JP5616207B2 - Method and apparatus for driving an electro-optic display - Google Patents

Description

  The present invention relates to a method for driving an electro-optic display, in particular a bistable electro-optic display, and an apparatus (controller) for use in such a method. More specifically, the present invention relates to a driving method intended to allow more precise control of the gray state of pixels of an electro-optic display. The present invention also allows the pixel to compensate for the “pause time” in which it retains a particular optical state prior to the transition, while the drive scheme used to drive the display can be DC balanced. The method relates to a driving method intended to allow such a display to be driven. The present invention is particularly but not exclusively intended for use with particle-based electrophoretic displays in which one or more types of electrically charged particles are contained in a liquid. Suspended and these particles are moved through the liquid by the influence of the electric field, changing the display on the display.

  The present application is closely related to Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5, and the reader is able to understand the state of the state of the art in driving an electro-optic display according to those patent documents. See background information about. The following description gives closeness to these applications, and these applications may hereinafter be referred to generically for convenience as “MEDOD” (Method for Driving Electro-Optical Displays) applications. .

  Although an electro-optic material can have or often have a space filled with liquid or gas inside, an electro-optic material in which the method of the present invention is used is said that the electro-optic material has a solid surface Often includes electro-optic materials that are solid in meaning. Such a display using a solid electro-optic material may hereinafter be referred to as a “solid electro-optic display” for convenience.

  The term “electro-optic” as applied to a material or display is used herein in the conventional sense in imaging technology and has a first display state and a second display state that differ in at least one optical characteristic. By referring to a material and applying an electric field to the material, the material changes from a first display state to a second display state. The optical property is typically a color that can be perceived by the human eye, but it is visible in the case of other optical properties such as optical transmission, reflectance, luminescence, or machine-readable displays. It may be a pseudo color in the sense of a change in the reflectance of the electromagnetic wave length outside the light range.

  The term “gray state” is used herein in the conventional sense in video technology to refer to an intermediate state between two extreme states of a pixel, and does not necessarily include the meaning of a black-and-white transition between these two extreme states. . For example, some patents and published applications mentioned below refer to electrophoretic displays in which the extreme states are white and dark blue, so that the intermediate “gray state” is actually light. Blue. Indeed, as already mentioned, the transition between two extreme states may not be a color change at all. The term “gray level” is used herein to indicate a possible optical state of a pixel, including two extreme optical states.

  The terms “bistable” and “bistable” are used herein in the conventional sense in the technical field relating to displays comprising display elements having first and second display states that differ in at least one optical characteristic. Used, the display is brought into either the first or second display state by a finite duration address pulse after any element is driven, and the state is changed at least several times after the address pulse is finished. Or, for example, it should last at least 4 degrees, which is the minimum duration of an address pulse required to change the state of the display element. US Pat. No. 6,057,059 shows that some particle-based electrophoretic displays capable of gray scale are stable not only in the extreme black-and-white state of the display, but also in the intermediate gray state. This is also true for some other types of electro-optic displays. Although the term “bistable” may be used herein to mean both bistable and multistable displays for convenience, this type of display is appropriate as “multistable” rather than bistable. Called.

  The term “impulse” is used herein in the conventional sense to be the integration of voltage over time. However, some bi-directional electro-optic media operate as charge transducers, and for such media an alternative definition of impulse, ie the integration of current over time (equal to the total charge applied) may be used. An appropriate definition of impulse should be used depending on whether the medium operates as a voltage-time impulse transducer or a charge impulse transducer.

  Many of the discussions below address how to drive one or more pixels of an electro-optic display by transitioning from an initial gray level to a final gray level (which may or may not be different from the initial gray level). Focus on. The term “waveform” is used to indicate the total voltage for a time curve that is used to achieve a transition from one particular initial gray level to a particular final gray level. Typically, as shown below, such a waveform comprises a plurality of waveform elements, which are essentially rectangular (ie, in this case, a defined element has a constant voltage for a period of time. The element may be referred to as a “voltage pulse” or a “drive pulse”. The term “drive scheme” refers to a set of waveforms sufficient to achieve all possible transitions between gray levels for a particular display.

  Several types of electro-optic displays are known. One type of electro-optic display is a rotating two-color member type. For example, Patent Document 7, Patent Document 8, Patent Document 9, Patent Document 10, Patent Document 11, Patent Document 12, Patent Document 13, Patent Document 14 Patent Document 15 describes. (This type of display is often referred to as a “rotating dichroic ball” display, but the term “rotating dichroic member” is more accurate in some of the above patents because the rotating member is not spherical. Such a display uses a large number of bodies (typically spherical or cylindrical) having two or more sections with different optical properties and internal dipoles. These bodies are drifted in vesicles filled with liquid in the matrix, which are filled with liquid so that the bodies rotate freely. The display of the display is changed to apply an electric field to it, thereby rotating the body to various positions and changing which section of the body is seen through the viewing surface.

  Another type of electro-optic display uses an electrochromic medium, for example, an electrochromic medium in the form of a nanochrome film, the nanochrome film comprising at least an electrode formed in a portion from a semiconductor metal oxide and the electrode And a plurality of dye molecules capable of reversible color change. For example, see Non-Patent Document 1 and Non-Patent Document 2. See also Non-Patent Document 3. This type of nanochrome film is also described, for example, in US Pat. This type of medium is also typically bistable.

  Another type of electro-optic display that has been the subject of intensive research and development for many years is a particle-based electrophoretic display in which multiple charged particles move in a fluid under the influence of an electric field. . Electrofluidic displays may have attributes of good brightness and contrast, wide viewing angle, state bistability, and low power consumption compared to liquid crystal displays. Nevertheless, the long term image quality problems of these displays have prevented their widespread use. For example, the particles that make up electrophoretic displays tend to sink, resulting in an inappropriate service life of these displays.

  As can be seen from the above, the electrophoretic medium requires the presence of a fluid. In most prior art electrophoretic media, the fluid is a liquid, but the electrophoretic media can be made using a gaseous fluid. For example, see Non-Patent Document 4 and Non-Patent Document 5. Patent Document 19, Patent Document 20, Patent Document 21, Patent Document 22, Patent Document 23, Patent Document 24, Patent Document 25, Patent Document 26, Patent Document 27, Patent Document 28, Patent Document 29, Patent Document 30, Patent See also Literature 31 and Patent Literature 32. When such a gas-based electrophoretic medium is used in an orientation that allows particle subsidence, for example, in a label where the medium is placed in a vertical plane, the gas-based electrophoretic medium is subject to particle subsidence. It appears to be susceptible to the same types of problems as the resulting liquid-based electrophoretic media. Indeed, particle settlement appears to be a more serious problem in gas-based electrophoretic media than in liquid-based electrophoretic media. The reason is that the low viscosity of the gaseous fluid compared to the liquid fluid allows more rapid settling of the electrophoretic particles.

  A number of patents and applications assigned to or under the name of Massachusetts Institute of Technology (MIT) and E Ink Corporation describe recently published and encapsulated electrophoretic media. Such an encapsulated medium comprises a number of small capsules, each of which is an internal phase containing electrophoretically movable particles suspended in a fluid, and a capsule wall surrounding the internal phase Is provided. Typically, the capsule itself is held in a polymeric binder, forming a coherent layer located between the two electrodes. This type of encapsulated medium is described in, for example, Patent Document 6, Patent Document 18, and Patent Documents 33-167.

  Many of the aforementioned patents and patent applications indicate that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thus creating a so-called “polymer dispersed electrophoretic display”. Recognize that in the display, the electrophoretic medium includes a plurality of discrete droplets of electrophoretic fluid and a continuous phase of polymeric material. Also, many of the aforementioned patents and patent applications show that the discrete droplets of electrophoretic fluid in such polymer dispersed electrophoretic displays are capsules or microcapsules, even though no discrete capsule membrane is associated with each individual droplet. Recognize that it can be considered a capsule. For example, see the aforementioned patent document 168. Thus, for the purposes of this application, such polymer dispersed electrophoretic media are considered subspecies of encapsulated electrophoretic media.

  Encapsulated electrophoretic displays are typically printed or coated on a wide variety of flexible and rigid substrate displays without suffering from the failure mode of clustering and subsidence of conventional electrophoretic devices. Provide additional benefits such as capabilities. (Use of the word “printing” includes, but is not limited to, the following techniques: pre-metered coatings such as patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating; (Knife over roll) coating; roll coating such as forward and backward roll coating; gravure coating; dip coating; spray coating; uneven coating; spin coating; brush coating; air knife coating; silk screen printing treatment; electrostatic printing treatment; Inkjet printing processing; and other similar techniques) As a result, the display is flexible. Further, since the display media can be printed (using a variety of methods), the display itself can be made inexpensively.

  A related type of electrophoretic display is the so-called “microcell electrophoretic display”. In microcell electrophoretic displays, charged particles and fluid are not encapsulated in capsules, but instead are held in a plurality of cavities formed in a carrier medium, typically a polymer film. For example, both are described in Sipix Imaging, Inc. See U.S. Pat. Nos. 6,099,069 and 1,096,170, assigned to U.S. Pat.

  Other types of electro-optic media may also be used in the display of the present invention.

  Although electrophoretic media are often opaque (eg, in many electrophoretic media, particles substantially block the transmission of visible light through the display) and operate in reflective mode, many electrophoretic displays Is made to operate in a so-called “shutter mode”, in which one display state is substantially opaque and in the other state it is light transmissive. For example, see the above-mentioned Patent Document 42 and Patent Document 43, and Patent Document 171, Patent Document 172, Patent Document 173, Patent Document 174, and Patent Document 175. A dielectrophoretic display that is similar to an electrophoretic display, but that relies on field strength variations, can operate in a similar mode. See Patent Document 176.

  Other electro-optic displays that display bistable or multistable operation of particle-based electrophoretic displays, and similar operations (such displays are referred to as “impulse-driven displays” for the sake of convenience below) are conventional liquid crystals (“ LC ") in marked symmetry with the action of the display. Twisted nematic liquid crystal operation is not bistable or multi-stable and operates as a voltage transducer so that when a given electric field is applied to a pixel of such a display, the pixel, regardless of the gray level previously present in that pixel A specific gray level is generated at. In addition, LC displays are driven in only one direction (from non-transparent or “dark” to transmissive or “bright”), and the reverse transition from bright to darker states is achieved by reducing or eliminating the electric field. Is done. Finally, the gray level of the pixels of the LC display is not sensitive to the polarity of the electric field, but only to the amplitude, and certainly for technical reasons, commercial LC displays usually have frequent drive field polarities. Reverse at regular intervals. In contrast, the bistable electro-optic display operates as an impulse transducer towards the first approximation, so that the final state of the pixel depends on the applied electric field and the time applied to this electric field. Not only depends on the state of the pixel before the application of the electric field.

  It may initially appear that the ideal way to address such impulse-driven electro-optic displays is the so-called “general grayscale image flow”. In that general grayscale image flow, the controller configures each writing of the image such that each pixel transitions directly from its initial gray level to its final gray level. However, there are necessarily some errors in writing images on impulse driven displays. Some such errors that are actually encountered include:

  (A) Prior state dependence; for at least some electro-optic media, the impulse required to switch the pixel to a new optical state depends not only on the current and required optical state, but also on the previous optical state of the pixel. Also depends on.

  (B) Pause time dependence; For at least some electro-optic media, the impulse required to switch a pixel to a new optical state depends on the time the pixel was in its various optical states. The exact nature of this dependence is not well understood, and in general, the longer the pixel is in the current optical state, the more impulses are required.

  (C) Temperature dependence; the impulse required to switch the pixel to a new optical state is very temperature dependent.

  (D) Humidity dependence; the impulse required to switch the pixel to a new optical state depends on the ambient humidity for at least some types of electro-optic media.

  (E) Mechanical uniformity; the impulse required to switch the pixel to a new optical state can be affected by mechanical variations in the display, such as variations in the thickness of the electro-optic medium or associated lamination adhesive. Other types of mechanical inhomogeneities can arise from the inevitable variations between different production batches of media, production tolerances and material variations.

  (F) Voltage error; the actual impulse applied to the pixel necessarily differs from the theoretically applied impulse due to the inevitable slight errors in the voltage supplied by the driver.

The general grayscale image flow suffers from the “error accumulation” phenomenon. For example, assume that temperature dependence results in a positive 0.2 L ^* error at each transition. (L ^* has the usual CIE definition, where R is the reflectivity and R ₀ is the standard reflectivity value,
L ^* = 116 (R / R ₀ ) ¹ / 3-16)
After 50 transitions, this error accumulates up to 10L ^* . Perhaps more realistically, the average error at each transition expressed in terms of the difference between the theoretical and actual reflectivity of the display is ± 0.2 L ^* . After 100 consecutive transitions, the pixels display their average deviation from their 2L ^* expected state. Such deviations are clearly visible to the average observer for certain types of images.

  The error accumulation phenomenon applies not only to errors due to temperature, but also to all types of errors listed above. As described in the aforementioned patent document 119, such errors can be compensated, but only to a limited accuracy. For example, temperature errors can be compensated by using a temperature sensor and lookup, but the temperature sensor can have a limited resolution and read a temperature slightly different from the temperature of the electro-optic medium. Similarly, previous state dependencies can be compensated for by storing previous states and by using a multidimensional transition matrix, but the controller memory can store the number of states that can be recorded and the transition matrix that can be stored. Limit the size of this, and put limits on the accuracy of this type of compensation.

  Therefore, the general grayscale image flow requires very precise control of the applied impulse to produce good results, and empirically, in the current state of the electro-optic display technology, the general grayscale image flow is , Has proven infeasible on commercial displays.

  Almost all electro-optic media have an inherent reset (error limit) mechanism, ie, the extreme (typically black and white) optical state of the media that functions as an “optical rail”. After a particular impulse is applied to a pixel of an electro-optic display, that pixel cannot obtain a whiter (or blacker) one. For example, in an encapsulated electrophoretic display, after a specific impulse is applied, all electrophoretic particles hit each other or the capsule wall and cannot move any further, thus limiting the optical state or optical rail Is generated. Due to the electrophoretic particle size and charge distribution in such media, some particles hit the rail before other particles, creating a “soft rail” phenomenon, thereby limiting the ultimate optical state of the transition. When approaching the black and white state, the required impulse accuracy is reduced, while the required optical accuracy increases dramatically at transitions that end near the center of the optical range of the pixel.

  Various drive schemes for electro-optic displays having the advantages of optical rails are known. For example, the related description in FIGS. 9 and 10 of the aforementioned patent document 119 and paragraphs [0177] to [0180] describes a “slide show” drive scheme, in which the entire display has a new image. Driven to at least one optical rail before writing. Obviously, a pure generic grayscale image flow drive scheme cannot rely on using optical rails to prevent errors in gray levels. The reason is that in such a drive scheme, any pixel can undergo an infinite number of changes in gray scale without touching either optical rail at all.

Before proceeding further, it is desirable to more accurately define the slide show drive scheme. The basic slide show driving scheme is achieved by making a transition from an initial optical state (gray level) to a final (desired) optical state (gray level) to a finite number of intermediate states, in which case That is, the minimum number is 1. Preferably, the intermediate state is at or near the extreme state of the electro-optic medium used. Transitions vary from pixel to pixel in the display. The reason is that the transition depends on the initial and final optical states. The waveform for a particular transition for a given pixel of the display is represented as follows: When there is at least one intermediate or goal state between the initial optical state R ₂ and the final optical state R _1,
R ₂ → Goal ₁ → Goal ₂ → ・ ・ ・ → Goal _n → R ₁ (Scheme 1)
It is. The goal state is generally a function of the initial and final optical states. The presently preferred number of intermediate states is 2, although more or fewer intermediate states can be used. Each individual transition within the overall transition is accomplished using sufficient waveform elements (typically voltage pulses) to drive the pixel from one state of the sequence to the next. For example, in the above symbolically waveform shown, the transition from R ₂ to the goal ₁ is typically achieved using a wave element or a voltage pulse. The waveform element may have a single voltage for a finite time (ie, a single voltage pulse) or may include various voltages so that an accurate goal ₁ state is achieved. This waveform element is followed by a second waveform element to achieve the transition from goal ₁ to goal ₂ . If only two goal states is used, the third waveform element is followed by the second waveform element, the third waveform element drives the pixel from the goal ₂ state to the final optical state R _1. The goal state may be independent of both R ₂ and R ₁ or may depend on one or both.

  The present invention seeks to provide an improved slide show drive scheme for electro-optic displays that achieves improved control of gray levels. The present invention is not particularly dedicated, but is intended for use in a pulse width modulation drive scheme, where the voltage applied to any given pixel of the display at any given time is , V can be any voltage, it can only be -V, 0, or + V. More specifically, the present invention provides two distinct improvement types in a slide show drive scheme: (a) inserting a correction element into the base waveform for such drive scheme, and (b) at least being Arranging the drive scheme such that the gray level is approached from a further optical rail than the desired gray level.

In another aspect, the invention relates to downtime compensation in a drive scheme for an electro-optic display. As discussed in the MEDEOD application, at least in the case of many particle-based electro-optic displays, changing a given pixel by an equivalent change in gray scale (determined by the human eye or standard optics) It has been found that the impulse required for this is not necessarily a constant and is not commutative. For example, consider a display in which each pixel can display 0 (white), 1, 2, or 3 (black) gray levels, advantageously with space. (The space between levels is linear in percent reflectance, as measured by the eye or instrument, but other spaces can also be used. For example, the space can be linear in L ^* or a specific gamma 2.2 gamma is often employed for monitors, and if an electro-optic display is used as an alternative to a monitor, a similar gamma is preferably used.) Pixel level 0 It was found that the impulse required to change from 1 to level 1 (hereinafter referred to as “0-1 transition” for convenience) is often not the same as the impulse required for the 1-2 or 2-3 transition. Furthermore, the impulse required for the 1-0 transition is not necessarily the same as the inverse of the impulse required for the 0-1 transition. Furthermore, some systems (for example) vary the impulse required for a 0-1 transition somewhat according to whether a particular pixel undergoes a 0-0-1, 1-0-1, or 3-0-1 transition. Seems to display a "memory" effect. (The notation “xyz” denotes a sequence of optical states that is performed in time sequential when x, y, and z are all in optical states 0, 1, 2, or 3.) These problems Can be reduced or resolved by driving all the pixels of the display to one of the extreme states for a substantial period of time before driving the required pixels to another state, but the resulting dark color This “flash” is often unacceptable. For example, an e-book reader may want to scroll down the body of the book on the screen, and may be distracted or lose position if the display needs to flash dark black or white frequently. obtain. Further, such a flash of the display can increase the energy consumption of the display and reduce the operating life of the display. Finally, at least in some cases, the impulse required for a particular transition is affected by temperature and the total operating time of the display, and compensates for these factors to ensure accurate grayscale execution. It turned out to be desirable.

  As briefly mentioned above, in at least some cases, it has been found that the impulse required for a given transition in a bistable electro-optic display varies with the residence time of the pixel in the optical state of the pixel. The term "" was used in some conventional documents, but this phenomenon is hereinafter referred to as "downtime dependence" or "DTD". Therefore, it may be desirable or even necessary in some practical cases to vary the impulse applied for a given transition as a function of pixel pause time in the initial optical state of the pixel.

The downtime dependent phenomenon will now be described in more detail with reference to FIG. 1 of the accompanying drawings. FIG. 1 shows the reflectivity of a pixel as a function of time of the sequence of transitions denoted R ₃ → R ₂ → R ₁ . At this time (when generalizing the names used above), each of the R _k nomenclatures indicates the gray level in the sequence of gray levels, R with a higher index is before R with a lower index Occurs. Also shown are transitions between R ₃ and R ₂ and between R ₂ and R ₁ . DTD is the change in the final optical state R ₁ caused by the change in time spent in the optical state R ₂ , referred to as the rest period. By choosing different waveforms with different pause times or different ranges of pause times in previous optical states, DTD may be compensated. This method of compensation is referred to as “dwell time compensation”, “DTC”, or simply “time compensation”.

  However, such DTC can conflict with other desirable characteristics of the drive scheme. In particular, for reasons discussed in detail in the MEDEOD application, for many electro-optic displays, for any series of transitions that start and end in the same optical state, the applied impulse (ie, applied voltage over time). It is highly desirable to ensure that the drive scheme used is direct current (DC) balanced, in the sense that the integral) is zero. This ensures that the net impulse (also called “DC imbalance”) experienced by any pixel of the display is defined by a known value, regardless of the exact series of transitions that the pixel undergoes. For example, a 15V, 300 ms pulse can be used to drive a pixel from white to black. After this transition, the pixel undergoes a DC unbalanced impulse of 4.5V seconds. If a -15V, 300 ms pulse is used to drive the pixel back to white, the pixel is DC balanced for all excursions from white to black and back to white. This DC balance persists during all possible excursions from one initial optical state to a series of optical states that are the same as or different from the first optical state and then back to the first optical state.

  The drive scheme can be compensated for downtime by adding or removing voltage features from the base drive scheme. For example, one may start with a driving scheme for a two optical state (black and white) display, which includes the following four waveforms:

This drive scheme is DC balanced. The reason is that any series of transitions that return a pixel to its original optical state is DC balanced, ie, the net region under the voltage profile for the entire series of transitions is zero.

  Optical errors can arise from the DTD of the display. For example, a pixel may start in a white state, drive to a black state, perform a primary pause, and then return to a white state. The final white state reflectivity is a function of the time spent in the black state.

  It is desirable to have a very small DTD. If this is not possible in a particular electro-optic display, it is desirable to compensate for DTD by selecting different waveforms for different ranges of pause times in previous optical states, according to one aspect of the invention. For example, the final white state in the present example can be found to be brighter after a short rest time in the previous black state than after a long rest time in the previous black state. One pause compensation scheme is to modify the duration of the pulse that makes the pixel layer black to white to attenuate this DTD in the final optical state. For example, when the pause time in the previous black state is short, the pulse length in the transition from black to white can be shortened, and the pulse can be maintained in a long state for a long pause time in the previous black state. This tends to produce a darker white for shorter pause times of the previous state, which diminishes the effects of DTD. For example, a waveform from black to white that varies with the rest time in the black state can be selected according to Table 2 below.

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O'Regan, B.M. Et al., Nature 1991, 353, 737 Wood, D.D. , Information Display, 18 (3), 24 (March 2002). Bach, U. Adv. Mater. , 2002, 14 (11), 845 Kitamura, T .; Et al., “Electrical toner for electronic paper-like display”, IDW Japan, 2001, Paper HCS1-1. Yamaguchi, Y .; “Toner display using insulative particles charged triboelectrically”, IDW Japan, 2001, Paper AMD4-4).

  The problem with the drive scheme approach to DTC is that the drive scheme as a whole is no longer DC balanced. The impulse for the black to white transition is a function of the time spent in the black state, and similarly, the impulse for the white to black transition can be a function of the pause time in the white state, so black, Net impulses over a sequence of white and black are generally not DC balanced. For example, this sequence uses a -15V voltage pulse for a 280 ms = -4.2V second impulse, with a black-to-white transition after a short pause in black, and a subsequent 6V second impulse. Assume that it is performed by a white-to-black transition after a long pause in the white state, using a voltage pulse of 15V for 400 milliseconds. The net impulse in this sequence (black-white-black loop) is −4.2 V seconds + 6 V seconds = −1.8 V seconds. By repeating this loop, a DC imbalance rises, which can be detrimental to display performance.

  Thus, this aspect of the invention provides a method for DC balance waveform or drive scheme dwell time compensation that preserves DC balance of the waveform or drive scheme.

  Another aspect of the present invention relates to a method and apparatus for driving an electro-optic display capable of rapid response to user input. The aforementioned MEDEOD application describes several methods and controllers for driving electro-optic displays. Most of these methods and controllers utilize a memory with two image buffers, the first image buffer storing the first or initial image (present at the beginning or rewriting of the display transition), and the first The second image buffer stores the final image, and the second buffer requires the final image to be placed on the display after rewriting. The controller compares the initial and final images, and if they are different, it applies a drive voltage to the various pixels of the display, which drive voltage is displayed at the end of the rewrite (alternatively called update) As formed above, the pixel is subjected to a change in the optical state.

  However, in most of the methods and controllers described above, once an update is initiated, the update operation is “atomic” in the sense that the memory cannot accept any new image data until the update is complete. This means that the controller will not respond to user input until an update is achieved, for example when a display is required to be used for an application that accepts user input via a keyboard or similar data input device. Cause difficulties. For electrophoretic media where the transition between two extreme optical states can take several hundred milliseconds, this non-response period can vary from about 800 milliseconds to about 1800 milliseconds, the majority of this period being electro-optic material. Is attributed to the required update cycle. The duration of the non-response period can be reduced by removing some performance artifacts that increase the update time and by improving the response speed of the electro-optic material, but with such technology alone, It is unlikely that the non-response period will be reduced below about 500 milliseconds. This is still longer than desired in interactive applications, such as electronic dictionaries where the user expects a quick response to user input. Accordingly, there is a need for an image update method and controller with reduced non-response periods.

  This aspect of the invention utilizes the concept of asynchronous image update to reduce the duration of the non-response period. (See the paper by Zhou et al., “Driving an Active Matrix Electrophoretic Display”, Proceedings of the SID 2004) The method described in this paper is a slight increase in controller complexity and memory requirements The structure developed for gray scale image displays is used to reduce the response period by up to 65 percent compared to prior art methods and controllers.

  Finally, the present invention relates to a method and apparatus for driving an electro-optic display in which the data used to define the drive scheme is compressed in a special way. The aforementioned MEDEOD application describes a method and apparatus for driving an electro-optic display in which data defining the drive scheme (or drive schemes) used is stored in one or more look-up tables (“LUTs”). Is described. Such an LUT must, of course, contain data defining a waveform for each waveform of each drive scheme, and a single waveform typically requires multiple bytes. As described in the MEDEDOD application, the LUT may take into account more than one optical state, along with adjustments for factors such as temperature, humidity, media operating time, and the like. Therefore, the amount of memory required to hold waveform information can be important. It is desirable to reduce the amount of memory allocated to waveform information in order to reduce the cost of the display controller. A simple compression scheme that can be practically accommodated in a display controller or host computer helps to reduce the cost of the display controller. The present invention relates to a simple compression scheme that appears to be particularly advantageous for electro-optic displays.

Accordingly, in one aspect, the present invention provides a method for driving an electro-optic display having at least one pixel capable of achieving at least three different gray levels including two extreme optical states. The method includes applying a base waveform to the pixel, the base waveform being followed by at least one reset pulse sufficient to drive the pixel to or near one of the extreme optical states. And at least one set pulse sufficient to drive the pixel to a different gray level than the one extreme optical state described above. However, the base waveform is modified by at least one of the following:
(A) inserting at least one balanced pulse pair into the base waveform; (b) deleting at least one balanced pulse pair from the base waveform; (c) inserting at least one period of zero voltage into the base waveform; “Balanced pulse pair” refers to a series of two pulses of opposite polarity such that the total impulse of the balanced pulse pair is substantially zero.

  For convenience, the method of the present invention is referred to as the “balanced pulse pair slide show” or “BPPSS” method of the present invention. When such a method includes modification of the base waveform by insertion or deletion of at least one balanced pulse pair (“BPP”), each of the two pulses of the balanced pulse pair is constant voltage but opposite in polarity and long Are equal. When the base waveform modification includes the deletion of at least one BPP, the period in the base waveform occupied by each deleted BPP can be replaced by a period of zero voltage. Alternatively, other elements of the base waveform may be shifted in time to account for the period previously occupied by each deleted BPP, with zero voltage periods occupied by each deleted BPP. It can be inserted at a different time point than the previous time point.

  In a preferred form of the BPPSS method of the present invention, the base waveform is continuous and includes a first reset pulse sufficient to drive the pixel to or near one of its extreme optical states and the other extreme optics. A second reset pulse sufficient to drive at or near one of the states, and at least one set pulse.

  The BPPSS method may be performed using a drive network capable of voltage modulation, pulse width modulation, or both. However, it has been found to be particularly useful for a tri-level drive scheme in which a voltage of 0, + V or −V is applied to the pixel at any time when V is a predetermined drive voltage.

  For reasons explained in detail below, in the BPPSS method, the total number of modifications to the base waveform (the total number of inserted or deleted balanced pulse pairs and zero voltage inserted periods) may be limited. desirable. In general, this total number of modifications does not exceed 6, preferably does not exceed 4, and preferably does not exceed 2.

  As discussed in the aforementioned MEDEOD application, the BPPSS method of the present invention is preferably DC balanced, and whenever possible, each individual waveform of the drive scheme used should also be DC balanced.

  The BPPSS method of the present invention may be used with any type of electro-optic display discussed above. Thus, the display may comprise, for example, a rotating dichroic member or an electrochromic medium. Alternatively, the display may comprise an electrophoretic electro-optic medium comprising a plurality of charged particles in a fluid that are capable of moving in the fluid when an electric field is applied to the fluid. In this type of display, the fluid can be a gas or a liquid. Charged particles and fluids can be confined within multiple capsules or microcells.

  The present invention can be extended to display controllers, application specific integrated circuits, or software code configured to perform the BPPSS method of the present invention.

  In another aspect, the present invention provides a method of driving an electro-optic display having a plurality of pixels, each pixel having the ability to achieve four different gray levels, including two extreme optical states. The method includes applying a waveform to each pixel, the waveform comprising a reset pulse sufficient to drive the pixel to or near one of the extreme optical states, followed by the above And a set pulse sufficient to drive the pixel to a final gray level different from one of the extreme optical states. In this case, the reset pulse is chosen so that the image on the display immediately before the set pulse is substantially a reverse monochrome projection of the final image following the set pulse.

  For convenience, this method of the present invention is referred to as the “reverse monochrome projection” or “IMP” method of the present invention. As described in more detail below, a monochrome projection of a grayscale image is a projection, in which all pixels in the grayscale image have a single extreme optical state, or a predetermined threshold (eg, A pixel that is in a gray state that is closer to its extreme optical state than a white or light gray pixel) is changed to its extreme optical state (e.g., white) or a state close thereto, while an inverse extreme optical state or a predetermined threshold (e.g. A pixel that is in a gray state that is closer to its inverse extreme optical state than a black or dark gray pixel) is changed to its inverse extreme optical state (eg, black) or closer to it. Inverse monochrome projection is the opposite of monochrome projection.

  In a preferred form of the IMP method of the present invention, a waveform is applied to each pixel, the waveform comprising a first reset pulse sufficient to drive each pixel to or near one of its extreme optical states; A second reset pulse sufficient to drive each pixel to or near one of the other extreme optical states and a set pulse, the first reset pulse being a second reset pulse It is chosen so that the image on the previous display is essentially a monochrome projection of the final image following the set pulse.

In the IMP method, the waveform can be modified by:
(A) inserting at least one balanced pulse pair into the waveform; (b) deleting at least one balanced pulse pair from the waveform; (c) inserting at least one period of zero voltage into the waveform; As defined above. In such a modified waveform, the two pulses of the balanced pulse pair can each be a constant voltage, but are of opposite polarity and of equal length. When the base waveform modification includes the deletion of at least one BPP, the period in the base waveform occupied by each deleted BPP can be replaced by a period of zero voltage. Alternatively, other elements of the base waveform may be shifted in time to account for the period previously occupied by each deleted BPP, with zero voltage periods occupied by each deleted BPP. It can be inserted at a different time point than the previous time point.

  As with the BPPSS method, the IMP method of the present invention can be implemented using a drive network capable of voltage modulation, pulse width modulation, or both. However, the IMP method has been found to be particularly useful for tri-level drive schemes where a voltage of 0, + V or −V is applied to the pixel at any time when V is a predetermined drive voltage. . Also, as for the BPPSS method, the IMP method can be used with any type of electro-optic display discussed above. Thus, for example, the display may comprise rotating dichroic members or electrochromic media. Alternatively, the display may comprise an electrophoretic electro-optic medium comprising a plurality of charged particles in a fluid that are capable of moving in the fluid when an electric field is applied to the fluid. In this type of display, the fluid can be a gas or a liquid. Charged particles and fluids can be confined within multiple capsules or microcells.

  The present invention can be extended to display controllers, application specific integrated circuits or software code configured to perform the IMP method of the present invention.

In another aspect, the present invention provides a method for driving an electro-optic display having at least one pixel capable of achieving at least two different gray levels. At least two different waveforms are used for the same transition between specific gray levels, depending on the duration of the pixel pause time in the state where the transition is initiated, and these two waveforms differ from each other by at least one of the following: .
(A) inserting at least one balanced pulse pair (b) deleting at least one balanced pulse pair (c) inserting at least one period of zero voltage where "balanced pulse pair" is defined above As it was done.

  For convenience, this method of the present invention will be referred to as the “pause time compensated balanced pulse pair” or “DTCBPP” method of the present invention. In such a method, the entire drive scheme is very desirably DC balanced, and preferably all waveforms are themselves DC balanced. When such a method includes modification of the base waveform by insertion or deletion of at least one BPP, the two pulses of the balanced pulse pair are each constant voltage but opposite in polarity and are equal in length. When the base waveform modification includes the deletion of at least one BPP, the period in the base waveform occupied by each deleted BPP can be replaced by a period of zero voltage. Alternatively, other elements of the base waveform may be shifted in time to account for the period previously occupied by each deleted BPP, with zero voltage periods occupied by each deleted BPP. It can be inserted at a different time point than the previous time point.

  As with the BPPSS and IMP methods, the DTCBPP method of the present invention can be implemented using a drive network capable of voltage modulation, pulse width modulation, or both. However, the DTCBPP method has been found to be particularly useful for tri-level drive schemes where a voltage of 0, + V or -V is applied to the pixel at any given time when V is a predetermined drive voltage. . For reasons explained in detail below, it is desirable to limit the total number of modifications to the base waveform (ie, the total number of balanced pulse pairs inserted and deleted and zero voltage inserted periods) in the DTCBPP method. . In general, this total number of modifications does not exceed 6, preferably does not exceed 4, and preferably does not exceed 2.

  Also, as with BPPSS and IMP methods, the DTCBPP method can be used with any type of electro-optic display discussed above. Thus, for example, a display may comprise a rotating dichroic member or an electrochromic medium. Alternatively, the display may comprise an electrophoretic electro-optic medium comprising a plurality of charged particles in a fluid that are capable of moving in the fluid when an electric field is applied to the fluid. In this type of display, the fluid can be a gas or a liquid. Charged particles and fluids can be confined within multiple capsules or microcells.

  The present invention can be extended to display controllers, application specific integrated circuits, or software code configured to perform the DTCBPP method of the present invention.

In another aspect, the present invention provides two related methods for reducing the non-response period when the electro-optic display is updated. The first of these methods is for use when driving an electro-optic display having a plurality of pixels, each of which is capable of achieving at least two different gray levels. Comprises the following:
(A) providing a final data buffer configured to receive data defining a required final state of each pixel of the display; (b) storing data defining an initial state of each pixel of the display. Providing an initial data buffer configured to (c) providing a target data buffer configured to store data defining a target state for each pixel of the display; (d) in the initial data buffer The time when the data and the data in the final data buffer are different is determined, and when such a difference is found, the value in the target data is updated by the following method. (I) When the initial data buffer and the final data buffer contain the same value for a particular pixel, the target data buffer is set to this value; (ii) the initial data buffer is greater than the final data buffer for a particular pixel When containing a large value, set the target data buffer to the initial data buffer value plus the increment, and (iii) when the initial data buffer contains a value less than the final data buffer for a particular pixel The data buffer is set to a value obtained by subtracting the above-described increment from the value of the initial data buffer. (E) The image on the display is set as the initial state and the final state of each pixel, respectively, in the initial data buffer and in the target data buffer. Data and (F) After step (e), copy the data from the target data buffer to the initial data buffer (g) until the initial data buffer and the final data buffer contain the same data (d) to Repeating step (f) The second of these two methods is a plurality of pixels, each of which is capable of achieving at least three different gray levels. Is used when driving, and the method includes the following.
(A) providing a final data buffer configured to receive data defining a required final state of each pixel of the display; (b) storing data defining an initial state of each pixel of the display. Providing an initial data buffer configured to (c) providing a target data buffer configured to store data defining a target state for each pixel of the display; (d) polarity for each pixel of the display Providing a polar bit array configured to store bits; (e) determining when the data in the initial data buffer differs from the data in the final data buffer, and when such a difference is found, the polar bit array And the value in the target data buffer Update by the method. (I) When the values for a particular pixel in the initial data buffer and the final data buffer are different and the value in the initial data buffer represents the extreme optical state of the pixel, the polarity bit for the pixel represents a transition to the reverse extreme optical state. (Ii) When the value for a particular pixel in the initial data buffer and the final data buffer are different, the target data buffer is incremented to the value of the initial data buffer according to the associated value in the polarity bit array. Set to a positive or negative value (f) update the image on the display using the value in the initial data buffer and the value in the target data buffer as the initial and final states of each pixel, respectively (g ) After step (f) Copy data from the data buffer to the initial data buffer. (H) Repeat steps (e) to (g) until the initial data buffer and the final data buffer contain the same data. These two related methods are referred to as the “target buffer” or “TB” method of the present invention. When it is desirable to distinguish between the two methods, the former may be referred to as a “nonpolar target buffer” or “NPBT” method, and the latter may be referred to as a “polar target buffer” or “PTB” method. The present invention extends to a display controller, application specific integrated circuit, or software configured to perform the TB method of the present invention.

  Finally, this method provides a way to reduce the amount of data that needs to be stored to drive an electro-optic display. Accordingly, the present invention provides a method of driving an electro-optic display having a plurality of pixels, each of which is capable of achieving at least two different gray levels, the method comprising: , Comprising:

Storing a base waveform defining a series of voltages to be applied at a particular transition by a pixel between gray levels storing a multiplication factor applying the series of voltages to the pixel for a period determined by the multiplication factor By achieving the above specific transition, for convenience, this method is referred to as the “waveform compression” or “WC” method of the present invention.
(Item 1)
A method of driving an electro-optic display having at least one pixel capable of achieving at least three different gray levels including two extreme optical states, the method applying a base waveform to the pixel And the base waveform is different from the one extreme optical state followed by at least one reset pulse sufficient to drive the pixel to or near one of the extreme optical states At least one set pulse sufficient to drive the pixel to a gray level, and the base waveform is
(A) inserting at least one balanced pulse pair into the base waveform;
(B) deleting at least one balanced pulse pair from the base waveform; and
(C) inserting at least one period of zero voltage into the base waveform.
A “balanced pulse pair” means a series of two pulses of opposite polarity such that the total impulse of the balanced pulse pair is substantially zero.
(Item 2)
The method according to item 1, wherein the base waveform is transformed by inserting at least one balanced pulse pair or by deleting at least one balanced pulse pair.
(Item 3)
Item 3. The method of item 2, wherein the two pulses of the balanced pulse pair are each a constant voltage, but of opposite polarity and of equal length.
(Item 4)
3. A method according to item 2, wherein the period in the base waveform occupied by each deleted balanced pulse pair is replaced by a period of zero voltage.
(Item 5)
At least one balanced pulse pair is deleted from the base waveform, and other elements of the base waveform are shifted in time to occupy the period previously occupied by each deleted balanced pulse pair, and zero voltage The method of item 2, wherein the period of is inserted at a different time than the time occupied by the or each deleted balanced pulse pair.
(Item 6)
The base waveform continuously includes a first reset pulse sufficient to drive the pixel to or near one of the extreme optical states and the pixel to or near the other extreme optical state. The method according to item 1, comprising a second reset pulse sufficient to drive the at least one set pulse and the at least one set pulse.
(Item 7)
Item 2. The method of item 1, wherein a voltage of 0, + V or -V is applied to the pixel at any time when V is a predetermined drive voltage.
(Item 8)
Item 2. The method of item 1, wherein the sum of the inserted balanced pulse pair, the deleted balanced pulse pair, and the inserted period of zero voltage does not exceed 6.
(Item 9)
9. A method according to item 8, wherein the sum of the inserted balanced pulse pair, the deleted balanced pulse pair, and the inserted period of zero voltage does not exceed 4.
(Item 10)
Item 10. The method of item 9, wherein the sum of the inserted balanced pulse pair, the deleted balanced pulse pair, and the inserted period of zero voltage does not exceed 2.
(Item 11)
The method of item 1, wherein the method is DC equilibrium.
(Item 12)
The method of item 1, wherein the display comprises a rotating dichroic member or an electrochromic medium.
(Item 13)
The display comprises an electrophoretic electro-optic medium comprising a plurality of electrically charged particles in a fluid and having a plurality of particles capable of moving in the fluid when an electric field is applied to the fluid. The method according to item 1, wherein:
(Item 14)
Item 14. The method according to Item 13, wherein the fluid is a gas.
(Item 15)
14. The method of item 13, wherein the charged particles and the fluid are confined within a plurality of capsules or microcells.
(Item 16)
A display controller, application specific integrated circuit, or software code configured to perform the method of item 1.
(Item 17)
A method of driving an electro-optic display having a plurality of pixels, each of which is capable of achieving at least four different gray levels including two extreme optical states, the method comprising: Is applied to each pixel, and the waveform includes a reset pulse sufficient to drive the pixel to or near one of the extreme optical states of the pixel, followed by the one extreme optical state. And a set pulse sufficient to drive the pixel to a final gray level different from the reset pulse, wherein the reset pulse is the final image following the set pulse substantially following the set pulse. The method chosen to be a reverse monochrome projection of the image.
(Item 18)
A waveform including a first reset pulse, a second reset pulse, and the set pulse is applied to each pixel, and the first reset pulse drives each pixel to or near one of its extreme optical states. A second reset pulse sufficient to drive each pixel to or near its other extreme optical state, the first reset pulse sufficient to 18. The method of item 17, wherein the reset pulse is selected such that the image on the display immediately prior to the second reset pulse is a monochrome projection of the final image following the set pulse.
(Item 19)
The above waveform is
(A) inserting at least one balanced pulse pair into the waveform;
(B) deleting at least one balanced pulse pair from the waveform; and
(C) inserting at least one period of zero voltage into the waveform;
18. A method according to item 17, wherein “balanced pulse pair” means a series of two pulses of opposite polarity such that the total impulse of the balanced pulse pair is substantially zero.
(Item 20)
20. A method according to item 19, wherein the two pulses of the balanced pulse pair are each constant voltage but opposite in polarity and of equal length.
(Item 21)
20. A method according to item 19, wherein the period in the base waveform occupied by each deleted balanced pulse pair is replaced by a period of zero voltage.
(Item 22)
At least one balanced pulse pair is deleted from the base waveform, and the other elements of the base waveform are shifted in time to occupy the period previously occupied by each deleted balanced pulse pair, and zero voltage 20. A method according to item 19, wherein a period is inserted at a different time than the time occupied by each deleted balanced pulse pair.
(Item 23)
Item 18. The method of item 17, wherein a voltage of 0, + V, or -V is applied to the pixel at any time when V is a predetermined drive voltage.
(Item 24)
18. A method according to item 17, wherein the display comprises a rotating dichroic member or an electrochromic medium.
(Item 25)
The display comprises an electrophoretic electro-optic medium comprising a plurality of electrically charged particles in a fluid that are capable of moving in the fluid when an electric field is applied to the fluid. 18. The method according to item 17.
(Item 26)
26. A method according to item 25, wherein the fluid is a gas.
(Item 27)
26. A method according to item 25, wherein the charged particles and the fluid are confined in a plurality of capsules or a plurality of microcells.
(Item 28)
18. A display controller, application specific integrated circuit, or software code configured to perform the method of item 17.
(Item 29)
A method of driving an electro-optic display having at least one pixel capable of achieving at least two different gray levels, comprising:
At least two different waveforms are used for the same transition between specific gray levels, the specific gray level depends on the duration of the pause time of the pixel in the state where the transition begins, and these two waveforms are ,
(A) Insert at least one balanced pulse pair
(B) deleting at least one balanced pulse pair; and
(C) inserting at least one period of zero voltage;
A “balanced pulse pair” means a series of two pulses of opposite polarity such that the total impulse of the balanced pulse pair is substantially zero.
(Item 30)
30. The method of item 29, wherein the method is DC equilibrium.
(Item 31)
30. The method of item 29, wherein all waveforms are DC balanced.
(Item 32)
30. A method according to item 29, wherein the waveforms are different from each other by insertion of at least one balanced pulse pair or deletion of at least one balanced pulse pair.
(Item 33)
33. A method according to item 32, wherein the two pulses of the balanced pulse pair are each a constant voltage but have opposite polarities and are equal in length.
(Item 34)
33. A method according to item 32, wherein the period occupied by the or each deleted balanced pulse pair is replaced by a period of zero voltage.
(Item 35)
At least one balanced pulse pair is deleted and the other elements of the base waveform are shifted in time to occupy the period previously occupied by the or each deleted balanced pulse pair, and the period of zero voltage is 33. The method of item 32, wherein the method is inserted at a different time than the time occupied by the or each deleted balanced pulse pair.
(Item 36)
30. The method of item 29, wherein when V is a predetermined drive voltage, a voltage of 0, + V, or -V is applied to the pixel at any time.
(Item 37)
30. The method according to item 29, wherein the total number of inserted balanced pulse pairs, deleted balanced pulse pairs, and inserted period of zero voltage does not exceed 6.
(Item 38)
38. The method of item 37, wherein the total number of inserted balanced pulse pairs, deleted balanced pulse pairs, and zero voltage inserted period does not exceed four.
(Item 39)
39. The method of item 38, wherein the total number of inserted balanced pulse pairs, deleted balanced pulse pairs, and zero voltage inserted period does not exceed two.
(Item 40)
30. A method according to item 29, wherein the display comprises a rotating dichroic member or an electrochromic medium.
(Item 41)
The display comprises an electrophoretic electro-optic medium comprising a plurality of electrically charged particles in a fluid, the particles having a plurality of particles capable of moving in the fluid when an electric field is applied to the fluid. 30. The method according to item 29.
(Item 42)
42. A method according to item 41, wherein the fluid is a gas.
(Item 43)
42. A method according to item 41, wherein the charged particles and the fluid are confined in a plurality of capsules or a plurality of microcells.
(Item 44)
A display controller, application specific integrated circuit, or software code configured to perform the method of item 29.
(Item 45)
A method of driving an electro-optic display having a plurality of pixels, each of which is capable of achieving at least two different gray levels, the method comprising:
(A) providing a final data buffer configured to receive data defining a required final state of each pixel of the display;
(B) providing an initial data buffer configured to store data defining an initial state of each pixel of the display;
(C) providing a target data buffer configured to store data defining a target state for each pixel of the display;
(D) determining when the initial data buffer and the final data buffer are different, and updating such values in the target data buffer when such a difference is found, comprising: (i) the initial data buffer And the final data buffer contain the same value for a particular pixel, set the target data buffer to this value, and (ii) the initial data buffer is larger than the final data buffer for a particular pixel When including a value, set the target data buffer to a value of the initial data buffer plus an increment, and (iii) When the initial data buffer includes a value less than the final data buffer for a particular pixel The target data buffer is mapped to the increment from the initial data buffer value. By setting the eggplant value and performing the update,
(E) updating the image on the display using the data in the initial data buffer and the data in the target data buffer as the initial state and final state of each pixel, respectively;
(F) after step (e), copying the data from the target data buffer to the initial data buffer;
(G) repeating the steps (d) to (f) until the initial data buffer and the final data buffer have the same data;
Including the method.
(Item 46)
A method of driving an electro-optic display having a plurality of pixels, each of which is capable of achieving at least three different gray levels, the method comprising:
(A) providing a final data buffer configured to receive data defining a required final state of each pixel of the display;
(B) providing an initial data buffer configured to store data defining an initial state of each pixel of the display;
(C) providing a target data buffer configured to store data defining a target state for each pixel of the display;
(D) providing a polarity bit array configured to store a polarity bit for each pixel of the display;
(E) Determine when the data in the initial data buffer and the data in the final data buffer are different, and update the value in the polarity bit array and the value in the target data buffer when such a difference is found (I) when the value for the particular pixel in the initial data buffer is different from the value for the particular pixel in the final data buffer, and the value of the initial data buffer represents the extreme optical state of the pixel; Setting the polarity bit of the pixel to a value that represents a transition to the inverse extreme optical state, and (ii) when the value for a particular bit in the initial data buffer is different from the value for a particular pixel in the final data buffer; The target data buffer depends on the associated value in the polarity bit array And setting the increment to the value of the initial data buffer plus or minus value,
(F) updating the image on the display using the data in the initial data buffer and the data in the target data buffer as the initial and final states of each pixel, respectively;
(G) after step (f), copying the data from the target data buffer to an initial data buffer;
(H) repeating the steps (e) to (g) until the initial data buffer and the final data buffer have the same data;
Including the method.

As already mentioned, FIG. 1 of the accompanying drawings shows the reflectivity of a pixel of an electro-optic display as a function of time and shows a pause time dependent phenomenon. FIG. 2A shows the transition waveform in a prior art three pulse slideshow drive scheme of the type described in the aforementioned MEDEOD application. FIG. 2B shows different transition waveforms from FIG. 2A in a prior art three pulse slide show drive scheme of the type described in the aforementioned MEDEOD application. FIG. 2C shows the variation over time of the reflectivity of the pixel of the electro-optic display to which the waveform of FIG. 2A is applied. FIG. 2D shows the variation over time of the reflectance of a pixel of an electro-optic display to which the waveform of FIG. 2B is applied. FIG. 3A shows transition waveforms in a prior art two-reset pulse slideshow drive scheme of the type described in the aforementioned MEDEOD application. FIG. 3B shows different transition waveforms from FIG. 3A in a prior art two-reset pulse slideshow drive scheme of the type described in the aforementioned MEDEOD application. FIG. 4A shows balanced pulse pairs that can be used to modify prior art slide show waveforms, such as those shown in FIGS. 2A, 2B, 3A and 3B, in accordance with the BPPSS method of the present invention. FIG. 4B shows balanced pulse pairs that can be used to modify prior art slide show waveforms, such as those shown in FIGS. 2A, 2B, 3A and 3B, in accordance with the BPPSS method of the present invention. FIG. 4C shows balanced pulse pairs that can be used to modify prior art slide show waveforms such as those shown in FIGS. 2A, 2B, 3A and 3B in accordance with the BPPSS method of the present invention. FIG. 5A shows the waveforms of a prior art two-reset pulse slideshow driving scheme. FIG. 5B shows the BPPSS waveform of the present invention generated by modifying the waveform of FIG. 5A. FIG. 5C shows the BPPSS waveform of the present invention generated by modifying the waveform of FIG. 5A. FIG. 5D shows the BPPSS waveform of the present invention generated by modifying the waveform of FIG. 5A. FIG. 6A shows the same prior art base waveform as in FIG. 5A. FIG. 6B shows the BPPSS waveform of the present invention generated by deleting the balanced pulse pair from the base waveform of FIG. 6A. FIG. 6C shows the BPPSS waveform of the present invention generated by deleting the balanced pulse pair from the base waveform of FIG. 6A. FIG. 6D shows the BPPSS waveform of the present invention generated by deleting the balanced pulse pair from the base waveform of FIG. 6A. FIG. 7A shows the BPPSS waveform of the present invention generated by inserting a balanced pulse pair between two base waveform elements of the base waveform. FIG. 7B shows a further BPPSS waveform of the present invention generated by inserting the same balanced pulse pair as in FIG. 7A into a single base waveform element of the same base waveform as in FIG. 7A. FIG. 8A shows the same prior art base waveform as in FIGS. 5A and 6A. FIG. 8B shows the BPPSS waveform of the present invention generated by inserting periods of zero voltage at different locations into the base waveform of FIG. 8A. FIG. 8C shows the BPPSS waveform of the present invention generated by inserting periods of zero voltage at different locations into the base waveform of FIG. 8A. FIG. 8D shows the BPPSS waveform of the present invention generated by inserting periods of zero voltage at different locations into the base waveform of FIG. 8A. FIG. 9A shows a prior art waveform that can be modified to produce the BPPSS waveform of the present invention. FIG. 9B shows a prior art waveform that can be modified to produce the BPPSS waveform of the present invention. FIG. 9C shows the BPPSS waveform of the present invention generated by inserting two balanced pulse pairs into the base waveform of FIG. 9B. FIG. 9D shows the BPPSS waveform of the present invention generated by inserting a balanced pulse pair and a zero voltage period into the base waveform of FIG. 9B. FIG. 10A shows a further BPPSS waveform of the present invention generated by modifying the base waveform of FIGS. 9A and 9B. FIG. 10B shows a further BPPSS waveform of the present invention generated by modifying the base waveform of FIGS. 9A and 9B. FIG. 10C shows a further BPPSS waveform of the present invention generated by modifying the base waveform of FIGS. 9A and 9B. FIG. 11A shows a further BPPSS waveform of the present invention generated by modifying the base waveform of FIGS. 9A and 9B. FIG. 11B shows a further BPPSS waveform of the present invention generated by modifying the base waveform of FIGS. 9A and 9B. FIG. 11C shows a further BPPSS waveform of the present invention generated by modifying the base waveform of FIGS. 9A and 9B. FIG. 12 is a symbolic representation of the inverse monochrome projection method of the present invention. FIG. 13 illustrates how the gray level of a grayscale image is mapped to the monochrome projection of the image, as can be achieved in the preferred inverse monochrome projection method of the present invention. FIG. 14 shows selected waveforms used during the first inverse monochrome projection method of the present invention. FIG. 15 shows selected waveforms used during the first inverse monochrome projection method of the present invention. FIG. 16 is a symbolic representation of the further inverse monochrome projection method of the present invention, similar to the symbolic representation of FIG. FIG. 17 shows one modification of the IMP waveform shown in FIG. 14 by inserting balanced pulse pairs into the waveform. FIG. 18 shows one modification of the IMP waveform shown in FIG. 14 by deleting the balanced pulse pair from the waveform. FIG. 19 shows one further modification of the IMP waveform shown in FIG. 17 due to variations in the position of insertion of balanced pulse pairs. FIG. 20 shows one further modification of the IMP waveform shown in FIG. 18 due to the variation in position where the balanced pulse pair is deleted. FIG. 21 shows the waveform of a further IMP scheme of the present invention in a highly schematic manner. FIG. 22 is a graph showing gray levels generated by the drive scheme shown in FIG. FIG. 23 is a graph showing a modified form of the IMP drive scheme shown in FIG. 21 in the same manner as FIG. FIG. 24 is a graph showing gray levels generated by the modified drive scheme shown in FIG. FIG. 25A shows a set of pause time compensation waveforms used in the first pause time compensated balanced pulse pair drive scheme of the present invention. FIG. 25B shows a set of pause time compensation waveforms used in the first pause time compensated balanced pulse pair drive scheme of the present invention. FIG. 25C shows a set of pause time compensation waveforms used in the first pause time compensated balanced pulse pair drive scheme of the present invention. FIG. 25D shows a set of pause time compensation waveforms used in the first pause time compensated balanced pulse pair drive scheme of the present invention. FIG. 25E shows a set of pause time compensation waveforms used in the first pause time compensated balanced pulse pair drive scheme of the present invention. FIG. 26A shows a set of pause time compensation waveforms used in the second pause time compensated balanced pulse pair drive scheme of the present invention. FIG. 26B shows a set of pause time compensation waveforms used in the second pause time compensated balanced pulse pair drive scheme of the present invention. FIG. 26C shows a set of pause time compensation waveforms used in the second pause time compensated balanced pulse pair drive scheme of the present invention.

From the foregoing summary, it can be seen that the present invention provides a number of different methods for driving electro-optic displays, particularly bistable electro-optic displays, and apparatus and software adapted to perform such methods. Although the various methods of the present invention are described primarily below separately, it should be understood that a single electro-optic display, or component thereof, may use more than one aspect of the present invention. For example, a single electro-optic display may utilize the BPPSS side, the IMP side, and the DTCBPP side of the present invention. Also, preferred forms of balanced pulse pairs are common to all aspects of the invention that utilize such pulse pairs, and the size of such pulse pairs and the insertion of such pairs and / or zero voltage periods. It should also be noted that the preferred limit to the method of adjusting the length of the waveform to provide deletion is. Finally, it should be noted that the desirable DC balance drive scheme and DC balance waveform are common to all aspects of the present invention, as discussed in the aforementioned MEDEOD application and below.
Section A: Balanced Pulse Pair Slideshow Method and Apparatus As already mentioned, the BPPSS method of the present invention has at least one pixel capable of achieving at least three different gray levels including two extreme optical states. A method for driving an electro-optic display. The method includes applying a base waveform to the pixel, the base waveform being followed by at least one reset pulse sufficient to drive the pixel to or near one of the extreme optical states. The base waveform is modified by at least one of the following: at least one set pulse sufficient to drive the pixel to a final gray level different from the one extreme optical state described above.
(A) inserting at least one balanced pulse pair into the base waveform; (b) deleting at least one balanced pulse pair from the base waveform; (c) inserting at least one period of zero voltage into the base waveform; As stated, the term “balanced pulse pair” refers to a series of two pulses of opposite polarity such that the total impulse of the balanced pulse pair is substantially zero. In the preferred form of BPPSS, the two pulses of the balanced pulse pair are each constant voltage but opposite in polarity and of equal length. The term “base waveform element” or “BWE” may be used below to refer to any reset or set pulse of the base waveform. The insertion of balanced pulse pairs and / or zero voltage periods (hereinafter may be referred to as “gaps”) may be achieved within a single base element or between two consecutive waveform elements. All these modifications have the property of not affecting the net impulse of the waveform, which means the integration of the waveform voltage curve integrated over the duration of the waveform. The balanced pulse pair and zero voltage pause will of course have a zero net impulse. Although the BPP pulses are typically inserted adjacent to each other, this is not essential and the two pulses can be inserted remotely.

  If the modification of the base waveform according to the BPPSS method includes the deletion of at least one BPP, the period previously occupied by each deleted BPP may be left as a zero voltage period. Alternatively, this period can be “closed” early in time by moving some or all of the later waveform elements, but in this case to ensure that the full length of the waveform is maintained. It is usually necessary to insert a period of zero voltage into the waveform at some later stage of the waveform, typically at the last stage. The reason is that it is usually necessary to ensure that all pixels of the display are driven with the same length waveform. Of course instead, the period is “closed” by inserting a period of zero voltage at the beginning of the waveform, typically at the beginning of the waveform, and moving some or all of the earlier waveform elements later in time. Can be done.

  As already indicated, the BPPSS waveform of the present invention is a modification of the base slide show waveform described in the aforementioned MEDEOD application. As discussed above, the slide show waveform comprises one or more reset pulses that move the pixel to, or at least close to, one extreme optical state (optical rail), and the waveform includes two or more reset pulses. In each case, each reset pulse after the first moves the pixel to the opposite extreme optical state, thus traversing substantially the entire optical range. (For example, if the display uses an electro-optic medium with a (for example) 4-40 percent reflectivity range, each first subsequent reset pulse causes the pixel to traverse with 8-35 percent reflectivity.) If more than one reset pulse is used, the successive reset pulses must of course be of opposite polarity.

  The slide show waveform further comprises a set pulse that drives the pixel from the extreme optical state where the pixel was left intact by the last reset pulse to the desired final gray level of the pixel. When this desired final gray level is one of the extreme optical states and the last reset pulse leaves the pixel in this desired extreme optical state, the set pulse can be zero duration. Similarly, if the initial state of the pixel prior to the application of the slide show waveform is in one of the extreme states, the first reset pulse may be zero duration.

  The preferred BPPSS waveform of the present invention will now be described by way of example only with reference to the accompanying drawings.

  Figures 2A and 2B of the accompanying drawings show the waveforms used for two different transitions in a prior art (base) slideshow drive scheme of the type described in the aforementioned MEDEOD application. This slide show driving scheme uses three reset pulses for each transition. 2C and 2D show the corresponding variation over time in the optical state (reflectance) of the pixel to which the waveforms of FIGS. 2A and 2B are applied, respectively. In accordance with the rules used in the aforementioned MEDEOD application, FIGS. 2C and 2D are drawn such that the lower horizontal line represents the black extreme optical state, the upper horizontal line represents the white extreme optical state, and its intermediate level represents the gray state. . Waveform reset and start and end of set pulses are shown in dashed lines in FIGS. 2A and 2B, and the various BWEs (ie, reset and set pulses) are shown as consisting of 10 or less equal length pulses. . However, in general, the BWE can be of any arbitrary length, and if it is composed of a series of equal length pulses, more than 10 such pulses are typically used for the maximum length BWE.

The base waveforms shown in FIGS. 2A and 2C (denoted generally as 100) achieve a white-to-white transition (ie, a “transition” where both the initial and final states of the pixel are white extreme states). . Waveform 100 includes a first negative (ie, black-bound) reset pulse 102 that drives the pixel to its black extreme optical state and a second positive (white-bound) reset pulse 104 that drives the pixel to its white extreme optical state. And a third negative (blackbound) reset pulse 106 that drives the pixel to its black extreme optical state and a set pulse 108 that drives the pixel to its white extreme optical state. Each of the four pulses 102, 104, 106, and 108 has a duration of up to 10 units. (To avoid the frustration often referred to as “duration units”, these units are hereinafter referred to as “time units” or “TUs”.)
FIGS. 2B and 2D show dark gray to light gray transition waveforms (denoted generally as 150) using the same 3 reset pulse drive scheme as in FIGS. 2A and 2C. Waveform 150 includes a first reset pulse 152 that is negative and black-bound, like first reset pulse 102 of waveform 100. However, since the transition in which waveform 150 is used starts from a dark gray level, the duration of first reset pulse 152 (shown as four TUs) is shorter than the duration of reset pulse 102. The reason is that a shorter first reset pulse is necessary to bring the pixel to its black extreme optical state at the end of the first reset pulse. During the remaining six TUs of the first reset pulse 152, a zero voltage is applied to the pixel. (FIGS. 2B and 2D show a first reset pulse 152 having four TUs of negative voltage at the end of the relevant period, but this is optional and the periods of negative voltage and zero voltage are arranged as required. obtain.)
The second and third reset pulses 104 and 106 of waveform 150 are identical to the corresponding pulses of waveform 100. The set pulse 158 of the waveform 150 is positive and white like the set pulse 108 of the waveform 100. However, since the transition in which waveform 150 is used ends at a light gray level, the duration of set pulse 158 (shown as 7 TUs) is shorter than the duration of set pulse 108. The reason is that a shorter set pulse is required to bring a pixel to its final light gray level. During the remaining three TUs of the set pulse 158, a zero voltage is applied to the pixel. (Again, the distribution of the positive and zero voltage periods within the set pulse 158 is optional and the periods can be arranged as required.)
From the foregoing, in the prior art slide show driving scheme shown in FIGS. 2A-2D, the duration of the first reset pulse and the set pulse varies according to the initial and final states of the pixel, respectively, and in some cases, One or both can be zero duration. For example, in the drive scheme of FIGS. 2A-2D, the black-to-black transition may have a first reset pulse with zero duration (because the pixel has reached the end of the first reset pulse 102 and 152). May have a zero duration set pulse (because at the end of the third reset pulse 106, the pixel is already in the required extreme black optical state). Is).

  In general, it is desirable to keep the entire waveform duration as short as possible so that the display can be rewritten quickly. This is for obvious reasons that users prefer displays that display new images quickly. Since each reset pulse occupies a substantial period, it is desirable to reduce the number of reset pulses to the minimum that matches the grayscale performance acceptable by the display, and generally one or two reset pulse slideshow drive schemes are preferred. It is. Figures 3A and 3B of the accompanying drawings show two different transition waveforms in a two-reset pulse prior art slideshow drive scheme of the type described in the aforementioned MEDEOD application.

  FIG. 3A shows a white to light gray with a reset pulse 202 that drives the pixel from its initial white state to black and a set pulse 208 (same as pulse 158 in FIG. 2B) that drives the pixel from black to light gray. A single reset pulse waveform (denoted generally as 200) is shown. Although waveform 200 uses only a single reset pulse, the reset pulse is a two-reset pulse slideshow drive with a first reset pulse of zero duration, as indicated by the period of the left zero voltage in FIG. 3A. It should be understood that it is part of the scheme.

  3B illustrates a first reset pulse 252 that drives the pixel from its initial black state to white, a second reset pulse 254 that drives the pixel from white to black, and a pixel that drives from black to light gray. 2 shows a black to light gray two reset pulse waveform (denoted generally as 250) with the same set pulse 208 as the reset pulse.

  As already mentioned, the BPPSS waveform of the present invention can include inserting at least one balanced pulse pair into the base waveform, removing at least one balanced balance pair from the base waveform, or at least one period of zero voltage. Is generated from the base slide show waveform, such as the waveforms shown in FIGS. 2A, 2B, 3A and 3B. In the case of BPP deletion, the resulting gap can either be closed or left as a zero voltage period. A combination of these modifications can be used.

  Figures 4A-4C illustrate suitable balanced pulse pairs for use in the BPPSS waveform of the present invention. The BPP shown in FIG. 4A (denoted generally as 300) comprises a constant voltage negative pulse 302 followed immediately by a positive pulse 304 of the same duration and voltage as pulse 302 but of opposite polarity. . It is clear that the BPP 300 applies a zero net impulse to the pixel. The BPP shown in FIG. 4B (generally designated 310) is identical to the BPP 300 except that the order of the pulses is reversed. The BPP shown in FIG. 4C (generally indicated as 320) is derived from the BPP 310 by introducing a zero voltage period 322 between the positive pulse 304 and the negative pulse 302.

  5A-5D illustrate the modification of the base 2 reset pulse slideshow waveform by BPP according to the present invention. FIG. 5A shows the base waveform (denoted generally as 400) used for the transition from white to light gray. Waveform 400 is generally similar to waveform 250 shown in FIG. 3B, except that the order of reset pulses is reversed. Thus, waveform 400 includes a 16TU negative blackbound first reset pulse 402 (which drives the pixel from its original white state to its black limit optical state) and a 16TU positive whitebound second reset pulse 404 (which is a pixel. And from the black limit optical state to the white limit optical state), and a 3TU negative blackbound set pulse 408 that drives the pixel from the white limit optical state to the final bright gray state required.

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

  FIG. 5C shows the BPPSS waveform of the present invention (generally indicated as 440) generated by inserting the BPP of FIG. 4C into the waveform 400 of FIG. 5A after the set pulse 408.

  FIG. 5D shows the BPPSS waveform of the present invention (generally indicated as 460) generated by further modification of the waveform 420 shown in FIG. 5B. Waveform 460 has second BPPs 304 ′ and 302 ′ inserted between first reset pulse 402 and second reset pulse 404, respectively, which second pulse will double the duration of both pulses. Other than the above, it is the same as BPP 304 and 302.

  As described above and shown in FIG. 5D, the BPPSS waveform of the present invention includes multiple BPPs, deletions, pauses, and combinations thereof (hereinafter collectively referred to as “additional waveform elements” or “AWE”). May be included. However, it is generally preferred to use the fewest number of AWEs consistent with the required accuracy in controlling the final gray level generated by the waveform. Both BPP and pauses lengthen the waveform, and some such BPP and / or pause combinations may require an undesired extension of the time required to rewrite the display. For example, the waveform 460 of FIG. 5D uses only a short 3TU set pulse 408, while the waveform 460 occupies the entire period for display updates (the period between the vertical dashed lines in FIG. 5D) and any additional BPP or pauses. The introduction of this requires an extension of this period. Thus, the total length of the modified waveform of the present invention desirably does not exceed the length of the corresponding base waveform, where the duration of the set pulse allows the pixel to move from one extreme optical state to the other extreme state. Enough to drive. In many cases (of course, due to the exact electro-optic medium used in the display and other characteristics of the drive electronics), good control of gray levels can be achieved with waveforms with at most two AWEs, Any further increase in AWE is generally undesirable, although at most 4 or less and usually at most 6 AWE may be required.

  6A-6D illustrate the modification of the base 2 reset pulse waveform by deleting the BPP according to the present invention. For comparison purposes, FIG. 6A shows the same waveform 400 as FIG. 5A. Waveform 400 is considered to end 7 TU after the end of set pulse 408. The reason is that FIG. 6A shows that in FIGS. 2A, 2B, 3A and 3B, 10 TU of the applied voltage is necessary to drive the pixel completely between its extreme optical states, so that the same drive scheme This is because it is considered necessary to extend the set pulse 408 to a maximum of 10 TU in other waveforms. FIG. 6B shows a modified BPPSS waveform of the present invention (generally indicated as 520) generated by deleting a BPP from waveform 400, which BPP includes the last 2TU of the first reset pulse 402, and the second Two modified pulses 404, the modified 14TU first reset pulse 402 'and the modified 14TU second reset pulse 404' separated by four TU pauses 522, during that period, A zero voltage is applied to the pixel.

  FIG. 6C shows the BPPSS waveform of the present invention (generally designated 540) generated by alternating modification of waveform 400 of FIG. 6A. Waveform 540 is deleted by deleting the BPP with the last TU of the second reset pulse 404 and the first TU of the set pulse 408 from the waveform 400 and moving the first and second reset pulses by 2 TU later in time. Generated by “closing” the period originally occupied by the BPP that was made. Thus, the waveform 540 comprises a 2TU pause 544, a 16TU first reset pulse 402, a 15TU second reset pulse 404 ", and a 2TU set pulse 408 '. The set pulse 408' is exactly the same as the set pulse 408 of the base waveform 400. Note that in time, 7TU ends before the end of the waveform.

  FIG. 6D shows the BPPSS waveform of the present invention (denoted generally as 560) generated by further modification of waveform 400 of FIG. 6A. Waveform 560 removes the BPP comprising the last 2TU of the first reset pulse 402 and the first 2TU of the second reset pulse 404 from the waveform 400, so that the second reset reset pulse and the set pulse are advanced by 4TU in time. Is created by “closing” the period originally occupied by the deleted BPP. Accordingly, the waveform 560 includes a 14TU first reset pulse 402 ′ (same as the reset pulse in FIG. 5B), a 14TU second reset pulse 404 ′ (same as the reset pulse in FIG. 5B except timing), and a 3TU pause 408. Prepare. Note that due to the shift of the second reset pulse 404 ′ and the set pulse 408, the final period 562 of zero voltage following the set pulse 408 is extended from 7 to 11 TU.

  The preferred BPPSS waveform modifications discussed so far involve the insertion or deletion of BPPs between successive base waveform elements or at the end of the base waveform. However, the BPPSS aspect of the present invention is not limited to such a modification, but extends to a modification in which the BPP is inserted into a single BWE, as shown with reference to FIGS. 7A and 7B. In FIG. 7A, BPPs 302 ′ and 304 ′ similar to those shown in FIG. 5D are inserted between the first reset pulse 402 and the second reset pulse 404 except that the order of the positive pulse and the negative pulse is reversed. FIG. 5 shows a BPPSS waveform 620 of the present invention that is generated by modifying the base waveform 400 (FIG. 5A or 6A). FIG. 7B also shows a further BPPSS waveform 640 of the present invention generated by modifying the base waveform 400 by inserting BPPs 302 ′, 304 ′, where BPPs 302 ′, 304 ′ are the second reset. Inserted at the midpoint of pulse 404, thus splitting this pulse into two separate sections 404A and 404B. Accordingly, the waveform 640 continuously includes a 16TU first reset pulse 402 (same as the reset pulse of the waveform 400), an 8TU pulse 404A, a first section of the second reset pulse, BPP 302 ′, 304 ′, an 8TU pulse 404B, A second section of 2 reset pulses and a 3TU reset pulse 408 (same as the reset pulse of waveform 400).

  As already mentioned, the BPPSS aspect of the present invention includes not only the insertion or deletion of BPP into the base waveform, but also the insertion into the base waveform of a pause (period of zero voltage), Insertion is now illustrated with reference to FIGS. For comparison, FIG. 8A shows the same base waveform 400 as FIGS. 5A and 6A. FIG. 8B shows a modified BPPSS waveform of the present invention (denoted generally 720) generated by introducing a 2TU pause 722 into the base waveform 400 between the second reset pulse 404 and the set pulse 408. It should be noted that the insertion of the pause 722 necessarily reduces the length of the zero voltage period following the set pulse 408 from 7 TU to 5 TU.

  FIG. 8C is generally similar to waveform 720 except that a 2TU pause is inserted after the first 12TU of the second reset pulse 404, thus dividing this second reset pulse into a first section 404C and a second section 404D. FIG. 6 shows another BPPSS waveform of the present invention (denoted generally as 740). Accordingly, the waveform 740 is a 16TU first reset pulse 402 (same as the reset pulse of the waveform 400), a 12TU pulse 404C, a first section of the second reset pulse, a 2TU pause 722 ′, a 4TU pulse 404D, and a second. A second section of the reset pulse and a 3TU reset pulse 408 (reset pulse of waveform 400) are provided.

  FIG. 8D shows the BPPSS waveform of the present invention (generally indicated as 760) that is regenerated by inserting a 2TU pause into the base waveform 400. FIG. However, in waveform 760, pause 722 "is inserted before first reset pulse 402. Thus, waveform 760 is continuously paused 722", first reset pulse 402, second reset pulse 404 and set. With the pulse 408, the last three elements are all identical to the corresponding elements of the base waveform 400.

  As already indicated, the BPPSS waveform provided by the present invention is useful for improving the gray level performance of electro-optic displays, particularly bistable electro-optic displays. The BPPSS waveform of the present invention may achieve such improved gray level performance while still maintaining the long term DC balance of the display. (For reasons discussed in detail in the aforementioned MEDEOD application, at least in the sense that the integration of the applied voltage over time for a given pixel is limited, regardless of the sequence of optical states in which the pixel is driven). It is important that the drive scheme used to drive some electro-optic displays is DC balanced). It has been found that the final gray level of a pixel can be adjusted by inserting or deleting BPPs and / or inserting pauses according to the BPPSS aspect of the present invention. It has also been found that the final gray level of a pixel is affected by the position at which BPP insertion or deletion and / or pause insertion is achieved. In general, good control of the final gray level can be achieved by inserting a BPP between adjacent BWEs, but to change the degree of “tunability” of the final gray level, as shown in FIG. 7B, A BPP can be inserted into a single BWE. For example, if the BPP applied between two reset pulses does not provide sufficiently fine tuning of the final gray level, moving the BPP to the midpoint of the BWE provides a finer adjustment of the final gray level. obtain.

  For example, the waveform 420 of FIG. 5B typically produces a gray level that is slightly darker than the gray level produced by the corresponding base waveform 400 of FIG. 5A. The reason is that the pulse 304 of the BPPs 304, 302 has little or no effect on the gray level of the pixel, which is the white limit optical state at the end of the second reset pulse 404, while the pulse 302 because the set pulse 408 is effectively lengthened to make the final gray level somewhat further from the white limit optical state (ie, slightly darker in color). In contrast, the waveform 540 shown in FIG. 6C typically produces a slightly lighter gray level than the gray level produced by the corresponding base waveform 400 of FIG. 6A. 5A, 6A and 6C are based on the assumption that the pixel can shift between its extreme optical states by applying the indicated voltage for 10 TU (above), so that the 16 TU 2 reset pulse 404 substantially “overdrives” the pixel to the white optical rail (white extreme optical state), ie, the second reset pulse 404 is also after the pixel has already reached its extreme white optical state. Continue for a substantial period of time. Thus, shortening the 16TU second reset pulse 404 by 1 TU to generate the 15TU second reset pulse 404 "of the waveform 540 has little or no effect on the gray level at the end of the second reset pulse 404". Does not affect. In contrast, shortening the 3TU set pulse 408 of the waveform 400 by 1 TU to generate the 2TU set pulse 408 ′ of the waveform 540 blackens the white limit optical state present at the end of the second reset pulse 404 ″. To the extent that it is driven towards the end, so that the final gray level at the end of waveform 540 is significantly darker than the gray level at the end of base waveform 400.

  As already indicated, it has also been found that pauses (periods of zero voltage) can be used to adjust the final gray level. For example, adding a pause between the last reset pulse and the set pulse affects the final gray level. Moving the pause to an earlier point in the last reset pulse also causes a slight change in the final gray level. Thus, the rest position can be used to adjust the final gray level generated by the BPPSS waveform. In general, pauses can be added at any point in the waveform. In addition, all BWEs of the waveform are shifted earlier or later in time within the assigned update time interval for complete rewriting of the display, so that in the overall transition from the initial state to the final state It may be advantageous to shift the relative temporal positions of the various transitions that occur. Such temporary shifts are more preferable for several reasons, for example, by reducing unwanted transient behavior of the display during transitions, for example by reducing variation between pixels that are intended to be at the same gray level. It may be advantageous for reasons such as leading to a final image.

  Further preferred BPPSS waveforms and drive schemes of the present invention will now be described with reference to FIGS. 9A-9D, 10A-10C and 11A-11C of the accompanying drawings. FIGS. 9A and 9B show two base waveforms of a prior art two-reset pulse slideshow drive scheme, in which the number of first and second reset pulses and set pulses can occupy up to 12 TUs. FIG. 9A shows a waveform 800 for achieving a black to white transition, wherein the waveform 800 includes a 12TU blackbound first reset pulse 802, a 12TU second whitebound reset pulse 804, and a 12TU blackbound set pulse 808. With. As discussed above with reference to FIGS. 2A and 2B, if the initial and final states of the pixel are intermediate gray levels between the black and white extreme optical states of the pixel, the first reset and The set pulse needs to be adjusted in length and FIG. 9B is a base comprising a 7TU first reset pulse 812, a 12TU second reset pulse 804 (identical to the corresponding pulse in waveform 800) and a 6TU set pulse 818. Waveform 810 is shown. To “padding” waveform 810 to the same 36 TU length as waveform 800, zero voltage 5 TU period 822 precedes first reset pulse 812, and zero voltage 6 TU period 824 follows set pulse 824.

  FIG. 9C shows the BPPSS waveform of the present invention (generally indicated as 840) generated by the modification of waveform 810 shown in FIG. 9B. In particular, the waveform 840 includes a first BPP including a negative pulse 844 similar to the positive 1TU pulse 842 immediately before the first reset pulse 812, and includes a second similar BPP 846 and 848 immediately after the set pulse 818. Extracted from waveform 810 by inserting 2BPP. Pulses 812, 804 and 818 are not changed, but to accommodate the BPP while maintaining the full length of waveform 840, the zero voltage initial period 822 ′ is reduced to 3TU and the zero voltage final period 824 ′ is 4TU. Reduced to

  Using two BPPs in the method shown in FIG. 9C allows more precise control of the final gray level than can be achieved with a single BPP in at least some cases. BBPs placed after the set pulse (such as BPP 844, 848 in waveform 840) cause significant changes in the final gray level, allowing the driver used to make a relatively coarse adjustment of the duration of each half of the BPP. Only (if this duration is only adjusted in increments of 1 TU in FIG. 9C, for example), the difference between gray levels made possible by changing each half duration of the BPP by the minimum increment is Can be unacceptably large. BPPs inserted into the waveform at a much earlier point in time (such as BPP 842, 844 in waveform 840) have a much smaller impact on the final gray level than BPPs inserted after the set pulse, and thus more of the final gray level. Fine variations are possible. Thus, waveform 840 controls the duration of BPP 844, 848 to achieve a coarse adjustment of the final gray level and by controlling the duration of BPP 842, 844 to achieve a fine adjustment of this gray level. Allows adjustment of a significant range of final gray levels.

  FIG. 9D shows the BPPSS waveform of the present invention (generally indicated as 860) generated by another modification of waveform 810. FIG. Like waveform 840, waveform 860 comprises BPP 846, 848 following set pulse 818. However, waveform 860 does not include the second BPP at an earlier point in the waveform, but instead includes a 4TU pause 850 between the second reset pulse 804 and the set pulse 818. The pause effect tends to be smaller than the same length BPP at the same point in the waveform, and the pause 850 is a BPP 842 of the waveform with a variation in the length of the pause 850 that contributes to achieve fine tuning of the final gray level. , 844 in the same manner. In waveform 860, the zero voltage final period 824 'is the same 4TU length as in waveform 840, but the duration of the zero voltage initial period 822 "is 4TU while still maintaining the full 36TU length of the waveform. Note that it is reduced to 1 TU to accommodate the pause 850.

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

  As discussed above with reference to FIG. 9C, varying the length of the BPP following the set pulse may not provide sufficient fine-tuning of the final gray level, and FIG. 10B illustrates this fine-tuning problem. FIG. 6 shows a waveform (generally designated 940) generated by further modifying waveform 920 to overcome Waveform 940 incorporates second BPP 842 ′, 844 ′ between second reset pulse 804 and set pulse 818. The effect on the final gray level by varying the length of BPP 842 ′, 844 ′ is less than the corresponding variation in the length of BPP 846 ′, 848 ′, and therefore BPP 842 ′, 844 ′ is a fine adjustment of the final gray level. Can be used for.

Although the effect on the final gray level by varying the length of BPP 842 ′, 844 is less than the corresponding variation in the length of BPP 846 ′, 848 ′, the BPP length inserted at an earlier point in time of the waveform, eg The effect of varying the lengths of BPP 842 and 844 in FIG. 9C is still greater. If the BPPs 842 ′, 844 ′ in the waveform 940 do not provide sufficient fine adjustment of the final gray level, the second BPP can be inserted earlier in the waveform, and in general, the earlier the time when the BPP is inserted into the waveform. The smaller the variation in the final gray level that is generated by a predetermined change in the length of the BPP. For example, FIG. 10C shows the BPPSS waveform of the present invention (denoted generally as 960), where the BPPSS waveform has BPP 842 ′, 844 ′ positioned between the first reset pulse 812 and the second reset pulse 804. Similar to waveform 940 except that it is replaced by BPP 962,964. (BPP 962,964 is opposite in polarity to BPP 842 ', 844' in the sense that negative pulse 962 precedes positive pulse 964, and the polarity of BPP will of course change its effect on the final gray level, (Some polar BPPs can be used anywhere in the waveform.)
Finally, FIGS. 11A-11C illustrate the modification of the base waveform by introducing BPP and pauses into the waveform. FIG. 11A modifies the base waveform 810 by inserting BPP 842 ′, 844 ′ between the second reset pulse 804 and the set pulse 818 and reducing the length of the zero voltage final period 824 ′ to the corresponding 4TU. To show the waveform that is generated (denoted generally as 1020). For the reasons discussed above, variations in the length of BPP 842 ′, 844 ′ may not provide sufficient fine tuning of the final gray level, and FIG. 11B shows a second reset in particular by further modification of waveform 1020. Shown is a BPPSS waveform (denoted generally as 1040) that is generated by introducing a 2TU pause 1042 into the pulse, thereby dividing the pulse into a first section 804A and a second section 804B. To accommodate the rest 1042, the length of the zero voltage initial period 822 'is reduced to 3TU. The length of the zero voltage final period 824 ′ remains 5TU.

  The pause 1042 is used for fine adjustment of the final gray level. For BPP, such fine-tuning can be done for the duration of the pause 1042 and / or the second reset pulse so that the effect of the pause on the final gray level varies not only with the pause length, but also with the location of the pause in the waveform. This can be achieved by varying the position of the pauses in 804A, 804B. The BPPSS aspect of the present invention is, of course, not limited to the use of a single pause, for example, pause 1042 can be replaced by two separate pauses, each of 1 TU duration, so that the second reset pulse is Divided into three sections rather than two.

As already mentioned, when the waveform does not occupy the entire period used to update the display (requires a period of at least 36 TU to update the display to accommodate a longer waveform 800 of the same drive scheme) However, it may be advantageous to shift the entire waveform within the update period, eg, to reduce temporary visual effects during the update, as for example with respect to waveform 810 of FIG. 9B, which occupies only 25 TUs. FIG. 11C shifts the entire waveform 1040 of FIG. 11B by 2 TUs forward (actually, a 2 TU gap is inserted immediately after the set pulse 818, as shown in FIG. 11C), so that the initial zero voltage FIG. 9 shows a waveform (denoted generally at 1060) generated by reducing the period 822 ″ to only 1 TU and increasing the zero voltage final period 824A length to 6 TU.
Section B: Inverse Monochrome Projection Method and Apparatus As already mentioned, the second aspect of the present invention is a plurality of pixels, each pixel achieving at least four different gray levels including two extreme optical states. A method for driving an electro-optic display having a plurality of pixels capable of performing the same is provided. The method includes applying a waveform to the pixel, the waveform comprising a reset pulse sufficient to drive the pixel to or near one of the extreme optical states followed by the one extreme optical as described above. And a set pulse sufficient to drive the pixel to a final gray level different from the state. The reset pulse is chosen so that the image on the display immediately before the set pulse is substantially a “reverse monochrome projection” of the final image following the set pulse. Such processing is referred to herein as the “reverse monochrome projection” or “IMP” method.

Using the term “goal state” as used in Scheme 1 above, an IMP method can be defined as a method where the final goal state is approximately the inverse monochrome projection of the required final state (R ₁ ) of the display. . In a preferred form of the IMP method, the goal state immediately before the final goal state (goal _n-1 in the terminology of Scheme ₁ ) is approximately a monochrome projection of the required final state (R ₁ ) of the display. Such a suitable IMP process may be represented symbolically as in Scheme 2 shown in FIG _{. m} represents a monochrome projection of R ₁ and overlining indicates image inversion.

  Monochromatic projection of the optical state is a map of all possible gray levels in the image to one of the two extreme optical states of each pixel or a state close to one of the extreme optical states (for reasons explained below). is there. For current purposes, gray levels are 1, 2, 3,. . . , N, where N is the number of gray levels, the gray level having the minimum reflectivity (typically black) is indicated by 1, the gray level having the minimum reflectivity is 2, and so on. The gray level (typically white) having the maximum reflectivity is indicated by N. In a monochrome projection of a grayscale image, gray levels below the threshold are mapped to gray level 1 or near, and gray levels greater than the threshold are mapped to gray level N or near. The threshold is most preferably N / 2, but in practice it can be effectively set anywhere within the middle half of the range from 1 to N, ie the threshold is at least N / 4 and at most 3N / 4.

  An example of monochrome projection is shown in FIG. In this example, the grayscale image (shown in symbolic fashion on the left side of FIG. 13) contains 8 grayscale levels and is shown from 1 to 8. Gray levels 1 to 3 are mapped to gray level 1 and gray levels 4 to 8 are mapped to gray level 8 as indicated by the connecting lines in the monochrome projection symbolically shown on the right side of the figure. The inverse monochrome projection is of course generated simply by reversing the two states used in monochrome projection.

  The previous reference to the IMP method produces a “substantially” inverse monochrome projection, which is a projection with an optical state “close” to one of the extreme optical states, but requires explanation. In principle, monochrome and inverse monochrome projections require projection to one of the extreme states. In practice, however, the drive scheme and waveform that drives the electro-optic display is defined in terms of voltage pulses or other waveform elements applied to individual pixels of the display, and application of defined voltage pulses or waveform elements. Are not defined in terms of the exact optical state that results from (but they are closely related). As discussed in detail in the aforementioned MEDEOD application, the response of at least some bistable electro-optic media to a given waveform or waveform element depends only on the initial optical state of the pixel and the exact waveform or waveform element. Rather, it also depends on factors such as the previous optical state of the pixel and how long it has been in the same optical state before the waveform or waveform element is applied (the pause time dependency problem described above). Since slide show waveforms typically do not allow all such related factors, the actual optical state achieved by the various pixels in a monochrome or inverse monochrome projection is theoretical in such a projection. It can be slightly different from the ultimate optical state achieved in a typical manner.

  This deviation of the actual optical state of the pixel from the extreme optical state is illustrated with reference to FIGS. 14 and 15, which are used for certain selected transitions in the two-reset pulse slide show IMP method of the present invention. This IMP method is driven from black (gray level 1) to white (gray level 4) using a + 15V 200 ms pulse and from white to black using a -15V 200 ms pulse. The resulting 4 gray level electro-optic medium is used. The first waveform shown in FIG. 14 (generally indicated as 1420) is a transition from black (gray level 1) to white (gray level 4) and a first reset pulse 1422 that drives the pixel from black to white. And a second reset pulse 1424 for driving the pixel from white to black and a set pulse 1426 for driving the pixel from black to white. FIG. 14 also shows a waveform 1440 for the transition from gray level 2 (dark gray) to gray level 4 (white). This waveform 1440 has a first reset pulse 1428 that is only 140 milliseconds long, rather than 200 milliseconds as in the reset pulse 1422 of waveform 1420. The second reset pulse 1424 and the set pulse 1426 of the waveform 1440 are the same as the pulses of the waveform 1420. Finally, FIG. 14 also shows a waveform 1460 for the transition from gray level 4 (white) to gray level 4. In this case, the first reset pulse is of zero duration (ie, there is simply a 200 millisecond period of zero voltage at the beginning of the waveform), but the second reset pulse 1424 and set pulse 1426 of waveform 1460 are waveform 1420. Is the same as the pulse.

  FIG. 15 shows further waveforms from the same drive scheme as in FIG. The first waveform shown in FIG. 15 (generally indicated as 1480) is for the transition from gray level 1 (black) to gray level 1 and is essentially the inverse of the waveform 1460 shown in FIG. . Waveform 1480 includes a first reset pulse that is zero duration (ie, simply having a 200 millisecond period of zero voltage at the beginning of the waveform), a second reset pulse 1482 that drives the pixel from black to white, And a set pulse 1484 for driving from white to black. FIG. 15 also shows a waveform 1500 used for the transition from gray level 1 (black) to gray level 3 (light gray). This waveform 1500 has a first reset pulse 1422 that is identical to the pulse of waveform 1420 shown in FIG. 14, which drives the pixel from black to white. Waveform 1500 also has a second reset pulse 1502 that drives the pixel from white to black and a 130 millisecond set pulse 1504 that drives the pixel from black to gray level 3 (light gray). Finally, for completeness, FIG. 15 repeats the black to white (gray level 1 to gray level 4) waveform from FIG.

14 and 15 reveal the following. The drive scheme shown is an IMP drive scheme, as shown by the overlined R _{1, m} just before the set pulse in the various waveforms, and the image on the display just before the set pulse is Inverse monochrome projection of the final image, more specifically, in all transitions ending with gray level 3 or 4, the pixel is black immediately before the set pulse, while all ending with gray level 1 or 2 For the transition, the pixel is white just before the set pulse. Further, according to a preferred variant of the IMP method, the image on the display just before the second reset pulse is the final image after the set pulse, as indicated by R _{1, m} just before the second reset pulse in the various waveforms. For all transitions that are monochrome projections and, more specifically, that end at gray level 3 or 4, the pixel is white just before the second reset pulse, whereas for all transitions that end at gray level 1 or 2 Thus, the pixel is black just before the second reset pulse.

  However, as can be estimated from FIGS. 14 and 15, the reflectance of a given gray level achieved at various points in various waveforms is not necessarily exactly the same. However, the difference between pixels that are probably at the same gray level is small compared to the overall dynamic range of the display (difference between the reflectivities of the two extreme optical states). For example, immediately before the second reset pulse, the pixels that receive waveforms 1420 and 1460 in FIG. 14 should both be at gray level 4 (white). However, the pixel that receives waveform 1420 has just completed the black-to-white transition at this point, while the pixel that receives waveform 1460 has been in the white state for some time (discussed in some of the aforementioned MEDEOD applications). While the optical state of the bistable electro-optic medium is not being driven, the optical state tends to “drift” (ie, gradually change over time). Thus, the actual white state of the pixel that receives waveform 1460 may be slightly different from the white state of the newly rewritten pixel that receives waveform 1420. Modifications to the IMP drive scheme as discussed below can modify the reflectivity achieved at various points in the various goal states and waveforms, so the reflectivity of the various goals and other states can be There can be considerable deviations from the reflectivity in the goal state that would have been achieved without modification.

  Although the IMP drive scheme shown in FIGS. 14 and 15 uses only two reset pulses, and thus uses two goal states, the IMP aspect of the present invention of course has a specific number of reset pulses and goal states. Not limited. For example, FIG. 16 shows the IMP drive scheme using symbols in the same way as in FIG. 12, and the IMP drive scheme is an intermediate black (B) state and white (before the monochrome and reverse monochrome projection goal states). W) including state.

It should be noted that not all pixels of the display will reach the same point in a given goal state (eg, reverse monochrome projection goal state) when the display is rewritten from the initial image to the desired final image. is there. The point in the transition where the goal state is reached is a function of the initial gray level R ₂ and the desired final gray level R ₁ . Ideally (and as normally indicated herein), the R ₂ and R ₁ time points are driven through the various goal states, and these goal states are all pixels. Match in the state reached simultaneously. However, it is often desirable to shift the relative timing of the various waveforms of the drive scheme. Waveform time shifts can be made to improve aesthetic reasons, such as the appearance of transitions or the resulting image. Also, variations such as those discussed below can shift the relative time position of the goal state so that the goal state is reached at different times during transitions by various combinations of R ₁ and R ₂ .

  An alternative definition of the IMP drive scheme can be given without explicit reference to the back monochrome projection. The IMP drive scheme is a scheme in which the various gray levels of the display can be divided by the threshold so that one extreme state and at least one non-extreme state are on each side of the threshold, with each set pulse crossing the threshold. A set pulse of the slide show driving scheme is defined to achieve the transition. As this definition makes clear, in the IMP drive scheme, the final set pulse of each waveform drives from the extreme optical state further away from the desired gray level to the desired final gray level. Here, “further” is used to indicate “on the opposite side of the threshold” rather than simply counting the difference in the number of gray levels between the desired final gray level and the two extreme optical states. The

  The IMP drive scheme has been found to allow precise control of the final gray level and provide a wide temperature run range. These benefits are the relatively long set pulse used to drive from the “further” extreme optical state to the final gray level and the resulting relatively constant power consumption in the drive circuitry during display updates. (But the present invention is in no way limited to this idea).

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

  The first type of modification of the IMP drive scheme is performed in a manner similar to that achieved in the BPPSS drive scheme, as discussed in section A above, and insertion and deletion of balanced pulse pairs and / or waveforms. Is the insertion of a zero voltage period. The balanced pulse pair used may have any form shown, for example, in FIGS. Deformation of the basic IMP waveform with BPP insertion or deletion or zero voltage (pause) period insertion can be achieved in any of the previously described methods. A BPP may be inserted between two consecutive base waveform elements or within a single base waveform element. In many cases this has the effect of increasing the pulse length both to and away from a particular goal state. The deleted BPP can be replaced by a period of zero voltage, or other base waveform elements can be shifted in time to “close” the period previously occupied by the deleted BPP, and zero Voltage periods can be inserted at other points in the waveform. As in the BPPSS drive scheme, the final gray level achieved is subject to the rule that the earlier the BPP is inserted or deleted or the pause is inserted, the less impact the change has on the final gray level. In addition to sensing the presence of BPP and the presence of pauses in, they also sense their positioning in the waveform.

  Such waveform deformation affects not only the final optical state (ie the final gray level) but also the reflectivity as well as the intermediate goal state. The goal state of the basic IMP waveform is generally close to one of the extreme optical states (optical rails) and, by definition, the optical for the last goal state or the last two goal states in the preferred form of the IMP drive scheme. Near the rail, the above deformation can shift the reflectivity of the goal state away from the optical rail. Small adjustments in the final optical state (gray level) are changes in the degree of drive towards the optical rail.

  It has been found desirable to keep each impulse of a voltage pulse comprising a BPP relatively small. The amplitude of the BPP can be defined by the parameter d, the absolute value of which describes the length of each of the two voltage pulses of the BPP, the symbol indicating the second symbol of the two pulses. For example, the BPP shown in FIGS. 4A and 4B may be assigned d value +1 and d value −1, respectively (while the BPP of FIG. 4C then inserts a gap deformation between the two pulses in a consistent scheme. , D value of -1 is assigned). In a preferred embodiment of the IMP drive scheme, every BPP used has a d value and its amplitude is less than PL, preferably less than PL / 2, where PL (for measuring BPP (In the same units used for) in two directions, either as the length of the voltage pulse required to drive the pixel from one extreme optical state to the other, or in the drive voltage characteristics of the drive scheme If the length of the transition is not the same, it is defined as the average value of this voltage pulse. In the present example, d is expressed in units of display scan frames, and the BPPs of FIGS. 4A and 4B have voltage pulses that are each one scan frame long. In this case, PL is also defined by the scan frame. All quantities can of course instead be expressed in units of time such as seconds or milliseconds.

  FIG. 17 of the accompanying drawings shows three waveforms generated by transforming the IMP waveform 1440 shown in FIG. 14 by inserting BPP. The first waveform shown in FIG. 17 (shown generally as 1700) is a waveform except that a BPP 1702 with a -15V10 millisecond pulse followed by a + 15V10 millisecond pulse is inserted at the end of the waveform. The same as 1440. 17 inserts BPP 1722, which is identical to BPP 1702, but is inserted between the second reset pulse and the set pulse of the waveform to accommodate BPP 1722. Thus, with a corresponding decrease in the first zero voltage period of the waveform, the two reset pulses are shifted to be advanced by 20 seconds. The third waveform shown in FIG. 17 (generally designated 1740) has BPP 1742 inserted between the first and second reset pulses of the waveform, and BPP 1742 is the opposite of BPP 1702 and 1722. It has a sequence of pulses, each pulse being 20 milliseconds long. To accommodate BPP 1742, the first reset pulse is shifted forward by 40 milliseconds with a corresponding decrease in the first zero voltage period of the waveform.

  FIG. 18 of the accompanying drawings shows three waveforms generated by transforming the IMP waveform 1440 shown in FIG. 14 by deleting the BPP from the waveform. The first waveform shown in FIG. 18 (denoted generally as 1760) is a BPP 1762 comprising the last 10 ms scan frame of the second reset pulse and the first scan frame of the set pulse, and changes in the remaining waveform elements. Is generated by deleting from the waveform 1440 without the. The second waveform shown in FIG. 18 (generally indicated as 1780) is a BPP 1782 comprising the last two scan frames of the first reset pulse and the first two scan frames of the second reset pulse. Generated by deleting from waveform 1440 with the remaining waveform elements unchanged, thus leaving the 40 millisecond period of zero voltage at the point occupied by the deleted BPP. Finally, the third waveform shown in FIG. 18 (generally indicated as 1800) deletes from the waveform 1440 the BPP comprising the last scan frame of the first reset pulse and the first scan frame of the second reset pulse. , By closing the resulting gap by moving the remaining scan frame of the first reset pulse 20 milliseconds later, with a corresponding increase in the zero voltage period at the beginning of the waveform.

  FIG. 19 of the accompanying drawings shows a possible further variation of the waveform 1720 shown in FIG. The upper part of FIG. 19 repeats the basic waveform 1720 including BPP 1722 from FIG. FIG. 19 is also similar to BPP 1722, but with a second modified waveform (generally designated 1920) with BPP 1922 inserted 40 milliseconds earlier before the last four scan frames of the second reset pulse. ). FIG. 19 is also similar to BPP 1722, but with a second modified waveform (generally denoted 1940) with BPP 1942 inserted 130 ms earlier before the last 13 scan frames of the second reset pulse. Show). As mentioned above, the final gray level achieved by a waveform such as that shown in FIG. 19 is a function of the position of the balanced pulse pair insertion, so that a deformation such as the one shown in FIG. Can be used for fine adjustment of level.

  FIG. 20 of the accompanying drawings shows a modified IMP waveform generated by inserting a zero voltage period (rest) into the basic IMP waveform 1440 shown in FIG. The first waveform shown in FIG. 20 (denoted generally as 2000) has two waveforms by inserting a 20 millisecond pause (denoted as 2002) between the second reset pulse and the set pulse of the waveform. The reset pulse is shifted 20 milliseconds early and is generated in the corresponding decreasing state in the zero voltage period at the beginning of the waveform. The second waveform shown in FIG. 20 (generally indicated as 2020) is generally similar to waveform 2000, but waveform 2020 is inserted 40 milliseconds after pause 2002 after the first four scan frames of the set pulse. That paused (denoted 2022). The third waveform shown in FIG. 20 (generally indicated as 2040) is also generally similar to waveform 2000, except that waveform 2040 is 130 mm from pause 2002 after the first 13 scan frames of the set pulse. With its pause (shown as 2042) inserted after 2 seconds. In both 2020 and 2040 waveforms, the scan frame of the set pulse preceding pause 2022 or 2042, respectively, is moved 20 milliseconds earlier compared to waveform 2000 to accommodate the pause. As already stated, the final gray level achieved by the waveform is sensitive to both the presence and location of pauses, and therefore a deformation of the base waveform, such as the deformation shown in FIG. 20, was generated by the waveform. Can be used to fine tune the final gray level.

  As described above, for any gray level loop (ie, any series of gray levels starting and ending at the same gray level), the IMP drive means that the sum of the algebra of impulses applied to the pixel is zero. The scheme is preferably DC balanced. An example of a gray level loop is as follows.

1 → 1
2 → 3 → 2
4 → 4 → 3 → 2 → 4
An irreducible gray level loop can be defined as a sequence of gray levels, in which the sequence starts with the first gray level, passes through zero or more gray levels, ends with the first gray level, and as described above, the first Do not go to any gray level more than once, except for the final gray level, which must be the same. Clearly, for any gray scale, there is a finite number of irreducible loops. In addition, any series of gray scales, eg complex sequences,
1 → 4 → 3 → 2 → 3 → 2 → 3 → 2 → 1 → 2 → 1
Can be reduced to a series of irreducible loops and irreducible loops embedded within the irreducible loops. For example, the sequence can be broken down into a finite set of irreducible loops. That is, two consecutive 2 → 3 → 2 embedded in a 1 → 4 → 3 → 2 → 1 loop and a loop 1 → 2 → 1 following the loop.

  If all irreducible loops are DC balanced, all possible sequences that start and end at the same gray level are DC balanced. The preferred embodiment of the IMP drive scheme is such that the net voltage impulse for all irreducible loops is zero, i.e., the waveform is DC balanced.

  It is not absolutely necessary to make the IMP waveform DC balanced. Large DC imbalances impair the image performance of the display, but slight DC imbalances can be tolerated. When it is not possible to achieve perfect DC balance, the IMP drive scheme is preferably controlled as follows. When Q is the lesser quarter of the absolute value of the net impulse for the transition between the two extreme optical states of the pixel, and when the impulse is determined using the characteristic voltage of the drive scheme, The irreducible loop net impulse divided by the number of transitions in any irreducible loop should be less than Q. The net impulse required to drive the image film from one extreme optical state to the other extreme optical state represents the characteristic impulse of the media, and the nearby DC imbalance is measured relative to this characteristic impulse.

  It is also often desirable that the IMP drive scheme be of the “picket fence” type. As described in the aforementioned MEDEOD application, it is often necessary or desirable to drive an electro-optic display using a drive network that can supply only two drive voltages. A bistable electro-optic medium usually needs to be driven in both directions between its extreme optical states, so at first it appears that at least three drive voltages are needed. That is, 0, + V, −V, where V is essentially any drive voltage, so that one electrode for a particular pixel (typically the common front electrode of a conventional active matrix display) ) Is held at 0, while the other electrode (the pixel electrode for that pixel) can be held at + V or -V, depending on the direction in which the pixel needs to be driven. When a two voltage drive network is used, each waveform of the drive scheme is divided into time segments, typically these time segments are equal in duration, but this is not necessarily the case. Not exclusively. In a non-hike and fence drive scheme, a positive drive voltage, a zero drive voltage, or a negative drive voltage can be applied to any particular pixel in any time segment. For example, in a three drive voltage system, the common front electrode can be held at 0, while the individual pixel electrodes are held at + V, 0, or -V. In the picket fence drive scheme, each time segment is effectively divided into two, and in one of the resulting two segments, only 0 or a negative drive voltage can be applied to any particular pixel, In the other segment of the result, only positive drive voltage or zero drive voltage can be applied to any particular pixel. For example, consider two drive voltage systems with drive voltages V and v when V> v. In the first of each pair of segments, the common front electrode is set to V, and the pixel electrode is set to either V (0 drive voltage) or v (negative drive voltage). In the second of each pair of segments, the common front electrode is set to v and the pixel electrode is set to either v (0 drive voltage) or V (positive drive voltage). The resulting waveform is twice as long as the corresponding non-hickett fence waveform.

  It is also often desirable that the IMP drive scheme allows local updates. As described in the aforementioned MEDEOD application, driving the electro-optic display in such a way that local updates of a particular area of the display undergoing change are possible with the remaining area of the display unchanged. That is often desirable. For example, it may be desirable to update an interactive box that enters text without the user updating the display background image. A locally updated version of any IMP drive scheme may be created by removing all non-zero voltages from the waveform for a zero transition (eg, transition from one gray level to the same gray level). For example, a waveform from gray level 2 to gray level 2 is usually composed of a series of voltage pulses. Removing the non-zero voltage from this waveform and doing so for all other zero transitions results in a locally updated version of the IMP waveform. Such local update versions can be advantageous when it is desirable to minimize irrelevant flushing during transitions.

  The experiment below demonstrates the use of the variants discussed above in fine-tuning the gray levels generated by the IMP drive scheme.

An encapsulated electrophoretic medium with an internal phase comprising polymer-coated titania and polymer-coated carbon black particles in a hydrocarbon liquid and encapsulated in gelatin / acacia capsules is described in US Pat. Are prepared and incorporated into an experimental single pixel display, substantially as all described in paragraphs [0069] to “0076”. The experimental display is then driven using a 4 gray level IMP drive scheme. The display is driven from gray level 4 (white) to gray level 1 (black) by a pulse of +15 V, 500 milliseconds, and a reverse transition is made by a pulse of -15 V, 500 milliseconds, and a basic two reset pulse IMP drive scheme. Was found to be configured accordingly. FIG. 21 of the accompanying drawings shows all 16 of this basic IMP drive scheme labeled [R ₁ R ₂ ] in a highly schematized manner so that a given first number represents the final gray state. Each waveform is shown. For example, the [14] waveform shown in the upper right corner of FIG. 21 achieves a transition from gray level 4 (white) to gray level 1 (black), and the first + 15V 500 millisecond reset pulse driving the pixel to black. A 2-15V 500 ms reset pulse that drives the pixel to white and a + 15V 500 ms set pulse that drives the pixel to black.

  The experimental display is driven using a basic IMP drive scheme through a varying series of gray levels and the display reflectivity measured at the end of each sequence, and the results are shown in FIG. Each point in FIG. 22 represents the reflectivity following a different series of gray levels before reaching the final gray level indicated on the abscissa. It can be seen from FIG. 22 that the reflectivity achieved at the same nominal gray level varies considerably, which is of course undesirable because such variations adversely affect the quality of the image produced by the multi-pixel display. . In particular, the human eye is very sensitive to small variations in gray levels that occur within a block of pixels that are considered to be at the same gray level, and FIG. It shows what can be expected as a result.

  The IMP drive scheme then achieves a consistent gray level after various gray level sequences, resulting in the insertion and deletion of balanced pulse pairs (deletion results) to produce the modified IMP drive scheme shown in FIG. With the gap closure), and in the manner described above by insertion or removal of zero voltage periods at the beginning and end of the various waveforms. FIG. 24 shows the gray levels generated by the modified IMP drive scheme of FIG. 23 using the same gray level sequence as in FIG. It can be seen from FIG. 24 that the modified IMP drive scheme of FIG. 24 produces a much more consistent gray level than the unmodified drive scheme of FIG.

Section C: Balanced Pulse Pair Pause Time Compensation Method and Apparatus As already mentioned, in the third aspect of the present invention, the present invention provides an electrical device having at least one pixel capable of achieving at least two different gray levels. A method for driving an optical display is provided. In this method, at least two different waveforms are used for the same transition between specific gray levels, depending on the duration of the pixel pause time in the state where the transition begins, and these two waveforms are at least one balanced pulse pair. Different from each other by at least one insertion and / or deletion, or insertion of at least one period of zero voltage, where “balanced pulse pair” has the previously defined meaning. In such a method, it is highly preferred that the drive scheme is DC balanced as defined above.

  In such a balanced pulse pair pause time compensation (BPPDTC) method (as in the previously described BPPSS and IMP methods), insertion or deletion of a balanced pulse pair and / or zero voltage period (pause) is within a single waveform element. Or it can be achieved either between two successive wave elements. The two waveforms used for the same transition following different pause times in the initial state where the transition begins may be referred to below as “alternative pause times” or “ADT”.

  The ADT waveforms may differ from each other depending on the location and / or duration of the BPP or pause in the waveform (see, for example, the discussion of FIGS. 25B-25E below) because such movement of BPP or pause is A combination of deleting a BPP or pause at a location and inserting a BPP or pause at a different location, or (if the duration changes at the same location) a different BPP or pause at the same location as deleting the BPP or pause at that location It can be considered formally as a combination with insertion.

  In the BPPDTC driving scheme, the insertion of BPP and / or pause deletion causes the same problem and can be handled in the same way as in the BPPSS and modified IMP driving scheme described in Sections A and B above. Thus, if the difference between ADT waveforms according to the BPPDTC aspect of the present invention includes the deletion of at least one BPP, the period previously occupied by each deleted BPP may be left as a zero voltage period. Instead, to ensure that the full length of the waveform is maintained, the waveform element usually involves inserting a period of zero voltage at some later stage of the waveform, typically at the end of the waveform. This period can be “closed” by moving some or all of them to advance in time. (Normally, in any actual display having at least several thousand pixels, if there is at least one pixel that receives every possible transition that would normally occur in any transition, and the waveforms of all the pixels are not the same length, the controller The logic becomes extremely complex.) Instead, of course, by moving some or all of the previous waveform elements earlier in time, the zero voltage is typically introduced earlier in the waveform, typically at the beginning. With the insertion of a period, the period can be “closed”.

  Similarly, the insertion of BPP adds to the total duration of the waveform if the period in which zero voltage is present is not removed at the same time. When one waveform of the driving scheme has an inserted BPP, all the waveforms of the driving scheme have the same overall length, so that to compensate for the increase in the total length of the waveform caused by the insertion of the BPP, All other waveforms in the drive scheme should have a period of zero voltage added to it, or some other variation should be made. For example, as shown in Table 1 above, if a 40 millisecond BPP is inserted into a black to white waveform (the waveform has a waveform length of 420 milliseconds), all waveforms have a 460 millisecond length. Thus, as shown in Table 1, a 40 millisecond pause can be added to the remaining three waveforms. Where apparently appropriate, the BPP can be added to the other three waveforms rather than pause, or some combination of BPP and a total of 40 milliseconds of pause can be used.

  Preferred drive schemes and waveforms for the BPPDTC aspect of the present invention will now be described by way of illustration only. The balanced pulse pairs used in such drive schemes and waveforms can be any of the types described above, and the types of BPPs shown in Figures 4A-4C can be used.

  Figures 25A-25E illustrate alternative pause time waveforms that may be used for a single transition in accordance with the BPPDTC aspect of the present invention. FIG. 25A shows the black to white waveform described in the third row of Table 1 and the last row of Table 2. This waveform is suitable for a black-to-white transition after a long pause in the black state, so to generate a waveform suitable for a black-to-white transition after a shorter pause in the black state It can be regarded as a black to white base waveform which is deformed according to the BPPDTC aspect of the present invention. As described above, the base waveform of FIG. 25A consists of a -15V, 400 ms pulse followed by 20 ms of 0V.

  FIG. 25B shows a modification of the base waveform of FIG. 25A, which is the final white state when a black to white transition is achieved after only a short pause time of 0.3 seconds or less in the initial black state. This is considered to be effective in reducing the reflectance. The waveform of FIG. 25B is generated by inserting a BPP similar to the BPP 300 shown in FIG. 4A at the end of the −15V, 400 ms pulse of the waveform of FIG. 25A, so that the waveform of FIG. A 15V, 420 millisecond pulse followed by a + 15V, 20 millisecond pulse and a 20 millisecond 0V.

  FIGS. 25C and 25D show two additional ADT waveforms for the same black to white transition as the waveforms of FIGS. 25A and 25B. The waveforms of FIGS. 25C and 25D normalize the reflectivity of the final white state when the black-to-white transition is achieved after 0.3-1 second rest period and 1-3 second rest time in the black state, respectively. It is thought that it is effective to do. The waveforms of FIGS. 25C and 25D are generated by inserting the same BPP as the BPP in FIG. 25B into the waveform of FIG. 25A, but the BPP is in a different location from that used in FIG. 25B. As mentioned above, the position where the BPP is inserted (or deleted) into the base waveform has a significant effect on the final optical state following the transition, and thus shifting the insertion position of the BPP with the base waveform. Is considered to be an effective means of compensating the waveform for variations in pixel downtime in the initial optical state.

  FIG. 25E is a preferred alternative to the waveform of FIG. 25A to achieve a black-to-white transition after a long pause in the black state (greater than 3 seconds). The waveform of FIG. 25E is generally similar to the waveforms of FIGS. 25B-25D in that it is generated by inserting the same BPP into the waveform of FIG. 25A. However, in FIG. 25E, the BPP is inserted at the beginning of the waveform and it may be desirable to make a 40 ms pulse rather than 20 ms in duration. This makes the total duration of the waveform 500 ms, so that when the waveform of FIG. 25E is used in conjunction with the waveforms of FIGS. 25B-25D, 40V of 0V at the end of the waveforms of FIGS. 25B-25D. The waveform needs to be “padded” by adding seconds. Accordingly, a preferred set of ADT waveforms for the transition from black to white is as shown in Table 3 below.

The impulse for the black to white transition is -15V ^* 400 milliseconds, ie 6V seconds for all of the ADT waveforms in Table 3, and thus for all initial pause times, resulting in a drive scheme Note that is DC balanced.

  As mentioned above, DTC can also be achieved by removing the BPP from the base waveform. For example, consider the drive scheme shown in Table 4 below.

In this drive scheme, not only the overall drive scheme, but all waveforms are “internally” DC balanced, and the desirability of such internal DC balance is discussed in detail in the above-mentioned Patent Document 3. I understand that. Again, although the DTC method is discussed with reference to the black-to-white transition, it should be understood that the DTC for the black-to-white transition is accomplished in a similar manner.

  In this case, the DTC of the black-to-white transition is obtained by eliminating one BPP, ie, simultaneously removing the similar part and equivalent duration of one voltage pulse of opposite polarity, This can be achieved by removing a portion of the voltage pulse and one duration. The deleted pulse section can be replaced with a period of zero voltage, or the rest of the waveform can be shifted in time to occupy the period previously occupied by the deleted pulse pair, and the total update time In other words, zero voltage segments that match the duration of the deleted pair can be added elsewhere, typically at the beginning or end of the waveform.

  FIGS. 26A, 26B and 26C schematically illustrate the process for black-to-white waveform transformation listed in the third row of Table 4 above for DTC with a short pause time of less than 0.3 seconds in the black state. Indicate. FIG. 26A shows the base waveform from Table 4. FIG. 26B is the removal of the BPP formed by the last 80 ms portion of the positive voltage pulse and the first 80 ms of the negative voltage pulse from the waveform of FIG. 26A, where the resulting gap is FIG. 26B schematically shows what is removed by shifting the negative pulse so as to advance in time as indicated by an arrow in FIG. 26B. FIG. 26C shows the resulting pause time compensation waveform, which comprises a 320 ms positive pulse, a 320 ms negative pulse, and a 180 ms duration of zero voltage. .

  In this case, all dwell time DTCs can be achieved by simply changing the deleted BPP length, and for a long dwell time of 3 seconds or more in the black state, the base waveform of FIG. 26A is sufficient. it is conceivable that. Therefore, the complete list of ADT waveforms for the transition from black to white in this case is as shown in FIG.

As mentioned above, when a BPP is deleted from the waveform in the manner shown in FIG. 26B, it is not essential that the remaining components are shifted in time, and the deleted BPP is dependent on a zero voltage period. Can simply be replaced. Table 6 below shows a modified set of ADT waveforms that are similar to the ADT waveforms of Table 5, but with the deleted BPP replaced by a zero voltage period.

Although the BPPDTC aspect of the present invention has been described above primarily with reference to a display having only two gray levels, it is not so limited and may be applied to displays having a greater number of gray levels. Also, in the specific waveform shown in the drawing, the insertion or deletion of the two elements of the BPP is achieved at one point in the waveform, but the present invention is a waveform in which the insertion or deletion of the BPP is achieved at one point. Without limitation, the two elements of the BPP can be inserted or deleted at different points, i.e., the two pulses that make up the BPP do not have to follow immediately but can be separated by a time interval. In addition, one or both pulses of the BPP can be subdivided into sections, which can then be inserted or deleted from the waveform for DTC. For example, a BPP may consist of + 15V, 60 ms pulses and -15V, 60 ms pulses. This BPP can be divided into two components, for example, a + 15V, 60 ms pulse, followed immediately by a -15V, 20 ms pulse, and a -15V, 40 ms pulse. Are simultaneously inserted or deleted from the waveform to achieve DTC.

  Inserting or deleting a zero voltage segment in the waveform is also considered to affect the final gray level after the transition, so such insertion or deletion of the zero voltage segment is therefore the final gray level to achieve DTC. A second method of adjusting is provided. Such insertion or deletion of the zero voltage segment can be used alone or in combination with BPP insertion or deletion.

  While the BPPDTC aspect of the present invention has been described above primarily with reference to pulse width modulated waveforms where the voltage applied to the pixel at any given time can only be -V, 0 or + V, the present invention Without being limited to being used with a simple pulse width modulated waveform, it may be used with a voltage modulated waveform or a waveform that uses both pulse and voltage modulation. The above definition of a balanced pulse pair can be satisfied by two pulses of opposite polarity with zero net impulse, and the two pulses do not need to be the same voltage or duration. For example, in a voltage modulation drive scheme, the BPP can consist of a + 15V, 20 ms pulse followed by a -5V, 60 ms pulse.

From the foregoing, the BPPDTC aspect of the present invention allows for drive scheme pause time compensation while maintaining DC balance of the drive scheme. Such a DTC can reduce the ghost level of an electro-optic display.
Section D: Target Buffer Method and Apparatus As already mentioned, the present invention is an electro-optic having a plurality of pixels, each of which can achieve at least two different gray levels. Two different ways of using a target buffer to drive the display are provided. The first, non-polar target buffer method of these two methods provides an initial data buffer, a final data buffer, and a target data buffer, and determines when the data in the initial data buffer and the data in the final data buffer are different. And when such a difference is found, comprises updating the value in the target data buffer by the following method. (I) When the initial data buffer and the final data buffer contain the same value for a particular pixel, the target data buffer is set to this value; (ii) the initial data buffer is greater than the final data buffer for a particular pixel When containing a large value, set the target data buffer to the value of the initial data buffer plus the increment, and (iii) when the initial data buffer contains a value less than the final data buffer for a particular pixel The buffer is set to a value obtained by subtracting the above-mentioned increment from the value of the initial data buffer, and the image on the display is used as the initial state and final state of each pixel, using the data in the initial data buffer and the data in the target data buffer, respectively. Update Then, the data is copied from the target data buffer to the initial data buffer, these steps is performed until the initial data buffer and the final data buffers contain the same data.

  A second, polarity target buffer method in these methods, wherein the final data buffer, the initial data buffer, and the target data buffer are again provided with a polarity bit array configured to store a polarity bit for each pixel of the display. Is done. Again, the data in the initial data buffer and the data in the target data buffer are compared, and when they are different, the value in the polarity bit array and the value in the target data buffer are updated by the following method. (I) When the values for a particular pixel in the initial data buffer and the final data buffer are different and the value in the initial data buffer represents the extreme optical state of the pixel, the pixel polarity bit causes a transition toward the opposite extreme optical state. The target data buffer is set to the value of the initial data buffer plus or minus the increment according to the associated value in the polarity bit array. The image on the display is then updated in the same manner as the first method, after which the data from the target data buffer is copied to the initial data buffer. These steps are repeated until the initial data buffer and the final data buffer contain the same data.

  Typically, prior art controllers for electro-optic displays use logic similar to that shown in Listing 1 below (all lists in this document are written in pseudocode).

With a controller operating in this manner, the display waits to receive new image information, and then when such new image information is received, before the new information is sent to the display. Perform a full update. That is, once a new image is accepted by the display, the display cannot accept the second new image until there is a rewrite of the display necessary to display the first new image. This rewrite procedure may take several hundred milliseconds compared to some of the drive schemes described in Sections A-C above. Thus, when the user scrolls or types, the display appears to be insensitive to user input during this full update (rewrite) time.

  In contrast, a controller that achieves the non-polar target buffer method of the present invention operates according to the logic illustrated by Listing 2 below (this type of controller is hereinafter referred to as “List 2 Controller” for convenience).

In this modified controller for the NPTB method, there are three image buffers. The initial and final buffers are the same as in the conventional controller, and the new third buffer is the “target” buffer. The display controller can accept new image data into the final buffer at any time. When the controller finds that the data in the final buffer is no longer equal to the data in the first buffer (ie, an image needs to be rewritten), the new target data set depends on the difference between the associated values in the initial and final buffers Thus, it is configured by incrementing or decrementing the values in the initial buffer by 1 (or leaving them unchanged). The controller then uses the data from the initial and target buffers to perform a display update in the normal manner. When this update is complete, the controller copies the value from the target buffer to the initial buffer, then repeats the difference operation between the initial and final buffers to generate a new target buffer, and the initial and final buffers have the same data. When you have a set, the full update is complete.

  Thus, in this NPTB method, a full update is accomplished by a series of sub-update operations, one of such sub-update operations being when the image is updated using the initial data buffer and the target data buffer. Occur. The term “meso-frame” is used hereinafter for the period required for each of these sub-update operations, and such meso-frame is, of course, the period required for a single scan frame of the display (described above). Indicates the time period between the superframe and the time period required to complete the full update.

  The NPTB method of the present invention improves interaction performance in two ways. First, in the prior art, the final data buffer is used by the controller during the update process so that no new data can be written to this final data buffer while the update is taking place, so the display is updated. No response to new input is possible during the entire period required for. In the NPTB method of the present invention, the final data buffer is used only for the calculation of the data set in the target data buffer, and since this calculation is a simple computer calculation, the update requires a physical response from the electro-optic material. Can be achieved much faster than arithmetic. Once the calculation of the data set in the target data buffer is complete, the update does not require further access to the final data buffer, so that the final data buffer can accept new data.

  For reasons discussed in the aforementioned MEDEOD application and further discussed below with respect to waveforms, it is often desirable that the pixels be driven in a cyclic manner in the following sense. Once a pixel is driven away from one extreme optical state by one polarity voltage pulse, a reverse polarity voltage pulse is applied to that pixel until the pixel reaches its other extreme optical state. Not applied. For example, see FIGS. 11A and 11B and the related description in the aforementioned patent document 119. This limitation is met by the PTB method of the present invention which may use a controller operating with the logic illustrated by Listing 3 below (this type of controller is referred to hereinafter as a “List 3 controller” for convenience, this list is Assume a four gray level system with gray levels numbered from black 1 to 4 white, although one skilled in the art can easily modify the pseudo code of operation with different numbers of gray levels. ).

This PTB method requires four image buffers, the fourth is a “polarity” buffer with a single bit for each pixel of the display, and this single bit is the current direction of the transition of the relevant pixel, ie The pixel indicates whether it is currently transitioning from white to black (0) or black to white (1). If the relevant pixel is not currently undergoing a transition, the polarity bit retains its value from the previous transition. For example, a pixel that was stationary in a light gray state and was previously white has a polarity bit of zero.

  In the PTB method, a polar bit array is considered when a new target buffer data set is constructed. If the pixel is currently black or white and a transition to the opposite state is required, the value of the polarity bit is set accordingly and the target value is set to the gray level closest to black or white, respectively. Alternatively, if the initial state of the pixel is an intermediate (gray) state, the target value is incremented by 1 according to the value of the polarity bit (+1 if polarity = 1, -1 if polarity = 0) or Calculated by decrementing.

  Note that in this drive scheme, the behavior of a pixel in an intermediate state is independent of the current value of that pixel's final state. As soon as the pixel begins a black-to-white or white-to-black transition, it continues in the same direction until it reaches the opposite optical rail (in the extreme optical state, typically black or white). If the desired image, and thus the target state, changes on transition, the pixel then goes back in the opposite direction and so on.

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

The structure of this transition matrix with black, white, and two intermediate gray states appears to be very similar to that used in conventional 2-bit drive schemes, such as the drive scheme described in the MEDEOD application. However, in the TB method of the present invention, these intermediate states do not correspond to a fixed gray state, but are just transition states, which exist only between the completion of one mesoframe and the next start, There is no restriction on the uniformity of the reflectance in the intermediate state.

  It should be noted that in the transition matrix shown in Table 7, many of the elements (indicated by dashes) are not allowed. Only the controller allows each transition to change the gray level by one unit in either direction, resulting in a transition with multiple changes in the gray level (eg, a direct 1-4 black to white transition). ) Is prohibited. Major diagonal elements of the transition matrix (corresponding to zero transitions) are prohibited for intermediate states, and such major diagonal elements are not recommended for white and black states, but are marked with an asterisk in Table 7. As indicated, it is not strictly prohibited.

In the monochrome NPTB method, the update sequence appears as a series of states that start and end in extreme optical states (optical rails), and the series of intermediate gray states are separated by zero pause times. For example, a simple transition from black to white is
1 → 2 → 3 → 4
Appears as On the other hand, if the final state of the display changes during the update, this transition is
1 → 2 → 3 → 2 → 1
It becomes. Numerous changes in the final state
1 → 2 → 3 → 2 → 3 → 4
And so on.

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

1 → 2 → 3 (→ 2 → 3) → 4
1 → 2 (→ 3 → 2) → 1
4 → 3 → 2 (→ 3 → 2) → 1
4 → 3 (→ 2 → 3) → 4
Here, the parenthesis means zero or more repetitions of the sequence within the parenthesis.
This class of optimization ("tuning") of the NPTB drive scheme ensures consistent reflectivity for the 1 (black) and 4 (white) states, regardless of the number of sequence repetitions in parentheses. It is necessary to adjust the non-zero elements of the transition matrix. The waveform must operate for any pause time in the black and white extreme optical states, but the pause time in the intermediate state is always zero, so that, as described above, the transition state reflectivity is not important. Absent.

  In general, the time required to update any single meso frame is equal to the length of the longest element in the transition matrix. Thus, the total update time is three times the length of this longest element. In the best case, the waveform from black to white and from white to black (1 → 4 and 4 → 1 respectively) can be divided into three equal length elements. This approach reduces the update latency to one third of the total update time while maintaining the same duration for all updates. The benefit becomes less substantial as the length of the mesoframe update, which can be the result of waveform optimization, increases. For example, if an element is twice as long, the latency increases to two thirds of the simple update time, and all transitions require twice as much time as before. While it is possible to verify finding the longest element present in a given mesoframe and dynamically adjust the update time to that length, the benefit of this extra computation is not likely to be significant.

  It should be taken into account which electro-optical properties of the media are only suitable for use with displays of this type with NPTB drive schemes of this type. First, the media downtime dependence should be 0 (ideally or at least very low). The reason is that this waveform combines a series of near zero pause times between mesoframes with a potentially much longer pause time between transitions. Second, the media has little or no sensitivity to the optical state preceding the initial state of a particular transition. The reason is that the direction of the transition can change in the flow. For example, a 2 → 1 transition can be preceded by either a 1 → 2 transition or a 3 → 2 transition. Finally, electro-optic media contrast in their response, especially near the black and white states. It is difficult to generate a DC balanced waveform that can perform a 1 → 2 → 1 transition or a 4 → 3 → 4 transition to reach the same black state or the same white state, respectively.

  For the above reasons, “intermediate inversion” in the NPTB drive scheme makes it very difficult to develop an optimal waveform. In contrast, PTB drive schemes significantly reduce the demand for electro-optic media, thus reducing many of the difficulties in optimizing NTPB drive schemes while still providing performance improvements.

The structure of the transition matrix for the PTB drive scheme is the same as the structure of the transition matrix for the NPTB drive scheme, but the PTB drive scheme allows only two black to white transitions and white to black transitions, That is,
1 → 2 → 3 → 4
4 → 3 → 2 → 1
It is. In fact, these two transitions are the same as ordinary 1 → 4 and 4 → 1 transitions with transitions divided into three equal parts. Some slight retuning is desirable for delays between mesoframes, but the adjustment is not complicated. For simple typing, this drive scheme results in a two-thirds reduction in latency.

  There are several disadvantages to the PTB method. Polar bit arrays require extra memory and more complex controllers operate this simpler drive scheme. The reason is that the permission for the direction of transition in each pixel needs to consider extra data (polarity bits) in addition to the initial and final states for the transition. The PTB method also reduces the waiting time to start the update, but the controller must wait until the update is complete before inverting the transition. This limitation is apparent when the user types a character and then immediately erases it. The delay before the characters are erased is equal to the total update time. This limits the usefulness of the PTB method with respect to cursor tracking or scrolling.

  Although the NPTB and PTB methods are primarily described above with respect to monochrome drive schemes, they are also compatible with grayscale drive schemes. The NPTB method is inherently fully compatible with grayscale. The gray scale compatibility of the PTB method is discussed below.

  From a driving scheme perspective, it is clear that generating an operable grayscale driving scheme for the NPTB method is more difficult than generating a corresponding monochrome driving scheme. This is because in a gray scale drive scheme, the intermediate states correspond to the actual gray levels, so the optical values of these intermediate states are limited. It is also quite difficult to generate a gray scale drive scheme for the PTB method. In order to reduce latency, the mesoframe transition must be significantly shortened. For example, a 2 → 3 transition may be a stand-alone transition, a final stage of a 1 → 2 → 3 transition, or an initial stage of a 2 → 3 → 4 transition. Therefore, there are competing requests to shorten this transition (to achieve a shorter full update) and be accurate (if the transition stops at gray level 3).

  The grayscale PTB method re-inserts elements into two or more steps that have been removed from the readable diagonal of the associated transition matrix, such as those shown in Table 7 above, by introducing multiple gray level steps. Correspondingly, by allowing the gray level to change between each meso frame by two or more units), which can be transformed, thus eliminating the degeneration of the meso frame step described in the previous paragraph To do. This variation can be achieved by replacing the polar bit matrix with a counter array, which counts from two or more bits to the number of bits required for full grayscale image representation for each bit of the display. including. The waveforms also include up to all N × N transitions with each waveform equally divided into four (or any other essentially any number of meso frames).

  The particular TB method discussed above is a 2-bit grayscale method with two intermediate gray levels, but the TB method can of course be used with any number of gray levels. However, the increased benefit of decreased latency tends to decrease as the number of gray scales increases.

Thus, the present invention provides two types of TB methods that significantly reduce the update latency in monochrome mode while minimizing the complexity of the controller algorithm. These methods may prove particularly useful in interactive 1-bit (monochrome) applications, such as personal digital assistance and electronic dictionaries where fast response to user input is paramount.
Section E: Waveform Compression Method and Apparatus As noted above, the last major aspect of the present invention relates to a method for reducing the amount of waveform data that must be stored to drive a bistable electro-optic display. More specifically, this aspect of the invention provides a “waveform compression” or “WC” method for driving an electro-optic display. The electro-optic display is a plurality of pixels, each pixel having a plurality of pixels capable of achieving at least two different gray levels. The method stores a base waveform defining a series of voltages applied during a particular transition by a pixel between gray levels, stores a multiplication factor for the particular transition, and for a period dependent on the multiplication factor. Achieving a particular transition by applying a series of voltages to the pixel.

  When an impulse driven electro-optic display is being driven, each pixel of the display has a voltage pulse to achieve a transition from one optical state to another, typically a transition between gray levels. (Ie, the voltage difference between the two electrodes associated with that pixel) or a series of voltage pulses (ie, a waveform). The data necessary to define the set of waveforms for each transition (which constitutes a complete drive scheme) is stored on a memory, typically a display controller. However, the data may instead be stored on a host computer or other auxiliary device. The drive scheme can comprise a large number of waveforms (as described in the aforementioned MEDEOD application), variations in environmental parameters such as temperature and humidity, and non-environmental variations such as the operating lifetime of electro-optic media. It may be necessary to store multiple sets of waveform data that allow Accordingly, the amount of memory required to hold the waveform data can be substantial. In order to reduce the cost of the display controller, it is desirable to reduce the amount of memory. A simple compression scheme that can be practically applied to a display controller or host controller is beneficial in reducing the amount of memory required for waveform data, thereby reducing display controller costs. The waveform compression method of the present invention provides a simple compression scheme that is particularly advantageous for electrophoretic displays and other known bistable displays.

  Uncompressed waveform data for a particular transition is typically stored as a series of bit data, with each bit set specifying a particular voltage to be applied at a particular point in the waveform. As an example, consider a tri-level voltage drive scheme. In this tri-level voltage drive scheme, the pixel is driven to black using a positive voltage (+ 10V in this example), to white using a negative voltage (−10V) and held in the current optical state at zero voltage. To be driven. A given time element (scan frame for an active matrix display) may be encoded using 2 bits (eg, as shown in Table 8 below).

Using this binary representation, a waveform used for an active matrix drive comprising a + 10V pulse that lasts for 5 scan frames followed by 2 scan frames of zero voltage is expressed as follows: The

01010101010000
A waveform with multiple time segments requires the storage of multiple bit sets of waveform data.

  In accordance with the WC method of the present invention, the waveform data is stored as a base waveform (as in the binary representation above) and a multiplication factor. The display controller (or other suitable hardware) applies a series of voltages defined by the base waveform to the pixels for a period that depends on the multiplication factor. In a preferred form of such a WC method, bit sets (such as those described above) are used to represent the base waveform, but the voltage defined by each bit set is applied to the pixels for the n time segment. Where n is the multiplication factor associated with the waveform. The multiplication factor must be a natural number. For multiplication factor 1, the applied waveform is unchanged from the base waveform. For multiplication factors greater than 1, the voltage series representation is compressed for at least some waveforms. That is, fewer bits are needed to represent these waveforms than would be necessary if the data was stored in uncompressed form.

As an example, using the binary representation of the three voltage levels in Table 8, 12 scan frames of + 10V, followed by 9 scan frames of -10V, followed by 6 scan frames of + 10V And a waveform that requires three scan frames at 0V followed by three scan frames. This waveform is expressed in uncompressed form as
01010101010101010101010111010101010101010100101010101101000000
In compression format,
Gain: 3
Base waveform: 01010101101010010100
The length of the voltage sequence that must be assigned to each waveform is determined by the longest waveform. For encapsulated electrophoretic displays and other electro-optic displays, the longest waveform is typically required at the lowest temperature, at which the electro-optic medium responds slowly to the applied field. . At the same time, the resolution required to successfully achieve a transition decreases when the response is slow, and thus the loss in optical state accuracy by grouping consecutive scan frames with the WC method of the present invention. There is almost no. Using this compression method, a number of scan frames (or generally time segments) that are appropriate for a waveform at moderately high temperatures with short update times can be assigned to each waveform. At low temperatures where the number of scan frames required can exceed memory allocation, multiplication factors greater than 1 can be used to generate long waveforms. This ultimately results in reduced memory requirements and cost reduction.

  The WC method of the present invention is in principle equivalent to simply changing the frame time of the active matrix at various temperatures. For example, the display may be driven at 50 Hz at room temperature and 25 Hz at 0 ° C. to extend the allowable waveform time. However, the WC method is superior because the backplane is designed to minimize capacitive and resistive voltage artifacts at a given scan rate. A significant departure in either direction from this optimal scan rate will result in at least one type of artifact. Therefore, it is better to keep the actual scan rate constant while grouping the scan frames using the WC method, and the WC method does not actually change the physical scan rate, Provides virtually a way to achieve virtual change.

Claims (15)

A method of driving an electro-optic display having at least one pixel capable of achieving at least two different gray levels, comprising:
At least two different waveforms are used for the same transition between specific gray levels, the specific gray level depending on the duration of the pixel pause time in the state where the transition begins, and the at least two different waveforms Is
(A) means for inserting at least one balanced pulse pair;
Differing by at least one of (b) means for deleting at least one balanced pulse pair, and (c) means for inserting at least one period of zero voltage, said (a), (b) or (c) The difference between the at least two different waveforms caused by at least one of the means is related to variations in the duration of the dwell time of the pixel at the state where the transition begins , Means a series of two pulses of opposite polarity, such that the total impulse of the balanced pulse pair is substantially zero.   The method of claim 1, wherein all waveforms are DC balanced.   The method of claim 1, wherein the waveforms differ from each other by insertion of at least one balanced pulse pair or deletion of at least one balanced pulse pair. The method of claim 3 , wherein the two pulses of the balanced pulse pair are each a constant voltage but opposite polarity and of equal length. The method of claim 3 , wherein the period occupied by the at least one deleted balanced pulse pair is replaced by a period of zero voltage. At least one balanced pulse pair is deleted and the other elements of the base waveform are shifted in time to occupy the period previously occupied by the at least one deleted balanced pulse pair, and the zero voltage period is 4. The method of claim 3 , wherein the method is inserted at a different time than the time occupied by the at least one deleted balanced pulse pair. The method of claim 1, wherein the voltage of the at least two different waveforms and the at least one balanced pulse pair at any point in time is 0, + V, or −V , and V is a predetermined drive voltage. The total number of balanced pulse pairs inserted and deleted is the first number of balanced pulse pairs , the total number of inserted periods of zero voltage is the second number of zero voltage periods, The method of claim 1, wherein the sum of the one number and the second number does not exceed six. The method of claim 8 , wherein the sum of the first number and the second number does not exceed four. The method of claim 9 , wherein the sum of the first number and the second number does not exceed two.   The method of claim 1, wherein the display comprises a rotating dichroic member or an electrochromic medium.   The display is an electrophoretic electro-optic comprising a plurality of electrically charged particles in a fluid, the plurality of electrically charged particles capable of moving in the fluid when an electric field is applied to the fluid The method of claim 1, comprising a medium. The method of claim 12 , wherein the fluid is a gas. The method of claim 12 , wherein the charged particles and the fluid are confined within a plurality of capsules or a plurality of microcells.   A computer readable medium having software code stored thereon that, when the computer executes the software code, causes the computer to perform the method of claim 1.