CN101800034B - Method for addressing bistable electro-optical medium - Google Patents

Method for addressing bistable electro-optical medium Download PDF

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CN101800034B
CN101800034B CN 201010159493 CN201010159493A CN101800034B CN 101800034 B CN101800034 B CN 101800034B CN 201010159493 CN201010159493 CN 201010159493 CN 201010159493 A CN201010159493 A CN 201010159493A CN 101800034 B CN101800034 B CN 101800034B
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pulse
pixel
display
electro
medium
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CN101800034A (en
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G·M·丹纳
K·R·阿蒙森
A·C·阿兰戈
J·B·埃温
R·W·泽纳
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E Ink Corp
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E Ink Corp
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Abstract

The invention provides a method suitable for addressing a bistable electro-optical display apparatus having at least one pixel. The method includes a step of driving the pixel into a first optical state by applying an addressing pulse, and a step of making the pixel in a second optical state different from the first optical state by not driving the pixel for a certain time period. According to the method, a refreshing pulse is applied to the pixel for substantially returning the pixel into the first optical state. The refreshing pulse is shorter than the addressing pulse.

Description

The method that is used for addressing bistable electro-optical medium
The application is again dividing an application of dividing an application the first time of the following PCT international application submitted on May 23rd, 2003: international application no be PCT/US03/16434, national applications number for 03813604.X, denomination of invention are " being used for driving the method for electro-optic displays ", the application number of dividing an application for the first time is 200810215240.8, denomination of invention is " being used for driving the method for electro-optic displays ".
The present invention relates to for driving the especially method and apparatus of bistable electro-optic displays of electro-optic displays.Method and apparatus of the present invention main (although unspecial) is used for driving the bistable electrophoretic display device (EPD).
The application relates to U.S. Patent No. 6,504, and 524 and No.6,531,997.The application also relates to common pendent International Application Serial No. PCT/US02/10267 (publication number No.WO02/079869) and PCT/US02/37241.
The term " electric light " that is applied to material or display as used herein is its conventional sense in imaging technique, refer to the material with first and second show states, at least a optical property of this first and second show state is different, makes this material be converted to the second show state from the first show state by apply electric field to this material.Although this optical property is the appreciable color of human eye normally, but also can be other optical property, such as optical transmission, reflectivity, brightness or the demonstration of being read by machine, counterfeit look on the electromagnetic reflectance varies meaning outside the visible range.
Term used herein " grey states " is its routine meaning in imaging technique, refers to the state between two extreme optical state of pixel, might not mean that the black and white between these two extremities changes.For example, described such electrophoretic display device (EPD) in a plurality of patents that the below quotes and the published application, wherein extremity is white and dark blue, thus middle " grey states " actual will be light blue.In fact, as previously mentioned, the transformation between two extremities also may not be the variation on the color.
Term used herein " bistable " and " bistability " are its routine meanings in the art, refer to comprise the display of the display element with first and second show states, described the first and second show states have at least a kind of optical property different, so that being driven into by the addressing pulse with finite duration, any point element presents its first or second show state, after addressing pulse stops, it is several times of times of minimum duration that change the required addressing pulse of state of this display element at least that this state will continue, and for example is four times of times at least.In the application that aforesaid common pendent sequence number is No.10/063236, illustrated: some based on particle can display gray scale electrophoretic display device (EPD) not only stable under its extreme black and white state, and stable under the grey states therebetween, the electro-optic displays of other type is like this equally.Such display is called " multistable " rather than bistable rightly, but term used herein " bistable " covers bistable and multistable display for convenience's sake.
Term used herein " impacts (impulse) " gets its conventional meaning: voltage is about the integration of time.Yet some bistable electro-optical mediums serve as charge sensor, for this medium can use impact another the definition, namely electric current is about the integration (total electrical charge that equals to apply) of time.Serve as voltage-time shock transducer or electric charge shock transducer according to medium, should use the suitable definition about impacting.
Known polytype bistable electro-optic displays.One type electro-optic displays is for example in U.S. Patent No. 5,808,783,5,777,782,5,760,761,6,054,071,6,055,091,6,097,531,6,128,124,6,137, disclosed rotation two color component types (rotating bichromal member) are (although such display often is called as " rotating two chromospheres " display in 467 and 6,147,791, but because rotating element is not spherical in more above-mentioned patents, that term " rotates two color components " is more accurate).This display uses a large amount of corpusculums (being typically spherical or cylindric) and internal dipole, and these corpusculums have two or more different parts of optical characteristics.These corpusculums are suspended in the vacuole that is full of liquid in the matrix, and these vacuoles are full of liquid so that these little physical efficiencys rotate freely.Apply electric field to this display, the appearance of this display changes, and therefore rotates these corpusculums to various positions and changes by observing those parts of the surperficial corpusculum of seeing.
The electro-optical medium of another kind of type uses electrochromic medium, the electrochromic medium of nanometer chromium (nanochromic) form of film for example, it comprise at least part of electrode that is formed by the semiconduction metal oxide and a plurality of be attached on this electrode can reversible color dye molecule; Referring to, for example, O ' Regan, the Nature such as B. 1991,353,737; And Wood, D., Information Display, 18 (3), 24 (in March, 2002).And referring to Bach, U. waits Adv.Mater., 2002,14 (11), 845.For example among U.S. Patent No. 6,301,038 and the international application published No.WO 01/27690 such nanometer chromium thin film is being described also.
The electro-optic displays of the another kind of type of being researched and developed in a large number over several years is based on the electrophoretic display device (EPD) of particle, and wherein a plurality of charged particles pass the suspending liquid motion under the impact of electric field.Compare with liquid crystal display, the contribution of electrophoretic display device (EPD) is to have good brightness and contrast, wide visual angle, state bistability and low-power consumption.Yet the long-term image quality problem of these displays has hindered being widely used of they.For example, the particle that consists of electrophoretic display device (EPD) trends towards sedimentation, causes the service life of these displays inadequate.
Transfer in a large number or announce recently with the patent of Massachusetts science and engineering (MIT) and the application of E Ink company, they have described the electrophoretic media of encapsulation.The medium of this encapsulation comprises a large amount of folliculus, and wherein each folliculus itself comprises interior phase and around the cyst wall of interior phase, but the wherein said interior particle that is suspended in the electrophoresis motion in the liquid suspension medium that contains mutually.Usually, these capsules itself are kept in the polymeric binder to form the adhesion layer between two electrodes.For example, in United States Patent (USP) NO.5,930,026; 5,961,804; 6,017,584; 6,067,185; 6,118,426; 6,120,588; 6,120,839; 6,124,851; 6,130,773; 6,130,774; 6,172,798; 6,177,921; 6,232,950; 6,249,721; 6,252,564; 6,262,706; 6,262,833; 6,300,932; 6,312,304; 6,312,971; 6,323,989; 6,327,072; 6,376,828; 6,377,387; 6,392,785; 6,392,786; 6,413,790; 6,422,687; 6,445,374; 6,445,489; 6,459,418; 6,473,072; 6,480,182; 6,498,114; 6,504,524; 6,506,438; 6,512,354; 6,515,649; 6,518,949; 6,521,489; 6,531,997; 6,535,197; 6,538,801; With 6,545,291 and U.S. Patent Application Publication No.200210019081; 2002/0021270; 2002/0053900; 2002/0060321; 2002/0063661; 2002/0063677; 2002/0090980; 2002/0106847; 2002/0113770; 200210130832; 2002/0131147; 2002/0145792; 2002/0154382,2002/0171910; 2002/0180687; 2002/0180688; 2002/0185378; 2003/0011560; 2003/0011867; 2003/0011868; 2003/0020844; 2003/0025855; 2003/0034949; 2003/0038755, and international application published No.WO 99/67678; WO 00/05704; WO00/20922; WO 00/26761; WO 00/38000; WO 00/38001; WO 00/36560; WO00/67110; WO 00/67327; WO 01/07961; With the medium of having described such encapsulation among the WO 01/08241.
Many above-mentioned patents and application recognize in the electrophoretic media of encapsulation can be with continuous mutually replacement around the wall that separates micro-capsule, thereby produce (polymer-dispersed) electrophoretic display device (EPD) of so-called polymer dispersed, wherein electrophoretic media comprises the droplet of separation of a plurality of electrophoretic fluid and the external phase of polymeric material, and relevant with each independent droplet even without the cyst membrane that separates, but the separation droplet of the electrophoretic fluid in the electrophoretic display device (EPD) of such polymer dispersed also can be considered to capsule or micro-capsule; Referring to, for example aforesaid 2002/0131147.Therefore, for the application's purpose, the subclass of the electrophoretic media that the electrophoretic media of this polymer dispersed is considered to encapsulate.
The electrophoretic display device (EPD) of encapsulation does not suffer gathering and the deposition invalidation pattern of conventional electrophoretic part usually, and additional advantage is provided, and is all if display is coated with or is printed on various flexibilities and the stiff base.(use word " printing " to be intended to unrestrictedly comprise printing and the coating of form of ownership: such as premeasuring (pre-metered) coating, slit or projection coating, slip or waterfall (cascade) coating, the showering of curtain formula of patch coating (patch die coating); Such as cutter (knife over roll) coating on roller, forward with the roll banding of reverse roll coating; The coating of gravure formula; Dip coated; Spraying; Crescent (meniscus) coating; Spin coating; Brush; Air knife is coated with; Silk-screen printing technique; Electrostatic printing process; Hot typography, ink-jet printing process; And other similar techniques.) therefore, the display of manufacturing can be flexible.In addition, owing to show that medium can print (make and in all sorts of ways), display itself can be made at an easy rate.
A kind of electrophoretic display device (EPD) of correlation type is so-called " microcell electrophoretic display ".In microcell electrophoretic display, charged particle and suspension are not sealed in the micro-capsule but remain in a plurality of chambeies that are formed in the carrier medium (normally polymer film).Referring to, for example, international application published No.WO 02/01281 and disclosed U. S. application No.2002-0075556 (all transferring Sipix Imaging, Inc.)
Although electrophoretic display device (EPD) normally opaque (because the basic block visible light transmission display of these particles device) and under reflective-mode, working, but electrophoretic display device (EPD) can be in so-called " shutter mode (shutter mode) " lower work, and particle is arranged at transverse movement in the display so that display has one is the show state of opaque show state and a printing opacity substantially in this pattern.Referring to, for example, aforesaid U.S. Patent No. 6,130,774 and 6,172,798, and U.S. Patent No. 5,872,552,6,144,361,6,271,823,6,225,971 and 6,184,856.Be similar to electrophoretic display device (EPD), but the dielectrophoretic displays that depends on the electric field intensity variation can worked under the pattern similarly also; Referring to U.S. Patent No. 4,418,346.The electro-optic displays of other type also can be worked under shutter mode.
Based on the bistable of the electrophoretic display device (EPD) of particle or the similar performance of multistable performance and other electro-optic displays, form distinct contrast with the performance of traditional liquid crystal (LC) display.The performance of twisted nematic liquid crystal is not bistable or multistable, but serves as voltage sensor, can produce a specific gray level in this pixel so that apply given voltage to a pixel of this display, and irrelevant with the gray level that before appeared on this pixel.In addition, only a direction (from non-transmissive or " secretly " to transmission or " bright ") driving LC display, the reverse transformation from brighter state to darker state is by reducing or eliminating the electric field realization.At last, the gray level of the pixel of LC display is insensitive to the polarity of electric field, and only to its magnitude, and in fact for technical reason, coml LC display will drive the reversal of poles of electric field usually with interval frequently.With first approximate contrast be, bistable electro-optic displays is served as shock transducer, thus the end-state of pixel not only depends on the electric field that applies and applies time of this electric field, also depends on the state of this pixel before applying electric field.
Although point out the front, the electro-optic displays performance bistability of electrophoresis and other type, but this bistability is not hard-core, image on this class display slowly weakens in time, if thereby image will keep the long cycle, this image must periodic refresh, writes the fashionable optical states that it has for the first time in order to image returned to.
Yet, this image refresh the problem that may cause himself.As aforesaid U.S. Patent No. 6,531,997 and 6,504,524 discuss, if the method that drives this display does not on average apply electric field at the net time that whole electro-optical medium is produced as zero (or approaching zero), may encounter problems and the mission life of this display reduces.Be produced as the driving method that zero net time on average applies electric field at whole electro-optical medium and typically refer to " dc balance " or " DC balance ".If keep for a long time image by applying refresh pulse, then the polarity of these pulses need to be identical with the polarity of the addressing pulse that is driven into the optical states that is keeping for the related pixel with this display, and this causes the uneven drive scheme of DC.
According to a further aspect in the invention, have been found that if use short pulse to realize refreshing that the image on then can refresh display reduces the harmful effect relevant with DC imbalance drive scheme simultaneously.
Another aspect of the present invention relates to such problem of processing: the driving of aforesaid bistable electro-optic displays requires to cause the conventional ADS driving method for driving LCD to be unsuitable for this bistable electro-optic displays.In addition, such as aforesaid U.S. Patent No.6,531,997 and 6,504,524 discuss, if the method that drives this display does not on average apply electric field at the net time that whole electro-optical medium is produced as zero (or approaching zero), may encounter problems and the mission life of this display reduces.Be produced as the driving method that zero net time on average applies electric field at whole electro-optical medium and typically refer to " dc balance " or " DC balance ".LCD also can run into similar problem, but because this class display is insensitive to the polarity of the electric field that applies, and have the arbitrarily ability of reversed polarity thereupon, so that the DC equilibrium problem is not very important in LCD.Yet, the DC balance need in the drive scheme of design bistable electro-optic displays (wherein electro-optical medium is to the polar sensitive of the electric field that applies), be significant consideration.
Therefore, another aspect of the present invention relates to the method and apparatus that drives electro-optic displays, and the method and device have reached the specific (special) requirements of bi-stable display previously discussed.Some method and apparatus of the present invention is mainly used in producing accurate gray scale rendition in bi-stable display.
Therefore, on the one hand, the invention provides the method that has the bistable electro-optic displays of at least one pixel for addressing, the method comprises: apply addressing pulse to drive described pixel to the first optical states;
Within a period of time, keep described pixel not driven, allow thus described pixel to present to be different from the second optical states of the first optical states;
Apply refresh pulse to described pixel, this refresh pulse returns to the first optical states with described pixel substantially, and is shorter with respect to this refresh pulse of addressing pulse.
Of the present invention this is called as " refresh pulse " of the present invention method on the one hand for convenience's sake hereinafter.
In this refresh pulse method, the impact of refresh pulse is not more than impact about 20% of addressing pulse usually, it is desirable to be not more than the about 10% of this impact, and preferably is not more than 5% of this impact.Owing to reason as explained below, the difference between common the first and second optical states is no more than the L of an about unit *(L wherein *Has common CIE definition); It is desirable to the L that this difference is no more than about 0.5 unit *, and preferably be no more than the L of about 0.2 unit *Can apply a plurality of refresh pulses to this pixel with regular interval.
In a kind of form of this refresh pulse method, after applying refresh pulse, apply the second addressing pulse to this display, this second addressing pulse drives this pixel to the 3rd optical states that is different from the first and second optical states, and the impact that is wherein applied by the second addressing pulse is following two sums: (a) this pixel is driven into the required impact of the 3rd optical states from the first optical states, and (b) and in the algebraic sum equal and opposite in direction that is applied to the refresh pulse on this pixel between the first and second addressing pulses and an opposite polarity impact.But the second addressing pulse may be to change the voltage constant duration.In comprising the display of a plurality of pixels, the second addressing pulse can be blanking pulse, and it is with all pixel drivers to one extreme optical states of this display.In the preferred form that this " blanking pulse/refresh pulse " processed, this display comprises a plurality of pixels, the first addressing pulse is applied to each pixel, and first group of pixel becomes in vain and second group of pixel becomes black in order to drive, at least one refresh pulse is applied to each pixel, and apply so that the first blanking pulse of all pixel blackening and the second blanking pulse of driving all pixel Cheng Bai to this display afterwards, these two blanking pulses apply with any order all can.The impact that is applied to each pixel of first group during the first blanking pulse is following two sums: (a) drive this pixel from white to black required impact, and (b) and between the first addressing pulse and the first blanking pulse, be applied to the algebraic sum equal and opposite in direction of refresh pulse of this pixel but an opposite polarity impact.Similar, the impact that is applied to each pixel of second group during the second blanking pulse is following two sums: (a) drive this pixel from black to white required impact, and (b) and between the first addressing pulse and the first blanking pulse, be applied to the algebraic sum equal and opposite in direction of refresh pulse of this pixel but an opposite polarity impact.
Refresh pulse method of the present invention can be used for the electro-optical medium of aforesaid any type.Therefore, in the method, display can be rotation two color components or electrochromic display device (ECD), perhaps electrophoretic display device (EPD), the electrophoretic display device (EPD) that it is desirable to encapsulate.
On the other hand, the invention provides a kind of method for addressing bistable electro-optical medium, the method comprises to this medium and applies the have direct current offset alternating-current pulse of (offset).
On the other hand, the invention provides a kind of method of addressing bistable electro-optical medium, the method comprises to this medium and applies alternating-current pulse, and changes the frequency of this pulse and at least one in the duty cycle, thereby changes the optical states of this electro-optical medium with this alternating-current pulse.
On the other hand, the invention provides the method that drives bistable electro-optic displays, this display comprises a plurality of pixels that are arranged in a plurality of row and a plurality of row; A plurality of column electrodes, each column electrode is relevant with one of these a plurality of row; A plurality of row electrodes, each row electrode is relevant with one of these a plurality of row; And drive unit, be arranged for selecting successively each in the column electrode and between the selecting period of any given column electrode, applying selected voltage to the row electrode, so that the pixel in the addressing row relevant with selected column electrode and the delegation that writes needed image at this display.The method comprises:
The first image is write display;
Receive representative and will write the data of the second image on this display;
This first and second image and the row of this display is divided into first group and second group relatively, at least one pixel in first group row between the first and second images is different, and pixel is identical between the first and second images in second group row; And
Column electrode by a select progressively and first group of line correlation writes the second image, and apply voltage to the row electrode only writing first group of row, thereby form the second image at this display.
On the other hand, the invention provides the electro-optic displays with a plurality of pixels, in these pixels at least one comprises mutually different a plurality of sub-pixels of area, and this display comprises drive unit, is arranged for changing independently of each other the optical states of described sub-pixel.In this display, its area of at least two sub-pixels that it is desirable in these sub-pixels differs 2 times substantially.
Describe the preferred embodiments of the present invention now with reference to accompanying drawing, but preferred embodiment only is exemplary, in the accompanying drawing:
The curve map of Fig. 1 shows in the display that uses the DC pulse addressing with pulse length modulation gray level over time;
The curve map of Fig. 2 is similar to Fig. 1, be use the DC pulse addressing with pulse-height modulation display gray level over time;
The curve map of Fig. 3 is similar to Fig. 1, be the alternating-current pulse addressing with direct current offset used according to the invention display gray level over time;
The curve map of Fig. 4 is similar to Fig. 1, be the alternating-current pulse addressing with duty cycle modulation used according to the invention display gray level over time;
The curve map of Fig. 5 shows in the display that uses the addressing of double prepulses magic lantern (slideshow) waveform gray level over time;
The curve map of Fig. 6 shows in the display that uses the addressing of single prepulsing magic lantern waveform gray level over time;
Fig. 7 A and 7B show may arranging of sub-pixel in the single pixel of display of the present invention.
Point out as front, the invention provides many improvement of the structure of the method for addressing electro-optical medium and display and these displays.To sequentially describe various aspects of the present invention now, but will be appreciated that single electro-optical medium or display can utilize a more than aspect of the present invention.For example, single electro-optic displays can use the AC pulsed drive with DC skew, and also uses refresh pulse.
Refresh pulse method of the present invention
As previously mentioned, the invention provides a kind of method, the method refreshes image on this display by apply the new pulse of whisk broom to electro-optic displays.Therefore, in the method for the invention, at first the pixel to bi-stable display applies addressing pulse, and this addressing pulse is enough to change the optical states of this pixel.Keeping this display after not driven a period of time, apply refresh pulse to this pixel, this refresh pulse is shorter with respect to this addressing pulse.Usually, the impact that refresh pulse applies is not more than 20% (it is desirable to be not more than 10%, and preferably be not more than 5%) of the impact that addressing pulse applies.For example, if pixel need to continue the addressing pulse of the 15V of 500 milliseconds (msec), refresh pulse can be 15V, continue 10 milliseconds (msec), its impact be addressing pulse impact 2%.
Should consider that human eye adjusts the time of refresh pulse in the method to the sensitivity of the subtle change of unexpected optical states.Human eye has relative patience for the gradually decay of image, so that, for example, usually measure as brightness L *(defined by common CIE; Referring to, Hunt for example, R.W.G.Measuring Color, 3rd edition.FountainPress, Kingston-upon-Thames, England (1998). (ISBN 0863433871)) the bistability of electro-optical medium of required time, two units of maximal value (or minimum value of black state) variation of the white optical state of after addressing pulse finishes, observing.Yet when applying refresh pulse to display, the brightness of related pixel occurs to change suddenly, and substantially less than 1 L of unit *Sudden change be easy to be discovered by human eye.According to the interval between the refresh pulse, the variation of the image that is caused by these pulses may show as " flicker " in image, and this flicker is disliked for most of observer.Other discernable variation in the image that causes for fear of this flicker or by refresh pulse, expectation be interval between selective addressing pulse and the first refresh pulse or the interval between the continuous refresh pulse so that each refresh pulse causes minimum variation in image.Therefore, the L that is caused by single refresh pulse *Variation should be less than about 1 L of unit *, it is desirable to less than about 0.5 unit, and more preferably less than about 0.2 unit.
Although the refresh pulse that uses in this method can be introduced some DC in drive scheme during applying this refresh pulse uneven, but be not precluded within the long-term DC balance of acquisition in this drive scheme, and have been found that the long-term but not DC balance of short-term is the principal element of the mission life of decision electro-optic displays.In order to obtain this long-term DC balance, after applying one or more refresh pulses, the pixel that has received these refresh pulses can be driven to its opposite optical states by " conversion " or the second addressing pulse, and can be adjusted at the impact that applies in this inversion address pulse so that DC balance (perhaps minimum at least DC is uneven) to be provided in the whole cycle that begins since the first addressing pulse, this adjustment is by adjusting the impact of this second addressing pulse, wherein the adjustment amount size equal and polarity in contrast to the algebraic sum that between these two addressing pulses, is applied to the refresh pulse of this pixel.For example, consider a display, it can be by applying ± impact of 15V, 500 milliseconds (msec) and changing between white and black light state.The pixel of supposing this display at first by apply 500 milliseconds (msec)+15V impacts and bleaches from black, and the white state of this pixel subsequently by apply at set intervals 10 milliseconds (msec)+10 refresh pulses of 15V are held.If behind these 10 refresh pulses, expectation makes this pixel get back to its black optic state, this can by apply 600 (rather than 500) millisecond (msec)-the 15V addressing pulse realizes, thereby all realized the DC balance between tour at the whole Hei-Bai of this pixel-Hei.
The such adjustment that changes addressing pulse can realize when new images writes on this display and therefore must change the optical states of some pixel.Perhaps, can during applying " blanking pulse " to this display, carry out this adjustment.Discuss among the PCT/US02/37241 as the aforementioned, usually must or expect to apply so-called " blanking pulse " with the rule time interval to electro-optic displays; This blanking pulse comprises at first all pixel drivers to one extreme optical state of this display (for example, white state), then drives all pixels to opposite optical states (for example, black), then writes needed image.The advantage that realizes this adjustment during blanking pulse is, all pixels can be substantially at one time by the DC balance; The technology of using the front to describe in detail, the pixel that in the image formerly (firm incipient image before the blanking pulse) is black can be the DC balance during with the blanking pulse of all pixel driver Cheng Bai, and is that white pixel can be the DC balance during the blanking pulse that all pixel drivers is become black in the image formerly.Equally, realize that during blanking pulse the advantage of this adjustment is, do not need clearly to know since its previous addressing pulse to begin how many refresh pulses are each independent pixel received; Suppose to refresh black and white pixel (fact of case is usually like this) every the identical time interval, and when changing, inserts each image blanking pulse, each pixel will need identical adjustment (except polarity) during this blanking pulse, this adjustment determines by work the quantity that is applied to the refresh pulse on this display since this previous blanking pulse.Equally, the impact that applies adjust ash-grey transformation in this display during realizes that during blanking pulse the DC balance provides a kind of this refresh pulse method is applied to have mode more than the electro-optic displays of two gray levels, because obviously may cause the undesired error of gray level.
Refresh pulse method of the present invention can as the substitute of the adjuvant of the bistability that increases electro-optical medium or with its combination.For example, the electrophoretic media that the present invention can describe in aforesaid 2002/0180687 is used, and this medium has the suspending liquid that polymkeric substance dissolving or that disperse is wherein arranged, and wherein this polymkeric substance increases the bistability of medium.
Provide now following example, only by the mode of explanation, an embodiment of refresh pulse method of the present invention is shown.
Example 1
This example uses the display of the anti-charge type medium of two particles that contains encapsulation, and this medium comprises polymer-coated titanium dioxide white particles and polymer-coated black particles, and suspending liquid is not painted.This display is substantially according to " method B " preparation of describing in aforesaid 2002/0180687 [0061]-[0068] section.
The display of preparation comprises a plurality of pixels as previously mentioned, can use continue 500 milliseconds (msec) ± the 15V addressing pulse changes these pixels between the black and white optical states.The bistability of this display is limited, and white optical state changes 2L in the environment around *The needed time of unit is about 15sec only.Yet, determine on the experience by apply 4sec/min ± the new pulse of whisk broom (duty cycle is approximately 6.7%) of 15V can keep this white and black optic state indefinitely.In order to avoid flicker in the standard picture (containing the black and white zone) that real test is provided and in these experiments, uses, after 500 milliseconds of (msec) addressing pulses of beginning, every about 100 milliseconds (msec) to the black and white pixel of this display apply 7 milliseconds of (msec) duration ± refresh pulse of 15V.
In order to determine the effect in each cycle of the uneven drive scheme of DC on the display, tested 4 kinds of drive schemes:
Scheme 480:
Use described standard picture to this display addressing, and use aforesaid refresh pulse that this image was kept 480 minutes.Then apply a series of blanking pulses, and the circulation of repetitive addressing and refresh pulse.Whenever do not apply the DC equalizing pulse.After 83 hours the work, apply a series of blanking pulse, and what then test this display has been respectively white and the zone of separating of black.Be retained as in the zone table below of this display of white with " 480W " expression at test period, and be that the zone of black is with " 480D " expression.The addressing pulse zone that each is tested of 500 milliseconds (msec) by standard is driven into its white optical state, and measures its number percent reflectance value; This value represents with " w% " in table.Then allow each tested zone in the situation that does not apply any refresh pulse, to keep 15sec, after this interval of 15 seconds, measure L *Variation; Resulting L *Variation be called " bright maintenance difference (bright holding difference) ", in described table with " bhdl " expression.After applying other blanking pulse, the addressing pulse zone that each is tested of 500 milliseconds (msec) by standard is driven into its black optic state, and measures its number percent reflectance value; This value represents with " d% " in described table.Then allow each tested zone in the situation that does not apply any refresh pulse, to keep 15 seconds, after this interval of 15 seconds, measure L *Variation, resulting L *Variation be called " secretly keeping difference ", in described table with " dhdl " expression.
Scheme 60:
This scheme is identical with scheme 480, and just image only kept 60 minutes before applying blanking pulse." 60W " expression is used in the zone that remains this display of white during this test period in following table, and remains zone " 60D " expression of black.
Scheme 10:
In this scheme, write image in the mode identical with scheme 480, and use and scheme 480 identical refresh pulses kept 10 minutes.Then apply opposite polarity 40sec pulse with this display of DC balance, then this image is rewritten, and repeats this circulation." 10W " expression is used in the zone that remains this display of white during this test period in following table, and remains zone " 10D " expression of black.
Scheme 1:
This scheme is identical with scheme 10, and just image only is held 1 minute, then applies 4 seconds the 2nd DC equalizing pulse, and repeats this circulation." 1W " expression is used in the zone that remains this display of white during this test period in following table, and remains zone " 1D " expression of black.
The result who obtains in these experiments is as shown in table 1 below.
Table 1
480W 480D 60W 60D
w％ 37.90 30.63 38.21 38.47
d％ 2.89 2.69 3.03 2.45
dhdl 2.05 0.64 4.79 1.05
bhdl -1.34 -4.06 -0.47 -2.72
10W 10D 1W 1D
w％ 37.31 37.39 37.20 37.20
d％ 2.75 2.75 3.14 3.13
dhdl 0.89 0.84 0.98 0.99
bhdl -2.24 -2.30 -2.02 -1.98
Find out that from the data of table 1 in highly uneven scheme 480, the white states reflectivity between the zone of this display that remains white and black during test period is obviously different, and the bright and dark difference that keeps is also significantly different.Therefore, this highly uneven drive scheme produces the basic variation of the optical states of this display, and is far from other effect of following this non-equilibrium drive scheme possible, such as the damage to electrode.Equally, shown such as the difference in the bright and dark maintenance difference, this imbalance drive scheme is introduced " biasing " to this display, also keeps white after namely the zone of long-term maintenance white trends towards, and keeps for a long time the zone of black to trend towards keeping afterwards black.The result who never obtains in the balance scheme 60 is similarly, but is not so significantly (just as expected).What contrast is that DC balance scheme 10 and 1 does not show difference substantially between the black and white zone of maintenance.
Therefore, these test demonstration, as long as long-term DC balance is to be produced by the blanking pulse that separates, can negative effect not arranged to the attribute of this display by the temporary transient DC imbalance of using the new pulse of whisk broom to cause so.
The electrophoretic media of using in refresh pulse method of the present invention can adopt same parts and the manufacturing technology in aforesaid EInk and MIT patent and the application, and the reader can and apply for to obtain further information with reference to these patents.
The fundamental element of gray level drive waveforms (comprise and use the AC pulse)
As aforesaid U.S. Patent No. 6,531,997 and 6,504, described in 524, current many displays make electro-optical medium saturated by applying sufficiently long potential pulse of duration, thereby (for example are converted to another extreme optical state from an extreme optical state, from black in vain, vice versa); For example in the electro-optical medium based on particle, make charged particle from start to finish forward or the rear electrode motion.The tradition of saturated this electro-optical medium of ability addressing need to not allow the middle gray state to exist until this optical states becomes.The electro-optic displays that obtains gray level provides significant advantage in image volume and picture quality.
For convenient, voltage waveform or the drive scheme that can obtain gray level in bistable electro-optic displays are called " gray level waveform " or " gray scale drive scheme " hereinafter.The basic gray level waveform elements that can use in this gray level waveform or drive scheme has 5; Term " gray level waveform elements " refers to potential pulse or the sequence of voltage pulses that can change in the optical states of electro-optic displays.Itself can produce gray level the gray level waveform elements, and the one or more gray level waveform elements that are arranged in particular sequence form the gray level drive waveforms together.The gray level drive waveforms can be converted to another from a grey states with the pixel of display.The sequence of one or more drive waveforms consists of drive scheme, and this scheme can show any grayscale image sequence at display.
The drive waveforms element is divided into two classes, namely direct current (DC) potential pulse with exchange (AC) potential pulse.In both of these case, pulse can Varying parameters be pulse height and pulse length.
Although producing the key of gray level optical states in electro-optical medium depends on voltage and is applied to mode on this medium, but this medium keeps the ability of described gray level optical states important too in the gray level addressing scheme in case after not applying voltage, and this ability will depend on the characteristic of this medium, in fact will depend on all greyscale transitions attributes.In this application, the electrophoretic media based on particle of main reference encapsulation is discussed the gray level addressing scheme, but think that for the technician in the described medium technical field it is apparent that the attribute of considering other type of bistable electro-optical medium carries out necessary modification to this scheme.
The infrastructure elements of gray level drive waveforms is as follows:
The DC pulse of pulse length modulation
One of the simplest method of the grey states of realizing ideal is to stop addressing being in from a kind of extreme optical state and being converted to pixel among the another kind of extreme optical state.In Fig. 1 of accompanying drawing, interpolation illustrates for the waveform elements that produces the DC pulse length modulation of greyscale transitions in the electrophoretic media (shown in the major part of this figure) of encapsulation.(herein and the display that uses in the following subsequent experimental substantially make according to aforementioned 2002/0180687 [0061]-[0068] section described " method B ".) three pulses using are respectively that 15V continues 200,400 and 600 milliseconds (msec), and three curves that produce are marked accordingly; Different in time scale in noting in the illustration and the master map.Therefore, for the difference variation of reflectivity, pulse height is fixed and the duration variation of pulse.In Fig. 1, drawn reflectivity (according to these potential pulses that apply, its reflective condition is from the black gray scale that changes to different stage) the temporal evolution curve of pixel; Can find out that long pulse length produces larger reflectance varies.
Tested display to the end response of the potential pulse that applies rapidly, and its optical states stops to develop.On micro-level, can suppose that electrophoresis particle stops the migration from an electrode to another electrode immediately, and keep being suspended in the centre position in the capsule.
The DC greyscale drive pulse advantage of pulse length modulation is the speed that reaches desirable grey states.
The DC pulse of pulse-height modulation
Another method that obtains desirable grey states is to come address pixel to make an extreme optical state of this pixel be converted to another extreme optical state fully with a voltage lower than needed voltage.In Fig. 2 of accompanying drawing, interpolation illustrates for the waveform elements that produces the DC pulse-height modulation of greyscale transitions in the electrophoretic media (shown in the major part of this figure) of encapsulation.Potential pulse length is fixed on maximal voltage level and changes the needed time span of this medium fully.Three pulses using are respectively 5,10 and 15V, continue 500 milliseconds (msec), and three curves of generation also are marked accordingly; Different in time scale in noting in the illustration and the master map.Therefore, for the difference variation of reflectivity, pulse length is fixed and the height change of pulse.In Fig. 2 of accompanying drawing, drawn reflectivity (according to these potential pulses that apply, its reflective condition is from the black gray scale that changes to different stage) the temporal evolution curve of pixel; Can find out that larger pulse height produces larger reflectance varies.
Can suppose that electrophoresis particle passes through suspending liquid with lower speed under lower voltage, and when stopping to apply driving voltage, keep suspending.
The advantage of the DC greyscale drive pulse of pulse-height modulation is the accurate control to the grey states that obtains.
AC pulse with DC offset modulation
The gray level of the electrophoretic media of aforesaid encapsulation drives the impact that has been subject to vibration (AC) electric field; Use the transition mechanisms of this AC field to be assumed to the mechanism that is different from realization in the DC of above-mentioned identical medium drives fully.In Fig. 3 of accompanying drawing, interpolation illustrates the AC pulse of DC offset modulation waveform elements, is used for producing greyscale transitions in the electrophoretic media of the encapsulation shown in the major part of this figure.Under any circumstance, the frequency of AC composition (approximately 10Hz) is set in a value, this value allows particle in response to this oscillating field, and the size and Orientation of DC skew (for three curves among Fig. 3, demonstration be 0 ,-1 or-2.5V) determine the final grey states that obtains of this pixel.As among the figure of front, the time scale in the interior illustration is different from the time scale in the master map.In Fig. 3, drawn reflectivity (according to these potential pulses that apply, its reflective condition is from the black gray scale that changes to different stage) the temporal evolution curve of pixel; Can find out that larger DC skew produces larger reflectance varies.
In case apply the AC field, electrophoresis particle vibrates in suspending liquid, and this vibration is the motion of observing as the cyclical variation that is superimposed upon the reflectivity in the whole variation of reflectivity, and this left side at Fig. 3 is easy to find out.Yet, until apply the DC skew, just can clean impact be arranged to reflectivity.Under the impact of DC skew, reflectivity after waveform applies a period of time near steady state value.As if having a kind of restoring force and the power that is applied on the particle owing to the DC offset voltage to resist mutually, otherwise particle will continue to flow to cell-wall.This restoring force may be because the motion of the fluid between cyst wall and the particle and/or since particle directly and the effect between the cell-wall.Consistent with other waveform elements, remove that the stability of optical states remains constant behind the voltage.
The advantage of AC waveform elements is to reach by the parameter of specified waveform element specific reflectivity state, and the DC waveform elements can only make reflectance varies.Having the AC waveform elements of DC skew do not need to be to the addressing pulse accurate timing with respect to the advantage of other AC waveform elements.
The AC pulse of duty cycle modulation
The another kind of mode of using oscillating field to introduce the DC biasing is the modulation duty cycle.In Fig. 4, interpolation illustrates the AC pulse of duty cycle modulation, and this pulse is for generation of the greyscale transitions in the major part of this figure.In each of these pulses, voltage is set to maximal value, and duty cycle (voltage is at the number percent of the time of positive dirction or negative direction) determines reflectivity.Three duty cycles using are 50%, 47% and 40%, as shown in Figure 4.As among the figure of front, the time scale of using in interior illustration is different from the time scale in the master map.In the figure, the reflectivity that has drawn pixel (according to these potential pulses that apply, its reflective condition changes to different grey level from black) is curve over time.
As can be seen from Figure 4, identical with AC/DC shift pulse for generation of curve shown in Fig. 3, curve shown in Figure 4 reaches steady state value after pulse applies a period of time.Therefore, consistent with the AC/DC skew, use the duty cycle modulation, as if there is a kind of restoring force, it forces particle to leave cell-wall, keeps grey states constant.The physical mechanism of this restoring force and previously discussed similar.Equally, grey states stops to change immediately after stopping to apply pulse.
The advantage of the AC waveform of duty cycle modulation do not need to be voltage modulated.
Warbled AC pulse
The another kind of method that realizes the AC greyscale transitions is to apply such AC field to electro-optical medium: this AC field causes the optical states vibration of this medium, then stops this AC field at the point that obtains ideal reflectivity in circulation.Voltage can be set to maximal value, changes the AC frequency to obtain greater or lesser reflectivity range.Frequency determines the amplitude of reflectivity vibration.
When this method be applied to encapsulate based on the electrophoretic media of particle the time, electrophoresis particle by near oscillatory response their initial position in the AC field.Because usually reflectivity does not reach extreme black or white light and learns state, minimize with interaction between the cell-wall and reflectivity is relative linear to the alive response of execute.
The advantage of warbled AC pulse is not need voltage modulated.
By the pulse in conjunction with the above-mentioned type, can develop the multiple waveforms element, each comprises unique changing the mechanism, and therefore provides to drive the different electro-optical medium the whole bag of tricks with different switching characteristic.
In concrete an application of above-mentioned drive scheme principle, use pulse-length modulation and AC pulse with the middle gray state in the acquisition electro-optic displays, otherwise this display can only obtain black and white state.
Discussed owing to top, very expectation can obtain gray level in electro-optic displays.Yet, suppose that the pulse-length modulation that a large amount of gray levels need to have arbitrarily high frame frequency driver or a driver that can voltage modulated (needs high frame frequency that pulse width " is cut " and becomes a plurality of intervals, therefore accurate gating pulse width, and then accurately control gray level).In these two kinds of drivers any is substantially all higher than simple three grades of (tri-level) driver costs, described three grades of drivers can only make the electromotive force of the single pixel of display be configured to respect to public front electrode potential+V ,-V and 0 (V is any work potential), and it is generally used for driving the display that can only show black and white state.
The invention provides a kind of drive scheme, this scheme can make the intermediate grey scales between deceiving of three grades of drivers generation bistable electro-optic displays and the white level.The easiest understanding from following table 2 of this drive scheme, this has expressed the voltage that applies during the successive frame of all kinds transformation in this display of the present invention:
Table 2
0 1 2 3 4 5 6 ... N-1 N
White to black + V + V + V + V + V + V + V ... +V + V
Black in white - V - V - V - V - V - V - V ... -V - V
White to ash + V + V + V + V - V + V - V ... +V - V
Black in ash - V - V - V - V + V - V + V ... -V + V
Ash is to black + V + V + V 0 0 0 0 0 0 0
Ash is to white - V - V - V 0 0 0 0 0 0 0
Can find out the same the transformation from black to white (vice versa) and scale-of-two (the only having black/white) display from top table 2.On the other hand, the transformation to gray scale has two parts.First is square waveform pulse (that is, a plurality of frames of same potential), and it has suitable polarity and length approaches the middle gray brightness that needs as far as possible so that the reflectivity of electro-optical medium becomes.Degree of accuracy with this step may will be subject to the frame frequency restriction of display.The second portion of addressing pulse comprises the potential pulse of the positive and negative that quantity equates, the width of each pulse equals a frame.With reference to Fig. 3 and 4 described, the front is verified as front: the surge medium based on particle that the AC square wave is applied to encapsulation causes that this medium " relaxation " is to some " middle gray " state.Therefore, no matter previous pulse is historical, the second portion of pulse will make all pixels become identical uniform middle gray state.Use has the short pulse of suitable polarity and realizes being addressed to from grey states black or white.
More generally, the AC of this pulse part does not change polarity at every frame, but can be with lower frequency transitions, is accompanied by that (frequency=frame frequency/2n) voltage carries out alternation every a frame (frequency=frame frequency/4) or common every n frame.
Therefore, the invention provides a kind of method, the method is only used simple three grades of drivers and is not used complexity and expensive voltage modulated driver, produces single gray level in other binary electro-optic displays.
In second concrete application of above-mentioned drive scheme principle, the invention provides the set of two-dimentional transition matrix, wherein how each the element regulation in the matrix arrives final optical states (using " column index represents " herein) from initial optical state (using " row index " expression herein, although be apparent that distributing to capable initial optical state is arbitrarily).Each element of this matrix is by a series of waveform elements (as defined above) structure, and usually for n position gray level display device, this matrix will comprise 2 (2N)Individual element.Matrix of the present invention has counted such consideration, such as the needs (as previously discussed) to the DC balance of drive scheme, in some electro-optical medium, " memory " effect is minimized (namely, the effect that applies the result of certain pulses to pixel not only depends on the current state of this pixel, also depend on some original state), thereby produce uniform optical states and with the maximization of the rate of transformation of display, under the restriction of driven with active matrix scheme, work simultaneously.The present invention also provides a kind of method, is used for determining for any certain electric optical media each optimal value of the element of this matrix.For this matrix and their application in driving electro-optic displays, the reader can be with reference to aforesaid PCTUS02/37241.
With regard to aforesaid pulse-length modulation (PWM), current preferred wave shape form of the present invention is as described below.Yet, use the AC modulation of pulse-height modulation or above-mentioned various mixed types also can obtain same or analogous result, and can in single waveform, use various dissimilar modulation, for example, for the pulse-length modulation of all parts except the decline of pulse, what follow later is back-page voltage modulated to this pulse.
The first two waveform of the present invention that the following describes is " magic lantern " waveform, and it got back to black state from a grey states before being addressed to next grey states.This waveform is the most compatible with the display update scheme of a wherein blanking of whole screen (as in slide projector).
Double prepulses magic lantern waveform
In this waveform, its preferred form has been shown among Fig. 5 of accompanying drawing, use partial pulse at first the pixel of electro-optical medium to be driven into (shown in 100) initial (first) grey states from deceiving.For with pixel from then on initial grey states change to different expectation (second) grey states, at first pixel is driven into white (102) from the first grey states, then from vain to black (104).At last, apply suitable pulse to reach the second grey states 106.Keep whole DC balance in order to ensure such waveform, the length sum of the white pulse at the addressing pulse at 106 places and 102 places must equal the length of the Bai at 104 places-Hei pulse.The maximal value of the medium fringe time that these waveform needs are three times (that is, single pixel is learned state-transition from black light and learned the required time of state to white light, and perhaps vice versa) is implemented in the transformation between any two any gray scales, therefore is called as the 3X waveform.
Single prepulsing magic lantern waveform
In this waveform, its preferred form has been shown among Fig. 6 of accompanying drawing, use partial pulse at first with the pixel of electro-optical medium from black (shown in 110) initial (first) grey states that is driven into, the double prepulses waveform of discussing in the mode of employing and top the 6th part is identical.For this pixel is changed to different (second) grey states of expecting from initial grey states, at first this pixel is driven into black (112) from the first grey states, then apply suitable pulse to arrive the second grey states 114.Obviously, before the second transformation, this pixel will be got back to 116 black again.Such waveform keeps the DC balance of whole waveform, and this is because equal respectively (except polarity) in 110 and 114 impacts that apply in 112 and 116 impacts that apply.This waveform needs the maximal value of medium fringe time of twice being implemented in any two arbitrarily transformations between the grey states, therefore is called as the 2X waveform.
Gray scale-greyscale waveforms
Replace using above-mentioned magic lantern waveform, can be by directly coming its addressing and refresh display without black or white state from a grey states to another grey states.Because obvious illusion (i.e. black and/or white " flicker ") is not followed in this transformation, so it is called as " gray scale-gray scale " addressing.Have the gray scale-greyscale waveforms of two kinds of principal modes, namely DC balance and DC are uneven.
In the gray scale-greyscale waveforms of DC balance, be implemented in transformation between these two states by being applied between two grey states the necessary modulating pulse with precise length of conversion.Electro-optical medium is black or white state without any centre.Because maximum impulse length equals the addressing time of ink, this waveform is also referred to as the 1X waveform.In order to keep the DC balance, for the display with n grey states, available free parameter has n-1 in the optimization of the transformation matrix relevant with any specific waveforms.This causes excessively limited system.For example, change and to equate and relative pulse (that is, except polarity, 2-3 must be identical with 3-2) for opposite transformation.
Uneven gray scale-the greyscale waveforms of DC is basic identical with the situation of DC balance, and just pulse length no longer is subject to the constraint of DC equilibrium-limited.So 2 in transformation matrix (2N)In each can be independent of all other variations.
Various waveform discussed above can be in Active Matrix Display the addressing gray level, use in personal digital assistant (PDA) and e-book are used is crucial for electro-optical medium for this.These waveforms minimize the memory effect in the electro-optical medium, and this memory can cause the image ghost image.By selecting optimal burst length and order, can in the minimum number pulse, obtain desirable gray-scale optical state.
Selective row drives
Another aspect of the present invention relates to by selecting to drive the row of this display, improves the performance of active matrix bistable electro-optic displays.
As previously mentioned, and discuss in more detail in patent and the application as the aforementioned, in order to keep needed image at traditional LC D, must refresh continuously whole image-region, this is not bistable because of common liquid crystal, and if do not refresh on the LCD image in a short period of time the image on the LCD will weaken.Technician such as active matrix field is known, in this display, the realization that refreshes continuously be by: use line driver to open the transistorized grid relevant with the one-row pixels of this display, apply the electromotive force that the relevant portion of the required image on this display is write the pixel in the selected row at row driver (being connected to the transistorized source electrode in every row of this display), and therefore write the selected row of this display.Then line driver is selected the next line of this display and is repeated this process, and row just is recycled and refreshes like this.(line driver is assigned to gate electrode and row driver is assigned to the source electrode is conventional, but also is arbitrarily substantially, certainly can put upside down if need.)
Because LCD needs refreshing continuously of image, the only part of shown image changes the part that is used as whole refresh process and processes.In the display that refreshes continuously, do not need to provide the more new portion of image; Because in fact per second has several times new images write display (in the situation of LCD), any variation of the parts of images of the display of feeding manifests effect at this display automatically in short interval.Therefore, the custom circuit that is used for LCD of having developed does not provide the only renewal of parts of images.
Contrast, bistable electro-optic displays does not need to refresh continuously, and in fact this refreshing continuously be harmful to, and this is because unnecessarily increased the energy consumption of display.In addition, during this refreshing, grid (OK) circuit may pass to pixel electrode with the capacitive voltage spike pulse, and any actuator voltage error or uncompensated grid feedthrough biased error may be accumulated; All of these factors taken together causes undesirable transformation of the optical states of display picture element.Therefore, in bistable electro-optic displays, it is desirable to provide some devices for upgrading parts of images and need to not rewriteeing whole image at display, an aspect of of the present present invention relates to is furnished with the bistable electro-optic displays that this " part is upgraded " installs.According to the present invention, this consecutive image by relatively will writing this display, be identified in row different in these two images and only the identified row of addressing realize.
In the method, for the part that realizes display is upgraded, only identification comprises the row of the display of the pixel that its optical states will change.In a preferred form of this method, for every row of display, display controller (referring to aforesaid PCT/US02/37241) checks all desirable pixel electrode output voltages.If for this row, all output voltages equal the electromotive force V of the public front electrode of this display Com(that is, if there is not pixel to need to rewrite in that row), the then synchronous (V of controller output Sync) pulse and data value is not written into row driver, and do not issue corresponding output enable (OE) order.The net effect of doing like this is that the token position of line driver is delivered to the next line of display and does not activate current line.Data only are written into row driver, and output enable is only for the row statement that wherein has at least one pixel to be rewritten.
The invention provides two kinds of different advantages.At first, for the pixel that is not rewritten, can eliminate a lot of stray voltage sources.Do not have capacitive grid spike (gate spike) for these pixels, and in the not addressed frame of pixel, the error of row driver voltage can not be delivered to this pixel.Since with liquid crystal phase relatively, a lot of electro-optical medium resistivity are relatively low, electrophoretic media especially, pixel electrode will trend towards relaxing towards actual front (front plane) voltage, therefore keep the hold mode of electro-optical medium.Secondly, the minimise power consumption of display.For the every delegation that is not rewritten, corresponding grid line does not need to be recharged.In addition, when output is not written into the row electrode of display, has also eliminated and crossed over the extra power consumption that display interface device comes Mobile data.
Area of space shake (dither)
Foregoing aspect of the present invention relates to for the waveform that drives electro-optic displays.The performance of this display also can change by the structural change that changes base plate, and one or more pixels (preferably each pixel) that this relates on the one hand with display of the present invention are divided into a plurality of sub-pixels with different area.
Mention as front, wish very much in electro-optic displays, to provide gray level.Also can obtain this gray level to the grey states between two extremity by the pixel driver with this display.Yet, if this medium can not obtain the intermediateness of ideal quantity, if perhaps this display is driven by the driver of the intermediateness that ideal quantity can not be provided, then must obtain with other method the state of ideal quantity, of the present invention this is related to this purpose and the spatial jitter used on the one hand.
A display can be divided into a plurality of " logic " pixel, and wherein each can show gray scale or other optical states of ideal quantity.Yet, obviously in each logical pixel a more than physically separated zone can appear, in fact this is common for color monitor utilization " panchromatic " logical pixel, and each of described " panchromatic " logical pixel comprises have primary colours three sub-pixels of (for example red, green, blue); Referring to for example aforesaid 2002/0180688.Similarly, can obtain gray level as logical pixel with the combination of sub-pixel, each in the sub-pixel can binary change.For example, comprise that 4 controlled logical pixel with sub-pixel of the same area of independence can be used for providing 2 gray levels.Yet for any situation more than 1 or 2 gray level, the quantity of sub-pixel becomes greatly inconveniently, because 1 of the every increase of gray level, the quantity of required sub-pixel doubles.
The invention provides a kind of electro-optic displays, it has at least one pixel, and this pixel comprises a plurality of sub-pixels, and these sub-pixels have different areas.In a preferred embodiment of the invention, the area of at least two sub-pixels differs 2 times substantially.Therefore, for example, logical pixel may have the sub-pixel that area is 1X, 2X and 4X, and wherein X is arbitrary area.Such logical pixel schematically shows in Fig. 7 of accompanying drawing A.This logical pixel only uses three electrodes to obtain 3-position gray level, will need 8 sub-pixels and use the sub-pixel that equates at area to obtain identical 3-position gray level.
When each sub-pixel is driven, the part of its reflection or transmission incident light, and the part amount is by the area decision of this sub-pixel.If reflection/transmission is average on the zone of this logical pixel, then obtain to drive the binary weights of area, therefore obtain the gray level of spatial jitter.
The area of sub-pixel is arbitrarily.The reflectivity weighting of sub-pixel shown in Fig. 7 A.(this is for the L that waits stepping if use nonlinear weight *Perhaps gamma correction gray scale interval is fit to), this area will correspondingly change.
Except the relative area of considering them, also should think over the shape of sub-pixel.Simple bulk as shown in Figure 7A allows array of sub-pixels simply to be shaped, but under certain conditions, these sub-pixels may the observed person be differentiated.Equally, if intergrade gray scale (thereby (such as) only has the zone 4 of Fig. 7 A driven in each logical pixel) be presented on the large zone (covering a lot of logical pixel), the observer will see line or the grid graph that occurs from the sub-pixel figure.
The resolution that increases logical pixel will reduce these problems, but need in a large number extra pixels because pixel quantity be with resolution square and increase.On the contrary, can reduce the observability of sub-pixel and/or the problem of eye diagram by the mutual sub-pixel (for example as shown in Fig. 7 B) that intersects; Notice that this figure is intended to illustrate mutual intersection, being inaccurate represents the relative area of sub-pixel.The cross one another figure that much is similar to Fig. 7 B can be used for improving picture quality.
The another kind of method of processing the problem of sub-pixel observability and/or eye diagram is the random orientation sub-pixel.For example, in pel array, each pixel is by the arrangement of subpixels shown in Fig. 7 A, and single pixel may have each in 4 possibility directions of arranging shown in Fig. 7 A at random." randomization " of this sub pixel helps partition graph and makes them more be difficult for seeing for the observer.
Although the embodiments of the invention shown in Fig. 7 A and the 7B produce 3-position gray level, are appreciated that the present invention can produce by increasing simply extra sub-pixel the gray level of any figure place.
The advantage of this aspect of the present invention is as follows:
(a) electro-optical medium itself does not need to have gray level; Basically display can be the black/white display, and the open and close sub-pixel is to produce gray level.In scanning array, can obtain to control for necessity of sub-pixel by extra row driver (for the row of equal number) is provided.This has reduced the requirement to electro-optical medium; For example, do not need to worry to exceed may the drifting about of gray level of electro-optical medium after its mission life.
(b) do not need complicated row driver; The present invention is compatible with the simple binary level driver that uses in a lot of traditional monitors that uses.Therefore, be conducive to use the various electro-optical mediums of easy acquisition, cheap " finished product " parts.Some produce the method for gray levels need to use the voltage modulated driver to the row electrode, this driver be not widely available and than the manufacturing of binary level driver more expensive/more difficult.
(c) needed more difficult unlike panchromatic for the design of the thin film transistor (TFT) (TFT) that uses active matrix array of the present invention, each pixel (for example has three sub-pixels in panchromatic, RGB), and need to offer the data volume of various parts can be not larger yet.Therefore in implementing active matrix base plate of the present invention, do not need development new technologies.
Miscellaneous technology
In the most traditional driven with active matrix scheme of electro-optic displays, the change in voltage of pixel electrode is in order to apply required voltage in pixel on the display base plate.End face keeps specific voltage usually, and it is favourable that this specific voltage is considered to for address pixel.For example, if the data line voltage that offers pixel electrode in zero volt special and voltage V 0Between change, then end face will remain on V 0/ 2, in order to allow the voltage drop on the pixel that V is arranged on both direction 0/ 2 is so large.
According to an aspect of the present invention, the voltage of end face can change to strengthen the addressing of electro-optical medium.For example, end face voltage can remain zero volt special in case allow total pixel voltage fall (end face negative pixel voltage) low to-V 0Rising end face voltage is to V 0, allowing pixel voltage to fall has V 0So large.These larger voltage drops allow quickly addressing of electro-optical medium.
More generally, advantageously end face voltage not only can be set as voltage zero and V 0, also can be set to other voltage.For example, advantageously consistent with the pixel-pixel voltage that is applied by base plate, the time that applies the overall situation at electro-optical medium changes voltage.
Knownly in electro-optic displays, provide capacitor at pixel electrode with between by the electrode that extends to form of selecting circuit, in order to fill same voltage with selecting circuit; As the aforementioned described in the WO01/07961, this electric capacity the rate of decay that has reduced the electric field on the pixel after removing driving voltage is provided.Convenient at another, the present invention has the electro-optic displays of holding capacitor, and this holding capacitor is formed between pixel electrode and (second) electrode, and the selection circuit that the voltage of described (second) electrode can be independent of this display changes.In a preferred embodiment, the second electrode is followed end face voltage, that is, the difference of its voltage and end face only is a constant that does not rely on the time.Compare with the holding capacitor that overlaps to form between the selection circuit of having been gone by adjacent (before) of pixel electrode and this display of control, provide such capacitor to greatly reduce the capacitive voltage spike of pixel experience.
Another aspect of the present invention relates to the harmful transformation that reduces or eliminates electro-optical medium by selection and data line.
As discussed above, selection and data line are the primary elements of active matrix panel, and they provide pixel electrode is charged to the required voltage of expectation value.Yet selection and data line may have the deleterious effect that changes the electro-optical medium adjacent with this data line.By using black mask to be hidden the observer by data line and/or the zone of selecting line to change, can eliminate the harmful optics artifact that is caused by this transformation.Yet, provide this black mask need to be with the front of display with thereafter in the face of neat, and reduced the electro-optical medium part that is exposed to the observer.The result compares with the situation of not using black mask to obtain, and display is darker and contrast is lower.
In another aspect of the present invention, little by data line side direction is in one direction prolonged, thereby so that they can not carry out sizable addressing to adjacent electro-optical medium during normal display operation, thereby avoided the use of black mask.This has been avoided the needs to black mask.
The modification that related fields of the present invention relate to the use of passivated electrodes and are used for driving the drive scheme of electro-optical medium.In in its film between two electrodes, impacting the electro-optical medium that drives can be by electrical addressing.Usually, electrode contacts with electro-optical medium.Yet, even there is the dielectric material with long the electron relaxation time between one or two electrode and this medium, also can this electrode of addressing.For fear of interacting at the base plate of display device or contrary chemistry or the galvanochemistry of front, the passivation of one or two electrode may need; Referring to aforesaid WO 00/38001.Although the appearance of dielectric layer is so that the ability of the voltage on the maintenance electro-optical medium reduces greatly, if this dielectric layer is suitably designed, voltge surge still can be applied to this medium and this medium can pass through these voltge surge addressing.
Yes that voltage on the pixel electrode realizes by changing in the change of the optical states of electro-optical medium.This voltage changes the voltage that causes on the electro-optical medium, and by medium since charge leakage so that the voltage attenuation on the electro-optical medium.If enough resistivity thin and electro-optical medium is enough large for external dielectric layers (that is, the dielectric layer between this medium and the electrode), then the voltge surge on this medium will be enough to cause that the optical states of this medium changes on demand.Therefore the electronically addressing of the electro-optical medium by dielectric layer is possible.Yet this addressing scheme is different from the electro-optical medium that its electrode of addressing and this medium directly contact, because under latter event, by applying voltage addressing medium in pixel, and in the previous case, is to realize addressing by causing to change in pixel voltage.In each variation, electro-optical medium experience voltge surge.
At last, the invention provides for the drive scheme of crosstalking that reduces the active matrix electro-optic displays.
Crosstalk between pixel (optical states that pixel of addressing affects other pixel) be harmful to, this has many reasons to cause.A reason is that electric current limited under off state flows through transistor.Because the current leakage of off state provides voltage (being intended to the pixel of charging) to charge to the transistor in the non-selection row to data line.Solution is to use the transistor with low cut-off state electric current.
Another crosstalk sources is the current leakage between neighbor.Electric current can spill by the element of base plate, or spills by the electro-optical medium that contacts with base plate.This solution of crosstalking is the large base plate of clearance for insulation between a kind of pixel electrode of design.The leakage current of the larger generation in gap is less.
As has been noted, the preferred type that is used for the present invention's electro-optical medium is the electrophoretic media based on particle of encapsulation.This electrophoretic media of using in method and apparatus of the present invention can be used identical parts and the manufacturing technology described in the patent of front E Ink and MIT and application, and the reader can and apply for to obtain further information with reference to these patents.

Claims (7)

1. method that is used for addressing bistable electro-optical medium, described bistable electro-optical medium is included in a plurality of charged particles that pass liquid under the impact of electric field, described method is characterised in that, apply alternating-current pulse to this medium, and change the duty cycle of this pulse and at least one in the frequency, after this alternating-current pulse, to change the optical states of electro-optical medium.
2. method according to claim 1, wherein said alternating-current pulse has the square wave form of alternation basically.
3. method according to claim 1 wherein applies alternating-current pulse a period of time to this medium constantly, and this section period is enough to so that this medium presents the optical states of substantial constant.
4. method according to claim 1, the duty cycle of wherein said alternating-current pulse changes, and the frequency of alternating-current pulse does not change.
5. method according to claim 4 wherein at first applies the alternating-current pulse with the skew of the first duty cycle to this medium, thus so that described medium presents the first optical states; Then apply the alternating-current pulse with the second duty cycle skew that is different from the skew of the first duty cycle to this medium, thus so that described medium presents the second optical states that is different from the first optical states
6. method according to claim 1, the Frequency generated of wherein said alternating-current pulse changes, and the duty cycle of described alternating-current pulse does not change.
7. method according to claim 1, wherein said electro-optical medium have basically the second show state of opaque the first show state and printing opacity.
CN 201010159493 2002-06-13 2003-05-23 Method for addressing bistable electro-optical medium Expired - Lifetime CN101800034B (en)

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US60/319,321 2002-06-18
US60/319321 2002-06-18
US10/065,795 US7012600B2 (en) 1999-04-30 2002-11-20 Methods for driving bistable electro-optic displays, and apparatus for use therein
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US10/065795 2002-11-20

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