TWI667648B - Method for driving an electrophoretic display and controller for an electrophoretic display - Google Patents

Abstract

A method for driving an electro-optic display, the electro-optic display has a front electrode, a back plate, and a display medium, the display medium includes at least three particles of different colors, wherein the medium is located on the front electrode and the back plate between. The method includes performing a reset phase and a color transition phase on the display such that the sum of all pulses results in an offset that maintains the DC balance of the entire display medium. The invention further comprises a controller for performing the method.

Description

Method for driving electrophoretic display and controller for electrophoretic display [Related applications]

This application claims priority from US Application Serial No. 15 / 454,276, filed on March 9, 2017. This application also claims priority to US Provisional Application No. 62 / 509,512, filed on May 22, 2017. The entire contents of the above application are incorporated herein by reference.

The present invention relates to a method for driving an electro-optical display, but is not particularly limited to being capable of exhibiting more than two colors using a single-layer electrophoretic material including a plurality of colored particles (for example, white, cyan, yellow, and magenta particles). An electrophoretic display in which two particles are positively charged and two particles are negatively charged, and one positively charged particle and one negatively charged particle have a thick polymer shell.

The term "color" as used herein includes black and white. White particles are usually light-scattering.

The term "gray state" is used here to refer to the state between the two extreme optical states of a pixel in its traditional meaning in imaging technology, and does not necessarily imply a black-white transition between the two extreme states. ). For example, several E Ink patents and published applications mentioned below describe electrophoretic displays, where the extreme states are white and dark blue, so that the middle gray state is actually light blue. Rather, as stated, the change in optical state may not be a change in color at all. The terms "black" and "white" may be used below to refer to the two extreme optical states of the display, and should be understood to generally include extreme optical states other than black and white, such as the aforementioned white and dark blue states.

The terms "bistable" and "bistability" are used herein in the traditional meaning of the technology to refer to a display including a first and a second display that are different in at least one optical property. The display element of the state, and after any given element is driven by the address pulse with a finite duration, its first or second display state is displayed, and after the address pulse is terminated, that state will last at least several times, For example, at least 4 times; the address pulse needs the shortest duration to change the state of the display element. U.S. Patent No. 7,170,670 shows that some particle-based electrophoretic displays with grayscale capabilities are 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-optical displays. in this way. This type of display may be properly referred to as multi-stable rather than bistable, but for convenience, the term "bistable" may be used herein to cover bistable and multistable displays.

When used to refer to the driving of an electrophoretic display, the term "impulse" is used herein to refer to the integral of the applied voltage with respect to time during the driving of the display.

Particles that absorb, scatter, or reflect light in a wide frequency band or at a selected wavelength are referred to herein as colored or pigmented particles. In the electrophoretic medium and display of the present invention, various materials that absorb or reflect light other than pigments (in the strict sense of the term, meaning insoluble colored materials), such as dyes or photonic crystals, can also be used.

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. When compared to liquid crystal displays, electrophoretic displays can have attributes of good brightness and contrast, wide viewing angles, bi-stable state, and low power consumption. However, problems with the long-term image quality of these displays have prevented their widespread use. For example, the particles that make up an electrophoretic display are prone to settling, 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 flow is liquid, but gaseous fluids can be used to generate the electrophoretic media; see, for example, Kitamura, T., et al., " Electrical toner movement for electronic paper-like display " , IDW Japan , 2001, Paper HCS1-1 and Yamaguchi, Y., et al., " Toner display using insulative particles charged triboelectrically " , IDW Japan, 2001, Paper AMD 4-4). See also US Patent Nos. 7,321,459 and 7,236,291. Such gas-based electrophoretic media appear to be susceptible to causal particles of liquid-based electrophoretic media when such media are used in an orientation that allows such settling (e.g., in the presence of media in a vertical plane). Affected by the same type of problems caused by settlement. More precisely, particle sedimentation seems to be more of a problem in gas-based electrophoretic media than in liquid-based electrophoretic media because the lower viscosity of gaseous suspension fluids allows electrophoresis compared to liquid suspensions. The particles settle faster.

Many patents and applications assigned to, or in the name of, the Massachusetts Institute of Technology (MIT) and E Ink Corporation describe various techniques used in capsule electrophoresis and other electro-optical media. Such a capsule-type medium includes a number of small capsules, each capsule itself including an internal phase of electrophoretic mobile particles contained in a fluid medium and a capsule wall surrounding the internal phase. Generally, the capsule itself is held in a polymer adhesive to form a coherent layer between the two electrodes. Techniques described in these patents and applications include: a) electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814; (b) capsules, adhesives, and packaging processes; see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719; (c) Microcell structures, wall materials, and methods of forming microcells; see, for example, US Patent Nos. 7,072,095 and 9,279,906; (d) methods of filling and sealing microcells; see, for example, US Patent Nos. 7,144,942 and 7,715,088; (e) films and sub-assemblies containing electro-optic materials; see, for example, US Patent Nos. 6,982,178 and 7,839,564; (f) backsheets, adhesive layers, and Other auxiliary layers and methods; see, e.g., U.S. Patent Nos. 7,116,318 and 7,535,624; (g) color formation and color adjustment; see, e.g., U.S. Patent 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; 3, 88.6, 8868; 8868, 8868, 8868; 8768 ; 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 Nos. 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; 2016/0 026062; 2016/0048054; 2016/0116816; 2016/0116818; and 2016/0140909; (h) a method for driving a display; see, for example, US Patent No. 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; 8,68,68 1,191; 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; 2 015/0109283; 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 This case may be referred to as a MEDEOD (method for driving an electro-optic display) application); (i) application of a display; see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348; and (j) non-electrophoretic displays, as in U.S. Patent No. No. 6,241,921; and U.S. Patent Application Publication Nos. 2015/0277160; and U.S. Patent Application Publications Nos. 2015/0005720 and 2016/0012710.

Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in a capsule-type electrophoretic medium can be replaced by a continuous phase, resulting in a so-called polymer-dispersed electrophoretic display, where the electrophoretic medium contains a plurality of discrete droplets of Fluid and continuous phase polymeric materials, and even if no discrete capsule film is associated with each individual droplet, discrete droplets of electrophoretic fluid within such a polymer-dispersed electrophoretic display can be considered as capsules or microcapsules; See, for example, US Patent No. 6,866,760. Therefore, for the purpose of this application, such a polymer-dispersed electrophoretic medium is regarded as a subspecies of a capsule-type electrophoretic medium.

A related type of electrophoretic display is a so-called microcell electrophoretic display. In microcell electrophoretic displays, charged particles and fluids are not encapsulated in microcapsules, but instead, they are held in a plurality of cavities formed in a carrier medium (usually, a polymeric film). See, for example, U.S. Patent Nos. 6,672,921 and 6,788,449, both of which are assigned to Sipix Imaging Inc.

Although electrophoretic media are often opaque (because, for example, in many electrophoretic media, particles generally block the transmission of visible light through the display) and operate in reflective mode, many electrophoretic displays can be put in a so-called grating mode (shutter mode) ) ", In the raster mode, a display state is substantially opaque, and a display state is translucent. 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. Dielectrophoretic displays (which are similar to electrophoretic displays but rely on changes in electric field strength) can operate in similar modes; see US Patent No. 4,418,346. Other types of electro-optic displays can also be operated in raster mode. An electro-optic medium operating in a raster mode can be used in a multilayer structure of a full-color display; in such a structure, at least one layer adjacent to the viewing surface of the display is operated in a raster mode to expose or conceal an off-view surface Further on the second floor.

Capsule-type electrophoretic displays generally do not suffer from clustering and settling failures of conventional electrophoretic devices and provide additional advantages, such as the ability to print or coat the display on a variety of flexible and rigid substrates. (The use of text printing is intended to include all forms of printing and coating, including but not limited to: pre-metered coatings (e.g., patch die coating, slits Slot or extrusion coating, slide or cascade coating and curtain coating); roll coating (e.g. : Roll over blade coating (knife over roll coating and forward and reverse roll coating); gravure coating (dip coating); spray coating (spray coating) ); Meniscus coating; spin coating; brush coating; air-knife coating; silk screen printing processes Electrostatic printing processes; thermal printing processes; ink jet printing processes; electrophoretic deposition (see US Patent No. 7,339,715); and other similar technologies Therefore, the obtained display is flexible. Furthermore, since the display medium can be printed (using various methods), the display itself can be manufactured inexpensively.

As mentioned above, most simple prior art electrophoretic media display essentially only two colors. Such an electrophoretic medium uses a single type of electrophoretic particles having a first color in a colored fluid having a second different color (in this case, when the particles are adjacent to the viewing surface of a display, the first color is displayed, and When the particles are separated from the viewing surface, the second color is displayed), or the first and second types of electrophoretic particles having different first and second colors in an uncolored fluid (in this case, when The particles of the first type are displayed in a first color when adjacent to the viewing surface of the display, and the particles of the second type are displayed in a second color when adjacent to the viewing surface). Usually, these two colors are black and white. If a full color display is desired, a color filter array can 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. Available display areas are shared among three or four primary colors (for example, red / green / blue (RGB) or red / green / blue / white (RGBW)), and filters can be one-dimensional (line) or two-dimensional (2 × 2) Repeat the pattern to arrange. Other choices of primary colors or more than three primary colors are also known in the art. Three (in the case of RGB displays) or four (in the case of RGBW displays) sub-pixels are selected small enough that they are visually mixed together at a desired viewing distance into a single with a uniform color stimulus Pixels ("mixed colors"). The inherent disadvantage of area sharing is that the toner 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 primary colors occupies a quarter of the display area (one of the four sub-pixels), with the white sub-pixel and the underlying monochrome display White is as bright, and each colored sub-pixel is no brighter than a third of the white of a monochrome display. The white brightness of the display as a whole cannot exceed half of the brightness of the white sub-pixels (by displaying one white sub-pixel of every four sub-pixels, the white area of the display is generated, and each colored sub-pixel in the colored form is equivalent to one One third of the white sub-pixel, so that the combined contribution of three colored sub-pixels does not exceed one white sub-pixel). The brightness and saturation of colors are reduced by switching the color pixels shared by the area to black. Area sharing is particularly problematic when yellow is mixed because it is brighter than any other color with the same brightness, and saturated yellow is almost as bright as white. Switching blue pixels (a quarter of the display area) to black will make yellow too dark.

Multi-layer stacked optical displays are known in the art; see, for example, J. Heikenfeld, P. Drzaic, J-S Yeo and T. Koch, Journal of the SID, 19 (2), 2011, pp. 129-156. In such a display, the ambient light passes through the image of each of the three primary colors in a manner similar to traditional color printing. US Patent No. 6,727,873 describes a stacked electrophoretic display in which three layers of switchable cells are placed above a reflective background. Similar displays are known in which colored particles move laterally (see, e.g., World Application No. WO 2008/065605), or use a combination of vertical and lateral motion to isolate them into microcells. In both cases, each layer is provided with electrodes for collecting or dispersing colored particles on a pixel-by-pixel basis, so that each of the three layers requires a layer of thin film transistors (TFT's). The two layers must be substantially transparent) and a light-transmitting counter electrode. Such complex electrode arrangements are expensive to manufacture, and in the current state of the art, it is difficult to provide sufficiently transparent pixel electrode plates, especially because the white state of the display must be viewed through several layers of electrodes. As the thickness of the display stack approaches or exceeds the pixel size, multilayer displays also suffer from parallax issues.

U.S. Patent Application Publication Nos. 2012/0008188 and 2012/0134009 describe multi-color electrophoretic displays having a single back plate including individually addressable pixel electrodes and a common light-transmitting front electrode. A plurality of electrophoretic layers are arranged 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 electric field experienced by particles in a particular layer is lower than in the case of a single electrophoretic layer addressed at the same voltage. In addition, the loss of light in the electrophoretic layer closest to the viewing surface (for example, due to light scattering or unnecessary 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. See, for example, U.S. Patent Application Publication No. 2013/0208338 describes a color display that includes an electrophoretic fluid that includes one or two types of pigment particles dispersed in a transparent and colorless or colored solvent, the electrophoresis The fluid is disposed between a common electrode and a plurality of pixels or driving electrodes. The driving electrode is configured to expose the background layer. US Patent Application Publication No. 2014/0177031 describes a method for driving a display unit filled with an electrophoretic fluid, which includes two types of charged particles with opposite charge polarity and two contrasting colors. These two types of pigment particles are dispersed in colored solvents, or uncharged or slightly charged colored particle solvents. This method includes driving a display unit with a driving voltage of about 1% to about 20% applied as a full driving voltage to display the color of a solvent or the color of 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 contains pigment particles of the first, second and third types, all pigment particles being dispersed in a solvent or a 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. These three types of pigment particles have different threshold voltage levels, different mobility levels, or both. Full color displays are not disclosed in these patent applications in the sense of using that term below.

US Patent Application Publication No. 2007/0031031 describes an image processing device for processing image data to display an image on a display medium, wherein each pixel can display white, black, and another color. US Patent Application Publication Nos. 2008/0151355; 2010/0188732; and 2011/0279885 describe a color display in which movable particles move through a porous structure. US Patent Application Publication Nos. 2008/0303779 and 2010/0020384 describe a display medium including first, second, and third particles of different colors. The first and second particles can form aggregates, and the smaller third particles can 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 element including a plurality of types of particles encapsulated between a pair of substrates, at least one substrate being translucent, and a plurality of individual types Each of the particles has the same polarity of electricity, has different optical properties, and has different migration speeds and / or critical values of the electric field for movement. The translucent display side electrodes are disposed on a translucent substrate. On the substrate side, a first back electrode is disposed on the other substrate side and faces the display-side electrode, and a second back electrode is disposed on the other substrate side and faces the display-side electrode; and a voltage control section that controls the application to the display-side electrode The voltages of the first back electrode and the second back electrode make the particles with the fastest migration speed among the various types of particles or the particles with the lowest critical value among the various types of particles according to each of the different types of particles Type sequentially moves to the first back electrode or the second back electrode, and then moves to the first back electrode The particles move to the display-side electrode. US 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 a threshold voltage. U.S. Patent Application Publication No. 2013/0222884 describes an electrophoretic particle including a colored particle containing a polymer containing a charged group and a coloring agent, and a reactive monomer attached to the colored particle and containing as a copolymerization component and at least one kind A branched silicone-based polymer of a 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, a group of colored electrophoretic particles dispersed in the dispersion medium and migrating in an electric field, non-migrating, and having a different from electrophoretic particles The color of the group is a non-electrophoretic particle group and a compound having a neutral polar group and a hydrophobic group, and the ratio of the compound contained in the dispersion medium is about 0.01 to about 1 mass percent based on the entire dispersion. U.S. Patent Application Publication No. 2013/0222886 describes a dispersion for a display, including floating particles including: core particles containing a colorant and a hydrophilic resin; and covering the surface of each core particle and including 7.95 (J / cm ³ ) A hydrophobic resin shell with a solubility parameter difference of ^1/2 or more. US 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 greater than the first colored particles And has the same charging characteristics as the first colored particle, and wherein the ratio of the charge amount Cs of the first colored particle to the charge amount C1 of the second colored particle per unit area of the display (Cs / C1) Less than or equal to 5. Some of these displays do provide full color, but at the cost of a long and tedious addressing method.

U.S. Patent Application Publication Nos. 2012/0314273 and 2014/0002889 describe an electrophoresis 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 includes a porous layer contained in an insulating liquid and formed of a fibrous structure. These patent applications are not full color displays in the sense of the term (full color display) used below.

See also U.S. Patent Application Publication No. 2011/0134506 and the above-mentioned application sequence 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 display that can be implemented The quality of the white state.

In order to obtain a high-resolution display, each pixel of the display must be addressable and free from interference from neighboring pixels. One way to achieve this 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. An addressing or pixel electrode for addressing a pixel is connected to an appropriate voltage source via an associated non-linear element. Generally, when the non-linear element is a transistor, the pixel electrode is connected to the drain of the transistor, and this configuration will be adopted in the following description, but it is substantially arbitrary and the pixel electrode may be connected to the source of the transistor. Generally, in a high-resolution array, pixels are arranged in a two-dimensional array of columns and rows, so that any particular pixel is uniquely defined by the intersection of a particular column and a particular row. The sources of all the transistors in each row are connected to a single row electrode, and the gates of all the transistors in each column are connected to a single column electrode; moreover, the source-to-column and gate-to-row assignment system It is common, but it is essentially arbitrary, and it can be the opposite if desired. The column electrodes are connected to a column driver. The column driver substantially ensures that only one column is selected at a given moment, that is, a selection voltage is applied to the selected column electrode to ensure that all the transistor systems in the selected column are on, and A selected selection voltage is applied to all other columns to ensure that all transistors in these unselected columns remain non-conductive. The row electrode is connected to a row driver, and the row driver sets a selected voltage on the various row electrodes to drive the pixels in the selected column to their desired optical state. (The aforementioned voltage is relative to the common front electrode, and the common front electrode is usually disposed on the opposite side of the electro-optic medium away from the non-linear array and extends across the entire display). After a preselected time interval called "line address time", the selected column is deselected, the next column is selected, and the voltage on the line driver is changed to write to the next line of the display. Repeat this procedure to write the entire display in columns, column by column.

Generally, each pixel electrode has a capacitor electrode associated with it so that the pixel electrode and the capacitor electrode constitute a capacitor; see, for example, World Patent Application No. WO 01/07961. In some embodiments, transistors may be formed using N-type semiconductors (eg, amorphous silicon), and the "selected" and "non-selected" voltages applied to the gate electrodes may be positive and negative, respectively.

Figure 1 of the attached drawings depicts an exemplary equivalent circuit of a single pixel of an electrophoretic display. As shown, the circuit includes a capacitor 10 formed between a pixel electrode and a capacitor electrode. The electrophoretic medium 20 is represented by a capacitor and a resistor connected in parallel. In some cases, the 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. Generally, the parasitic capacitance 30 is much smaller than the parasitic capacitance of the storage capacitor 10, and when the pixel column of the display is selected or deselected, the parasitic capacitance 30 may cause a small negative offset voltage to the pixel electrode, also referred to as "kickback voltage kickback voltage) ", which is usually less than 2 volts. In some embodiments, in order to compensate for the unwanted "kickback voltage", the common potential V _com may be supplied to the upper plate electrode and the capacitor electrode associated with each pixel, so that when V _com is set equal to the kickback voltage (V _KB ), each voltage supplied to the display may shift by the same amount without experiencing a net DC imbalance.

However, when V _com is set to a voltage that is not compensated for the kickback voltage, a problem may occur. This may happen when it is desired to apply a higher voltage to the display than obtained from the backplane alone. It is well known in the art that, for example, if the backplane is supplied with options such as nominal + V, 0, or -V, and _Vcom is supplied with -V, the maximum voltage applied to the display may double. The maximum voltage experienced in this case is + 2V (that is, below the backplane relative to the upper board), while the minimum value is zero. If a negative voltage is required, the V _com potential must be raised to at least zero. Therefore, the waveforms used to address a display with positive and negative voltages using top plane switching must have a specific frame assigned to each of more than one V _com voltage setting.

A set of waveforms for driving a color electrophoretic display with four particles is described in U.S. Application Serial No. 14 / 849,658, which is incorporated herein by reference. In US Application Serial 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 the maximum voltage that can be processed by an amorphous silicon thin film transistor. In this case, a suitable high voltage can be obtained by using on-board switching. When V _{com is} intentionally set to V _KB (as described above), a separate power supply can be used. However, it is expensive and inconvenient to use as many independent power supplies as there are V _com settings when using on-board switching. Furthermore, it is known that the switching of the upper board will increase the kickback, thereby reducing the stability of the color state. Therefore, a method for compensating the DC offset caused by the kickback voltage is needed using the same power supply for the backplane and V _com . Of course, a full DC offset will result in a longer pulse sequence and therefore a longer image update time.

The present invention relates to a driver configured to transmit a two-part reset pulse wave to a pixel in a color electrophoretic display. The two-part reset pulse effectively removes the final state information, but does not require more energy or time than required. As a result, the controller allows three (or more) particle electrophoretic displays to be updated more quickly while using less energy. Surprisingly, when the reset pulse is adjusted for individual colors, the controller also provides a larger color gamut. The present invention further provides a method for driving an electro-optic display, which is DC-balanced despite changes in kickback voltage and voltage applied to the front electrode.

In one aspect, the present invention relates to a method for driving an electrophoretic display, the electrophoretic display having a front electrode, a back plate, and a display medium located between the front electrode and the back plate. The display medium includes three Set of particles of different colors. The method includes 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 varying with time, and a first duration; applying a second signal during the first duration On the backplane, the second signal has a second polarity opposite to the first polarity and a second amplitude that changes with time; a third signal is applied to the front electrode during a second duration, and the third signal The signal has the second polarity opposite to the first polarity and a third amplitude that changes with time; a fourth signal is applied to the backplane during the second duration, the fourth signal includes the first polarity and The first amplitude over time plus a pulse offset proportional to the kickback voltage experienced by the display medium. The color transition stage includes applying a fifth signal to the front electrode, the fifth signal having the second polarity, a fourth amplitude that varies with time, and a third duration after the first and second durations; A sixth signal is applied to the backplane, the sixth signal has the first polarity, a fifth amplitude that changes with time, and a fourth duration after the first and second durations; Integrate the sum of the first and second amplitudes over time over a duration and integrate the sum of the first, second, and third amplitudes over time over the second duration and over the third Integrating the fourth amplitude that changes with time over the duration and integrating the fifth amplitude that changes with time over the fourth duration produces a pulse offset that is designed to be in the reset phase and the The color transition stage maintains the DC balance of the display medium. In some embodiments, the reset phase erases previous optical properties presented 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 the 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 present invention includes a method for driving an electrophoretic display, the 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 particles of different colors. The method includes 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 varying with time, and a first duration; no signal is applied to the first duration On the back plate; a second signal is applied to the front electrode during a second duration, the second signal has a second polarity opposite to the first polarity, and a second amplitude that varies with time; during the second duration A third signal is applied to the backplane during time, the third signal has the first polarity and a third amplitude that changes with time. The color transition phase 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 after the first and second durations; A fifth signal is applied to the backplane. The fifth signal has the second polarity, a fifth amplitude that changes with time, and a fourth duration after the first and second durations. Integrating the sum of the first amplitude over time over a duration and integrating the sum of the second and third amplitude over time over the second duration and integrating over time over the third duration Integrating the changed fourth amplitude and integrating the fifth time-varying fifth amplitude over the fourth duration produces a pulse offset that is designed to maintain the display during the reset phase and the color transition phase DC balance of the medium. In some embodiments, the reset phase erases previous optical properties presented 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 the 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 present invention includes a controller for an electrophoretic display. The electrophoretic display includes a front electrode, a back plate, and a display medium located between the front electrode and the back plate. The display medium includes The controller is operatively connected to the front electrode and the back plate of three sets of particles of different colors, and is configured to perform 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 varying with time, and a first duration; applying a second signal during the first duration On the backplane, the second signal has a second polarity opposite to the first polarity and a second amplitude that changes with time; a third signal is applied to the front electrode during a second duration, and the third signal The signal has a second polarity opposite to the first polarity and a third amplitude that changes with time; a fourth signal is applied to the backplane during the second duration, and the fourth signal includes the first polarity and the The first amplitude of the time change plus a pulse offset proportional to the kickback voltage experienced by the display medium. The color transition stage includes applying a fifth signal to the front electrode, the fifth signal having the second polarity, a fourth amplitude that varies with time, and a third duration after the first and second durations; A sixth signal is applied to the backplane, the sixth signal has the first polarity, a fifth amplitude that changes with time, and a fourth duration after the first and second durations, wherein, at the first Integrate the sum of the first and second amplitudes over time over a duration and integrate the sum of the first, second, and third amplitudes over time over the second duration and over the third Integrating the fourth amplitude that changes with time over the duration and integrating the fifth amplitude that changes with time over the fourth duration produces a pulse offset that is designed to be in the reset phase and the The color transition stage maintains the DC balance of the display medium. In some embodiments, the controller implements different reset phases according to 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 present invention includes a controller for an electrophoretic display. The electrophoretic display includes a front electrode, a back plate, and a display medium located between the front electrode and the back plate. The display medium includes The controller is operatively connected to the front electrode and the back plate of three sets of particles of different colors, and is configured to perform 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 varying with time, and a first duration; no signal is applied to the first duration On the back plate; a second signal is applied to the front electrode during a second duration, the second signal has a second polarity opposite to the first polarity, and a second amplitude that varies with time; during the second duration A third signal is applied to the backplane during time, the third signal has the first polarity and a third amplitude that changes with time. The color transition phase 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 after the first and second durations; A fifth signal is applied to the backplane. The fifth signal has the second polarity, a fifth amplitude that changes with time, and a fourth duration after the first and second durations. Integrating the sum of the first amplitude over time over a duration and integrating the sum of the second and third amplitude over time over the second duration and integrating over time over the third duration Integrating the varying fourth amplitude and integrating the fifth amplitude varying with time over the fourth duration produces a pulse offset that is designed to maintain the display during the reset phase and the color transition phase DC balance of the medium. In some embodiments, the controller implements different reset phases according to 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 one of those described in the aforementioned application No. 14 / 849,658. Such a medium includes one generally white light-scattering particle and three substantially non-light-scattering particles. The electrophoretic medium of the present invention may take any of the forms discussed above. Therefore, the electrophoretic medium may be unencapsulated, encapsulated in discrete capsules surrounded by a capsule wall, or in the form of a polymer dispersed or microunit medium.

1‧‧‧ particles

2‧‧‧ particles

3‧‧‧ particles

4‧‧‧ particles

10‧‧‧Capacitor

20‧‧‧ Electrophoretic medium

30‧‧‧Coupling capacitor

V _com ‧‧‧ Common potential

FIG. 1 illustrates an exemplary equivalent circuit of a single pixel of an electrophoretic display.

FIG. 2 is a schematic cross-sectional view showing the positions of various colored particles in the electrophoretic medium of the present invention when the three primary colors of black, white, subtractive, and primary three colors are displayed.

Figure 3 shows schematically the four types of different pigment particles used in a multi-particle electrophoretic medium; Figure 4 shows schematically the relative strength of the interactions between particle pairs in a multi-particle electrophoretic medium; Figure 5 shows The behavior of many different particles in an electrophoretic medium when subjected to an electric field of different intensity and duration; Figure 6 is an exemplary waveform including a two-part reset phase (A) and a color transition phase (B); Figure 7 is before the display Electrode and pixel electrode and the voltage versus time diagram of the time-varying voltage obtained across the electrophoretic medium used to generate a color waveform in the driving method of the present invention; FIG. 8A shows the voltage generated by various voltage combinations in the two-part reset stage Experimental data of color gamut; Figure 8B shows 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; Figure 9 shows the DC balance reset pulse Example; Figure 10 shows the DC balance reset pulse of Figure 9 as experienced by electrophoretic particles.

As mentioned above, the present invention can be used in electrophoretic media containing one light-scattering particle (usually white) and three other particles providing three subtractive primary colors. Such a system is shown schematically in Figure 2, and it can provide white, yellow, red, magenta, blue, cyan, green, and black at each pixel.

The three particles that provide the subtractive three primary colors may be substantially non-light scattering ("SNLS"). The use of SNLS particles allows color mixing and provides more color results than can be achieved with the same number of scattering particles. The aforementioned US8,587,859 uses particles with degradable primary colors, but requires two different voltage thresholds for independent addressing of non-white particles (ie, the display is addressed with three positive and three negative voltages). These thresholds must be sufficiently separated to avoid crosstalk, and this separation requires the use of high addressing voltages for certain colors. In addition, addressing colored particles with the highest critical value will also move all other colored particles.

The particles and these other particles must then switch to their desired position 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 stepwise 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 needed in the display, two positive Voltage, two negative voltages, and zero voltage, but as described in some embodiments below, more different voltages may preferably be used to address the display).

As described above, the second figure in the drawing is a schematic sectional view showing the positions of various particles in the electrophoretic medium of the present invention when the three primary colors of black, white, subtraction, and addition are displayed. In FIG. 2, it is assumed that the viewing surface of the display is on the top (as shown in the figure), that is, the user views the display from this direction, and light is incident from this direction. As mentioned earlier, in the preferred embodiment, only one of the four particles used in the electrophoretic medium of the present invention substantially scatters light, and in Figure 2, this particle is considered to be a white pigment. Basically, this light-scattering white particle forms a white reflector. With the white reflector as the background, any particles above the white particles can be viewed (as shown in Figure 2). The light entering the viewing surface of the display passes through these particles, reflects back from the white particles, passes back through the particles, and exits the display. Therefore, 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 arranged below the white particles (behind the viewing angle of the user) are obscured by the white particles, and thus do not affect the color of the display. Because the second, third, and fourth particles are essentially non-light-scattering, their order or arrangement with respect to each other is not important, but for the reasons described above, they are relative to the order or arrangement of white (light-scattering) particles. Pivotal.

More specifically, when the cyan, magenta, and yellow particles are below the white particles (case [A] in FIG. 2), no particles are above the white particles, and thus the pixels display only white. When a single particle is above a white particle, the color of that single particle is shown as yellow, magenta, and cyan in the cases [B], [D], and [F] in Figure 2, respectively. When the two particles are above the white particles, the displayed color is the combination of the colors of the two particles; in the case [C] of Fig. 2, the magenta and yellow particles show red, and in the case [E] The cyan and magenta particles show blue, and in case [G], the yellow and cyan particles show green. Finally, when all three colored particles are above the white particles (case [H] in Figure 2), all the incident light is absorbed by the subtractive three primary colored particles, so the pixels appear black.

It is possible that the light-scattering particles can exhibit a reduced primary color, so that the display includes two types of light-scattering particles, one of which is white and the other type of light-scattering particles colored of. However, in this case, the position of the light-scattering colored particles relative to the other colored particles covering the white particles will be important. For example, in rendering black (when all three colored particles are above white particles), scattering colored particles cannot be above non-scattering colored particles (otherwise, they would be partially or completely hidden behind the scattering particles, thus rendering The color will be the color of the scattered colored particles, not black).

If more than one type of colored particles scatter light, it will not be easy to appear black.

Figure 2 shows the ideal case where the color is uncontaminated (ie, any particles that are completely behind the white particles are completely obscured by the light-scattering white particles). In fact, shielding with white particles may be incomplete, so that ideally the particles that are to be completely shielded may absorb a little light. Such contamination usually reduces the brightness and chroma of the colors presented. In the electrophoretic medium of the present invention, such color contamination should be minimized so that the formed colors meet the industry standard for color reproduction. A particularly advantageous standard is the SNAP (Newspaper Advertising Production Standard), which specifically specifies the L *, a *, and b * values for each of the eight primary colors mentioned above. (Hereinafter, "primary colors" will be used to represent eight colors, that is, as shown in Figure 2, the three primary colors of black, white, subtractive, and additive three.)

The method for electrophoretically arranging a plurality of different colored particles in a "layer" as shown in Fig. 2 has been described in the prior art. The simplest approach involves "race" pigments with different electrophoretic mobilities; see, for example, US Patent No. 8,040,594. Because the motion of the charged pigment itself changes the electric field locally experienced in the electrophoretic liquid, this competition is more complicated than it might be understood at first. For example, when positively charged particles move toward the cathode and negatively charged particles move toward the anode, their charge shields the electric field experienced by the charged particles in the middle between the two electrodes. It can be considered that although the pigment race is involved in the electrophoresis of the present invention, it is not the only cause of the particle arrangement shown in FIG. 2.

A second phenomenon that can be used to control the motion of a plurality of particles is hetero-aggregation between different pigment types; see, for example, the aforementioned US 2014/0092465. Such aggregation may be charge-mediated (Coulomb's law) or may result from, for example, hydrogen bonding or Van der Waals interactions. The strength of the interaction may be affected by the choice of surface treatment of the pigment particles. For example, when the closest distance approached by oppositely charged particles is maximized by a steric barrier (usually a polymer that is grafted or adsorbed to one or two particle surfaces), Coulomb interactions may be impaired. In the present invention, as described above, such a polymer 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.

As described in detail in the aforementioned application No. 14 / 277,107, it can be used to control the voltage or current-dependent mobility of the third present image of the movement of the plurality of particles.

FIG. 3 shows a schematic cross-sectional view of four pigment types (1-4) used in a preferred embodiment of the present invention. The polymer shell adsorbed to the core pigment is represented by dark shading, while the core pigment itself is represented by no shading. Various shapes can be used for core pigments: spherical, needle-like, or other asymmetrical, smaller particle aggregates (that is, "grape bunches"), composite particles containing small pigment particles or dyes dispersed in an adhesive Wait is well known in this technology. The polymer shell may be a covalently bonded polymer made by a grafting method or a chemical adsorption method that is well known in the art, or may be physically adsorbed on the particle surface. For example, the polymer may be a block copolymer containing insoluble and soluble segments. Some methods for attaching a polymer shell to a core pigment are described in the examples below.

The first and second particle types in one embodiment of the present invention preferably have a stronger polymer shell than the third and fourth particle types. Light-scattering white particles are of the first or second type (negatively charged or positively charged). In the following discussion, it is assumed that white particles are negatively charged (that is, belong to type 1), but it will be apparent to those skilled in the art that the general principles described will apply to a group of white particles that are positively charged particle.

In the present invention, the electric field required to separate aggregates formed from a mixture of particles of types 3 and 4 in a suspension solvent containing a charge control agent is larger than that required to separate aggregates formed from any other combination of two types of particles Electric field. On the other hand, the electric field required to separate aggregates formed between the first and second type particles is smaller than the electric field required to separate aggregates formed between the first and fourth particles or the second and third particles (of course, (Less than the electric field required to separate the third and fourth particles).

In Figure 3, it is shown that the core pigment containing particles has approximately the same size, and it is assumed that the zeta potential (although not shown) of each particle is approximately the same. The thickness of the polymer shell surrounding each core pigment varies. As shown in Figure 3, particles of types 1 and 2 have a thicker polymer shell than particles of types 3 and 4-and this is actually a better situation for some embodiments of the invention.

In order 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 particle pairs. In fact, aggregates may be composed of a large number of particles, and the situation will be more complicated than that of simple pairwise interactions. However, particle pair analysis does provide some guidance for understanding the invention.

The force acting on one of a pair of particles in an electric field is calculated by the formula: F _Total = F _App + F _C + F _VW + F _D (1)

Among them, F _App is the force exerted on the particle by the applied electric field, F _C is the Coulomb force exerted on the particle by the second particle with the opposite charge, and F _VW is the force of attraction of the second particle on the particle. Watt force, F _D is the attractive force exerted on particle pairs by depletion flocculation caused by the suspension solvent containing a stable polymer (optional).

The force F _App exerted on the particles by the applied electric field is calculated by the following formula: F _App = qE = 4 πε _r ε ₀ ( a + s ) ζ E (2)

Among them, the charge of q-series particles is related to the zeta potential (ζ) shown in equation (2) (about within the Huckel limit), where a is the radius of the core pigment, and the thickness of the s-series solvent-swelling polymer shell, And other symbols have traditional meanings known to this technology.

The magnitude of the force exerted by another particle on one particle due to Coulomb interaction is roughly calculated by the following formula for particles 1 and 2:

Note that the F _App force applied to each particle is used to separate the particles, while the other three forces are the attraction between the particles. According to Newton's third law, if acting on a particle is greater than the force acting on the F _App another force F _App particles (particles as the charge on a particle is higher than the charge on the other), then the force of the separation of the particles Provided by the weaker of the two F _App forces.

It can be seen from (2) and (3) that the difference between the Coulomb term of attraction and separation is calculated by the following formula: F _App - F _C = 4 πε _r ε ₀ (( a + s ) ζ ｜ E ｜- ζ ² ) (4)

If the particles have the same radius and zeta potential, making (a + s) smaller or zeta larger will make the particles more difficult to separate. Therefore, in an embodiment of the present invention, it is preferable that particles of types 1 and 2 are larger and have a relatively low zeta potential, and particles 3 and 4 are smaller and have a relatively large zeta potential.

However, if the thickness of the polymer shell increases, the van der Waals force between the particles can also change significantly. The polymer shell on the particles is swelled by the solvent and further separates the surface of the core pigment through Van der Waals interaction. For spherical core pigments with a radius (a ₁ , a ₂ ) that is much larger than the distance between them (s ₁ + s ₂ ),

Among them, A is the Hamaker constant. As the distance between the core pigments increases, the formula becomes more complex, but the effect remains the same: increasing s ₁ or s ₂ has a significant effect on reducing the interaction between the van der Waals attracting particles.

With this background, it becomes possible to understand the logical basis of the particle types shown in Figure 3. Type 1 and 2 particles have a strong polymer shell that is swollen by the solvent, allowing the core pigments to be further separated, thus reducing the particle size between them compared to Type 3 and Type 4 particles with smaller or no polymer shells. Van der Waals interact more. Even if the particles have approximately the same size and zeta potential, according to the present invention, the strength of the interaction between the paired aggregates can be arranged to meet the above requirements.

For more details on the preferred particles used in the display of Figure 3, the reader is referred to the aforementioned application number 14 / 849,658.

Figure 4 shows schematically the strength of the electric field required to separate the paired aggregates of the particle types of the invention. The interaction between particles of types 3 and 4 is stronger than the interaction between particles of types 2 and 3. The interaction between particles of types 2 and 3 is approximately equal to the interaction between particles of types 1 and 4, but it is stronger than the interaction between particles of types 1 and 2. All interactions between pairs of particles with the same charge sign are as weak or weaker than the interactions between particles of types 1 and 2.

Figure 5 shows how these interactions can be used to form all the primary colors (subtractable primary colors, additive primary colors, black and white) as generally discussed in Figure 2.

When addressing with a low electric field (Figure 5 (A)), particles 3 and 4 aggregate without separation. Particles 1 and 2 can move freely in an electric field. If Particle 1 is a white particle, the color seen from the left is white, and the color seen from the right is black. Reverse the polarity of the electric field to switch between the black state and the white state. However, the transient colors between the black state and the white state are colored. The aggregates of particles 3 and 4 move very slowly relative to particles 1 and 2 in the electric field. It can be found that particle 2 has moved past particle 1 (to the left), while the aggregates of particles 3 and 4 have not moved significantly. In this case, particle 2 will be seen from the left, while aggregates of particles 3 and 4 will be seen from the right. In some embodiments of the invention, the aggregates of particles 3 and 4 are weakly positively charged and are therefore located near particle 2 at the beginning of such a transition.

When addressing with a high electric field (Figure 5 (B)), particles 3 and 4 are separated. When viewed from the left, which of the particles 1 and 3 (each particle has a negative charge) will be visible depends on the waveform (see below). As shown, particle 3 can be seen from the left, and the combination of particles 2 and 4 can be seen from the right.

Starting from the state shown in Figure 5 (B), a low voltage of the opposite polarity will move the positively charged particles to the left and the negatively charged particles to the right. However, positively charged particles 4 will encounter negatively charged particles 1 and negatively charged particles 3 will encounter positively charged particles 2. The result is that the combination of particles 2 and 3 will be seen from the left, while particle 4 will be seen from the right.

As described above, it is preferred that Particle 1 is white, Particle 2 is cyan, Particle 3 is yellow, and Particle 4 is magenta.

As is well known in electrophoretic display technology, the core pigment for white particles is usually 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 fluid of the present invention can be used to construct a display device in several ways known in the art. The electrophoretic fluid can be encapsulated in microcapsules or incorporated into a microcell structure that is subsequently sealed with a polymeric layer. The microcapsule or microunit layer can be coated or embossed onto a plastic substrate or film with a transparent coating of a conductive material. This assembly can be laminated to a back plate with a pixel electrode using a conductive adhesive.

A first embodiment for realizing the waveform of each particle arrangement shown in FIG. 2 will now be described. In this discussion, it is assumed that the first particle system is white and negatively charged, the second particle system is cyan and positively charged, the third particle system is yellow and negatively charged, and the fourth particle system is magenta and positively charged. Those skilled in the art will understand how, when one of the first and second particles is assumed to be white, the color transition will change if the color distribution of these particles is changed. Similarly, the polarity of the charges on all particles can be reversed, and if the polarity of the waveform (see the next paragraph) also used to drive the medium is reversed, the electrophoretic medium will still function in the same way.

In the following discussion, the waveform (voltage vs. time curve) applied to the pixel electrodes of the back plate of the display of the present invention is described and plotted, while assuming that the front electrode is grounded (ie, 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 they are separated. The display is usually viewed through its front electrode, so that particles adjacent to the front electrode control the color displayed by the pixel, and it is sometimes easier to understand the light-excitation transition involved if the potential of the front electrode relative to the back plate is considered ( optical transitions); this can be done simply by reversing the waveforms discussed below.

These waveforms require that each pixel of the display can have five different addressing voltages (expressed as + V _high , + V _low , 0, -V _low, and -V _high , which are represented by 30V, 15V, 0, -15V, and -30V). Description) to drive. In practice, a larger number of addressing voltages can preferably be used. If only three voltages are available (i.e., + V _high , 0, and -V _high ), it is possible to achieve this at lower voltages by addressing with pulses with a voltage V _high but a duty cycle of 1 / n ( For example, V _high / n, where n is a positive integer greater than 1) addresses the same result.

The waveform used in the present invention may include three phases: a DC balance phase, in which a DC imbalance due to a previous waveform applied to a pixel is corrected or a DC imbalance caused in a subsequent color reproduction transition is corrected (as in this technique (Known); a "reset" phase in which the pixels return to an initial configuration that is at least approximately the same regardless of the previous optical state of the pixels; and a "color rendering" phase described below. Depending on the requirements of the particular application, the DC balancing and reset phases are optional and can be omitted. If used, the "reset" phase may be the same as the magenta color rendering waveform described below, or it may involve continuously driving the largest possible positive and negative voltages, or it may be some other pulse mode, as long as it enables The display returns to a state where subsequent colors 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 (for example, as shown in FIG. 2). As shown). 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. Those of ordinary skill in the art to which the invention pertains will clearly know that if the distribution of pigment colors is changed, the colors presented by the display will change.

The maximum positive and negative voltages applied to the pixel electrode (indicated by ± Vmax in Figure 6) are generated by the second and fourth particles (cyan and magenta to generate blue-see Figure 2 [E]). A mixture or a color formed solely by a third particle (yellow-see Fig. 2 [B]-white pigment scatters light and lies between colored pigments). These blues and yellows are not necessarily the best blues and yellows that a display can achieve. Medium-order positive and negative voltages (indicated as ± V _{mid in} Figure 6) applied to the pixel electrodes produce black and white colors, respectively (but not necessarily the best black and white that the display can achieve-see Section 5 (A) Figure).

From these blue, yellow, black, or white optical states, other things can be obtained by moving only the second particle (in this case, the turquoise particle) relative to the first particle (in this case, the white particle). The four primary colors are achieved using the lowest applied voltage (indicated by ± Vmin in Figure 6). Therefore, moving cyan to blue (by applying -Vmin to the pixel electrode) can produce magenta (see Figures 2 [E] and 2 [D] for blue and magenta, respectively); moving cyan into Yellow (by applying + Vmin to the pixel electrode) provides green (see Figures 2 [B] and 2 [G] for yellow and green, respectively); moving cyan to black (by applying -Vmin to the pixel electrode) ) Can provide red (see Figure 2 [H] and 2 [C] for black and red respectively), and moving cyan into white (by applying + Vmin to the pixel electrode) can provide cyan (see separately Figures 2 [A] and 2 [F] on white and turquoise).

Although these general principles are useful in a configuration for generating a waveform of a specific color in the display of the present invention, the above-mentioned ideal behavior may not be observed in practice, and it is desirable to adopt a modification of the basic method.

The general waveforms used to address the color electrophoretic display of the present invention will be described in Figure 6, where the abscissa represents time (arbitrary unit) and the ordinate represents the voltage difference between the pixel electrode and the common front electrode. The three positive voltages used in the driving method shown in FIG. 6 may be between about + 3V and + 30V, and the three negative voltages used are between about -3V and -30V. In a preferred embodiment, the maximum positive voltage + V _max as the + 30V, an intermediate positive voltage + V _mid is 15V, the minimum positive voltage + V _min is 9V. In a similar manner, the negative voltage -V _max, this embodiment is -30V, -15V and -9V -V _mid and -V _min in a preferred embodiment. The voltage magnitude | + V | = | -V | is not necessary for any of the three voltage levels, but this is better in some cases.

There are two different phases in the general waveform shown in Figure 6. In the first stage, a pulse wave (where "pulse wave" means a unipolar square) for erasing a previous image presented on the display (ie, "resetting" the display) is provided at + V _max and -V _max . (Ie, a constant voltage is applied at a predetermined time). The length of these pulses (t ₁ and t ₃ ) and the remaining time (that is, the zero voltage period between them (t ₂ and t ₄ )) can be selected such that the entire waveform (that is, shown in FIG. 6) The integral of voltage over time for the entire waveform is DC-balanced (ie, the integral of voltage over time is essentially zero). The DC balance can be achieved by adjusting the length of the pulse wave and the remaining time in stage A, so that the net pulse provided in this stage and the net pulse provided in stage B have the same amplitude and opposite sign. During stage B The display is switched to a specific desired color.

Here, the term "frame" means a single update of all columns in the display. Those of ordinary skill in the art to which the invention pertains will clearly know that in the display of the present invention driven by a thin film transistor (TFT) array, the available time increment on the abscissa of FIG. 6 will usually be the display frame Rate to quantify. It is also obvious that the display is addressed by changing the potential of the pixel electrode relative to the front electrode, and this can be achieved by changing the potential of the pixel electrode or the front electrode or both. In the current state of the art, there is usually a pixel electrode matrix on the back plate, and the front electrode is common to 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 in Figure 6 above is the same whether or not a variable voltage is applied to the front electrode.

The general waveform shown in Figure 6 requires the driving electronics to provide up to seven different voltages to the data lines during a selected column update of the display. Although multi-level source drivers capable of transmitting seven different voltages are available, many commercially available source drivers for electrophoretic displays allow only three different voltages to be transmitted during a single frame (typically, positive voltage, zero voltage And negative voltage). The general waveform in Figure 6 can be modified to fit the 3rd order source driver architecture. As long as the three voltages (usually + V, 0 and -V) provided to the panel can be changed from one frame to the next ( That is, for example, a voltage (+ V _max , 0, -V _min ) can be supplied in the frame n, and a voltage (+ V _mid , 0, -V _max ) can be supplied in the frame n + 1.

Sometimes it may be necessary to control the electrophoretic display using a so-called "on-board switching" driving method. In the method of switching on the upper plate, the common electrode on the upper plate 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 used, When at 0 voltage, pixel transitions in one direction are processed, and when the common electrode is at + V, pixel transitions in the other direction are processed.

When the on-board switching is used in combination with a 3rd-order source driver, the same general principles as described in Figure 6 above apply. When the source driver cannot supply a voltage as high as the preferred V _max , the on-board switching may be better. The method of using an on-board switch to drive an electrophoretic display is well known in the art.

(E Ink) Typical waveforms of conventional techniques are shown in Table 1 below, where the numbers in parentheses correspond to the number of frames driven with the indicated backplane voltage (relative to the upper plate considered to be zero potential) .

During the reset phase of this waveform, pulses of maximum negative voltage and positive voltage are provided to erase the previous state of the display. The frame offset of each voltage is offset by a number (represented by Δx for color x), and this number compensates for the net pulses in the high / medium-order voltage and low / medium-order voltage stages of color rendering. In order to achieve DC balance, △ x is selected as half of the net pulse. The reset phase does not have to be implemented exactly as shown in the table; for example, when using on-board switching, a certain number of frames must be allocated to the negative and positive drivers. In such cases, it is preferable to provide the maximum number of high voltage pulses consistent with achieving DC balance (ie, subtract 2Δx from the negative or positive frame, where appropriate).

In the high / medium order voltage stage, as described above, a sequence of N repeats of one pulse wave sequence suitable for each color is provided, where N may be 1-20. As shown, this sequence includes 14 frames that are assigned a positive or negative voltage or zero voltage of the magnitude Vmax or Vmid. The pulse wave sequence shown fits the discussion given above. It can be seen that at this stage of the waveform, the pulse wave sequences showing white, blue, and cyan colors are the same. Similarly, at this stage, the pulse wave sequences showing yellow and green are the same (because green is realized from the yellow state).

In the low / medium order voltage phase, blue and cyan colors are obtained from white, and green colors are obtained from yellow.

The previous discussion of waveforms, especially the discussion of DC balance, ignores the issue of kickback voltage. In fact, as mentioned earlier, each backplane voltage is offset from the power supply voltage by an amount equal to the kickback voltage V _KB . Therefore, if the power supply used provides three voltages + V, 0, and -V, the backplane will actually receive the voltages V + V _KB , V _KB, and -V + V _KB (note that In the case of a crystal, V _KB is usually negative). However, the same power supply will supply + V, 0, and -V to the front electrode without any kickback voltage offset. So, for example, when the front electrode is supplied with -V, the display will experience a maximum voltage of 2V + V _KB and a minimum voltage of V _KB . Instead of using a separate power supply to supply V _KB to the front electrode (which can be expensive and inconvenient), the waveform can be divided into parts that supply the front electrode with positive voltage, negative voltage, and V _KB .

As mentioned above, in some of the waveforms described in the aforementioned application serial number 14 / 849,658, seven different voltages can be applied to the pixel electrode: 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 processed by an amorphous silicon thin film transistor in the state of the art at the time. In such a case, a high voltage can be obtained through the use of on-board switching, and the driving waveform can be configured to compensate for the kickback voltage and the DC balance can be substantially performed by the method of the present invention. FIG. 7 schematically depicts one such waveform for displaying a single color. As shown in Figure 7, the waveform of each color has the same basic form: that is, the waveform is essentially DC-balanced and can include two parts or stages: (1) Used to provide a "reset" of the display to Obtain a reproducible initial series of frames in the state of any color, and in the meantime provide a series of frames equal to and opposite to the DC imbalance of the rest of the waveform, and (2) a series of frames specific to the color to be rendered; See parts A and B of the waveform shown in Figure 6.

During the first "reset" phase, the reset of the display ideally erases any memory of the previous state, which includes the residual voltage and pigment configuration specific to the previous display color. This erasure is most effective when the display is addressed at the maximum possible voltage during the "Reset / DC Balance" phase. In addition, sufficient frames can be allocated at this stage to allow the most unbalanced balance of color transitions. Because some colors require positive DC balance in the second part of the waveform and other colors require negative balance, set the front electrode voltage V _com to V _pH in about half of the frame in the "Reset / DC Balance" phase (The maximum possible negative voltage allowed between the back plate and the front electrode), and in the rest, V _{com is} set to V _nH (the maximum possible positive voltage allowed between the back plate and the front electrode). According to experience, it has been found that the V _com = V _pH frame is better than the V _com = V _nH frame.

The "desired" waveform (that is, the actual voltage versus time curve expected to be applied to the electrophoretic medium) is described below in Fig. 7, and the above is shown to be implemented by switching over the board, where the application to the front electrode ( _Vcom ) is illustrated And the potential of the backplane (BP). It is assumed that the row driver is used to connect to a power supply capable of supplying the following voltages: V _pH , V _nH (highest positive and negative voltage, usually in the range of ± 10-15V), V _pL , V _nL (lower positive and negative voltage, usually in the range of ± 1- 10V range) and zero voltage. In addition to these voltages, a kickback voltage V _KB (small value specific to the particular backplane used, which is measured as described in, for example, US Patent No. 7,034,783) can be supplied to the front electrode by an additional power supply.

As shown in Figure 7, each backplane voltage is offset from the voltage supplied by the power supply by V _KB (expressed as a negative number). However, except when the front electrode is explicitly set to V _KB as described above, the front electrode voltage is not So offset.

Although the display of the present invention has been described as generating eight primary colors, in practice, it is preferable to generate as many colors as possible at the pixel level. Then, a technique well known to those skilled in imaging technology can be used to render a full-color grayscale image by dithering between these colors. For example, in addition to the eight primary colors generated as described above, the display may be configured to present an additional eight colors. In one embodiment, these additional colors are: light red, light green, light blue, dark green, dark magenta, dark yellow, and two gray levels between black and white. The terms "light" and "dark" used in this context mean that they have a hue angle that is approximately the same as the reference color in a color space (e.g., CIE L * a * b *), but each has a higher hue angle. Or lower L * colors.

Generally, light colors are obtained in the same way as dark colors, but using waveforms with slightly different net pulses in phases B and C. Therefore, for example, the light red, light green, and light blue waveforms have negative net pulses in phases B and C than the corresponding red, green, and blue waveforms, and the cyan, dark magenta, and dark yellow waveforms are in the phase B and C have net pulses that are more positive than the corresponding cyan, magenta, and yellow waveforms. The change in the net pulse can be achieved by changing the length of the pulse wave, the number of pulse waves, or the amplitude of the pulse wave in phases B and C.

Grey is usually achieved by a pulse sequence that oscillates between low or medium voltages.

Those skilled in the art who are familiar with the technical field to which the invention belongs will clearly know that in the display of the present invention driven by a thin film transistor (TFT) array, the available time increment on the abscissa of FIG. Box rate to quantify. As such, it will be apparent that the display is addressed by changing the potential of the pixel electrode relative to the front electrode, and this can be achieved by changing the potential of the pixel electrode or the front electrode or both. In the current state of the art, there is usually a matrix of pixel electrodes on the backplane, and the front electrodes are common to 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 in Figure 7 above is the same regardless of whether a variable voltage is applied to the front electrode.

The general waveform shown in Figure 7 requires the driving electronics to provide up to seven different voltages to the data lines during a selected column update of the display. Although multi-level source drivers capable of transmitting seven different voltages are available, many commercially available source drivers for electrophoretic displays allow only three different voltages to be transmitted during a single frame (typically, positive voltage, zero voltage And negative voltage). The term "frame" means a single update of all columns in the display. The general waveform in Figure 7 can be modified to fit the 3rd order source driver architecture. As long as the three voltages (usually + V, 0 and -V) provided to the panel can be changed from one frame to the next (also That is, for example, a voltage (+ V _max , 0, -V _min ) can be supplied in the frame n, and a voltage (+ V _mid , 0, -V _max ) can be supplied in the frame n + 1.

Referring now to Figure 6, it can be seen from Phase A (reset phase) that this phase is divided into two parts (represented by dashed lines) with equal duration. When using the upper plate switch, the upper plate is held at a potential in the first of these sections and at a potential of the opposite polarity in the second section. In the specific case of Figure 6, during the first such part, the upper plate will remain at V _p H and the back plate will remain at V _n H to achieve the potential of V _n HV _p H for the entire electrophoretic fluid Drop (where it is customary to refer to the backplane potential relative to the topplane potential). During the second part, the upper plate will remain at V _n H and the back plate will remain at V _p H. As shown, during the second part, the electrophoretic fluid will experience a potential of V _p HV _n H, which is the highest potential available. However, for some color renderings, exposure to such high voltages may make it difficult to achieve an initial pigment arrangement from which to achieve the desired final configuration. For example, as described in the prior art, in order to exhibit cyan, it is necessary to confine a magenta pigment (which has the same charge polarity as the cyan pigment) and a yellow pigment in one aggregate. Such aggregates will be separated by a high applied potential, so magenta will not be controlled and will pollute cyan.

However, it is not necessary to use the maximum possible voltage in both parts of Phase A of the waveform. What phase A needs is to erase the previous color state so that no matter what color is first, the newly rendered color is the same, and the net pulse provided in phase A balances the net pulse in phase B.

Therefore, an experiment was performed in which phase B of the waveform of the type shown in Table 1 was kept constant while the voltage applied in each of the two parts of phase A was changed (but distributed in each case) The same number of frames are given to stage A: a total of 120 frames, 60 frames in the first part, and 60 frames in the second part). After addressing the display, measure the CIELab L *, a *, and b * values for each primary color.

Table 2 shows the preset situation in which the maximum possible negative and positive voltages are applied in the first and second parts of Phase A. This can be done using an upper board switch, where the first listed voltage is applied to the backplane and the second listed voltage is applied to the upper board. The color gamut measured by the volume of the convex hull containing the eight points listed in Table 2 is 21,336 △ E ³ .

Table 3 shows how the backplane remains at zero voltage during the first part of Phase A. The applied voltage is smaller in this case than in the case of Table 2. The voltage applied in the second part of phase A is the same as in the case of Table 2. In order to maintain the DC balance, the application time of the lower voltage must of course be relatively long. The color gamut measured by the volume of the convex hull containing the eight points listed in Table 2 is 20,987 △ E ³ .

Table 4 shows how the backplane remains at zero voltage during the second part of Phase A. The voltage applied in the first part of Phase A is the same as in the case of Table 2. The color gamut measured by the volume of the convex hull containing the eight points listed in Table 2 is 20,339 △ E ³ .

Figure 8A shows the results of these experiments as projections on the a * / b * plane: the abscissa represents a * and the ordinate represents b *. It can be seen that certain colors (for example, red, magenta, and blue) will appear better through the phase A settings corresponding to Table 2 or 3, while other colors (cyan, green, and yellow) correspond to Table 4 through The Phase A setting will render better.

Interestingly, the replacement experiment that reversed the order of the first and second parts of stage A gave very poor results, all colors were contaminated with yellow.

Table 5 shows the best color combinations according to this experiment. The color gamut measured by the volume of the convex hull containing the eight points listed in Table 2 is 28,092 △ E 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 Figure 8B.

The method of the present invention is particularly important when it is desired to make the waveform as short as possible. In the case where there is a fixed voltage in phase A, in order to compensate for the deviation introduced for some colors in phase A, phase B needs to be made longer.

Although the invention is described using only two parts in Phase A, those skilled in the art will understand that any reasonable number of parts can be used. However, when the upper board is switched, the same structure that fixes the upper board potential regardless of the color to be presented. According to the present invention, the back plate corresponding to each upper plate potential is set to change in phase A of the waveform according to the color to be presented, but does not violate the condition of the DC balance of the overall waveform system including phases A and B.

The DC balance of the reset pulse can be achieved in the following way: For the DC balance reset process, a set of voltages must be selected for all transitions in the waveform. Choosing 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 individually balanced, but in the case of an upper board switch, each transition is linked together through the upper board, which forces the transitions to align with each other. The source driver standard imposes an additional limitation, which currently limits the number of simultaneous backplane voltages to three.

The conversion is a sequence of voltages applied to the backplane and the upper board. ,among them, Is the backplane voltage used to convert j in frame i , The voltage of the upper board when it is in frame i . Before implementing a DC balance reset, let Is the total pulse of T _j , where n _j is the update length of T _j (in frames) and V _KB is the kickback voltage of the display.

Let σ _j denote the desired DC balance pulse (time * V), and d _r denote the expected total duration of the DC balance reset. There are two pulses in the DC balance reset, so it is necessary to select the upper plate voltage for each pulse, and to select the back plate voltage for each pulse and each conversion. Let Is the voltage of the k ^{th th} pulse of T _j , where, Is the backplane voltage used to convert the k ^{th th} reset pulse of T _j , and This is the upper board voltage for the k ^th reset pulse. It is important to choose the voltage of the two pulses so that and It has the opposite sign for each transition.

Need to choose "zero" voltage, which is ideally 0V, which is not always possible

among them,

Next, calculate the overall maximum duration of each of the two pulses

Then, calculate the "ideal" duration of each pulse for each transition, which is The duration of the case. Definition notation . then,

We then break down each pulse into an "effective" part and a "zero" part to balance the transitions:

Now we are ready to construct the DC balance reset phase of the waveform. On the board To drive a duration , Followed by To drive a duration . As shown in Figure 9, for each transition T _j , we take Drive for a duration , Followed by Drive for a duration And then start with Drive for a duration , Followed by Drive for a duration . The resulting waveform experienced by the ink is shown in Figure 10.

At first glance, it appears that continuous scanning of different columns of an active matrix display may disrupt the above calculations designed to ensure accurate DC balance of the waveform and driving method, because when the voltage of the front electrode is changed (usually the Between scans), each pixel of the display will experience an "incorrect" voltage until the scan reaches the relevant pixel and adjusts the voltage on its pixel electrode to compensate for changes in the front electrode voltage, and the changes in the front panel voltage and scan The period between the times of reaching the relevant pixel varies depending on the column in which the relevant pixel is located. However, further research will show that the actual "error" of the pulses applied to the pixels is proportional to the period between the change in front panel voltage multiplied by the change in front panel voltage and the time that the scan reaches the relevant pixel. Assuming the scan rate does not change, the latter period is fixed so that for any series of changes in the front plate voltage that make the final front plate voltage equal to the original front plate voltage, the sum of the "errors" of the pulses will be zero and will not Affects the overall DC balance of the drive method.

Therefore, the present invention provides a DC balanced waveform for a multi-particle electrophoretic display. Having described several aspects and embodiments of the technology of the present application in this manner, it will be understood that those skilled in the art to which the invention pertains will readily think of various changes, modifications, and improvements. Such changes, modifications, and improvements are intended to fall within the spirit and scope of the technology described in this application. For example, a person of ordinary skill in the art to which the invention pertains will readily think of various other means and / or structures for performing functions and / or obtaining the results and / or advantages described herein, and each such Changes and / or modifications are 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. Therefore, it will be understood that the foregoing embodiments have been presented by way of example only, and that within the scope of the appended claims and their equivalents, the embodiments of the invention may be implemented in a manner different from the detailed description. In addition, if such features, systems, objects, materials, kits and / or methods are not mutually inconsistent, any combination of more than two features, systems, objects, materials, kits and / or methods described herein is included in this Within the scope of the disclosure.

Claims (18)

A method for driving an electrophoretic display, the electrophoretic display having a front electrode, a back plate, and a display medium located between the front electrode and the back plate, the display medium including three groups of particles of different colors, the method Including: 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 changes with time, and A first duration; a second signal is applied to the backplane during the first duration, the second signal has a second polarity opposite to the first polarity, and a second amplitude that varies with time; A third signal is applied to the front electrode during the duration, the third signal has a second polarity opposite to the first polarity, and a third amplitude varying with time; a fourth is applied during the second duration A signal on the backplane, the fourth signal includes the first polarity and the first amplitude that changes with time plus a pulse offset proportional to the kickback voltage experienced by the display medium; The color transition stage includes: applying a fifth signal to the front electrode, the fifth signal having the second polarity, a fourth amplitude that varies with time, and a third duration after the first and second durations; A sixth signal is applied to the backplane, the sixth signal has the first polarity, a fifth amplitude that changes with time, and a fourth duration after the first and second durations; Integrate the sum of the first and second amplitudes over time over a duration and integrate the sum of the first, second, and third amplitudes over time over the second duration and over the third Integrating the fourth amplitude that varies with time over the duration and integrating the fifth amplitude that varies with time over the fourth duration produces the pulse offset, which is offset from the kickback experienced by the display medium. The voltage is proportional and designed to maintain the DC balance of the display medium during the reset phase and the color transition phase. The method of claim 1, wherein the reset phase erases previous optical properties presented on the display. The method of claim 1, wherein the color transition stage substantially changes the optical properties displayed by the display. The method of claim 1, wherein the first polarity is a negative voltage. The method of claim 1, wherein the first polarity is a positive voltage. The method of claim 1, wherein the fourth duration occurs during the third duration. The method of claim 6, wherein the third duration starts simultaneously with the fourth duration. A method for driving an electrophoretic display. The electrophoretic display has a front electrode, a back plate, and a display medium located between the front electrode and the back plate. The display medium includes three groups of particles of different colors. The method includes : 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 changes with time, and a first A duration; no signal is applied to the backplane during the first duration; a second signal is applied to the front electrode during a second duration; the second signal has a first polarity opposite to the first polarity; A second polarity, a second amplitude that changes with time; a third signal is applied to the backplane during the second duration, the third signal has the first polarity and a third amplitude that changes with time; the color transition The phase 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 period after the first and second durations. Three 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 after the first and second durations; wherein , Integrating the sum of first amplitudes that change over time over the first duration and integrating the sum of second and third amplitudes that change over time over the second duration and over the third duration Integrating the fourth amplitude that changes over time and integrating the fifth amplitude that changes over time over the fourth duration produces a pulse offset that is designed to be in the reset phase and the color transition The stage maintains the DC balance of the display medium. The method of claim 8, wherein the fourth duration occurs during the third duration. The method of claim 9, wherein the third duration starts simultaneously with the fourth duration. A controller for an electrophoretic display. The electrophoretic display includes a front electrode, a back plate, and a display medium located between the front electrode and the back plate. The display medium includes three groups of particles of different colors. The controller Operatively connected to the front electrode and the back plate, and configured to perform 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 The signal has a first polarity, a first amplitude that changes with time, and a first duration; a second signal is applied to the backplane during the first duration, and the second signal has a first polarity opposite to the first polarity A second polarity, a second amplitude that changes with time; a third signal is applied to the front electrode during a second duration, the third signal has a second polarity that is opposite to the first polarity, and a third that changes over time Amplitude; a fourth signal is applied to the backplane during the second duration, the fourth signal includes the first polarity and the first amplitude that changes with time plus the experience experienced by the display medium The pulse shift is proportional to the kickback voltage; the color transition phase includes: applying a fifth signal to the front electrode, the fifth signal having the second polarity, a fourth amplitude that varies with time, and the first And a third duration after the second duration; applying a sixth signal to the backplane, the sixth signal having the first polarity, a fifth amplitude varying with time, and the first and second durations A fourth duration thereafter; wherein the sum of the first and second amplitudes that change over time is integrated over the first duration and the first, second, and Integrating the sum of the third amplitude 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 produces the pulse offset, which The pulse offset is proportional to the kickback voltage experienced by the display medium and is designed to maintain the DC balance of the display medium during the reset phase and the color transition phase. For example, the controller of claim 11, wherein the controller implements different reset stages according to the color to be displayed on the electrophoretic display. The controller of claim 11, wherein the display medium includes white, cyan, yellow, and magenta particles. The controller of claim 11, wherein the display medium includes white, red, blue, and green particles. A controller for an electrophoretic display. The electrophoretic display includes a front electrode, a back plate, and a display medium located between the front electrode and the back plate. The display medium includes three groups of particles of different colors. The controller Operatively connected to the front electrode and the back plate, and configured to perform a reset phase and a color transition phase on the display, the reset phase includes: 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 changes with time, and a first duration; no signal is applied during the first duration The back plate; applying a second signal to the front electrode during a second duration, the second signal having a second polarity opposite to the first polarity and a second amplitude varying with time; A third signal is applied to the backplane during the duration, the third signal has the first polarity and a third amplitude that changes with time; the color transition stage includes: applying a fourth No. on the front electrode, the fourth signal has the first polarity, a fourth amplitude that varies with time, and a third duration after the first and second durations; a fifth signal is applied to the back plate The fifth signal has the second polarity, a fifth amplitude that changes with time, and a fourth duration after the first and second durations; wherein the first time duration Integrate the sum of the first amplitudes and integrate the sum of the second and third amplitudes over time over the second duration and integrate the fourth amplitude of the time variations over the third duration and at Integrating the fifth amplitude that changes with time over the fourth duration produces a pulse offset that is designed to maintain the DC balance of the display medium during the reset phase and the color transition phase. For example, the controller of claim 15, wherein the controller implements different reset phases according to the color to be displayed on the electrophoretic display. The controller of claim 15, wherein the display medium includes white, cyan, yellow, and magenta particles. The controller of claim 15, wherein the display medium includes white, red, blue, and green particles.