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WO1992002925A1 - Adressage multiplex d'affichage a cristaux liquides ferro-electriques - Google Patents

Adressage multiplex d'affichage a cristaux liquides ferro-electriques Download PDF

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Publication number
WO1992002925A1
WO1992002925A1 PCT/GB1991/001263 GB9101263W WO9202925A1 WO 1992002925 A1 WO1992002925 A1 WO 1992002925A1 GB 9101263 W GB9101263 W GB 9101263W WO 9202925 A1 WO9202925 A1 WO 9202925A1
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WIPO (PCT)
Prior art keywords
strobe
waveform
pulse
addressing
voltage
Prior art date
Application number
PCT/GB1991/001263
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English (en)
Inventor
Jonathan Rennie Hughes
Edward Peter Raynes
Original Assignee
The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland
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Publication date
Application filed by The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland filed Critical The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland
Priority to EP91914038A priority Critical patent/EP0542804B1/fr
Priority to KR1019930700355A priority patent/KR100231216B1/ko
Priority to CA002088770A priority patent/CA2088770C/fr
Priority to DE69119771T priority patent/DE69119771T2/de
Publication of WO1992002925A1 publication Critical patent/WO1992002925A1/fr
Priority to GB9301627A priority patent/GB2262831B/en
Priority to US08/902,519 priority patent/US5963186A/en

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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
    • 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
    • G09G2310/02—Addressing, scanning or driving the display screen or processing steps related thereto
    • G09G2310/0202—Addressing of scan or signal lines
    • G09G2310/0205—Simultaneous scanning of several lines in flat panels
    • 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
    • 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
    • G09G2310/063—Waveforms for resetting the whole screen at once
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/04—Maintaining the quality of display appearance
    • G09G2320/041—Temperature compensation

Definitions

  • This invention relates to multiplex addressing of ferro-electric liquid crystal displays.
  • Such displays use a tilted chiral smectic C, I, or F liquid crystal material.
  • Liquid crystal devices commonly comprise a thin layer of a liquid crystal material contained between two glass slides. Optically transparent electrodes are formed on the inner surface of both slides. When an electric voltage is applied to these electrodes the resulting electric field changes the molecular alignment of the liquid crystal molecules. The changes in molecular alignment are readily observable and form the basis for many types of liquid crystal display devices.
  • ferro electric liquid crystal devices the molecules switch between two different alignment directions depending on the polarity of an applied electric field. These devices have a degree of bistability and tend to remain in one of the two switched states until switched to the other switched state. This allows the multiplex addressing of quite large displays.
  • One common multiplex display has display elements, ie pixels, arranged in an x, y matrix format for the display of e.g., alpha numeric characters.
  • the matrix format is provided by forming the electrodes on one slide as a series of column electrodes, and the electrodes on the other slide as a series of row electrodes. The intersections between each column and row form addressable elements or pixels.
  • Other matrix layout are known, e.g, polar co-ordinate (r - ⁇ ), and seven bar numeric displays.
  • a common feature is application of a voltage, called a strobe voltage to each row or line in sequence.
  • a strobe voltage to each row or line in sequence.
  • appropriate voltages called data voltages
  • the differences between the different schemes lies in the shape of the strobe and data voltage waveforms.
  • European Patent Application 0,306,203 describes one multiplex addressing scheme for ferro electric liquid crystal displays.
  • the strobe is a unipolar pulse of alternating polarity, and the two data waveforms are rectangular waves of opposite sign.
  • the strobe pulse width is one half the data waveform period. The combination of the strobe and the appropriate one of the data voltages provides a switching of the liquid crystal material.
  • the material may be switched between its two states by two strobe pulses of opposite sign, in conjunction with a data waveform.
  • a blanking pulse may be used to switch the material into one state, and a single strobe pulse used with an appropriate data pulse to selectively switch back pixels to the other state.
  • a single strobe pulse used with an appropriate data pulse to selectively switch back pixels to the other state.
  • Blanking pulses are normally greater in amplitude and length of application than the strobe pulses so that the material switches irrespective of which of the two data waveforms is applied to any one intersection. Blanking pulses may be applied on a line by line basis ahead of the strobe, or the whole display may be blanked at one time, or a group of lines may be simultaneously blanked.
  • One known blanking scheme uses blanking pulse of equal voltage (V) time (t) product Vt, but opposite polarity, to the strobe pulse Vt product.
  • the blanking pulse has an amplitude of half and a time of application of twice that of the strobe pulse. These values ensure the blanking and strobe have a net zero d.c. value without periodic reversal of polarity. Experimental use has shown the scheme to have a poor performance.
  • the feature of d.c. balance is particularly important in projection displays since if it is desired to switch the gap between pixels to one optical state then periodic reversal of polarities is not permissible.
  • One problem with existing displays is the time taken to address complex displays. In order to drive complex displays at video frame rates it is necessary to address the display quickly. Contrast ratio can also be improved by addressing quickly so that the column waveform is at a correspondingly high frequency. However, merely increasing the speed of addressing will not always result in correct switching.
  • An object of the present invention is to reduce the time taken to address a matrix display and to improve display contrast.
  • a method of multiplex addressing a ferro electric liquid crystal matrix display formed by the intersections of a first set of electrodes and a second set of electrodes comprises the steps of:- addressing each electrode individually in the first set of electrodes, such addressing being either by application of a strobe waveform of pulses of positive and negative values, or by application of a blanking pulse followed by a strobe pulse with periodic polarity reversal to maintain a net zero d.c.
  • the strobe waveform may be first a zero in the first period, ts, followed by a non zero voltage (main) pulse for a period greater than ts. eg (1.5. 2.0, 2.5. 3.0 or more) x ts.
  • the strobe waveform may have a non zero voltage in the first ts period of the same or different polarity to the remainder of the strobe; this first voltage pulse being of variable amplitude to provide a temperature compensation.
  • the strobe waveform may be followed by a non zero voltage for a time period of opposite polarity to the main voltage pulse, eg greater than ts, ts, or less than ts.
  • the liquid crystal material may be switched between its two states by coincidence of a strobe pulse and an appropriate data waveform.
  • the material may be switched into one of its state by a blanking pulse and subsequently selected pixels switched back to the other state by coincidence of a strobe pulse and an appropriate data waveform;
  • the blanking pulse may be in two parts; a first part of opposite polarity to the second. Both parts of the blanking pulse are arranged to have a voltage time product Vt that combines with the Vt product of the single strobe to give a net zero d.c. value.
  • Extending the time length of the strobe pulse means an overlapping of addressing in sucessive electrodes in the first set of electrodes. Such overlapping effectively increases the width of the switching pulse whilst not affecting the other waveforms and thus reduces the total time taken to address a complete display whilst maintaining a good contrast ratio between elements in the two different switched states.
  • Each strobe pulse may be immediately preceded by a smaller prepulse of the same or opposite sign to that of the associated strobe pulse. This prepulse may be used to change the switching characteristics of the liquid crystal material. It may be used as part of a temperature compensation. In this case the temperature of the material is sensed and the amplitude of the prepulse adjusted as appropriate.
  • Each strobe pulse may be immediately followed by a pulse of opposite sign.
  • a multiplex addressed liquid crystal display comprises: a liquid crystal cell formed by a layer of liquid crystal material contained between two cell walls, the liquid crystal material being a tilted chiral smectic material having a negative dielectric anisotropy, the cell walls carrying electrodes formed as a first series of
  • Electrodes on one wall and a second series of electrodes on the other cell walls the electrodes being arranged to form collectively a matrix of addressable intersections, at least one of the cell walls being surface treated to provide surface alignment to liquid crystal
  • driver circuits for applying a strobe waveform in sequence to each electrode in the first set of electrodes; driver circuits for applying data waveforms to the second set of electrodes; waveform generators for generating a strobe waveform, and two data waveforms for applying to the driver circuits; and means for controlling the order of data waveforms so that a desired display pattern is obtained;
  • a data waveform generator that generates two sets of waveforms of equal amplitude and frequency but opposite sign, each data waveform comprising d.c. pulses of alternate sign
  • a strobe generator that generates a strobe pulse of greater duration than one half a data waveform period, each strobe pulse extending into an address period of the next electrode.
  • Emin is the field at which the response time-voltage switching characteristic of the liquid crystal material exhibits a minimum response time
  • ⁇ o is the permittivity of free space
  • ⁇ is the (negative) dielectric anisotropy of the liquid crystal material
  • ⁇ is the cone angle of the liquid crystal material
  • Ps is the spontaneous polarisation
  • Figure 1 is a diagrammatic view of a time multiplex addressed x, y matrix
  • Figure 2 is a cross section of part of the display of Figure 1 to an enlarged scale
  • Figure 3 is a graph of log time against log voltage showing
  • Figures 4-8 show different strobe and data waveform diagrams that can be used
  • Figure 9 show waveform diagrams having a strobe modified from that of Figure 4.
  • Figure 10 show blanking, strobe and data waveforms diagrams
  • Figure 11 show strobe, data, and addressing waveforms used in a prior art display.
  • Figures 12 a, b show waveform diagrams for addressing the 4 ⁇ 4 element display shown in Figure 13;
  • Figure 13 is a 4 ⁇ 4 element array showing some intersections
  • Figures 16-20 are log time against log applied voltage graphs
  • Figures 21, 22 show different blanking, strobe and data
  • Figures 23, 24 show row and column waveforms for a prior art
  • Figures 25, 26 show row and column waveforms for a modification of
  • the display 1 shown in Figures 1, 2 comprises two glass walls 2, 3 spaced about 1-6 ⁇ m apart by a spacer ring 4 and/or distributed spacers.
  • Electrode structures 5. 6 of transparent tin oxide are formed on the inner face of both walls. These electrodes are shown as row and column forming an X, Y matrix but may be of other forms. For example, radial and curved shape for an r, ⁇ display, or of segments form for a digital seven bar display.
  • a layer 7 of liquid crystal material is contained between the walls 2, 3 and spacer ring 4.
  • Polarisers 8, 9 are arranged in front of and behind the cell 1. Row 10 and column 11 drivers apply voltage signals to the cell. Two sets of waveforms are generated for supplying the row and column drivers 10, 11. A strobe wave form generator 12 supplies row waveforms, and a data waveform generator 13 supplies ON and OFF waveforms to the column drivers 11. Overall control of timing and display format is controlled by a control logic unit 14. Temperature of the liquid crystal layer 7 is measured by a thermocouple 15 whose output is fed to the strobe generator 12. The thermocouple 15 output may be direct to the generator or via a proportioning element 16 e.g. a programmed ROM chip to vary one part of the strobe pulse and or data waveform.
  • a proportioning element 16 e.g. a programmed ROM chip to vary one part of the strobe pulse and or data waveform.
  • the cell walls Prior to assembly the cell walls are surface treated in a known manner, e.g. by applying a thin layer of polyimide or polyamide, drying and, where appropriate, curing and buffing with a cloth (e.g. rayon) in a single direction, R1, R2.
  • a cloth e.g. rayon
  • a thin layer of e.g. silicon monoxide may be evaporated at an oblique angle.
  • R1, R2 may be parallel or anti parallel.
  • suitable unidirectional voltages are applied the molecules director align along one of two directions D1, D2 depending on polarity of the voltage. Ideally the angle between D1, D2 is about 45°. In the absence of an applied electric field the molecules adopt an intermediate alignment direction between R1, R2 and the directions D1, D2.
  • the device may operate in a transmissive or reflective mode. In the former light passing through the device e.g. from a tungsten bulb is selectively transmitted or blocked to form the desired display. In the reflective mode a mirror is placed behind the second polariser 9 to reflect ambient light back through the cell 1 and two polarisers. By making the mirror partly reflecting the device may be operated both in a transmissive and reflective mode.
  • Pleochroic dyes may be added to the material 7. In this case only one polariser is needed and the layer thickness may be 4-10 ⁇ m.
  • Suitable liquid crystal materials are:
  • Mixture A which contains 5% racemic dopant and 3% chiral dopant in the host;
  • Mixture B which contains 9.5% racemic dopant and 3.5% chiral dopant in the host.
  • Mixture A has the phase sequence Sc 100°C Sa 111°C N 136°C.
  • Mixture B has the phase sequence Sc 87°C 118°C N 132°C.
  • Liquid crystal material at an intersection of a row and column electrode is switched by application of an addressing voltage.
  • Vs instantaneous value of strobe waveform
  • Vd instantaneous value of data waveform
  • the switching characteristic is independent of the sign of the voltage; i.e. the material switches for either a positive or a negative voltage of a given amplitude.
  • the direction to which the materal switches is dependent on the polarity of voltage.
  • Two curves are shown in Figure 3 because the switching characteristic depends upon the shape of the addressing voltage pulse combination.
  • the upper curve is obtained when the addressing voltage is immediately preceded by a small prepulse of opposite sign; e.g. a small negative pulse followed by a larger positive pulse.
  • the material behaves the same on application of a small positive pulse followed by a large negative pulse. This upper curve usually exhibits a turn round or a minimum response time at one voltage.
  • the small prepulse may be termed a leading pulse (Lp) and the larger addressing pulse a trailing pulse (Tp).
  • Lp leading pulse
  • Tp trailing pulse
  • the upper curve applies for a negative value of the ratio Lp/Tp.
  • the lower curve is obtained when the addressing voltage is immediately preceded by a small pre-pulse of the same sign; i.e. a small positive pulse followed by a larger positive pulse. The same applies for a small negative pulse followed by a large negative pulse.
  • the lower curve has a positive Lp/Tp ratio. This lower curve has a different shape to that of the upper curve; for some materials it may not have a minimum value of a voltage time curve.
  • the strobe waveform is first a zero for a time period ts followed by +3 for twice ts. This is applied to each row in sequence, i.e. one time frame period.
  • the second part of the strobe is a zero for one ts period followed by +3 for twice ts. Again this is applied to each row in sequence for one time frame period.
  • Complete addressing of a display takes two time frame periods.
  • the values of +3, -3 are units of voltage given for the purpose of illustration, actual values are given later for specific materials.
  • Data waveforms are arbitrarily defined as data ON and data OFF, or D1, and D2.
  • Data ON has first a value of +1 for a first time period of ts followed by a -1 for a time period ts. This is repeated; i.e. data ON is an alternating signal of amplitude 1 and period 2ts.
  • Data OFF is similar but has an inital value of -1 followed by +1; i.e. the inverse of data ON.
  • the first part of the data waveform e.g. for data ON the value of +1 for a time period ts, is coincident with the first part of the strobe waveform, i.e. zero for time period ts.
  • the addressing waveform is the sum of strobe and data.
  • the combination of a positive strobe pulse and data ON is :- -1, 4, 2, 1, -1, 1 etc.
  • the value 4 immediately preceded by -1 ensures the material switch characteristics are governed by the upper curve of Figure 3 *
  • the combination of a negative strobe pulse and data ON is:- -1, -2, -4, 1, -1, 1 etc.
  • the combination of smaller pulses of the same sign as the large (-4) pulse ensures the material switch characteristics are governed by the lower curve in Figure 3.
  • a positive strobe pulse and data OFF combine to give:- 1, 2, 4, -1, 1 etc; and a negative strobe pulse and data OFF combine to give:- 1, -4, -2, -1, 1, -1 etc.
  • each row is earthed, i.e. receives a zero voltage.
  • Each column receives either data ON or data OFF
  • intersections receive an alternating signal, caused by the data waveforms, when not being addressed.
  • This provides an a.c. bias to each intersection and helps maintain material in its switched state. Larger amounts of a.c. bias lead to improved contrast by the known a.c. stabilisation described in Proc 4th IDRC 1984, pp 217-220.
  • a.c. bias may be provided, e.g. from a 50 KHz source, direct onto those rows not receiving a strobe pulse.
  • the effect on contrast ratio of a.c. bias, both magnitude and pulse width is shown in Figures 14 and 15 for the materials SCE8 and mixture A. These show inherent contrast ratio (CR) measured as a function of a.c. frequency as a cell is switched between its two bistable states and measured at various levels of a.c. bias.
  • FIG. 5 Alternative strobe waveforms are shown in Figures 5 to 8.
  • the strobe is first a zero for 1 ⁇ ts, and 3 for 3 ⁇ ts, followed by its inverse.
  • the strobe waveforms is first a zero for 1 ⁇ ts and 3 for 4 ⁇ ts, followed by its inverse.
  • the strobe waveform is first a zero for 1 ⁇ ts, a 3 for 2 ⁇ ts, and -1 for 1 ⁇ ts; this is followed by its inverse.
  • Figure 8 is a modification of Figure 4 and uses a non zero prepulse in the strobe waveform. As shown the first part of the strobe is between -1 and 1, not the zero value of Figure 4. The remainder of the strobe is the same as in Figure 4,- i.e. amplitude 3 for twice ts. The resulting addressing waveform -is then a first pulse of between -2 and -1 for both first and second fields. The effect of this prepulse is to change the position of the switching curves. Figure 3 etc. Varying the value of the prepulse varies the shape and vertical position of the curves as explained wth reference to Figures 16, and 17 below. Table 8 below shows how the switching time varies with temperature.
  • Figure 9 shows a modification of Figure 4. Is this modification the strobe waveform is zero for the first ts and 3 for the next 1.5ts. This 1.5ts is merely one example since any value greater than ts can be used up to about 5ts.
  • Figure 10 shows a single blanking pulse of amplitude 4 applied for 4ts. This switches all the intersections to one switched state. A strobe is then used to switch selected intersections to the other switched state. Periodically the sign of the blanking and strobe are reversed to maintain overall net zero d.c. voltages.
  • the use of a blanking pulse and single strobe can be applied to all the schemes of Figures 4-8.
  • An advantage of blanking and strobe systems is that the whole display can be addressed in a single field time period.
  • FIG. 11 shows strobe, data, and addressing waveforms for a prior art display scheme, a mono pulse addressing scheme.
  • Figures 21, 22 show addressing schemes of this invention using a blanking pulse and a single strobe pulse that provide a net zero d.c. value.
  • the blanking pulse is in two parts, a prepulse of opposite sign to the main and blanking pulse.
  • the function of the prepulse is to give zero d.c. balance.
  • the prepulse has a value of 3 for 4ts immediately followed by -3 for 6ts.
  • the strobe pulse is first a zero for Its immediately followed by 3 for 2ts; this strobe is the same as the strobe in Figure 4.
  • Data waveforms D1 , D2 are also the same as in Figure 4.
  • the combination of blanking and D1 or D2 shows a large negative Vt product which switches all pixels in the addressed row to OFF.
  • the strobe pulse in combination with D2 switches required pixels to ON as described above with reference to Figure 4.
  • Figure 22 is similar to Figure 21 but has a different shape of blanking pulse.
  • This blanking pulse has a prepulse of amplitude 3 for 4ts immediately followed by -4.5 for 4ts.
  • the strobe pulse has amplitude 3 for 2ts as in Figure 4.
  • the combination of blanking pulse and D1 and D2 is shown to provide a large negative Vt product that switches all addressed rows to an OFF state. Again, selected pixels are switched to ON by the strobe and D2.
  • the blanking pulses of Figures 21, 22 can be applied with the other forms of strobe pulses shown in Figures 5-9 with amplitude and or Vt product arranged to give net zero d.c.
  • the amplitude of the pre and/or main blanking pulse is also adjusted to maintain a net zero d.c. value.
  • the blanking pulse may precede the strobe pulse by a variable amount but there is an optimum position for response time, contrast and visible flicker in the display. This is typicaly with blanking pulse starting six lines ahead of the strobe pulse but is dependent upon material parameters and the detail of the multiplex scheme.
  • Figures 12 a, b show the waveforms involved in addressing a 4 ⁇ 4 matrix array showing information as shown in Figure 13. Solid circles are arbitrarily shown as ON electrode intersections, i.e. display elements, unmarked intersections are OFF.
  • the addressing scheme is that used in Figure 4.
  • the positive, or leading, strobe pulse is applied to each row 1 to 4 in turn; this comprises the first field.
  • the negative, or trailing, strobe pulse is applied to each row 1 to 4 in turn and comprises the second field. Note there is an overlap between rows. For example the third ts period for row 1 occurs at the same as the first ts period of row 2. This overlap is more noticable for displays using the strobe waveforms shown in Figures 5, 6.
  • the data waveform data ON applied to column 1 remains constant because each intersection in column is always ON.
  • the data waveform is data OFF and remains constant because all intersections in column 2 are OFF.
  • the data waveform is data OFF whilst rows 1 and 2 are addressed, changing to data ON whilst row 3 is addressed, then changing back to data OFF whilst row 4 is addressed. This means that column 3 receives data OFF for 4 ⁇ ts, data ON for 2 ⁇ ts, data OFF for 2 ⁇ ts, a period of one field time, the time taken for the positive strobe pulse to address every row.
  • the data waveform is data OFF for 2ts, data ON for 2ts, data OFF for 2ts, and data ON for 2ts. This is repeated for a further field period whilst the negative strobe pulse is applied. Two field periods are required to provide one frame period and completely address the display. The above is .repeated until a new display pattern is needed.
  • intersection row 1 column 1 (R1,C1) the material does not switch during the first field period because the material switching follows the upper curve of Figure 3. and time and applied voltage level are made to lie below the switching curve. Instead the material switches during the second field period where the material switches because of the lower voltage/time requirements shown by the lower curve of Figure 3. A similar reasoning applies to intersection R1.C2 where the material switches during the first field period.
  • intersection R3.C3 the material switches during the second field period because the time/voltage applied during the first field period does not reach the higher value required by the upper curve of Figure 3.
  • Intersection R4,C4 switches at the end of the second field period whilst a negative strobe pulse is being applied.
  • the contrast ratio (CR) curves Figure 14 (mixture A) and Figure 15 (mixture SCE 8) indicate the inherent contrast of a device when switched between its two bistable positions in the presence of an ac bias.
  • Figure 16 shows a log time/voltage graph showing switching
  • the axes of the graph are log ts and log pulse amplitude voltage.
  • the curves are obtained in a calibration cell simulating the addressing waveforms shown in Figure 4.
  • Two different addressing waveforms are used.
  • the first one, waveform I is a small negative pulse (of -1) applied for a time ts, followed by a larger positive pulse (of 5) applied for a time 2ts, ie the Lp/Tp ratio is -0.166.
  • a period of zero volts is then followed by the inverse, i.e. a small positive pulse (of 1) and a negative larger pulse (of -5).
  • a 50 KHz square wave signal is imposed on the addressing to give an a.c. bias and simulate a data waveform.
  • the small pulse is 0.166 the value of the large pulse at all the voltage levels used to provide the curve.
  • This first addressing waveform provides the upper curve. Values of
  • the second addressing waveform, II is first a positive small pulse of 1 applied for ts immediately followed by a larger positive pulse of 4 applied for 2ts. After a period of zero volts this is inverted.
  • Figure 17 shows time voltage characteristics for the same addressing scheme used in Figure 16 namely that of Figure 4, but modified by use of a small pre pulse in the strobe waveform as in Figure 8.
  • Figure 17 shows that the effect of the pre pulse is to move the vertical position of the curves. This useful for temperature compensation where movement of the curves due to temperature changes is counteracted by changing the value of the pre pulse.
  • a 50 KHz waveform is superimposed to provide a.c. bias.
  • Figure 18 is similar to Figure 16 with an identical cell but using simulations of the addressing waveforms of Figure 5- Thus the
  • Vs 50
  • Vd 10
  • the lower curve switches at 38 ⁇ s
  • the upper curve switches at about 210 ⁇ s.
  • Figure 19 is similar to Figure 16 with an identical cell but using simulations of the addressing waveforms of Figure 1.
  • the switching is complicated since the upper curve has a re-entrant area where the material switches on the trailing pulse instead of the main pulse.
  • the lower curve, Vs - Vd - 40 switches at 58 to 240 and again at greater than 300 ⁇ s when switching is to the trailing pulse.
  • multiplex operation on the main pulse occurs between 58 and 24 ⁇ s and on the trailing pulse at greater than 300 ⁇ s.
  • the log time/voltage characteristics are given in Figure 20 for a conventional mono pulse addressing scheme using a simulation of the strobe and data waveforms of Figure 11 in the same cell as for Figure 11.
  • the simulation addressing waveform is a negative pulse of amplitude 1 unit for ts followed by a positive 6 units for ts.
  • the addressing waveform is a positive pulse of 1 unit for ts followed by a positive pulse of 4 units for ts.
  • the pulse amplitudes are described as units to indicate relative values; the curves are obtained at the illustrated voltages.
  • strobe, Vs, and data, Vd, voltage amplitude were selected to give addressing voltage values such that switching voltages lay above the lower curve of Figure 3 and non switching voltages lay below the upper curve of Figure 3. and the value of ts, in ⁇ seconds, adjusted to give a clear switching display. This ensured the cell was operating in the area indicated by hatched lines of Figure 3.
  • contrast ratio is the ratio of light transmitted in one switched state relative to that transmitted in the other switched state; it is a measure of the clarity of the display.
  • CR is measured at the extremes of the pulse width ts, or at specified values of ts.
  • CR has been optimised by adjusting one of the switched positions of the director in the liquid crystal to correspond to a minimum transmission.
  • Vs Vd ts CR (at lowest ts)
  • Operating Range is:- longest slot time / fastest slot time
  • Brightness (%) is compared with no cell between parallel polarisers.
  • A151 is: -
  • the * denotes chirality, without it the material iis racemic.
  • ferroelectric liquid crystal devices it is known to reduce peak row and column voltages by applying additional waveforms to both row and column electrodes.
  • Figures 23-24 show two different schemes for reducing the peak voltage of prior art monopulse drive systems of Figure 9.
  • a strobe (row) waveform is alternately a zero for 1.ts and a positive pulse of Vs for 1.ts in the first field followed by a zero for 1.ts and a negative pulse of -Vs for 1 ts in the second
  • the additional waveform is a positive Vs/2 during the first field followed by a -Vs/2 in the second field.
  • the resultant strobe waveform varies between Vs/2 and -Vs/2 as shown.
  • the data (column) waveforms are alternate Vd and -Vd pulses each lasting for 1.ts.
  • the additional waveform applied to each column is Vs/2 for the first field followed by -Vs/2 for a second field time.
  • the resultant data waveform is as shown to vary between Vd + Vs/2 and -(Vs/2 + Vd).
  • the effect of the additional waveform is to reduce the peak voltage of e.g. 50 volts to 35 volts.
  • FIG. 24 An alternative to Figure 23 is shown in Figure 24.
  • normal strobe pulses are a zero for 1.ts and a positive Vs for 1. ts in the first field time and a zero for 1.ts then -Vs for 1.ts in the second field time.
  • the additional waveform is a rectangular waveform of period 2.ts applied for the first field time followed by its inverse for the second field time, each varying between Vs/2 and -Vs/2 volts.
  • the resultant strobe (row) waveforms are as shown.
  • the data (column) waveforms are rectangular varying between +Vd and -Vd.
  • the additional waveform is the same as applied to the row electrodes.
  • the data (column) resultant waveform is as shown and varies between Vs/2 + Vd and -(Vs/2 + Vd). Again this reduces the peak voltage needed by display drivers from e.g. 50 volts to 35 volts.
  • Figures 23. 24 may be applied to the addressing scheme of Figures 4-8 above. This is shown in Figure 25 which is a modification of the scheme of Figure 5. Strobe pulses of a zero for 1.ts are followed by Vs for 3.ts in the first field time. Strobe pulses of zero for 1.ts and then -Vs for 3.ts follow in the second field time.
  • the strobe waveform is shown for rows 1, 2, 3 and 4 of a 4 row display; two different strobes are shown for row 4 for reasons explained later.
  • the additional waveform applied to row (and also column) electrodes is shown as Vs/2 for the first field time then -Vs/2 for the second field time.
  • the resultant row waveform for row 1 is shown to be -Vs/2 for 1.ts, Vs/2 for 3.ts, -Vs/2 for 4.ts, Vs/2 for 1.ts, -Vs/2 for 3.ts, and Vs/2 for 4.ts in the first and second field times.
  • the resultant of strobe and additional waveform and the row indicated as row 4a is shown to have a large peak value of + and 3Vs/2.
  • the additional waveform is Vs/2 for one field time, and -Vs/2 for the second field time.
  • the resultant column waveform is shown to vary between +/- (Vd + Vs/2).
  • Vs 50 volts
  • Vd - 10 volts the scheme of Figures 25, 26 reduces peak voltage to 35 volts.

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  • Engineering & Computer Science (AREA)
  • 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 Display Device Control (AREA)
  • Liquid Crystal (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)

Abstract

Une cellule de cristaux liquides ferro-électrique est constituée par des électrodes en rangées et colonnes formant une matrice x, y d'éléments d'affichage. Un signal d'impulsion d'attaque est appliqué à chacunes des rangées de façon séquentielle, tandis que des signaux de données appropriés sont appliqués à toutes les électrodes en colonnes. A chaque élément d'affichage, le matériau reçoit un signal d'adressage servant à le commuter sur un de seux deux états de commutation en fonction de la polarité du signal d'adressage. les caractéristiques de commutation des matériaux ferro-électriques dépendent de la forme du signal d'adressage. Deux formes différentes de signaux d'adressage sont utilisées pour produire deux caractéristiques de commutation différentes et séparées. Il se peut qu'au moins une courbe de caractéristique de commutation présente un temps de réaction minimum pour une valeur de tension et l'affichage s'effectue à des tensions supérieures. Les signaux de données sont des impulsions alternativement positives et négatives de période 2ts. Le signal d'impulsion d'attaque est de zéro pour une période ts suivie par une impulsion de tension unipolaire d'une durée supérieure à ts, par exemple 1,5ts ou davantage. Ceci provoque un chevauchement de l'adressage dans les rangées contigües, c'est-à-dire que la fin d'une impulsion d'attaque sur une rangée chevauche le début d'une impulsion d'attaque sur la prochaine rangée. Les éléments d'affichage peuvent éventuellement se commuter sur l'un de leurs deux états par l'intermédiaire de l'une de deux impulsions d'attaque de polarité opposée. De façon alternative, une impulsion d'effacement peut éventuellement commuter tous les éléments sur un état et une impulsion d'attaque s'utiliser pour commuter les éléments sélectionnés sur l'autre état.
PCT/GB1991/001263 1990-08-07 1991-07-26 Adressage multiplex d'affichage a cristaux liquides ferro-electriques WO1992002925A1 (fr)

Priority Applications (6)

Application Number Priority Date Filing Date Title
EP91914038A EP0542804B1 (fr) 1990-08-07 1991-07-26 Adressage multiplex d'affichage a cristaux liquides ferro-electriques
KR1019930700355A KR100231216B1 (ko) 1990-08-07 1991-07-26 강유전체 액정 표시 장치의 다중 어드레싱
CA002088770A CA2088770C (fr) 1990-08-07 1991-07-26 Attaque multiplex d'afficheurs a cristaux liquides ferro-electriques
DE69119771T DE69119771T2 (de) 1990-08-07 1991-07-26 Multiplex-adressierung von ferroelektrischen flüssigkristallanzeigen
GB9301627A GB2262831B (en) 1990-08-07 1993-01-27 Multiplex addressing of ferro-electric liquid crystal displays
US08/902,519 US5963186A (en) 1990-08-07 1997-07-29 Multiplex addressing of ferro-electric liquid crystal displays

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB909017316A GB9017316D0 (en) 1990-08-07 1990-08-07 Multiplex addressing of ferro-electric liquid crystal displays
GB9017316.2 1990-08-07

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JP (1) JP3356430B2 (fr)
KR (1) KR100231216B1 (fr)
CN (1) CN1025454C (fr)
CA (1) CA2088770C (fr)
DE (1) DE69119771T2 (fr)
GB (2) GB9017316D0 (fr)
MY (1) MY108630A (fr)
WO (1) WO1992002925A1 (fr)

Cited By (12)

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Publication number Priority date Publication date Assignee Title
WO1994018665A1 (fr) * 1993-02-15 1994-08-18 The Secretary Of State For Defence Adressage en multiplex d'affichages a cristaux liquides ferro-electriques
WO1994027275A1 (fr) * 1993-05-08 1994-11-24 The Secretary Of State For Defence Adressage d'affichages a cristaux liquides ferroelectriques
US5437814A (en) * 1993-04-26 1995-08-01 Sharp Kabushiki Kaisha Ferroelectric liquid crystal mixture and liquid crystal device using the same
WO1995024715A1 (fr) * 1994-03-07 1995-09-14 The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland Compensation en temperature de dispositifs d'affichage a cristaux liquides ferroelectriques
EP0691639A2 (fr) 1994-07-04 1996-01-10 Sharp Kabushiki Kaisha Méthode et dispositif de commande d'un panneau d'affichage à cristaux liquides ferro-électriques
GB2294797A (en) * 1994-11-01 1996-05-08 Sharp Kk Method of addressing a liquid crystal display
WO1996037875A1 (fr) * 1995-05-25 1996-11-28 Central Research Laboratories Limited Ameliorations apportees a l'adressage d'afficheurs a cristaux liquides
GB2301450A (en) * 1994-03-07 1996-12-04 Secr Defence Temperature compensation of ferroelectric liquid crystal displays
WO1997023863A1 (fr) * 1995-12-21 1997-07-03 The Secretary Of State For Defence Adressage multiplexe pour afficheurs a cristaux liquides ferroelectriques
GB2312542A (en) * 1995-12-21 1997-10-29 Secr Defence Multiplex addressing of ferroelectric liquid crystal diplays
GB2314446B (en) * 1996-06-20 2000-05-10 Sharp Kk Matrix array bistable device addressing
KR100434250B1 (ko) * 2002-02-16 2004-06-04 이정열 미생물 및 그 배양액을 용해성이 뛰어나고, 토양에서의생존율이 높은 단일 및 복합 미생물제제로 입상의 형태로담체화하는 방법

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GB9407116D0 (en) * 1994-04-11 1994-06-01 Secr Defence Ferroelectric liquid crystal display with greyscale
GB2313225A (en) * 1996-05-17 1997-11-19 Sharp Kk Liquid crystal array device
GB2313224A (en) 1996-05-17 1997-11-19 Sharp Kk Ferroelectric liquid crystal device
GB2337608B (en) 1998-05-16 2003-01-15 Sharp Kk Reduction of ionic memory effect in ferroelectric liquid crystal material
GB9904071D0 (en) * 1999-02-24 1999-04-14 Sharp Kk overnment Of The United Kingdom Of Great Britain And Northern Ireland The Matrix array bistable devices
CN102622972B (zh) * 2011-01-30 2013-09-04 苏州汉朗光电有限公司 近晶态液晶显示屏单向脉冲驱动方法
CN102682722B (zh) * 2011-03-07 2013-10-02 苏州汉朗光电有限公司 一种近晶相液晶显示屏用扫描驱动方法
CN102681228B (zh) * 2011-03-17 2014-08-20 苏州汉朗光电有限公司 像素点独立控制式近晶相液晶显示屏的驱动方法

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EP0197742A2 (fr) * 1985-04-03 1986-10-15 Nortel Networks Corporation Adressage de cellules à cristaux liquides

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GB197742A (en) 1922-02-21 1923-05-22 Herbert Fleetwood Holworthy New or improved means for cleaning, scouring, sharpening, or performing similar functions of domestic character

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EP0197742A2 (fr) * 1985-04-03 1986-10-15 Nortel Networks Corporation Adressage de cellules à cristaux liquides

Cited By (25)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994018665A1 (fr) * 1993-02-15 1994-08-18 The Secretary Of State For Defence Adressage en multiplex d'affichages a cristaux liquides ferro-electriques
GB2290160A (en) * 1993-02-15 1995-12-13 Secr Defence Multiplex addressing of ferro-electric liquid crystal displays
GB2290160B (en) * 1993-02-15 1996-10-23 Secr Defence Multiplex addressing of ferro-electric liquid crystal displays
US5437814A (en) * 1993-04-26 1995-08-01 Sharp Kabushiki Kaisha Ferroelectric liquid crystal mixture and liquid crystal device using the same
GB2293909B (en) * 1993-05-08 1996-10-23 Secr Defence Addressing ferroelectric liquid crystal displays
GB2293909A (en) * 1993-05-08 1996-04-10 Secr Defence Addressing ferroelectric liquid crystal displays
US5748166A (en) * 1993-05-08 1998-05-05 The Secretary Of State For Defense Addressing ferroelectric liquid crystal displays
WO1994027275A1 (fr) * 1993-05-08 1994-11-24 The Secretary Of State For Defence Adressage d'affichages a cristaux liquides ferroelectriques
WO1995024715A1 (fr) * 1994-03-07 1995-09-14 The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland Compensation en temperature de dispositifs d'affichage a cristaux liquides ferroelectriques
US5825344A (en) * 1994-03-07 1998-10-20 The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland Temperature compensation of ferro-electric liquid crystal displays
GB2301450B (en) * 1994-03-07 1998-01-14 Secr Defence Temperature compensation of ferro-electric liquid crystal displays
GB2301450A (en) * 1994-03-07 1996-12-04 Secr Defence Temperature compensation of ferroelectric liquid crystal displays
US6115021A (en) * 1994-07-04 2000-09-05 Sharp Kabushiki Kaisha Method and apparatus for driving a liquid crystal panel using a ferroelectric liquid crystal material having a negative dielectric anisotropy
EP0691639A2 (fr) 1994-07-04 1996-01-10 Sharp Kabushiki Kaisha Méthode et dispositif de commande d'un panneau d'affichage à cristaux liquides ferro-électriques
GB2294797A (en) * 1994-11-01 1996-05-08 Sharp Kk Method of addressing a liquid crystal display
US5844537A (en) * 1994-11-01 1998-12-01 Sharp Kabushiki Kaisha Liquid crystal display, data signal generator, and method of addressing a liquid crystal display
US6100866A (en) * 1995-05-25 2000-08-08 Central Research Laboratories Addressing of liquid crystal displays
WO1996037875A1 (fr) * 1995-05-25 1996-11-28 Central Research Laboratories Limited Ameliorations apportees a l'adressage d'afficheurs a cristaux liquides
WO1997023863A1 (fr) * 1995-12-21 1997-07-03 The Secretary Of State For Defence Adressage multiplexe pour afficheurs a cristaux liquides ferroelectriques
GB2312542B (en) * 1995-12-21 2000-02-23 Secr Defence Multiplex addressing of ferroelectric liquid crystal displays
GB2312542A (en) * 1995-12-21 1997-10-29 Secr Defence Multiplex addressing of ferroelectric liquid crystal diplays
US6127996A (en) * 1995-12-21 2000-10-03 The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland Multiplex addressing of ferroelectric liquid crystal displays
KR100444006B1 (ko) * 1995-12-21 2004-12-13 키네티큐 리미티드 강유전체액정디스플레이및멀티플렉스어드레싱방법
GB2314446B (en) * 1996-06-20 2000-05-10 Sharp Kk Matrix array bistable device addressing
KR100434250B1 (ko) * 2002-02-16 2004-06-04 이정열 미생물 및 그 배양액을 용해성이 뛰어나고, 토양에서의생존율이 높은 단일 및 복합 미생물제제로 입상의 형태로담체화하는 방법

Also Published As

Publication number Publication date
JP3356430B2 (ja) 2002-12-16
GB2262831A (en) 1993-06-30
GB9017316D0 (en) 1990-09-19
CA2088770A1 (fr) 1992-02-08
DE69119771D1 (de) 1996-06-27
KR100231216B1 (ko) 1999-11-15
JPH05509419A (ja) 1993-12-22
EP0542804B1 (fr) 1996-05-22
DE69119771T2 (de) 1996-11-14
MY108630A (en) 1996-10-31
CA2088770C (fr) 2002-11-12
GB2262831B (en) 1994-06-29
EP0542804A1 (fr) 1993-05-26
KR930701803A (ko) 1993-06-12
GB9301627D0 (en) 1993-04-14
CN1025454C (zh) 1994-07-13
CN1058850A (zh) 1992-02-19

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