, 2004/0012839, 2004/0014265, 2004/0027327, 2004/0075634, 2004/0094422, 2004/0105036, 2004/0112750, and 2004/0119681, and international application publication nos. wo99/67678, WO00/05704, WO00/38000, WO00/38001, WO00/36560, WO00/67110, WO00/67327, WO01/07961, WO01/08241, WO03/107315, WO2004/023195, WO2004/049045, WO2004/059378, WO2004/088002, WO2004/088395, and WO 2004/090857.

Many of the foregoing patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced with a continuous phase, resulting in a so-called polymer dispersed electrophoretic display, wherein the electrophoretic medium comprises a plurality of discrete droplets of an electrophoretic liquid and a continuous phase of a polymeric material; it is also appreciated that the discrete droplets of electrophoretic liquid in such polymer dispersed electrophoretic displays may be considered as capsules or microcapsules, although a discrete capsule film is not associated with each droplet, see for example the aforementioned patent application 2002/0131147. Thus, from the perspective of the present application, such polymer dispersed electrophoretic media are considered to be a subspecies of encapsulated electrophoretic media.

A related type of electrophoretic display is the so-called "microcell electrophoretic display". In microcell electrophoretic displays, the charged particles and the suspending liquid are not encapsulated within microcapsules, but are held within a plurality of cavities formed within a carrier medium (typically a polymer film). See, for example, International application publication No. WO02/01281 and published U.S. patent application No.2002/0075556, both assigned to Sipiximaging, Inc.

Many of the aforementioned EInk and MIT patents and applications also contemplate microcell electrophoretic displays and polymer dispersed electrophoretic displays. The term "encapsulated electrophoretic display" may refer to all of these display types, which may also be collectively described as a "microcavity electrophoretic display" to summarize the wall topography.

Another type of electro-optic display is the electrowetting display developed by Philips under the title "PerformingPixels" in the period 9, 25/9 of Nature journal 2003: movingimagesonelectronic paper "is described. It is shown in pending U.S. application No.10/711802 (see also the corresponding international application PCT/US2004/32828) filed on 6.10.2004 that such electrowetting displays can be made bistable.

Other types of electro-optic materials may also be used in the present invention. Of particular interest, bistable ferroelectric liquid crystal displays (FLCs) are known in the art.

Although electrophoretic media are often opaque (because, for example, in many electrophoretic media, the particles substantially block transmission of visible light through the display) and operate in a reflective mode, many electrophoretic displays can be made to operate in a so-called "shutter mode," in which one display state is substantially opaque and one display state is light-transmissive. See, for example, the aforementioned U.S. patent nos. 6130774 and 6172798 and U.S. patent nos. 5872552, 6144361, 6271823, 6225971, and 6184856. Dielectrophoretic displays are similar to electrophoretic displays but rely on a change in the strength of the electric field and can operate in a similar fashion, see U.S. patent No. 4418346. Other types of electro-optic displays may also operate in a shutter mode.

Encapsulated or microcell electrophoretic displays generally do not suffer from the clustering and settling failure modes of conventional electrophoretic devices and may provide additional advantages such as the ability to print or coat the display on many flexible and rigid substrates. (the use of the word "printing" is intended to include all forms of printing and coating including, but not limited to, premeasured coating such as spot die coating, slot or extrusion coating, slide or cascade coating, roll coating such as roll-on-blade coating, forward and reverse roll coating, gravure coating, dip coating, spray coating, meniscus coating, spin coating, brush coating, air knife coating, screen printing processes, xerographic processes, thermal printing processes, ink jet printing processes, electrophoretic deposition, and other similar techniques). Thus, the resulting display may be flexible. Furthermore, since the display media can be printed (using various methods), the display itself is inexpensive to manufacture.

The bistable or multistable behaviour of particle-based electrophoretic displays, and other electro-optic displays exhibiting similar behaviour (such displays are hereinafter referred to for convenience as "impulse-driven displays"), is in marked contrast to that of conventional Liquid Crystal (LC) displays. Twisted nematic liquid crystals are not bistable or multistable but act as voltage converters such that the application of a particular electric field to a pixel of such a display produces a particular grey level at that pixel which is independent of the previous grey level at the pixel. Furthermore, LC displays are driven in only one direction (transition from non-transmissive or "dark" to transmissive or "bright"), and the reverse transition from the lighter state to the darker state can be achieved by reducing or eliminating the electric field. Finally, the grey levels of the pixels on an LC display are not sensitive to the polarity of the electric field but only to their intensity, and indeed for technical reasons commercial LC displays usually reverse the polarity of the driving electric field at frequent intervals. In contrast, bistable electro-optic displays act, to a first approximation, as pulse translators, so that the final state of a pixel depends not only on the applied electric field and the time for which it is applied, but also on the state of the pixel before the application of the electric field.

Also, to achieve a high resolution display, individual pixels of the display must be addressable without interference from adjacent pixels. One way of achieving this goal is to provide an array of non-linear elements, such as transistors or diodes, at least one of which is associated with each pixel, thereby creating an "active matrix" display. The addressing electrode or pixel electrode addressing a pixel is connected to a suitable voltage source via an associated non-linear element. In general, when the non-linear element is a transistor, the pixel electrode is connected to a drain of the transistor, and this arrangement will be adopted hereinafter, the connection being substantially arbitrary and the pixel electrode being connectable to a source of the transistor. Traditionally, in high resolution arrays, pixels are arranged in a two-dimensional array of rows and columns, such that any particular pixel is uniquely defined by the intersection of one particular row with one particular column. The sources of all transistors in each column are connected to a single column electrode, while the gates of all transistors in each row are connected to a single row electrode; also, it is conventional to assign the sources to rows and the gates to columns, but this assignment is essentially arbitrary and the reverse can be made if desired. The row electrodes are connected to a row driver which essentially ensures that only one row is selected at any particular time, i.e. a voltage is applied to the selected row electrodes to ensure that all transistors in the selected row are conductive, and to all other rows to ensure that all transistors in these non-selected rows remain non-conductive. The column electrodes are connected to a column driver which applies selected voltages to the various column electrodes to drive the pixels in the selected row to their desired optical states. (the foregoing voltages are relative to a common front electrode, which is conventionally provided on the side of the electro-optic medium opposite the non-linear array, and extends across the display.) after a preselected selected interval (known as the "line addressing time"), the selected row is deselected, the next row is selected, and the voltage on the column driver is changed to the voltage that writes the next line of the display. This process is repeated so that the entire display is written in a row-by-row fashion.

In addition to the layer of electro-optic material, an electro-optic display typically includes at least two other layers, one of which is an electrode layer, disposed on opposite sides of the electro-optic material. In most such displays, both layers are electrode layers, with one or both electrode layers being patterned to define the pixels of the display. For example, one electrode layer may be patterned into elongate row electrodes, and the other patterned into column electrodes at right angles to the row electrodes, with pixels being defined by the intersections of the row and column electrodes. Alternatively and more generally, one electrode layer is in the form of a single continuous electrode and the other electrode layer is patterned into a matrix of pixel electrodes, each pixel electrode defining a pixel of the display. In another type of electro-optic display (intended for a stylus printhead or similar movable electrode separate from the display), only one layer adjacent the electro-optic layer comprises an electrode, the layer on the opposite side of the electro-optic layer typically being a protective layer for preventing damage to the electro-optic layer from the movable electrode.

Whether or not the electro-optic medium used is bistable, in order to achieve a high resolution display, individual pixels of the display must be addressable without interference from adjacent pixels. One way of achieving this goal is to provide an array of non-linear elements, such as transistors or diodes, at least one of which is associated with each pixel, thereby creating an "active matrix" display. The addressing electrode or pixel electrode addressing a pixel is connected to a suitable voltage source via an associated non-linear element. In general, when the non-linear element is a transistor, a pixel electrode is connected to a drain of the transistor, and this arrangement will be adopted hereinafter, the connection being substantially arbitrary, and the pixel electrode may be connected to a source of the transistor. Traditionally, in high resolution arrays, pixels are arranged in a two-dimensional array of rows and columns, such that any particular pixel is uniquely defined by the intersection of one particular row with one particular column. The sources of all transistors in each column are connected to a single column electrode, while the gates of all transistors in each row are connected to a single row electrode; also, it is conventional to assign the sources to rows and the gates to columns, but this assignment is essentially arbitrary and the reverse can be made if desired. The row electrodes are connected to a row driver which essentially ensures that only one row is selected at any particular time, i.e. a voltage is applied to the selected row electrodes to ensure that all transistors in the selected row are conductive, and to all other rows to ensure that all transistors in these non-selected rows remain non-conductive. The column electrodes are connected to a column driver which applies selected voltages to the various column electrodes to drive the pixels in the selected row to their desired optical states. (the foregoing voltages are relative to a common front electrode, which is conventionally provided on the side of the electro-optic medium opposite the non-linear array, and extends across the display.) after a preselected selected interval (known as the "line addressing time"), the selected row is deselected, the next row is selected, and the voltage on the column driver is changed to the voltage that writes the next line of the display. This process is repeated so that the entire display is written in a row-by-row fashion.

As previously mentioned, and as previously mentioned at 2003/0137521, pending application serial number 10/814205 filed on 3.31.2004, and pending application serial number 10/879335 filed on 29.6.2004 (see also corresponding international applications WO2004/090857 and PCT/US2004/21000, respectively), bistable electro-optic displays act as pulse converters in a first approximation such that the final state of a pixel depends not only on the applied electric field and the time at which it is applied, but also on the state of the pixel before the application of the electric field. Furthermore, it has now been found that, at least inIn the case of many particle-based electro-optic displays, the pulse required to change a particular pixel by an equivalent change in gray level (as judged by the eye or standard optical instrumentation) need not remain constant, nor need the pulse be switchable. For example, consider a display in which each pixel can display a 0 (white), 1, 2, or 3 (black) gray level, the gray levels are preferably separated. (the spacing between levels may be a linear relationship of percent reflectivity, which may be measured by eye or instrument, although other spacings may be used^*Linear change (wherein L^*With the general CIE definition:

L^*＝116(R/R₀)^1/3-16

wherein R is the reflectance, R₀Standard reflectance values) or the interval is selected to provide a particular gamma; monitors typically employ a gamma of 2.2, and when the display of the present invention is used as a substitute for a monitor, a similar gamma is desirably used. ) It has been found that the pulses required to change a pixel from level 0 to level 1 (hereinafter for convenience referred to as a "0-1 transition") are often different from the pulses required for a 1-2 or 2-3 transition. Furthermore, the pulses required for a 1-0 transition need not be the same as the pulses required for a reverse 0-1 transition. Furthermore, some systems appear to exhibit a "memory" effect, such that the pulses required for, for example, a 0-1 transition vary slightly depending on whether a particular pixel undergoes a 0-0-1, 1-0-1, or 3-0-1 transition (where "x-y-z" is labeled, where x, y, z are all optical states and 0, 1, 2, 3 represent a chronological order of the optical states listed from front to back). Although these problems can be reduced or overcome by driving all pixels of the display to one extreme state and holding for a long time before driving the desired pixels to the other state, the resulting "sparkle" of a single color is generally unacceptable; for example, readers of electronic books require the text of the book to scroll down on the screen, and the readers may be distracted or lose interest if the display needs to frequently blink pure black or white. Furthermore, such sparkling of the display increases power consumption, possibly reducing the displayThe working life of the display. Finally, it has been found that, at least in some cases, the pulses required for a particular transition are affected by the temperature and overall operating time of the display, and by the time a particular pixel remains in a particular optical state before a given transition; it has also been found that these factors need to be compensated for in order to ensure accurate reproduction of the grey levels. Therefore, methods of controlling and applying well-defined pulses to electro-optic media are needed to produce good image reproduction in electro-optic displays.

Charging and discharging of the column electrodes is a significant source of power consumption when an active matrix electro-optic display is being rewritten (i.e. when a new image is placed on the display or an image is being refreshed). (the charging and discharging of the row electrodes also consumes some power, but the power consumption of the row electrodes is very small, since any particular row electrode is charged and discharged only once during the period in which the entire display is written, while the column electrodes are charged and discharged each time a new row of the display is rewritten, typically several hundred rows for active matrix displays.) this is the most severe case of column electrode power consumption when the stripes or grid in the displayed image are inverted; in this case, each column line transitions through the entire voltage range (i.e., to support a white to black or black to white pixel optical state change) when writing each row of the display. In this case, the capacitive power used to charge and discharge the column electrodes is:

P＝1/2fCV²(A)

where P is the power consumed by the display when scanning, C is the combined capacitance of all the column electrodes being converted, V is the full "swing voltage" (i.e. the full voltage operating range) of the column driver, and f is the effective frequency of the waveform seen at the column electrodes.

In displays that use relatively high voltages (e.g., some electro-optic displays), a large portion of the display power consumption comes from this. In one aspect the present invention seeks to provide a method of driving an active matrix electro-optic display which reduces power consumption due to column electrode transitions. The invention also provides a modified drive for carrying out this method; these drivers may be designed to reduce average and peak power consumption.

It has been mentioned above that a second aspect of the invention relates to a large area electro-optic display, and a driver for such a large area display. In particular, this aspect of the invention relates to a display driver having integrated controller logic for driving such large area electro-optic displays.

Typically, electronic (including electro-optic) displays are rigid devices that include components mounted to a rigid support structure. To fabricate large area displays, multiple rigid display subsystems are combined by adhering the subsystems to a rigid frame. Such large area displays are heavy and expensive, and upgrading to larger sizes is significantly limited. The present invention aims to provide a flexible large area electro-optic display that can be manufactured using relatively inexpensive materials and using sub-components of a low cost process including printing and lamination steps.

Thus, large area signs (signs) may be made that include electro-optic displays that have many advantages over similar conventional displays. These advantages include light weight, lower power consumption, visibility under various lighting conditions, upgrades, and improved large area manufacturing capability. The sign is substantially maintenance-free and waterproof and can be used both indoors and outdoors. Large area signs using electro-optic displays are therefore particularly desirable in a wide range of commercial and non-commercial applications.

One challenge in constructing such large area signs, however, is the design of the drive electronics. As explained previously, the driving requirements of the electro-optic medium typically employ known drivers designed to drive liquid crystal displays, which are not suitable for driving bistable electro-optic displays without customized modification.

Circuit drivers specifically designed for driving electro-optic displays are described in the aforementioned 2003/0317521, WO2004/090857, and PCT/US 2004/21000. However, these drivers are optimized for driving the data lines of an active matrix display and therefore do not include external logic, provided with shift registers that do not cascade the drivers one by one. This means that in large area or long signs using such drivers, the controller must load two bits per display pixel for each pixel in a particular row sequentially before the display can be updated. Such data loading takes a significant amount of time. Also, since data is typically transmitted at a relatively high frequency, the data path may be too fragile, possibly resulting in data corruption.

Disclosure of Invention

The present invention aims to provide a driver that addresses these disadvantages of known drivers for large area signs including electro-optic displays. In particular, the present invention aims to provide a driver which can enable character data to be transferred to a large number of display drivers with a relatively low bandwidth, thereby reducing power consumption and reducing the likelihood of data corruption. The present invention is also directed to reducing the amount of electromagnetic interference from the display by using a low voltage data interface and providing a driver that is compatible with existing character display modules, thereby allowing the display to include a non-uniform mix of display drivers on the same sign. Finally, the present invention aims to provide improved integration between controller functionality and the electro-optic medium, each display module thus actually having its own controller, thereby allowing each module to be replaced with a newer module, possibly having significantly different properties, without affecting the operation of the rest of the sign elements.

In one aspect, the invention provides a method of driving an electro-optic display comprising an electro-optic medium, a pixel electrode capable of applying an electric field to the electro-optic medium, and a column electrode associated with the pixel electrode, the method comprising changing the voltage on the column electrode from a first value to a second value different from the first value, thereby causing the pixel electrode to cause a change in the optical state of the electro-optic medium, wherein the voltage on the column electrode is first changed from the first value to a third value (between the first and second values) and held for a time sufficient to allow charge to flow from or to the column electrode, and thereafter the voltage on the column electrode is changed from the third voltage to the second voltage.

For convenience, this aspect of the invention will be referred to hereinafter as the "two-step voltage modification method" ("TSVCM") of the invention, although it will be appreciated that this method is not limited to the use of only two steps, and that more than two steps may be employed in practice by employing more than one intermediate voltage between the first and second voltages.

In the two-step voltage changing method of the present invention, the first and second voltages may be opposite polarities, and the third voltage may be a ground voltage. The third voltage may be substantially equal to an arithmetic average of the first and second voltages. When the display comprises a front electrode disposed on the electro-optical medium on the side opposite the pixel electrodes (as is typically the case for active matrix displays), the front electrode is maintained at a substantially constant voltage and the third voltage may be equal to, or at least substantially equal to, the voltage on the front electrode. Also, when the display comprises a column driver connected to the column electrodes and arranged to apply the first, second and third voltages to the column electrodes, and comprises voltage providing means arranged to provide at least two voltages to the column driver (as is often the case in practice), the TSVCM may be implemented such that charges flowing from or to the column electrodes do not flow through the voltage providing means when the voltage on the common electrode is set to the third value.

As is well known to those skilled in the art of electro-optic displays, such displays typically use a column driver connected to column electrodes having "allow output" ("OE") inputs in an ON and OFF state, such that when the OE input is in the ON state, the column driver can apply at least three different voltages to the column electrodes, but when the OE input is in the OFF state, the column driver applies only a single voltage (typically the voltage of a common front electrode) to the column electrodes. When the TSVCM of the present invention is used in such a display, the method can be implemented by: the third voltage is applied to the column electrodes by the column driver by setting the OE input to an OFF state, and the second voltage is applied to the column electrodes by the column driver by setting the OE input to an ON state. Also, as will be discussed in more detail below, TSVCM ideally includes the step of comparing the initial state and the expected final state of the column electrodes, with the OE input being set to the OFF state only if the two states of the column electrodes are different. More particularly, if the electro-optic display is of a conventional type comprising a plurality of column electrodes and a plurality of pixel electrodes, such that each pixel electrode is connected to a column electrode, in TSVCM, when an image on the display is being rewritten, an initial voltage on each column electrode during a step of the rewriting process is compared to a final voltage on the column electrode during a subsequent step of the rewriting process, and the third voltage is applied to the column electrode only when the initial voltage and the final voltage are different.

TSVCM is applicable to any type of electro-optic display, including, for example, the so-called "direct drive" displays of the aforementioned EInk and MIT patents and applications, in which a separate conductive path is provided for each pixel electrode (the "column electrode") through which the voltage on the pixel electrode can be controlled. TSVCM can also be used for passive matrix addressed displays. However, TSVCM is particularly useful for active matrix displays that include a two-dimensional array of pixel electrodes on one side of an electro-optic medium and a common electrode on the opposite side of the electro-optic medium, a plurality of column electrodes connected to columns of the two-dimensional array of pixel electrodes and a plurality of row electrodes connected to rows of the two-dimensional array of pixel electrodes such that each pixel electrode is uniquely defined by the intersection of a particular column electrode and a particular row electrode.

The TSVCM may be used with any type of electro-optic medium, including any of the electro-optic media described previously. Thus, for example, the electro-optic medium may be a rotating bichromal member or an electrochromic medium, or a particle-based electrophoretic medium comprising a suspension and a plurality of charged particles held in the suspension and capable of moving therein upon application of an electric field to the suspension. The suspension may be a liquid or a gas. The electrophoretic medium may be an encapsulated medium having a continuous phase that separates the suspension and charged particles into a plurality of discrete droplets (it may be better to refer to "voids" when the suspension is a gas).

The invention also provides an apparatus for use in the two-step voltage control method of the invention. Accordingly, the present invention provides apparatus for driving an electro-optic display comprising an electro-optic medium, pixel electrodes capable of applying an electric field, and column electrodes associated with the pixel electrodes, the apparatus comprising:

a column driver capable of applying at least first, second and third voltages to the column electrodes, the first and second voltages being different from each other, the third voltage being between the first and second voltages; and

logic means arranged to determine when a change in voltage applied to a column electrode from a first voltage to a second voltage is required, and when it is detected that such a change is required, to cause the column driver to first apply a third voltage to the column electrode and hold it for a time sufficient to allow charge to flow from or to the column electrode, and thereafter to cause the column driver to apply the second voltage to the column electrode.

In another aspect, the present invention provides an electro-optic display system that includes a flexible substrate and a plurality of flexible electro-optic display cells adhered to the flexible substrate.

For convenience, this aspect of the invention will be referred to hereinafter as the "flexible large area display" ("FLAD") of the invention, where this aspect is primarily, but not exclusively, for large area displays. The flexible large area display may further comprise an adhesive layer securing the plurality of display units to the flexible substrate. Typically, the flexible substrate is light transmissive (substantially transparent, although the presence of certain colors is not excluded, e.g. for color correction or anti-reflection or anti-glare purposes of the display). The display unit may be used in any known display medium, including electro-optic media of the various types described previously, liquid crystal media (including polymer dispersed and plastic based liquid crystal media), electroluminescent media, and organic light emitting diodes. The flexible substrate may be provided with any known optical filter or surface treatment properties; for example, the flexible substrate may have ultraviolet filtering properties or an anti-glare surface treatment.

In the FLAD of the present invention, the display unit will typically be oriented for viewing through the flexible substrate. The FLAD may be provided with a mask adjacent the substrate that effectively conceals the inactive portion of the display cell. The color of the mask substantially matches the color of the display cell or one of its colors. When an adhesive layer is present, the layer is typically substantially transparent. The adhesion layer may comprise, for example, at least one of the following materials: vinyl acetate, polyvinyl butyrate, thermoset materials, thermoplastic materials, and radiation curable materials. The adhesive layer may be in the form of a thin layer, or comprise a liquid.

The FLAD may also include a protective film and a second adhesive layer between the protective film and the flexible substrate. The protective layer may be thermoformed and/or comprise a thin layer of substantially transparent plastic. The flexible substrate may comprise at least one of the following materials: polyesters, acrylics, polycarbonates, polycarbonate-PVF composites, and transparent fluoropolymers. The FLAD may include a mounting block embedded within the adhesive layer (when present). In the FLAD, the display units may overlap at their edges.

The invention also provides a process for manufacturing an electro-optic display system that includes providing a flexible substrate, providing a plurality of flexible electro-optic display units, and adhering the plurality of flexible electro-optic display units to the flexible substrate.

In the "FLAD process", the display unit is typically adhered to the flexible substrate by lamination. The lamination may be a vacuum lamination, which may be performed by heating. The stack may also be a roll stack. The stacking may be performed using a hot melt adhesive, wherein the adhesive comprises at least one of: vinyl acetate, polyamide, polyurethane; and/or the lamination may be achieved by applying a liquid adhesive comprising at least one of silicone, epoxy, and polyurethane.

In another aspect, the present invention provides a display module driver arrangement for controlling an image to be displayed on a display module, the display module comprising a plurality of pixels, each pixel having a pixel electrode associated therewith, the driver arrangement comprising:

an input means for receiving data representing initial and final images to be displayed;

a transformation tool for transforming the data received by the input tool into a pixel-wise representation of the initial and final images;

storage means for storing a representation of the pixel-wise pattern of the initial and final images;

a plurality of output means arranged to control the voltage to be applied to the pixel electrodes of the display; and

logic means arranged to receive data from the storage means and to generate a required output from the data on the plurality of output means.

In such a display module driver arrangement ("DMDD") of the invention, the logic means may be arranged to change the output within the output means in dependence on at least one of the following parameters: an environmental parameter, a parameter indicative of an operational lifetime of the display module, and a parameter indicative of an electro-optic characteristic of the display module.

The DMDD is primarily intended for use in electro-optic displays comprising any of the types of electro-optic media described above. The DMDD is particularly suitable for use in displays of the aforementioned direct drive type, in which the display is divided into a series of pixels, each provided with a separate electrode, the display further comprising switching means for independently controlling the voltage applied to each separate electrode. The DMDD can also be used in large area direct drive matrix displays where the overall cost of providing driver connections for each pixel is relatively low compared to other costs such as the cost of the electro-optic medium.

The present invention also provides a display assembly ("DMDD assembly" of the invention) comprising a plurality of display modules, each display module comprising a display module driver apparatus of the invention associated therewith and controlling the image displayed on its associated display module, and display assembly input means arranged to receive image data representing the image to be displayed on the display assembly and to provide at least part of the image data to each display module driver apparatus.

In such a DMDD assembly, the distribution of image data within the various DMDDs can be accomplished in any known manner, a preferred method of such data distribution being described in detail below. Typically, these DMDDs are "daisy-chains" (daisy-chained); in the daisy chain, each DMDD has a data output means (separate from the output means controlling the voltage on the pixel) connected to the input means of the next DMDD in the chain.

The DMDD of the present invention may be arranged to perform any of the drive methods described in the aforementioned 2003/0137521, WO2004/090857, and PCT/US2004/21000, including optional aspects of these drive methods such as correcting for temperature, relative humidity, operating life of the electro-optic medium, etc. Thus, the DMDD may contain additional electronics or sensors required for these driving methods, such as temperature or humidity sensors, or timers that measure the operating time of the associated electro-optic display module.

Drawings

FIG. 1 is a flow chart of a two-step voltage change method for addressing a display according to the present invention.

Fig. 2A is a block diagram of a column driver and associated apparatus for performing the method of fig. 1.

Fig. 2B is a block diagram similar to fig. 2A showing an apparatus for performing the related art driving method.

Fig. 2C shows a graphical representation of the voltage applied to the column electrodes and the value of a particular control signal over time in the driving method of fig. 2B.

Fig. 2D is a block diagram similar to fig. 2B, but showing a later stage of the prior art driving method.

Fig. 3A is a block diagram similar to fig. 2B, but illustrating the first stage of the two-step voltage change method of the present invention.

Fig. 3B is similar to the graph of fig. 2C, showing a graph of the voltage applied to the column electrodes and the value of a particular control signal over time in the two-step voltage change method of fig. 3A.

FIG. 3C is a block diagram similar to FIG. 3A, but illustrating a second phase of the two-step voltage change method.

Fig. 3D is a block diagram similar to fig. 3A and 3C, but illustrating the final stages of the two-step voltage change method.

Fig. 4A shows a view similar to that of fig. 2C and 3B, but showing the corresponding signals of the prior art driving method when it is desired to apply a number of consecutive periods of the same voltage on the column electrodes.

Fig. 4B shows a diagram similar to fig. 4A, illustrating the two-step voltage change method of the present invention under the same conditions as fig. 4A.

Fig. 5 is a block diagram of one channel of a prior art column driver (i.e. a part of such a driver for controlling one column electrode).

FIG. 6 is a block diagram similar to FIG. 5 showing one column of trim drivers used in the two-step voltage control method of the present invention.

Fig. 7 is a diagram similar to fig. 2C, 3B, 4A, and 4B showing the variation with time of the voltages applied to the pixels of the same column of the display but located in two adjacent lines and the specific control signals when the preferred two-step voltage changing method of the present invention is performed using the driver of fig. 6.

FIG. 8 is a top view of a flexible large area display of the present invention.

Fig. 9 is a schematic cross-section along line 9-9 of fig. 8.

Fig. 10 is a roll lamination process that may be used to manufacture the flexible large area display shown in fig. 8 and 9.

Fig. 11 is a block diagram of a display module driver apparatus of the present invention.

FIG. 12 is a flow chart illustrating a method of operation of the display module driver apparatus of FIG. 11.

Detailed Description

As already mentioned above, the present invention comprises three main aspects, namely, (a) a two-step voltage modification method and an apparatus for performing such a method; (b) a flexible large area display; and (c) display module driver apparatus and display assemblies including such apparatus. These various aspects of the invention will be described separately below, although it should be appreciated that a single display or method of driving the same may utilize more than one aspect of the invention. For example, the DMDD module of the present invention can implement the two-step voltage modification method of the present invention and can be used to drive the flexible large area display of the present invention.

Two-step voltage change method and apparatus for performing the same

It has been mentioned that the present invention provides a two-step voltage modification method (TSVCM) for driving an electro-optic display comprising an electro-optic medium, a pixel electrode capable of applying an electric field to the electro-optic medium, and a column electrode associated with the pixel electrode. TSVCM involves varying the voltage on the column electrodes in two steps: in a first step the voltage is changed from a first value to a third value between the first (initial) value and the second (final) value and is held for a time sufficient to allow charge to flow from or to the column electrode. Thereafter, in a second step, the voltage on the column electrode is changed from the third voltage to the second voltage. Also, as previously described, the TSVCM is used to reduce the power consumption of the display.

TSVCM is based on the recognition that, in the absence of current supplied by the power supply, the column electrode is initially set to an intermediate (third) voltage between the initial (first) voltage and the final (second) voltage required for the change, and the change in column electrode voltage is then completed by charging the column electrode with current supplied by the power supply, which allows the change in column electrode voltage to be achieved with lower power consumption. Typically, when applying TSVCM to a display comprising a plurality of column electrodes (a commercial display may have hundreds of column electrodes), the same third voltage is used for all column electrodes, which may be ground potential or a voltage held by a common front electrode on the electro-optical medium on the opposite side to the pixel electrodes. Thus, in TSVCM, the power supply provides only a portion of the charge required for the change in column electrode voltage, thus reducing the power provided by the power supply.

In TSVCM, it is preferred that the third voltage be an arithmetic average of the first and second voltages, as this provides the greatest reduction in power consumption from the average. The third voltage, using an arithmetic mean, doubles or doubles the frequency f in equation a above, while effectively reducing the voltage V that the power supply needs to provide by a factor of two, and ultimately the power P by a factor of two. Thus, by allowing charge leakage when a portion of the display is updated, rather than by actively applying current when the portion is updated, the voltage change portion driven by the power supply element is reduced, thereby reducing display power consumption.

TSVCM may utilize display image numerical data signals known to those of ordinary skill in the art of electronic display technology. For example, the display may include a controller, such as a video card, that processes the image bitmap data and sends the image data to the logic circuitry. Logic circuitry known in the art may receive numeric voltage pulse data that characterizes the voltage signal, horizontal timing data, and vertical timing data. The logic circuit may then provide the numerical signals to the row and column drivers.

Since the power drawn from the power supply is related to the square of the output voltage, reducing the voltage applied by the driver components in order to achieve a change in the display column voltage can achieve a substantial reduction in the overall power consumption. Some embodiments of the invention do not require the provision of additional circuitry in a conventional column driver to achieve a reduction in peak power output. Other embodiments that do not require the provision of additional circuitry may reduce the average and peak power.

The above and further advantages of the invention will be apparent from the following description with reference to the accompanying drawings. In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

FIG. 1 is a flow chart showing the broad features of the TSVCM of the present invention. The method comprises the following steps: providing a pixel associated with a column electrode having a voltage; defining a voltage transition of a column electrode from a first voltage to a second voltage associated with an image state transition of a pixel; and extracting charge from the column electrode to cause the voltage of the column electrode to at least partially transition to the second voltage. The charge can be extracted without the support of the power supply and therefore does not consume power from the power supply. The power supply may support only a portion of the full voltage transition, enabling a reduction in the peak and/or average power consumption of the display. Thereafter, optionally, a power supply provides a second charge to the column electrode to complete the transition of the column electrode voltage to the second voltage.

Fig. 2A is a block diagram of an apparatus, generally designated 100, for addressing a column of a display. The device includes an input line 102 carrying, for example, +3V from a battery. The input line is connected to a +15V boost power supply 104 and a-15V boost power supply 106, the +15V and-15V outputs provided by these boost power supplies being provided to a column driver 108, which in turn is connected to ground or to a column line or electrode 110 of the display. The display is an active matrix display with a common front electrode voltage of 0V; the combined column capacitance is 20nF and the row addressing time (i.e. the time during which each row is selected during the display scan) is 30 microseconds. Boost power supplies 104 and 106 are 80% efficient.

Assume a worst case scenario where the image being written comprises alternating black and white rows, such that the column electrode 110 must transition between +15V and-15V each time a new row is selected. In a conventional method of writing such an image, as shown in FIGS. 2B and 2C, when the Line Enable (LE) signal is high, the column driver 108 outputs Q using a boost power supply 106 of-15V₁A charge of coulomb to transition the column electrode 110 from +15V to-15V, as shown at 112 in fig. 2C.

When the next row of the display is selected after 30 microseconds, the column electrode 110 needs to make a reverse transition from-15V to + 15V. Thus, as shown in fig. 2C and 2D, when LE goes high again, the column driver 108 boosts the power supply 104 using +15V to thereby change Q₁The coulomb of charge is output to the column electrode 110 as shown at 114 in figure 2C.

In these two consecutive transitions that occur at 112 and 114, Q may be calculated as follows₁The value of (c):

Q₁＝CV

Q₁＝20nF*30V

Q₁＝600nC

positive transitions (e.g., for a transition from white to black) will occur on alternate rows or every 60 microseconds. Thus within one second, the +15V supply will provide a 600nC charge for 1 second/60 microsecond times, which results in a current draw of 10 mA. If the efficiency of the boost power supply is 80%, this corresponds to an average current of 62.5mA at the 3.0V input, or a power draw of 187.5 mW.

Similarly, for negative transitions, the-15V power supply 106 provides Q₁The charge of coulomb (e.g., convert the remaining rows from black to white), whichResulting in 187.5mW of power at the other input, resulting in 375mW total capacitive power.

(As is conventional, the column driver 108 is provided with an "output allowed" ("OE") input, so that when the OE input is high, the column driver 108 can provide +15V, 0V, or-15V to the column electrodes 110, but when OE is low, the column driver provides only 0V, and the same voltage is provided to the common front electrode of the display, regardless of the display data loaded into the driver. typically, the OE input is used to power up or power down the display, or sometimes to implement a sleep (low power) mode. As shown in FIG. 2C, in prior art driving methods, OE remains high throughout, and therefore has no effect on the output of the column driver 108.)

Fig. 3A to 3D illustrate the use of the same apparatus as shown in fig. 2A to 2D for carrying out the two-step voltage change method of the present invention. This TSVCM differs from the prior art process of FIGS. 2A through 2D in that: instead of using the boost power supplies 104 and 106 to charge the column electrodes to the desired final value before using one of the boost power supplies 104 and 106, the column electrodes 110 are discharged to 0V using the OE input of the driver 108 at the time the column electrode voltage transitions.

FIG. 3B shows the same series of column electrode voltage transitions as FIG. 2C, again assuming the worst case scenario, i.e., where the column electrode voltage must change from +15V to-15V, or from-15V to +15V, each time a new row is selected. As will be explained in detail below, according to the TSVCM of the present invention, a complete black-white-black period for transitioning from one black row to the next black row after two rows can be achieved in four phases.

The first part of the cycle is the transition of the column electrode voltage from +15V to-15V and this transition is effected in two stages. In the first phase, OE goes low (while LE remains low), as shown at 312 in FIGS. 3A and 3B, thus forcing the output of the column driver 108 to 0V and extracting Q from the column electrode 110₂To the ground of the column driver 108. This phase does not drive any current from the power supply 104 or 106.

In the second part of the period, shown as 322 in FIG. 3B, after a short time (long enough for at least a substantial portion of the column electrodes 110 to complete discharge to 0V), both LE and OE are driven high. This produces the following effect: re-enabling the driver 110 also latches the newly loaded row data to its output. This results in driver 110 outputting Q₂A coulomb charge to-15V power supply 106, as shown in figure 3C, whereby the +15V to-15V transition is accomplished in two stages.

The third and first phases of the cycle are very similar, as shown at 324 in fig. 3B. OE goes low again (while LE remains low), thus forcing the output of the column driver 108 to 0V and extracting Q from the ground output of the column driver 108₂To the column electrode 110; in other words, the situation is the same as shown in fig. 3A, except that the currents are reversed. Also, this phase does not require any current from the power supplies 104 and 106.

Finally, in the fourth phase of the cycle, both LE and OE are driven high as shown at 326 in FIG. 3B. This produces the following effect: re-enabling the driver 110 also latches the newly loaded row data to its output. This results in the power supply 104 outputting Q₂Coulomb's charge goes to the column driver 108 as shown in fig. 3D, thereby completing the-15V to +15V transition in two stages.

In the TSVCM shown in FIGS. 3A to 3D:

Q₂＝CV

Q₂＝20nF*15V

Q₂＝300nC

from this fact, it can be seen that the voltage of the TSVCM of the present invention is half that of the prior art method.

Thus:

Q₁＝2Q₂

that is, in the present method, the charge supplied by the power source is only that of FIGS. 2A to 2DHalf of the prior art method, the voltage at which the method actually provides power to the column electrodes is only half of that of the prior art method. In the prior art approach, the charge provided over one complete (black-white-black) period (two rows) is 2Q by OE remaining high all the time₁Coulombs. In the method of the invention, the charge flowing into or out of the column electrodes is 4Q₂But only needs to provide 2Q₂(ii) a Thus, half of the current of the prior art method is supplied by the power supply, resulting in a total capacitive power of 187.5mW input.

The TSVCM shown in FIGS. 3A-3D has the advantage of being usable with most conventional column drivers without any circuit modifications. However, when OE needs to be driven low to cause charge to be extracted from one or more column electrodes, it does require that all column driver channels of the entire display be forced to 0V. Thus, in the case where a new row is selected at any time without transitioning the column electrode 110 between +15V and-15V, the TSVCM method results in lower power consumption than optimal power usage. For example, the method of fig. 3A to 3D is not well suited for transitions between full black and full white screens (or more generally, a large number of adjacent pixels on the same column electrode need to undergo the same transition at the same time, which is common when the image to be displayed comprises a large area of monochrome), because in these cases the column electrode 110 can stay at +15V or-15V for an extended period of time with little or no capacitive power being drawn from the power supply. This is illustrated in fig. 4A, which shows the voltage on the column electrode 110 (assumed to be +15V) and the OE and LE signals on several consecutive scan lines.

Fig. 4B shows the same signals as fig. 4A when the TSVCM of fig. 3A to 3D is applied to the same case. As shown in FIG. 4B, each time OE goes low (i.e., just before each new row is selected), the column electrodes are forced to empty their charge to ground, and the column electrodes 110 must then be charged back to +15V using the +15V power supply 104, which is thus required to provide Q each time a new row is selected₂So that the power consumed is about half of the power consumed in the alternate row example of fig. 3A-3D. However, inIn this case, each transition back to +15V can be achieved without consuming power, since there is no need to empty the charge to lower the column electrode voltage level to the common voltage level.

Such unnecessary power consumption can be avoided by the more elaborate method of the present invention, which requires modification of the driver circuit, and one such method will now be described with reference to fig. 5 to 7. The method to be described allows a single column electrode to be extracted in the same way as is done in the method of figures 3A to 3D, but only when the column electrode voltage needs to be changed; when the column electrode voltage remains the same, it is possible to avoid emptying the charge to ground, whereby unnecessary power consumption due to the need to recharge the column electrode can also be avoided.

Figure 5 illustrates one channel of a column driver, generally designated 500, i.e. the part of the column driver controlling one column electrode. The channel of the column driver 500 comprises a first (next) data register 502, a second (current) data register 504, and an output stage 506. The current data register 504 receives the LE signal, while the inputs of the output stage 506 include +15V, -15V, ground potential, and (at the "enable" input) the global OE signal, and include an output connected to the column electrode 110.

The apparatus shown in fig. 5 operates in the following manner. Two bits of input data are loaded into the next data register 502 by an input clock and input shift register logic (neither shown in fig. 5). When LE goes high, data from the next data register 502 is loaded into the current data register 504. Output stage 506 is active asynchronously from registers 502 and 504 and outputs +15V, 0 (ground potential), or-15V on column electrode 110, depending on the value of the data bit in the current data register 504 and the OE signal, according to the following table, where D1 and D0 are the most significant and least significant bits in the current data register 504, respectively, and X represents 0 or 1:

table:

OE	D1	D0	output on column electrode
				1	0	0	0(GND)
1	0	1	+15V
				1	1	0	-15V
1	1	1	0(GND)
				1	X	X	0(GND)

Fig. 6 shows one channel of a modified column driver (generally designated 600) resulting from the column driver 500 shown in fig. 5, but used to implement the TSVCM of the present invention, in which the charge purged from the column electrodes is controlled on a channel-by-channel basis. The column driver 600 comprises a next data register 502, a current data register 504, and an output stage 506, all of which are identical to the corresponding integers of the column driver 500; the exception is that the enable input of output stage 506 does not receive the global OE signal, but rather receives a control signal generated as described below, and the clock of the next data register 502 is changed to the falling edge of the LE signal.

The column driver 600 further comprises an XOR gate 612 whose inputs receive the two-bit data values from the next data register 502 and the current data register 504. Thus, the XOR gate 612 goes high only when the values in the two data registers are different (indicating a change in input data). The output of XOR gate 612 is transmitted to one input of NAND gate 614, and the other input of gate 614 receives the LE signal. Thus, the output of the NAND gate 614 goes low only when the output of the XOR gate 612 is high (indicating a change in input data) and LE is high. The output of NAND gate 614 is transmitted to one input of AND gate 616, AND the other input of AND gate 616 receives the global OE signal. The output of AND gate 616 is transmitted to the enable input of output stage 506.

Those skilled in the art of display driver design will appreciate that other logical combinations may be used in place of gates 612, 614, and 616 to produce the same effect.

Fig. 7 illustrates the change in column electrode voltage placed on the column electrode 110 over time by the column driver 600 of fig. 6, where the uppermost graph of fig. 7 shows the transition without changing the column electrode voltage, and the middle graph of fig. 7 shows the transition where the column electrode voltage needs to transition from +15V to-15V or from-15V to +15V when each successive row is selected. In the former case, no charge draining occurs, while in the latter case, TSVCM is performed in substantially the same manner as FIG. 3B, except that the time of the column voltage change is slightly offset relative to the change in the LE signal. FIG. 7 also shows values for OE and LE. It can be seen that OE is always held high, regaining its original function, i.e. only powering up or down the display or transitioning the display to sleep mode.

More particularly, the column driver 600 processes the transitions shown in FIG. 7 in the following manner. If LE goes high but the data is unchanged, the output of XOR gate 612 remains low, the output of NAND gate 614 remains high, AND the output of AND gate 616 remains high (keeping in mind that OE now always remains high). A high input formed at the enable input of the output stage 506 causes the output stage to maintain the same voltage on the column electrode 110 and prevents any charge emptying, as shown in the upper part of figure 7.

However, if a data change occurs when LE becomes high level, the output of the XOR gate 612 becomes high level, the output of the NAND gate 614 becomes low level, AND the output of the AND gate 616 becomes low level. If the column electrode 110 was previously at a voltage other than ground potential, as shown in the middle portion of fig. 7, a low input formed at the enable input of the output stage 506 causes the output stage to empty charge to/from the column electrode 110 to the GND input of the output stage 506. This charge dump continues as long as LE remains high. Thus, in fig. 7, the rising edge of the signal LE is synchronized with the start of charge emptying, rather than with the start of recharging of the column electrodes as shown in fig. 3B.

The LE remains high long enough that most or all of the charge required to change the voltage is drained from the column electrodes, typically in a few microseconds. When LE subsequently goes low, the current data register 504 is updated with data from the next data register 502, the output of the XOR gate 612 goes low, and the enable input of the output stage 506 receives a high signal which re-enables the output stage 506 and causes the output stage 506 to apply a voltage corresponding to the data in the current data register 504 to the column electrode 110. In the middle part of fig. 7, this voltage is assumed to be-15V. It will be readily appreciated that the transition from-15V to +15V can be handled in a completely similar manner.

The modification of the prior art column driver 500 of figure 5 to make the driver 600 of the present invention requires only the addition of three logic gates per channel, and this change can be implemented in an integrated circuit without a significant increase in die size, and therefore has very little impact on the cost of the column driver. However, driver 600 reduces both the average and peak capacitive power consumption by a factor of two compared to prior art column driver 500.

In summary, a simple form of column driver of the invention, such as that shown in figures 3A to 3D, which does not require a change in circuitry, can reduce peak power requirements and so can be used, for example, in some situations where there is an upper limit to the extraction of instantaneous current, for example in devices powered by alkaline batteries. A more complex form of the column driver of the present invention, which does not require circuit changes, such as shown in fig. 6 and 7, can substantially simultaneously reduce the average and peak capacitive powers by about a factor of two at a particular drive voltage.

Flexible large area display

As previously mentioned, in a second main aspect the present invention provides an electro-optic display system comprising a flexible substrate and a plurality of flexible electro-optic display cells adhered to the flexible substrate, and a process for manufacturing the electro-optic display system, the process comprising: the method includes providing a flexible substrate, providing a plurality of flexible electro-optic display units, and adhering the plurality of flexible electro-optic display units to the flexible substrate.

This aspect of the invention is based on the insight that by laminating a plurality of smaller flexible display units onto a flexible thin layer, a low cost, light weight large area flexible display system can be manufactured. The large area display of the present invention can be manufactured using relatively inexpensive materials and subcomponents, using low cost process steps such as printing and lamination steps, and is therefore relatively inexpensive to manufacture. This aspect of the invention can, for example, produce inexpensive large area signs for indoor and outdoor use. The large area display is substantially maintenance free and waterproof.

A preferred flexible large area display system (FLAD) of the present invention will now be described with reference to figures 8 and 9 of the accompanying drawings. Fig. 8 is a schematic top view of such a FLAD (generally designated 800) and fig. 9 is a cross-section taken along line 9-9 of fig. 8. The FLAD800 includes a flexible substrate 804, which may be a transparent plastic film, and a flexible display unit 802 adhered to the substrate 804 using a transparent adhesive layer 806. (the display system 800 and the single display unit 802 are both referred to herein as a "display" when not confusing.) thus, the FLAD800 thereby achieves a large display area by combining multiple display units 802 to form a single display system. Rather than providing a large, rigid, expensive to manufacture display system, the display system of the present invention can be relatively thin and light, and thus easy and inexpensive to manufacture.

The display unit 802 comprises a flexible material such as a polymer substrate. The display unit may be based on a reflective display medium, for example an electro-optic medium of any of the aforementioned types. The size of the display system can thus be easily increased by using larger area substrates and larger or more display cells. The total thickness of the display system need not increase with increasing area. For portability, the display system may be rolled up into a relatively compact tube shape, for example.

In addition to the adhesion layer 806, the FLAD800 includes a mask layer 808 that covers the optically inactive area of the FLAD, i.e., the area between the display cells 802, as well as possibly (depending on the nature of the display cells 802) the periphery or bezel area of the display cells themselves. The provision of the masking layer 808 is also optional and can also be achieved by: another layer of the FLAD, such as a front protective sheet (described below), is painted or surface treated, or masking inserts are provided between the display units 802. Indeed, although the FLAD800 shown is not configured in this manner, the display unit 802 may be inserted into an aperture in a masking layer that may be used to hold the display unit in the correct position when the FLAD is assembled.

The FLAD800 further includes a protective sheet 810 for protecting the display unit 802 from mechanical damage and a cover sheet 812 secured to the substrate 804 by an adhesive layer 814; the protective sheet 810, the cover sheet 812, and the adhesive layer 814 are optional components of the FLAD. Although not shown in fig. 8 and 9, alignment marks may be provided on one or more layers of the display to assist in positioning the display unit 802 relative to the substrate 804 or other substrate or layer of the FLAD.

The viewing surface of the display unit 802 is preferably oriented to be viewed towards the substrate 804 or through the substrate 804, i.e. from below in fig. 9. The substrate 804 or the thin covering layer 812 may have anti-glare properties. For example, any of these layers may have a rough surface, or may be coated with an anti-glare material.

The layers of the display system are preferably laminated together, for example under vacuum. Lamination can support a relatively simple and low cost manufacturing process. The lamination may also support the manufacture of a weatherproof, reliable display system for outdoor use.

Figure 10 is a schematic cross-sectional view of a process for the manufacture of the FLAD of the present invention. A roll 1002 of flexible substrate material (of the substrate 802 that will form the final FLAD) and a roll 1004 of the display unit 802 (on a carrier) feed the substrate material and display unit, respectively, to a lamination station (shown schematically at 1006) of the manufacturing process. For example, the adhesive may be provided at the time of lamination, or may be included in one of the roller members. Those skilled in the art of lamination processing will appreciate that many display system configurations can be supported by modifying the process shown in fig. 10 in accordance with the principles of the present invention.

The FLAD method of the present invention allows for the assembly of flexible display units into flexible display systems. The method also allows the display unit to be optically coupled into the front layer, which may reduce glare and/or viewing angle, for example. The display system may include an encapsulating agent to provide, for example, resistance to atmospheric exposure and damage. The display system of the present invention may provide for relatively easy assembly. Optical coupling of the substrate to the display unit may, for example, reduce primary surface reflections.

In the method of manufacturing a large area display according to the present invention, a transparent plastic thin layer may be used as a substrate. Suitable transparent plastic sheets can be made using, for example, polyesters, acrylics, polycarbonates, polycarbonate-polyvinyl fluoride composites, and transparent fluoropolymers. The front surface of the thin layer is roughened, for example to reduce glare. The thin layer may provide a filter for ultraviolet radiation to protect the display. The back surface may be printed with a masking pattern, such as opaque or light-filtering ink, and windowed to display the display unit through the windows. Included in the display may be a liquid or thin layer of adhesive.

The display unit is then arranged on the front foil so as to correspond to the printed window. An alignment mask may be printed on the back side of the front lamina to assist alignment. On the back of the display unit, further adhesive or further cover sheets may be applied. Alternatively, the back may be open. The structures are then stacked to provide bubble free coupling between the adhesive and the display unit.

Suitable adhesives include hot melt materials such as vinyl acetate, polyamide, and polyurethane, and liquid materials such as silicone, epoxy, and polyurethane. The stacking step may employ, for example, roll lamination and/or vacuum lamination.

The methods and structures described above may utilize, for example, any type of plastic-based electronic display unit, such as any of the electro-optic media or other imaging media previously described.

Display module driver apparatus and related display assembly

It has been mentioned above that a third main aspect of the invention provides a display module driver apparatus for controlling an image to be displayed on a display module, wherein the display module comprises a plurality of pixels, each having a respective pixel electrode associated therewith. The driver device includes: an input means for receiving data representing an initial image and a final image to be displayed; a conversion tool for converting data received by the input tool into a pixel-wise representation of the initial and final images; storage means for storing a representation of the pixel-wise pattern of the initial and final images; a plurality of output means arranged to control the voltage to be applied to the pixel electrodes of the display; and logic means arranged to receive the data from the storage means and to generate the required output from the data on the plurality of output means. This third main aspect of the invention also provides a display assembly comprising a plurality of display modules each comprising a display module driver device of the invention associated therewith and controlling the image displayed on its associated display module, and display assembly input means arranged to receive image data representing the image to be displayed on the display assembly and to provide at least part of the image data to each display module driver device.

As previously mentioned, prior art electro-optic displays (such as those described in the aforementioned 2003/0137521, WO2004/090857, and PCT/US2004/21000) are typically addressed using a single controller that effects the conversion of the received image into the "displayable" format required by the display (although the controller may pass the conversion to an external data processing tool, such as a personal computer for driving the display) in a "non-displayable" format (which does not correspond to the pixel-by-pixel data required by the display). The non-displayable format may be a non-bitmap format, such as ASCII text, or a compressed bitmap format, such as a TIF or JPEG file, or any of a variety of LZW compressed bitmaps. Regardless of the exact non-displayable format of the received data and the exact location of the transition, in this type of display, the controller outputs the image data in a displayable format as required by the display. This displayable data is then passed to one or more substantially "dump" drivers that drive the pixels of the display using the displayable data.

While this type of centralized processing and data transformation done by a single controller is satisfactory for many displays, problems arise in the following situations: when the display is a high resolution display having a very large number of pixels or display components, wherein the display components (e.g., the FLAD of the present invention) include a number of discrete modules each having a discrete driver. Displayable data is typically much larger than non-displayable data, so moving this data from the central controller to a series of discrete modules requires providing a high bandwidth data distribution channel. These channels may be more expensive than low bandwidth channels and may be more susceptible to data corruption, for example due to electromagnetic interference or "noise".

In practice, the practical situation is more complex than outlined above, at least for pulse-driven bistable electro-optic displays. As described in the aforementioned 2003/0137521, WO2004/090857, and PCT/US2004/21000, in such displays the waveform applied to any particular pixel during a transition from one image to another is a function not only of the expected final optical state of that pixel, but also of its initial state (i.e. the state at which the transition was initiated). Depending on the exact drive scheme being used, the waveform may also be a function of: one or more previous states (prior to the initial state) of the pixel, one or more environmental parameters such as temperature and humidity, and other non-environmental parameters such as the total operating time of the electro-optic medium being used. Furthermore, as described in these co-pending publications, it is desirable to use a relatively complex waveform in which a single transition of a pixel requires the application of a series of different voltages to the pixel electrode associated with that pixel, so that rather than outputting data defining a pure one of the voltages applied to a pixel during a transition, the controller outputs data defining a series of such voltages. This further increases the bandwidth of the data transmission channel. Finally, as previously described, it takes a significant amount of time to load data through the display driver.

The display module driver arrangement (DMDD) and related DMDD assembly of the present invention aim to overcome or at least alleviate these problems by: the data conversion is essentially transferred "downstream" to the individual display modules, thereby keeping the image data in an undisplayable, low-bandwidth form for as long as possible.

In the DMDD component of the present invention, it is generally necessary to distribute data from a single "global" input (whereby the component receives data from an external source such as a video card) into the various DMDDs within the component, and (at least in the case where each display module will only display a portion of the complete image that the component is to display) it is necessary to ensure that each DMDD only acts on the portion of data associated with that portion of the image. Those skilled in the art of data distribution and processing will appreciate various techniques for this purpose, any known technique may be used in the DMDD components of the present invention. For example, the data may be distributed using a daisy chain arrangement whereby each DMDD is provided with a data output means (separate from the output means controlling the voltage on the pixel) connected to the next DMDD input means in the chain. An example of such a daisy-chain arrangement is a daisy-chain arrangement implemented in a supertexthv 577 integrated circuit; in this arrangement, an output on a first DMDD is connected to an input on a second DMDD, an output on the second DMDD is connected to an input on a third DMDD, and so on. Upon receiving the first timing pulse, the first DMDD loads a fixed amount of data from the global data input. Upon receiving the second timing pulse, the first DMDD passes the data already present therein to the second DMDD and loads a second amount of data from the input. This process is performed until all the DMDDs in the chain have loaded data, at which point all the DMDDs receive a control signal to latch the data they contain into the appropriate data storage registers.

Alternatively, data from the global data input may be sent to all DMDDs in a parallel manner, ensuring that each DMDD only holds data related to itself. This can be achieved, for example, by a token passing method. In this approach, a data bus extends in parallel from the global input to each DMDD of the plurality of DMDDs. Each DMDD has a token input and a token output, with one token input connected to the controller and the other token input connected to the token output of another DMDD, thereby essentially daisy chaining the DMDDs therein. A first set of data is placed on the bus and an electronic token is sent from the controller to the DMDD whose token input is directly connected to the controller. The DMDD reads a first set of data from the bus and places it in a storage register. A second set of data is then placed on the bus, and the DMDD reading the first set of data sends the electronic token to a second DMDD in the chain, thereby causing the second DMDD to read the second set of data from the bus into a storage register within the second DMDD. This process is repeated until all the DMDDs have read a set of data from the bus, at which point the electronic token is returned to the controller.

The third possible arrangement is commonly referred to as the "chip enable method", and is similar to the second arrangement in that: the data bus extends in parallel from the global input to all DMDDs. However, the token arrangement is replaced by a set of chip enable lines, each such line extending from the controller to each DMDD. A first set of data is placed on the bus and a chip enable line is selected, thereby causing the DMDD associated with the chip enable line to read the first set of data from the bus into a storage register within the DMDD. A second set of data is then placed on the bus, a different chip enable line is selected, and the process continues until all the DMDDs have received the data.

Other arrangements may of course be used. For example, the controller may simply broadcast a series of addressed data packets and a set of data to all of the DMDDs, each data packet including the address of the DMDD that is to receive the data. All DMDDs will receive all packets but the records in their memory only register the data set addressed to that DMDD.

The DMDD of the present invention receives data at its input tool representing the initial and final images to be displayed. The conversion facility of the DMDD converts each of these data sets into binary representations of the two images and stores these binary representations in the storage facility of the DMDD. The transition module or storage tool then sends the binary representation of the image to a logic tool that uses the binary representation to determine the desired output on the output tool, i.e., the various elements of the output signal waveform. The logic tool may be arranged to vary the required output in dependence on at least one of the following parameters: an environmental parameter (such as temperature or relative humidity), a parameter indicative of the operational lifetime of the display module, and a parameter indicative of the electro-optic characteristics of the display module. (Note that this ability to vary the output based on parameters indicative of the electro-optic characteristics of the display module facilitates the replacement of individual modules within the display assembly if the correct parameters are provided for the associated DMDD, then modules containing a certain type of electro-optic medium can be removed from the assembly and replaced with modules containing electro-optic media having different characteristics without affecting the overall appearance of the display assembly.) the output means then sends the associated output to the electrodes that apply the voltage to the electro-optic medium.

Fig. 11 is a block diagram of a DMDD according to the present invention. Data, such as characters (e.g., ASCII text) or 1-bit matrix data, is received at an input tool or terminal 1100 from a data source (not shown). The data may be generated in real time and communicated to the input terminal 1100 directly or through, for example, a wired or wireless network. The data may also be stored data from, for example, an optical or magnetic storage medium. The input terminal 1100 can be a serial port, a parallel port, a USB port, or an IEEE1394 port. Input terminal 1100 is compliant with, for example, I2C, LVDS, or other industry standard signal interfaces. Input terminal 1100 can accept input data in a variety of formats including, for example, ASCII format, Unicode format, bitmap format, RLE compressed bitmap format, or any format for representing characters or matrix data.

The input terminal 1100 sends the input data to a conversion tool or module 1105. (As shown schematically at 1106, the input terminal 1100 may also send the input data to the next DMDD in the chain.) the conversion module 1105 serves to convert the input data, typically in the form of characters or bitmaps, into a pixilated binary representation of the image to be displayed. For mosaic, starburst, or n-segment displays, the data conversion performed by the conversion module 1105 may be fixed by the backplane graphics. In the case of a matrix display, the data conversion of the alphanumeric characters may be based on an embedded font. Alternatively, the data conversion may be based on fonts stored in rewritable or write-once memory, or even fonts embedded in the input data. For non-alphanumeric characters, the conversion tool 1105 can interpret various compression procedures to reproduce the original image.

The conversion module 1105 then passes the data to a storage facility or module 1110 that is used to store the data output of the conversion module 1105 for immediate or future use. The memory module 1110 typically includes rewritable memory. However, the storage module 1110 may also include write-once memory. Further, the storage module 1110 may be in the form of a database, but need not have the ability to create data structures or support data areas. When the amount of data to be stored is large, it is preferable to provide the storage module 1110 with a data compression/decompression tool to reduce the amount of data actually stored and reproduce the original data when necessary.

From the above explanation, it will be appreciated that the conversion module 1105 generates and the storage module 1110 stores data representing at least two consecutive images (the initial and final images used to overwrite the image displayed on the associated display module at one time) so that the control module 1115 (described below) can use the data of the two images to calculate the output required on the output tool. Depending on the exact drive scheme used, the storage module 1110 may store data relating to more than two images, and may also store data relating to the aforementioned environmental and non-environmental parameters.

The DMDD further includes logic means, which for explanation is shown in fig. 11 as including a control module 1115 and a control logic modifier 1120, although in practice both modules may simply be in the form of software in a single data processing unit. The control module 1115 receives data representing two or more images, wherein the data is transmitted from at least one of the conversion module 1105 and the storage module 1110. Upon receiving the data, the control module 1115 generates a corresponding waveform. For example, the control module 1115 may use a look-up table ("LUT") to determine a series of voltages to apply to the display. Such a LUT may be hard coded into the control module 1115 or alternatively may be stored in the memory module 1100 or any other form of data storage.

Control module 1115 then sends the generated waveform to control logic modifier 1120. The control logic modifier 1120 adjusts the waveform based on any one or more of the following parameters, such as the temperature of the display module, the operating life of the display module, or the characteristics of the display material. The adjusted waveform is then sent to a plurality of output tools or terminals 1125.

The output terminal 1125 is typically in electrical communication with an electrode of the display module associated with the DMDD; the display module is not shown in figure 11 but may be a set of column electrodes of a typical active matrix display or a direct drive display, techniques which are well known to those skilled in the art of electro-optic displays; representative electrode arrangements are set forth in a number of the aforementioned EInk and MIT patents and applications. The invention does not exclude the possibility of: additional circuitry (e.g., latch circuitry) is interposed between the output terminal of the DMDD and the actual electrode of the associated module. For example, output terminal 1125 can transition each output to-V, 0, + V, or alternatively can transition each output to a voltage selected from a select array in the range-V to + V. Alternatively, output terminal 1125 can transition each output voltage to a voltage selected from any known output architecture. Typically, if the DMDD is used in a module of the aforementioned "direct drive" type, the number of output terminals 1125 is an integer multiple of the number of pixels used to represent a single character in the associated display unit module.

FIG. 12 is a flow chart illustrating a method of operating the DMDD or similar DMDD shown in FIG. 11. First, data from a data source is received (step 1200). The received data may be in various forms including, for example, ASCII format, Unicode format, bitmap format, RLE compressed bitmap format, or any format for representing character or matrix data.

Next, the received data is converted into a binary representation of the image to be displayed (step 1205). The received data is typically in character or bitmap format, often converted to a binary representation in pixels. The data conversion may be performed using various processes. For example, backplane graphics may be used for fixing, or may be based on embedded fonts. Alternatively, the data conversion may be based on fonts stored in rewritable or write-once memory or fonts embedded in the input data itself. For non-alphanumeric characters, the transformation process of step 1205 can interpret various compression procedures to reproduce the original image.

The binary representation of the image to be displayed is then stored (step 1210). The storage medium is typically a rewritable memory, but may also be a write-once memory. It will be appreciated from the foregoing description that although the step 1200 of receiving data and the step 1205 of data transformation are performed on data relating to one image at a time, the storing step 1210 is performed such that data relating to at least two (and possibly more) successive images is available within the data storage tool for use by the logic tool. Next, an output signal waveform is created based on the binary representation of the two or more images (step 1215). For example, a LUT may be used to determine a series of voltages to be applied to the display.

The output signal waveform created in step 1215 is then modified based on one or more parameters (step 1220). Such parameters may include, for example, the temperature of the display module, the operating life of the display module, or the characteristics of the display material. The adjusted output signal waveform is then sent to the display (step 1225). More specifically, the output signal waveform is sent to the addressing electrodes of the display module. Such a display module may be any type of display, including a liquid crystal display. However, as previously mentioned, the invention is particularly, but not exclusively, applicable to impulse driven electro-optic displays, which may be any of the aforementioned types of displays.

The DMDD and DMDD assemblies of the present invention provide a number of advantages. First, allowing character data to be transferred to a large number of display modules at a relatively low bandwidth saves power and reduces the likelihood of data corruption. Second, it allows the use of any number of low voltage data interfaces, which can reduce the amount of electromagnetic interference from the display. Third, some embodiments of the invention add a character interface to existing drivers that is compatible with existing character display modules and may allow the display to achieve a non-uniform mix of electro-optic and other display technologies on the same sign on a module-by-module basis. Finally, allowing for tight integration between controller functionality and the electro-optic material; each display module actually has a respective controller. This allows each module to be swapped with a different or newer module, possibly with completely different electro-optic characteristics, without affecting the operation of the remaining modules of the display assembly.

Those skilled in the art will appreciate that many modifications and adaptations may be made in the specific embodiments of the present invention described above. For example, the displays of the present invention may be used with any of the foregoing types of electro-optic media. Electrophoretic media, and in particular encapsulated electrophoretic media, tend to be the preferred media, but many other types of imaging media may be used. When an electrophoretic medium is used, the medium may comprise any known element, such as for example, as described in the aforementioned EInk and MIT patents and applications.

Claims (7)

1. A display module driver apparatus for controlling an image to be displayed on a display module, the display module comprising a plurality of pixels, each pixel having a pixel electrode associated therewith, the driver apparatus characterized by:

input means for receiving data representing an initial image and a final image to be displayed, wherein the initial image and the final image are two successive images for overwriting an image displayed on an associated display module at a time;

a conversion tool for converting data received by the input tool into a pixel-wise representation of the initial image and the final image;

storage means for storing a representation of the pixel-wise pattern of the initial image and the final image;

a plurality of output means arranged to control the voltage to be applied to the pixel electrodes of the display; and

logic means arranged to receive data from the storage means and to generate a required output from the data on the plurality of output means.

2. A display module driver apparatus according to claim 1, wherein the logic means is arranged to vary the output within the output means in dependence on at least one of the following parameters: an environmental parameter, a parameter indicative of an operational lifetime of the display module, and a parameter indicative of an electro-optic characteristic of the display module.

3. An electro-optic display comprising the display module driver apparatus of claim 1 and an electro-optic medium.

4. An electro-optic display according to claim 3 wherein the electro-optic medium is a rotating bichromal member or an electrochromic medium.

5. The electro-optic display of claim 3, wherein the electro-optic medium is a particle-based electrophoretic medium comprising a suspension and a plurality of electrically charged particles held in the suspension and capable of moving therein upon application of an electric field to the suspension.

6. The electro-optic display of claim 5 wherein the electrophoretic medium is an encapsulated medium having a continuous phase that separates the suspension and the charged particles into a plurality of discrete droplets.

7. A display assembly having a plurality of display modules each comprising a display module driver apparatus as claimed in claim 1 associated therewith and arranged to control the image displayed on its associated display module, and display assembly input means arranged to receive image data representing the image to be displayed on the display assembly and to provide at least part of the image data to each display module driver apparatus.