EP0614563B1 - Dispositif d'affichage a cristaux liquides - Google Patents

Dispositif d'affichage a cristaux liquides Download PDF

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Publication number
EP0614563B1
EP0614563B1 EP93921094A EP93921094A EP0614563B1 EP 0614563 B1 EP0614563 B1 EP 0614563B1 EP 93921094 A EP93921094 A EP 93921094A EP 93921094 A EP93921094 A EP 93921094A EP 0614563 B1 EP0614563 B1 EP 0614563B1
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EP
European Patent Office
Prior art keywords
line
voltage
value
column
rms
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.)
Expired - Lifetime
Application number
EP93921094A
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German (de)
English (en)
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EP0614563A1 (fr
Inventor
Theo L. Welzen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Citizen Watch Co Ltd
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Citizen Watch Co Ltd
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Publication date
Application filed by Citizen Watch Co Ltd filed Critical Citizen Watch Co Ltd
Publication of EP0614563A1 publication Critical patent/EP0614563A1/fr
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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
    • 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
    • G09G2320/02—Improving the quality of display appearance
    • G09G2320/0209—Crosstalk reduction, i.e. to reduce direct or indirect influences of signals directed to a certain pixel of the displayed image on other pixels of said image, inclusive of influences affecting pixels in different frames or fields or sub-images which constitute a same image, e.g. left and right images of a stereoscopic display

Definitions

  • the present invention relates to a display device, comprising a liquid-crystal material between two support plates held at a defined spacing from one another and having surfaces facing one another, a pattern of N line electrodes being provided on one surface and a pattern of column electrodes on the other surface in which the line electrodes cross the column electrodes and a matrix of display elements is thus formed at the position of the crossovers, and the device comprises a control circuit for presenting square-wave data signals to the column electrodes and a line-scanning circuit for periodically scanning the line electrodes and presenting square-wave line selection voltages signals.
  • the first reference shows an addresssable matrix which consists of liquid crystals defined by the crossing regions of row and column electrodes.
  • the state of such a liquid crystal is related to the magnitude of electrical signals applied to those electrodes and to the number of elements in the matrix.
  • the electric signals are modified according to the number of elements in the matrix so that the operating margin between on and off potentials can be maximized.
  • a certain number of columns are scanned and energized in succession while the states of the certain number of elements displayed in each row are prestored and ciculated in a register for that row. Via a circuit the voltage levels for on and off are determined to be applied to the row electrode according to each bit in the register and an elector is operated as each column in turn is scanned.
  • the second reference shows a very similar device where the scanning electrodes are formed on one of two subtrates between which a liquid-crystal-layer is interposed.
  • Scanning electrode voltage driving wave forms consisting of selective and non-selective voltages are applied to the scanning electrodes of the liquid-crystal-panel.
  • Such display devices are normally operated with multiplex addressing in accordance with the so-called RMS mode.
  • the picture elements are switched from a first state to a second state which is optically different therefrom with the aid of the line-scanning circuit which periodically scans the line electrodes with a line-selection pulse of magnitude V s and with the aid of the control circuit for presenting data signals to the column electrodes, which control circuit feeds data voltages of magnitude +/- V d to the column electrodes for the time in which a line electrode is scanned, in such a way that the optical state which is achieved in a display element is determined by the so-called root-mean-square (RMS) voltage value across the element concerned.
  • RMS root-mean-square
  • Figure 2 diagrammatically shows a transmission-voltage characteristic of a picture cell belonging to this display device.
  • Figure 1 diagrammatically shows a portion of a matrix-oriented display device 1 having N max selection lines (row electrodes) 2 and describes the operating principle of the abovementioned RMS multiplex address method.
  • This address method is generally referred to as "line-at-a-time" RMS multiplex addressing.
  • the information to be displayed is presented on the data lines (column electrodes) 3.
  • the display elements 4 are in an on state or an off state.
  • the picture information (data voltage +/- V d ) is supplied synchronously with the selection of the lines or row electrodes with the aid of the line-selection voltage V s .
  • the line 2 a is selected for a period t 1 (also referred to as line time), which line, together with the information then present on the data lines 3 a , 3 b , 3 c (i.e. +/- V d ) determines the optical state of the picture elements 4 aa , 4 bb , 4 cc .
  • the line 2 b is selected for the period t 1 .
  • the information then present on the data lines 3 determines the state of the picture elements 4 ba , 4 bb , 4 bc .
  • the display element responds to the cumulative effect of a number of address pulses (or selection pulses).
  • a liquid-crystal display element responds in the same way as if it has been addressed by a sinusoidal or square-wave signal having the same RMS voltage value as that of the 'on' and 'off' voltages V 2 and V 1 given by the expressions (1) and (2).
  • the maximum number of selection lines N max is related to the value of the ratio V 2 /V 1 (threshold steepness).
  • FRAME RESPONSE This multi-line addressing is used to reduce or to eliminate the so-called "FRAME RESPONSE” behavior.
  • "FRAME RESPONSE” behavior results in loss of contrast and brightness.
  • N max is in turn determined in accordance with expression (3) derived for RMS behavior occurring.
  • the actual RMS voltage value for an "on" element (or selected display element) in a column in which all the picture elements are in the "on” state may differ from the RMS voltage value for a selected display element in a column in which the picture elements are, for example, alternately "on” and "off".
  • crosstalk or “ghost” phenomena
  • ghost perceptible in highly multiplexed dot-matrix liquid-crystal display devices.
  • This method makes use of a special polarity change sequence in which the polarities of the address-voltage signals always change in sign after scanning 2 lines during the raster scan. The start position of these polarity changes is also changed or shifted for successive frames.
  • the object of the invention which will be described in this patent application is to provide a display device in which the abovementioned crosstalk effect is reduced as much as possible without making use of special polarity-change sequences.
  • the control circuit should comprise a "counter unit” which registers the number of "on” -"off" transistions in each column of the matrix of the display device.
  • the (increasing) loss in RMS voltage value over a certain picture element as a consequence of a (increasing) number of "on"-"off" transistions in the column concerned can be compensated for by using a modified (or higher) amplitude of the data voltage during the raster scan.
  • FIG. 3 diagrammatically shows the way in which the voltage V lc across an LC element (represented as a capacitor C) increases with time on presenting a voltage jump of V in in the presence of a resistor R.
  • V RMS 2 (V in 2 /T) ⁇ T C (1 - exp(-t/ ⁇ )) 2 dt
  • V RMS 2 1 - ⁇ /2T * (exp(-2T/ ⁇ ) - 1) + 2 ⁇ /T * (exp(-T/ ⁇ ) - 1)
  • the effective (RMS) voltage is determined by the number of square-wave voltages and therefore, in reality, by the number of passages through zero.
  • Figure 4B diagrammatically shows the voltage across element B with the assumption that only one "on"-"off” transition occurs in column j.
  • V RMS V RMS
  • a data-voltage amplitude which is higher than prescribed according to the Alt and Pleshko relationships (in which case ideal, undeformed square-wave voltage signals are assumed).
  • the height of the data-voltage levels for compensating for V RMS losses can, however, also be determined experimentally by means of transmission (or brightness) measurement of an "on" element as a function of the number of "on"-"off" transitions.
  • transmission (or brightness) measurement of an "on” element as a function of the number of "on"-"off" transitions.
  • the number of voltage levels required can be reduced appreciably because the use of one and the same V d value in the case of, for example, X au and (X au + 1) transitions does not necessarily result in visually perceptible brightness differences.
  • V d values are used for columns with different X au values during the raster scan.
  • V RMS losses as a consequence of "on"-"off" transitions can also be achieved by using the same V d value during the scanning of the N-line matrix for columns having different X au values and by presenting a voltage pulse whose amplitude V j (X au ) is dependent on the X au value in the column concerned simultaneously to the separate columns j after every frame scan for a certain time interval t x (for example, equal to the line time t 1 ).
  • t x for example, equal to the line time t 1 .
  • the height of the voltage pulse to be supplied V j (X au ) can be determined relatively simply experimentally with the aid of transmission measurements according to a procedure such as is described for the determination of the different column voltages V d (X au ) which are used in the first-mentioned compensation method.
  • the polarities of both the data signals and of the line-select signals should change in sign, for example after every raster time; this is done in order to prevent the occurrence of direct-voltage components. In practice, this polarity change is often used after a certain number of line times, the number being less than N.
  • X au can therefore be better interpreted as the number of changes in polarity of V d during a raster time or, still more generally, as the number of times the level of the data voltage changes.
  • FM is described, inter alia, in SID Digest of Technical Papers XIV, pages 32-33, 1983.
  • a disadvantage of FM is the occurrence of "flicker" in fast-switching liquid-crystal display devices.
  • PWM is described, inter alia, in SID Digest of Technical Papers XI, pages 28-29, 1980.
  • PWM has, inter alia, the disadvantage that highfrequency signals are necessary for a large number of grey levels.
  • a third method of achieving grey levels makes use of pulse-height modulation (PHM) and is essentially used in display devices in which each picture element is provided with an active electronic switch such as, for example, a thin-film transistor.
  • PPM pulse-height modulation
  • a grey level is in fact achieved for a picture element by supplying the element concerned with a voltage having a certain amplitude.
  • This method cannot, however, readily be used in the matrix display devices which are described in this patent application and which are addressed by the line-at-a-time or multi-line RMS addressing.
  • V on 2 (V s + V d ) 2 /N + (N - 2)*V d 2 /N + (f*V d ) 2 /N
  • V on 2 (V s + V d ) 2 /N + (N - 2)*V d 2 /N + (f*V d ) 2 /N
  • the loss in RMS voltage can be compensated for by supplying a voltage pulse to the column concerned after each frame scan (for, for example, a line time t 1 ).
  • a voltage pulse for, for example, a line time t 1 .
  • the height of this voltage pulse is dependent on the number of elements in the column concerned having a particular grey level, expressed, for example, in the value of the factor f, in which case completely "on” and completely “off” may also be regarded as grey levels.
  • the height of the voltage pulse can in principle be determined (or calculated) by deriving expressions under these circumstances for, for example, the RMS voltage of an "on” and an “off” element and equating the RMS voltage values calculated in this way to those according to expressions (1) and (2).
  • EXAMPLE 4-line matrix, in which one "on" element and three picture elements having different grey levels (or f values) occur in a particular column.
  • a 5th line is, as it were, added to the 4-line matrix. This line does not actually need to be present: it is a virtual line.
  • V on 2 (S 5 + D 5 ) 2 /5 + (f i *D 5 ) 2 /5 + (f 2 *D 5 ) 2 /5 + (f 3 *D 5 ) 2 /5 + V c 2 /5
  • f i *D 5 is the amplitude of the data voltage which is supplied to the element i concerned having a grey value with parameter value f i .
  • V c 2 /5 arises because, during selection of the 5th (virtual) line, a certain voltage is presented to the column.
  • V f1 2 (S 5 + f 1 *D 5 ) 2 /5 + D 5 2 /5 + (f 2 *D 5 ) 2 /5 + (f 3 *D 5 ) 2 /5 + V c 2 /5
  • V f1 2 (S 4 + f 1 *D 4 ) 2 /4 + (4/4)*D 4 2 - (1/4)*(f 1 *D 4 ) 2
  • V c SQRT((N+1)/N) * SN
  • D N+1 SQRT((N+1)/N) * DN.
  • the height of the voltage pulse V c to be supplied (to the column concerned), which ensures that grey levels can be achieved with the aid of PHM while maintaining the correct RMS voltages of the "on" and "off” elements, can be determined.
  • the device comprises an electronic circuit unit which registers the accosicated value of the parameter X au (j), which is defined in the above mentioned description, for each column j of the matrix of display element s and for each raster scan.
  • the display device of the present invention is further characterized in that during the raster scan, the amplitude V d of the data voltage +/- V d (which is across a picture element during the non-select period in the case of the given description of the line-at-a-time addressing) is different for columns having a different X au value.
  • multi-level data voltages are ures; for example, for 3-line addressing, 4 voltage levels will be used with 2 different amplitudes; +/- V 3 and +/- V 3 /3.
  • V 3 the value of V 3 will be chosen as different, as mentioned above.

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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)

Claims (1)

  1. Dispositif d'affichage comprenant un cristal liquide disposé entre deux plaques de support maintenues à une distance déterminée l'une de l'autre et ayant des surfaces se faisant face, un motif d'électrodes à N lignes étant disposé sur une surface et un motif d'électrodcs en colonnes sur l'autre surface, dans lequcl les électrodes de lignes croisent les électrodes de colonnes et une matrice d'éléments d'affichage est ainsi formée à la position des croisements, et le dispositif comprend un circuit de commande pour appliquer des signaux de données à onde carrée aux électrodes de colonnes et un circuit de balayage de lignes pour le balayage périodique des électrodes des lignes et appliquer des signaux de voltage de sélection de ligne à onde carrée;
       caractérisé en ce que le dispositif d'affichage comprend une unité de circuit électronique qui génère des niveaux de gris au moyen d'une modulation de hauteur d'impulsion et qui enregistre la valeur associée du paramètrc Xau (j) qui est défini comme étant le nombre de changements de niveau du voltage de données pour chaque colonne j de la matrice d'éléments d'affichage et pour chaque balayage de matrice, de telle sorte que, pendant le balayage de la matrice, l'amplitude Vd du voltage de données ± Vd à travers un élément d'image pendant la période où celui-ci n'est pas sélectionné dans le cas de la description donnée de l'adressage ligne par ligne, est différente pour des colonnes ayant une valeur de Xau différente et la valeur choisie de Vd est supérieure dans la mesure où Xau est supérieur et en particulier, en fonction de la relation Vd = Vd (Xau) qui est déterminée en partant de la condition requise que les éléments d'image qui sont censés être dans le même état mais apparaissent dans des colonnes ayant une valeur différente de Xau doivcnt avoir des voltages VRMS égaux ou pratiquement égaux, et que de plus, la même valeur de voltage Vd est utilisée pour une gamme de valeurs de Xau, à savoir de Xau jusqu'à (Xau+n) inclus, où n = 1, 2, 3, et qu'un voltage approprié dont l'amplitude (AMPc) est déterminée par la valeur Xau de la colonne concernée est appliquée aux différentes colonnes pendant un certain intervalle de temps après chaque balayage de matrice, si bien que la même valeur AMPc est utilisée pour une gamme de valeurs Xau, à savoir de Xau jusqu'à (Xau+n) inclus, où n = 1,2, 3...
EP93921094A 1992-09-30 1993-09-30 Dispositif d'affichage a cristaux liquides Expired - Lifetime EP0614563B1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
NL9201692 1992-09-30
NL9201692A NL9201692A (nl) 1992-09-30 1992-09-30 Reduktie van Vertikale "Cross-talk" in Dot-Matrix Vloeibaar-Kristal Weergeefinrichtingen, en Realisatie van Grijs-niveau's met behulp van Puls-Hoogte-Modulatie.
PCT/JP1993/001403 WO1994008330A1 (fr) 1992-09-30 1993-09-30 Dispositif d'affichage a cristaux liquides

Publications (2)

Publication Number Publication Date
EP0614563A1 EP0614563A1 (fr) 1994-09-14
EP0614563B1 true EP0614563B1 (fr) 1999-01-13

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EP93921094A Expired - Lifetime EP0614563B1 (fr) 1992-09-30 1993-09-30 Dispositif d'affichage a cristaux liquides

Country Status (6)

Country Link
EP (1) EP0614563B1 (fr)
JP (1) JPH07501636A (fr)
KR (1) KR100343381B1 (fr)
DE (1) DE69323059T2 (fr)
NL (1) NL9201692A (fr)
WO (1) WO1994008330A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6693613B2 (en) * 2001-05-21 2004-02-17 Three-Five Systems, Inc. Asymmetric liquid crystal actuation system and method

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2020875B (en) * 1978-05-03 1982-03-03 Marconi Co Ltd Addressable matrices
US5151690A (en) * 1987-08-13 1992-09-29 Seiko Epson Corporation Method and apparatus for driving a liquid crystal display panel
DE3856011T2 (de) * 1988-06-07 1998-03-12 Sharp Kk Verfahren und Einrichtung zum Steuern eines kapazitiven Anzeigegeräts

Also Published As

Publication number Publication date
NL9201692A (nl) 1994-04-18
EP0614563A1 (fr) 1994-09-14
KR100343381B1 (ko) 2002-11-30
WO1994008330A1 (fr) 1994-04-14
DE69323059T2 (de) 1999-07-15
DE69323059D1 (de) 1999-02-25
JPH07501636A (ja) 1995-02-16

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