EP1471496A1 - Verfahren zum Steuern eines Flüssigkristallanzeigegeräts - Google Patents

Verfahren zum Steuern eines Flüssigkristallanzeigegeräts Download PDF

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Publication number
EP1471496A1
EP1471496A1 EP03425252A EP03425252A EP1471496A1 EP 1471496 A1 EP1471496 A1 EP 1471496A1 EP 03425252 A EP03425252 A EP 03425252A EP 03425252 A EP03425252 A EP 03425252A EP 1471496 A1 EP1471496 A1 EP 1471496A1
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EP
European Patent Office
Prior art keywords
row
functions
signals
matrix
time period
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Withdrawn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
EP03425252A
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English (en)
French (fr)
Inventor
Santo Ilardo
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.)
STMicroelectronics SRL
Original Assignee
STMicroelectronics SRL
SGS Thomson Microelectronics SRL
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 STMicroelectronics SRL, SGS Thomson Microelectronics SRL filed Critical STMicroelectronics SRL
Priority to EP03425252A priority Critical patent/EP1471496A1/de
Publication of EP1471496A1 publication Critical patent/EP1471496A1/de
Withdrawn legal-status Critical Current

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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
    • G09G3/2007—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
    • 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
    • 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
    • G09G3/3674—Details of drivers for scan electrodes
    • G09G3/3681—Details of drivers for scan electrodes suitable for passive matrices only
    • 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
    • G09G3/3685—Details of drivers for data electrodes
    • G09G3/3692—Details of drivers for data electrodes suitable for passive matrices only
    • 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
    • G09G3/2018—Display of intermediate tones by time modulation using two or more time intervals
    • G09G3/2022—Display of intermediate tones by time modulation using two or more time intervals using sub-frames
    • 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
    • G09G3/2077—Display of intermediate tones by a combination of two or more gradation control methods

Definitions

  • the present invention relates to a driving method for a liquid crystal display.
  • the liquid crystal displays are actually used in a more and more increasing number of products as the cellular phones, the notebooks, etc.
  • the displays which may be of black and white, or gray shade or colour type, are typically made up of a matrix of rows and columns electrodes which, suitably driven by application of a voltage signal, determine at the crossing points, the so-called pixels, a modification in optic behavior of the liquid crystal interposed.
  • the image visualized on the display is obtained by means of different driving methods of the rows and of the columns.
  • FIG. 1 a schematic block diagram of a liquid crystal display 1 is shown which has a flat panel structure in which a liquid crystal layer is interposed between a group 2 of N row electrodes and a group 3 of M column electrodes.
  • a Super Twisted Nematic (STN) or a Twisted Nematic (NT) liquid crystal can be used as liquid crystal layer.
  • a control means 6 is connected with a circuit stage 4 adapted to drive the row electrodes 2 and it is also connected with a circuit stage 5 adapted to drive the column electrodes 3.
  • a voltage circuit 7 supplies a voltage level necessary for generating a column signal by means of the circuit stage 5 and it supplies a voltage level for generating a row signal by means of the circuit stage 4.
  • a known driving scheme, implemented by the control means 6, is the so called line by line addressing, wherein the N rows 2 of the matrix display 1 are sequentially selected one at a time for a time period T.
  • an orthonormal function generating means 8 generate a plurality of orthonormal functions which are orthonormal to each other and said means 8 supply them sequentially to the circuit stage 4.
  • the circuit stage 4 adequately selects a voltage level, provided by the voltage level circuit 7, in accordance with the orthonormal functions and supplies it to the group 2 of row electrodes as row signal.
  • LCDs are slow devices, with response time in the range of a few tens to few hundred milliseconds; for this reason the scanning time NT must be short as compared to the response times of the LCD display.
  • RMS Root Mean Square
  • MLA Multi Line Addressing
  • the MLA method causes the simultaneous selection of a plurality of row electrodes 2 at the same time period.
  • the column electrodes 3 can independently be controlled by means of the period NT.
  • Said plurality of waveforms r1, ..., rn represents the voltage levels in correspondence with respective column elements of the liquid crystal display panel 1.
  • the plurality of waveforms r1, ..., r4 of row electrodes 2 represents a set of the entirety of the wave forms r1, ..., m.
  • the column electrodes voltage series are determined by the sequence of one and zero of said plurality of waveforms r1, ..., r4.
  • FRC Frame Rate Control
  • many frames are required for a multiple gray scale information.
  • seven frames F1, F2, ..., F7 are required in FRC for codifying the gray scales because three memory bits for each pixel are needed to codify the eight gray levels, wherein, particularly, the first four frames, that is F1, F2, F3, and F4, codify the most significant bit (MSB), the fifth and sixth frames, that is F5 and F6, codify the medium significant bit (mSB) and the seventh frame, that is F7, codifies the less significant bit (LSB), according to Figure 3.
  • MSB most significant bit
  • mSB medium significant bit
  • LSB less significant bit
  • FIG 4 a table 13 wherein the stored data in a read access memory (RAM) for each pixel of the flat display 1, is shown.
  • RAM read access memory
  • the first frame F1 represents symbolically the sequence of four scanning steps over all the row electrodes, based each one on a different row pattern (four columns of matrix R1 of Figure 2c).
  • the maximum time distance among the frames wherein the value of the said memory RAM is evaluated in the case of the LSB is of six frames, in the case of the mSB is of five frames and in the case of the MSB is of three frames. Such a time distance produces a phenomenon called flickering.
  • PAM Pulse Width Modulation
  • This technique suffers the cross-talk problem which is due to an increase of the all the charge quantity which is transferred onto the adjacent pixels instead that onto the destination pixel. This is due to the different factors: to the fact that a waveform deformation of the approximatively exponential type is associated to each transition, to the fact that the queue of a row pulse in a period of elementary time T1 is partially overlapped to the column pulses of the successive time period T1, to the transient induced by the commutations of the row electrodes on the column electrodes.
  • the cross-talk effect causes a contrast reduction in the display LCD and a decreasing of the transmittance of the off pixels.
  • a driving method for a liquid crystal display having a multiplicity of display elements arranged at the intersections of a matrix provided with N row electrodes and M column electrodes with N and M entire numbers, said method comprising a first phase for scanning all the row electrodes of said matrix in a scanning time period, said first phase comprising the sequential generation of a plurality of first signals each one adapted to excite at least one row electrode of said matrix for a first prefixed time period, the generation of second signals respectively adapted to excite each column electrode of said matrix simultaneously to the excitation of the at least one row electrode, said second signals being adapted to determine the gray shade of each display element of the excited row electrode, said first prefixed time period being smaller than the scanning time period, characterized in that a word formed by G bits corresponds to each gray shade and in that each one of said first signals is defined by means of the following equation wherein r i (t) is the i-th first signal as a function of the time t, the functions f i
  • the method comprises a first phase for scanning all the row electrodes of said matrix in a scanning time period NT.
  • the first phase comprises the sequential generation of a plurality of first signals each one adapted to excite at least one respective row electrode of said matrix for a first prefixed time period T and the generation of second signals adapted to excite each one column electrode of said matrix simultaneously to the excitation of the at least one row electrode; the second signals determine the gray shade of each display element of the excited row electrode.
  • gray shades can be generated wherein the gray shades can be represented by words composed by G-bits, for example with words composed by six bits as illustrated in table 2 in Figure 6; a transmittance value and a rms voltage value are associated to each word composed by six bits.
  • Each pixel has a different gray shade determined by a word composed by G-bits; for example the word "00...00” represents the full white pixel and the word “11...11” represents the full black pixel; the intermediate words "b G-1 ...b 0 " represent the intermediate gray shades.
  • This driving method comprises the driving of the N rows by means of NG orthogonal functions.
  • coefficients A K modulate the amplitude of the functions f ik (t) for generating the gray shades and are chosen suitably, for example as shown in table 1 in Figure 6.
  • Each column j-th is driven by means of a signal c j (t) of the this type: , where the coefficients B k modulate the amplitude of the functions f nk (t) for generating the gray shades; the functions f nk (t) are the NG orthogonal functions, preferably orthonormal.
  • the voltage level number is determined by the coefficients A k and B k and by the choice of the orthogonal functions f nk (t).
  • the root mean square value of the electric field between the two plates of the i-th row and the j-th column is given by:
  • V th the display threshold, that is the voltage wherein it has the 50% of transmittance, it is given by: Therefore the dynamic range of the voltage (given by is limited, in fact: from which: where has its maximum if In such case where
  • the products A k B k can be fixed by using the least squares values with all the 2 G points and a function modelling the transmittance.
  • the coefficients A k and B k can be applied to each group of orthonormal functions.
  • each row For example eight gray shades can be obtained by using three orthonormal functions by each row, as shown in Figure 9 in the case of line by line addressing.
  • the orthonormal functions f 0,0 , f 0,1 and f 0,2 are employed for the row 0 r 0 (t) while the orthonormal functions f 1,0 , f 1,1 and f 1,2 are employed for the row 1 r 1 (t); the functions r 0 (t) and r 1 (t) assume the time waveform shown in the respective graphics.
  • a column signal c 0 (t) is obtained which is given by the waveform shown in Figure.
  • the pulses of the orthonormal functions have the same time duration it is obtained that the frequency and the voltage level number grows in logarithmic manner with respect to the gray shade number, as shown in Figure 8 where the possible voltage level V of a column signal c j (t) are shown in the case of a row i or a row i+1.
  • the orthonormal functions p 0,0 , p 0,1 and p 0,2 are used for the row 0 r 0 (t) while the orthonormal functions p 1,0 , p 1,1 and p 1,2 are used for the row 1 r 1 (t); the functions r 0 (t) and r 1 (t) assume the time waveform shown in the respective graphics, as shown in Figure 9.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)
EP03425252A 2003-04-23 2003-04-23 Verfahren zum Steuern eines Flüssigkristallanzeigegeräts Withdrawn EP1471496A1 (de)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP03425252A EP1471496A1 (de) 2003-04-23 2003-04-23 Verfahren zum Steuern eines Flüssigkristallanzeigegeräts

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Application Number Priority Date Filing Date Title
EP03425252A EP1471496A1 (de) 2003-04-23 2003-04-23 Verfahren zum Steuern eines Flüssigkristallanzeigegeräts

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0522510A2 (de) * 1991-07-08 1993-01-13 Asahi Glass Company Ltd. Steuerverfahren für ein Flüssigkristallanzeigeelement
EP0569974A2 (de) * 1992-05-14 1993-11-18 In Focus Systems, Inc. Graupegeladressierung für LCD's
EP0598913A1 (de) * 1992-05-08 1994-06-01 Seiko Epson Corporation Steuerungsverfahren und -schaltung für flüssigkristallelemente und bildanzeigevorrichtung
EP0618562A1 (de) * 1993-03-30 1994-10-05 Asahi Glass Company Ltd. Anzeigevorrichtung und Steuerverfahren für Anzeigevorrichtung

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0522510A2 (de) * 1991-07-08 1993-01-13 Asahi Glass Company Ltd. Steuerverfahren für ein Flüssigkristallanzeigeelement
EP0598913A1 (de) * 1992-05-08 1994-06-01 Seiko Epson Corporation Steuerungsverfahren und -schaltung für flüssigkristallelemente und bildanzeigevorrichtung
EP0569974A2 (de) * 1992-05-14 1993-11-18 In Focus Systems, Inc. Graupegeladressierung für LCD's
EP0618562A1 (de) * 1993-03-30 1994-10-05 Asahi Glass Company Ltd. Anzeigevorrichtung und Steuerverfahren für Anzeigevorrichtung

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
SEUNG-WOO LEE ET AL: "Realization of video-rate STN display using row voltage modulation method", MICROELECTRONICS AND VLSI, 1995. TENCON '95., IEEE REGION 10 INTERNATIONAL CONFERENCE ON HONG KONG 6-10 NOV. 1995, NEW YORK, NY, USA,IEEE, US, 6 November 1995 (1995-11-06), pages 464 - 467, XP010160162, ISBN: 0-7803-2624-5 *

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