EP0754338A1 - Image display system allowing multiple users to view a single display or a single user to view multiple displays - Google Patents

Image display system allowing multiple users to view a single display or a single user to view multiple displays

Info

Publication number
EP0754338A1
EP0754338A1 EP95913774A EP95913774A EP0754338A1 EP 0754338 A1 EP0754338 A1 EP 0754338A1 EP 95913774 A EP95913774 A EP 95913774A EP 95913774 A EP95913774 A EP 95913774A EP 0754338 A1 EP0754338 A1 EP 0754338A1
Authority
EP
European Patent Office
Prior art keywords
image display
viewing
panel
display panel
viewing direction
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP95913774A
Other languages
German (de)
French (fr)
Inventor
Donald E. Newsome
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.)
Boeing Co
Original Assignee
Boeing Co
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 Boeing Co filed Critical Boeing Co
Publication of EP0754338A1 publication Critical patent/EP0754338A1/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
    • 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
    • G09G2320/028—Improving the quality of display appearance by changing the viewing angle properties, e.g. widening the viewing angle, adapting the viewing angle to the view direction

Definitions

  • the present invention relates to an image display system allowing multiple users to view single display or a single user to view multiple displays.
  • LCDs Liquid crystal displays
  • CRTs cathode ray tubes
  • CRTs typically produce a higher quality image and provide greater display capabilities.
  • a CRT produces substantial contrast between display background and the display characters
  • the image provided by the CRT can be discerned when lighting conditions are less favorable than those needed to discern the image provided by an LCD.
  • Another limitation with using an LCD is that the range of viewing angles relative to the normal to the display panel is smaller than for a CRT because the contrast of the image is more strongly dependent on viewing angle. Further, the color of display characters tends to change in relation to viewing angle.
  • the restricted range of viewing angles limits the use of LCDs in applications where several users are required to view the same display concurrently, for example in an airplane cockpit.
  • the limited range of viewing angles of an LCD restricts the number of displays that can be used effectively.
  • the display panel may be reoriented or realigned to face the operator directly. Orienting a display panel is not always feasible in a display system where the panel is mounted in a cabinet or located out of the viewer's reach, for example in an airplane instrument array or an overhead display.
  • an image display system comprising an image display panel, said panel being such that the maximum contrast viewing direction of the panel is electrically alterable in response to a control signal, means defining first and second viewing stations for allowing first and second users to view the panel in first and second viewing directions respectively, and means for supplying an electrical control signal to the image display panel so that the maximum contrast viewing direction of the panel is intermediate the first and second viewing directions.
  • an image display system comprising at least first and second image display panels, at least the first panel being such that its maximum contrast viewing direction is electrically alterable, means defining a viewing station from which a user is able to view the first and second panels in first and second viewing directions respectively, and means for supplying an electrical control signal to the first display panel so that the maximum contrast viewing direction of the panel substantially coincides with the first viewing direction.
  • FIG. 1 is a diagram illustrating the orientation of liquid crystal molecules in a twisted nematic mode cell
  • FIG. 2 is a diagram illustrating the orientation of liquid crystal molecules in a twisted nematic mode cell after application of a first electric field
  • FIG. 3 is a _ agram illustrating the orientation of liquid crystal molecules in a twisted nematic mode cell after application of a second electric field
  • FIG. 4 is an illustration of a circuit configuration for pixel control in a normally white liquid crystal display
  • FIG. 5 is a graph illustrating the relationship between the luminance of a liquid crystal cell and viewing direction in a horizontal plane when the display is adjusted for normal viewing;
  • FIG. 6 is a graph illustrating the relationship between the contrast ratio of a liquid crystal cell and viewing direction in a horizontal plane for several values of the field present in the cell;
  • FIG. 7 is a diagram illustrating multiple liquid crystal displays with the maximum contrast viewing angle for each display being directed to the same user location.
  • FIG. 8 is a diagram illustrating multiple liquid crystal displays with the maximum contrast viewing angle for each display being adjusted for multiple user viewing..
  • FIG. 1 illustrates schematically a portion of a twisted nematic liquid crystal display panel having a rectangular array of Nx*Ny separately addressable picture elements or pixels.
  • the panel comprises two linear polarizers 2 and 16 wherein linear polarizer 2 is positioned facing the outer surface of glass substrate 4 and linear polarizer 16 is positioned facing the outer surface of glass substrate 14.
  • Polarizer 2 has a polarization direction 3 while polarizer 16 has a polarization direction 15 orthogonal to polarization direction 3.
  • a rectangular array of discrete transparent pixel electrodes is deposited on the inner surface of glass substrate 4 and a single continuous transparent common electrode 12 is deposited on the inner surface of the glass substrate 14. Only one of the pixel electrodes, designated 6, is shown in FIG. 1.
  • a liquid crystal cell 9 is defined between each transparent pixel electrode 6 and transparent electrode 12. Liquid crystal cell 9 corresponds to a pixel location in the liquid crystal display panel.
  • the panel is viewed from the side of polarizer 16 that is remote from substrate 14.
  • a light source (not shown) provides a light beam 1 that is incident on polarizer 2 normal to the plane of the display panel, and light transmitted by polarizer 2 passes through glass substrate 4, transparent electrode 6, liquid crystal cell 9, transparent electrode 12 and glass substrate 14 to polarizer 16.
  • Liquid crystal cell 9 contains liquid crystal molecules, represented schematically as molecules 18, 20, 22, 24, 256, 28, 30, 32, and 34.
  • the liquid crystal molecules are illustrated in FIG. 1 in typical orientations that they assume when there is no potential difference between electrodes 6 and 12. In this condition, the molecules are oriented transverse to the normal to the display panel.
  • the orientation of a molecule has two components, known as twist and tilt. Twist refers to the orientation of a molecule about the display panel normal, and the twist angle is designated ⁇ . Tilt refers to the angular position of a molecule relative to a plane that is perpendicular to the display panel normal, and the tilt angle is designated a.
  • the twist angle is independent of the electric field existing in the cell, whereas the tilt angle depends on the electric field.
  • Molecules 18 and 34 which are adjacent electrodes 6 and 12 respectively, are bound to the substrates 4 and 16 and their orientations are substantially fixed.
  • the twist angle depends on the treatment of the surfaces of glass substrates 4 and 14.
  • the glass substrates are treated so that the molecule 18 is oriented parallel to the linear polarization direction 3 of polarizer 2, i.e. horizontally, and the molecule 34 is oriented parallel to the linear polarization direction 15 of polarizer 16, i.e. vertically.
  • molecule 18 has a twist angle of ⁇ o, + 90 e .
  • Each of the molecules 20-32 tends to assume a twist angle that is intermediate the twist angles of the two adjacent molecules.
  • Molecule 20, for example is rotated in the counterclockwise direction (looking in the direction of the light beam 1 ) relative to molecule 18 and toward the twist angle of molecule 34.
  • Molecules 22 and 24 successively increase in twist angle.
  • Molecule 26 has a twist angle half way between the twist angle of molecule 18 and that of molecule
  • Molecules 18 and 34 are each oriented with a tilt angle of OCQ. When no field is applied between electrodes 6 and 12, the tilt angle tends to decrease with distance from the substrates 4 and 14.
  • the tilt angle of molecule 20 is less than the tilt angle of molecule 18 while molecules 22 and 24 successively decrease in tilt angle.
  • Molecule 26 has a tilt angle of 0 e .
  • Light transmitted by polarizer 2 is plane-polarized in direction 3 and passes through glass substrate 4 and transparent electrode 6.
  • the plane of polarization of the polarized light is rotated progressively until it leaves the liquid crystal cell with its polarization direction rotated through 90 9 from polarization direction 3.
  • the plane-polarized light passes through transparent electrode 12 and glass substrate 14 before reaching polarizer 16, whose polarization direction is aligned with the plane of polarization of light exiting liquid crystal cell 9.
  • Polarizer 16 thus allows the polarized light to pass, providing a white appearance when viewed from the exterior of the panel.
  • FIG. 2 illustrates liquid crystal cell 9 in the condition in which an electric field exists between electrodes 6 and 12.
  • molecule 20 exhibits a greater tilt angle as compared to molecule 20 in FIG. 1.
  • Molecule 22 has a larger tilt angle, and molecules 24, 26 and 28 each have a maximum tilt angle oc m ax*
  • FIG. 3 illustrates the liquid crystal cell 9 with its molecules oriented by an electric field that is of sufficient magnitude to create predominantly parallel molecular orientations in relation to the normal to the liquid crystal display panel.
  • the polarization direction of light that enters the cell is not influenced significantly by propagation through the cell and polarizer 16 blocks light transmitted by the cell. Therefore, the cell appears opaque to the viewer. Because of this manner of operation, a liquid crystal display panel of the kind described with reference to FIGs. 1 -3 is referred to as a normally white display panel.
  • a field effect transistor (FET) 40j is provided at each pixel location and has its drain connected to an electrode 6j j its source connected through a_column drive line 42j to a column driver circuit 44, and its gate connected through a row drive line 46j to a row driver circuit 48.
  • Row driver circuit 48 and column driver circuit 46 represent typical display driver circuitry well known to those skilled in the art.
  • circuit 48 is depicted as comprising row drivers 48j having their inputs connected to variable voltage source 52 and their outputs connected to row drive lines 46j.
  • Lines 54j contained within a control bus 54, supply enable signals for row drivers 48j respectively.
  • driver circuit 44 comprises column drivers 44j having their inputs connected to a voltage source 50 and their outputs connected to column drive lines 42j respectively.
  • a control bus 56 has control lines 56j for supplying enable signals to the column drivers 44j respectively.
  • Control buses 56 and 54 are connected to a video controller 58 for selectively enabling drivers 48 and 44.
  • Each FET 40 controls the state of a liquid crystal cell 9. If video controller 58 does not enable both line 56j and line 54; the channel of FET 40j j is not conductive and no electric field is established in liquid crystal cell 9 Cell 9j is then in the OFF state (white state). However, if video controller 58 places enable signals on lines 56j an 54j, column driver 44j supplies a voltage to the sources of FETs 40j where y represents all values of j, and row driver 48j supplies a voltage to the gates of FETs 40 x j, where x represents all values of i.
  • FET 40i j has a gate to source voltage that is sufficient to render the channel of the FET conductive and it has a source to drain voltage that depends on the gate to source voltage of the FET.
  • An electric field is established in the cell 9j j' and at a suitable value of the field cell 9 ⁇ is in the ON state (black state). Adjustment of the voltage source 52 allows the voltage between electrode 6- and electrode 12, and hence the electric field in cell 9[ to be adjusted.
  • FIG. 5 illustrates variation in luminance of a normally white liquid crystal display cell as a function of angle in a horizontal plane. Curve 66 in FIG. 5 shows that the white luminance ordinarily has a maximum value at a viewing direction normal to the display panel and is somewhat dependent on viewing angle. When the field is sufficient to align the majority of molecules with the normal to the panel, as shown in FIG.
  • the black luminance has a minimum value at a viewing direction normal to the display panel and varies quite strongly with viewing direction, as shown by the curve 68 in FIG. 5. Therefore, the contrast ratio (curve 70, FIG. 5) also varies with viewing direction, and the maximum contrast viewing direction (the viewing direction at which the contrast ratio is a maximum) is normal to the display panel.
  • the orientation of the liquid crystal molecules in the black state depends on the electric field existing in the cell in the black state and affects the direction at which the minimum luminance is observed by the viewer.
  • the electric field in the black state can therefore be used to adjust the maximum contrast viewing angle.
  • the minimum luminance is observed to one side of the normal, for example to the right of the normal as shown by the curve 72 in FIG. 6, and the maximum contrast ratio occurs at 40° to the right of normal as represented by dotted line curve 64 in FIG. 6.
  • Increasing the field in the liquid crystal cell in the black state to a second value E2 results in the minimum luminance being observed somewhat less to the right (curve 76), with the result that the maximum contrast ratio occurs at 20° to the right of normal as represented by dashed curve 62. It can therefore be seen that by varying the voltage applied between the electrodes 6 and 12 of the liquid crystal cell, it is possible to adjust the angle in the horizontal plane at which the maximum contrast ratio occurs. Therefore, referring again to FIG. 4, the maximum contrast viewing angle may be altered by adjusting variable voltage source 52.
  • FIG. 7 illustrates a method for redirecting the maximum contrast viewing angle for multiple coplanar liquid crystal display panels to allow all the panels to be viewed from the same observation location.
  • User 90 is positioned directly in front of LCD panel 86, to the left of LCD panel 88 and to the right of LCD panels 82 and 84.
  • the maximum contrast viewing angle is normal to the panel.
  • the voltage employed in LCD panel 82 to establish the black state is selected to provide a maximum contrast viewing angle ⁇ 3, so that user 90 is able to view the display at the maximum contrast viewing angle.
  • the voltage employed in display panel 84 is selected so that the maximum contrast occurs at viewing angle ⁇ 2 and the voltage employed in display panel 88 is selected so the maximum contrast occurs at viewing angle ⁇ j .
  • the voltage across LCD 86 is such that the maximum contrast is observed in direction normal to the display screen. A single user is therefore able to view a number of spatially separated screens from the same observation location.
  • FIG. 8 illustrates plural display panels viewed concurrently by multiple users.
  • User 96 is positioned directly in front of display panel 94 while user 98 is directly in front of display panel 92.
  • User 96 is located at a viewing angle of 60° from the normal to display panel 92 while user 98 is located at a viewing angle of 60° from the normal to display panel 94.
  • both display panels can be viewed in an improved manner by both users, e.g. where the maximum contrast viewing angle for display panel 92 is adjusted 30° to the left of normal and panel 94 is adjusted for a maximum contrast viewing angle 30° to the right of normal.
  • the maximum contrast viewing angle for neither display panel is optimum for either user 96 or user 98, having the maximum contrast viewing direction between the two users allows sufficient contrast at each user location so that each user can effectively read each screen.
  • the panel 94 is adjusted to have a maximum contrast viewing angle normal to the display panel and the display panel 92 is adjusted to provide a maximum contrast viewing angle half-way between the viewing directions of the two users as described above.
  • the maximum contrast viewing angle is also adjustable to limit user display viewing. For example, when displaying confidential information it may be desirable for only one user to read a display panel. The maximum contrast viewing angle may therefore be adjusted out of the effective viewing range of a second user, thereby minimizing unauthorized reading of information.
  • the invention is not restricted to the maximum contrast viewing direction being shifted in a horizontal plane, since by rotating the liquid crystal panel about its normal, the direction in which maximum contrast is observed likewise rotates, describing a conical surface.

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  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
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Abstract

An image display system comprises an image display panel whose maximum contrast viewing direction is electrically alterable in response to a control signal. First and second viewing stations allow first and second users to view the panel in first and second viewing directions respectively. An electrical control signal is supplied to the image display panel so that the maximum contrast viewing direction of the panel is intermediate the first and second viewing directions.

Description

IMAGE DISPLAY SYSTEM ALLOWING MULTIPLE
USERS TO VIEW A SINGLE DISPLAY OR A
SINGLE USER TO VIEW MULTIPLE DISPLAYS
Background of the Invention
The present invention relates to an image display system allowing multiple users to view single display or a single user to view multiple displays.
Liquid crystal displays (LCDs) are thin and require little power to operate and are therefore advantageously used as substitutes for cathode ray tubes (CRTs). However, CRTs typically produce a higher quality image and provide greater display capabilities. For example, since a CRT produces substantial contrast between display background and the display characters, the image provided by the CRT can be discerned when lighting conditions are less favorable than those needed to discern the image provided by an LCD. Another limitation with using an LCD is that the range of viewing angles relative to the normal to the display panel is smaller than for a CRT because the contrast of the image is more strongly dependent on viewing angle. Further, the color of display characters tends to change in relation to viewing angle.
The restricted range of viewing angles limits the use of LCDs in applications where several users are required to view the same display concurrently, for example in an airplane cockpit. In alternative applications where a single user must observe multiple displays from a single position, the limited range of viewing angles of an LCD restricts the number of displays that can be used effectively. To correct for the diminishing contrast ratio of an LCD as viewed from oblique, i.e. off-normal, directions, the display panel may be reoriented or realigned to face the operator directly. Orienting a display panel is not always feasible in a display system where the panel is mounted in a cabinet or located out of the viewer's reach, for example in an airplane instrument array or an overhead display. Summary of the Invention
According to a first aspect of the present invention there is provided an image display system comprising an image display panel, said panel being such that the maximum contrast viewing direction of the panel is electrically alterable in response to a control signal, means defining first and second viewing stations for allowing first and second users to view the panel in first and second viewing directions respectively, and means for supplying an electrical control signal to the image display panel so that the maximum contrast viewing direction of the panel is intermediate the first and second viewing directions.
According to another aspect of the present invention there is provided an image display system comprising at least first and second image display panels, at least the first panel being such that its maximum contrast viewing direction is electrically alterable, means defining a viewing station from which a user is able to view the first and second panels in first and second viewing directions respectively, and means for supplying an electrical control signal to the first display panel so that the maximum contrast viewing direction of the panel substantially coincides with the first viewing direction.
The subject matter of the present the invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.
Brief Description of the Drawings
FIG. 1 is a diagram illustrating the orientation of liquid crystal molecules in a twisted nematic mode cell;
FIG. 2 is a diagram illustrating the orientation of liquid crystal molecules in a twisted nematic mode cell after application of a first electric field; FIG. 3 is a _ agram illustrating the orientation of liquid crystal molecules in a twisted nematic mode cell after application of a second electric field;
FIG. 4 is an illustration of a circuit configuration for pixel control in a normally white liquid crystal display;
FIG. 5 is a graph illustrating the relationship between the luminance of a liquid crystal cell and viewing direction in a horizontal plane when the display is adjusted for normal viewing;
FIG. 6 is a graph illustrating the relationship between the contrast ratio of a liquid crystal cell and viewing direction in a horizontal plane for several values of the field present in the cell;
FIG. 7 is a diagram illustrating multiple liquid crystal displays with the maximum contrast viewing angle for each display being directed to the same user location; and
FIG. 8 is a diagram illustrating multiple liquid crystal displays with the maximum contrast viewing angle for each display being adjusted for multiple user viewing..
Detailed Description
FIG. 1 illustrates schematically a portion of a twisted nematic liquid crystal display panel having a rectangular array of Nx*Ny separately addressable picture elements or pixels. The panel comprises two linear polarizers 2 and 16 wherein linear polarizer 2 is positioned facing the outer surface of glass substrate 4 and linear polarizer 16 is positioned facing the outer surface of glass substrate 14. Polarizer 2 has a polarization direction 3 while polarizer 16 has a polarization direction 15 orthogonal to polarization direction 3. A rectangular array of discrete transparent pixel electrodes is deposited on the inner surface of glass substrate 4 and a single continuous transparent common electrode 12 is deposited on the inner surface of the glass substrate 14. Only one of the pixel electrodes, designated 6, is shown in FIG. 1. A liquid crystal cell 9 is defined between each transparent pixel electrode 6 and transparent electrode 12. Liquid crystal cell 9 corresponds to a pixel location in the liquid crystal display panel.
For the sake of convenience in the following description, it will be assumed that the panel is disposed vertically and that the polarization direction 3 is horizontal.
The panel is viewed from the side of polarizer 16 that is remote from substrate 14. A light source (not shown) provides a light beam 1 that is incident on polarizer 2 normal to the plane of the display panel, and light transmitted by polarizer 2 passes through glass substrate 4, transparent electrode 6, liquid crystal cell 9, transparent electrode 12 and glass substrate 14 to polarizer 16.
Liquid crystal cell 9 contains liquid crystal molecules, represented schematically as molecules 18, 20, 22, 24, 256, 28, 30, 32, and 34. The liquid crystal molecules are illustrated in FIG. 1 in typical orientations that they assume when there is no potential difference between electrodes 6 and 12. In this condition, the molecules are oriented transverse to the normal to the display panel. The orientation of a molecule has two components, known as twist and tilt. Twist refers to the orientation of a molecule about the display panel normal, and the twist angle is designated β. Tilt refers to the angular position of a molecule relative to a plane that is perpendicular to the display panel normal, and the tilt angle is designated a. In general, the twist angle is independent of the electric field existing in the cell, whereas the tilt angle depends on the electric field. Molecules 18 and 34, which are adjacent electrodes 6 and 12 respectively, are bound to the substrates 4 and 16 and their orientations are substantially fixed.
The twist angle depends on the treatment of the surfaces of glass substrates 4 and 14. The glass substrates are treated so that the molecule 18 is oriented parallel to the linear polarization direction 3 of polarizer 2, i.e. horizontally, and the molecule 34 is oriented parallel to the linear polarization direction 15 of polarizer 16, i.e. vertically. Thus, if molecule 18 has a twist angle of βo, + 90e. Each of the molecules 20-32 tends to assume a twist angle that is intermediate the twist angles of the two adjacent molecules. Molecule 20, for example, is rotated in the counterclockwise direction (looking in the direction of the light beam 1 ) relative to molecule 18 and toward the twist angle of molecule 34. Molecules 22 and 24 successively increase in twist angle. Molecule 26 has a twist angle half way between the twist angle of molecule 18 and that of molecule
34.
Molecules 18 and 34 are each oriented with a tilt angle of OCQ. When no field is applied between electrodes 6 and 12, the tilt angle tends to decrease with distance from the substrates 4 and 14. The tilt angle of molecule 20 is less than the tilt angle of molecule 18 while molecules 22 and 24 successively decrease in tilt angle. Molecule 26 has a tilt angle of 0e.
Light transmitted by polarizer 2 is plane-polarized in direction 3 and passes through glass substrate 4 and transparent electrode 6. Upon passing through liquid crystal cell 9 in the condition shown in FIG. 1 , the plane of polarization of the polarized light is rotated progressively until it leaves the liquid crystal cell with its polarization direction rotated through 909 from polarization direction 3. The plane-polarized light passes through transparent electrode 12 and glass substrate 14 before reaching polarizer 16, whose polarization direction is aligned with the plane of polarization of light exiting liquid crystal cell 9.
Polarizer 16 thus allows the polarized light to pass, providing a white appearance when viewed from the exterior of the panel.
When an electric field is applied across a twisted nematic cell, the liquid crystal molecules that are spaced from the boundaries of the cell tend to orient themselves parallel to the applied field. FIG. 2 illustrates liquid crystal cell 9 in the condition in which an electric field exists between electrodes 6 and 12. As shown in FIG. 2, molecule 20 exhibits a greater tilt angle as compared to molecule 20 in FIG. 1. Molecule 22 has a larger tilt angle, and molecules 24, 26 and 28 each have a maximum tilt angle ocmax*
At a somewhat greater value of the electric field across the liquid crystal cell, the maximum tilt angle αmax is larger, but at a limiting value of the electric field the molecules of the entire cell, except for the molecules bound at the external surfaces of the liquid crystal cell, become oriented in the direction of the applied field such that the majority of the molecules are aligned with the normal to the panel, and a further increase in field does not affect the maximum tilt angle. FIG. 3 illustrates the liquid crystal cell 9 with its molecules oriented by an electric field that is of sufficient magnitude to create predominantly parallel molecular orientations in relation to the normal to the liquid crystal display panel. In this condition, the polarization direction of light that enters the cell is not influenced significantly by propagation through the cell and polarizer 16 blocks light transmitted by the cell. Therefore, the cell appears opaque to the viewer. Because of this manner of operation, a liquid crystal display panel of the kind described with reference to FIGs. 1 -3 is referred to as a normally white display panel.
FIG. 4 illustrates a portion of a rectangular array of liquid crystal cells 9j (i = 1 ... Nx; j = 1 ... Ny), each of which corresponds to a pixel location of a liquid crystal display panel. A field effect transistor (FET) 40j is provided at each pixel location and has its drain connected to an electrode 6j j its source connected through a_column drive line 42j to a column driver circuit 44, and its gate connected through a row drive line 46j to a row driver circuit 48. Row driver circuit 48 and column driver circuit 46 represent typical display driver circuitry well known to those skilled in the art. For illustrative purposes circuit 48 is depicted as comprising row drivers 48j having their inputs connected to variable voltage source 52 and their outputs connected to row drive lines 46j. Lines 54j, contained within a control bus 54, supply enable signals for row drivers 48j respectively. Similarly, driver circuit 44 comprises column drivers 44j having their inputs connected to a voltage source 50 and their outputs connected to column drive lines 42j respectively. A control bus 56 has control lines 56j for supplying enable signals to the column drivers 44j respectively. Control buses 56 and 54 are connected to a video controller 58 for selectively enabling drivers 48 and 44.
Each FET 40 controls the state of a liquid crystal cell 9. If video controller 58 does not enable both line 56j and line 54; the channel of FET 40j j is not conductive and no electric field is established in liquid crystal cell 9 Cell 9j is then in the OFF state (white state). However, if video controller 58 places enable signals on lines 56j an 54j, column driver 44j supplies a voltage to the sources of FETs 40j where y represents all values of j, and row driver 48j supplies a voltage to the gates of FETs 40x j, where x represents all values of i. FET 40i j has a gate to source voltage that is sufficient to render the channel of the FET conductive and it has a source to drain voltage that depends on the gate to source voltage of the FET. An electric field is established in the cell 9j j' and at a suitable value of the field cell 9\ is in the ON state (black state). Adjustment of the voltage source 52 allows the voltage between electrode 6- and electrode 12, and hence the electric field in cell 9[ to be adjusted.
The contrast ratio of an LCD cell in any given viewing direction is defined as the ratio of luminance of the cell in the given viewing direction when the cell is in the white state to luminance of the cell in the given viewing direction when the cell is in the black state (i.e., contrast ratio = white luminance/black luminance). FIG. 5 illustrates variation in luminance of a normally white liquid crystal display cell as a function of angle in a horizontal plane. Curve 66 in FIG. 5 shows that the white luminance ordinarily has a maximum value at a viewing direction normal to the display panel and is somewhat dependent on viewing angle. When the field is sufficient to align the majority of molecules with the normal to the panel, as shown in FIG. 3, the black luminance has a minimum value at a viewing direction normal to the display panel and varies quite strongly with viewing direction, as shown by the curve 68 in FIG. 5. Therefore, the contrast ratio (curve 70, FIG. 5) also varies with viewing direction, and the maximum contrast viewing direction (the viewing direction at which the contrast ratio is a maximum) is normal to the display panel.
The orientation of the liquid crystal molecules in the black state depends on the electric field existing in the cell in the black state and affects the direction at which the minimum luminance is observed by the viewer. The electric field in the black state can therefore be used to adjust the maximum contrast viewing angle.
At the field E\ that is somewhat lower than the field used to generate curve 68 in FIG. 5, the minimum luminance is observed to one side of the normal, for example to the right of the normal as shown by the curve 72 in FIG. 6, and the maximum contrast ratio occurs at 40° to the right of normal as represented by dotted line curve 64 in FIG. 6. Increasing the field in the liquid crystal cell in the black state to a second value E2 results in the minimum luminance being observed somewhat less to the right (curve 76), with the result that the maximum contrast ratio occurs at 20° to the right of normal as represented by dashed curve 62. It can therefore be seen that by varying the voltage applied between the electrodes 6 and 12 of the liquid crystal cell, it is possible to adjust the angle in the horizontal plane at which the maximum contrast ratio occurs. Therefore, referring again to FIG. 4, the maximum contrast viewing angle may be altered by adjusting variable voltage source 52.
FIG. 7 illustrates a method for redirecting the maximum contrast viewing angle for multiple coplanar liquid crystal display panels to allow all the panels to be viewed from the same observation location. User 90 is positioned directly in front of LCD panel 86, to the left of LCD panel 88 and to the right of LCD panels 82 and 84. For a typical LCD panel under its usual operating conditions, the maximum contrast viewing angle is normal to the panel. For the screen configuration illustrated in FIG. 7, if the maximum contrast viewing angle for LCD panel 82 were normal (i.e. Θ = 0°), user 90 would either not be able to read the display or would have to read the display at a reduced contrast. This increases user eye strain and the possibility of display information being misinterpreted. To eliminate low contrast viewing problems, the voltage employed in LCD panel 82 to establish the black state is selected to provide a maximum contrast viewing angle Θ3, so that user 90 is able to view the display at the maximum contrast viewing angle. Similarly, the voltage employed in display panel 84 is selected so that the maximum contrast occurs at viewing angle ©2 and the voltage employed in display panel 88 is selected so the maximum contrast occurs at viewing angle Θj . In the case of an LCD panel whose maximum contrast viewing angle varies with electric field in the manner described with reference to FIG. 6, it would be necessary to rotate the panel in order to provide maximum contrast at the angle Θj . Since user 90 is positioned directly in front of display panel 86, the voltage across LCD 86 is such that the maximum contrast is observed in direction normal to the display screen. A single user is therefore able to view a number of spatially separated screens from the same observation location.
FIG. 8 illustrates plural display panels viewed concurrently by multiple users.
User 96 is positioned directly in front of display panel 94 while user 98 is directly in front of display panel 92. User 96 is located at a viewing angle of 60° from the normal to display panel 92 while user 98 is located at a viewing angle of 60° from the normal to display panel 94. By adjusting maximum contrast viewing angles, both display panels can be viewed in an improved manner by both users, e.g. where the maximum contrast viewing angle for display panel 92 is adjusted 30° to the left of normal and panel 94 is adjusted for a maximum contrast viewing angle 30° to the right of normal. Although the maximum contrast viewing angle for neither display panel is optimum for either user 96 or user 98, having the maximum contrast viewing direction between the two users allows sufficient contrast at each user location so that each user can effectively read each screen.
In an alternative situation, if the user 94 is required to read both panels 92 and 94 and the user 98 is only required to red the panel 92 that is directly in front of him, the panel 94 is adjusted to have a maximum contrast viewing angle normal to the display panel and the display panel 92 is adjusted to provide a maximum contrast viewing angle half-way between the viewing directions of the two users as described above.
The maximum contrast viewing angle is also adjustable to limit user display viewing. For example, when displaying confidential information it may be desirable for only one user to read a display panel. The maximum contrast viewing angle may therefore be adjusted out of the effective viewing range of a second user, thereby minimizing unauthorized reading of information.
It will be appreciated that the invention is not restricted to the particular embodiments that have been described and illustrated, and that variations may be made therein without departing from the scope of the invention as defined in the appended claims and equivalents thereof. For example, although the invention has been described with reference to a normally white LCD display panel, the invention is also applicable to a so-called normally black panel, in which the two polarizers are oriented parallel to each other, instead of perpendicular, so that light transmitted by the LCD cell when no electric field is applied between the electrodes is blocked by the second polarizer. In the case of a normally black
LCD panel, adjustment of the voltage applied to the cell in the white state influences the viewing direction at which maximum luminance is observed, and in this fashion allows a maximum contrast viewing direction other than normal to the display panel to be established. Further, the invention is not restricted to the maximum contrast viewing direction being shifted in a horizontal plane, since by rotating the liquid crystal panel about its normal, the direction in which maximum contrast is observed likewise rotates, describing a conical surface.

Claims

Claims
1. (Amended) An image display system comprising:
a twisted nematic liquid crystal image display panel having a plurality of discrete pixels and addressing means for electrically addressing selected pixels to display an image by applying a potential difference across each selected pixel, said panel being such that the maximum contrast viewing direction of the panel for viewing the image is dependent on the potential difference applied to the selected pixels of the panel,
means defining first and second viewing stations for allowing first and second users to view the panel in first and second viewing directions respectively, and
adjustable voltage means connected to the addressing means and applying a predetermined potential difference to each selected pixel, said predetermined potential difference being established such that the maximum contrast viewing direction of the panel for viewing the image is intermediate the first and second viewing directions.
2. (Thrice Amended) An image display system according to claim 1 , further comprising:
a second twisted nematic liquid crystal image display panel, having a plurality of discrete pixels and addressing means for electrically addressing selected pixels of the second image display panel to display a second image by applying a potential difference across each selected pixel of the second image display panel, said second image display panel being such that its maximum contrast viewing direction for viewing the second image is dependent on the potential differences applied to the selected pixels of the second image display panel, the second image display panel being positioned for viewing by the first and second users in third and fourth viewing directions respectively, and
second adjustable voltage means connected to the addressing means of the second image display panel and applying a second predetermined potential difference to each selected pixel of the second panel, said second predetermined potential difference being such that the maximum contrast viewing direction of the second image display panel for viewing the second image is intermediate the third and fourth viewing directions.
3. (Thrice Amended) An image display system according to claim 1 , further comprising:
a second twisted nematic liquid crystal image display panel, having a plurality of discrete pixels and addressing means for electrically addressing selected pixels of the second image display panel to display a second image by applying a potential difference across each selected pixel of the second image display panel, said second image display panel being such that its maximum contrast viewing direction for viewing the second image is dependent on the potential difference applied to the selected pixels of the second image display panel, the second image display panel being positioned for viewing by the first and second users in viewing third and fourth directions respectively, and
second adjustable voltage means connected to the addressing means of the second image display panel and applying a second predetermined potential difference to each selected pixel of the second image display panel, said second predetermined potential difference being such that the maximum contrast viewing direction of the second image display panel for viewing the second image substantially coincides with the third viewing direction.
(Twice Amended) An image display system comprising:
at least first and second twisted nematic liquid crystal image display panels, at least the first panel having a plurality of discrete pixels and addressing means for electrically addressing selected pixels to display an image by applying a potential difference across each selected pixel, and said first panel being such that its maximum contrast viewing direction for viewing the image is dependent on the potential difference applied to the selected pixels.
means defining a viewing station from which a user is able to view the first and second panels in first and second viewing directions respectively, and adjustable voltage means connected to the addressing means and applying a predetermined potential difference to each selected pixel, said predetermined potential difference being established such that the maximum contrast viewing direction of the first panel for viewing the image substantially coincides with the first viewin *ge direction.
5. An image display system according to claim 4, wherein the display panels have respective normals, and the normals are substantially parallel.
6. (Amended) An image display system according to claim 1 , wherein each pixel comprises first and second electrodes, first and second polarizers and a liquid crystal cell therebetween, and the addressing means comprises means for applying a potential difference between the first and second electrodes of each selected pixel.
7. (Amended) An image display system according to claim 2, wherein each pixel of the second panel comprises first and second electrodes, first and second polarizers and a liquid crystal cell therebetween, and the addressing means of the second panel comprises means for applying a potential difference between the first and second electrodes of each selected pixel of the second panel.
8. (Amended) An image display system according to claim 3, wherein each pixel of the second panel comprises first and second electrodes, first and second polarizers and a liquid crystal cell therebetween, and the addressing means of the second panel comprises means for applying a potential difference between the first and second electrodes of each selected pixel of the second panel.
9. (Amended) An image display system according to claim 4, wherein each pixel of the first panel comprises first and second electrodes, first and second polarizers and a liquid crystal cell therebetween, and the addressing means comprises means for applying a potential difference between the first and second electrodes of each selected pixel.
10. An image display system according to claim 1 wherein said first viewing direction is at first angle relative to the maximum contrast viewing direction and said second viewing direction is at a second angle relative to the maximum contrast viewing direction, said second angle being of an opposite sign relative to said first angle.
1 1 . An image display system according to claim 10 wherein said first angle is on the order of thirty degrees.
12. An image display system according to claim 2 wherein said first viewing direction is at a first angle relative to the maximum contrast viewing direction of the first image display panel and said second viewing direction is at a second angle relative to the maximum contrast viewing direction of the first image display panel, said second angle being of an opposite sign relative to said first angle, and wherein said third viewing direction is at a first angle relative to the maximum contrast viewing direction of said second image display panel and said fourth viewing direction is at a second angle relative to the maximum contrast viewing direction of said second image display panel, said first angle relative to the maximum contrast viewing direction of said second image display panel being of an opposite sign relative to said second angle relative to the maximum contrast viewing direction of said second image display panel.
13. An image display system according to claim 3 wherein said first viewing direction is at first angle relative to the maximum contrast viewing direction is at a second angle relative to the maximum contrast viewing direction of the first image display panel, said second angle being of an opposite sign relative to said first angle.
14. An image display system according to claim 13 wherein said first angle is on the order of thirty degrees.
15. (Amended) An aircraft display system, said aircraft including an image display system comprising:
a twisted nematic liquid crystal image display panel having a plurality of discrete pixels and addressing means for electrically addressing selected pixels to display an image by applying a potential difference across each selected pixel, said panel being such that the maximum contrast viewing direction of the panel for viewing the image is dependent on the potential difference applied to the selected pixels of the panel,
means defining first and second viewing stations for allowing first and second users of the aircraft to view the panel in first and second viewing directions respectively, and
adjustable voltage means connected to the addressing means and applying a predetermined potential difference being established such that the maximum contrast viewing direction of the panel for viewing the image is intermediate the first and second viewing directions.
16. (Amended) An aircraft according to claim 15 further comprising:
a second twisted nematic liquid crystal image display panel to display a second image by applying a potential difference across each selected pixel of the second image display panel, said second image display being such that its maximum contrast viewing direction for viewing the second image is dependent on the potential difference applied to the selected pixels of the panel, the second image display panel being positioned for viewing by the first and second users of the aircraft in third and fourth viewing directions respectively, and
second adjustable voltage means connected to the addressing means of the second image display panel and applying a second predetermined potential difference to each selected pixel of the second image display panel, said second predetermined potential difference being established such that the maximum contrast viewing direction of the second image display panel for viewing the second image is intermediate the third and fourth viewing directions.
19. (Amended) The aircraft display system according to claim 16 wherein said first viewing direction is at a first angle relative to the maximum contrast viewing direction of the first image display panel for viewing the first mentioned image and said second viewing direction is at a second angle relative to the maximum contrast viewing direction of the first image display panel for viewing the first mentioned image, said second angle being of an opposite sign relative to said first angle, and wherein said third viewing direction is at a first angle relative to the maximum contrast viewing direction of said second image display panel for viewing the second image and said fourth viewing direction is at a second angle relative to the maximum contrast viewing direction of said second image display panel for viewing the second image, said first angle relative to the maximum contrast viewing direction of said second image display panel being of an opposite sign relative to the maximum contrast viewing direction of said second image display panel.
22. A method for providing an image display system having a user controllable angle of maximum contrast comprising the steps of:
providing a twisted nematic liquid crystal image display panel having a plurality of discrete pixels and addressing means for electrically addressing selected pixels to display an image by applying a potential difference across each selected pixel, and
providing adjustable voltage means connected to said addressing means and applying an adjustable range of voltage potential to said pixels such that the maximum contrast viewing direction of the panel for viewing the image is user variable.
23. The method of claim 22 including the further steps of:
providing each pixel with first and second electrodes and first and second polarizers with a liquid crystal cell therebetween; and
further providing said addressing means as compromising means for applying potential differences between the first and second electrodes of each selected pixel.
24. A method for providing an informational display to the flight crew of an aircraft comprising the steps of:
providing a twisted nematic liquid crystal image display panel having a plurality of predetermined positioned, discrete pixels, each pixel comprising first and second electrodes and first and second polarizers with a twisted nematic liquid crystal cell therebetween;
providing electrical addressing means for electrically addressing each pixel in said panel to control the display produced by said panel; and
providing adjustable voltage means for applying an adjustable voltage to the electrodes of the pixels,
whereby the flight crew can vary the voltage applied by the adjustable voltage means to said pixels to thereby control the angle of maximum contrast produced by said panel for optimum viewing by the flight crew.
EP95913774A 1994-04-07 1995-03-20 Image display system allowing multiple users to view a single display or a single user to view multiple displays Withdrawn EP0754338A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US22440194A 1994-04-07 1994-04-07
US224401 1994-04-07
PCT/US1995/003450 WO1995027973A1 (en) 1994-04-07 1995-03-20 Image display system allowing multiple users to view a single display or a single user to view multiple displays

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EP0754338A1 true EP0754338A1 (en) 1997-01-22

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CN (1) CN1146252A (en)
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JPH10240186A (en) * 1997-02-28 1998-09-11 Toshiba Corp Display control device and method thereof
GB2405516A (en) * 2003-08-30 2005-03-02 Sharp Kk Multiple view display

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DE3534703A1 (en) * 1985-09-28 1987-04-09 Philips Patentverwaltung CONTROL CIRCUIT FOR A LIQUID CRYSTAL DISPLAY UNIT
FR2682798B1 (en) * 1991-10-22 1994-01-21 Sextant Avionique METHOD AND DEVICE FOR OPTIMIZING THE PERFORMANCE OF A LIQUID CRYSTAL MATRIX SCREEN AS A FUNCTION OF THE ANGLE OF OBSERVATION.

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AU2103695A (en) 1995-10-30
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CN1146252A (en) 1997-03-26

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