EP2178079A1 - Energiesparendes Verfahren zum Markieren eines Bereichs eines Flüssigkristallbildschirms - Google Patents

Energiesparendes Verfahren zum Markieren eines Bereichs eines Flüssigkristallbildschirms Download PDF

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Publication number
EP2178079A1
EP2178079A1 EP08290975A EP08290975A EP2178079A1 EP 2178079 A1 EP2178079 A1 EP 2178079A1 EP 08290975 A EP08290975 A EP 08290975A EP 08290975 A EP08290975 A EP 08290975A EP 2178079 A1 EP2178079 A1 EP 2178079A1
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EP
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Prior art keywords
signal
pixel
state
zone
stable
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EP08290975A
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English (en)
French (fr)
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EP2178079B1 (de
Inventor
Ivan Dozov
François Leblanc
Jean-Denis Laffite
Stéphane Joly
Philippe Martinot-Lagarde
Jacques Angele
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France Brevets SAS
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Nemoptic SA
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Priority to EP08290975.5A priority Critical patent/EP2178079B1/de
Priority to PCT/FR2009/001190 priority patent/WO2010043780A1/fr
Priority to US13/698,987 priority patent/US20130076610A1/en
Priority to TW098134864A priority patent/TW201033985A/zh
Publication of EP2178079A1 publication Critical patent/EP2178079A1/de
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Publication of EP2178079B1 publication Critical patent/EP2178079B1/de
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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
    • 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
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2300/00—Aspects of the constitution of display devices
    • G09G2300/04—Structural and physical details of display devices
    • G09G2300/0469—Details of the physics of pixel operation
    • G09G2300/0478—Details of the physics of pixel operation related to liquid crystal pixels
    • G09G2300/0482—Use of memory effects in nematic liquid crystals
    • G09G2300/0486—Cholesteric liquid crystals, including chiral-nematic liquid crystals, with transitions between focal conic, planar, and homeotropic states
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2310/00—Command of the display device
    • G09G2310/06—Details of flat display driving waveforms
    • 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
    • G09G5/00—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators
    • G09G5/08—Cursor circuits

Definitions

  • the invention relates to a method of addressing a liquid crystal display screen and a display device implementing this method.
  • the present invention relates to liquid crystal bistable displays. It is particularly applicable to nematic liquid crystal bistable displays whose two stable textures differ by a twist of about 180 °.
  • the thickness of the cell thus formed is made constant for example by distributing, between the blades, beads whose diameter is equal to the desired thickness (typically 1 to 6 microns).
  • Monostable liquid crystal devices are known. In the absence of an electric field, the liquid crystal is oriented in a single texture. This texture corresponds to an absolute minimum of the elastic energy of the liquid crystal in the cell, given the anchors on the two blades. Under an electric field, this texture is continuously deformed and its optical properties vary according to the applied voltage.
  • Anchoring layers maintain the direction of the molecules near the blades, which varies little, both in the plane of the substrate (azimuth plane) and in the direction perpendicular to it (direction zenithale): a strong anchoring of the molecules near the blades on the alignment layer corresponds to a strong azimuthal anchoring (maintaining a fixed direction in the plane of the substrate) and a strong zenith anchorage (maintaining a direction close to the plane substrate, that is to say, little or no lifting molecules to the direction perpendicular to the substrate, parallel to the electric field, and whatever the voltage applied).
  • the nematic is recalled by the anchors on the two blades. It returns according to the unique stable texture without applied field.
  • the device is monostable.
  • TN twisted nematic
  • STN supertordus
  • EOB electrically controlled birefringence
  • VAN vertically aligned
  • these displays can be addressed directly (very low resolution), in passive multiplexed mode (medium resolution) or in active mode (high resolution).
  • the addressing signals When the addressing is multiplexed, that is to say carried out line by line, for the image to appear visually stable, the addressing signals must be sent at a frequency of several tens of hertz: as soon as the pixel is no longer energized, it relaxes to the stable state without an applied field.
  • the object of the present invention is to improve the performance of liquid crystal display devices.
  • the object of the invention is to make it possible, by the use of new means, to mark part or all of the information displayed on a liquid crystal display, while maintaining a reduced energy consumption compared to that of a standard liquid crystal display.
  • steps A and B are preferably spaced apart by a duration less than a duration of retinal persistence of the observer, so as to obtain a visual effect of static marking of the zone.
  • the method according to the invention may further comprise a displacement of the pixel area on the screen between at least two iterations of steps A and B.
  • the pixels of the layer are preferably arranged in lines of parallel pixels and parallel columns of pixels, the lines being substantially perpendicular to the columns.
  • the perturbation signal applied to a pixel preferably comprises a column signal applied to the column on which this pixel is situated and furthermore preferably comprises a line signal applied to the line on which this pixel is situated, this perturbation signal being of preference proportional or equal to a difference between the column signal and the line signal.
  • the area may comprise a set of adjacent lines or a set of adjacent columns.
  • the area may include an intersection of a set of adjacent lines and a set of adjacent columns.
  • the two stable states preferably comprise a blocking state and an on state, the on state having a luminance (Lib) perceived by the observer greater than the luminance (Lid) of the blocking state, the disturbed state of a pixel initially in the on state having a luminance (Lpb) perceived by the observer lower by at least 5% with respect to the luminance (Lib) of the initial state passing from this pixel.
  • the on state having a luminance (Lib) perceived by the observer greater than the luminance (Lid) of the blocking state
  • the disturbed state of a pixel initially in the on state having a luminance (Lpb) perceived by the observer lower by at least 5% with respect to the luminance (Lib) of the initial state passing from this pixel.
  • the disturbance signal may comprise an electrical signal having an RMS value of voltage greater than 1.65 times a Freedericksz voltage of the liquid crystal layer.
  • the disturbance signal is preferably bipolar.
  • the pixels are arranged in parallel pixel lines and parallel pixel columns, the lines being substantially perpendicular to the columns.
  • the liquid crystal of the layer is of the nematic type.
  • the liquid crystal layer is placed between two blades, the assembly constituting a liquid crystal cell.
  • Each blade comprises a substrate, preferably made of glass, on which a conductive electrode has been deposited, followed by a so-called anchoring layer, also called a layer. alignment.
  • the anchoring layer exerts on the neighboring liquid crystal molecules a return torque which tends to orient them parallel to a direction called easy axis.
  • the anchoring layers are preferably made by a brushed polymer deposit to create the direction of the easy axis. This direction of the easy axis is preferably very close to the brushing direction.
  • the thickness of the cell thus formed (that is to say the distance between the blades between which is included the liquid crystal layer), called d, is made constant for example by distributing, between the blades, balls of which the diameter is equal to the desired thickness (typically 1 to 6 ⁇ m).
  • the liquid crystal of the layer is "bistable": this type of liquid crystal operates by switching between two stable states in the absence of an electric field. An external electric field is applied only for the time necessary to switch the texture of the liquid crystal from one state to another. In the absence of an electrical control signal, the display remains in the state obtained. By its operating principle, this type of display consumes energy proportional to the number of image changes. Thus, when the frequency of these changes decreases, the power required for the operation of the display tends to zero.
  • the figure 1 illustrates, for the first embodiment of the device according to the invention, two different states of a liquid crystal pixel between two portions of the blades.
  • This first mode uses a flexo-electric effect to switch, that is to say the sign of the applied electric field. This is the pretilt, ie the angle that the liquid crystal molecule close to the surface with it, which varies between two stable values without applied field.
  • This bistability is obtained using a network serving as alignment layer (cf documents [1], [2], [3] and figure 1 ).
  • This technology is called ZBD (Zenithal Bistable Display).
  • One of the alignment layers is constituted by a periodic network allowing the vicinity of the surface of this network two orientations of the liquid crystal molecules, one planar, the other homeotropic.
  • the figure 2 is a sectional and sectional view of a portion of the liquid crystal cell of the second device embodiment according to the invention.
  • This second bistable embodiment uses a surface effect: a break of the zenith anchorage on at least one of the alignment layers. This break allows switching between two textures whose torsions differ by an angle between 150 ° and 180 ° in absolute value.
  • BiNem The operation of this display called BiNem is described in the following paragraph.
  • the BiNem display (documents [4] to [8]) is schematically presented on the figure 2 , and has a general configuration identical to that of the liquid crystal cell type ZBD which also uses substrates, electrodes, polarizers, liquid crystal.
  • the BiNem display preferably uses two twisted textures that differ by a twist of approximately +/- 180 ° (located in absolute value between 150 ° and 180 °).
  • a preferred but nonlimiting variant consists of a uniform or slightly twisted texture called U (illustrated on the left of the figure 2 ) in which the molecules are substantially parallel to each other, and of a strongly twisted texture called T (illustrated on the right of the figure 2 ).
  • the least twisted U texture has a twist between 0 ° and 20 ° in absolute value.
  • the liquid crystal layer 30 is placed between the two blades 20 and 10, which are respectively called master blade and slave blade.
  • the master blade 20 comprises a substrate 21, an electrode 22 and an anchoring layer 24 forming a strong azimuth and zenith anchorage of the liquid crystal, that is to say an anchorage of the same type as that used in crystal displays. monostable liquid.
  • the slave blade 10 comprises a substrate 11, an electrode 12 and an anchoring layer 14 providing a specific anchorage, corresponding to a weak zenith anchor and a medium or strong azimuthal anchoring of the liquid crystal.
  • the usually transparent electrodes 12 and 22 are typically made of a material called ITO deposited on the substrates 11 and 21. They make it possible to apply an electric field perpendicular to the plates 10 and 20.
  • each of the substrates 11 and 21, typically but not exclusively outside the cell makes it possible to associate each texture with an optical state, for example dark for the texture U and clear for the texture T or vice versa, according to the angles of the two polarizers with respect to the directions of the anchors.
  • the cell evolves towards one or the other of the bistable textures U and T (see figure 2 ).
  • the control signals used induce a strong flow of the liquid crystal in the vicinity of the master blade 20, the hydrodynamic coupling 26 between the master blade 20 and the slave blade 10 creates a sufficient hydrodynamic flow (or flow) near the slave blade to induce the texture T.
  • the texture U is obtained by elastic coupling 28 between the two blades 10 and 20, aided by the possible inclination of the weak anchor.
  • switching of a screen element or pixel of a BiNem-type display will be used to make the molecules of the liquid crystal pass from an initial stable texture (U or T or a coexistence thereof). two textures) towards a final stable texture (U or T or a coexistence of these textures). This name is also valid for the two stable textures of the ZBD type display.
  • the signal applied to the pixel is conventionally made up of several levels.
  • the signal applied to the pixel VP is typically two-stage, but can also be multi-stage [13] or single-stage. If the voltage drop between two stages exceeds a certain absolute value, and that it operates in a sufficiently short time, the "jump" of tension is sufficient for the texture T is obtained. If the jump is not sufficient, or if the transition time is too long, the hydrodynamic flow is insufficient, the texture T becomes impossible, and the texture U is obtained.
  • the 3 addressing modes developed for the standard liquid crystal can be used for the BiNem or ZBD display.
  • the most common addressing mode is multiplexed passive addressing, but active addressing using thin-film transistors is also possible [14].
  • the display (of type Binem or ZBD) is a matrix screen formed of N x M screen elements called pixels, N being the number of rows of pixels and M the number of columns of pixels. , and addressing is done line by line.
  • These strips 50, 52 perpendicular are deposited on each blade.
  • the area between two adjacent conductive strips carried by the same substrate is called interpixel space.
  • the area consisting of all the pixels is called matrix area.
  • a marking area Zm is a part of this matrix area.
  • the matrix area corresponds to the display area, on which area the image content that is to be displayed is displayed. Outside the matrix area, the aforementioned conductive strips 50, 52 are transformed into tracks which make the connection to the control circuits generating the addressing signal.
  • These control circuits may be located on the substrate or remote.
  • the displays are addressed using components or control circuits that we will call “drivers” located for example on flexible connection elements welded to the screen.
  • the drivers consisting mainly of analog gates controlled by shift registers, make it possible to make the link between the control electronics and the tracks.
  • the conductive electrodes are made of a transparent conductive material called ITO (mixed oxide of Indium and tin). But when the display is reflective, the electrodes located on the opposite side to the observer can be made with an opaque conductive material, for example aluminum.
  • the passive mode is applied by orthogonal electrode strips constituting the rows and the columns, the intersections of which constitute the pixels, whereas during active addressing, the electrical voltage is applied to the transistors associated with each pixel by fine wires. All the transistors of the same line are passing during the activation of this line.
  • the addressing is carried out line by line.
  • an electrical signal is applied on this line, which is then called “activated”.
  • activation signal line addressing signal VLn In the case of a standard passive multiplexing, the signal VLn is identical for all the lines, and we will call it VL.
  • the first phase essentially consists of obtaining an anchoring break, ie the homeotropic texture on the line considered, by applying for example a voltage V1L> Vcass on the signal of line addressing for a duration T1, which constitutes a first level of VL.
  • V1L is between 6V and 30V over the 0 ° - 50 ° temperature range.
  • a signal V2L is applied on the line for a duration T2, which constitutes a second and last level of VL.
  • V2L is between 2V and 12V over the 0 ° -50 ° temperature range.
  • the line addressing signal is in this two-stage example, but it can also be single-stage or multi-stage.
  • a variant uses a line signal lower than the breaking voltage, the column signal enabling switching in one or the other of the textures [20]; or, according to a two-step variant, all the pixels are first switched in the same texture, then the column voltage causes the break but only in the pixels to switch in the other texture.
  • This time is typically but not limited to between 10 ⁇ s and 10 ms.
  • This addressing "one-step addressing".
  • the order of activation of the lines (first n-1, then n, then n + 1) defines the scanning direction 46 (see figure 3 ).
  • the addressing time of the display is the time required to address all its lines, so as to display new image content.
  • the document [15] describing the achievement of gray levels provides three variants for obtaining gray levels (FIG. 23 of document [15]) by modifying the parameters of VC.
  • the brushing direction of the alignment layers is orthogonal to the direction of the lines of the display, this type of display is called "orthogonal brushing" (document [15]).
  • bipolar pulses for the Vpre signal and for the VL signal can be used.
  • the field to be applied, to orient the molecules most often has a threshold.
  • a threshold For example, consider a positive dielectric anisotropy nematic placed in a planar and parallel anchored cell on both blades; without a field, the molecules are parallel to each other and parallel to the slides throughout the cell.
  • An electric field, applied perpendicularly to the blades, begins to orient the molecules only when the voltage is greater than a certain threshold called the Freedericksz VF threshold or Freedericksz VF voltage (document [16]).
  • Freedericksz VF threshold Freedericksz VF voltage (document [16]).
  • Freedericksz VF threshold Freedericksz VF voltage
  • VFd is slightly higher than VFs.
  • pretilt When the inclination of the molecules on a blade (pretilt) is high, the threshold disappears. For intermediate pretilts, typically a few degrees, the threshold remains but it is less marked. When the cells are bent or doped, but still planar, the threshold remains but the threshold voltage can vary up to about 30% compared to the theoretical VF voltage obtained with a planar and parallel anchored cell.
  • V0 a threshold voltage
  • Disturbance signal Sp applied according to the invention is Disturbance signal Sp applied according to the invention.
  • the invention makes it possible to mark a pixel or an area of a matrix bistable display comprising two stable liquid crystal textures without an applied field, by an original method, which is not applicable on monostable displays.
  • the concept of marking is defined by a visually detectable optical modification of this area relative to the rest of the image.
  • the proposed method is to apply, over a whole marking zone Zm comprising a set of pixels to be marked, during the time t1, an electrical signal called disturbance signal Sp having a defined amplitude not including a zero continuous range, then no longer apply a signal during time t2.
  • This disturbance signal Sp distorts the two textures corresponding to the two states of the pixels: their optical properties are modified, the contrast decreases to the value of the disturbance signal for which the zone takes a uniform hue.
  • the marking of the zone is in this case maximum.
  • the signal applied to a pixel is the difference between the signal on its line and that on its column.
  • the difficulty with respect to the previous case is to optically disturb only the zone situated at the intersection of the excited lines and columns, while the other pixels of the excited lines and columns not belonging to the zone to be marked are not disturbed. This result will be obtained by taking advantage of the existence of the threshold voltage of the display V0.
  • a first option is illustrated on the figure 9 .
  • the zone marked Zm is in black, the strip of excited lines is horizontal and in light gray, and the band of excited columns is vertical and dark gray.
  • V0 RMS 3 times V0 RMS is applied to the excited lines and + V0 RMS to the other lines, 0V RMS to the excited columns, and 2xV0 RMS to the non-excited columns.
  • an RMS voltage V0 to the whole screen except the pixels of the zone to be marked Zm which receive 3 times V0 RMS, which is more than enough to obtain a disturbance of the previously registered image.
  • the pixels subjected to V0, threshold voltage will not react to this voltage and remain stable.
  • a second option is illustrated on the figure 10 .
  • the zone marked Zm is in black, the strip of excited lines is horizontal and in light gray, and the band of excited columns is vertical and dark gray.
  • This second option makes it possible to apply a potential difference only on the excited lines and columns, which is less energy consuming.
  • V0 is applied twice to the excited lines and V0 to the other lines, 0V to the excited columns, and V0 to the non-excited columns.
  • a zero voltage or V0 is applied to the pixels outside the flashing zone Zm, and V0 is applied twice to the pixels of the flashing zone Zm.
  • the disturbance signal here is 2 times V0 compared to 3 times V0 for the previous variant.
  • a third variant of the invention is to mark (statically or flashing) a mobile marking zone Zm, called "cursor".
EP08290975.5A 2008-10-15 2008-10-15 Energiesparendes Verfahren zum Markieren eines Bereichs eines Flüssigkristallbildschirms Not-in-force EP2178079B1 (de)

Priority Applications (4)

Application Number Priority Date Filing Date Title
EP08290975.5A EP2178079B1 (de) 2008-10-15 2008-10-15 Energiesparendes Verfahren zum Markieren eines Bereichs eines Flüssigkristallbildschirms
PCT/FR2009/001190 WO2010043780A1 (fr) 2008-10-15 2009-10-08 « procédé économique en énergie pour marquer une zone d'un écran à cristal liquide »
US13/698,987 US20130076610A1 (en) 2008-10-15 2009-10-08 Energy-saving method for marking an area of a liquid crystal screen
TW098134864A TW201033985A (en) 2008-10-15 2009-10-15 Energy-saving method for marking an area of a liquid crystal screen

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Application Number Priority Date Filing Date Title
EP08290975.5A EP2178079B1 (de) 2008-10-15 2008-10-15 Energiesparendes Verfahren zum Markieren eines Bereichs eines Flüssigkristallbildschirms

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EP2178079A1 true EP2178079A1 (de) 2010-04-21
EP2178079B1 EP2178079B1 (de) 2014-07-30

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EP (1) EP2178079B1 (de)
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TW201033985A (en) 2010-09-16
EP2178079B1 (de) 2014-07-30
WO2010043780A1 (fr) 2010-04-22

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