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WO1994009475A1 - Dispositif d'affichage et son procede de commande - Google Patents

Dispositif d'affichage et son procede de commande Download PDF

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Publication number
WO1994009475A1
WO1994009475A1 PCT/US1993/010062 US9310062W WO9409475A1 WO 1994009475 A1 WO1994009475 A1 WO 1994009475A1 US 9310062 W US9310062 W US 9310062W WO 9409475 A1 WO9409475 A1 WO 9409475A1
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WO
WIPO (PCT)
Prior art keywords
transmittance
light
pixels
pixel
state
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.)
Ceased
Application number
PCT/US1993/010062
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English (en)
Inventor
Jemm Y. Liang
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.)
Panocorp Display Systems
Original Assignee
Panocorp Display Systems
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 Panocorp Display Systems filed Critical Panocorp Display Systems
Priority to AU54458/94A priority Critical patent/AU5445894A/en
Publication of WO1994009475A1 publication Critical patent/WO1994009475A1/fr
Anticipated expiration legal-status Critical
Ceased 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
    • G09G3/3406—Control of illumination source
    • G09G3/342—Control of illumination source using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
    • 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
    • G09G3/3607—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 for displaying colours or for displaying grey scales with a specific pixel layout, e.g. using sub-pixels
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
    • H04N3/10—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical
    • H04N3/12—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by switched stationary formation of lamps, photocells or light relays
    • H04N3/127—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by switched stationary formation of lamps, photocells or light relays using 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
    • G09G2310/00—Command of the display device
    • G09G2310/02—Addressing, scanning or driving the display screen or processing steps related thereto
    • G09G2310/0235—Field-sequential colour display
    • 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
    • G09G2310/02—Addressing, scanning or driving the display screen or processing steps related thereto
    • G09G2310/024—Scrolling of light from the illumination source over the display in combination with the scanning of 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
    • G09G2310/00—Command of the display device
    • G09G2310/08—Details of timing specific for flat panels, other than clock recovery
    • 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
    • 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
    • G09G2320/0252—Improving the response speed
    • 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
    • G09G2320/0261—Improving the quality of display appearance in the context of movement of objects on the screen or movement of the observer relative to the 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
    • G09G2320/00—Control of display operating conditions
    • G09G2320/02—Improving the quality of display appearance
    • G09G2320/0285—Improving the quality of display appearance using tables for spatial correction of display data
    • 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
    • G09G2320/04—Maintaining the quality of display appearance
    • G09G2320/041—Temperature compensation
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2340/00—Aspects of display data processing
    • G09G2340/16—Determination of a pixel data signal depending on the signal applied in the previous frame

Definitions

  • This invention relates in general to an efficient display device capable of displaying monochro ⁇ matic, multi-color and full-color images of high brightness and resolution.
  • the invention relates to a front end unit with light shutters such as liquid crystal device (LCD) cells without color filters, where the LCD is illuminated by a back lighting source, which emits monochromatic light or light of multiple colors, such as the three primary colors of red, blue and green.
  • LCD liquid crystal device
  • LCDs are one of the most widely used type of devices. However, most of the LCDs used today are monochromatic. While multi-color and full-color LCDs have been proposed, their development has been hindered by a number of technical difficulties. In most of the multi-color and full-color LCDs proposed, a back light source is employed. However, in most cases, the back light source employed is white light. Therefore, to produce composite images of different color, red, blue and green filter arrays have been used. For each pixel, the white light directed towards a portion of the pixel is filtered to permit only red light to pass, and white light directed toward another portion of the same pixel is filtered to permit only blue light to pass and the white light directed towards the remaining portion is filtered to permit only green light to pass. Thus only a small part of the energy of the white light is transmitted through the LCD.
  • LCD cells respond slowly to voltages applied across them. Typically, when scanning voltages are first applied to a LCD cell, the cell has low transmis ⁇ sion rate. The transmission rate rises slowly during the scanning cycle so that a low percentage of light is passed by the red, blue and green filters and transmit- ted through the LCD cells during the scanning cycle. This is a notable drawback of passive matrix type LCD color displays, where no drivers are used contiguous to the LCD cells for driving the cells.
  • active matrix LCD cells are proposed by adding at least three thin film transistors for each LCD cell or pixel for accelerating the turning on and off of the three portions of the cell or pixel for light transmission of the three different colors.
  • Such transistors and the data bus necessary to control them are opaque and occupy a signifi ⁇ cant area of the LCD cell. In other words, the total transmission rate of the back light is lowered because of the reduction of the area of the cell that actually transmits light.
  • a color sequential scheme is a method where each frame of color image is further decomposed into three fields, one red, one green and one blue. These fields of color image are then cycled at a speed faster than the fusion frequency, and the image observed by the human viewer will be a color image. In other words, color mixing is performed in the time domain in color sequential displays.
  • the fusion frequency depends on the brightness of display devices and their intended application.
  • the current television standards are 50Hz for PAL and 60Hz for NTSC. Due to the close viewing distance, a computer monitor has a higher standard and a frame rate of around 70 Hz is considered to be desirable.
  • the field frequency will be three times higher than the frame frequency. For example, the field frequency for a 60Hz frame rate will be 180Hz.
  • a sequential display device known to those skilled in the art includes a light shutter front end and a color backlight source. Combining the effect of color changes of backlight pulses and the light trans- mittance change of the individual light shutters, color images are displayed.
  • the light shutter needs to change the transmittance faster than 180 times per second to have a frame rate of 60Hz or higher. This corresponds to a shutter response time of about 5.5 milliseconds, close to the limit of response time of twisted nematic (TN) LCDs.
  • TN twisted nematic
  • the response time of liquid crystal can be de ⁇ scribed by the following formula: ⁇ — n (i) r ⁇ ef 2 -ic ⁇ 2
  • ⁇ r or the rise time, is the time it takes for a liquid crystal display (LCD) to change its transmittance in response to an applied signal from the time the signal is applied;
  • ⁇ d or the decay time, is the time it takes for the transmittance to change when the applied signal is removed;
  • d is cell gap;
  • n liquid crystal twist viscosity;
  • V is the applied signal voltage;
  • ⁇ e is dielectric anisotropy of liquid crystal.
  • the response time for the transition from one intermediate gray scale to another intermediate gray scale can be two to three times as long as a bi- level transition from fully ON to fully OFF.
  • the apparatus comprises a front end unit and a front end control unit.
  • the front end unit has an array of row electrodes and an array of column elec ⁇ trodes transverse to the array of row electrodes, said row electrodes overlapping column electrodes over a layer of light modulating material when viewed in a viewing direction to define consecutive rows of pixels at the layer, so that light transmittance through the pixels is controlled by electrical signals applied to the row and column electrodes, said light transmittance through the pixels defining a state of transmittance of such pixels.
  • the front end control unit applies consecutively two or more sequences of transmittance control signals to the row and column electrodes to cause the light transmittance through the pixels to sequentially change one row at a time, defining a scanning process sequentially scanning the rows of pixels during which one row of pixels is scanned at a time, each sequence corresponding to one of a plurality of colors, wherein each sequence of transmittance control signals controls the light transmittance of the rows of pixels for passage of light of the corresponding color.
  • the apparatus also include a back end unit and a back end control unit.
  • the back end unit has two or more subsections generating light of said plurality of colors, each subsection overlapping at least one corresponding row of pixels in the front end unit when viewed in the viewing direction, so that light emitted by each subsection is directed substantially towards said at least one corresponding row of pixels.
  • the back end control unit controls light emission of the subsec ⁇ tions so that each subsection emits light of one of said plurality of colors at a predetermined time delay after the application of transmittance control signals in the sequence corresponding to such color to change the light transmittance of the at least one row of pixels corre ⁇ sponding to such subsection for passage of light of such color, and so that said predetermined time delays for light emission of all the subsections are substantially the same.
  • Another aspect is a method for displaying images in response to input signals employing said front and back end units described above.
  • the method compris ⁇ es applying two or more sequences of transmittance control signals to the row and column electrodes, each sequence causing the light transmittance through the pixels to sequentially change one row at a time, defining a scanning process sequentially scanning the rows of pixels during which one row of pixels is scanned at a time, each sequence corresponding to one of said plurality of colors, wherein each sequence of transmit- tance control signals controls the light transmittance of the rows of pixels for passage of light of the corresponding color.
  • the method also includes causing each subsection to emit light of one of said plurality of colors at a predetermined time delay after the application of transmittance control signals in the sequence corresponding to such color to change the light transmittance of the at least one row of pixels corre ⁇ sponding to such subsection for passage of light of such color, and so that said predetermined time delays for light emission of all the subsections are substantially the same.
  • Display devices such as the LCD, display images in response to input data signals.
  • the transmission rate of the LCD may be proportional to the magnitudes of the input data signals.
  • the color images are degraded because the differ ⁇ ent gray tones cannot be achieved in time for a high refresh rate of about 180 Hz.
  • another aspect of the invention is directed towards a system for applying an adaptive boost (or cut) to the input data to compen- sate the signals before the compensated signals are applied to the electrodes controlling the transmittance of LCD to reduce error in gray tones.
  • the apparatus comprises a front end unit, said unit defining therein a plurality of pixels, each pixel including at least one light shutter, and a back end unit generating light toward the pixels in the front end unit.
  • the apparatus further includes a device including a lookup table, said device generating transmittance control signals in response to the input signals according to the lookup table, said device providing said transmittance control signals to the front end unit to address each pixel in the front end unit and to control the light transmittance there- through, said light transmittance defining a state of transmittance of such pixel; and means for causing the back end unit to produce light directed towards the front end unit to produce color images according to the input signals.
  • Yet another aspect covers a method for display ⁇ ing images in response to input signals employing an apparatus comprising the front and back end units described in the paragraph immediately above.
  • the method comprises generating transmittance control signals in response to the input signals and according to a lookup table; applying said transmittance control signals to the front end unit to address each pixel in the front end unit and to control the light transmit ⁇ tance therethrough, said light transmittance defining a state of transmittance of such pixel; and causing the back end unit to produce light directed towards the front end unit to produce images according to the input signals.
  • Fig. 1 is a perspective view of the embodiment shown with the desired viewing position.
  • Fig. 2 is a functional block diagram of the embodiment.
  • Fig. 3 is a simplified time domain illustration of relationships between various waveforms and between different subsections of the embodiment.
  • Figs. 4A-4D illustrate in more detail the timing relationships in reference to one of the subsec ⁇ tions of Fig. 3.
  • Fig. 4A shows the back lighting pulses
  • Fig. 4B the activation signals for one of the rows of pixels generated by the row driver RD.
  • Fig. 4C is a transmittance transition curve for one pixel where the activation signals of Fig. 4B are applied without compensation to the front end unit
  • Fig. 4D is the transmittance curve for the same pixel after the activation signals have been compensated according to the invention.
  • Fig. 5 is a flow chart illustrating a method for compiling a lookup table for making the compensation illustrated in Fig. 4D.
  • Figs. 6A-6D are schematic circuit diagrams to illustrate different implementations for the lookup table to make the compensation illustrated in Fig. 4D.
  • Fig. 6E is a timing diagram to illustrate the boosting or cutting of input signals before they are applied to drive LCD cells, thereby reducing transient errors in gray tones.
  • Fig. 7A is a graphical illustration of the relation between light transmittance of a normally white
  • Fig. 7B is a graphical illustration of the TFT gate pulses applied to a row of pixels during a number of scanning cycles, and of the light transmittance states during the cycles using only the DLDB scheme in
  • Figs. 6C, 6D Fig. 7C is a graphical illustration of the TFT gate pulses applied to a row ofs pixel during a number of scanning cycles, and of the light transmittance states during the cycles using the DLDB scheme of Figs. 6A, 6B improved with color correction.
  • the preferred embodiment is a display apparatus including a front end unit FE and its associated drivers, a back end unit BE and its associated drivers, a device responsive to input data signals for generating transmittance control signals to address the pixels in the front end unit and to control the light transmit ⁇ tance therethrough, and means for causing the back end unit to produce light pulses.
  • the device includes a data processing unit DP and interface port INPUT.
  • An optional sensor TMP to sense the operating temperature of the front end unit may also be employed.
  • the causing means includes control unit CU and interface ports CNTRL and CLK. The control unit CU responds to the control and timing information received from port CNTRL and CLK and produces control signals to various drivers and the data processing unit to operate the display device.
  • the front end unit FE is a matrix-addressable device such as an active-matrix liquid-crystal-display (AM-LCD) .
  • Each addressable unit is a light shutter whose transmittance can be controlled by signal fed from an input (not shown) through data driver DD.
  • FE is controlled in a line scanning method where row driver RD will activate one line of pixels P (not drawn to scale in Fig. 2) at a time to receive data signals from DD.
  • Each pixel occupies an area including one or more light shutters such as LCD cells.
  • the pixels are arranged in an array of rows and columns along the X and Y direc- tions respectively, each of the rows and columns being a line of pixels.
  • the scanning of FE is performed in a substantially sequential fashion.
  • the back end unit BE is a light generating device such as a vacuum fluorescent display (VFD) , a microtip fluorescent display (MFD) or a electron fluorescent display (EFD) , whose light emitting area substantially covers and overlaps the light shuttering area of FE.
  • VFD vacuum fluorescent display
  • MFD microtip fluorescent display
  • EFD electron fluorescent display
  • the back end unit BE is further separated into about 20 or more subsections; a simplified version of only 4 subsections is illustrated by reference to Fig. 3.
  • Each subsection corresponds to a number of rows or columns (i.e. lines) of pixels in the front end unit FE.
  • Each pixel includes one or more light shutters such as LCD cells.
  • the scanning operation below will refer only to scanning of rows, it being understood that scanning column by column may be accomplished in essentially the same manner.
  • Each subsection can be controlled by backlight driver BD to generate light pulses, of pulse widths shorter than about 1 millisec- ond, of three primary colors: red, green and blue.
  • An optional diffuser layer DFU may be inserted between the FE and the BE to enhance the smoothness of the displayed image.
  • the front end unit FE is scanned row by row sequentially.
  • the row and data drivers RD, DD apply appropriate scanning and data signals to the row and column electrodes of FE unit row by row to change the levels or states of light transmittance of the rows of pixels.
  • TFT thin film transistors
  • gate pulses are also applied to enable (activate) the scanning and data pulses to change the levels or states of light transmittance of the rows of pixels.
  • the control unit CU controls the backlight driver BD to activate one or more BE subsections adjacent to row N to generate a light pulse of red, green or blue color.
  • the above process is repeated for all rows of pixels on the FE once for red subfield, and then once for green subfield and then once for blue subfield.
  • the frame rate is faster than about 60Hz, the synchronized change of pixel transmittance and the color of the backlight pulses produces color images when viewed from the viewing position indicated in Fig. 1.
  • the front end unit FE includes an array of row electrodes RE, and an array of column electrodes CE that are transverse (preferably perpendicular) to the array of RE.
  • RE row electrodes
  • CE column electrodes
  • the two arrays of electrodes overlap over areas at a layer of light modulating material (not shown) in between RE and CE, such as liquid crystal material, at areas referred to herein as pixels, when viewed in a viewing direction V as shown in Fig. 1.
  • the back end unit BE is divided into subsections, where each subsection overlap at least one row of pixels when viewed in the viewing direction V of Fig. 1, so that light emitted by such subsection will be directed to such corresponding at least one row of pixels.
  • BE has only four subsections. As shown in Fig. 3, assuming that the front end unit has 480 rows of pixels evenly divided into four subsets with each subset having 120 rows, each subset corresponding to and overlap one of the four subsections.
  • the pixel rows corresponding to sub- section 1 of the back end unit illustrated in Fig. 2 are numbered from row 1 to row 120 of pixels.
  • the LCD TFT gate will apply pulse 20 to row 1 and pulse 20' to row 120, where the time delay between pulses 20, 20' is about one quarter of the scanning cycle Tc for scanning all rows of pixels in the entire front end unit once.
  • Other pulses (not shown) applied between the application of pulses 20, 20' are used to control light transmit ⁇ tance of pixel rows between rows 1 and 120. All of such pulses, together with pulses 20, 20', control the light transmittance of rows 1 through 120 for passage of a green light pulse to exhibit the green component of color image.
  • the L.C. transmittance curve for row 120 is shown in dotted line 21*, which is delayed relative to the transmittance curve 21 for row 1 (transmittance of row 1) by about 1/4(Tc). As shown in Fig.
  • the pulse 22 is applied by the LCD TFT gate to row 121 in subset 2 (corresponding to subsection 2 of the back end unit) after pulse 20', and pulse 22' is applied to row 240 at about 1/2(Tc) after pulse 20, and the trans it- tance curve of row 240 is delayed relative to transmit ⁇ tance curve of row 121 by about 1/4(Tc). Therefore, when the back light pulses 32 are emitted by the corresponding subsection of the back end unit, the transmittances of the rows 1 through 120 (i.e. those in the subset 1) are substantially at their stable trans- mittance level whereas the rows 121 through 480 are not at their stable transmittance level.
  • the delay between the transmittance curves is reduced to 5% or less, rather than 25% or 1/4 of Tc as illustrated in Fig. 3, and then the transmittance curves such as 21. 21' of rows of pixels may all be made to substantially converge. In such event, the time shift between the transmittance curves may be ignored, so that the back light pulses 32 may be considered as generated at a fixed time interval Td after the application of the LCD TFT gate pulses.
  • the above described scheme is advantageous in that the generation of the back light pulses 32 is greatly simplified since their timing may be fixed at a particular delay in reference to a particular scanning pulse applied to the corresponding subset of rows of pixels.
  • all of the subsections are caused to generate back light pulses at substantially the same delay after the application of the scanning and data signals to the pixel rows overlap ⁇ ping and corresponding to such subsection, where such delay may be Tc or a time interval slightly less or more than Tc.
  • Td may be substantially equal to or slightly less or more than Tc.
  • a color sequential display device is illustrat ⁇ ed in Fig. 1.
  • the device includes a light shutter front end FE, such as an LCD, and a color backlight source or back end unit BE.
  • the back end unit is separated into multiple subsections. Each of these subsections can independently generate light pulses of red, green and blue color.
  • the LCD front end functions as a matrix of light shutters controlling the transmit ⁇ tance of backlight pulses at each pixel. The shades of various colors are achieved by controlling the mix of red, green and blue lights. According to the required color mix, the transmittance of each LCD pixel is modulated in a periodical fashion, in synchronization with the backlight color pulses (Figs. 3 and 4) . Combining the effect of the color change of backlight pulses and the transmittance change of each individual pixel, color images are displayed when the device is viewed in the viewing direction V, as indicated in Fig. 1.
  • the sequence and amount of transmittance level changes depends on the required R/G/B mix and is deterministic for any given color/brightness. This fixed sequence will be repeated until the information displayed by the pixel is changed. As long as the field cycle time is longer than the bi-level response time of the LCD front end, it is always possible to change the LCD input data signal or, more specifically, to boost or reduce (cut) the difference between two successive data signals, such that toward the end of each scanning cycle the transmit- tance of the pixel reaches the desired level. Due to the deterministic nature (explained below) of the time sequence between the transmittance level transitions, the amount of boost or compensation to the data signal can be predetermined by calculations and measurements.
  • the backlight or back end unit is partitioned into many subsections, each corresponds to a roughly equal number of scan lines in the LCD light shutter front end, and each subsection is to be pulsed at a fixed delay after the corresponding LCD lines of pixels are scanned by the signal of the corresponding color field of the subsection, then the frame refresh rate of the device can be up to
  • N is the number of subsections in the backlight unit
  • L is a number larger than or equal to 1 and is related to the time between backlight pulses and the time pixels are addressed by data of the next field
  • ⁇ is the bi-level response time of the LCD light shutter front end
  • the factor 3 is for the red, green, blue three-color subfields.
  • DLDB DLDB
  • a data processing unit DP will boost or reduce the difference between various gray scale signal levels by amounts predetermined through experiments and calculations such that the light shutter transmittance will change from any given starting level to any given target levels at a fixed time delay Td after the application or activation of the signals to the row and column electrodes RE, CE in FE, where Td is substantial ⁇ ly equal to or slightly shorter than the field cycle time Tc (Fig. 4D) .
  • Source input signals representing ratios of red, green and blue color mixes will be converted to level-difference-boosted data through parameter set calculations, table lookup or other data processing techniques. These boosted (reduced) signals are then applied to the front end light shutter to control the transmittance of each individual pixel. The corresponding subsections of the back end lighting unit will then be controlled to produce light pulses of appropriate color delayed approximately by Td after the application of a signal to a corresponding portion of the front end light shutters.
  • the frame rate will be determined mainly by the bi-level response time of the LCD, not the number of desired gray levels. For simplicity, as in Fig. 3, only the back light pulses R. , G ...
  • TFT enabling gate pulses G R1 , G G1 , ... etc are shown in Figs. 4A, 4B, to illustrate the timing relationship between the address ⁇ ing of the front end unit FE (to change light transmit ⁇ tance level or state) and the light emission of the back light unit BL.
  • the elapse time Td between the signal application to the LCD pixels and the backlight pulses can be considered as fixed through ⁇ out the screen.
  • the drive signals (such as the input data signals from another source, not shown) of LCD pixels can be boosted or reduced (cut) by a predetermined amount to new signals that correspond to levels Bl, B2, B3 that would be reached upon settlement without transition time restriction such that, at a delay Td after the signals are applied, the transmittance of the pixel will reach the desired gray transmittance levels LI, L2, L3 from the given starting level.
  • LI, L2, L3 are three of the many gray levels that are possible.
  • the original signal which corresponds to the value required for the pixel to settle to the desired transmittance level after a prolonged delay, regardless of the starting transmittance level before the signal applica ⁇ tion, will be changed to a value that will allow the pixel transmittance to reach the desired level from the particular starting level, at an elapsed time of exactly Td after the signal has been applied.
  • Another aspect of this invention is about a method and structure of combining sensors, such as thermocouple, placed near the front end unit, and a controller such that the controller will use the sensor's output to control the amount of level-difference-boosting by selecting appropriate lookup tables, changing coefficients used by the data processing unit, and so on.
  • the device needs to repeat the r/g/b subfields at a rate of over 180 field per second or less than about 5.5 milliseconds per field.
  • a TN LCD with a bi-level response time of about 5 mS is used in the above-described scheme, errors (E2, E3) in transmittance level will happen for interme ⁇ diate gray level transitions between subfields.
  • This differential signal level dependence of TN LCD will either cause the color quality to degrade or will limit the number of colors that can be displayed faithfully.
  • the amount of boost (reduction) will be higher for smaller gray scale transitions, i.e., the amount of boost depends not only on the target gray scale level but also on the initial start gray scale level. In other words, both the starting transmittance level or state before scanning and data signals are applied to the row and column electrodes and the target transmittance level or state reached after the application will affect the amount of boost or cut needed.
  • the exact level-differ ⁇ ence-boosting function can be calculated in the design phase through detail modeling of liquid crystal behav ⁇ iors, or it can be actually measured through different procedures. One possible procedure is shown in the flow chart of Fig. 5. The determined function can then be captured in lookup tables or in sets of parameters that can be built into the signal processing unit of the display device.
  • level- difference-boosting functions or lookup tables each optimized for a specific range of operating tempera ⁇ tures, as is indicated by LDB1, LDB2 and LDB3.
  • the control unit will select a particular level-difference-boosting function LDBx based on the output of temperature sensor TMP placed near the front end unit, the data processing unit DP will then convert the data received from the INPUT port into level-difference-boosted signals through function LDBx. These level-difference-boosted data signals will then be sent to the data bus driver DD to control the transmittance of the pixels in the front end unit FE.
  • Figs. 6A, 6B show two types of DP implementa ⁇ tion of table lookup method applicable to adjust the input data signals applicable to each pixel.
  • Fig 6A is a direct lookup where IN is the connection to the INPUT data port.
  • the control unit CU presents the control signal FIELD to select the signal for red, green or blue color field. If DLDB is implemented as a memory device then IN and FIELD will serve as the address and the data read out of the memory device will be the OUT which will then sent to the LCD data bus driver DD for controlling the transmittance of the pixel concerned.
  • DLDB lookup table can be integrated into one memory device as shown in Fig. 6B where the extra 2 bits address input T, generated by the control unit CU, further partition the memory device into four different tables each optimized for a specific tempera ⁇ ture ranges.
  • a different implementation of DP utilizing finite state machine theory is shown in Fig. 6C. This implementation is based on the observation that the amount of signal boost or cut can be determined from knowledge of previous states of a LCD light shutter pixel and the current input.
  • two state memory buffers STB1 and STB2 are used to store the state of previous LCD pixel transmittance states, where STB1 stores the state of the last state (ST1) and STB2 stores the state before the last state (ST2) .
  • the level of state memory can be 1 and does not have to be 2. Although the light transmittance levels or states resulting from the signal conversion will be more accurate with more levels of state memory, the improve ⁇ ment of accuracy will diminish very quickly.
  • the two state memory can be implemented in one memory device STB where ST1 occupies one part of each word, for example the least significant J bits, while ST2 occupies other part of the word, for example, the most significant K bits.
  • the input data IN together with ROW and COL represent ⁇ ing the row and column position of the current data IN, are presented to the data processing unit DP.
  • ROW and COL are used to address the state memory buffer STB.
  • the previous states STl, ST2 of the pixel data currently being processed will show up in the output port of state memory.
  • states ST2 and STl will address the proper entry in state transition table STBL to produce the output OUT, ignoring the block NSG for the moment.
  • the entry in STB corresponding to the ROW, COL entry will also be updated by the new input data IN such that the most significant K bits of STl become the new ST2 (ST2') and the most significant J bits of IN become the new STl (STl 1 ).
  • STl', ST2' are written back to the state memory buffer STB for later use.
  • a next state generation circuit NSG may be used to derive the next states STl' , ST2' from the input IN and supply such states to state buffer memory STB, which later supplies stored states STl, ST2 to STBL.
  • Fig. 6C An alternative to Fig. 6C is shown in fig. 6D.
  • the state memory includes ST as opposed to STl and ST2.
  • the generation of next state ST* is from state transition table STBL as opposed to from bit shifting of IN and STl.
  • a feedback path applies the next state ST' to the buffer STB.
  • Many other variation of Fig. 6C and 6D are possible.
  • Fig. 6C and 6D are more general than the ones shown in Fig. 6A and 6B in that they do not require knowledge of the color of current field and therefore are not confined to a fixed sequence of transmittance change.
  • the schemes shown in Fig. 6A and 6B will produce extra transient errors after each change while the schemes of Fig. 6C and 6D will not.
  • the scheme shown in Fig. 6C or 6D can be applied to conven- tional LCD displays with a monolithic back end light source to improve their gray scale response time and is not restricted to the color sequential operation as dis ⁇ cussed in this invention. As shown in Fig.
  • the level-difference-boosted signals (dotted line signals) in the sequence of transmittance control signals are applied to the data driver block DD for application to the front end unit.
  • the implementation shown in Figs. 6C and 6D can no longer produce correct color mixing ratio, since Tc is shorter than the LCD response time, it may not be possible to complete the transition between two arbi ⁇ trary subsequent transmittance levels.
  • the implementation shown in Figs. 6A and 6B can still produce correct color if a color correction scheme is employed.
  • the color correction scheme is based on the fact that the rise time ⁇ r (formula shown above) can be accelerated by the applied signal beyond the bi-level response time. Therefore, in a normally white mode LCD (transmittance to signal voltage curve shown in Fig.
  • Figs. 7A is a graphical illustration of the TFT gate pulses applied to a row of pixels during a number of scanning cycles, and of the light transmittance states during the cycles using only the DLDB scheme described above in reference to Figs. 6C, 6D. As shown in Figs.
  • Fig. 7C is a graphical illustration of the TFT gate pulses applied to a row of pixels during a number of scanning cycles, and of the light transmit ⁇ tance states during the cycles using the DLDB scheme of Figs. 6A, 6B improved with color correction.
  • Fig. 7B illustrates a case where LCD response speed is slower than Tc and a DLDB scheme such as shown in Fig. 6C is used.
  • the error in color mixing ratio is created since in every transition the DLDB scheme shown in Fig.
  • a table lookup scheme such as those schemes shown in Figs. 6A and 6B can make sure the three color transition is such that, while the brightness may be sacrificed somewhat, the color mixing ratio is not changed. This can be achieved by incorporating correct judgment criteria in an algorithm such as the one shown in Fig. 5 which can be used to create the lookup table.
  • the loop can consist of first determining the transmittance for one of the OFF transition (or raising transmittance) as compared to the desired level of transmittance.
  • the ratio between this actual transmittance level and the desirable transmit ⁇ tance level will be used to modify the target transmit- tance level of the other two colors. For example, if the desired level of transmittance is 10-8-0 for red- green-blue and the actual achievable OFF transition can only raise the transmittance from 0 to 7, then the new transmittance mix becomes 7-5.6-0.
  • These two sets of transmittance states 10-8-0 and 7-5.6-0 will produce the same color mixing ratio but with different brightness.
  • the loop is continued to calculate the signals to be applied to the front end unit pixel for accomplishing the transition from 7 to 5.6 and from 5.6 to 0.
  • both of these are ON transitions (lower transmittance) they can be accelerated by raising the applied signal levels.
  • a new set of transmittance level mix is determined by scaling down all three transmit ⁇ tance with a common multiplying factor such as the case where the transmittance is scaled down from 10-8-0 to 7- 5.6-0.
  • the color correction loop should complete in two cycles, since within three transmittance levels there can only be two transitions raising transmittance.
  • a scale factor is applied to scale up or down the target level to be achieved after the transition. For example, if a transition from 0 to 10 is not possible, while from 0 to 7 is possible, the target level is scaled down to 7 from 10 in order to determine whether the red color is correct. Then this scale factor is applied as well to the other two colors, unless the transition for any one of green and blue colors calls for a larger scale factor.

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Abstract

Procédé, appelé amplification déterministe de la différence de niveau (DLDB), permettant de compenser l'accroissement du temps de réponse d'une cellule ACL (FE) lorsque des dispositifs de ce type sont utilisés en mode séquentiel couleurs comme modulateur analogique de transmittance afin d'afficher diverses couleurs. Ce procédé consiste à transformer les données d'entrée des rapports de mélanges de couleurs, en un autre ensemble de signaux préalablement calculés ou mesurés, avant l'envoi de ces signaux à l'ACL (FE) afin de réguler sa transmittance. Le signal compensé se sert du caractère périodique des variations de transmittance en mode séquentiel couleurs pour minimiser les erreurs dues au ralentissement de la réponse de l'ACL. Lorsque le temps de réponse de l'ACL est trop long pour assurer la transition vers le niveau cible voulu de transmittance, le niveau cible diminue pour toutes les couleurs à afficher au niveau des pixels, afin de garder un rapport de mélange de couleurs correct. En outre, on a prévu un dispositif d'affichage comportant une partie entrée d'ACL (FE), une source lumineuse en couleurs (BE) et une unité (CU) pouvant effectuer la transformation de données précitée.
PCT/US1993/010062 1992-10-20 1993-10-20 Dispositif d'affichage et son procede de commande Ceased WO1994009475A1 (fr)

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Cited By (14)

* Cited by examiner, † Cited by third party
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EP0927416A1 (fr) * 1997-07-22 1999-07-07 Koninklijke Philips Electronics N.V. Dispositif afficheur
WO2000004529A1 (fr) * 1998-07-15 2000-01-27 Siemens Aktiengesellschaft Procede pour faire fonctionner un dispositif d'affichage a cristaux liquides, et dispositif d'affichage a cristaux liquides a compensation de temperature
WO2000077769A1 (fr) * 1999-06-10 2000-12-21 Koninklijke Philips Electronics N.V. Amelioration de la purete des couleurs dans un afficheur a cristaux liquides a sequence de couleurs
WO2004003884A1 (fr) * 2002-06-27 2004-01-08 Koninklijke Philips Electronics N.V. Correction d'erreurs de couleur dans des affichages sequentiels de couleur
WO2004044878A3 (fr) * 2002-11-05 2004-07-01 3M Innovative Properties Co Eclairage par balayage permettant de reduire la remanence lcd dans les afficheurs a projection frontale et a projection par transparence
EP1449193A1 (fr) * 2001-11-26 2004-08-25 Samsung Electronics Co., Ltd. Afficheur a cristaux liquides et procede de commande de celui-ci
WO2004111985A1 (fr) * 2003-06-13 2004-12-23 Koninklijke Philips Electronics, N.V. Panneau d'affichage a cristaux liquides comprenant un procede d'eclairage segmente par eclairage en defilement des segments correspondants du panneau
WO2005020205A3 (fr) * 2003-08-22 2005-04-21 Philips Intellectual Property Procede et systeme etalonnage d'un systeme de pilotage de moyens de restitution d'images exposes a des effets d'inertie
US6909472B2 (en) 1998-04-17 2005-06-21 Barco N.V. Conversion of a video signal for driving a liquid crystal display
WO2005101364A1 (fr) * 2004-04-13 2005-10-27 Genesis Microchip Inc. Surexcitation de pixels pour panneau lcd a pixels a temps de reponse tres lent
CN100390850C (zh) * 2003-11-29 2008-05-28 三星Sdi株式会社 显示装置的像素电路及其驱动方法
US7952545B2 (en) 2006-04-06 2011-05-31 Lockheed Martin Corporation Compensation for display device flicker
WO2013079253A1 (fr) * 2011-11-30 2013-06-06 Tp Vision Holding B.V. Appareil et procédé d'attaque de dispositif d'affichage
US10467964B2 (en) 2015-09-29 2019-11-05 Apple Inc. Device and method for emission driving of a variable refresh rate display

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US5128782A (en) * 1989-08-22 1992-07-07 Wood Lawson A Liquid crystal display unit which is back-lit with colored lights

Patent Citations (1)

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US5128782A (en) * 1989-08-22 1992-07-07 Wood Lawson A Liquid crystal display unit which is back-lit with colored lights

Cited By (24)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0927416A1 (fr) * 1997-07-22 1999-07-07 Koninklijke Philips Electronics N.V. Dispositif afficheur
KR100632713B1 (ko) * 1997-07-22 2006-10-13 코닌클리케 필립스 일렉트로닉스 엔.브이. 디스플레이 장치
US6909472B2 (en) 1998-04-17 2005-06-21 Barco N.V. Conversion of a video signal for driving a liquid crystal display
WO2000004529A1 (fr) * 1998-07-15 2000-01-27 Siemens Aktiengesellschaft Procede pour faire fonctionner un dispositif d'affichage a cristaux liquides, et dispositif d'affichage a cristaux liquides a compensation de temperature
WO2000077769A1 (fr) * 1999-06-10 2000-12-21 Koninklijke Philips Electronics N.V. Amelioration de la purete des couleurs dans un afficheur a cristaux liquides a sequence de couleurs
US6492969B1 (en) 1999-06-10 2002-12-10 Koninklijke Philips Electronics N. V. Combining two successive colors gets colors pure
CN100377193C (zh) * 2001-11-26 2008-03-26 三星电子株式会社 液晶显示器及其驱动方法
EP1449193A1 (fr) * 2001-11-26 2004-08-25 Samsung Electronics Co., Ltd. Afficheur a cristaux liquides et procede de commande de celui-ci
US7095393B2 (en) 2001-11-26 2006-08-22 Samsung Electronics Co., Ltd. Liquid crystal display and a driving method thereof
WO2004003884A1 (fr) * 2002-06-27 2004-01-08 Koninklijke Philips Electronics N.V. Correction d'erreurs de couleur dans des affichages sequentiels de couleur
JP2005531040A (ja) * 2002-06-27 2005-10-13 コーニンクレッカ　フィリップス　エレクトロニクス　エヌ　ヴィ 色順次表示器のための色再マッピング
US6972778B2 (en) 2002-06-27 2005-12-06 Koninklijke Philips Electronics N.V. Color re-mapping for color sequential displays
WO2004044878A3 (fr) * 2002-11-05 2004-07-01 3M Innovative Properties Co Eclairage par balayage permettant de reduire la remanence lcd dans les afficheurs a projection frontale et a projection par transparence
US7196687B2 (en) 2002-11-05 2007-03-27 3M Innovative Properties Company Swept illumination to reduce LCD lag in front and rear projection displays
WO2004111985A1 (fr) * 2003-06-13 2004-12-23 Koninklijke Philips Electronics, N.V. Panneau d'affichage a cristaux liquides comprenant un procede d'eclairage segmente par eclairage en defilement des segments correspondants du panneau
WO2005020205A3 (fr) * 2003-08-22 2005-04-21 Philips Intellectual Property Procede et systeme etalonnage d'un systeme de pilotage de moyens de restitution d'images exposes a des effets d'inertie
CN100390850C (zh) * 2003-11-29 2008-05-28 三星Sdi株式会社 显示装置的像素电路及其驱动方法
US7345663B2 (en) 2004-04-13 2008-03-18 Genesis Microchip Inc. Pixel overdrive for an LCD panel with a very slow response (sticky) pixel
JP2007532979A (ja) * 2004-04-13 2007-11-15 ジェネシス・マイクロチップ・インコーポレーテッド 非常に応答の遅い画素を含むｌｃｄパネルのための画素オーバドライブ
WO2005101364A1 (fr) * 2004-04-13 2005-10-27 Genesis Microchip Inc. Surexcitation de pixels pour panneau lcd a pixels a temps de reponse tres lent
US7952545B2 (en) 2006-04-06 2011-05-31 Lockheed Martin Corporation Compensation for display device flicker
US8675029B2 (en) 2006-04-06 2014-03-18 Drs Signal Solutions, Inc. Compensation for display device flicker
WO2013079253A1 (fr) * 2011-11-30 2013-06-06 Tp Vision Holding B.V. Appareil et procédé d'attaque de dispositif d'affichage
US10467964B2 (en) 2015-09-29 2019-11-05 Apple Inc. Device and method for emission driving of a variable refresh rate display

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