EP2169656A1 - Système de commande d'affichage à cristaux liquides - Google Patents

Système de commande d'affichage à cristaux liquides Download PDF

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Publication number
EP2169656A1
EP2169656A1 EP08016775A EP08016775A EP2169656A1 EP 2169656 A1 EP2169656 A1 EP 2169656A1 EP 08016775 A EP08016775 A EP 08016775A EP 08016775 A EP08016775 A EP 08016775A EP 2169656 A1 EP2169656 A1 EP 2169656A1
Authority
EP
European Patent Office
Prior art keywords
voltage
row
liquid crystal
crystal display
pixel
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Withdrawn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
EP08016775A
Other languages
German (de)
English (en)
Inventor
Philipp WÖHRLE
Hermann Link
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.)
Harman Becker Automotive Systems GmbH
Original Assignee
Harman Becker Automotive Systems GmbH
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 Harman Becker Automotive Systems GmbH filed Critical Harman Becker Automotive Systems GmbH
Priority to EP08016775A priority Critical patent/EP2169656A1/fr
Publication of EP2169656A1 publication Critical patent/EP2169656A1/fr
Withdrawn legal-status Critical Current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
    • G09G3/34—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
    • G09G3/3655—Details of drivers for counter electrodes, e.g. common electrodes for pixel capacitors or supplementary storage capacitors
    • 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
    • G09G2320/0247—Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
    • 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
    • G09G2320/06—Adjustment of display parameters
    • G09G2320/0606—Manual adjustment
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2360/00—Aspects of the architecture of display systems
    • G09G2360/14—Detecting light within display terminals, e.g. using a single or a plurality of photosensors
    • G09G2360/145—Detecting light within display terminals, e.g. using a single or a plurality of photosensors the light originating from the display screen
    • 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
    • G09G3/3614—Control of polarity reversal in general

Definitions

  • This invention relates to a liquid crystal display control system and to a method for controlling a liquid crystal display.
  • a liquid crystal display is a flat display device containing a number of pixels arrayed in front of a light source or reflector.
  • Each pixel of a LCD typically contains a layer of molecules aligned between two transparent electrodes and two polarizing filters, the axes of transmission of which are perpendicular to each other. With no liquid crystal between the polarizing filters light passing through the first filter is blocked by the second crossed polarizer.
  • CTR cathode ray tube screen
  • LCD screens have an array of pixels constantly lit by a back light. The constancy of the light removes the type of flicker found in CRT screens.
  • the voltage applied between the two electrodes is responsible for the amount of transmitted light. The voltage controls the alignment of the liquid crystal molecules in the electric field between the two electrodes of a pixel of the LCD screen. If the voltage between the two electrodes is large enough, no light can pass the two electrodes and the pixel will appear black.
  • the video source signal to be displayed on the LCD screen typically ranges from 0 V to 10 V, the applied voltage for each pixel corresponding to the intensity information that appears across the pixel.
  • the bottom of the pixel is normally connected to a back plane of the LCD screen.
  • the voltage common to all the bottoms of the pixels is known as V com . Assuming the V com voltage is at ground, the voltage across the pixel varies from 0 to 10 V resulting in an average of 5 V. This would lead to a substantial DC voltage across each pixel, what would result in an accelerated aging of the LCD screen.
  • a LCD screen is now configured in such a way that, as shown in Fig. 3 , the common voltage V com is set to the midpoint of the video signal.
  • the brightness at every pixel is determined by the difference between the voltage and the voltage V com .
  • the relationship between the light emitted from a pixel and the voltage applied is a non-linear S-shaped curve.
  • the light transmitted only depends on the voltage difference, so that the same transmittance is obtained for the voltages V+ and V-.
  • Most liquid crystal display screens switch alternating pixels between one polarity and the other, resulting in an average DC voltage across the display of 0 V.
  • the V com voltage needs to be placed exactly at the midpoint of the video signal to avoid flicker. If V com is not exactly set to the midpoint, e.g.
  • the full-scale voltage will be different on each pixel, on one pixel the full scale voltage will be 4.7 V, whereas on the other pixel the full-scale voltage will be 5.3 V.
  • This difference in voltage translates to a difference in intensity experienced as a flicker when the voltage is inverted from image frame to image frame.
  • a liquid display control system comprising a LCD having a first region in which, in every second row, a voltage determining a light transmission applies to each pixel as inverted between the image frames, whereas the voltage is kept constant for the other rows.
  • the liquid crystal display furthermore comprises a second region in which in every second pixel of a row the voltage determining the light transmission applied to each pixel is inverted between the image frames, whereas the voltage is kept constant for the other pixels of said row.
  • a control unit is provided allowing to adapt a common voltage applied to each pixel.
  • the liquid crystal display displaying the two different regions has the advantage that the frequency of the flicker corresponding to the frequency of the image frames is set such that it is perceivable for the human eye. Additionally, the difference between the positive and the negative polarity is emphasized and the flicker can be easily detected for both types of LCD screens known on the market. If the LCD screen is a screen for which the voltage is inverted row by row, the first region shows a flicker for a not well adjusted V com . However, when the LCD screen is a screen using a pixel-wise inversion, a flicker will appear in the second region of the screen.
  • the voltage distribution applied to the different pixels in a row adjacent to said row is shifted by one column compared to the pixels of said row, resulting in a chequered pattern of the pixels.
  • the pixels for which the voltage is inverted from frame to frame and for which the voltage is kept constant are arranged in an alternating manner resulting in a chequered pattern.
  • the voltage that is kept constant is 0, resulting in a black pixel, whereas the voltage applied to the different pixels that is inverted should lie between 30 and 70% of the maximum voltage applied.
  • the voltage applied is selected in such a way that approximately 50% of light is transmitted through the pixels resulting in a gray.
  • the image displayed by the LCD screens shows in the first region alternating black and gray rows.
  • the pixels of the black rows do not change in intensity in case the voltage is inverted, whereas the intensity of the gray pixels may change when the voltage is not exactly at half of the video signal voltage.
  • the different gray levels due to the voltage inversion are responsible for the flicker.
  • the gray pixels arranged in the chequered pattern also suffer from a varying intensity in the case of a not correctly fixed voltage V com .
  • the LCD control system displaying a screen with the two different regions shows the flicker for the two different kinds of LCD screens known, so that independent of the type of screen used a flicker will be detected.
  • the first region comprises a first part and a second part
  • the voltage distribution applied to the different pixels of the second part is shifted by one row compared to the voltage distribution applied to the different pixels of the first part.
  • the second region comprises a first part and a second part resulting in a voltage distribution of the pixels of the second part being shifted by one row compared to the voltage distribution of the first part of the second region. If the two different parts for one region are displayed one next to the other, both polarities are visible at the same time.
  • the voltage applied to every second row is inverted for every second row in one image frame.
  • the LCD control system may further comprise an optical sensor detecting an intensity modulation of the liquid crystal display displaying the different regions.
  • the optical sensor now may control the control unit in such a way that the intensity modulation is minimized.
  • a flicker of the display can be detected independent of the type of LCD screen used.
  • a method for controlling a liquid crystal display comprising the steps of providing the first region of the liquid crystal display as described above and the second region as described above. Furthermore, the common voltage V com applied to each pixel is adapted in such a way that the intensity modulation of the display is minimized.
  • a liquid crystal display control system is shown in which a liquid crystal display 10 comprises a control unit 11, the control unit allowing the adaption of a common voltage V com as shown in Fig. 3 .
  • the possibility to adapt the common voltage V com is schematically illustrated by a control button 12, with which the common voltage V com can be adjusted to half of the video signal voltage.
  • a V com amplifier (not shown) can be used to supply a very stable reference voltage for all the pixels of the liquid crystal display.
  • the brightness at every pixel depends on the difference between the voltage applied to each pixel and this common voltage V com .
  • the gamma curve shown in Fig. 3b can be either positive- or negative-referenced to V com .
  • V + as shown in Fig. 3 is applied to one pixel
  • V- is applied to another pixel
  • both pixels should have the same amount of light transmitted.
  • alternating pixels are switched between one polarity and the other.
  • the polarity of this pixel voltage is reversed on alternate image frames.
  • the voltage is inverted depending on the position of the pixel in one image frame.
  • LCDs are used using a row inversion scheme in which the applied voltage is inverted from row to row.
  • a dot inversion pattern is known in which the polarity of nearby pixels is in antiphase.
  • a screen of the LCD screen is shown with which a badly adjusted voltage V com can be recognized and with which the resulting flicker can be minimized.
  • the LCD screen 20 shown in Fig. 2 comprises two main regions, the main region 21 shown in the upper part and the main region 22 shown in the lower part of the screen 20. In the embodiment of Fig. 2 only a few pixels are shown, namely the pixels located in the neighborhood where one region neighbors another region.
  • the first region 21 comprises a first part 21a and a second part 21b.
  • every second row is controlled with an inverted voltage meaning that in row 2 the voltage V + is applied, resulting in a transmission shown by the hatched area in Fig. 2 .
  • row 4 the voltage V-is applied, resulting in a transmission of light displayed by the hatched area.
  • No voltage is applied to the other rows of region 21a (rows 1 and 3 of the embodiment shown), these rows having a black appearance, as no light is transmitted.
  • a black row is followed by a row to which voltage is applied, e.g. having a gray appearance.
  • V com is not well-regulated, a low-frequency flicker occurs, in the range of 50 or 60 Hz depending on the image frame rate. This flicker can be observed by a user of the liquid crystal display.
  • the voltage pattern is shifted by one row, so that the black rows of region 21a are gray and region 21 b and vice versa.
  • the flicker will occur in the first region 21.
  • the display used is a display in which the voltage is inverted from pixel to pixel
  • the second region 22 will indicate that the liquid crystal display is not well-adjusted.
  • the second region 22 comprises a first part 22a and a second part 22b.
  • the result is a chequered pattern with black pixels and gray pixels, the gray pixels being indicated as hatched.
  • both polarities are visible at the same time.
  • a flicker can be recognized for any type of LCD used.
  • the flicker can be minimized by either manually controlling control unit 11 in such a way that the intensity modulation is minimized, or this can be done automatically by using an optical sensor 13 as shown in Fig. 1 .
  • the optical sensor 13, when detecting the screen as shown in Fig. 2 can minimize the intensity modulation by controlling the control unit 11.
  • the LCD is a display with a row inversion scheme
  • the upper part of the display shown will flicker.
  • the LCD is a display using a dot inversion scheme
  • the lower part of the screen will flicker.
  • the intensity modulation will be detected by the light sensor 13 and the light sensor 13 can control the control unit 11 in such a way that the flicker is minimized.
  • a screen as shown in Fig. 2 is used, a not well-adjusted common voltage can be detected by the human eye, as the frequency is low enough.
  • the different between positive and negative polarity is emphasized by using a pattern as shown in Fig. 2 and as it is possible to securely minimize a flicker for any kind of liquid crystal display.
  • the different possible inversion schemes used in liquid crystal displays can be recognized and an eventual flicker can be minimized.
EP08016775A 2008-09-24 2008-09-24 Système de commande d'affichage à cristaux liquides Withdrawn EP2169656A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP08016775A EP2169656A1 (fr) 2008-09-24 2008-09-24 Système de commande d'affichage à cristaux liquides

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP08016775A EP2169656A1 (fr) 2008-09-24 2008-09-24 Système de commande d'affichage à cristaux liquides

Publications (1)

Publication Number Publication Date
EP2169656A1 true EP2169656A1 (fr) 2010-03-31

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013185039A1 (fr) * 2012-06-08 2013-12-12 Apple Inc. Systèmes et procédés permettant de réduire ou d'éliminer un effet mura au moyen d'une imagerie améliorée des contrastes

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6313818B1 (en) * 1996-06-07 2001-11-06 Kabushiki Kaisha Toshiba Adjustment method for active-matrix type liquid crystal display device
US20050162365A1 (en) * 2003-11-27 2005-07-28 Seiko Epson Corporation Method for adjusting electro-optical apparatus, adjusting apparatus of electro-optical apparatus, and electronic system
US20050259092A1 (en) * 2004-05-20 2005-11-24 Seiko Epson Corporation Image-correction-amount detecting device, circuit for driving electro-optical device, electro-optical device, and electronic apparatus

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6313818B1 (en) * 1996-06-07 2001-11-06 Kabushiki Kaisha Toshiba Adjustment method for active-matrix type liquid crystal display device
US20050162365A1 (en) * 2003-11-27 2005-07-28 Seiko Epson Corporation Method for adjusting electro-optical apparatus, adjusting apparatus of electro-optical apparatus, and electronic system
US20050259092A1 (en) * 2004-05-20 2005-11-24 Seiko Epson Corporation Image-correction-amount detecting device, circuit for driving electro-optical device, electro-optical device, and electronic apparatus

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
WWW.LAGOM.NL: "Inversion (pixel walk) - Lagom LCD test", INTERNET CITATION, 9 March 2008 (2008-03-09), Retrieved from the Internet <URL:http://web.archive.org/web/20080309001649/http://www.lagom.nl/lcd-test/inversion.php> [retrieved on 20101208] *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013185039A1 (fr) * 2012-06-08 2013-12-12 Apple Inc. Systèmes et procédés permettant de réduire ou d'éliminer un effet mura au moyen d'une imagerie améliorée des contrastes
US9013384B2 (en) 2012-06-08 2015-04-21 Apple Inc. Systems and methods for reducing or eliminating mura artifact using contrast enhanced imagery

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