CN1938746A - Methods for driving bistable electro-optic displays, and apparatus for use therein - Google Patents

Abstract

A bistable electro-optic display having at least one pixel is driven using a waveform V(t) such that the integral of the product of this waveform and M(t), a memory function that characterizes the reduction in efficacy of the remnant voltage to induce dwell-time-dependence arising from a short pulse at time zero, integrated over the length of the waveform, is less than 1 volt sec.

Description

Be used to drive the method for bistable electro-optic displays

Technical field

The present invention relates to be used to drive the method for electro-optic displays, particularly drive the method for bistable electro-optic displays, and the device that in these methods, uses.More particularly, the present invention relates to be intended to control more accurately the driving method of gray states of the pixel of electro-optic displays.The present invention especially but be not intended to specially for using based on the electrophoretic display device (EPD) of particle, in this electrophoretic display device (EPD), one or more charged particles are suspended in the fluid, thereby and move through the outward appearance that this liquid changes display under electric field effects.

Background technology

As the term " electric light " that is applied to material or display uses by its conventional sense in imaging field in this article, thereby this term relates to the material with first and second show states, this first and second show state is being different aspect at least one optical property, makes this material become its second show state from its first show state by apply electric field to this material.Although optical property is the perceptible color of human eye normally, but also can be other optical property, as optical transmission, reflectivity, fluorescence, perhaps under the situation that is used for the display that machine reads, described optical property is the pseudo-colours on the meaning of the reflectance varies of the electromagnetic wavelength outside the visible range.

Term " gray states " uses by its conventional sense in imaging field in this article, thereby this term relates to a state in the middle of two extreme optical state of pixel, and this term hints that not necessarily Hei-the Bai between these two extremities changes.Electrophoretic display device (EPD) has been described in several patents that for example relates to below and open application, and wherein extremity is white and dark blue, and therefore in the middle of " gray states " is actually pale blue.In fact, as already mentioned, the transformation between two extremities may not be a color change.

Term " bistable state " and " bistability " are used by its conventional sense in the art in this article, thereby this term relates to the display that comprises display element, described display element has first and second show states, these two show states are being different aspect at least one optical property, therefore after the addressing pulse by means of finite duration drives any point element, suppose that it is in first or second show state, after addressing pulse stops, the time of this state continuance is several times at least of minimum duration that change the needed addressing pulse of state of display element, for example at least four times.It is stable in its extreme black and white state not only that some electrophoretic display device (EPD)s with gray scale based on particle have been shown in No. the 2002/0180687th, laid-open U.S. Patents application, and gray states therebetween also is stable, and also is applicable to the electro-optic displays of some other types.Such display suitably is called as " multistable " rather than " bistable state ", although term " bistable state " also can be used for covering bistable state and multistable display in this article for simplicity.

Term " pulse " uses with respect to the conventional sense of the integration of time about voltage in imaging field by it.But some bistable state electric light media can serve as the electric charge transducer, and utilize these media can use the definition selected of pulse, i.e. in time integration of electric current (its equal applied total electrical charge).Should serve as voltage-time pulse transducer or serve as the suitable definition that the charge pulse transducer uses pulse according to medium.

The electro-optic displays of several types is known.One type electro-optic displays is for example at United States Patent (USP) 5808783; 5777782; 5760761; 6054071; 6055091; 6097531; 6128124; Rotation described in 6137467 and 6147791 double-colored (bichroma1) member type (although such display so-called " rotation twin color ball " display, it is preferably more accurate that term " rotates double-colored member ", because in some patents of mentioning in the above, rotating member is not spherical).The a large amount of corpusculum of this display utilization (normally sphere or cylindricality), these corpusculums have the different two or more parts of the optical characteristics of making, and inner dipole.These corpusculums are suspended in the vacuole of full of liquid in the matrix, thereby these vacuole fulls of liquid can rotate freely corpusculum.Thereby make these corpusculums rotate to each position and which that watch the corpusculum seen of surface partly changed by the electric field that puts on display and change the outward appearance of display.Such electro-optical medium is normally bistable.

The electro-optic displays of another kind of type utilizes electrodeposited chromium (e1ectrochromic) medium, the electrodeposited chromium medium of millimicro chromium form membrane for example, it comprises electrode that is formed by semiconductive metal oxide to small part and the many dye molecules that can carry out reversible color change that are attached to this electrode; Referring to for example O ' Regan, people's such as B. Nature 1991,353,737; And Wood, the Information Display of D., 18 (3), 24 (in March, 2002).Also referring to Bach, people's such as U. Adv.Mater., 2002,14 (11), 845.For example, in open WO 01/27690 of international application and the U.S. Patent application 2003/0214695 such millimicro chromium film has been described also in U.S. Pat 6301038.Such medium also is bistable usually.

Become conscientious research and development the electro-optic displays of another kind of type of many year subject be based on the electrophoretic display device (EPD) of particle, wherein many charged particles move through suspension under electric field effects.Electrophoretic display device (EPD) has following attribute when comparing with LCD: good brightness and contrast, wide visual angle, bistability state and low-power consumption.However, the problem of the long-term image quality of these displays has stoped being extensive use of of they.For example, the particle of forming electrophoretic display device (EPD) is easy to sedimentation (settle), causes the deficiency in serviceable life of these displays.

As above speak face to face, need there be suspension in electrophoretic medium.In the electrophoretic medium of most prior art, this suspension is a liquid, but also can utilize suspension electrogenesis in the next life swimming medium of gaseous state; Referring to, for example, Kitamura, T. wait people " Electricaltoner movement for electronic paper-like display (the electric toner motion of Electronic Paper class display) ", IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y. wait people " Toner display using insulative particlescharged triboelectrically (utilizing the toner display of the insulating particle of frictional electrification) ", IDW Japan, 2001 Paper AMD4-4).Also referring to european patent application 1429178; 1462847; 1482354 and 1484625; And International Application No. WO 2004/090626; WO2004/079442; WO2004/077140; WO2004/059379; WO2004/055586; WO2004/008239; WO2004/006006; WO2004/001498; WO03/091799 and WO03/088495.When with orientation that this sedimentation allow to occur (for example placing symbol in the vertical plane with this medium) when using this medium, this electrophoretic medium based on gas is because particle precipitation appears to be subjected to easily and based on the influence of the electrophoretic medium same-type problem of liquid.In fact, it is more serious problem that particle precipitation appears in based on the electrophoretic medium of gas with comparing in the electrophoretic medium based on liquid, because the lower viscosity that the gaseous suspension fluid is compared with liquid suspension makes electrophoresis particle sedimentation more apace.

Recently announced and transferred Massachusetts Institute ofTechnology (MIT) and E Ink Corporation or in its numerous patents and application under one's name, it has described the electrophoretic medium of wrapping with capsule.This medium of wrapping with capsule comprises many folliculus, in each folliculus itself all comprises mutually and in this mutually cyst wall, it is improved to contain the electrophoresis that is suspended in the liquid suspension medium mutually in described.Usually, these capsules oneself remain in the polymeric binder it to form the adhesive coating (coherent layer) between two electrodes.Such medium of wrapping with capsule for example is documented in the following patent and patented claim: United States Patent (USP) 5930026; 5961804; 6017584; 6067185; 6118426; 6120588; 6120839; 6124851; 6130773; 6130774; 6172798; 6177921; 6232950; 6249271; 6252564; 6262706; 6262833; 6300932; 6312304; 6312971; 6323989; 6327072; 6376828; 6377387; 6392785; 6392786; 6413790; 6422687; 6445374; 6445489; 6459418; 6473072; 6480182; 6498114; 6504524; 6506438; 6512354; 3515649; 6518949; 6521489; 6531997; 6535197; 6538801; 6545291; 6580545; 6639578; 6652075; 6657772; 6664944; 6680725; 6683333; 6704133; 6710540; 6721083; 6727881; 6738050; 6750473; 6753999; 6816147; 6819471; 6822782; 6825068; 6825829; 6825970; 6831769; 6839158; 6842279; 6842657 and 6842167; U.S. Patent Application Publication 2002/0060321; 2002/0060321; 2002/0063611; 2002/0090980; 2002/0113770; 2002/0130832; 2002/0131147; 2002/0171910; 2002/0180687; 2002/0180688; 2003/0011560; 2003/0020844; 2003/0025855; 2003/0102858; 2003/0132908; 2003/0137521; 2003/0151702; 2003/0214695; 2003/0214697; 2003/0222315; 2004/0012839; 2004/0014265; 2004/0027327; 2004/0075634; 2004/0094422; 2004/0105036; 2004/0112750; 2004/0119681 He; 2004/0196215; 2004/0226820; 2004/0233509; 2004/0239614; 2004/0252360; 2004/0257635; 2004/0263947; 2005/0000813; 2005/0001812; 2005/0007336; 2005/0007653; 2005/0012980; 2005/0017944; 2005/0018273 He; 2005/0024353; And the open WO99/67678 of international application; WO00/05704; WO00/38000; WO00/38001; WO00/36560; WO00/67110; WO00/67327; WO01/07961; WO01/08241; WO03/107315; WO2004/023195; WO2004/049045; WO2004/059378; WO2004/088002; WO2004/088395; WO2004/090857 and WO2004/099862.

Many above-mentioned patents and application are all approved and can enough external phase be replaced the wall that discontinuous micro-capsule centers in the electrophoretic medium that will wrap with capsule, produce the electrophoretic display device (EPD) of so-called polymer dispersed like this, wherein electrophoretic medium comprises the external phase of many discontinuous electrophoretic fluid drops and polymeric material, and approve that the discontinuous electrophoretic fluid drop in the electrophoretic display device (EPD) of this polymer dispersed can be considered to capsule or micro-capsule, the drop independent even without discontinuous cyst membrane and each is associated; Referring to for example above-mentioned 2002/0131147.Therefore, for the application, the electrophoretic medium of this polymer dispersed is considered to the subspecies of the electrophoretic medium wrapped with capsule.

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 to pack in the micro-capsule, but are retained in the many chambeies that form in the mounting medium, and mounting medium is the film of polymerization normally.Referring to international application WO 02/01281 is disclosed for example, and the U. S. application of announcing 2002/0075556, these two applications all have been transferred to Sipix Imaging company limited.

The electro-optic displays of another kind of type is an electric moistening display, it is by Philips exploitation and be documented in the paper of periodical " Nature " that first phase on the 25th September in 2003, and the exercise question of this paper is " Performing Pixels:Moving Images on Electronic Paper (finish pixel: the live image on the Electronic Paper) ".The common pending application sequence number that this electric moistening display was submitted on October 6th, 2004 is shown in 10/711802, and this electric moistening display can be made into bistable.

The electrooptical material of other type also can be with in the present invention.What be concerned about especially is that bistable ferroelectric liquid crystal display (FLC) is well known in the art.

Although electrophoretic medium is normally opaque (because for example in many electrophoretic mediums, particle is block visible light transmission display device basically), and under reflective-mode, work, but many electrophoretic display device (EPD)s also can be formed in so-called " shutter mode " work down, in " shutter mode ", a kind of show state is opaque basically, and a kind of display mode is a printing opacity.Referring to for example above-mentioned United States Patent (USP) 6130774 and 6172798, and United States Patent (USP) 5872552; 6144361; 6271823; 6225971 and 6184856.Dielectrophoretic displays (dielectrophoretic display) is similar with electrophoretic display device (EPD), but it relies on the variation of electric field intensity, and can similarly work under the pattern; Referring to United States Patent (USP) 4418346.The electro-optic displays of other type also can be worked under shutter mode.

Electrophoretic display device (EPD) or the microcell electrophoretic display wrapped with capsule can not experience trooping of conventional electrophoretic and sedimentation failure mode usually, and more advantage can be provided, as can print or apply display on various flexibilities and rigid substrate.(employed word " printing " is intended to comprise the printing and the coating of form of ownership, includes but not limited to: pre-metering coating, as the firm mould coating of sticking patch, groove or extrusion coating, slip or jet flow coating, curtain-type showering; Roller coat applies, and applies as the coating of the scraper on the roller, forward and reverse roller coat; Gravure coating; Dip coating; Spraying; The meniscus coating; Spin coating; Brush; The air knife blade coating; Silk-screen printing technique; Electrostatic printing process; Thermal printing method; Ink jet printing method; Electrophoretic deposition; And other similar techniques.) like this, the display that obtains at last can be flexible.

In addition, print display mediums, therefore can make display at an easy rate owing to can (utilize the whole bag of tricks).

Based on the electrophoretic display device (EPD) of particle and show the bistable state of other electro-optic displays (this display can be called " pulsed drive display " hereinafter for convenience's sake) of similar characteristics or multistable characteristic and conventional liquid crystal (" LC ") display form significant contrast.Twisted nematic liquid crystal does not show bistable state or multistable, but serves as the voltage transducer, therefore no matter the gray level that this pixel is sentenced before, exists, and will be as long as apply given electric field in the specific gray level of pixel place generation to the pixel of this display.And, can be only along a direction (from light tight or " secretly " to printing opacity or " bright ") drive the LC display, by reducing or eliminating electric field and realize that the reverse from brighter state to dark state becomes.At last, the gray level of the pixel of LC display is insensitive to the polarity of electric field, only is insensitive to its size, and in fact for technical reason, commercial LC display makes the polarity reversal of Driving Field usually with the frequent time interval.

In contrast, for first kind approximate, bistable electro-optic displays serves as pulse transduce, so the end-state of pixel do not depend on the electric field that is applied and apply the time of this electric field, but depends on the pixel status before applying electric field.And, have been found that now, at least under the situation of many electro-optic displays based on particle, it is not necessarily constant, also not necessarily tradable that the equal variation (as judging with eyes or with the normalized optical instrument) by gray level changes the required pulse of given pixel.For example, consider that each pixel can both show the display of the gray level of 0 (in vain), 1,2 or 3 (deceiving), advantageously these gray levels are spaced apart from each other.(interval between the level can be linear in reflectivity percentages, as measuring with eyes or with instrument, but also can use other at interval.For example, can in L*, be linear at interval, (wherein L* has common CIE definition:

L ^*＝116(R/R ₀) ^1/3-16，

Wherein R is a reflectivity, R ₀Be the standard reflectivity value), perhaps described interval can be chosen as the gamma (gamma) that provides specific; Usually adopt 2.2 gamma for monitor, display wherein of the present invention is as the replacement of monitor, desirablely is to use similar gamma.) have been found that that pixel is become 1 grade (being called " 0-1 transformation " hereinafter for simplicity) required pulse from 0 grade is inequality with the required pulse of 1-2 or 2-3 transformation usually.And, 1-0 change required pulse not necessarily with reverse 0-1 change required pulsion phase with.In addition, some systems appear to demonstrate " memory " effect, make (for example) 0-1 changes whether required pulse experiences 0-0-1,1-0-1 according to specific pixel slightly or the 3-0-1 transformation changes.(wherein, the sequence of the optical states that representation " x-y-z " expression arrives in chronological order, wherein x, y and z are all optical states 0,1,2 or 3.Although) arrive before the another kind of extremity in quite over a long time all pixels of driving display and reach a kind of extremity and can reduce or overcome these problems by driving required pixel, as a result of " flicker " of the pure color of Chan Shenging is normally unacceptable;

For example, display is with frequent time interval flicker black or pure white if desired, and the reader of e-book may wish that the text of these books rolls below screen so, and it may be transferred or forgets and see which page or leaf.And this flicker of display has increased its energy consumption, and may reduce the mission life of this display.At last, have been found that, at least in some cases, the required pulse of special transformation is subjected to temperature and total working time of display and is subjected to specific pixel in the influence that is retained in the time under the particular optical state before the given transformation, also has been found that to wish that these factors of compensation reproduce to guarantee accurate gray scale.

Have been found that, at least in some cases, in bistable electro-optic displays the required pulse of given transformation along with pixel in its optical states residence time and change, as if this phenomenon do not discussed in the past in the literature, be called " residence time correlativity " or " DTD " hereinafter, although term " residence time sensitivity " has been used in during some uses the preceding.Like this, may wish or even in fact need the pulse that to apply for given transformation to change in some cases as the function of the residence time of pixel under its initial optical state.

Another problem in driving bistable electro-optic displays is that the little residual voltage at the electro-optical medium two ends can continue after transition waveforms.This residual voltage is called residual voltage in this article, and it can cause the skew of the optical states that is obtained.This phenomenon is called selfdemagnetization.

Explain the phenomenon of residence time correlativity in more detail referring now to the single accompanying drawing in the accompanying drawing, this illustrates for using R ₃→ R ₂→ R ₁The transformation sequence of expression is as the reflectivity of the pixel of the function of time, wherein each R _KItem all shows the gray level in gray scale sequence, has occurred having before having less target R down and has descended target R more greatly.This figure has also shown at R ₃And transformation between the R2 and R ₂And R ₁Between transformation.DTD is by optical states R ₂In the variation of time of being consumed and the final optical states R that causes ₁Variation, the described time is called the residence time.

Summary of the invention

The present invention relates to be used for when driving bistable electro-optic displays, reducing the method for residence time correlativity.

In one aspect, the invention provides (first kind) method that drives the bistable electro-optic displays with at least one pixel, this method comprises to pixel and applies waveform V (t), thereby makes:

$J=\underset{0}{\overset{T}{\∫}}V\left(t\right)M(T-t)\mathrm{dt}---\left(1\right)$

(wherein T is the length of waveform, integration is the integration on the duration of waveform, V (t) is the waveform voltage as the function of time t, M (t) is a memory function, it is characterized in that reducing the effect of residual voltage, this residual voltage constantly can cause the residence time correlativity that is produced by short pulse zero) less than about 1 volt of second.

In first method of the present invention, hope be integration J less than about 0.5 volt of second, what wish most is less than about 0.1 volt of second.In fact, this integration should be as far as possible little, and ideal is to be zero.In a kind of form of this method, waveform comprise have voltage, polarity and first pulse of duration, and second pulse, this second pulse has the magnitude of voltage substantially the same with first pulse, polarity is opposite with the polarity of first pulse, and the duration is basically less than duration of first pulse.

In a kind of form of first method, integration is calculated by following formula:

$J=\underset{0}{\overset{T}{\∫}}V\left(t\right)\exp (-\frac{T-t}{\mathrm{\τ}})\mathrm{dt}---\left(2\right)$

Wherein τ is decay (relaxation) time of being scheduled to.Schedule time τ can be from about 0.2 to about 2 seconds scope, and hope is from about 0.5 to about 1.5 seconds scope, preferably from about 0.7 to about 1.3 seconds scope.

In a kind of form of first method, waveform comprises two paired pulses, but it is opposite with the duration polarity that equates that each paired pulses all has substantially the same magnitude of voltage, and the duration of second paired pulses is than the longer duration of first paired pulses, and it is right to apply these two pulses according in the following order any:

(a) first pair first pulse; Second pair first pulse; Second pair second pulse; First pair second pulse.

(b) first pair first pulse; First pair second pulse; Second pair first pulse; Second pair second pulse.

In the advantageous version of this method, this waveform further comprises the 3rd paired pulses, but it is opposite with the duration polarity that equates that the 3rd paired pulses has substantially the same magnitude of voltage, and the duration of the 3rd paired pulses is shorter than duration of second paired pulses, and it is right to apply these three pulses according in the following order any:

(a) first pair first pulse; The 3rd pair first pulse; The 3rd pair second pulse; Second pair first pulse; Second pair second pulse; First pair second pulse.

(b) first pair first pulse; The 3rd pair first pulse; The 3rd pair second pulse; First pair second pulse; Second pair first pulse; Second pair second pulse.

The memory function M (t) of first method of the present invention can have various forms.For example, M (t) can equal 1, perhaps M (t) can be a plurality of exponential functions and, as follows:

$M\left(t\right)=\underset{k=1}{\overset{N}{\mathrm{\Σ}}}{\mathrm{\α}}_k\exp (-t/{\mathrm{\τ}}_k)---\left(3\right)$

Wherein, N exponential term and in each all have amplitude a _kWith τ die-away time _k

First method of the present invention does not need to be applied to all waveforms of drive scheme, expression used herein can be implemented in the gray level set one group of waveform that might change.

When first method being applied to a kind of display, when each pixel can both show at least four gray levels in this display, for a transformation that the gray level place begins and finishes in not comprising the interior intensity level group of two extreme gray levels, the absolute value of integration J can remain on about 1 volt below second, not necessarily remains on about 1 volt below second but change for other.

First method of the present invention can be used with the bistable state electric light medium of any type discussed above.Like this, for example, this method can be used with the display that comprises the electrophoresis electro-optical medium, and this electrophoretic medium is included in the many charged particles in the suspension, and can move through suspension when suspension applies electric field.Suspension can be gaseous state or liquid.Electrophoretic medium can be wrapped with capsule, and promptly charged particle and suspension can be limited in many capsules or the micro unit.First method also can be used with the display that comprises double-colored member of rotation or electrodeposited chromium medium.

The present invention also provides (second kind) method that drives the bistable electro-optic displays with at least one pixel, and this method comprises to pixel and applies waveform V (t), thereby makes:

$J_d=\underset{0}{\overset{T+\mathrm{\Δ}}{\∫}}V\left(t\right)M(T+\mathrm{\Δ}-t)\mathrm{dt}---\left(4\right)$

(wherein T is the length of waveform, integration is the integration on the duration of waveform, V (t) is the waveform voltage as the function of time t, M (t) is a memory function, it is characterized in that reducing the effect of residual voltage, this residual voltage constantly can cause the residence time correlativity that is produced by short pulse zero, and Δ is the positive period less than period T) less than about 1 volt of second.

In second method of the present invention, Δ can be less than about 0.25T, and desirable is less than about 0.15T, preferably less than about 0.10T.

The present invention also provides (the third) method that drives the bistable electro-optic displays with at least one pixel, this pixel can show at least three kinds of different optical states, this method comprises applying to pixel is enough to make this pixel experience one group of waveform V (t) that institute might change in its various optical states, and this group waveform makes according to the integration J of top equation (4) calculating _d(but wherein Δ can be zero) is less than changing about 40% of pulse.This transformation pulse is defined as the pulse that the monopulse by constant voltage applies, and the value of this constant voltage equals to be organized the ceiling voltage that arbitrary waveform applies and be enough to drive pixel just from an one extreme optical state to another extreme optical state (normally white to black or deceive in vain) by this.

In the third method of the present invention, integration J _dCan be less than the transformation pulse of the transformation that is realized about 30%, wish less than about 20%, preferably less than about 10%.

As discussed above, second kind and the third method of the present invention can be used the electro-optical medium with the same wide region of first method.

Description of drawings

As already mentioned, the Fig. 1 in the accompanying drawing demonstrates the curve map that changes and illustrate the phenomenon of residence time correlativity along with the time of the optical states of a pixel in the display.

Fig. 2,3 and 4 illustrates the waveform of the preferred type in any that can be used in three kinds of methods of the present invention.

Embodiment

As already mentioned, the invention provides the multiple method that is used to drive bistable electro-optic displays, these methods are intended to reduce residence time correlativity (DTD).Although the present invention never is subjected to the restriction about any theory of its starting point, DTD seems to be caused by the remaining electric field that electro-optical medium experienced to a great extent.These remaining electric fields are the remainders that put on the driving pulse of this medium.Market practice is to refer to by the caused residual voltage of applying pulse, and residual voltage only is according to the common mode that is suitable for the static theory scalar potential corresponding with remaining electric field.These residual voltages can cause the optical states of display film to be offset in time.They also can change the effect of driving voltage subsequently, therefore change the final optical states of being realized after pulse subsequently.In this manner, the end-state in the time of can making end-state after subsequently the waveform completely separate from each other with twice transformation from the residual voltage of a transition waveforms is different." separate fully " and mean in time and fully separate that therefore the residual voltage from first transition waveforms had decayed basically before second transition waveforms that applies.

Show that by transition waveforms and the measurement that puts on the caused residual voltage of other simple pulse of electro-optical medium residual voltage decays in time.This decay shows as dull, rather than shows as index simply.But, as first kind approximate, decay can be approximately and be index, die-away time is constant, under the situation of the electrophoretic medium that the great majority of test are wrapped with capsule, be about 1 second die-away time, and expect that other electro-optical medium shows similar die-away time.

Therefore, method of the present invention is established to be counted and is utilized the waveform that produces little residual voltage and therefore produce low DTD.According to first method of the present invention, the integration J (referring to top equation (1)) of the product of waveform and memory function on waveform length remained less than 1 volt of second, hope is less than 0.5 volt of second, preferably less than 0.1 volt of second, memory function is characterised in that the effect that reduces the residual voltage that causes DTD.In fact, J should be set to as far as possible little, and ideal is zero.

Can be by producing composite pulse with Waveform Design for low-down J value is provided, and so provide very little DTD.For example, the negative voltage pulse of the length before short positive voltage pulse (value of voltage amplitude is identical, but opposite in sign) can cause DTD to descend a lot.Obviously, if desired, the polarity of two pulses can be reverse.Can believe (although the present invention never is subjected to the restriction of this view), two pulses provide opposite symbol to residual voltage.When the length of correctly setting two pulses than the time, the residual voltage major part of these two pulses is cancelled each other.The adequate rate of the length of two pulses can be determined by the memory function of residual voltage.

As mentioned above, in the preferred form of first method of the present invention, relatively more top equation (2), memory function shows exponential decay.

For some electrophoretic mediums of wrapping with capsule, have been found that with experimental technique the waveform that produces little J value also produces low especially DTD, and the big DTD of waveform generation with king-sized J value.In fact, obtained good mutual relationship between the J value of being used by top equation (2) by following setting that τ calculated, τ is set at 1 second, equals mensuration die-away time of residual voltage after the applying voltage pulse roughly.Have reason to believe that the bistable state electric light medium of other type will work similarly, although the value of τ can change with the accurate type of used medium certainly.

Like this, advantageously, the method for describing is used such waveform in above-mentioned patent and application, wherein utilize the waveform of the J value that provides little to realize each transformation (or most of at least transformation the look-up table) from a gray level to another gray level.This J value is preferably zero, but rule of thumb have been found that at least for the electrophoretic medium of describing in above-mentioned patent and the application of wrapping with capsule, as long as the value of J is less than about 1 volt of second at ambient temperature, the residence time correlativity that obtains so at last is just quite little.

Like this, the invention provides a kind of waveform that is used to be implemented in one group of transformation between the optical states, wherein change for each, the J value that calculates has little value.Calculate the value of J by the memory function of possibility monotone decreasing.Memory function is not arbitrarily, but can estimate for the residence time correlativity of univoltage pulse or composite voltage pulse by the pixel of observation display.For instance, can apply the transformation that potential pulse is realized from first to second optical states, wait for a residence time, apply second potential pulse then to realize from second the transformation to the tertiary voltage pulse to pixel.As the moving of function the 3rd optical states of the residence time, can determine the approximate shapes of memory function by monitoring.The shape of this memory function roughly is similar to the difference of its value in the 3rd optical states in long residence time very, and it is as the function of the residence time.Memory function provides this shape then, and has unified amplitude when its independent variable is zero.This method only produces the approximate of memory function, and for various final optical states, the shape that records of expectation memory function changes a little.But total feature should be similar for various optical states, the decay characteristics time of described feature such as memory function.But if there is significant difference in shape in final optical states, the shape of the best memory function that will adopt is the shape that is obtained when the 3rd optical states is in the trisection center section of optical range of display mediums so.The total characteristic of memory function should also be estimated by the decay of measuring residual voltage after applying voltage pulse.

Though, discussed in this articlely be used to estimate that the method for memory function is not very accurate, have been found that according in addition the J value calculated of approximate memory be good guide with waveform of low DTD.Useful memory function is represented the total characteristic of the temporal correlation of aforesaid DTD.Like this, the τ value in the superincumbent equation (2) will change along with used electro-optical medium, also can change along with temperature.For example, have been found that the memory function that is index die-away time when being 1 second works well in the prediction waveform that low DTD is provided.To become the validity of the J value that can as the fallout predictor of low DTD waveform, not destroy to obtain at last in 0.7 or 1.3 second die-away time.But unattenuated but memory function that be consistent indefinite duration is the same with fallout predictor obvious not too useful, the memory function with very short die-away time is not the good predict device of low DTD waveform, and described very short die-away time was as 0.05 second.

The example that the waveform of little J value is provided is the waveform shown in Figure 17,18 and 20 of the open WO 2004/090857 of international application, and these accompanying drawings copy as the Fig. 2,3 and 4 in the accompanying drawing respectively.

Waveform shown in Fig. 2, i.e. first waveform, comprise two paired pulses (be designated as x and y to), each paired pulses has identical magnitude of voltage basically, and have the equal duration, but polarity is opposite, and the duration of second paired pulses is longer than first paired pulses, and it is right to apply these two pulses in the following order:

-y，+y，-x，+x，

(should be appreciated that the value of x and y can be born), wherein all duration of x and y pulse are all much smaller than the characteristic attenuation time of memory function.This waveform plays a role well when this condition satisfies, because this waveform is made up of order reverse impulse element, the residual voltage of described pulse element is tended to roughly offset.But for unlike the characteristic attenuation time of memory function much smaller x and the y value big unlike this die-away time, have been found that waveform that x and y have a contrary sign tends to the J value that provides lower, and can find that in fact x and y duration of pulse allow very little J value, because each impulse element provides the residual voltage of cancelling each other or cancelling each other at least to a great extent after applying waveform.

Fig. 3 illustrates the distortion of waveform shown in Fig. 2, wherein+and the end of waveform is transferred in the y pulse immediately after-y pulse, so the order of pulse is:

-y，-x，+x，+y。

Fig. 4 illustrates the another kind distortion of waveform shown in Fig. 2.In this distortion, this waveform comprises the 3rd paired pulses (being designated as " z " and "+z ").As first pair and second paired pulses, the 3rd paired pulses has identical magnitude of voltage and duration of equating but polarity is opposite basically.The 3rd paired pulses also has the duration shorter than second paired pulses.Waveform shown in Fig. 4 can be considered to insert immediately after first pulse of first pair from pulse shown in Figure 3 that the 3rd paired pulses obtains, and therefore has a following structure:

-y，-z，+z，-x，+x，+y。

Can produce the waveform of array structure down like this by after+y pulse, inserting the 3rd pulse to revising the waveform shown in Fig. 2 similarly:

-y，+y，-z，+z，-x，+x。

Top equation (1) relates to the value at the appointment integral of pulse shape J that changes the end, and top discussion concentrates on and remains this integration as far as possible little.But it also is favourable making integration very little in the short time after upgrading end.Consider this possibility, can define interchangeable integration J according to top equation (4) _dΔ can not be big arbitrarily, but must be positive, and less than T update time.Desirable is that Δ is less than about 0.25T, preferably less than 0.15T, most preferably less than 0.1T.

Equation (4) and second method of the present invention are based on following understanding, the benefit that promptly will not reduce residual voltage is restricted to after changing and immediately this voltage is remained very little (little J, as defined by equation (1)), but also can this voltage is very little realizes (little J by making in considerable time after change finishing _d, as defined by equation (4)).Particular importance when this point is not the single index form at memory function because in this case, makes that J is little can not to guarantee J _dAlso very little; Fully reasonably memory function can make the very little transition waveforms of its extremely difficult structure J, but is easy to make J _dVery little, sizable benefit is provided thus.

With reference to equation (2) a preferred memory function of used single damped expoential type among the present invention has been described above.Other useful memory function comprises:

(a) M(t)＝1

This is the J or the J of equation (1) or (4) _dIntegration is equal to the special circumstances of the clean voltage waveform of transition waveforms.This special integral may be prescribed as I, wherein:

$I=\underset{0}{\overset{T}{\∫}}V\left(t\right)\mathrm{dt}---\left(5\right)$

Make that J is equivalent to I when memory function all equals 1 if having time in institute.Have been found that by utilizing I to equal or approaching zero transition waveforms and can reduce stop state correlativity considerably.

(b) memory function be a plurality of exponential decay and.In this case, memory function has given form in the top equation (3).This memory function is useful, because it can describe the decay of residual voltage effect preferably, and for example decay of residual voltage effect after potential pulse.

In general, memory function is the monotonic decay function, but also can have other suitable form, as so-called expansion (stretched) exponential function.

The invention is not restricted to wherein limit J and/or J _dThe drive scheme of value.In some cases, change and all limit J and/or J _dMay be desirable.In other cases, may be difficult to limit the J and/or the J of some transformation _d, particularly be converted to extreme gray level or from extreme greyscale transitions, perhaps only some changes restriction J and/or J for other reasons _dThe mixed mode transition scheme may be desirable.Have been found that two kinds of following situations are useful for the electro-optic displays with at least four gray levels:

(a) for inner transformation, | I|＜ε (that is, original state and end-state all belong to the transformation of limited middle gray level group).

Utilize R _jAnd R _kBetween this wavelength integral constraint of changing can realize the present invention, wherein R _jAnd R _kGray level set in belonging to, this constraint is not necessarily satisfied at R _jAnd R _kIn one or two do not belong in the transformation between the two of gray level when set.In gray level set can be not in 1/4th extreme gray levels, promptly the darkest 25% or the brightest 25% (the perhaps situation that is equal under the situation of bi-chrome display) in the set of all gray levels.For example, in 4 gray level display devices, two intermediate grey scales are in middle gray level set, and two extreme gray levels are in this in gray level set.In 32 grades of gray scales, the set of middle gray level can comprise all gray levels except the darkest four gray levels and the brightest four gray levels.

(b) for inner transformation, | J|＜ε

In this case, for inner transformation, obey more generally integral constraint, as stipulating in the earlier paragraphs.

As showing, the present invention relates to reduce selected integration I, J or J _dValue.Although the maximum permissible value of these integrations has been defined in above in the absolute pulse value (promptly, with the volt term of second), in at least some cases, consider that with respect to the integrated value (as top defined) for pixel amount of required transformation pulse from an extreme optical state to another extreme optical state of driving display may be actual.For example, some E Ink patent above-mentioned and application instructed 15V pulse by 300 milliseconds of duration can drive some electrophoretic medium of wrapping with capsule from an extreme optical state to another extreme optical state.For this transformation, change pulse and (be expressed as G ₀) be 4.5V second.Selected integration I, the J or the J that think very little any given transformation for the object of the invention _d, this integration usually should be less than changing the about 40% of pulse, and desirable is less than changing the about 30% of pulse, preferably less than changing about 20% of pulse.Under very overcritical situation, even may be such value, this value be restricted to integrated value less than changing about 10% of pulse.When each pixel of display can have a large amount of gray levels (for example eight or more), clearly, the selection principal value of integral of some transformation between next-door neighbour's gray level was very little with respect to changing pulse.For example, change gray level 5 even only utilize single driving pulse of constant voltage and polarity to be implemented in 8 gray-level pixels into from gray level 4, the integration of this transformation is usually also less than changing 20% of pulse.But, have been found that the institute for drive scheme changes, keep selected integration very for a short time be very important (promptly, be enough to be implemented in the various gray levels of pixel one group of waveform that might change), because may adverse effect be arranged to subsequently one and a plurality of transformations by a residual voltage that change to produce, therefore the invention provides the method for utilizing this drive scheme to drive electro-optic displays.

The present invention can be applicable to various waveforms and drive scheme.Utilize a plurality of parameters to describe designed waveform configuration, calculate its J value, and select suitable parameter value to make the J value minimum, reduce the DTD of waveform thus for each of these parameters is worth.

Claims (22)

1. a driving has the method for the bistable electro-optic displays of at least one pixel, and this method comprises to pixel and applies waveform V (t), it is characterized in that:

$J=\underset{0}{\overset{T}{\∫}}V\left(t\right)M(T-t)\mathrm{dt}$

(wherein T is the length of waveform, integration is the integration on the duration of waveform, V (t) is the waveform voltage as the function of time t, M (t) is a memory function, it is characterized in that reducing the effect of residual voltage, this residual voltage constantly can cause the residence time correlativity that is produced by short pulse zero) less than 1 volt of second.

2. according to the process of claim 1 wherein that J is less than 0.5 volt of second.

3. according to the method for claim 2, wherein J is less than 0.1 volt of second.

4. according to the method for claim 1, wherein waveform comprise have voltage, polarity and first pulse of duration, and second pulse, this second pulse has substantially the same magnitude of voltage, polarity is opposite with the polarity of first pulse, and the duration is basically less than duration of first pulse.

5. according to the process of claim 1 wherein that J is calculated by following formula:

$J=\underset{0}{\overset{T}{\∫}}V\left(t\right)\exp (-\frac{T-t}{\mathrm{\τ}})\mathrm{dt}$

Wherein τ is decay (relaxation) time of being scheduled to.

6. according to the method for claim 5, wherein τ is in from 0.2 to 2 second scope.

7. according to the method for claim 6, wherein τ is in from 0.7 to 1.3 second scope.

8. according to the method for claim 1, wherein waveform comprises two paired pulses, but it is opposite with identical duration polarity that each paired pulses all has a substantially the same magnitude of voltage, and the duration of second paired pulses is than the longer duration of first paired pulses, and it is right to apply these two pulses according in the following order any:

(a) first pair first pulse; Second pair first pulse; Second pair second pulse; First pair second pulse;

(b) first pair first pulse; First pair second pulse; Second pair first pulse; Second pair second pulse.

9. method according to Claim 8, wherein this waveform further comprises the 3rd paired pulses, but it is opposite with the duration polarity that equates that the 3rd paired pulses has substantially the same magnitude of voltage, and the duration of the 3rd paired pulses is shorter than duration of second paired pulses, and it is right to apply these three pulses according in the following order any:

(a) first pair first pulse; The 3rd pair first pulse; The 3rd pair second pulse; Second pair first pulse; Second pair second pulse; First pair second pulse;

(b) first pair first pulse; The 3rd pair first pulse; The 3rd pair second pulse; First pair second pulse; Second pair first pulse; Second pair second pulse.

10. according to the process of claim 1 wherein M (t)=1, perhaps M (t) be a plurality of exponential functions and, as follows:

$M\left(t\right)=\underset{k=1}{\overset{N}{\mathrm{\Σ}}}{a}_k\exp (-t/{\mathrm{\τ}}_k)$

Wherein, N exponential term and in each all have amplitude a _kWith τ die-away time _k

11. method according to claim 1, wherein each pixel of electro-optic displays can both show at least four gray levels, and for a transformation that the gray level place begins and finishes in not comprising the interior intensity level group of two extreme gray levels, the absolute value of integration J remains on 1 volt below second, but not necessarily remains on 1 volt below second for other transformation.

12. according to the process of claim 1 wherein that this display comprises the electrophoresis electro-optical medium, this electrophoretic medium is included in the many charged particles in the suspension, and can move through suspension when suspension applies electric field.

13. according to the method for claim 12, wherein this suspension is a gaseous state.

14. according to the method for claim 12, wherein charged particle and suspension are limited in many capsules or the micro unit.

15. according to the process of claim 1 wherein that this display comprises double-colored member of rotation or electrodeposited chromium medium.

16. a driving has the method for the bistable electro-optic displays of at least one pixel, the method is characterized in that to pixel to apply waveform V (t), thereby makes:

$J_d=\underset{0}{\overset{T+\mathrm{\Δ}}{\∫}}V\left(t\right)M(T+\mathrm{\Δ}-t)\mathrm{dt}$

(wherein T is the length of waveform, integration is the integration on the duration of waveform, V (t) is the waveform voltage as the function of time t, M (t) is a memory function, it is characterized in that reducing the effect of residual voltage, this residual voltage constantly can cause the residence time correlativity that is produced by short pulse zero, and Δ is the positive period less than period T) less than 1 volt of second.

17. according to the method for claim 16, wherein Δ is less than 0.25T.

18. according to the method for claim 17, wherein Δ is less than 0.15T.

19. a driving has the method for the bistable electro-optic displays of at least one pixel, this pixel can show at least three kinds of different optical states, this method comprise to pixel apply be enough to make this pixel experience in its various optical states one group of waveform V (t) that might change, the method is characterized in that this group waveform all makes:

$J_d=\underset{0}{\overset{T+\mathrm{\Δ}}{\∫}}V\left(t\right)M(T+\mathrm{\Δ}-t)\mathrm{dt}$

(wherein T is the length of waveform, integration is the integration on the duration of waveform, V (t) is the waveform voltage as the function of time t, M (t) is a memory function, it is characterized in that reducing the effect of residual voltage, this residual voltage constantly can cause the residence time correlativity that is produced by short pulse zero, and Δ is the positive period less than period T, or 0) less than changing 40% of pulse.

20. according to the method for claim 19, wherein for all waveforms of this group, integration J _dLess than changing 30% of pulse.

21. according to the method for claim 20, wherein for all waveforms of this group, integration J _dLess than changing 20% of pulse.

22. according to the method for claim 21, wherein for all waveforms of this group, integration J _dLess than changing 10% of pulse.

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