WO1999065013A1 - Procede d'attaque pour un afficheur a cristaux liquides - Google Patents

Procede d'attaque pour un afficheur a cristaux liquides Download PDF

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Publication number
WO1999065013A1
WO1999065013A1 PCT/US1999/012521 US9912521W WO9965013A1 WO 1999065013 A1 WO1999065013 A1 WO 1999065013A1 US 9912521 W US9912521 W US 9912521W WO 9965013 A1 WO9965013 A1 WO 9965013A1
Authority
WO
WIPO (PCT)
Prior art keywords
electric field
liquid crystal
pixel
crystal display
pulsed
Prior art date
Application number
PCT/US1999/012521
Other languages
English (en)
Inventor
Mark R. Munch
Murthy Simhambhatla
Original Assignee
Tyco Electronics Corporation
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Tyco Electronics Corporation filed Critical Tyco Electronics Corporation
Publication of WO1999065013A1 publication Critical patent/WO1999065013A1/fr

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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
    • G09G3/3611—Control of matrices with row and column drivers
    • G09G3/3648—Control of matrices with row and column drivers using an active matrix
    • 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
    • G09G3/2011—Display of intermediate tones by amplitude modulation
    • 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

Definitions

  • the present invention relates to a method of driving a liquid crystal display to improve its gray scale switching speed.
  • High resolution, high speed liquid crystal displays for depicting graphical or linguistic information comprise many pixels, each of which may be driven or controlled by an active matrix element such as a transistor.
  • Illustrative publications relating to such displays include Edmonds, US 3,832,034 (1974); Hamaguchi, US 4,838,654 (1989); Bowman et la., US 4,910,579 (1990); Shannon, US 4,931,787 (1990); Te Velde, US 5,005,951 (1991); Flasck, US 5,022,750 (1991); Flasck, US 5,024,524 (1991); Flasck, US 5,108,172 (1992); Kamath et al., US 5,233,445 (1993); IBM, EP 0,112,417 (1984); N.V.
  • the active matrix elements are disposed in an array, each element helping define a pixel and controlling the optical state of liquid crystal material associated therewith.
  • a voltage electric field
  • the liquid crystal material is switched from one optical state to another.
  • a pixel in the "field-on" state may permit incident light to be transmitted through the liquid crystal material and to be specularly reflected by a reflector positioned behind it, back towards the incidence side (albeit angularly displaced by operation of the laws of reflection), while a pixel in the "field-off state may prevent such reflection by scattering or absorbing the light.
  • the optical effect is associated with a reorientation of the alignment directors of the liquid crystal material.
  • the combination of many "on” and “off pixels generates an image that can be viewed directly, or projected onto a screen for viewing, or viewed as a virtual image with the aid of appropriate optics.
  • the display present a gray scale image, in which pixels are not either entirely “on” or “off but only partially so, with the result that an image having subtle shades of gray is presented, instead of a stark black-and-white image.
  • FIG. 1 A schematic illustration is shown in Fig. 1, in the form of a simplified liquid crystal display 1 consisting of four pixels 2a, 2b, 2c, and 2d.
  • Pixel 2a is in the "field-off state and is, in this depiction, arbitrarily shown as white.
  • Pixel 2d is in the full "field-on” state and is shown arbitrarily as black.
  • Pixels 2b and 2c are in intermediate switching states, corresponding to respective intermediate voltages that are non-zero but are less than the "field-on” voltage, and have progressively darker gray tones (the voltage applied to pixel 2c being greater than that applied to pixel 2b). (The electric field experienced by the hquid crystal material depends on the applied voltage and the thickness of the hquid crystal material.
  • Fig. 1 illustrates this relationship for one type of hquid crystal material, a liquid crystal composite comprising plural volumes or droplets of liquid crystals contained within a polymer matrix, such as disclosed in Fergason, US 4,435,047 (1984).
  • gray scale response can be much slower than full off/on response.
  • the time needed for a pixel to switch from the field-off optical state to the intermediate optical state corresponding to 2.5 volts is about 1,100 msec, compared to the 100 msec required for full field-on switching at about 4.0 volts.
  • this invention provides a method of driving a pixel in a liquid crystal display having a plurality of pixels, comprising the steps of: a. providing a liquid crystal display comprising a plurality of pixels comprising liquid crystal material and having a plurality of optical states that differ in their transmittivities to incident light as a function of the electric field to which the liquid crystal material is subjected; b. selecting a pixel to be driven, the pixel being at a first optical state Pi and the liquid crystal material therein being subjected to a corresponding first electric field Ei; c. selecting, for the pixel, a desired second optical state P 2 and a corresponding second electric field E 2 , wherein d. subjecting the liquid crystal material of the pixel to a pulsed electric field Ep wherein
  • Fig. 1 shows a liquid crystal display having four pixels displaying varying degrees of a gray scale.
  • Fig. 2 shows how the gray scale response time of a liquid crystal display varies with the applied electric field.
  • Fig. 3a illustrates the pulsed driving method of this invention.
  • Fig. 3b shows how the pulsed driving method of this invention lowers the switching time of a liquid crystal display.
  • Fig. 4 shows an embodiment of this invention with a fixed pulse duration but a variable pulse amplitude.
  • Fig. 5 shows an alternative embodiment of this invention with a variable pulse duration but a fixed pulse amplitude.
  • Figs. 3a and 3b show how the driving method of this invention leads to lower switching times (i.e., faster switching speeds or responses) in a gray scale liquid crystal display.
  • the figures depict, plotted against a common time X-axis, the electric field applied to a pixel of a liquid crystal display (Fig. 3a) and the pixel's optical state (Fig. 3b).
  • the pixel is initially at a first optical state Pi corresponding to a first electric field Ei.
  • the scale of the electric field axis in Fig. 3a is arbitrary, so first electric field Ei can be zero (i.e., no electric field has been applied and the pixel is in the field-off state), or it can be nonzero (i.e., the pixel is at an intermediate gray scale state).
  • a pulsed electric field Ep is applied the pixel, the pulsed electric field being greater than second electric field E2. Then, the electric field applied to the pixel is reduced to second electric field E2, corresponding to the desired second optical state P 2 .
  • the application of pulsed electric field Ep has the effect of giving the pixel a greater initial switching impetus towards second optical state P2, although the equilibrium optical state eventually reached is that determined by the second electric field E2, namely P 2 . The result is that the pixel reaches second optical state P2 faster, as shown by curve B of Fig. 3b.
  • pulsed electric field Ep If the amphtude of pulsed electric field Ep is increased, the boost in initial switching impetus is greater, resulting in even faster switching. This effect is illustrated by curve C in Fig. 3b, where the pulsed electric field Ep applied is greater in the instance of curve C than in the instance of curve B.
  • the waveform of pulsed electric field Ep is not critical, although a rectangular waveform is typical. Its duration (indicated as Tp in Figs. 3a and 3b) is preferably between 1 and 16 msec.
  • Curve D in Fig. 3b illustrates an overshoot situation that is preferably avoided.
  • the amphtude and duration of pulsed electric field Ep are such that the optical state of the pixel passes beyond P2 before returning to P2. While a modest overshoot (for example, preferably less than about 10% and more preferably less than about 5%) is not detrimental, a significant overshoot can be optically noticeable and is therefore undesirable.
  • the duration of the pulsed electric field Ep no greater than the time required for the pixel to switch from first optical state Pi to second optical state P2 when subjected to the pulsed electric field Ep.
  • the duration of the pulsed electric field Ep no greater than the time required for the pixel to switch from first optical state Pi to second optical state P2 when subjected to the pulsed electric field Ep.
  • Tp is the duration of the pulse of pulsed electric field Ep and T(P, ⁇ P 2 ) L is the time required for the pixel's optical state to transition from Pi to P2 under an applied electric field equal in amplitude to Ep.
  • Fig. 4 shows how a pulse of constant duration (15 msec) but varying amplitude can be used to increase gray-scale switching speed.
  • the solid line represents the calculated optical response upon the application of a voltage equal to second electric field E 2
  • the dotted line represents the calculated optical response upon the application of a pulsed driving method according to this invention.
  • the pixel's switching time under a given set of conditions may be approximated as the time taken for the optical response to reach the "knee" of a curve.
  • Line E links the switching times for the instances in which no pulsing is employed (i.e., conventional driving) and line F links the switching times needed to reach the same optical response when pulsing is employed.
  • Switching times read from Fig. 4 is tabulated in Table IA below.
  • switching speed is defined as the time required for the transmission to increase from
  • Table IB provides information on the switching speed using this alternative definition (referred to herein as the ⁇ o. ⁇ -o.9 switching speed):
  • Fig. 5 shows an alternative embodiment of the invention, in which the pulse amplitude is held constant, but the pulse duration is varied for different second electric fields E2.
  • Curves sets VI through X correspond to increasing second electric fields E2 (with the solid and dotted lines having the significance as in Fig. 4).
  • Line G connects the switching times in the absence of pulsing, while line H connects the switching times with pulsing.
  • Table IIA Relevant information on switching speed improvement under constant - amplitude pulsing is provided in Tables IIA (using the "knee” definition) and IIB (using the ⁇ o.1-0.9 definition). Table IIA
  • Tables IIA and IIB are generally similar to those shown in Tables LA and IB.
  • Tables IA/B and IIA/B in combination show that the benefits of pulsed driving are available either in a constant pulse duration/variable pulse amplitude embodiment, or in a variable pulse duration/constant amplitude embodiment.
  • the extent of the pulsing effect depends on the pulse duration and the pulse amplitude.
  • the advantages of this invention are most noticeable in the middle of the gray scale range. If Es is the saturation electric field, corresponding to a full "field-on" optical effect, then it is preferred that
  • hquid crystal display for which the present invention is especially suitable employs a liquid crystal composite comprising plural volumes (or droplets) of liquid crystals contained (i.e., dispersed, encapsulated, or embedded) within a polymer matrix.
  • liquid crystal composites have been referred to in the art alternatively as encapsulated liquid crystal material, nematic curvilinear aligned nematic (NCAP) materials or as polymer dispersed hquid crystal (PDLC) materials.
  • Exemplary disclosures include Fergason, US 4,435,047 (1984); West et al., US 4,685,771 (1987); Pearlman, US 4,992,201 (1991); Andrews et al., US 5,202,063 (1993); Kamath et al., US 5,233,445 (1993); Reamey, US 5,328,850 (1994); Reamey et al., US 5,405,551 (1995); Wartenberg et al., US 5,427,713 (1995); Reamey et al., US 5,543,944 (1996): Havens et al., US 5,585,947 (1996); Cao et al., US 5,738,804 (1998); Raychem WO 96/19547 (1996); and Dainippon Ink, EP 0,313,053 (1989); the disclosures of which are incorporated herein by reference.
  • such composites are light scattering and/or absorbing in the absence of a sufficient electric field (the field-off state), but are substantially light transmissive in the presence of such electric field (the field-on state).
  • the present invention is particularly advantageous with NCAP/PDLC materials, as they are susceptible to stress-whitening even at fairly low stress levels.

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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 (AREA)

Abstract

Procédé d'attaque amélioré permettant d'augmenter la vitesse de commutation d'afficheurs à cristaux liquides à échelle de gris. L'application d'un champ électrique pulsé supérieur au champ électrique final désiré au début du cycle d'attaque permet de provoquer une amplification de l'impulsion de commutation initiale qui augmente la vitesse de commutation.
PCT/US1999/012521 1998-06-10 1999-06-04 Procede d'attaque pour un afficheur a cristaux liquides WO1999065013A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US9517798A 1998-06-10 1998-06-10
US09/095,177 1998-06-10

Publications (1)

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WO1999065013A1 true WO1999065013A1 (fr) 1999-12-16

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002086607A1 (fr) 2001-04-20 2002-10-31 Sony Corporation Dispositif electrique de gradation de lumiere et son procede d'entrainement
WO2006114732A1 (fr) * 2005-04-26 2006-11-02 Koninklijke Philips Electronics N.V. Ecrans a cristaux liquides pourvus de mecanismes d'actionnement sequentiel

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4435047A (en) * 1981-09-16 1984-03-06 Manchester R & D Partnership Encapsulated liquid crystal and method
WO1987001468A1 (fr) * 1985-09-06 1987-03-12 Consolidated Technology Pty. Ltd. Procede et appareil de commande d'un dispositif a cristaux liquides
US5521611A (en) * 1992-10-30 1996-05-28 Sharp Kabushiki Kaisha Driving circuit for a display apparatus

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4435047A (en) * 1981-09-16 1984-03-06 Manchester R & D Partnership Encapsulated liquid crystal and method
WO1987001468A1 (fr) * 1985-09-06 1987-03-12 Consolidated Technology Pty. Ltd. Procede et appareil de commande d'un dispositif a cristaux liquides
US5521611A (en) * 1992-10-30 1996-05-28 Sharp Kabushiki Kaisha Driving circuit for a display apparatus

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002086607A1 (fr) 2001-04-20 2002-10-31 Sony Corporation Dispositif electrique de gradation de lumiere et son procede d'entrainement
EP1380875A1 (fr) * 2001-04-20 2004-01-14 Sony Corporation Dispositif electrique de gradation de lumiere et son procede d'entrainement
EP1380875A4 (fr) * 2001-04-20 2006-08-02 Sony Corp Dispositif electrique de gradation de lumiere et son procede d'entrainement
US7230598B2 (en) 2001-04-20 2007-06-12 Sony Corporation Electric dimming device and its driving method
KR100852720B1 (ko) 2001-04-20 2008-08-19 소니 가부시끼 가이샤 전기조광소자 및 그 구동방법
WO2006114732A1 (fr) * 2005-04-26 2006-11-02 Koninklijke Philips Electronics N.V. Ecrans a cristaux liquides pourvus de mecanismes d'actionnement sequentiel

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