HK40007937A - Drivers providing dc-balanced refresh sequences for color electrophoretic displays - Google Patents
Drivers providing dc-balanced refresh sequences for color electrophoretic displays Download PDFInfo
- Publication number
- HK40007937A HK40007937A HK19131482.2A HK19131482A HK40007937A HK 40007937 A HK40007937 A HK 40007937A HK 19131482 A HK19131482 A HK 19131482A HK 40007937 A HK40007937 A HK 40007937A
- Authority
- HK
- Hong Kong
- Prior art keywords
- duration
- signal
- amplitude
- display
- particles
- Prior art date
Links
Description
Cross Reference to Related Applications
This application claims priority from U.S. application serial No. 15/454,276, filed on 3,9, 2017. This application also claims priority from U.S. provisional application serial No. 62/509,512 filed on 22/5/2017. The entire contents of the above application are hereby incorporated by reference.
Technical Field
The present invention relates to a method for driving an electro-optic display and in particular, but not exclusively, to an electrophoretic display capable of rendering more than two colors using a single layer of electrophoretic material comprising a plurality of colored particles (e.g., white, cyan, yellow and magenta particles), wherein two of the particles are positively charged, two of the particles are negatively charged and one of the positively charged particles and one of the negatively charged particles has a thick polymer shell.
Background
The term "colored" as used herein includes black and white. The white particles are typically of the light scattering type.
The term "grey state" is used herein in its conventional meaning in the imaging arts to refer to a state between two extreme optical states of a pixel, and does not necessarily imply a black-white transition between the two extreme states. For example, several of the E Ink patents and published applications mentioned below describe electrophoretic displays in which the extreme states are white and deep blue, so that the intermediate gray state is effectively light blue. Rather, as mentioned, the change in optical state may not be a color change at all. The terms "black" and "white" may be used below to denote the two extreme optical states of the display, and should be understood to generally include extreme optical states other than black and white at all, for example the aforementioned white and deep blue states.
The terms "bistable" and "bistability" are used herein in their conventional meaning in the art to refer to displays comprising display elements having first and second display states which differ in at least one optical property, and such that any given element, after being driven by an addressing pulse of finite duration, assumes its first or second display state and, after the addressing pulse has been terminated, that state will persist at least several times, for example at least 4 times, for the minimum duration required for the addressing pulse to change the state of the display element. U.S. patent No. 7,170,670 shows that some particle-based electrophoretic displays with gray scale capability can be stable not only in their extreme black and white states, but also in their intermediate gray states, as well as some other types of electro-optic displays. This type of display may be referred to as a multi-stable rather than bistable, but for convenience the term bistable may be used herein to encompass both bistable and multi-stable displays.
When used to refer to the driving of an electrophoretic display, the term "pulse" is used herein to denote the integration of the applied voltage with respect to time during driving of the display.
Particles that absorb, scatter, or reflect light in a broad band or at a selected wavelength are referred to herein as colored or pigmented particles. Various materials that absorb or reflect light other than pigments (which term is meant strictly as insoluble colored materials), such as dyes or photonic crystals, may also be used in the electrophoretic media and displays of the present invention.
Particle-based electrophoretic displays have been the subject of intensive research and development for many years. In such displays, a plurality of charged particles (sometimes referred to as pigment particles) move through a fluid under the influence of an electric field. Electrophoretic displays have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption compared to liquid crystal displays. However, problems with the long-term image quality of these displays have prevented their widespread use. For example, the particles that make up electrophoretic displays tend to settle, resulting in insufficient lifetime of these displays.
As mentioned above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, this fluid is a liquid, but gaseous fluids can be used to produce the electrophoretic medium; see, for example, kitamura, T., et al, "electric tuner movement for electronic paper-like display", IDW Japan,2001, paper HCS1-1, and Yamaguchi, Y., et al, "tuner display using insulating substrates charged switchgear", IDW Japan,2001, paper AMD4-4). See also U.S. Pat. nos. 7,321,459 and 7,236,291. Such gas-based electrophoretic media are susceptible to particle settling, as are liquid-based electrophoretic media, when the media are used in an orientation that allows such settling (e.g., in the performance of a medium disposed in a vertical plane). More specifically, particle settling appears to be a more serious problem in gas-based electrophoretic media than in liquid-based electrophoretic media, because the lower viscosity of gaseous suspending fluids allows electrophoretic particles to settle more quickly than liquid suspending fluids.
Many patents and applications assigned to or in the name of the Massachusetts Institute of Technology (MIT) and E Ink Corporation describe a number of various techniques used in capsule-type electrophoresis and other electro-optic media. Such capsule-type media comprise a number of small capsules, each of which itself comprises an internal phase of electrophoretically mobile particles contained in a fluid medium and a capsule wall surrounding the internal phase. Typically, the capsules themselves are held in a polymeric adhesive to form an adhesive layer (coherent layer) between two electrodes. The techniques described in these patents and applications include:
a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Pat. nos. 7,002,728 and 7,679,814;
(b) Capsule, adhesive and packaging processes; see, for example, U.S. Pat. nos. 6,922,276 and 7,411,719;
(c) Microcell structures, wall materials, and methods of forming microcells; see, for example, U.S. patent nos. 7,072,095 and 9,279,906;
(d) Methods of filling and sealing microcells; see, for example, U.S. Pat. nos. 7,144,942 and 7,715,088;
(e) Films and sub-assemblies (sub-assemblies) comprising electro-optic material; see, for example, U.S. Pat. nos. 6,982,178 and 7,839,564;
(f) Backsheets, adhesive layers and other auxiliary layers and methods for use in displays; see, for example, U.S. Pat. nos. 7,116,318 and 7,535,624;
(g) Color formation and color adjustment; see, e.g., U.S. Pat. Nos. 6,017,584;6,545,797;6,664,944;6,788,452;6,864,875;6,914,714;6,972,893;7,038,656;7,038,670;7,046,228;7,052,571;7,075,502; 7,167,155;7,385,751;7,492,505;7,667,684;7,684,108;7,791,789;7,800,813;7,821,702;7,839,564; 7,910,175;7,952,790;7,956,841;7,982,941;8,040,594;8,054,526;8,098,418;8,159,636;8,213,076;8,363,299;8,422,116;8,441,714;8,441,716;8,466,852;8,503,063;8,576,470;8,576,475;8,593,721;8,605,354;8,649,084;8,670,174;8,704,756;8,717,664;8,786,935;8,797,634;8,810,899;8,830,559;8,873,129;8,902,153;8,902,491;8,917,439;8,964,282;9,013,783;9,116,412;9,146,439;9,164,207;9,170,467;9,170,468;9,182,646;9,195,111;9,199,441;9,268,191;9,285,649;9,293,511;9,341,916;9,360,733;9,361,836;9,383,623; and 9,423,666; and U.S. patent application publication No. 2008/0043318;2008/0048970;2009/0225398;2010/0156780;2011/0043543;2012/0326957;2013/0242378;2013/0278995;2014/0055840;2014/0078576;2014/0340430;2014/0340736;2014/0362213;2015/0103394;2015/0118390;2015/0124345;2015/0198858;2015/0234250;2015/0268531;2015/0301246;2016/0011484;2016/0026062;2016/0048054;2016/0116816;2016/0116818; and 2016/0140909;
(h) A method for driving a display; see, for example, U.S. Pat. nos. 5,930,026;6,445,489;6,504,524;6,512,354;6,531,997;6,753,999;6,825,970;6,900,851;6,995,550;7,012,600;7,023,420;7,034,783;7,061,166;7,061,662;7,116,466;7,119,772;7,177,066;7,193,625;7,202,847;7,242,514;7,259,744;7,304,787;7,312,794;7,327,511;7,408,699;7,453,445;7,492,339;7,528,822;7,545,358;7,583,251;7,602,374;7,612,760;7,679,599;7,679,813;7,683,606;7,688,297;7,729,039;7,733,311;7,733,335;7,787,169;7,859,742;7,952,557;7,956,841;7,982,479;7,999,787;8,077,141;8,125,501;8,139,050;8,174,490;8,243,013;8,274,472;8,289,250;8,300,006;8,305,341;8,314,784;8,373,649;8,384,658;8,456,414;8,462,102;8,514,168;8,537,105;8,558,783;8,558,785;8,558,786;8,558,855;8,576,164;8,576,259;8,593,396;8,605,032;8,643,595;8,665,206;8,681,191;8,730,153;8,810,525;8,928,562;8,928,641;8,976,444;9,013,394;9,019,197;9,019,198;9,019,318;9,082,352;9,171,508;9,218,773;9,224,338;9,224,342;9,224,344;9,230,492;9,251,736;9,262,973;9,269,311;9,299,294;9,373,289;9,390,066;9,390,661; and 9,412,314; and U.S. patent application publication Nos. 2003/0102858;2004/0246562;2005/0253777;2007/0091418;2007/0103427;2007/0176912;2008/0024429;2008/0024482;2008/0136774;2008/0291129;2008/0303780;2009/0174651;2009/0195568;2009/0322721;2010/0194733;2010/0194789;2010/0220121;2010/0265561;2010/0283804;2011/0063314;2011/0175875;2011/0193840;2011/0193841;2011/0199671;2011/0221740;2012/0001957;2012/0098740;2013/0063333;2013/0194250;2013/0249782;2013/0321278;2014/0009817;2014/0085355;2014/0204012;2014/0218277;2014/0240210;2014/0240373;2014/0253425;2014/0292830;2014/0293398;2014/0333685;2014/0340734;2015/0070744;2015/0097877;2015/0109283;2015/0213749;2015/0213765;2015/0221257;2015/0262255;2015/0262551;2016/0071465;2016/0078820;2016/0093253;2016/0140910; and 2016/0180777 (these patents and applications may be referred to below as MEDEOD (method for driving electro-optic displays) applications);
(i) An application for a display; see, for example, U.S. Pat. nos. 7,312,784 and 8,009,348; and
(j) Non-electrophoretic displays, such as those described in U.S. Pat. nos. 6,241,921; and U.S. patent application publication No. 2015/0277160; and U.S. patent application publication Nos. 2015/0005720 and 2016/0012710.
Many of the above patents and applications recognize that the walls surrounding the discrete microcapsules in a capsule-type electrophoretic medium may be replaced by a continuous phase, resulting in a so-called polymer-dispersed electrophoretic display, wherein the electrophoretic medium contains a plurality of discrete droplets of an electrophoretic fluid and a continuous phase of a polymeric material, and the discrete droplets of electrophoretic fluid within such a polymer-dispersed electrophoretic display may be considered as capsules or microcapsules, even if no discrete capsule film is associated with each individual droplet; see, for example, U.S. patent No. 6,866,760. Accordingly, for the purpose of the present application, such polymer-dispersed electrophoretic media are considered to be subspecies of capsule-type electrophoretic media.
A related type of electrophoretic display is the so-called microcell electrophoretic display. In microcell electrophoretic displays, charged particles and a fluid are not encapsulated in microcapsules, but instead are held in a plurality of cavities (capsules) formed within a carrier medium (typically, a polymeric film). See, for example, U.S. Pat. nos. 6,672,921 and 6,788,449, both of which are assigned to Sipix Imaging inc.
Although electrophoretic media are typically opaque (because, for example, in many electrophoretic media, the particles substantially block the transmission of visible light through the display) and operate in a reflective mode, many electrophoretic displays can be made to operate in a so-called raster mode (shutter mode), in which one display state is substantially opaque and one display state is transmissive. See, for example, U.S. Pat. nos. 5,872,552, 6,130,774, 6,144,361, 6,172,798, 6,271,823, 6,225,971, and 6,184,856. A dielectrophoretic display (which is similar to an electrophoretic display but relies on changes in electric field strength) may operate in a similar mode; see U.S. Pat. No. 4,418,346. Other types of electro-optic displays are also capable of operating in a raster mode. Electro-optic media operating in a raster mode may be used in the multilayer structure of a full color display; in such a configuration, at least one layer adjacent to the viewing surface of the display operates in a raster mode to expose or conceal a second layer further from the viewing surface.
Capsule type electrophoretic displays generally do not suffer from the failure modes of traditional electrophoretic device clustering (clustering) and settling (settling) and provide additional advantages such as the ability to print or coat displays on a wide variety of flexible and rigid substrates. (the use of letter printing is intended to include all forms of printing and coating including, but not limited to, pre-metered coating (e.g., block die coating), slot or extrusion coating (slot extrusion coating), slide or cascade coating (slide coating), roll coating (e.g., knife over roll coating and reverse roll coating), coating (grain coating), spray coating (spray coating), meniscus coating (mesh coating), spin coating (spray coating), brush coating (brush coating), air-knife coating (air-knife coating), and flexible printing processes (see also the manufacturing of flexible printing processes), and thus the flexible printing processes (see also the manufacturing of flexible printing processes) (see also the U.S. Pat. No. 7), and thus the flexible printing processes (see also the manufacturing of flexible printing processes), as well as the use of flexible printing processes (see also the manufacturing of flexible printing processes) (see also the manufacturing of the U.S. Pat. No. 339).
As mentioned above, most simple prior art electrophoretic media display substantially only two colors. Such electrophoretic media use a single type of electrophoretic particle having a first color in a colored fluid having a second, different color (in which case the first color is displayed when the particle is adjacent to the viewing surface of the display and the second color is displayed when the particle is spaced from the viewing surface), or first and second types of electrophoretic particles having different first and second colors in an uncolored fluid (in which case the first color is displayed when the first type of particle is adjacent to the viewing surface of the display and the second color is displayed when the second type of particle is adjacent to the viewing surface). Typically, the two colors are black and white. If a full color display is desired, a color filter array may be deposited on the viewing surface of a monochrome (black and white) display. Displays with color filter arrays rely on area sharing and color mixing to generate color stimuli. The available display area is shared between three or four primary colors, e.g., red/green/blue (RGB) or red/green/blue/white (RGBW), and the filters may be arranged in a one-dimensional (line) or two-dimensional (2 × 2) repeating pattern. Other choices of primary colors or more than three primary colors are also known in the art. The three (in the case of an RGB display) or four (in the case of an RGBW display) sub-pixels are chosen to be small enough so that they visually blend together into a single pixel with a uniform color stimulus ("color mixing") at the intended viewing distance. An inherent disadvantage of area sharing is that colorant is always present and the color can only be adjusted by switching the corresponding pixel of the underlying monochrome display to white or black (turning the corresponding primary color on or off). For example, in an ideal RGBW display, each of the red, green, blue and white primaries occupies one quarter of the display area (one of the four subpixels), where the white subpixel is as bright as the underlying monochrome display white, and each colored subpixel is not brighter than one third of the monochrome display white. The white luminance displayed by the display as a whole cannot exceed half the luminance of the white sub-pixel (the white area of the display is generated by displaying one white sub-pixel out of every four sub-pixels, plus each colored sub-pixel in colored form amounts to one third of one white sub-pixel, so that the combined contribution of the three colored sub-pixels does not exceed one white sub-pixel). The brightness and saturation of the color is reduced by switching the area-shared color pixels to black. When mixing yellow, region sharing is particularly problematic because it is brighter than any other color of equal brightness, and saturated yellow is almost as bright as white. Switching the blue pixels (one quarter of the display area) to black will make the yellow too dark.
Multilayer stacked electrophoretic displays are known in the art; see, e.g., J.Heikenfeld, P.Drzaic, J-S Yeo and T.Koch, journal of the SID,19 (2), 2011, pp.129-156. In such displays, ambient light passes through the image in each of the three subtractive primary colors in a manner that closely resembles conventional color printing. U.S. patent No. 6,727,873 describes a stacked electrophoretic display in which three layers of switchable cells are placed over a reflective background. Similar displays are known in which colored particles are moved laterally (see, for example, international application No. WO 2008/065605), or isolated into microcells using a combination of vertical and lateral motion. In both cases each layer is provided with electrodes for collecting or dispersing the colored particles pixel by pixel, so that each of the three layers requires a layer of thin film transistors (TFT's), of which two must be substantially transparent, and a light-transmissive counter electrode. Such a complex electrode arrangement is expensive to manufacture and it is difficult in the current state of the art to provide a pixel electrode plate which is sufficiently transparent, in particular because the white state of the display must be viewed through several layers of electrodes. Multi-layer displays also suffer from parallax problems as the thickness of the display stack approaches or exceeds the pixel size.
Us patent application publications nos. 2012/0008188 and 2012/0134009 describe multicolor electrophoretic displays having a single backplane comprising independently addressable pixel electrodes and one shared light-transmissive front electrode. A plurality of electrophoretic layers are disposed between the back plate and the front electrode. The displays described in these applications are capable of rendering any primary color (red, green, blue, cyan, magenta, yellow, white and black) at any pixel location. However, the use of multiple electrophoretic layers between a single set of addressing electrodes has disadvantages. The particles in a particular layer are subjected to a lower electric field than in the case of a single electrophoretic layer addressed with the same voltage. Furthermore, light loss in the electrophoretic layer closest to the viewing surface (e.g., due to light scattering or unwanted light absorption) may affect the appearance of the image formed in the underlying electrophoretic layer.
Attempts have been made to provide full color electrophoretic displays using a single electrophoretic layer. For example, U.S. patent application publication No. 2013/0208338 describes a color display comprising an electrophoretic fluid comprising one or both types of pigment particles dispersed in a transparent and colorless or colored solvent, the electrophoretic fluid being disposed between a shared electrode and a plurality of pixel or drive electrodes. The driving electrode is configured to expose the background layer. U.S. patent application publication No. 2014/0177031 describes a method for driving a display cell filled with an electrophoretic fluid comprising two types of charged particles with opposite charge polarities and two contrasting colors. Both types of pigment particles are dispersed in a colored solvent, or an uncharged or slightly charged solvent with colored particles. This method includes driving the display cell by applying a drive voltage that is about 1% to about 20% of the full drive voltage to display the color of the solvent or the color of the uncharged or slightly charged colored particles. U.S. patent application publication nos. 2014/0092465 and 2014/0092466 describe an electrophoretic fluid and a method for driving an electrophoretic display. The fluid comprises a first, a second and a third type of pigment particles, all of which are dispersed in a solvent or solvent mixture. The first and second types of pigment particles carry opposite charge polarities, and the third type of pigment particles have a charge level that is less than about 50% of the charge level of the first or second type. The three types of pigment particles have different threshold voltage levels or different mobility levels, or both. The term full-color display as used below is not disclosed in these patent applications in any sense.
U.S. patent application publication No. 2007/0031031 describes an image processing apparatus for processing image data to display an image on a display medium, in which each pixel is capable of displaying white, black, and another color. U.S. patent application publication No. 2008/0151355; 2010/0188732; and 2011/0279885 describes a color display in which the movable particles move through a porous structure. U.S. patent application publication nos. 2008/0303779 and 2010/0020384 describe a display medium containing first, second, and third particles of different colors. The first and second particles may form an aggregate and the smaller third particles may move through the pores left between the aggregated first and second particles. U.S. patent application publication No. 2011/0134506 describes a display device including an electrophoretic display module including a plurality of types of particles encapsulated between a pair of substrates, at least one of the substrates being translucent, and each of the respective plurality of types of particles carrying electricity of the same polarity, having different optical properties, and having different migration speeds and/or electric field critical values for movement, a translucent display side electrode disposed on a substrate side where the translucent substrate is disposed, a first back electrode disposed on the other substrate side and facing a display side electrode, and a second back electrode disposed on the other substrate side and facing the display side electrode; and a voltage control section that controls voltages applied to the display side electrode, the first back electrode, and the second back electrode such that a type of particle having a fastest migration speed among the plurality of types of particles or a type of particle having a lowest critical value among the plurality of types of particles sequentially moves to the first back electrode or the second back electrode according to each type of the different types of particles, and then the particle moving to the first back electrode moves to the display side electrode. U.S. patent application publication Nos. 2011/0175939;2011/0298835;2012/0327504; and 2012/0139966 describe color displays that rely on the aggregation of multiple particles and threshold voltages. U.S. patent application publication No. 2013/0222884 describes electrophoretic particles comprising colored particles containing a polymer having a charged group and a colorant, and a branched silicon-based polymer (branched silicone-based polymer) attached to the colored particles and containing a reactive monomer as a copolymerization component and at least one monomer selected from a specific monomer group. U.S. patent application publication No. 2013/0222885 describes a dispersion for an electrophoretic display, which includes a dispersion medium, colored electrophoretic particle groups dispersed in the dispersion medium and migrating in an electric field, non-electrophoretic particle groups that do not migrate and have a color different from that of the electrophoretic particle groups, and a compound having a neutral polar group and a hydrophobic group, the compound being contained in the dispersion medium in a proportion of about 0.01 to about 1 mass% based on the entire dispersion. U.S. patent application publication No. 2013/0222886 describes a dispersion for a display comprising floating particles comprising: a core particle containing a colorant and a hydrophilic resin; and a shell covering a surface of each core particle and comprising a hydrophobic resin having a solubility parameter difference of 7.95 (J/cm 3) 1/2 or more. U.S. patent application publication nos. 2013/0222887 and 2013/0222888 describe an electrophoretic particle having a specific chemical composition. Finally, U.S. patent application publication No. 2014/0104675 describes a particle dispersion that includes first and second colored particles that move in response to an electric field and a dispersion medium, the second colored particles having a diameter larger than that of the first colored particles and having charging characteristics identical to those of the first colored particles, and wherein a ratio (Cs/Cl) of a charge amount Cs of the first colored particles per unit area of the display to a charge amount C1 of the second colored particles is less than or equal to 5. Some of the above displays do provide full color, but at the cost of requiring long and cumbersome addressing methods.
U.S. patent application publication nos. 2012/0314273 and 2014/0002889 describe an electrophoretic device including a plurality of first and second electrophoretic particles contained in an insulating liquid, the first and second particles having different charging characteristics from each other; the device further comprises a porous layer contained in the insulating liquid and formed by the fibrous structure. These claims are not intended to be full color displays in the sense described below.
See also U.S. patent application publication No. 2011/0134506 and the above application serial No. 14/277,107; the latter describes a full-color display using three different types of particles in a colored fluid, but the presence of the colored fluid limits the quality of the white state that the display can achieve.
In order to obtain a high resolution display, individual pixels of the display must be addressable and not disturbed by adjacent pixels. One way to achieve this goal is to provide an array of non-linear elements, such as transistors or diodes, where at least one non-linear element is associated with each pixel to produce an "active matrix" display. The addressing or pixel electrodes for addressing the pixels are connected via associated non-linear components to a suitable voltage source. In general, when the nonlinear element is a transistor, a pixel electrode is connected to a drain of the transistor, and this configuration will be adopted in the following description, but an electrode of substantially any pixel may be connected to a source of the transistor. Typically, in high resolution arrays, pixels are arranged in a two-dimensional array of rows and columns, so that any particular pixel can be uniquely identified by the intersection of a particular column and a particular row. The sources of all transistors in each column are connected to a single column electrode, while the gates of all transistors in each row are connected to a single row electrode; furthermore, the source to row and gate to column assignments are also common, and are essentially arbitrary, and can be reversed if desired. The row electrodes are connected to a row driver which essentially ensures that only one row is selected at a given time, i.e. a selection voltage is applied to the selected row electrode to ensure that all transistors in the selected row are conductive, while a selection voltage is applied to all other rows to ensure that all transistors in these non-selected rows remain non-conductive. The column electrodes are connected to a column driver which sets selected voltages on the various column electrodes to drive the pixels in the selected row to their desired optical states. (the foregoing voltages are relative to a shared front electrode, which is typically disposed on the opposite side of the electro-optic medium from the non-linear array and extends across the entire display). After a preselected time interval called the "line address time", the selection of the selected row is deselected, the next row is selected, and the voltage on the column drivers is changed in order to write the next row of the display. This procedure is repeated to write the entire display row by row.
Typically, each pixel electrode has a capacitor electrode associated therewith such that the pixel electrode and the capacitor electrode form a capacitor; see, for example, international patent application No. WO 01/07961. In some embodiments, the transistor may be formed using an N-type semiconductor (e.g., amorphous silicon), and the "select" and "unselect" voltages applied to the gate electrode may be positive and negative, respectively.
Fig. 1 of the accompanying drawings depicts an exemplary equivalent circuit for a single pixel of an electrophoretic display. As shown, the circuit includes a capacitor 10 formed between the pixel electrode and the capacitor electrode. Electrophoretic medium 20 is represented by a capacitor and a resistor in parallel. In some cases, direct or indirect coupling capacitance 30 between the gate electrode of the transistor associated with the pixel and the pixel electrode (commonly referred to as "parasitic capacitance") may generate unwanted noise to the display. Typically, the parasitic capacitance 30 is much smaller than that of the storage capacitor 10Parasitic capacitance, and when a row of pixels of the display is selected or deselected, parasitic capacitance 30 may cause a small negative offset voltage, also known as a "kick back voltage," to the pixel electrode, which is typically less than 2 volts. In some embodiments, to compensate for unwanted "kickback voltage," the shared potential V may be used com Is supplied to the upper plate electrode and capacitor electrode associated with each pixel such that when V is com Is set equal to a kickback voltage (V) KB ) At the same value, each voltage supplied to the display may be offset by the same amount and not experience a net dc imbalance.
However, when V com A problem may occur when the voltage is set to a voltage that does not compensate for the kickback voltage. This may occur when it is desired to apply a higher voltage to the display than would be obtained from the backplane alone. It is well known in the art, for example, if the backplane is supplied with a choice such as nominal + V, 0 or-V, and V is supplied with-V com The maximum voltage applied to the display may be doubled. The maximum voltage seen in this case is +2V (i.e., under the backplate versus the upper plate), while the minimum value is zero. If a negative voltage is required, then V com The potential must be raised to at least zero. Therefore, the waveform for addressing the display with positive and negative voltages using top plate switching (top plate switching) must have a distribution to multiple V com A particular frame shape (frame) for each of the voltage settings.
A set of waveforms for driving a color electrophoretic display having four particles is described in U.S. application serial No. 14/849,658, which is incorporated herein by reference. In U.S. application Ser. No. 14/849,658, seven different voltages are applied to the pixel electrodes: three positive voltages, three negative voltages and zero voltage. However, in some embodiments, the maximum voltage used in these waveforms is higher than can be handled by an amorphous silicon thin film transistor. In this case, a suitably high voltage can be obtained by using upper plate switching. When (as described above) V is turned on com Is intentionally set to V KB When used, a separate power supply may be used. However, use is made ofAnd V when using upper plate to switch com Setting as many independent power supplies is expensive and inconvenient. Furthermore, upper plate switching is known to increase kickback, thereby reducing color state stability. Therefore, it is necessary to use for the back plate and V com To compensate for dc offset caused by kickback voltage. Of course, a full dc offset will result in a longer pulse sequence and thus a longer image update time.
Disclosure of Invention
The invention relates to a driver configured to deliver two-part reset pulses to pixels in a color electrophoretic display. The two-part reset pulse effectively removes the last state information, but does not require more energy or time. As a result, the controller allows the three (or more) particle electrophoretic display to be updated more quickly while using less energy. Surprisingly, the controller also provides a larger color gamut when the reset pulse is adjusted for individual colors. The invention additionally provides a method of driving an electro-optic display which is dc balanced despite the presence of kickback voltages and variations in the voltage applied to the front electrode.
In one aspect, the present invention relates to a method for driving an electrophoretic display having a front electrode, a back plate and a display medium between the front electrode and the back plate, the display medium comprising three sets of particles of different colors. The method includes implementing a reset phase and a color transition phase for the display. The reset phase includes applying a first signal to the front electrode, the first signal having a first polarity, a first amplitude varying with time, and a first duration; applying a second signal to the backplate during the first duration, the second signal having a second polarity opposite the first polarity, a second amplitude that varies over time; applying a third signal to the front electrode during a second duration, the third signal having a third amplitude with time of the second polarity opposite the first polarity; applying a fourth signal equal to the sum of the first and second amplitudes to the backplate during the second duration. The color transition phase comprises applying a fifth signal to the front electrode, the fifth signal having the second polarity, a fourth amplitude over time, and a third duration after the first and second durations; applying a sixth signal to the backplate, the sixth signal having the first polarity, a fifth amplitude that varies with time, and a fourth duration that is subsequent to the first and second durations; wherein integrating the sum of the first and second amplitudes over time over the first duration and integrating the sum of the first, second and third amplitudes over time over the second duration and integrating the fourth amplitude over time over the third duration and integrating the fifth amplitude over time over the fourth duration produces a pulse offset designed to maintain a dc balance of the display medium during the reset phase and the color transition phase. In some embodiments, the reset phase erases previous optical properties present on the display. In some embodiments, the color transition stage substantially changes the optical properties displayed by the display. In some embodiments, the first polarity is a negative voltage. In some embodiments, the first polarity is a positive voltage. In some embodiments, the pulse offset is proportional to a kickback voltage experienced by the display medium. In some embodiments, the fourth duration occurs during the third duration. In some embodiments, the third duration begins simultaneously with the fourth duration.
In another aspect, the invention includes a method for driving an electrophoretic display having a front electrode, a back plate, and a display medium between the front electrode and the back plate, the display medium including three sets of differently colored particles, the method comprising performing a reset phase and a color transition phase on the display. The reset phase includes applying a first signal to the front electrode, the first signal having a first polarity, a first amplitude that varies with time, and a first duration; applying no signal to the backplate during the first duration; applying a second signal to the front electrode during a second duration, the second signal having a second polarity opposite the first polarity, a second amplitude that varies over time; applying a third signal to the backplate during the second duration, the third signal having the first polarity and a third amplitude that varies with time. The color transition stage includes applying a fourth signal to the front electrode, the fourth signal having the first polarity, a fourth amplitude over time, and a third duration after the first and second durations; applying a fifth signal to the backplane, the fifth signal having the second polarity, a fifth amplitude that varies with time, and a fourth duration that follows the first and second durations, wherein integrating the sum of the first amplitude that varies with time over the first duration and integrating the sum of the second and third amplitudes that vary with time over the second duration and integrating the fourth amplitude that varies with time over the third duration and integrating the fifth amplitude that varies with time over the fourth duration produce a pulse offset that is designed to maintain dc balance of the display medium during the reset phase and the color transition phase. In some embodiments, the reset phase erases previous optical properties present on the display. In some embodiments, the color transition stage substantially changes the optical properties displayed by the display. In some embodiments, the first polarity is a negative voltage. In some embodiments, the first polarity is a positive voltage. In some embodiments, the pulse offset is proportional to a kickback voltage experienced by the display medium. In some embodiments, the fourth duration occurs during the third duration. In some embodiments, the third duration begins simultaneously with the fourth duration.
In another aspect, the invention includes a controller for an electrophoretic display comprising a front electrode, a back plate, and a display medium between the front electrode and the back plate, the display medium comprising three sets of particles of different colors, the controller being operatively connected to the front electrode and the back plate and configured to implement a reset phase and a color transition phase for the display. The reset phase includes applying a first signal to the front electrode, the first signal having a first polarity, a first amplitude that varies with time, and a first duration; applying a second signal to the backplate during the first duration, the second signal having a second polarity opposite the first polarity, a second amplitude that varies over time; applying a third signal to the front electrode during a second duration, the third signal having a second polarity opposite the first polarity, a third amplitude over time; applying a fourth signal to the backplate during the second duration, the fourth signal being equal to the sum of the first and second amplitudes. The color transition stage includes applying a fifth signal to the front electrode, the fifth signal having the second polarity, a fourth amplitude over time, and a third duration after the first and second durations; applying a sixth signal to the backplane, the sixth signal having the first polarity, a fifth amplitude over time, and a fourth duration after the first and second durations, wherein integrating the sum of the first and second amplitudes over time over the first duration and integrating the sum of the first, second, and third amplitudes over time over the second duration and integrating the fourth amplitude over time over the third duration and integrating the fifth amplitude over time over the fourth duration produces a pulse offset designed to maintain dc balance of the display medium during the reset phase and the color transition phase. In some embodiments, the controller implements different reset stages depending on the color to be displayed by the electrophoretic display. In some embodiments, the display medium includes white, cyan, yellow, and magenta particles. In some embodiments, the display medium includes white, red, blue, and green particles.
In another aspect, the invention includes a controller for an electrophoretic display comprising a front electrode, a back plate, and a display medium between the front electrode and the back plate, the display medium comprising three sets of particles of different colors, the controller being operatively connected to the front electrode and the back plate and configured to implement a reset phase and a color transition phase for the display. The reset phase includes applying a first signal to the front electrode, the first signal having a first polarity, a first amplitude that varies with time, and a first duration; applying no signal to the backplate during the first duration; applying a second signal to the front electrode during a second duration, the second signal having a second polarity opposite the first polarity, a second amplitude that varies over time; applying a third signal to the backplate during the second duration, the third signal having the first polarity and a third amplitude that varies with time. The color transition stage includes applying a fourth signal to the front electrode, the fourth signal having the first polarity, a fourth amplitude that varies with time, and a third duration that is subsequent to the first and second durations; applying a fifth signal to the backplane, the fifth signal having the second polarity, a fifth amplitude that varies with time, and a fourth duration that follows the first and second durations, wherein integrating the sum of the first amplitude that varies with time over the first duration and integrating the sum of the second and third amplitudes that vary with time over the second duration and integrating the fourth amplitude that varies with time over the third duration and integrating the fifth amplitude that varies with time over the fourth duration produce a pulse offset that is designed to maintain a dc balance of the display medium during the reset phase and the color transition phase. In some embodiments, the controller implements different reset phases depending on the color to be displayed by the electrophoretic display. In some embodiments, the display medium includes white, cyan, yellow, and magenta particles. In some embodiments, the display medium includes white, red, blue, and green particles.
The electrophoretic medium used in the display of the present invention may be any of those described in the aforementioned application serial No. 14/849,658. Such a medium comprises one light-scattering particle, which is usually white, and three substantially non-light-scattering particles. The electrophoretic medium of the present invention may take any of the forms discussed above. Thus, the electrophoretic medium may be unencapsulated, encapsulated in discrete capsules surrounded by a capsule wall, or in the form of a polymer dispersed or microcell medium.
Drawings
Fig. 1 is an exemplary equivalent circuit of a single pixel of an electrophoretic display.
FIG. 2 is a schematic cross-sectional view showing the position of various colored particles in an electrophoretic medium of the invention when displaying three primary colors, black, white, subtractive colors, and additive colors.
FIG. 3 is a schematic representation of four different types of pigment particles used in a multi-particle electrophoretic medium;
FIG. 4 is a schematic representation of the relative strengths of interactions between pairs of particles in a multi-particle electrophoretic medium;
FIG. 5 is a graph showing the behavior of a plurality of different particles in an electrophoretic medium when subjected to electric fields of different strengths and durations;
FIG. 6 is an exemplary waveform including a two-part reset phase (A) and a color transition phase (B);
FIG. 7 is a voltage versus time graph showing the voltage versus time obtained across an electrophoretic medium for a front electrode and a pixel electrode and waveforms used to generate color in the driving method of the present invention;
FIG. 8A is experimental data showing color gamuts produced with various voltage combinations for a two-part reset phase;
FIG. 8B is a graph showing the total experimental color gamut that can be obtained by implementing a controller that changes the two-part reset phase according to the desired color;
FIG. 9 is a diagram showing an embodiment of DC counterweight pulse;
FIG. 10 is a graph showing the DC-balanced pulse of FIG. 9 as experienced by an electrophoretic particle.
Detailed Description
As mentioned above, the invention can be used for electrophoretic media comprising one light-scattering particle (usually white) and three other particles providing three subtractive primary colors. Such a system is schematically shown in fig. 2 and it may provide white, yellow, red, magenta, blue, cyan, green and black at each pixel.
The three particles providing the subtractive primary colors may be substantially non-light scattering ("SNLS"). The use of SNLS particles allows color mixing and can provide more color results than the same number of scattering particles. The aforementioned US8,587,859 uses particles with reducible primary colors, but requires two different voltage thresholds for independent addressing of the non-white particles (i.e. the display is addressed with three positive and three negative voltages). These critical values must be sufficiently separated to avoid cross talk and this separation requires the use of high addressing voltages for certain colors. In addition, addressing the colored particles with the highest threshold value will also move all other colored particles.
The particles and these other particles must then be switched to their desired positions at a lower voltage. Such a stepwise color addressing method produces unwanted color flicker and longer transition times. The present invention does not require the use of such a step-wise waveform, and addressing all colors can be achieved with only two positive voltages and two negative voltages as described below (i.e., only five different voltages are required in the display, two positive voltages, two negative voltages, and zero voltage, but it may be preferable to use more different voltages to address the display as described below in some embodiments).
As described above, fig. 2 is a schematic cross-sectional view showing positions of various particles in the electrophoretic medium of the present invention when displaying black, white, three primary colors of subtraction, and three primary colors of addition. In fig. 2 it is assumed that the viewing surface of the display is on top (as shown), i.e. the user views the display from this direction, and light is incident from this direction. As previously mentioned, in the preferred embodiment, only one of the four particles used in the electrophoretic medium of the present invention substantially scatters light, and in FIG. 2, this particle is considered a white pigment. Basically, such light scattering white particles form a white reflector against which any particles above the white particles can be viewed (shown in fig. 2). Light entering the viewing surface of the display passes through the particles, reflects off the white particles, passes back through the particles, and exits the display. Thus, the particles above the white particles can absorb various colors, and the color presented to the user is generated by the combination of the particles above the white particles. Any particles disposed below the white particles (behind the user's viewing angle) are obscured by the white particles and therefore do not affect the displayed color. Since the second, third and fourth particles are substantially non-light scattering, their order or arrangement with respect to each other is not important, but for the reasons mentioned above, their order or arrangement with respect to the white (light scattering) particles is critical.
More specifically, when the cyan, magenta, and yellow particles are located below the white particles (case [ a ] in fig. 2), no particles are above the white particles, and thus the pixel displays only white. When a single particle is above a white particle, the color of that single particle is displayed as yellow, magenta, and cyan in cases [ B ], [ D ], and [ F ] of fig. 2, respectively. When two particles are above a white particle, the color displayed is a combination of the colors of the two particles; in case [ C ] of fig. 2, magenta and yellow particles show red, in case [ E ], cyan-green and magenta particles show blue, and in case [ G ], yellow and cyan-green particles show green. Finally, when all three colored particles are located above the white particles (case [ H ] in fig. 2), all incident light is absorbed by the subtractive primary colored particles and the pixel appears black.
It is possible that the reducible primary color can be presented by the light scattering particles, so the display comprises two types of light scattering particles, wherein one type of light scattering particles is white and the other type of light scattering particles is colored. However, in this case the position of the light scattering colored particles relative to other colored particles overlaying the white particles will be important. For example, in rendering black (when all three colored particles are above a white particle), the scattering colored particles cannot be above non-scattering colored particles (otherwise they will be partially or completely hidden behind the scattering particles, and thus the color rendered will be that of the scattering colored particles, not black).
If more than one type of colored particles scatters light, it will not be easy to appear black.
Fig. 2 shows an ideal situation in which the color is not contaminated (i.e. the light scattering white particles completely obscure any particles behind the white particles). In practice, shading with white particles may not be complete, so ideally the particles to be fully shaded may absorb a bit of light. Such contamination typically reduces the brightness and chromaticity of the color presented. In the electrophoretic media of the present invention, such color contamination should be minimized so that the resulting color meets industry standards for color rendition. A particularly supported criterion is SNAP (newspaper advertisement production criteria) which specifies the values of L, a and b for each of the eight primary colors mentioned above. (hereinafter, "primary colors" will be used to mean eight colors, i.e., the three primary colors of black, white, subtractive color, and additive color shown in FIG. 2.)
Methods for electrophoretically arranging a plurality of differently colored particles in a "layer" as shown in FIG. 2 have been described in the prior art. The simplest approach is to "race" pigments with different electrophoretic mobilities; see, for example, U.S. patent No. 8,040,594. This competition is potentially more complex than initially understood because the movement of the charged pigment itself alters the electric field locally experienced in the electrophoretic fluid. For example, when positively charged particles move towards the cathode and negatively charged particles move towards the anode, their charge shields the electric field experienced by the charged particles midway between the two electrodes. It is considered that although the pigment competition is involved in the electrophoresis of the present invention, it is not the cause of the only phenomenon as the particle arrangement shown in fig. 2.
A second phenomenon that can be used to control the movement of multiple particles is heterogeneous aggregation between different pigment types (heter-aggregation); see, for example, the aforementioned US 2014/0092465. Such aggregation may be charge-mediated (coulomb's law) or may occur due to, for example, hydrogen bonding or van der waals interactions. The strength of the interaction may be affected by the surface treatment method of the pigment particles. For example, coulombic interaction may be attenuated when the closest proximity of oppositely charged particles is maximized by a steric barrier (usually grafting or adsorbing the polymer to one or both particle surfaces). In the present invention, as described above, such a polymeric barrier is used for the first and second types of particles, and may or may not be used for the third and fourth types of particles.
A third phenomenon that may be used to control the motion of multiple particles is voltage or current dependent mobility, as described in detail in the aforementioned application Ser. No. 14/277,107.
FIG. 3 shows a schematic cross-sectional view of four pigment types (1-4) used in a preferred embodiment of the present invention. The outer polymer shell adsorbed onto the core pigment is indicated by dark shading, while the core pigment itself is indicated by unshaded shading. Various shapes can be used for the core pigment: spherical, acicular, or other anisometric, aggregates of smaller particles (i.e., "grape clusters"), composite particles comprising small pigment particles or dyes dispersed in a binder, and the like are well known in the art. The polymer shell may be a covalently bonded polymer made by grafting or chemisorption methods well known in the art, or may be physisorbed on the particle surface. For example, the polymer may be a block copolymer comprising insoluble and soluble segments. Some methods for attaching the polymeric shell to the core pigment are described in the examples below.
The first and second particle types preferably have a stronger polymer shell than the third and fourth particle types in one embodiment of the invention. The light scattering white particles are of the first or second type (negatively or positively charged). In the following discussion, it is assumed that the white particles have a negative charge (i.e., belong to type 1), but it will be apparent to those skilled in the art that the general principles described will apply to a set of particles in which the white particles are positively charged.
In the present invention, the electric field required to separate aggregates formed by the mixture of the types 3 and 4 particles in the suspension solvent containing the charge control agent is larger than the electric field required to separate aggregates formed by any other combination of the two types of particles. On the other hand, the electric field required to separate the aggregates formed between the first and second types of particles is smaller than the electric field required to separate the first and fourth particles or the aggregates formed between the second and third particles (of course, smaller than the electric field required to separate the third and fourth particles).
Fig. 3 shows that the core pigments comprising particles are of approximately the same size and that the zeta potential of each particle (although not shown) is assumed to be approximately the same. The thickness of the polymer shell surrounding each core pigment is varied. As shown in fig. 3, the particles of types 1 and 2 have a thicker polymer shell than the particles of types 3 and 4-and this is actually the preferred case for certain embodiments of the present invention.
To understand how the thickness of the polymer shell affects the electric field required to separate aggregates of oppositely charged particles, it may be helpful to consider the force balance between the particle pairs. In practice, aggregates may be composed of a large number of particles, and the situation will be much more complex than in the case of simple pair-wise interactions. However, particle pair analysis does provide some guidance for understanding the present invention.
The force acting on one of the pair of particles in the electric field is calculated by the following equation:
wherein, F App Is the force exerted on the particles by the applied electric field, F C Is the coulomb force, F, exerted on the particle by a second particle of opposite charge VW Is the van der Waals force exerted by the second particle to attract on the particle, F D Is the attractive force exerted on the particle pairs by vacancy flocculation (depletionflocculation) caused by the suspension solvent containing the stabilizing polymer (optional).
Force F exerted on the particle by the applied electric field App Calculated from the following formula:
where q is the charge of the particle, which is related to the zeta potential (zeta) shown in equation (2) (approximately within the Huckel limit), where α is the core pigment radius, s is the thickness of the solvent-swellable polymer shell, and the other symbols have the conventional meaning known in the art.
The magnitude of the force exerted on one particle by another particle due to coulomb interaction is roughly calculated from the following equation for particles 1 and 2:
note that F is applied to each particle App The forces are used to separate the particles, while the other three forces are the attraction between the particles. According to Newton's third law, if F acts on a particle App Force greater than F acting on another particle App Force (because the charge on one particle is higher than the charge on the other), the force used to separate the particle pairs is composed of two F App The weaker of the forces.
As can be seen from (2) and (3), the magnitude of the difference between the attraction and separation coulomb terms is calculated by the following equation:
making (α + s) smaller or zeta larger makes the particles more difficult to separate if the particles have the same radius and zeta potential. Thus, in one embodiment of the present invention, it is preferred that the particles of types 1 and 2 are larger and have a relatively low zeta potential, while the particles 3 and 4 are smaller and have a relatively larger zeta potential.
However, if the thickness of the polymer shell is increased, the van der waals forces between the particles may also change significantly. The polymer shell on the particle is swollen by the solvent and further surface of the core pigment through van der Waals force interactionAnd (4) separating. For radius (alpha) 1 ,α 2 ) Than the distance(s) therebetween 1 +s 2 ) The much larger number of spherical core pigments,
wherein A is the Hamaker constant (Hamaker constant). As the distance between the core pigments increases, the formula becomes more complex, but the effect remains the same: increase of s 1 Or s 2 Has a significant effect on reducing attractive van der waals interactions between particles.
With this background, the logical basis for the particle types shown in FIG. 3 can be understood. Particles of types 1 and 2 have a strong polymer shell swollen by the solvent, allowing the core pigment to separate further, thus reducing more van der waals interactions between them than particles of types 3 and 4, which have little or no polymer shell. Even if the particles have approximately the same size and magnitude of zeta potential, the strength of the interaction between pairs of aggregates can be arranged to meet the above requirements according to the invention.
For more details regarding preferred particles for use in the display of FIG. 3, the reader is referred to the aforementioned application Ser. No. 14/849,658.
Figure 4 shows in a schematic way the electric field strength required to separate the paired aggregates of the particle type of the invention. The interaction between the particles of types 3 and 4 is stronger than the interaction between the particles of types 2 and 3. The interaction between the particles of types 2 and 3 is approximately equal to the interaction between the particles of types 1 and 4, but stronger than the interaction between the particles of types 1 and 2. All interactions between pairs of particles having the same charge sign are as weak or weaker than the interactions between particles of types 1 and 2.
Fig. 5 shows how these interactions can be utilized to form all of the primary colors (subtractive primary, additive primary, black and white) as generally discussed in fig. 2.
When addressed with a low electric field (fig. 5 (a)), the particles 3 and 4 aggregate without separating. The particles 1 and 2 are free to move in the electric field. If the particles 1 are white particles, the color seen from the left side is white and the color seen from the right side is black. Reversing the polarity of the electric field can switch between a black state and a white state. However, the instantaneous color between the black and white states is chromatic. The aggregates of particles 3 and 4 move very slowly in the electric field relative to particles 1 and 2. It can be found that: particle 2 has moved through particle 1 (to the left), while the aggregate of particles 3 and 4 has not moved significantly. In this case, particle 2 would be seen from the left side, while the aggregate of particles 3 and 4 would be seen from the right side. In certain embodiments of the present invention, the aggregates of particles 3 and 4 are weakly positively charged and therefore are located near particle 2 at the beginning of such a transition.
When addressed with a high electric field (fig. 5 (B)), the particles 3 and 4 are separated. Which of the particles 1 and 3 (each with a negative charge) is visible when viewed from the left will depend on the waveform (see below). As shown, particle 3 can be seen from the left side and the combination of particles 2 and 4 can be seen from the right side.
The state shown in fig. 5 (B) begins and a low voltage of opposite polarity will move positively charged particles to the left and negatively charged particles to the right. However, the positively charged particles 4 will encounter the negatively charged particles 1, while the negatively charged particles 3 will encounter the positively charged particles 2. The result is that the combination of particles 2 and 3 will be seen from the left side, while particle 4 can be seen from the right side.
As described above, preferably, the particles 1 are white, the particles 2 are cyan, the particles 3 are yellow, and the particles 4 are magenta.
As is well known in electrophoretic display technology, the core pigment for the white particles is typically a metal oxide with a high refractive index. Examples of white pigments will be described in the following examples.
As mentioned above, the core pigments used to make particles of types 2-4 provide three subtractive primary colors: cyan, magenta, and yellow.
The electrophoretic fluids of the present invention can be used to construct display devices in several ways known in the art. The electrophoretic fluid may be encapsulated in microcapsules or incorporated into a microcell structure that is subsequently encapsulated with a polymeric layer. The microcapsules or microcell layers may be coated or embossed onto a plastic substrate or film with a transparent coating of conductive material. This assembly can be laminated to a backplane with pixel electrodes using a conductive adhesive.
A first embodiment of a waveform for realizing each particle arrangement shown in fig. 2 will now be described. In this discussion, it is assumed that the first particles are white and negatively charged, the second particles are cyan and positively charged, the third particles are yellow and negatively charged, and the fourth particles are magenta and positively charged. One skilled in the art will understand how the color transition will change if the assignment of the colors of the first and second particles is changed when one of the particles is assumed to be white. Likewise, the polarity of the charge on all the particles can be reversed, and the electrophoretic medium will still function in the same way provided that the polarity of the waveform used to drive the medium is also reversed (see next paragraph).
In the following discussion, the waveform (voltage versus time curve) applied to the pixel electrode of the display backplane of the present invention is described and plotted, while assuming that the front electrode is grounded (i.e., at zero potential). The electric field experienced by the electrophoretic medium is of course determined by the potential difference between the back plate and the front electrode and the distance separating them. The display is usually viewed through its front electrode, so the color displayed by the pixel is controlled by the particles adjacent to the front electrode, and the optical transitions involved are sometimes more easily understood if the potential of the front electrode relative to the backplane is considered; this can be done simply by inverting the waveforms discussed below.
These waveforms require that each pixel of the display can be addressed by five different addressing voltages (at + V) high 、+V low 、0、-V low and-V high To indicate that it is illustrated as 30V, 15V, 0, -15V and-30V). In practice, a larger number of addressing voltages may be preferably used. If only three voltages are available (i.e., + V) high 0 and-V high ) Then possibly by having a voltage V high But with a duty cycle of 1/n to achieve the same at lower voltages (e.g., V) high Where n is a positive integer greater than 1) address the same result.
The waveform used in the present invention may include three phases: a dc-balancing phase in which dc-imbalance due to previous waveforms applied to the pixels is corrected or dc-imbalance caused in subsequent color rendering transitions is corrected (as is known in the art); a "reset" phase in which the pixels return to at least approximately the same starting configuration regardless of the previous optical state of the pixels; and the "color development" stage described below. The dc balancing and reset phases are optional and may be omitted depending on the requirements of a particular application. If employed, the "reset" phase may be the same as the magenta development waveform described below, or may involve driving the maximum possible positive and negative voltages continuously, or may be some other pulse pattern as long as it returns the display to a state where the subsequent color can be reproducibly obtained.
The general principle of generating eight primary colors (white, black, cyan, magenta, yellow, red, green and blue) using a second driving method suitable for the display of the present invention will now be described (e.g. as shown in fig. 2). It is assumed that the first pigment is white, the second pigment is cyan, the third pigment is yellow and the fourth pigment is magenta. It will be clear to those of ordinary skill in the art that if the distribution of the color of the pigment is changed, the color presented by the display will change.
Maximum positive and negative voltages (in figure 6 at + -V) applied to the pixel electrode max To produce blue-see figure 2[ e ] by producing second and fourth particles (cyan-green and magenta, respectively)]) Or the third particles alone (yellow-see FIG. 2[ B ])]White pigments scatter light and are located between colored pigments). These blue and yellow colors are not necessarily the best achievable blue and yellow colors for the display. A middle-order positive and negative voltage (in figure 6 at V) applied to the pixel electrode mid To represent) produce black and white colors, respectively (but with the exception ofNot necessarily the best black and white achievable by the display-see fig. 5 (a)).
From these blue, yellow, black or white optical states, the other four primary colors can be obtained by moving only the second particles (in this case, cyan particles) relative to the first particles (in this case, white particles), using the lowest applied voltage (at ± V in fig. 6) min To be shown) are implemented. Thus, the cyan-green color is shifted out of blue (by applying-V) min To the pixel electrode) magenta can be produced (see FIG. 2[ E ] for blue and magenta, respectively]And figure 2[ 2 ], [ D ]]) (ii) a Shift the cyan-green into yellow (by applying + V) min To the pixel electrode) can be provided with green (see figure 2[ B ] for yellow and green, respectively]And 2[ 2 ], [ G ]]) (ii) a The cyan color was shifted out of black (by applying-V) min To the pixel electrode) can be provided with red (see FIG. 2[ H ] for black and red, respectively]And 2[ 2 ], [ C ]]) And shifts the cyan-green color into white (by applying + V) min To the pixel electrode) may be provided with cyan (see FIG. 2[ A ] for white and cyan, respectively]And figure 2[ 2 ], [ F ]])。
While these general principles are useful in creating a waveform configuration of a particular color in the display of the present invention, the ideal behavior described above may not be observed in practice, and thus modifications to the basic approach are desirable.
A general waveform for addressing a color electrophoretic display of the present invention will be described in fig. 6, where the abscissa represents time (arbitrary units) and the ordinate represents the voltage difference between the pixel electrode and the shared front electrode. The magnitude of the three positive voltages used in the driving method shown in fig. 6 may be between about +3V and +30V, while the three negative voltages used are between about-3V and-30V. In a preferred embodiment, the highest positive voltage + V max Is +30V, and has an intermediate positive voltage of + V mid 15V, lowest positive voltage + V min Is 9V. In a similar manner, a negative voltage-V max ，-V mid and-V min And in a preferred embodiment-30V, -15V and-9V. The voltage magnitude + V | = | -V | is not necessary for any of the three voltage levels, but this is preferred in some cases.
There are two distinct phases in the general waveform shown in fig. 6. In the first stage, at + V max and-V max A pulse is provided for erasing a previous image presented on the display (i.e., "resetting" the display) (where "pulse" represents a unipolar square wave, i.e., applying a constant voltage at a predetermined time). The lengths of these pulses (t 1 and t 3) and the remaining time (i.e., the zero voltage period between them (t 2 and t 4)) may be selected such that the entire waveform (i.e., the voltage-versus-time integral of the entire waveform shown in fig. 6) is dc-balanced (i.e., the voltage-versus-time integral is substantially zero). The dc balance can be achieved by adjusting the length of the pulse and the remaining time in phase a so that the net pulse provided in this phase is of the same amplitude and opposite sign to the net pulse provided in phase B during which the display is switched to the particular desired color.
Here, the term "frame" means a single update of all rows in the display. It will be clear to those skilled in the art that in displays of the present invention driven using Thin Film Transistor (TFT) arrays, the available time increments on the abscissa of fig. 6 will typically be quantified at the frame rate of the display. It will also be apparent that the display is addressed by varying the potential of the pixel electrode relative to the front electrode, and this can be achieved by varying the potential of the pixel electrode or the front electrode, or both. In the state of the art, there is typically a matrix of pixel electrodes on the backplane, while the front electrode is shared by all pixels. Therefore, when the potential of the front electrode is changed, the addressing of all pixels is affected. The basic structure of the waveform described above in fig. 6 is the same regardless of whether a varying voltage is applied to the front electrode.
The general waveform shown in fig. 6 requires that the drive electronics provide up to seven different voltages to the data lines during the refresh of a selected row of the display. Although multi-level source drivers capable of delivering seven different voltages are available, many commercially available source drivers for electrophoretic displays only allow three different voltages to be delivered during a single frame(typically, positive, zero, and negative). The general waveforms of fig. 6 may be modified to accommodate a 3-level source driver architecture as long as the three voltages (typically + V, 0, and-V) provided to the panel can be changed from one frame to the next (i.e., so that, for example, a voltage (+ V) can be supplied in frame n max 、0、-V min ) And a voltage (+ V) may be supplied in the frame n +1 mid 、0、-V max ))。
It may sometimes be necessary to control an electrophoretic display using a so-called "top-plate switching" driving method. In the top plate switching driving method, the top plate common electrode can be switched between-V, 0 and + V, and the voltage applied to the pixel electrode can also be changed from-V, 0 to + V, and when the common electrode is at 0 voltage, the pixel transition in one direction is processed, and when the common electrode is at + V, the pixel transition in the other direction is processed.
The same general principles as described above with respect to fig. 6 apply when upper-plate switching is used in conjunction with a 3-level source driver. When the source driver can not supply the preferred V max At the same high voltage, upper plate switching may be better. Methods of driving an electrophoretic display using top-panel switching are well known in the art.
Typical waveforms of the (E Ink) prior art are shown below in table 1, where the numbers in parentheses correspond to the number of frames driven with the indicated backplane voltage (relative to the upper plate, which is considered to be zero potential).
TABLE 1
In the reset phase of this waveform, pulses of maximum negative and positive voltages are provided to erase the previous state of the display. The frame number of each voltage is offset by an amount (denoted as deltax for color x) that compensates for the net pulse in the high/mid-order voltage and low/mid-order voltage phases of the rendered color. To achieve dc balance, Δ x is chosen to be half the net pulse. The reset phase need not be implemented exactly in the manner shown in the table; for example, when using upper-panel switching, it is necessary to assign a certain number of frame shapes to the negative and positive drivers. In such cases, it is preferable to provide a maximum number of high voltage pulses (i.e., 2 Δ x subtracted from the negative or positive frame, as appropriate) consistent with achieving dc balance.
In the high/medium voltage phase, a sequence of N repetitions of a sequence of pulses suitable for each color is provided, as described above, where N can be 1-20. As shown, this sequence includes 14 frames, which are assigned a size V max Or V mid Or a negative or zero voltage. The pulse sequence shown corresponds to the discussion given above. It can be seen that the pulse sequences for the white, blue and cyan colors are the same during this phase of the waveform. Also in this phase, the sequence of pulses that appear yellow and green is the same (since green is achieved starting from the yellow state).
In the low/medium voltage phase, the colors of blue and cyan are obtained from white, and the color of green is obtained from yellow.
The previous discussion of waveforms, particularly dc balancing, neglects the problem of kickback voltage. In fact, as mentioned above, there is an offset between each backplane voltage and the power supply voltage, which is equal to the kickback voltage V KB The numerical value of (c). Thus, if the power supply used provides three voltages + V, 0 and-V, the backplane will actually receive the voltage V + V KB 、V KB and-V + V KB (Note that, in the case of an amorphous silicon thin film transistor, V KB Usually a negative number). However, the same power supply will supply + V, 0 and-V to the front electrode without any kickback voltage offset. Thus, for example, when the front electrode is supplied at-V, the display will experience 2V + V KB Maximum voltage sum V KB The minimum voltage of (c). Instead of using separate power supplies to supply V KB To the front electrode (which may be expensive and inconvenient), the waveform may be divided into positive, negative and V KB Part of the front electrode is supplied.
As described above, in some of the waveforms described in the aforementioned application Ser. No. 14/849,658, seven different voltages may be applied to the pixel electrodes: three positive voltages, three negative voltages and zero voltage. Preferably, the maximum voltage used in these waveforms is higher than the maximum voltage that can be handled by amorphous silicon thin film transistors in the state of the art. In such a case, a high voltage may be obtained through the use of upper plate switching, and the drive waveform may be configured to compensate for kickback voltage and may be substantially dc balanced by the method of the present invention. Fig. 7 schematically depicts one such waveform for displaying a single color. As shown in fig. 7, the waveform of each color has the same basic form: that is, the waveform is dc balanced in nature and may include two portions or stages: (1) A preliminary series of frame shapes for providing a "reset" of the display to reproducibly obtain any color state, and during which a dc imbalance equal and opposite to that of the remainder of the waveform is provided, and (2) a series of frame shapes specific to the color to be rendered; see portions a and B of the waveforms shown in fig. 6.
During the first "reset" phase, the reset of the display ideally erases any memory of the previous state, including the residual voltages and pigment arrangements characteristic of the previously displayed colors. Such an erase is most effective when the display is addressed with the maximum possible voltage during the "reset/dc balance" phase. Furthermore, enough frames may be allocated in this stage to allow balancing of the most unbalanced color transitions. Since some colors require positive DC balance in the second part of the waveform, while others require negative balance, the front electrode voltage V is applied in about half of the frame shape during the "reset/DC balance" phase com Is set to V pH (allowing the maximum possible negative voltage between the back plate and the front electrode), and in the rest, V com Is set to V nH (allowing the maximum possible positive voltage between the back plate and the front electrode). Empirically, V has been found com ＝V pH Frame shape at V com ＝V nH A frame-like preamble is preferred.
The "desired" waveform is described below in figure 7 (i.e.,the actual voltage versus time curve expected to be applied to the electrophoretic medium) and is shown above it implemented with plate switching, where the application to the front electrode (V) is illustrated (V) com ) And the potential of the Back Plate (BP). Assume that the column driver is to be connected to a power supply capable of supplying the following voltages: v pH 、V nH (maximum positive and negative voltage, usually within a range of 10-15V), V pL 、V nL (lower positive and negative voltages, typically in the range of + -1-10V) and zero voltage. In addition to these voltages, the kickback voltage V may also be supplied by an additional power supply KB (a decimal value specific to the particular back plate used, measured as described in U.S. Pat. No. 7,034,783) to the front electrode.
As shown in FIG. 7, each backplane voltage is offset by V from the voltage supplied by the power supply KB (expressed as a negative number), except however that the front electrode is explicitly set to V as described above KB The front electrode voltage does not have this shift.
Although the display of the present invention has been described as producing eight primary colors, in practice it is preferred to produce as many colors as possible at the pixel level. Full color grayscale images can then be rendered by color mixing between these colors using techniques well known to those skilled in the imaging arts. For example, the display may be configured to present eight additional colors in addition to the eight primary colors generated as described above. In one embodiment, these additional colors are: light red, light green, light blue, dark cyan, dark magenta, dark yellow and two gray levels between black and white. The terms "light" and "dark" as used in the context mean colors having substantially the same hue angle (hue angle) as a reference color in color space (e.g., CIE L a b), respectively, but a higher or lower L, respectively.
In general, the way in which light and dark colors are obtained is the same, except that waveforms with slightly different net pulses are used in phases B and C. Thus, for example, the light red, light green, and light blue waveforms have net impulses that are more negative than the corresponding red, green, and blue waveforms in phases B and C, while the dark cyan, dark magenta, and dark yellow waveforms have net impulses that are more positive than the corresponding cyan, magenta, and yellow waveforms in phases B and C. The variation of the net pulse can be achieved by varying the length of the pulses, the number of pulses or the amplitude of the pulses in stages B and C.
The grey color is usually achieved by a sequence of pulses oscillating between a low or medium voltage.
It will be clear to those skilled in the art that in displays of the present invention driven using Thin Film Transistor (TFT) arrays, the available time increments on the abscissa of fig. 7 will typically be quantified by the frame rate of the display. As such, it will be apparent that the display is addressed by varying the potential of the pixel electrode relative to the front electrode, and this can be achieved by varying the potential of the pixel electrode or the front electrode, or both. In the current state of the art, there is typically a matrix of pixel electrodes on the backplane, with the front electrode being shared for all pixels. Therefore, when the potential of the front electrode is changed, the addressing of all pixels is affected. The basic structure of the waveform described above in fig. 7 is the same regardless of whether a varying voltage is applied to the front electrode.
The general waveform shown in fig. 7 requires that the drive electronics provide up to seven different voltages to the data lines during the refresh of a selected row of the display. Although multi-level source drivers capable of delivering seven different voltages are available, many commercially available source drivers for electrophoretic displays only allow three different voltages (typically, a positive voltage, zero voltage, and a negative voltage) to be delivered during a single frame. The term "frame-shaped" herein means a single update of all rows in the display. The general waveforms of fig. 7 can be modified to accommodate a 3-level source driver architecture as long as the three voltages (typically + V, 0 and-V) provided to the panel can be changed from one frame shape to the next (i.e., so that, for example, the voltage (+ V) can be supplied in frame shape n max 、0、-V min ) And a voltage (+ V) may be supplied in the frame n +1 mid 、0、-V max ))。
Referring now to fig. 6, it can be seen from phase a (reset phase) that this phase is divided into phases of equal durationTwo portions of time (shown in dashed lines). When upper plate switching is used, the upper plate is held at one potential in a first of the sections and at an opposite polarity potential in a second section. In the particular case of fig. 6, during the first such portion, the upper plate will remain at V P H, and the back plate will remain at V n H to achieve a total electrophoretic fluid having V n H-V P H (where the back plate potential is customarily referenced relative to the top plate potential). During the second part, the upper plate will remain at V n H, while the back plate is held at V p H. As shown, during the second portion, the electrophoretic fluid will be subjected to V p H-V n H, which is the highest potential available. However, for the re-rendering of certain colors, exposure to such high voltages may result in such an initial pigment alignment that it is difficult to achieve the desired final configuration therefrom. For example, as described in the prior art, in order to represent cyan, it is necessary to confine the magenta pigment (which has the same charge polarity as the cyan pigment) and the yellow pigment in one aggregate. Such aggregates will be separated by a high applied potential and thus magenta will not be controlled and will contaminate cyan.
However, it is not necessary to use the maximum possible voltage in both parts of waveform phase a. All that is required for phase a is to erase the previous color state so that the newly presented color is the same regardless of which color was previous, and the net pulse provided in phase a balances the net pulse in phase B.
Thus, an experiment was conducted in which phase B of the type of waveform shown in Table 1 was held constant while the voltage applied in each of the two portions of phase A was varied (but the same number of frames was assigned to phase A in each case: a total of 120 frames, a first portion of 60 frames, and a second portion of 60 frames). After addressing the display, CIELab L, a, and b values for each primary color were measured.
Table 2 shows the default case, where the maximum possible negative and positive voltages are applied in the first and second part of phase a. This can be done using a top plate switch, whichThe voltage of the first column is applied to the back plate, and the voltage of the second column is applied to the top plate. The color gamut, measured as a convex hull (convex hull) volume containing the eight points listed in table 2, was 21,336 Δ Ε 3 。
Table 3 shows the case where the back plate is held at zero voltage during the first part of phase a. The applied voltage is also smaller in this case than in the case of table 2. The voltages applied in the second part of phase a are the same as in the case of table 2. In order to maintain dc balance, the application time of the lower voltage must of course be relatively long. The color gamut, measured as the convex hull volume containing the eight points listed in table 2, is 20,987 Δ Ε 3 。
Table 4 shows the case where the back plate is held at zero voltage during the second part of phase a. The voltages applied in the first part of phase a are the same as in the case of table 2. The color gamut, measured as the convex hull volume containing the eight points listed in Table 2, was 20,339 Δ E 3 . TABLE 2
| First reset voltage | Second reset voltage | Colour(s) | L* | a* | b* |
| V n H–V p H | V p H–V n H | K | 24.67 | 2.68 | -12.53 |
| V n H–V p H | V p H–V n H | B | 37.26 | 0.97 | -14.51 |
| V n H–V p H | V p H–V n H | R | 43.2 | 16.16 | 11.34 |
| V n H–V p H | V p H–V n H | M | 43.56 | 21.93 | -10.65 |
| V n H–V p H | V p H–V n H | G | 36.29 | -19.89 | 13.13 |
| V n H–V p H | V p H–V n H | C | 48.34 | -9.82 | -6.73 |
| V n H–V p H | V p H–V n H | Y | 67.99 | -10.29 | 56.06 |
| V n H–V p H | V p H–V n H | W | 70.29 | -1.24 | 7.83 |
TABLE 3
| First reset voltage | Second reset voltage | Colour(s) | L* | a* | b* |
| 0–V p H | V p H–V n H | K | 27.82 | 2.2 | -15.78 |
| 0–V p H | V p H–V n H | B | 37.99 | 0.41 | -14.78 |
| 0–V p H | V p H–V n H | R | 43.7 | 17 | 11.4 |
| 0–V p H | V p H–V n H | M | 44.02 | 22.03 | -10.39 |
| 0–V p H | V p H–V n H | G | 37.37 | -21.57 | 13.38 |
| 0–V p H | V p H–V n H | C | 49.06 | -9.96 | -7.78 |
| 0–V p H | V p H–V n H | Y | 67.73 | -10.25 | 53.71 |
| 0–V p H | V p H–V n H | W | 70.02 | -0.99 | 6.7 |
TABLE 4
| First reset voltage | Second reset voltage | Colour(s) | L* | a* | b* |
| V n H–V p H | 0–V n H | K | 27.42 | -4.03 | -10.77 |
| V n H–V p H | 0–V n H | B | 31.99 | -7.38 | -11.16 |
| V n H–V p H | 0–V n H | R | 46.19 | 8.49 | 21.11 |
| V n H–V p H | 0–V n H | M | 47.46 | 12.8 | -3.05 |
| V n H–V p H | 0–V n H | G | 33.33 | -24.63 | 11.2 |
| V n H–V p H | 0–V n H | C | 43.03 | -19.38 | -9.32 |
| V n H–V p H | 0–V n H | Y | 67.21 | -9.44 | 59.36 |
| V n H–V p H | 0–V n H | W | 70.12 | -3.49 | 14.26 |
Fig. 8A shows the results of these experiments as projections on a/b planes: the abscissa indicates a, and the ordinate indicates b. It can be seen that some colors (e.g., red, magenta, and blue) will appear better through the phase a settings corresponding to tables 2 or 3, while other colors (cyan, green, and yellow) will appear better through the phase a settings corresponding to table 4.
Interestingly, an alternative experiment reversing the order of the first and second part of phase a gave very poor results, all colors being contaminated with yellow.
Table 5 gives the optimal color combinations for this experiment. The color gamut, measured as the convex hull volume containing the eight points listed in table 2, was 28,092 Δ Ε 3 . Therefore, by appropriately selecting the voltage applied in the reset phase (phase a) of the waveform, the color gamut is increased by about 50%. The results of table 5 are depicted in fig. 8B.
The method of the present invention is particularly important when it is desired to make the waveform as short as possible. With a fixed voltage in phase a, phase B needs to be made longer in order to compensate for the deviations introduced for certain colors in phase a.
Although the invention is described in stage a with only two sections, one skilled in the art will appreciate that any reasonable number of sections may be used. However, when using upper plate switching, the same structure of the upper plate potential is fixed, regardless of which color is to be presented. According to the present invention, the back plate setting corresponds to each upper plate potential, which varies in phase a of the waveform depending on the color to be represented, but does not violate the condition that the overall waveform including phases a and B is dc-balanced.
TABLE 5
| First reset voltage | Second reset voltage | Colour(s) | L* | a* | b* |
| V n H-V p H | V p H-V n H | K | 24.67 | 2.68 | -12.53 |
| 0-V p H | V p H-V n H | B | 37.99 | 0.41 | -14.78 |
| 0-V p H | V p H-V n H | R | 43.7 | 17 | 11.4 |
| 0-V p H | V p H-V n H | M | 44.02 | 22.03 | -10.39 |
| V n H-V p H | 0-V n H | G | 33.33 | -24.63 | 11.2 |
| V n H-V p H | 0-V n H | C | 43.03 | -19.38 | -9.32 |
| V n H-V p H | 0-V n H | Y | 67.21 | -9.44 | 59.36 |
| 0-V p H | V p H-V n H | W | 70.02 | -0.99 | 6.7 |
The dc balance of the reset pulse can be achieved by:
for the dc-balancing procedure, a set of voltages must be selected for all transitions in the waveform. Selecting a set of voltages can be problematic because some palette colors require high voltages while others require low voltages. For devices with a large number of simultaneous backplane voltages, this is not a problem, as each transition can be balanced individually, but in the case of an upper-plate switch, each transition is tied together through the upper-plate, which forces the transitions to align with each other. The source driver standard imposes an additional limit that currently limits the number of simultaneous backplane voltages to three.
The transition is a sequence of voltages applied to the back plate and the top plate,wherein the content of the first and second substances,is the backplane voltage used to convert j in frame i,is the upper plate voltage at frame i. Let it before implementing DC balance resetIs T j Of total pulses of (2), wherein n j Is T j Update length (in units of frame shape), and V KB Is the kickback voltage of the display.
Let σ be j Is the desired DC balance pulse offset (time V), d r Is the desired total duration of the dc-balancing weight. The dc balance reset has two pulses in it, so the top plate voltage needs to be selected for each pulse, and the back plate voltage needs to be selected for each pulse and each transition. LetTo convert T j The voltage of the kth pulse of (1), wherein,is used for converting T j The back plate voltage of the kth reset pulse, andis the upper plate voltage for the kth reset pulse. It is important that the two pulse voltages are selected such thatAndwith opposite signs for each transition.
It is necessary to select a "zero" voltage, which ideally is 0V, which is not always possible
Wherein, the first and the second end of the pipe are connected with each other,
next, the total maximum duration of each of the two pulses is calculated
Then, the "ideal" duration of each pulse wave for each transition is calculated, which is atThe duration of the case (1). Definition tokenThen, the process of the present invention is carried out,
then, we decompose each pulse into an "active" part and a "zero" part to balance the transitions:
we now prepare the dc-balancing phase to build the waveform. Go up the board withTo drive for a duration of timeThen is followed byTo drive for a duration of timeFIG. 9 shows, for each transition T j Let us turn toDriven for a duration of timeThen is followed byDriven for a duration of timeThen is provided withDriven for a duration of timeThen is followed byDriven for a duration of timeThe resulting waveform experienced by the ink is shown in fig. 10.
At first sight it appears that successive scans of different rows of an active matrix display may disturb the above calculations designed to ensure accurate dc-balancing of the waveforms and the driving method, because when the voltage of the front electrode is changed (typically between successive scans of the active matrix), each pixel of the display will experience an "incorrect" voltage until the scan reaches the relevant pixel and the voltage on its pixel electrode is adjusted to compensate for the change in the voltage of the front electrode, and the period between the change in the front plate voltage and the time the scan reaches the relevant pixel varies depending on the row in which the relevant pixel is located. However, further studies will show that the actual "error" applied to a pixel pulse is proportional to the change in the front plate voltage times the period between the change in the front plate voltage and the time the scan reaches the relevant pixel. Assuming no change in scan rate, the duration of the latter is fixed, so that for any series of changes in the front plate voltage that make the final front plate voltage equal to the initial front plate voltage, the sum of the "errors" of the pulses will be zero and will not affect the overall dc balance of the driving method.
The present invention thus provides a dc-balanced waveform for a multi-particle electrophoretic display. Having thus described several aspects and embodiments of the technology of the present application, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art to which the invention pertains. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the technology described herein. For example, various other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein will be readily apparent to those of ordinary skill in the art to which the invention pertains, and each such variation and/or modification is considered to be within the scope of the embodiments described herein. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described. In addition, any combination of two or more features, systems, objects, materials, kits, and/or methods described herein is included within the scope of the present application if such features, systems, objects, materials, kits, and/or methods are not mutually inconsistent.
Claims (19)
1. A method for driving an electrophoretic display having a front electrode, a back plate and a display medium between the front electrode and the back plate, the display medium comprising three sets of particles of different colors, the method comprising:
implementing a reset phase and a color transition phase for the display, the reset phase comprising:
applying a first signal to the front electrode, the first signal having a first polarity, a first amplitude and a first duration;
applying a second signal to the backplate during the first duration, the second signal having a second polarity opposite the first polarity, a second amplitude;
applying a third signal to the front electrode during a second duration, the third signal having the second polarity opposite the first polarity, a third amplitude;
applying a fourth signal to the backplate during the second duration, the fourth signal having an amplitude equal to the sum of the first and second amplitudes;
the color transition stage comprises:
applying a fifth signal to the front electrode, the fifth signal having the second polarity, a fourth amplitude, and a third duration after the first and second durations;
applying a sixth signal to the backplane, the sixth signal having the first polarity, a fifth amplitude, and a fourth duration after the first and second durations;
wherein integrating the sum of the first and second amplitudes over the first duration and integrating the sum of the first, second and third amplitudes over the second duration and integrating the fourth amplitude over the third duration and integrating the fifth amplitude over the fourth duration produces a pulse offset designed to maintain a dc balance of the display medium during the reset phase and the color transition phase.
2. The method of claim 1, wherein the reset phase erases previous optical properties presented on the display.
3. The method of claim 1, wherein the color transition stage substantially changes an optical property displayed by the display.
4. The method of claim 1, wherein the first polarity is a negative voltage.
5. The method of claim 1, wherein the first polarity is a positive voltage.
6. A method according to claim 1, wherein the pulse offset is proportional to a kickback voltage experienced by the display medium.
7. The method of claim 1, wherein the fourth duration occurs during the third duration.
8. The method of claim 1, wherein the third duration begins simultaneously with the fourth duration.
9. A method for driving an electrophoretic display having a front electrode, a back plate and a display medium between the front electrode and the back plate, the display medium comprising three sets of particles of different colors, the method comprising:
implementing a reset phase and a color transition phase for the display, the reset phase comprising:
applying a first signal to the front electrode, the first signal having a first polarity, a first amplitude and a first duration;
applying no signal to the backplate during the first duration;
applying a second signal to the front electrode during a second duration, the second signal having a second polarity opposite the first polarity, a second amplitude;
applying a third signal to the backplate during the second duration, the third signal having the first polarity and a third amplitude;
the color transition stage comprises:
applying a fourth signal to the front electrode, the fourth signal having the first polarity, a fourth amplitude, and a third duration after the first and second durations;
applying a fifth signal to the backplate, the fifth signal having the second polarity, a fifth amplitude, and a fourth duration after the first and second durations;
wherein integrating the sum of the first amplitude over the first duration and integrating the sum of the second and third amplitudes over the second duration and integrating the fourth amplitude over the third duration and integrating the fifth amplitude over the fourth duration produces a pulse offset designed to maintain the dc balance of the display medium during the reset phase and the color transition phase.
10. The method of claim 9, wherein the fourth duration occurs during the third duration.
11. The method of claim 10, wherein the third duration begins simultaneously with the fourth duration.
12. A controller for an electrophoretic display comprising a front electrode, a back plate and a display medium between the front electrode and the back plate, the display medium comprising three sets of particles of different colors, the controller being operatively connected to the front electrode and the back plate and being configured to perform a reset phase and a color transition phase for the display,
the reset phase includes:
applying a first signal to the front electrode, the first signal having a first polarity, a first amplitude and a first duration;
applying a second signal to the backplate during the first duration, the second signal having a second polarity opposite the first polarity, a second amplitude;
applying a third signal to the front electrode during a second duration, the third signal having a second polarity opposite the first polarity, a third amplitude;
applying a fourth signal to the backplate during the second duration, the fourth signal having an amplitude equal to the sum of the first and second amplitudes;
the color transition stage comprises:
applying a fifth signal to the front electrode, the fifth signal having the second polarity, a fourth amplitude, and a third duration after the first and second durations;
applying a sixth signal to the backplane, the sixth signal having the first polarity, a fifth amplitude, and a fourth duration after the first and second durations;
wherein integrating the sum of the first and second amplitudes over the first duration and integrating the sum of the first, second and third amplitudes over the second duration and integrating the fourth amplitude over the third duration and integrating the fifth amplitude over the fourth duration generates a pulse offset designed to maintain a dc balance of the display medium during the reset phase and the color transition phase.
13. The controller of claim 12, wherein the controller implements different reset phases depending on the color to be displayed by the electrophoretic display.
14. The controller of claim 12, wherein the display medium comprises white, cyan, yellow, and magenta particles.
15. The controller of claim 12, wherein the display medium comprises white, red, blue, and green particles.
16. A controller for an electrophoretic display comprising a front electrode, a back plate and a display medium between the front electrode and the back plate, the display medium comprising three sets of particles of different colors, the controller being operatively connected to the front electrode and the back plate and being configured to implement a reset phase and a color transition phase for the display,
the reset phase includes:
implementing a reset phase and a color transition phase for the display, the reset phase comprising:
applying a first signal to the front electrode, the first signal having a first polarity, a first amplitude and a first duration;
applying no signal to the backplate during the first duration;
applying a second signal to the front electrode during a second duration, the second signal having a second polarity opposite the first polarity, a second amplitude;
applying a third signal to the backplate during the second duration, the third signal having the first polarity and a third amplitude;
the color transition stage comprises:
applying a fourth signal to the front electrode, the fourth signal having the first polarity, a fourth amplitude, and a third duration after the first and second durations;
applying a fifth signal to the backplate, the fifth signal having the second polarity, a fifth amplitude, and a fourth duration after the first and second durations;
wherein integrating the sum of the first amplitude over the first duration and integrating the sum of the second and third amplitudes over the second duration and integrating the fourth amplitude over the third duration and integrating the fifth amplitude over the fourth duration produces a pulse offset designed to maintain the dc balance of the display medium during the reset phase and the color transition phase.
17. The controller of claim 16, wherein the controller implements different reset phases depending on the color to be displayed by the electrophoretic display.
18. The controller of claim 16, wherein the display medium comprises white, cyan, yellow, and magenta particles.
19. The controller of claim 16, wherein the display medium comprises white, red, blue, and green particles.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US15/454276 | 2017-03-09 | ||
| US62/509512 | 2017-05-22 |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| HK42022066115.1A Division HK40080858B (en) | 2017-03-09 | 2019-10-25 | Drivers providing dc-balanced refresh sequences for color electrophoretic displays |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| HK42022066115.1A Addition HK40080858B (en) | 2017-03-09 | 2019-10-25 | Drivers providing dc-balanced refresh sequences for color electrophoretic displays |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| HK40007937A true HK40007937A (en) | 2020-06-05 |
| HK40007937B HK40007937B (en) | 2023-01-13 |
Family
ID=
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US11404012B2 (en) | Drivers providing DC-balanced refresh sequences for color electrophoretic displays | |
| CN115410535B (en) | Driver providing a DC balance update sequence for a color electrophoretic display | |
| CN109074781B (en) | Method for driving an electro-optical display | |
| JP2023541267A (en) | Improved drive voltages for advanced color electrophoretic displays and displays with improved drive voltages | |
| KR102789344B1 (en) | Drive sequences for removing previous state information from color electrophoretic displays | |
| HK40080858A (en) | Drivers providing dc-balanced refresh sequences for color electrophoretic displays | |
| HK40007937B (en) | Drivers providing dc-balanced refresh sequences for color electrophoretic displays | |
| HK40007937A (en) | Drivers providing dc-balanced refresh sequences for color electrophoretic displays | |
| HK40080858B (en) | Drivers providing dc-balanced refresh sequences for color electrophoretic displays | |
| HK40087402A (en) | Driving sequences to remove prior state information from color electrophoretic displays | |
| HK1258165B (en) | Methods for driving electro-optic displays |