EP0838802A2 - Verfahren und Einrichtung zum Adressieren einer ferroelektrischen Flüssigkristallanzeige und eine ferroelektrische Flüssigkristallanzeige - Google Patents

Verfahren und Einrichtung zum Adressieren einer ferroelektrischen Flüssigkristallanzeige und eine ferroelektrische Flüssigkristallanzeige Download PDF

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Publication number
EP0838802A2
EP0838802A2 EP97307638A EP97307638A EP0838802A2 EP 0838802 A2 EP0838802 A2 EP 0838802A2 EP 97307638 A EP97307638 A EP 97307638A EP 97307638 A EP97307638 A EP 97307638A EP 0838802 A2 EP0838802 A2 EP 0838802A2
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EP
European Patent Office
Prior art keywords
pulse
strobe
picture element
polarity
grey level
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.)
Withdrawn
Application number
EP97307638A
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English (en)
French (fr)
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EP0838802A3 (de
Inventor
Michael John Towler
Akira Tagawa
Paul Bonnet
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Sharp Corp
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Sharp Corp
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Publication date
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Publication of EP0838802A2 publication Critical patent/EP0838802A2/de
Publication of EP0838802A3 publication Critical patent/EP0838802A3/de
Withdrawn legal-status Critical Current

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    • 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
    • G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
    • G09F9/00—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements
    • 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
    • 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
    • G09G3/2044—Display of intermediate tones using dithering
    • G09G3/2051—Display of intermediate tones using dithering with use of a spatial dither pattern
    • 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
    • G09G3/207—Display of intermediate tones 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
    • 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
    • G09G3/2074—Display of intermediate tones using sub-pixels

Definitions

  • the present invention relates to a method of and apparatus for addressing a ferroelectric liquid crystal device (FLCD) and to an FLCD.
  • FLCDs may be used to provide high resolution display panels, for instance for use in personal computers and high definition television (HDTV).
  • FLCD display panels comprise rows and columns of picture elements (pixels) provided with row and column electrodes for passive matrix addressing.
  • Strobe signals are supplied in sequence to the row electrodes whereas data signals are supplied simultaneously and in synchronism with the strobe signals to the column electrodes.
  • the display is refreshed by writing display data to the pixels a row at a time. Once a complete frame of image data has been supplied, the process is repeated.
  • Such drive schemes rely on the bistability of the ferroelectric liquid crystal (FLC) to retain the image data i.e. the desired optical state, between consecutive pixel refreshes.
  • FLC ferroelectric liquid crystal
  • each row refresh cycle uses a strobe signal which comprises a blanking pulse for resetting all the pixels of the row to a predetermined state, such as maximally opaque (black) or maximally transparent (white), followed by a strobe pulse which is simultaneous with data pulses of the data signals on the column electrodes.
  • a strobe signal which comprises a blanking pulse for resetting all the pixels of the row to a predetermined state, such as maximally opaque (black) or maximally transparent (white), followed by a strobe pulse which is simultaneous with data pulses of the data signals on the column electrodes.
  • Various addressing or drive schemes are known for achieving this.
  • JP-HO 6-1309 and GB2249653A disclose drive schemes in which an additional pulse is provided between the blanking pulse and the strobe or main switching pulse. The purpose of the additional pulse is to improve switching times for black and white i.e. two grey level displays in which each pixel has a single switching threshold.
  • WO 95/27971 also discloses a drive
  • FLCDs are prime contenders for use in HDTV panels and high resolution display applications, particularly because of the rapid refresh rates which can be achieved and which allow such panels to operate at video speeds.
  • such applications require the production of grey levels, for instance a minimum of 256 grey levels for HDTV.
  • Digital techniques known as spatial dither and temporal dither have been used to produce grey levels but, even when used in combination, have been limited to 64 grey levels in practical display panels.
  • FLCDs having two or more different threshold levels within each pixel have been proposed, for instance in JPS 62-145216 and in P.W. Ross et al, SID International Symposium, Digest of Technical Papers, 147, XXV, 1994.
  • the different threshold levels are achieved by subdividing each pixel into subpixels of different cell thickness.
  • a method of addressing a ferroelectric liquid crystal device picture element having a plurality of switching thresholds corresponding to a plurality of grey levels comprising applying to the picture element an electric field having a resetting pulse of a first polarity for resetting the picture element to a reset grey level, a compensating pulse of a second polarity opposite the first polarity for reducing ⁇ min shift, and a waveform for achieving a selected grey level.
  • the RMS voltage of the compensating pulse may be less than the RMS voltage of the resetting pulse.
  • the reset grey level may be a maximally opaque level of the picture element.
  • the reset grey level may be a maximally transparent level of the picture level.
  • the method may be used for a device of the type comprising a plurality of picture elements arranged as rows and columns, strobe signals may be applied in turn to the rows and data signals may be supplied simultaneously to the columns in synchronism with the strobe signals for simultaneously selecting the selected grey levels of the picture elements of each row.
  • Each strobe signal may comprise the resetting pulse, the compensating pulse and a strobe pulse.
  • the strobe pulse may be of the second polarity.
  • the or each picture element may comprise a plurality of regions having the plurality of switching thresholds.
  • the regions may be of different thicknesses.
  • an apparatus for addressing a ferroelectric liquid crystal device picture element having a plurality of switching thresholds corresponding to a plurality of grey levels comprising a waveform generator for applying to the picture element an electric field, characterised in that the waveform generator is arranged to apply an electric field having a resetting pulse of a first polarity for resetting the picture element to a reset grey level, a compensating pulse of a second polarity opposite the first polarity for reducing ⁇ min shift, and a waveform for achieving a selected grey level.
  • a ferroelectric liquid crystal device characterised by comprising an apparatus according to the second aspect of the invention, in which the or each picture element comprises a plurality of regions having the plurality of switching thresholds.
  • the regions may be of different thicknesses.
  • the device may be of passive matrix type.
  • analogue grey levels are required to produce 256 grey levels for each pixel.
  • the four analogue grey levels can be achieved and reliably addressed by means of the present drive scheme. It is thus possible to produce display panels which are suitable for use in HDTV and in high resolution displays operating at video rates.
  • Figure 1 shows an FLCD display panel comprising a 4x4 array of pixels.
  • a 4x4 array of pixels.
  • such a display would comprise many more pixels arranged as a square or rectangular matrix but a 4x4 array has been shown for the sake of simplicity of description.
  • the display panel comprises four column electrodes 1 connected to respective outputs of a data signal generator 2 so as to receive data signals Vd1 to Vd4.
  • the generator 2 has a data input 3 for receiving data to be displayed, for instance one row at a time.
  • the generator 2 has a synchronising input 4 for receiving timing signals so as to control the timing of the supply of the data signals Vd1 to Vd4 to the column or data electrodes 1.
  • the display further comprises four row electrodes 5 connected to respective outputs of a strobe signal generator 6 so as to receive respective strobe signals Vs1 to Vs4.
  • the generator 6 has a synchronising input which is also connected to receive timing signals for controlling the timing of supply of the strobe signals Vs1 to Vs4 to the row or strobe electrodes 5.
  • the display further comprises an FLC arranged as a layer between the data electrodes 1 and the strobe electrodes 5.
  • the FLC has negative dielectric anisotropy and has a minimum in its ⁇ -V characteristic.
  • the intersections between the data and strobe electrodes define individual pixels which are addressable independently of each other.
  • the FLC is bistable and the display is of the passive matrix addressed type.
  • One of the pixels of the display shown in Figure 1 is shown in Figure 2 in more detail.
  • the pixel is divided into subpixels shown as first and second regions 7 and 8, although each pixel may be divided into more than two subpixels.
  • the first and second regions 7 and 8 are of different thicknesses so as to have different switching thresholds.
  • Such an arrangement allows an additional grey level to be provided by a technique known as the Multi-Threshold Modulation (MTM) method.
  • MTM Multi-Threshold Modulation
  • the regions 7 and 8 are of different thicknesses. However, any technique may be used for achieving different switching characteristics in the regions 7 and 8.
  • Figure 3 illustrates the switching characteristics of the first and second regions by unbroken and broken lines forming ⁇ -V curves 9 and 10, respectively, where ⁇ is the length of a switching signal and V is the amplitude of the switching signal.
  • ⁇ is the length of a switching signal
  • V is the amplitude of the switching signal.
  • the first region 7 is switched to one of its stable states whereas, for switching signals below the curve 9, the first region 7 remains in its other stable state.
  • the switching characteristic for the second region 8 is of the same type. Accordingly, for a switching signal whose period and amplitude are in a region 11 which is above the curve 9 and below the curve 10, the first region 7 switches but the second region 10 does not switch. Similarly, for the region 12, the second region 8 switches but the first region 7 does not.
  • both of the regions 7 and 8 switch.
  • neither of the regions 7 and 8 switches.
  • the first and second regions 7 and 8 are of the same area, it is possible to select independently three grey levels corresponding to "black”, "white”, and an intermediate grey level. For instance, waveforms whose ⁇ and V fall within the regions 14, 13 and 11 would achieve this. If the regions 7 and 8 are of different areas, an additional intermediate grey level may be achieved by also using the area 12 of the ⁇ -V plane illustrated in Figure 3.
  • one technique for achieving MTM is for the regions such as 7 and 8 to be of different thicknesses.
  • the difference between the applied voltages for switching regions of different thicknesses is almost proportional to the difference in thicknesses.
  • varying the thickness of the pixel region results in a Vmin shift in the ⁇ -V plane as illustrated in Figure 3.
  • Figure 5 illustrates data and strobe signals which achieve this performance
  • Figure 6 shows actual experimental results achieved by the waveforms shown in Figure 5 for a standard test cell comprising parallel-rubbed aligning layers to provide approximately 5 degrees of surface tilt and ferroelectric liquid crystal type FLC-1 of negative dielectric anisotropy developed by Sharp K.K. in Japan.
  • the ⁇ -V curves shown in Figures 3 and 4 are represented by single lines, the ⁇ -V curves actually comprise two curves which are referred to as the 0% curve and the 100% curve.
  • the pixel begins to switch at some point, which defines the 0% curve.
  • the switched area of the pixel increases until finally the whole area of the pixel is switched to give the 100% curve.
  • driving conditions i.e. combinations of pulse width and pulse height
  • driving conditions below the 0% curve give non-switching.
  • the pixel is not switched at all under driving conditions below the 0% curve for the worst data voltage.
  • applying driving conditions above the 100% curve for the best data ensures that the pixel is totally switched.
  • a blanking pulse is provided before the main switching or strobe pulse. All the pixels of the line currently being strobed are thus reset to a fully switched state by the blanking pulse. Following this, the resultant between the main or strobe pulse and the data voltage during the selected period results in the desired grey level of the pixel being selected.
  • the blanking pulse is necessary in order to ensure reliability of selection of the grey levels.
  • FIG. 7 illustrates the waveform of a strobe signal having no banking pulse but having main switching on strobe pulses of amplitude Vs or -Vs having a duration of two slot widths.
  • Figure 8 illustrates typical ⁇ -V curves of thinner and thicker regions with each pixel comprising one of each. Thus, only Vmin is changed by variation of the thickness.
  • Figure 9 illustrates a waveform having the same "monopulse" as in Figure 7 but having a preceding blanking pulse of amplitude -1 ⁇ 2Vs and duration of four slot widths.
  • the ⁇ -V curves for this waveform are shown in Figure 10, from which it is apparent that not only does Vmin shift but ⁇ min also shifts.
  • the ⁇ -V characteristic is modified. As shown in Figure 11(b), the minimum switching time is increased, whilst the voltage at which the switching time is a minimum is decreased. To prevent the minimum switching time being increased in this way, it is usual to provide a large time interval (for example, at least ten times greater than the line address time between the blanking pulse and the switching pulse.
  • the ⁇ min in the thicker region is larger than that in the thinner region.
  • some driving conditions such as those including blanking pulses cause ⁇ min to shift also.
  • the drive window 13 for the intermediate grey level is substantially reduced and in fact may disappear because of the ⁇ min shift effect.
  • the presence of the blanking pulses causes the unexpected ⁇ min shift which makes the driving window 13 narrower. This is particularly apparent from comparing Figure 12 with Figure 4, which illustrates the driving window 13 in the absence of such ⁇ min shift.
  • a compensating pulse of opposite polarity to the blanking pulse is provided between the blanking pulse and the strobe or main switching pulse. It has been found that the presence of such a compensating pulse increases the width of the drive window 13 for intermediate grey levels as compared with the use of a blanking pulse without the compensating pulse.
  • Figure 13 illustrates at A a conventional waveform for a strobe signal having a strobe pulse of amplitude Vs occupying two time slots and a preceding blanking pulse of amplitude -1 ⁇ 2Vs occupying four time slots.
  • Figure 13 shows at B a strobe signal which differs from that shown at A in that the blanking pulse is extended forward by two time slots and a compensating pulse 20 of amplitude Vs and occupying one time slot immediately follows the blanking pulse.
  • Figure 14 shows at C another strobe signal which differs from that shown at A by the provision of the compensating pulse 20 of amplitude Vs occupying one time slot.
  • the strobe waveform shown at B is DC balanced whereas that shown at C is unbalanced.
  • the waveform shown at C may have a small DC offset during part or all of a frame.
  • the waveform shown at C may be inverted in alternate frame refresh cycles for each row.
  • Figure 14 illustrates the effective electric field across a pixel corresponding to the use of the strobe signals shown in Figure 13 together with a data signal of the type having an amplitude Vd and a positive value in the two time slots before the strobe pulse and a negative value in the two time slots occupied by the strobe pulse.
  • These waveforms correspond to a so-called switching pulse in the JOERS/ALVEY driving scheme referred to hereinbefore.
  • These waveforms were used to measure the ⁇ -V curves for FLC cells showing different thickness variations.
  • a cell A had two regions of different thickness, one having a thickness of 1 micrometer and the other a thickness of 1.4 micrometer.
  • a cell B had a region of thickness 1 micrometer and another region of thickness 1.8 micrometer.
  • the cells A and B were parallel-rubbed to provide approximately 5 degrees of surface tilt.
  • the FLC material used in the cells was material known as FLC-1 of negative dielectric anisotropy developed by Sharp K.K. in Japan.
  • Figure 15 illustrates data and strobe signals for achieving three grey levels in a pixel of the type shown in Figure 2 having two MTM regions.
  • the strobe signal labeled "strobe (a)” is of the conventional blanking pulse type whereas the strobe signal labelled "strobe (b)” is of the type in which the blanking pulse is followed by a compensating pulse.
  • These signals were applied to an FLC cell containing FLC-1 and parallel-rubbed to provide approximately 5 degrees of surface tilt.
  • the thinner region of the cell or pixel was 1 micrometre thick whereas the thicker region was 1.4 micrometre thick.
  • the measured ⁇ -V curves shown in Figures 16(a) and (b) correspond to the use of the strobe (a) and strobe (b) waveforms, respectively, shown in Figure 15.
  • the driving window for the conventional strobe waveform without the compensating pulse is very narrow so that reliable switching to the intermediate grey level would be difficult to achieve.
  • the use of the compensating pulse 20 results in a much wider driving window for the intermediate grey level, which can therefore be more reliably selected.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Computer Hardware Design (AREA)
  • Liquid Crystal Display Device Control (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)
  • Liquid Crystal (AREA)
EP97307638A 1996-09-30 1997-09-29 Verfahren und Einrichtung zum Adressieren einer ferroelektrischen Flüssigkristallanzeige und eine ferroelektrische Flüssigkristallanzeige Withdrawn EP0838802A3 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9620395A GB2317735A (en) 1996-09-30 1996-09-30 Addressing a ferroelectric liquid crystal display
GB9620395 1996-09-30

Publications (2)

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EP0838802A2 true EP0838802A2 (de) 1998-04-29
EP0838802A3 EP0838802A3 (de) 1998-07-29

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EP97307638A Withdrawn EP0838802A3 (de) 1996-09-30 1997-09-29 Verfahren und Einrichtung zum Adressieren einer ferroelektrischen Flüssigkristallanzeige und eine ferroelektrische Flüssigkristallanzeige

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EP (1) EP0838802A3 (de)
JP (1) JPH10153762A (de)
KR (1) KR100236433B1 (de)
GB (1) GB2317735A (de)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6914589B2 (en) * 2001-10-13 2005-07-05 Lg. Philips Lcd Co., Ltd. Method of driving ferroelectric liquid crystal display
WO2011117192A1 (en) 2010-03-22 2011-09-29 Carlsberg Breweries A/S A method and apparatus of cleaning and flushing a beverage dispensing system

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4712877A (en) * 1985-01-18 1987-12-15 Canon Kabushiki Kaisha Ferroelectric display panel of varying thickness and driving method therefor
GB2271011A (en) * 1992-09-23 1994-03-30 Central Research Lab Ltd Greyscale addressing of ferroelectric liquid crystal displays.
EP0621580A1 (de) * 1993-04-20 1994-10-26 Canon Kabushiki Kaisha Ansteuerungsverfahren für eine Flüssigkristall-Vorrichtung
US5469281A (en) * 1992-08-24 1995-11-21 Canon Kabushiki Kaisha Driving method for liquid crystal device which is not affected by a threshold characteristic change
EP0710945A2 (de) * 1994-11-01 1996-05-08 Sharp Kabushiki Kaisha Verfahren und Einrichtung zum Steuern einer ferroelektrischen Flüssigkristallanzeige

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB9407116D0 (en) * 1994-04-11 1994-06-01 Secr Defence Ferroelectric liquid crystal display with greyscale

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4712877A (en) * 1985-01-18 1987-12-15 Canon Kabushiki Kaisha Ferroelectric display panel of varying thickness and driving method therefor
US5469281A (en) * 1992-08-24 1995-11-21 Canon Kabushiki Kaisha Driving method for liquid crystal device which is not affected by a threshold characteristic change
GB2271011A (en) * 1992-09-23 1994-03-30 Central Research Lab Ltd Greyscale addressing of ferroelectric liquid crystal displays.
EP0621580A1 (de) * 1993-04-20 1994-10-26 Canon Kabushiki Kaisha Ansteuerungsverfahren für eine Flüssigkristall-Vorrichtung
EP0710945A2 (de) * 1994-11-01 1996-05-08 Sharp Kabushiki Kaisha Verfahren und Einrichtung zum Steuern einer ferroelektrischen Flüssigkristallanzeige

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6914589B2 (en) * 2001-10-13 2005-07-05 Lg. Philips Lcd Co., Ltd. Method of driving ferroelectric liquid crystal display
WO2011117192A1 (en) 2010-03-22 2011-09-29 Carlsberg Breweries A/S A method and apparatus of cleaning and flushing a beverage dispensing system

Also Published As

Publication number Publication date
KR19980025163A (ko) 1998-07-06
GB2317735A (en) 1998-04-01
KR100236433B1 (ko) 2000-07-01
JPH10153762A (ja) 1998-06-09
GB9620395D0 (en) 1996-11-13
EP0838802A3 (de) 1998-07-29

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