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WO1999010870A1 - Procede d'excitation d'un dispositif a cristaux liquides cholesteriques bistables - Google Patents

Procede d'excitation d'un dispositif a cristaux liquides cholesteriques bistables Download PDF

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Publication number
WO1999010870A1
WO1999010870A1 PCT/JP1998/003691 JP9803691W WO9910870A1 WO 1999010870 A1 WO1999010870 A1 WO 1999010870A1 JP 9803691 W JP9803691 W JP 9803691W WO 9910870 A1 WO9910870 A1 WO 9910870A1
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WIPO (PCT)
Prior art keywords
liquid crystal
pulse
metastable
state
cell
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/JP1998/003691
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English (en)
Inventor
Harald Reinhart Bock
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Sharp Corp
Original Assignee
Sharp Corp
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Filing date
Publication date
Priority to KR10-1999-7005448A priority Critical patent/KR100497691B1/ko
Application filed by Sharp Corp filed Critical Sharp Corp
Priority to JP2000508103A priority patent/JP2001514399A/ja
Priority to KR1020007001743A priority patent/KR100335159B1/ko
Publication of WO1999010870A1 publication Critical patent/WO1999010870A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
    • G09G3/3611—Control of matrices with row and column drivers
    • G09G3/3622—Control of matrices with row and column drivers using a passive matrix
    • G09G3/3629—Control of matrices with row and column drivers using a passive matrix using liquid crystals having memory effects, e.g. ferroelectric liquid crystals
    • G09G3/3637—Control of matrices with row and column drivers using a passive matrix using liquid crystals having memory effects, e.g. ferroelectric liquid crystals with intermediate tones displayed by domain size control
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2300/00—Aspects of the constitution of display devices
    • G09G2300/04—Structural and physical details of display devices
    • G09G2300/0469—Details of the physics of pixel operation
    • G09G2300/0478—Details of the physics of pixel operation related to liquid crystal pixels
    • G09G2300/0482—Use of memory effects in nematic liquid crystals
    • G09G2300/0486—Cholesteric liquid crystals, including chiral-nematic liquid crystals, with transitions between focal conic, planar, and homeotropic states
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2310/00—Command of the display device
    • G09G2310/06—Details of flat display driving waveforms
    • G09G2310/061—Details of flat display driving waveforms for resetting or blanking
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2310/00—Command of the display device
    • G09G2310/06—Details of flat display driving waveforms
    • G09G2310/065—Waveforms comprising zero voltage phase or pause
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/2007—Display of intermediate tones

Definitions

  • the invention relates to a liquid crystal device.
  • tilt as used herein is defined to mean the angle in the plane of a liquid crystal cell through which the liquid crystal director rotates from one surface of the cell to the other surface.
  • bistable twisted nematic (BTN) effect is disclosed in EP 0 018 180, US 4 239 345 and "New Bistable Liquid Crystal Twist Cell", D. . Berre an et al, J. Appl. Phys., 1981, volume 52(4), page 3032.
  • Figure 1 of the accompanying drawings illustrates a simple example of the BTN mode of operation.
  • a cholesteric (twisted nematic) material with a pitch of substantially twice the cell gap in a cell with parallel or antiparallel alignment direc- tions adopts an initial state with a twist of 180° . In the antiparallel alignment, the 180° twist state has the disadvantage of being splayed.
  • the stable "twist-splay" state is illustrated at 1 in a liquid crystal cell with antiparallel alignment layers 2 and 3.
  • An initial reset pulse 4 is applied across electrodes (not shown) between which the liquid crystal 5 and the alignment layers 2 and 3 are disposed.
  • the reset pulse 4 has an amplitude and duration sufficient to cause a transition to the homeotropic state which is illustrated at 6 and in which the liquid crystal molecules 5 in the bulk of the layer ( away from the immediate vicinity of the alignment layers 2 and 3 ) are oriented perpendicular to tne cell surfaces as illustrated, for instance, by molecule 7 .
  • One of two types of selective addressing pulse 8 is then applied to the electrodes to select the desired state of the device.
  • One type of selective addressing pulse causes the homeotropic state 6 to switch to the metastable black state which is illustrated at 9 and in which the liquid crystal has a 360° twist. This is the maximally attenuating or black state where the cell is disposed between orthogonal polarisers .
  • the other type of addressing pulse 8 causes the liquid crystal to switch from the homeotropic state 6 to the metastable white state 10, in which there is 0° of twist and the cell appears minimally attenuating or white with the orthogonal polarisers .
  • the prior art mentioned hereinbefore provides the selective addressing pulses 8 by reducing the voltage from the initial reset pulse 4 abruptly or gradually.
  • EP 0 569 029 discloses addressing a BTN liquid crystal device (LCD) by a selection pulse of variable voltage following the initial reset pulse.
  • JP H7-248485 discloses a technique for providing faster addressing by inserting a preset pulse between the initial reset pulse " and the addressing pulse.
  • EP 0 579 247 discloses techniques for optimising the polariser and analyser positions to provide optimum contrast in a BTN LCD.
  • EP 0 613 116 discloses a technique for providing short address times by optimising the position in time after the reset pulse of a short selection pulse. This is illustrated in Figure 2 of the accompanying drawings.
  • the BTN LCD is arranged as a rectangular array of picture elements (pixels) to form a panel with row electrodes common to each row of pixels receiving strobe waveforms and column electrodes common to the pixels of each column receiving data signals.
  • a typical strobe or row waveform is illustrated at 11
  • a typical data or column waveform is illustrated at 12
  • the resulting voltage across the liquid crystal layer is illustrated at 13
  • the agni- tude or modulus of the resulting voltage is illustrated at 14.
  • the optical transmission of the cell is illustrated at 15.
  • the liquid crystal is shown in the metastable black state 9 at the start of the addressing interval illustrated in Figure 2.
  • the reset pulse 4 resets the liquid crystal to the homeotropic state 6 and is followed by a select pulse 16.
  • the data waveform for selecting the desired state of the liquid crystal is applied to the column electrodes as illustrated at 17. This results in a voltage and hence electric field across the liquid crystal of an amplitude 18 such that the liquid crystal relaxes to the white metastable state 10.
  • a further reset pulse 4' resets the liquid crystal to the homeotropic state 6 and a further select pulse 16' cooperates with the appropriate data waveform 17' to produce a resulting pulse amplitude 18' which causes the liquid crystal to relax into the black metastable state 9.
  • a disadvantage of the known BTN LCDs is that, because it is a bistable mode, only black and white states can be addressed.
  • various techniques may be used. For instance, mixtures of black and white areas may be created within each pixel by subpixellation such that the subpixels are smaller than the resolution of the eye.
  • such an arrangement requires more driver circuitry and faster switching liquid crystal mixtures if the technique is not to be limited to relatively small low definition display panels. Also, greater construction accuracy is required.
  • Another known technique is to apply different voltages or voltage sequences to a pixel so as to provide different amounts of black and white areas. For instance, this may be achieved with non-uniform pixels where different areas of the pixel have different properties which require different switching voltages.
  • This technique is known as "multi-threshold modulation" and again requires subpixellation implying additional fabrication steps and requiring greater construction accuracy.
  • none of the known types of BTN LCD allow grey level addressing to be achieved without spatial or temporal multiplexing and the associated disadvantages in terms of increased addressing speed, increased constructional complexity, or both.
  • EP 0 234 624 discloses a super-twisted nematic (STN) LCD which is capable of displaying grey levels by multidomain techniques.
  • the electro-optic (voltage/transmission) characteristic of this device exhibits hysteresis. Different grey levels can be achieved by applying and maintaining across the liquid crystal cell electric fields of different magnitudes.
  • a liquid crystal device having at least three different optical attenuation levels and comprising a bistable twisted nematic liquid crystal cell having a first metastable state, which has a first degree of twist and is metastable in the absence of a substantial applied field, and a second metastable state, which has a second degree of twist different from the first degree of twist and is metastable in the absence of a substantial applied field.
  • the device includes an address generator for applying across the cell a field having a waveform including: a first - portion for resetting the liquid crystal to a reset state having the first degree of twist; a second portion for allowing the liquid crystal to relax into a relaxed state having the second degree of twist; and a third portion including any one of at least three different waveforms for selecting the at least three different optical attenuation levels, respectively, wherein, in at least one of the attenuation levels, a first portion of the liquid crystal of the cell is in the first metastable state and a second portion of the liquid crystal of the cell is in the second metastable state.
  • the second portion of the waveform may comprise a space, i.e.: may be of a sufficiently low magnitude to allow relaxation.
  • the relaxed state may be the second metastable state.
  • the at least three different optical attenuation levels may include a maximum attenuation level, a minimum attenuation level and at least one intermediate attenuation level .
  • At least one of the first and third portions may include at least one pulse.
  • the at least one pulse may include a monopolar pulse.
  • the at least one pulse may comprise a bipolar pulse.
  • Each bipolar pulse may include first and second subpulses of substantially equal amplitude and opposite polarity.
  • the third portion may include a first part and a second part.
  • the first part may comprise first and second pulses .
  • the second pulse may be spaced from the first pulse.
  • the amplitude of the first pulse may be less than the amplitude of the second pulse.
  • the second part may comprise a plurality of pulses of progressively decreas- ing amplitude.
  • the pulses of the second part may be contiguous .
  • the address generator may include a data signal generator and a strobe signal generator.
  • the cell may comprise a liquid crystal layer disposed between a plurality of strobe electrodes for receiving strobe signals from the strobe signal generator and a plurality of data electrodes for receiving data signals from the data signal generator, the data electrodes intersecting the strobe electrodes to define picture elements .
  • the data signal generator may be arranged to supply to the data electrodes data signals whose amplitudes are less than the Fredericksz transition voltages of the first and second metastable states.
  • the liquid crystal may have an initial stable state and the amplitudes of the data signals may be less than the Fredericksz transition voltage of the initial stable state.
  • All of the data signals may include pulses of the same amplitude. All of the data signals may include symmetrical bipolar pulses. All of the data signals may include monopolar pulses. All of the data signals may be of the same root mean square voltage. The data signals for selecting different ones of the optical attenuation levels may have different pulse widths.
  • the amplitude of the strobe signals may be greater than the Fredericksz transition of the less twisted one of the first and second metastable states .
  • the amplitude of the strobe signals may be less than four times the Fredericksz transition of the less twisted one of the first and second metastable states.
  • the liquid crystal of the cell may be disposed between first and second polarisers.
  • the first and second polarisers may be linear polarisers with polarising directions oriented substantially orthogonally.
  • the polarising directions may be oriented at between 80° and 100° to each other.
  • the liquid crystal of the cell " may be disposed between first and second alignment layers for providing substantially antiparallel alignment oriented substantially at 45° to the polarising directions.
  • the antiparallel alignment may be oriented at between 40° and 50" to the polarising directions.
  • the first and second alignment layers may have first and second alignment directions oriented at an included angle of between 135° and 225°.
  • the included angle may be between 170° and 190°.
  • the included angle may be between 175° and 185°.
  • the included angle may be between 178° and 182°.
  • each of the first and second alignment layers may be arranged to provide a pretilt of between 1° and 25°.
  • the pretilt may be between 3° and 15°.
  • the pretilt may be between 5° and 10°.
  • the liquid crystal of the cell may have a thickness of between 1 and 3 micrometers .
  • the difference between the twists of the liquid crystal layer in the first and second metastable states may be substantially equal to 360° .
  • the liquid crystal layer may have twists substantially equal to 0° and 360° in the first and second metastable states, respectively.
  • the liquid crystal layer twist in each of the first and second metastable states may differ from that in an initial stable state by substantially 180° .
  • the ratio of the thickness to the bulk pitch of the liquid crystal of the cell may be between 0.2 and 1.2.
  • the ratio may be between 0.5 and 0.95.
  • the ratio may be between 0.6 and 0.9.
  • the device may include a matrix of rows and columns of picture elements, the address generator being arranged to supply each frame of image data as n consecutive subfra es, where n is an integer greater than one, such that each ith ⁇ ubfra e, where i is an integer such that 0 ⁇ i ⁇ n, comprises the (i+n «m)th rows, where m is a non- negative integer .
  • Figure 1 is a schematic diagram illustrating operation of a known type of BTN LCD
  • Figure 2 is a diagram illustrating waveforms and liquid crystal modes of a known type of BTN LCD
  • FIG. 3 is a schematic diagram of a passively addressed BTN LCD constituting an embodiment of the invention.
  • Figure 4 is a diagrammatic cross sectional view of the device of Figure 3;
  • Figure 5 illustrates the orientation of various optical components in the device of Figure 3
  • Figure 6 illustrates various waveforms for use in and the resulting performance of the device of Figure 3;
  • Figure 7 illustrates diagrammatically known types of addressing waveforms
  • Figure 8 illustrates diagrammatically various types of waveforms which may be used in the device of Figure 3;
  • Figure 9 illustrates another set of waveforms for use in and the resulting optical performance of the device of Figure 3;
  • Figure 10 illustrates a further set of waveforms for use in the device of Figure 3.
  • Figure 11 shows microscope photographs illustrating the performance of the device of Figure 3 using the waveforms illustrated in Figure 9.
  • Figure 3 illustrates a passive matrix BTN LCD constitut- ing an embodiment of the invention.
  • the device comprises a waveform generator, illustrated as a data signal generator 20 and a strobe signal generator 21 for supplying addressing waveforms to a rectangular matrix of pixels.
  • the data and strobe signal generators 20 and 21 have inputs connected to a timing input 22 for receiving timing signals.
  • the data signal generator 20 has a data input 23 for receiving data to be displayed.
  • the data signal generator is connected to n column electrodes 24 whereas the strobe signal generator 21 is connected to m row electrodes 25.
  • Each column electrode 24 is common to the pixels of that column whereas each row electrode 25 is common to the pixels of that row.
  • the pixels are defined at intersections between the column and row electrodes where a column electrode overlaps a row electrode, for instance as indicated at 26.
  • the data signal generator 20 is arranged to supply data signals Vdl,..,Vdn simultaneously to the n column electrodes 24 so as to refresh the pixels a row at a time.
  • the strobe signal generator 21 is arranged to supply strobe signals Vsl, ... ,Vsm to the m row electrodes 25 one at a time in a repeating sequence so as to strobe the new image data a row at * a time into the pixels .
  • FIG 4 is a diagrammatic cross sectional view illustrating the construction of the BTN LCD of Figure 3 in the form of a transmissive display, although a reflective display could also be provided.
  • the device comprises a polariser 30 fixed to the exterior surface of a transparent substrate 31, for example made of glass.
  • the sub- strate 31 carries the row electrodes 25 made of a transparent conductor such as indium tin oxide ( ITO ) and an alignment layer 3, ⁇ for instance comprising rubbed polyimide.
  • a polariser 32 is fixed to the external surface of another transparent substrate 33, for instance made of glass.
  • the substrate 33 carries on its internal surface the column electrodes 24 which are made of a transparent conductor, such as ITO, and an alignment layer 2, for instance comprising rubbed polyimide.
  • the device is assembled with the alignment layers 2 and 3 facing each other and spaced apart by spacers 34. The resulting gap is filled with a cholesteric liquid crystal 5 to form a layer which is sealed in any suitable way.
  • the polariser and alignment directions of the polarisers 30 and 32 and the alignment layers 2 and 3 are illustrated in Figure 5.
  • the polarising directions of the polarisers 30 and 32 are illustrated at 35 and 36, respectively, whereas the surface alignment directions of the alignment layers 2 and 3 are illustrated at 37.
  • the polarisation directions 36 and 35 are substantially orthogonal whereas the alignment directions 37 are antiparallel and oriented at substantially 45° to the polarising directions 35 and 36.
  • the liquid crystal 5 has substantially twisted and substantially untwisted metastable states . .
  • the twisted state is illustrated by the orientation of liquid crystal molecules shown at 38 and, in this state has a twist of substantially 360°.
  • the untwisted state is illustrated at 39 with all the molecules aligned in the directions 37.
  • FIG. 6 illustrates waveform diagrams of the data and strobe signals supplied by the data and strobe signal generators 20 and 21.
  • the strobe or row waveform 11 comprises a first portion followed by a second portion which, in turn, is followed by a third portion comprising first and second parts.
  • the first portion comprises a reset pulse 41.
  • The. second portion comprises a space or reset period.
  • the first part of the third portion comprises what is termed as a partial reset pulse 42.
  • the second part of the third portion comprises what is termed as a change-favouring pulse 43.
  • the column or data waveform comprises bipolar pulses of constant amplitude but of varying width so as to select the desired grey level of the pixels.
  • the data pulses are bipolar and are such as to have no net DC component.
  • the strobe pulses are monopolar and their polarities may be changed periodically, for instance from frame to frame, so as to preserve DC balance and avoid degradation of the liquid crystal 5.
  • the resulting waveforms appearing across the liquid crystal are shown at 13 and the amplitude or modulus of the waveform is shown at 14.
  • the reset pulse 41 is supplied by the strobe signal generator 21 to the appropriate row electrode 25 while other rows are being refreshed.
  • the modulus of the resultant voltage shown at 44 is greater than the Fredericksz transition voltage so that the liquid crystal is reset to the homeotropic state 6 having zero twist.
  • the pixels of the row being refreshed receive only the data signal waveforms. These are of sufficiently small amplitude to allow the liquid crystal to relax to a state having 360° of twist, which is believed to be the twisted or black metastable state 9 but which may be or include a partially homeotropic state having a 360° twist.
  • a partial reset pulse 42 is applied to the row electrode 25 and, together with the data waveform, supplies a voltage whose modulus 45 is intended to select a relatively light grey.
  • the height and width of the pulse 42 are selected so as to achieve what is presently believed to be partial blanking or resetting.
  • the degree of blanking or resetting therefore varies in different areas of the pixel. This variation may be caused by director fluctuations in the cholesteric or by inhomogeneous flow during the Fredericksz transition.
  • the change-favouring pulse 43 is then applied and, it is presently believed, acts as a "kick white" pulse to create white in the -areas in the prewhite state. Areas in the preblack state are not affected by the pulse 43 and relax to the black state.
  • the change-favouring pulse 43 is chosen such that the data voltage which is simultaneously applied does subsequently not affect which final state is selected.
  • An alternative addressing technique differs from that described hereinbefore in that the pulses 42 and 43 are chosen in such a way that the resulting transmission is substantially determined by the data voltage supplied during the pulse 43.
  • the pulse 43 is believed to contribute to the Fredericksz transition begun during the pulse 42 and thus influence the ratio of prewhite and preblack areas. As described hereinbefore, the pulse 43 is also believed to support the relaxation of prewhite areas to the white relaxed state.
  • the local differences in the degree of blanking are believed to be caused by thermal fluctuations in the cholesteric liquid crystal or by voltage-change induced dynamic inhomogenei ies or both.
  • the liquid crystal molecules cannot all move in the same way and so they temporarily acquire different orientations in different locations.
  • analogue selection ⁇ of grey level can be achieved. For instance, the data waveform shown at 46 results in a waveform whose modulus 47 selects or addresses a darker grey level than that addressed by the modulus 45.
  • Figure 7 illustrates diagrammatically the type of waveforms used in the known addressing arrangement described hereinbefore whereas Figure 8 illustrates diagrammatically various types of waveform which may be used in accordance with the present invention.
  • Figure 7 illustrates at (a) the type of waveform disclosed in EP 0 018 180 in which the reset pulse 41 decays rapidly as shown at 50 to address black or more slowly as shown at 51 to address white.
  • Figure 7 illustrates at (b) and (c) two types of waveform as disclosed in EP 0 569 029.
  • the reset pulse 41 is followed by a variable pulse 52 which is contiguous in (b) and spaced from the reset pulse 41 in (c).
  • Figure 8 shows at ( a ) the resetting pulse 41 followed by a space followed by the partial reset pulse 42 and the change-favouring pulse 43.
  • the pulses 42 and 43 are spaced apart in time.
  • the pulses 42 and 43 may be spaced from each other in time or may be contiguous in time and each may comprise a combination of pulses.
  • the partial reset pulse 42 may be divided into two parts 42a and 42b, which may be contiguous as shown at (b) or may be spaced in time as shown at (c).
  • the first part 42a is of lower amplitude than the second part 42b and the second part 42b is shaped so that only data supplied during the first part 42a influences the grey level selection.
  • the single change-favouring pulse 43 may comprise a series of pulses of decreasing amplitude as shown at (d), (e) and (f) in combination with the pulses 42, 42a, 42b shown at (a), (b) and (c), respectively.
  • the partial reset pulse 42 and the change-favouring pulse 43 may not be clearly distinguishable in the waveform, for instance as illustrated at (d) to (i).
  • Figure 9 illustrates waveform diagrams and optical transmission for a waveform of the type shown in Figure 8 at (c).
  • the column waveform 12(a) cooperates with the first part 42a of the bipolar partial reset pulse 42 to cause substantially the whole pixel to be switched to the transparent or white state as shown at 15(a).
  • the column or data waveform shown at 12(b) controls addressing of an intermediate or grey level as illustrated by the transmission curve 15(b).
  • the column or data waveform illustrated at 12(c) results in switching of substantially the whole pixel to black as illustrated by 15(c).
  • the performance illustrated in Figure “ 9" is achieved with a device of the type .illustrated in Figures 3 to 5 having a liquid crystal thickness of 2 micrometers and using a liquid crystal comprising a nematic liquid crystal mixture ZLI-4792 doped with a chiral dopant R-1011 to a cholesteric pitch of 3 micrometers (both materials are available from Merck).
  • the alignment layers 2 and 3 comprise antiparallel polyimide with a pretilt of approximately 5°.
  • the row waveform 11 comprises a reset pulse 41 having a duration of 3 milliseconds and an amplitude of 37 volts.
  • the column waveform comprises bipolar pulses with an amplitude of 2.5 volts and being based on a pulse duration of 25 microseconds.
  • Figure 10 illustrates data waveforms for providing ten grey levels including black and white for a display of the type illustrated, in Figures 3 to 5.
  • the polarising directions 35 and 36 are at 4° and 86° with the alignment direction 37 at 45°.
  • the alignment layers 2 and 3 comprise antiparallel polyimide arranged to provide a pretilt of approximately 7°, such as RN 715 available from Merck.
  • the liquid crystal layer has a thickness of 1.4 micrometers and comprises a nematic liquid crystal mixture ZLI-4792 doped with a chiral dopant R-1011 comprising approximately 1.3% by weight.
  • the row waveform 11 comprises the bipolar reset pulse 41 having a duration of 3 milliseconds and an amplitude of 30 volts followed by a gap of 4.2 milliseconds.
  • the monopolar pulse 42 has a duration of 88 microseconds and an amplitude of 17.1 volts and is followed by a gap of 0.204 milliseconds _ " This is followed by the bipolar pulse train 43 having a duration of 1 millisecond and an amplitude of 5.3 volts. There is then a gap of 24.308 milliseconds before the row waveform repeats.
  • the polarity of the pulse 41 changes halfway through the duration of the pulse 41 whereas the pulse 42 changes polarity at every repeat.
  • the pulse train 43 comprises individual pulses having a width of 8 microseconds offset by 4 microseconds from polarity changes in the column waveform 12.
  • the column waveform comprises bipolar pulses of length 8 microseconds and of amplitude 1.7 volts.
  • Figure 11 shows at (a), (b) and (c) results obtained using the device described hereinbefore with the waveforms illustrated in Figure 9.
  • the black corresponding to the transmission 15(c) is shown at (c) in Figure 11.
  • the white obtained by the column waveform 12(a) as illustrated by the transmission curve 15(a) is illustrated at (a) in Figure 11.
  • the grey level indicated by the transmission curve 15(b) is shown at (b) in Figure 11.

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  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Liquid Crystal (AREA)
  • Liquid Crystal Display Device Control (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)

Abstract

Un dispositif à cristaux liquides présente au moins trois niveaux d'atténuation optique et comporte une cellule à cristaux liquides nématiques torsadés bistables pouvant être dans un premier état métastable dans lequel il présente un premier degré de torsion et il est métastable en l'absence d'un champ appliqué, et dans un deuxième état métastable, dans lequel il présente un deuxième degré de torsion et est métastable en l'absence de champ appliqué. Le dispositif de l'invention comprend un générateur d'adresse utilisé pour l'application aux bornes de la cellule d'un champ ayant une forme d'onde comprenant une première partie pour la remise du cristal liquide à l'état initial dans lequel il présente un premier degré de torsion, une deuxième partie permettant au cristal liquide de se mettre à l'état de relaxation dans lequel il présente un deuxième degré de torsion et une troisième partie ayant au moins trois formes d'onde différentes, quelles qu'elles soient, pour la sélection respective d'au moins trois niveaux d'atténuations optiques différents. Dans un moins un des niveaux d'atténuation, une première partie du cristal liquide de la cellule est dans le premier état métastable et une deuxième partie du cristal liquide de la deuxième cellule est dans le deuxième état métastable.
PCT/JP1998/003691 1997-08-21 1998-08-20 Procede d'excitation d'un dispositif a cristaux liquides cholesteriques bistables Ceased WO1999010870A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
KR10-1999-7005448A KR100497691B1 (ko) 1997-08-21 1996-12-18 개구율 향상에 적합한 횡전계 방식 액정 표시 장치
JP2000508103A JP2001514399A (ja) 1997-08-21 1998-08-20 双安定コレステリック液晶デバイスの駆動方法
KR1020007001743A KR100335159B1 (ko) 1997-08-21 1998-08-20 쌍안정 콜레스테릭 액정 장치의 구동 방법

Applications Claiming Priority (2)

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GBGB9717597.0A GB9717597D0 (en) 1997-08-21 1997-08-21 Liquid crystal device
GB9717597.0 1997-08-21

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WO1999010870A1 true WO1999010870A1 (fr) 1999-03-04

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WO2003044765A3 (fr) * 2001-11-20 2003-12-11 E Ink Corp Procedes pour piloter des afficheurs electro-optiques bistables
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US7034783B2 (en) 2003-08-19 2006-04-25 E Ink Corporation Method for controlling electro-optic display
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CN100428320C (zh) * 2003-04-16 2008-10-22 精工爱普生株式会社 电光装置的驱动方法、电光装置和电子设备
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US9530363B2 (en) 2001-11-20 2016-12-27 E Ink Corporation Methods and apparatus for driving electro-optic displays
US9564088B2 (en) 2001-11-20 2017-02-07 E Ink Corporation Electro-optic displays with reduced remnant voltage
US9620067B2 (en) 2003-03-31 2017-04-11 E Ink Corporation Methods for driving electro-optic displays
US9966018B2 (en) 2002-06-13 2018-05-08 E Ink Corporation Methods for driving electro-optic displays
US10331005B2 (en) 2002-10-16 2019-06-25 E Ink Corporation Electrophoretic displays
US10726798B2 (en) 2003-03-31 2020-07-28 E Ink Corporation Methods for operating electro-optic displays
US11250794B2 (en) 2004-07-27 2022-02-15 E Ink Corporation Methods for driving electrophoretic displays using dielectrophoretic forces

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US7012600B2 (en) 1999-04-30 2006-03-14 E Ink Corporation Methods for driving bistable electro-optic displays, and apparatus for use therein
US7119772B2 (en) 1999-04-30 2006-10-10 E Ink Corporation Methods for driving bistable electro-optic displays, and apparatus for use therein
US7193625B2 (en) 1999-04-30 2007-03-20 E Ink Corporation Methods for driving electro-optic displays, and apparatus for use therein
US7312794B2 (en) 1999-04-30 2007-12-25 E Ink Corporation Methods for driving electro-optic displays, and apparatus for use therein
FR2808891A1 (fr) * 2000-05-12 2001-11-16 Nemoptic Dispositif bistable d'affichage en reflexion
US6831716B2 (en) 2000-05-12 2004-12-14 Nemoptic Reflective bistable display device incorporating a liquid crystal material
WO2001086618A1 (fr) * 2000-05-12 2001-11-15 Nemoptic Dispositif bistable d'affichage en reflexion
KR100880319B1 (ko) * 2001-09-28 2009-01-28 소니 가부시끼 가이샤 액정 표시 장치
US7528822B2 (en) 2001-11-20 2009-05-05 E Ink Corporation Methods for driving electro-optic displays
US9564088B2 (en) 2001-11-20 2017-02-07 E Ink Corporation Electro-optic displays with reduced remnant voltage
WO2003044765A3 (fr) * 2001-11-20 2003-12-11 E Ink Corp Procedes pour piloter des afficheurs electro-optiques bistables
US9886886B2 (en) 2001-11-20 2018-02-06 E Ink Corporation Methods for driving electro-optic displays
US9881564B2 (en) 2001-11-20 2018-01-30 E Ink Corporation Electro-optic displays with reduced remnant voltage
US9530363B2 (en) 2001-11-20 2016-12-27 E Ink Corporation Methods and apparatus for driving electro-optic displays
CN102789764A (zh) * 2001-11-20 2012-11-21 伊英克公司 驱动双稳态电光显示器的方法
US9412314B2 (en) 2001-11-20 2016-08-09 E Ink Corporation Methods for driving electro-optic displays
WO2003044763A1 (fr) * 2001-11-22 2003-05-30 Koninklijke Philips Electronics N.V. Appareil a cristaux liquides bistable presentant deux modes de commande
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KR20010023121A (ko) 2001-03-26
GB9717597D0 (en) 1997-10-22
KR100335159B1 (ko) 2002-05-04
JP2001514399A (ja) 2001-09-11

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