WO1999063399A1 - Eclairement d'un affichage a cristaux liquides - Google Patents

Eclairement d'un affichage a cristaux liquides Download PDF

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Publication number
WO1999063399A1
WO1999063399A1 PCT/US1999/012652 US9912652W WO9963399A1 WO 1999063399 A1 WO1999063399 A1 WO 1999063399A1 US 9912652 W US9912652 W US 9912652W WO 9963399 A1 WO9963399 A1 WO 9963399A1
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WO
WIPO (PCT)
Prior art keywords
imaging element
light source
light
normal
liquid crystal
Prior art date
Application number
PCT/US1999/012652
Other languages
English (en)
Inventor
Akira Tomita
Mark R. Munch
Original Assignee
Tyco Electronics Corporation
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 Tyco Electronics Corporation filed Critical Tyco Electronics Corporation
Priority to EP99928422A priority Critical patent/EP1084444A1/fr
Priority to JP2000552549A priority patent/JP2002517783A/ja
Priority to CA002333989A priority patent/CA2333989A1/fr
Publication of WO1999063399A1 publication Critical patent/WO1999063399A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/133553—Reflecting elements
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1334—Constructional arrangements; Manufacturing methods based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/12—Picture reproducers
    • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
    • H04N9/3102—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM] using two-dimensional electronic spatial light modulators
    • H04N9/3111—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM] using two-dimensional electronic spatial light modulators for displaying the colours sequentially, e.g. by using sequentially activated light sources
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/12—Picture reproducers
    • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
    • H04N9/3141—Constructional details thereof
    • H04N9/315—Modulator illumination systems
    • H04N9/3155—Modulator illumination systems for controlling the light source
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/1336—Illuminating devices
    • G02F1/133602—Direct backlight
    • G02F1/133611—Direct backlight including means for improving the brightness uniformity
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/1336—Illuminating devices
    • G02F1/133616—Front illuminating devices
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/1336—Illuminating devices
    • G02F1/133621—Illuminating devices providing coloured light
    • G02F1/133622—Colour sequential illumination
    • 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
    • G09G2310/08—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
    • 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

Definitions

  • the present invention relates generally to liquid crystal display panels and, more particularly, to a method and apparatus for utilizing thin liquid crystal displays in a high contrast frame sequential color display.
  • Light valves having an electro-optically active element comprising a liquid crystal composite have been used in displays (directly driven, passive matrix, and active matrix addressed), windows, and privacy panels.
  • a liquid crystal composite plural volumes or droplets of a liquid crystal material are dispersed, encapsulated, embedded, or otherwise contained within a matrix material such as a polymer.
  • Exemplary disclosures include Fergason, US 4,435,047; West et al, US 4,685,771; Pearlman, US 4,992,201; and Dainippon Ink, EP 0,313,053, incorporated herein by reference.
  • the liquid crystal composite is disposed between electrodes, at least one of the electrodes typically being patterned to form a matrix.
  • the electrodes are supported by substrates.
  • the voltage to the pair of electrodes is switched off, the electric field no longer exists and the liquid crystal composite between the electrodes changes its optical state to one in which incident light is substantially scattered and/or absorbed. In this state the material will typically be opaque with a frosty appearance if scattering is predominant or dark gray if absorption is predominant.
  • the electrode matrix can be transparent or reflective and is typically a matrix of thin film transistors (TFT), MOS transistors, MIM diodes, or crossed patterned electrodes.
  • TFT thin film transistors
  • MOS transistors MOS transistors
  • MIM diodes MIM diodes
  • crossed patterned electrodes The graphical image can be viewed directly, projected onto a viewing screen, or viewed as a virtual image in the eye.
  • red, green, and blue images either via sequential illumination, for example, using field-sequential color with red, green, and blue light or via dedicated red, green, and blue pixels, a colored image may be formed.
  • the prior art approaches to color displays typically use three separate imaging elements for imparting an image to each of the light components (e.g., red, green, and blue).
  • the imaging elements are generally comprised of liquid crystal composites, the use of three different imaging elements is very expensive. This is especially true for high resolution displays due to the large number of pixels per imaging element plus the means for addressing the individual pixels.
  • many of the prior art color displays utilize twisted nematic type liquid crystals in the display elements that may require a polarizer, thus leading to a loss of brightness. Therefore a color display that only requires a single imaging element that can operate in the absence of a polarizer is desirable.
  • the present invention provides a rapid response liquid crystal imaging element with high brightness and contrast levels.
  • the invention uses a liquid crystal composite that is less than 4 micrometers thick, and preferably less than 2.5 micrometers thick.
  • the display is illuminated by at least one light source that is positioned at an angle of less than 30 degrees off of the display normal, and preferably less than 20 degrees off of the normal.
  • the viewing system is positioned on the same side of the display as the light source and is located approximately normal to the display.
  • the voltage applied across the electrodes of an individual pixel are varied between a first voltage necessary to place the selected pixel into the on state and a second voltage necessary to place the selected pixel into the off state.
  • the second voltage may either be a zero voltage or a non-zero minimum voltage.
  • a non-zero minimum voltage is used in order to avoid the contrast reversal that occurs in thin liquid crystal composites at small illumination angles.
  • At least three light sources of different colors illuminate a liquid crystal imaging element.
  • the sources are all located within an angle of approximately 30 degrees, and preferably less than 20 degrees from the imaging element normal.
  • the viewing system is located on the same side of the imaging element as the light sources and may be comprised of a virtual image viewing system, a direct viewing system, or a projection viewing system.
  • a processor is coupled to both the light sources and the imaging element, thereby allowing the individual color light sources to be synchronized with the output of the imaging element.
  • the controlled switching rate of the light sources and the imaging element are sufficient to avoid frame flicker and color break-up.
  • Fig. 1 is a cross-sectional view of a liquid crystal light valve in the on state according to the prior art
  • Fig. 2 is a cross-sectional view of the liquid crystal light valve of Fig. 1 in the off state.
  • Fig. 3 is a cross-sectional view of a liquid crystal display panel according to the prior art
  • Fig. 4 is a top view of the liquid crystal display panel of Fig. 3.
  • Fig. 5 is an illustration of a liquid crystal display operating in the normal mode.
  • Fig. 6 is an illustration of a liquid crystal display operating in the reverse mode.
  • Fig. 7 schematically illustrates a color frame sequential projector.
  • Fig. 8 is an illustration of an alternative frame sequential color display according to the prior art.
  • Fig. 9 is an illustration of the relationship of a liquid crystal display to an illumination source and a viewer according to the present invention.
  • Fig. 10 is an illustration of a testing system used in conjunction with the invention.
  • Fig. 11 is a graph comparing the brightness of a thick liquid crystal composite to a thin liquid crystal composite for three different illumination angles.
  • Fig. 12 is a graph illustrating the illumination angle dependence of the light scattering characteristics of a thin liquid crystal composite.
  • Fig. 13 is an illustration of a liquid crystal display suitable for use with the present invention
  • Fig. 14 is an illustration of the liquid crystal display shown in Fig. 13 with a specular reflection controlling reflector
  • Fig. 15 is an illustration of the invention utilizing multiple light sources.
  • Fig. 16 is an illustration of the invention for use in a frame sequential color display while Fig. 17 illustrates a timing sequence suitable for use with the embodiment of the invention shown in Fig. 16.
  • FIG. 1 is a cross-sectional view of a typical liquid crystal display 100 according to the prior art.
  • a medium 101 e.g., a polymer
  • a transparent conductive material such as indium tin oxide.
  • Droplets 103 may be individually encapsulated in one or more encapsulation layers as taught by Fergason, US 4,435,047; Reamey et al, US 5,405,551; and Havens et al, US 5,585,947, the disclosures of which are incorporated herein.
  • Electrodes 105 are coupled to a voltage source 107. When voltage source 107 is in an on state, a voltage is applied across electrodes 105 creating an electric field. Due to the positive dielectric anisotropy of liquid crystal droplets 103, the material comprising the droplets aligns parallel to the electric field as shown. In this state light incident along a path 109 will pass through droplets 103.
  • the voltage applied to electrodes 105, and the transparency of electrodes 105, medium 101, and aligned droplets 103, transmission rates of 70% or greater may be achieved.
  • voltage source 107 When voltage source 107 is in an off state as illustrated in Fig. 2, the electric field between electrodes 105 is effectively zero. As a result, liquid crystal droplets 103 no longer are uniformly aligned. Due to the random orientation of droplets 103, light incident along path 109 is randomly scattered, both in a forward direction and a backward direction as illustrated by scatter paths 201. The scattering of the incident light causes display 100 to appear opaque or frosty.
  • Fig. 3 is a cross-sectional view of a liquid crystal display panel 300 that may be used to display graphical information.
  • panel 300 includes both medium 101 and liquid crystal volumes 103.
  • the liquid crystal composite comprising medium 101 and liquid crystal volumes 103 is a polymer dispersed liquid crystal (i.e., a PDLC composite).
  • panel 300 includes a plurality of bottom electrodes 301 and a common top electrode 303 to form a plurality of electrode pairs.
  • the electrode pairs divide panel 300 into an array of separately controllable display elements or pixels.
  • Panel 300 also includes a top support member 305 preferably made of a conductive transparent material such as indium tin oxide (/. e. , ITO) coated polyethylene terephthalate or ITO coated glass.
  • the display can be designed to be either reflective or transparent. If a reflective display is desired, the reflective coating may either be applied to a surface of a bottom support member 307 or to a surface of pixel electrodes 301.
  • electrodes 301 are reflective electrodes made of aluminum or silver. While the panel configuration illustrated in Fig. 3 is common, it is understood that other configurations are well known by those of skill in the art and that this configuration is intended only to be illustrative, not limiting.
  • switching element 309 Electrically coupled to each electrode 301 is a switching element 309 that is used to control the application of a voltage across common electrode 303 and electrodes 301.
  • switching elements 309 are thin film transistors when display 300 is a transparent mode display and MOS transistors (as shown in Fig. 3) when display 300 is a reflective mode display. Switching elements 309 act as switches for each electrode “pair” thus allowing any combination of pixels to be activated.
  • panel 300 is designed so that the voltage that causes switching elements 309 to operate is the threshold voltage of liquid crystal volumes 103.
  • switching elements 309 are MOS transistors, other switching elements such as thin film transistors, MIMs, diodes, or varistors may be used as an alternative.
  • the application of voltage across electrodes 301 and 303, and therefore the activation of individual pixels, is controlled by a processor.
  • capacitive elements 311 are added to the transistor circuit in order to store charge.
  • Fig. 4 is a top view of panel 300.
  • panel 300 is comprised of a 20 by 20 array of square pixels 401.
  • Panel 300 may be comprised, however, of greater or lesser numbers of pixels.
  • the pixel shape is not limited to squares nor is the pixel shape limited to four sided configurations.
  • all of the pixels within the panel need not be of a uniform shape or size.
  • Liquid crystal display panels may be utilized in a variety of different configurations to create direct view, projection, and virtual images.
  • Examples of direct view include computer monitor screens and instrument panel readouts.
  • Examples of projection systems include front and rear systems projecting to a large screen or to a screen in a microdisplay.
  • a virtual microdisplay typically consists of one or more light sources, a liquid crystal composite, electrode elements, and imaging optics that form a virtual image in the eye of the user.
  • liquid crystal displays may be designed to function in either a transmissive or a reflective mode. Basically there are two configurations in which a high contrast image can be formed; normal mode and reverse mode. In a normal mode configuration, the image is formed from the reflected, or transmitted, non-scattered light while the scattered light is blocked.
  • Fig. 5 is an illustration of a reflective liquid crystal display operating in the normal mode. In this mode both the light source 501 and the viewer 503 are on the same side of the panel. As the illustrated panel is a reflective display, either bottom support member 505 is reflective or pixels 507 and 509 are reflective.
  • the construction of reflective member 505 is well known in the art, see, for example, Rowland, US 3,935,359; Kuney, Jr., US 4,957,335; Nelson et al, US 4,938,563; Belisle et al, US 4,725,494; Appledorn et al, US 4,775,219; Tung et al, US 4,712,219; Malek, US
  • the pixels defined by electrodes 507 are in an on state, thereby causing the liquid crystal volumes in the pixels defined by these electrodes to become transparent. Due to the transparency of these pixels, light from source 501 (e.g., ambient light, directed light, etc.) will pass through the pixels and be reflected by substrate reflector 505 or, in an alternate configuration, by the reflective electrode. The reflected specular light forms a bright image at location 503, typically after first passing through imaging optics 511 and an aperture stop 513. The liquid crystal volumes in those pixels defined by non-activated electrodes 509 are scattered in multiple directions 515, only a fraction of which will pass through optics 511 and aperture stop 513 to reach viewing location 503.
  • source 501 e.g., ambient light, directed light, etc.
  • neither the pixel electrodes nor the bottom substrate are reflective, and the image is formed by the light transmitted through those pixels in the on state, i.e., pixels 507.
  • Fig. 6 is an illustration of a display panel operating in the reverse mode.
  • a reverse mode panel may be used either in a reflective configuration as illustrated, or in a transparent configuration.
  • This panel is basically the same as that illustrated in Fig. 5. However in this configuration it is the scattered light 515 that is collected by imaging optics 511 to form an image at location 503.
  • the specular light either reflected as shown by an exemplary light ray 601 or passing through the display in the case of a transparent configuration, is blocked with stop 513.
  • a dark image is formed by those pixels 507 in an on state.
  • liquid crystal display panels may also be used to produce color images.
  • pleochroic or isotropic dyes may be included within the liquid crystal material, thereby achieving a colored visual effect.
  • colored filters or colored source light may be used in conjunction with the liquid crystal displays to provide a colored image. By sequentially combining multiple colored images, for example, red, green, and blue images, an image of good color purity may be produced.
  • Fig. 7 One type of frame sequential display is schematically illustrated in Fig. 7. This system is described in detail in Jones, US 5,398,081, the complete disclosure of which is incorporated herein.
  • the light from a white light source 701 is directed at a color modulator 703, for example, a dichroic cube color separator.
  • the dichroic cube has three color selective reflective surfaces positioned behind three sets of light valves.
  • the three color selective surfaces may be the three primary colors (e.g., red, green, and blue) or some other combination such as three complementary colors (e.g., cyan, yellow, and magenta).
  • the light valves are controlled by a computer that switches the valves between a substantially transparent state and a substantially non-transparent state. Thus three distinct colors may be obtained from the incident white light of source 701.
  • the color modulated light from modulator 703 is directed at an imaging element 705, also computer-controlled.
  • Element 705 imparts an image onto the incident light that corresponds to the particular color of light reaching it.
  • Projection system 707 sequentially projects the colored images onto a screen, thus creating a colored image. Since the computer controls both the switching of color modulator 703 and the image presented on imaging element 705, the color output and the image may be synchronized. Assuming the switching speed is at a high enough rate, the alternating images are not resolvable as distinct colors. Thus the viewer only perceives a composite colored image.
  • Fig. 8 is an illustration of an alternative frame sequential color display according to the prior art.
  • Color filtering means 803 includes a plurality of liquid crystal light valves 805 aligned with a plurality of color filters 807.
  • color filters 807 e.g., red, green, and blue. Therefore in order to transmit only one color through filtering means 803, for example blue, only light valves 805 corresponding to blue filters 807 are switched to an on or transparent state while all remaining light valves 805 are switched to an off or scattering state. As a result of this switching, in this example only blue light would pass through filtering means 803.
  • the color modulated light exiting filtering means 803 is spread by a light spreading means 809, such as a lens or diffusion plate. Element 809 insures that the light from filtering means 803 is relatively uniform, eliminating the effects of discrete color filters 807.
  • the color modulated light then passes through a liquid crystal array 811, array 811 forming the desired image through individual control of the array pixels.
  • a processor 813 synchronizes the image to the image color.
  • a low operating voltage i.e., the voltage required to place a pixel in an on state.
  • the overall power consumption of the device similarly increases.
  • high voltage transistors are expensive primarily because common transistor technology is low voltage. Besides requiring more power, a high operating voltage generates more heat that must be dissipated. The higher temperatures may also lead to local temperature fluctuations that may result in thermally induced mechanical stresses.
  • a low field E 90 is preferred for direct view and projection applications.
  • a low operating field allows the use of a lower applied voltage or, for a given applied voltage, allows for a thicker layer of liquid crystal composite to be used thereby yielding a lower transmissivity when the pixel is in the off state (i.e., T off ), thus creating a higher contrast image.
  • the present invention will now be described in more detail.
  • the present invention utilizes thin liquid crystals, typically with a thickness of less than 4 micrometers, and preferably with a thickness of less than 2.5 micrometers.
  • Fig. 9 is an illustration of the relationship of a liquid crystal display 901 to the illumination source and the viewer according to the present invention.
  • the liquid crystal composite in display 901 has a thickness of less than 4 micrometers, and preferably less than 2.5 micrometers. It is illuminated by at least one light source 903 that is positioned at an angle, ⁇ , of less than 30 degrees off of the normal from display 901, and preferably less than 20 degrees off of the normal.
  • a viewing system 905 is located approximately at the normal to display 901. This configuration provides superior image quality in an extremely rapid response time display.
  • Fig. 10 is an illustration of a testing system used to show the improvements offered by the present invention.
  • a sample 1001 was illuminated by an argon laser 1003 operating at a wavelength of 514 nanometers.
  • Fig. 11 is a graph of the brightness of sample 1001 as a function of the applied voltage. Two different samples were tested; a 1.83 micrometer thick liquid crystal and a 4.9 micrometer thick liquid crystal. At 45 degrees illumination, the thick sample (test run #1101) produced approximately twice the brightness of the thin sample (test run #1103). At 30 degrees illumination, the thick sample (test run #1105) and the thin sample (test run #1107) produced approximately the same brightness.
  • Fig. 12 is a graph illustrating the illumination angle dependence of the light scattering characteristics of a 1.83 micrometer thick liquid crystal composite using the testing apparatus shown in Fig. 10.
  • the illumination angle, ⁇ was varied from 10 to 50 degrees in 2 degree increments.
  • the viewing angle remained constant at the sample normal.
  • the brightness is shown as a function of the voltage applied to the composite.
  • the sample scatter, and therefore brightness increases.
  • the brightness decreases as the voltage increases from 0 to 10 volts.
  • the brightness reaches a maximum value at a non-zero voltage in the range of 2 to 3 volts.
  • the optimum contrast is achieved between the operating voltage and some non-zero voltage. For example, at a 10 degree illumination angle, the optimum contrast is achieved by setting the minimum voltage to 3 volts.
  • Fig. 13 is an illustration of one embodiment of the invention utilizing a reverse mode configuration.
  • sample 901 is comprised of a thin liquid crystal composite 1301, upper electrode 1303, lower pixel electrodes 1305, and upper and lower support members 1307 and 1309, respectively.
  • upper electrode 1303 is " made of an optically transparent conductive coating (e.g. , ITO) and lower electrodes 1305 are made of optically reflective and electrically conductive materials (e.g., aluminum, silver, etc.).
  • lower electrodes 1305 may be transparent and lower support member 1309 reflective.
  • the electrode pairs controlling the state of each pixel are controlled by a processor 1311.
  • the lower voltage extreme may be either 0 volts or, alternatively, a non-zero voltage.
  • a non-zero voltage is used in order to avoid contrast reversal from occurring, as noted above. If a non-zero voltage is used, it is typically in the range of 2 to 3 volts.
  • Source 903 is positioned at an angle of less than 30 degrees off of the normal from display 901, and preferably less than 20 degrees off of the normal.
  • Fig. 13 illustrates a reverse mode configuration
  • the image is formed by collecting scattered rays 1313.
  • the light rays passing through those pixels that are in an on state and reflected back as a specular reflection are preferably eliminated with the use of an aperture stop.
  • both electrodes 1305 and substrate 1309 are transparent, light rays passing through activated pixels are either eliminated with a light trap (e.g., absorbing coating) or reflected away from the display and the viewing system.
  • a light trap e.g., absorbing coating
  • a virtual image is created for viewing at a location 1315.
  • the virtual image is formed by imaging optics 1307 which collects a portion of scattered rays 1313.
  • imaging optics 1307 are similar to those used in a microscope.
  • imaging optics 1307 are comprised of a projection optical system.
  • the projection optical system can be used to project an image onto a screen. Given the relatively small angle between source 903 and the display normal, it is important to prevent specular reflections from entering the viewing system.
  • lower member 1309 includes a tilting reflective member 1401. Reflective member 1401 is used to direct the specularly reflected light rays 1403 of source 903 sufficiently away from viewer 1315 so that they are not collected by optics 1307. Reflective member 1401 may either reflect the light rays further away from viewer 1315 as illustrated, or reflect the light rays back at source 903.
  • reflective member 1401 is comprised of a plurality of individual tilted reflective surfaces, each of said individual reflective surfaces corresponding to a display pixel.
  • the individual tilted surfaces may be simple planar surfaces or more complex surfaces such as cones, the latter configuration suitable for use with multiple light sources.
  • Fig. 15 is a top view of display 901. As disclosed above, viewing system 905 is positioned normal to the display. In this embodiment multiple sources 903 are positioned around viewing system 905 and within an angle of approximately 30 degrees, and preferably less than 20 degrees from the display normal. Although four sources 903 are shown in Fig. 15, both fewer and greater numbers of sources may be used with the invention. Additional increases in contrast levels may be achieved by positioning sources 903 to minimize their alignment with the pixel edges as shown in Fig. 15, and as disclosed in co-pending U.S. Patent Application Serial No. 09/090,749, filed 4 June 1998, entitled High Contrast Micro Display With Off- Axis Illumination.
  • Fig. 16 is an alternate embodiment of the invention providing a frame sequential color display system. This embodiment is substantially the same as that previously illustrated except that at least three different color sources 903 are used to sequentially illuminate sample 901.
  • sources 903 may be comprised of a red source 1601, a blue source 1602, and a green source 1603. If improved brightness and uniformity are desired as illustrated in Fig. 15, each color light may be provided by multiple sources (e.g., sources 1601', 1602' and 1603').
  • the processor that controls the state of the individual pixels of display 901 also controls the activation of the individual color light sources 1601-1603.
  • the individual colors are synchronized with the images displayed on liquid crystal panel 901. Assuming a fast enough switching speed, only a composite colored image is perceived by the viewer.
  • Fig. 17 illustrates a timing sequence suitable for use with the embodiment of the invention shown in Fig. 16. Three colors, red, green, and blue, are shown although other combinations may be used with the invention as discussed above.
  • a frame rate of at least 180 Hz is desired. This requires a combination of the liquid crystal response time and the active matrix array setup time to be shorter than 5.6 milliseconds.
  • Light sources 903 are preferably not turned on during the array setup time nor during the liquid crystal response time as illustrated. If the sources are turned on during either of these times, there may be a color shift in the middle of the display.
  • the active matrix is addressed from the top to the bottom of the display using a line at a time scheme.
  • the array is divided into multiple zones with dedicated light sources per zone, thereby reducing the array setup time by the number of zones.
  • the liquid crystal response time requirement is reduced from 3.6 milliseconds to 4.6 milliseconds.
  • This embodiment also allows the pulse width of the light sources to be extended, thus increasing the display brightness.
  • the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof.
  • the invention may be used with a variety of different liquid crystal materials, display panel designs, pixel sizes, pixel shapes, and electrode configurations. Accordingly, the disclosures and descriptions herein are intended to be illustrative, but not limiting, of the scope of the invention which is set forth in the following claims.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Chemical & Material Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Mathematical Physics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Dispersion Chemistry (AREA)
  • Liquid Crystal (AREA)
  • Liquid Crystal Display Device Control (AREA)
  • Video Image Reproduction Devices For Color Tv Systems (AREA)
  • Devices For Indicating Variable Information By Combining Individual Elements (AREA)

Abstract

La présente invention concerne un système d'imagerie à cristaux liquides, à réponse rapide et à contraste élevé. L'élément d'imagerie (901) utilise un composite de cristaux liquides (c'est à dire, constitué de cristaux liquides encapsulés) dont l'épaisseur est inférieure à 4 microns, et de préférence inférieure à 2,5 microns. L'élément d'imagerie est éclairé par au moins une source de lumière (903) placée de manière à faire un angle inférieur à 30 degrés par rapport à la normale à l'affichage. Le système de vision (1307) est placé du même côté de l'affichage que la source de lumière, de manière pratiquement normale à l'affichage. Dans une réalisation, le composite de cristaux liquides est soumis à un fonctionnement en mode inversé et une image virtuelle est créée. Dans une autre réalisation, au moins trois sources de lumière de couleurs différentes éclairent un élément d'imagerie à cristaux liquides. Les sources sont toutes placées à un angle faisant à peu près 30 degrés avec la normale à l'élément d'imagerie. Un microprocesseur (1311) est couplé à la fois aux sources de lumière (903) et à l'élément d'imagerie (901), ce qui permet ainsi de synchroniser les sources individuelles à lumière colorée avec la sortie de l'élément d'imagerie.
PCT/US1999/012652 1998-06-04 1999-06-04 Eclairement d'un affichage a cristaux liquides WO1999063399A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
EP99928422A EP1084444A1 (fr) 1998-06-04 1999-06-04 Eclairement d'un affichage a cristaux liquides
JP2000552549A JP2002517783A (ja) 1998-06-04 1999-06-04 液晶ディスプレイの照明装置
CA002333989A CA2333989A1 (fr) 1998-06-04 1999-06-04 Eclairement d'un affichage a cristaux liquides

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US9076898A 1998-06-04 1998-06-04
US09/090,768 1998-06-04

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WO1999063399A1 true WO1999063399A1 (fr) 1999-12-09

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1145072B1 (fr) * 1998-06-22 2003-05-07 E-Ink Corporation Methode d'adressage d'un afficheur a microcapsules
GB2431767A (en) * 2005-10-27 2007-05-02 Avago Tech Ecbu Ip Frame sequential LCD display

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120050148A1 (en) * 2010-08-31 2012-03-01 Jiandong Huang Three-Dimensional Display Using Angular Projection Backlight

Citations (4)

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Publication number Priority date Publication date Assignee Title
US4090219A (en) * 1974-12-09 1978-05-16 Hughes Aircraft Company Liquid crystal sequential color display
US4999619A (en) * 1987-06-10 1991-03-12 U.S. Philips Corporation Electro-optic display device for use in the reflection mode
WO1993016410A1 (fr) * 1992-02-14 1993-08-19 Raychem Corporation Affichage a cristaux liquides eclaire a l'avant
EP0643318A1 (fr) * 1993-03-29 1995-03-15 Seiko Epson Corporation Dispositif d'affichage et appareil electronique

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4090219A (en) * 1974-12-09 1978-05-16 Hughes Aircraft Company Liquid crystal sequential color display
US4999619A (en) * 1987-06-10 1991-03-12 U.S. Philips Corporation Electro-optic display device for use in the reflection mode
WO1993016410A1 (fr) * 1992-02-14 1993-08-19 Raychem Corporation Affichage a cristaux liquides eclaire a l'avant
EP0643318A1 (fr) * 1993-03-29 1995-03-15 Seiko Epson Corporation Dispositif d'affichage et appareil electronique

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1145072B1 (fr) * 1998-06-22 2003-05-07 E-Ink Corporation Methode d'adressage d'un afficheur a microcapsules
GB2431767A (en) * 2005-10-27 2007-05-02 Avago Tech Ecbu Ip Frame sequential LCD display
GB2431767B (en) * 2005-10-27 2009-01-21 Avago Tech Ecbu Ip LCD display

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EP1084444A1 (fr) 2001-03-21
CA2333989A1 (fr) 1999-12-09
JP2002517783A (ja) 2002-06-18

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