WO2008012727A1 - Display device - Google Patents

Display device Download PDF

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Publication number
WO2008012727A1
WO2008012727A1 PCT/IB2007/052829 IB2007052829W WO2008012727A1 WO 2008012727 A1 WO2008012727 A1 WO 2008012727A1 IB 2007052829 W IB2007052829 W IB 2007052829W WO 2008012727 A1 WO2008012727 A1 WO 2008012727A1
Authority
WO
WIPO (PCT)
Prior art keywords
display panel
display
mode
panel
output
Prior art date
Application number
PCT/IB2007/052829
Other languages
French (fr)
Inventor
Lucas J. F. Geurts
Eliav I. Haskal
Original Assignee
Koninklijke Philips Electronics N.V.
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 Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2008012727A1 publication Critical patent/WO2008012727A1/en

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Classifications

    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
    • G09F9/00—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements
    • G09F9/30—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements
    • G09F9/35—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements being liquid crystals
    • 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
    • G02F1/133555—Transflectors
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/14—Digital output to display device ; Cooperation and interconnection of the display device with other functional units
    • G06F3/1423—Digital output to display device ; Cooperation and interconnection of the display device with other functional units controlling a plurality of local displays, e.g. CRT and flat panel display
    • G06F3/1431—Digital output to display device ; Cooperation and interconnection of the display device with other functional units controlling a plurality of local displays, e.g. CRT and flat panel display using a single graphics controller
    • 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
    • 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
    • G02F1/1343—Electrodes
    • G02F1/134309—Electrodes characterised by their geometrical arrangement
    • G02F1/134363—Electrodes characterised by their geometrical arrangement for applying an electric field parallel to the substrate, i.e. in-plane switching [IPS]
    • 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 
    • G02F1/165—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 translational movement of particles in a fluid under the influence of an applied field
    • G02F1/166—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 translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect
    • G02F1/167—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 translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect by electrophoresis
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/14—Digital output to display device ; Cooperation and interconnection of the display device with other functional units
    • G06F3/1423—Digital output to display device ; Cooperation and interconnection of the display device with other functional units controlling a plurality of local displays, e.g. CRT and flat panel 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
    • G09G2300/00—Aspects of the constitution of display devices
    • G09G2300/02—Composition of display devices
    • G09G2300/023—Display panel composed of stacked panels
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2300/00—Aspects of the constitution of display devices
    • G09G2300/04—Structural and physical details of display devices
    • G09G2300/0421—Structural details of the set of electrodes
    • G09G2300/0434—Flat panel display in which a field is applied parallel to the display plane
    • 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
    • G09G2310/0243—Details of the generation of driving signals
    • G09G2310/0245—Clearing or presetting the whole screen independently of waveforms, e.g. on power-on
    • 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
    • G09G2320/10—Special adaptations of display systems for operation with variable images
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2330/00—Aspects of power supply; Aspects of display protection and defect management
    • G09G2330/02—Details of power systems and of start or stop of display operation
    • G09G2330/021—Power management, e.g. power saving
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2380/00—Specific applications
    • G09G2380/06—Remotely controlled electronic signs other than labels
    • 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
    • G09G3/3433—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 light modulating elements actuated by an electric field and being other than liquid crystal devices and electrochromic devices
    • G09G3/344—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 light modulating elements actuated by an electric field and being other than liquid crystal devices and electrochromic devices based on particles moving in a fluid or in a gas, e.g. electrophoretic devices

Definitions

  • This invention relates to display devices.
  • Thin display devices such as LCD displays are becoming increasingly popular and replacing cathode ray tube displays in a number of areas.
  • LCD displays are already the most common form of computer monitor supplied with new desktop computers, and are of course used with laptop computers. These offer significant space savings and portability compared to CRT displays.
  • these displays are hung on a wall, requiring no floor space, and also giving the flexibility for optimum positioning.
  • a display device comprising: a first, light emitting display panel; a second, bistable display panel provided on top of the first display panel, wherein the device is operable in first and second modes, a first mode in which the second display panel is in a transparent mode to allow viewing of a display output from the underlying first display panel, and a second mode in which the second display panel is in a reflective display mode to provide a reflective display output and the first display panel is turned off.
  • the invention thus provides a display which can function as a normal display device, or can function to provide a reflective image in a low power bistable mode of operation.
  • the device can provide an output so that the display device can take the appearance of a framed picture, although of course the image chosen can be changed to match the mood, decor of the room, lighting etc etc. This is of particular interest for in- home entertainment applications, where large display screens are considered an eyesore.
  • the device is further operable in a third mode in which the first display panel functions as a backlight for a transmissive mode of operation of the second panel.
  • This can provide a way of displaying an image (in an emitting rather than reflecting mode) which changes slowly, with low power consumption.
  • Using the first display as a backlight, and providing an image using the second panel can eliminate the power consumption associated with the addressing cycles of a display, as the bistable display panel is used to generate the image, and the first display (e.g. an LCD) is simply operated as a continuous light source.
  • the device may be operable in a fourth mode in which the second display panel provides a frame image to supplement the output of the first display panel.
  • the two display panels can thus function together to provide the desired output.
  • slowly changing image data may be displayed by the second display, such as an on-screen menu, whereas more rapidly changing video data can be displayed by the first display panel.
  • the first display panel preferably comprises a colour video display panel, such as an LCD panel or an electroluminescent display panel.
  • a colour video display panel such as an LCD panel or an electroluminescent display panel.
  • it may be operable in a transparent mode, so that the device as a whole is further operable in a fifth mode in which the first and second display panels are in transparent modes. In this way, the device can provide a window function.
  • the second display panel preferably comprises an electrophoretic display panel, for example an in-plane switching electrophoretic display panel.
  • This type of display has the required reflective and transmissive modes of operation.
  • the invention also provides a method of controlling a display device, comprising: in a first mode of operation, controlling a first light emitting display panel to provide a video output and controlling a second display panel on top of the first display panel to be in a transparent mode to allow viewing of the display output from the underlying first display panel; and in a second mode of operation, switching off the first display panel and controlling the second display panel to be in a reflective bistable display mode to provide a reflective display output.
  • the invention also provides a display controller for controlling a display device, adapted to: in a first mode of operation, control a first light emitting display panel to provide a video output and control a second display panel on top of the first display panel to be in a transparent mode to allow viewing of the display output from the underlying first display panel, and in a second mode of operation, switch off the first display panel and control the second display panel to be in a reflective bistable display mode to provide a reflective display output.
  • Figure 1 shows a display device of the invention
  • Figure 2 shows the device of Figure 1 in one mode of operation
  • Figure 3 shows the device of Figure 1 in another mode of operation.
  • Figure 1 shows a display device 10 of the invention, comprising a first, light emitting display panel 12 and a second, bistable display panel 14 provided on top of the first display panel.
  • the first display panel 12 is for providing full video output, and thus preferably has a 50Hz, 60Hz, or even 100Hz frame rate.
  • the first display panel is an emissive display device, and a backlight 16 is shown schematically in Figure 1, although the display pixels themselves may be light emitting.
  • the second display panel 14 is bistable, and this means it can retain an image with very low or zero power consumption.
  • the second display panel 14 operates as a reflective display device.
  • the second display panel 14 also has a transparent mode so that an image from the underlying first display panel 12 can be viewed.
  • the second display panel is not required to display rapidly changing video data, and may have a much slower response time.
  • a normal video output mode can be considered to be a first mode, in which the second display panel 14 is in a transparent mode to allow viewing of a display output from the underlying first display panel 12
  • a static image output mode can be considered to be a second mode, in which the second display panel 14 is in a reflective display mode to provide a reflective display output and the first display panel 12 (including the backlight 16) is turned off.
  • Figure 3 shows an image of a big tractor. Also shown in Figure 3 is that part of the display area of Figure 2 has been used to provide an image of a picture frame.
  • the display device can function as a normal display device, or function to provide a reflective image in a low power bistable mode of operation.
  • the device can provide an output so that the display device can take the appearance of a framed picture, although of course the image chosen can be changed to match the mood, decor of the room, lighting etc etc. This is of particular interest for in- home entertainment applications, where large display screens are considered an eyesore.
  • the image In the low power bistable mode, the image only needs to be written to the second display panel once.
  • the device can include automatic control settings so that whenever the first display panel is turned off, the desired image is reloaded to the second display panel before the device powers down.
  • new static images can be selected, and indeed downloaded from external sources into the device.
  • the device is described as having two display “panels”, these panels may not be discrete separate components, and could be integrated into a single device.
  • the reference to display panels is intended to be functional, although the device of the invention can of course be implemented simply by physically overlaying and mounting two separate panel devices and controlling them appropriately.
  • the first display panel 12 can be a conventional LCD panel. However, it may instead comprise an electroluminescent (LED) display device, or a plasma display. Essentially, the first display panel can comprise any desired light emitting display technology which provides the desired image quality and frame rate.
  • LED electroluminescent
  • the first display panel can comprise any desired light emitting display technology which provides the desired image quality and frame rate.
  • the second display panel can comprise an electrophoretic display device.
  • Electrophoretic display devices are one example of bistable display technology, which use the movement of charged particles within an electric field to provide a selective light scattering, subtractive or absorption function.
  • electrophoretic display devices enable low power consumption as a result of their bistability (an image is retained with no voltage applied), and they can enable thin display devices to be formed as there is no need for a backlight or polariser. They may also be made from plastics materials, and there is also the possibility of low cost reel-to-reel processing in the manufacture of such displays.
  • a segmented reflective electrophoretic display has low power consumption, good brightness and is also bistable in operation, and therefore able to display information even when the display is turned off.
  • CMYK colour subtractive particles
  • an electrophoretic display device which uses so-called "in plane switching".
  • This type of device uses selective movement of the particles selectively laterally in the display material layer. When the particles are moved towards lateral electrodes, an opening appears between the electrodes, through which an underlying surface can be seen. This provides the transmissive mode of operation required for the functionality of the device explained above.
  • the in-plane electrodes may all be provided on one substrate, or else both substrates may be provided with electrodes, although this raises costs due to alignment needs.
  • the particles When the particles are randomly dispersed, they block the passage of light to the underlying surface and the particle colour is seen.
  • the particles may be coloured and the underlying surface black or white, or else the particles can be black or white, and the underlying surface coloured.
  • the underlying surface will for example comprise an LCD panel which is turned off, and this will typically take the form of a black screen.
  • the in-plane switching device can thus be adapted for transmissive operation, or transflective operation.
  • the movement of colour subtractive particles creates a passageway for light, so that both reflective and transmissive operation can be implemented through the material. This means the device can also operate with backlight illumination rather than only with reflective operation.
  • the first display panel 12 functions as a backlight for a transmissive mode of operation of the second panel 14.
  • This can provide a way of displaying an image using an emitting rather than reflecting mode with low power consumption.
  • the second display panel 14 may have low refresh rate, so that this may be suitable for slowly changing images. This provides a lower power way of displaying an image in a light emitting mode than simply using the first display panel 12. In particular, the power consumption associated with the refreshing of the first display panel 12 is avoided, as it is simply used as a backlight.
  • the two display outputs can be combined to define the overall output image.
  • the first display panel 12 can be used for the motion parts of an image whereas the second display panel 14 can be used for static parts of an image.
  • the second display panel 14 can define a decorative frame for an image displayed by the first panel 12.
  • the second display panel 14 can be used for static parts of an image such as an on-screen menu, whereas the video content is displayed by the first display panel 12.
  • the second display panel is driven to the transparent mode in the areas where it is not used for providing the static image.
  • the first display panel 12 may comprises an electroluminescent display device.
  • This type of device can provide all of the functions outlined above, as full colour high speed light emitting displays can be formed using this technology. However, they can be made transparent, which provides an additional window mode of operation for the device of the invention. In this mode, both displays are set to transparent, and the device can function as a window with a built in display function. This may be of interest for shop frontage, offices, shops, vehicles etc.
  • the two different types of display panel required to implement the display device of the invention are readily available, and for this reason, a detailed description has not been given of the actual display technology.
  • a controller is required to synchronise the operation of the two display panels (including the backlight). This is shown schematically as 18 in Figure 1.
  • the implementation of the controller 18 will be routine to those skilled in the art.
  • the second display panel is simply driven to the transmissive state whenever the first display panel is in use, and the second display panel is driven to display a static image whenever the first display panel is not in use.
  • the slightly more complicated modes of operation described above require different parts of the two display outputs to be synchronised to provide a desired combined effect, but the implementation of this will be routine to those skilled in the art. For this reason, the controller required to oversee the operation of the two display panels has not been described in detail.
  • the invention may find applications in LCD TV screens and LCD monitors, but also for small screens such as mobile phone screens. In all cases, the appearance of the screen when turned off can display an image of the user's choice.
  • the invention can also be applied to signage applications, and enables a single sign design to have the ability to display full video or bistable static images, and maintain the respective benefits of each display mode as desired.
  • a transparent implementation also enables window applications, such as shop windows, windscreens (functioning as an integrated head up display), offices etc. to be used.
  • window applications such as shop windows, windscreens (functioning as an integrated head up display), offices etc.

Abstract

A display device (10) comprises a first, light emitting display panel (12) and a second, bistable display panel (14) provided on top of the first display panel. The device is operable in a first mode in which the second display panel (14) is in a transparent mode to allow viewing of a display output from the underlying first display panel, and a second mode in which the second display panel (14) is in a reflective display mode to provide a reflective display output and the first display panel is turned off. The display can function as a normal display device, or can function to provide a reflective image for example taking the appearance of a framed picture.

Description

Display device
This invention relates to display devices.
Thin display devices such as LCD displays are becoming increasingly popular and replacing cathode ray tube displays in a number of areas. LCD displays are already the most common form of computer monitor supplied with new desktop computers, and are of course used with laptop computers. These offer significant space savings and portability compared to CRT displays.
Larger LCD displays as well as large plasma display panels are also becoming less expensive and have improved performance so that they can now compete with large CRT displays for use in the home.
Typically, these displays are hung on a wall, requiring no floor space, and also giving the flexibility for optimum positioning.
Large LCD displays can however be considered to be unsightly, and there have been proposals to hide the screen from view when not providing a display output, for example by using a semi-transparent mirror on the LCD surface.
According to the invention, there is provided a display device, comprising: a first, light emitting display panel; a second, bistable display panel provided on top of the first display panel, wherein the device is operable in first and second modes, a first mode in which the second display panel is in a transparent mode to allow viewing of a display output from the underlying first display panel, and a second mode in which the second display panel is in a reflective display mode to provide a reflective display output and the first display panel is turned off.
The invention thus provides a display which can function as a normal display device, or can function to provide a reflective image in a low power bistable mode of operation. In this way, the device can provide an output so that the display device can take the appearance of a framed picture, although of course the image chosen can be changed to match the mood, decor of the room, lighting etc etc. This is of particular interest for in- home entertainment applications, where large display screens are considered an eyesore.
There are also commercial applications. In one example, the device is further operable in a third mode in which the first display panel functions as a backlight for a transmissive mode of operation of the second panel. This can provide a way of displaying an image (in an emitting rather than reflecting mode) which changes slowly, with low power consumption. Using the first display as a backlight, and providing an image using the second panel can eliminate the power consumption associated with the addressing cycles of a display, as the bistable display panel is used to generate the image, and the first display (e.g. an LCD) is simply operated as a continuous light source.
The device may be operable in a fourth mode in which the second display panel provides a frame image to supplement the output of the first display panel. The two display panels can thus function together to provide the desired output. In another example, slowly changing image data may be displayed by the second display, such as an on-screen menu, whereas more rapidly changing video data can be displayed by the first display panel.
The first display panel preferably comprises a colour video display panel, such as an LCD panel or an electroluminescent display panel. In the case of an electroluminescent display panel, it may be operable in a transparent mode, so that the device as a whole is further operable in a fifth mode in which the first and second display panels are in transparent modes. In this way, the device can provide a window function.
The second display panel preferably comprises an electrophoretic display panel, for example an in-plane switching electrophoretic display panel. This type of display has the required reflective and transmissive modes of operation. The invention also provides a method of controlling a display device, comprising: in a first mode of operation, controlling a first light emitting display panel to provide a video output and controlling a second display panel on top of the first display panel to be in a transparent mode to allow viewing of the display output from the underlying first display panel; and in a second mode of operation, switching off the first display panel and controlling the second display panel to be in a reflective bistable display mode to provide a reflective display output. The invention also provides a display controller for controlling a display device, adapted to: in a first mode of operation, control a first light emitting display panel to provide a video output and control a second display panel on top of the first display panel to be in a transparent mode to allow viewing of the display output from the underlying first display panel, and in a second mode of operation, switch off the first display panel and control the second display panel to be in a reflective bistable display mode to provide a reflective display output.
Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:
Figure 1 shows a display device of the invention; Figure 2 shows the device of Figure 1 in one mode of operation; and
Figure 3 shows the device of Figure 1 in another mode of operation.
Figure 1 shows a display device 10 of the invention, comprising a first, light emitting display panel 12 and a second, bistable display panel 14 provided on top of the first display panel.
The first display panel 12 is for providing full video output, and thus preferably has a 50Hz, 60Hz, or even 100Hz frame rate. The first display panel is an emissive display device, and a backlight 16 is shown schematically in Figure 1, although the display pixels themselves may be light emitting.
The second display panel 14 is bistable, and this means it can retain an image with very low or zero power consumption. When displaying an image, the second display panel 14 operates as a reflective display device. However, the second display panel 14 also has a transparent mode so that an image from the underlying first display panel 12 can be viewed.
The second display panel is not required to display rapidly changing video data, and may have a much slower response time.
By controlling the two display panels 12,14 independently, the overall display device 10 is operable in a number of modes. A normal video output mode can be considered to be a first mode, in which the second display panel 14 is in a transparent mode to allow viewing of a display output from the underlying first display panel 12
This mode is illustrated schematically in Figure 2 which shows a bouncing ball.
A static image output mode can be considered to be a second mode, in which the second display panel 14 is in a reflective display mode to provide a reflective display output and the first display panel 12 (including the backlight 16) is turned off.
This mode is illustrated schematically in Figure 3 which shows an image of a big tractor. Also shown in Figure 3 is that part of the display area of Figure 2 has been used to provide an image of a picture frame.
These two basic modes of operation enable the display device to function as a normal display device, or function to provide a reflective image in a low power bistable mode of operation. In this way, the device can provide an output so that the display device can take the appearance of a framed picture, although of course the image chosen can be changed to match the mood, decor of the room, lighting etc etc. This is of particular interest for in- home entertainment applications, where large display screens are considered an eyesore. In the low power bistable mode, the image only needs to be written to the second display panel once.
The device can include automatic control settings so that whenever the first display panel is turned off, the desired image is reloaded to the second display panel before the device powers down. Of course, new static images can be selected, and indeed downloaded from external sources into the device.
Although the device is described as having two display "panels", these panels may not be discrete separate components, and could be integrated into a single device. Thus, the reference to display panels is intended to be functional, although the device of the invention can of course be implemented simply by physically overlaying and mounting two separate panel devices and controlling them appropriately.
The first display panel 12 can be a conventional LCD panel. However, it may instead comprise an electroluminescent (LED) display device, or a plasma display. Essentially, the first display panel can comprise any desired light emitting display technology which provides the desired image quality and frame rate.
The second display panel can comprise an electrophoretic display device. Electrophoretic display devices are one example of bistable display technology, which use the movement of charged particles within an electric field to provide a selective light scattering, subtractive or absorption function.
It has been recognised that electrophoretic display devices enable low power consumption as a result of their bistability (an image is retained with no voltage applied), and they can enable thin display devices to be formed as there is no need for a backlight or polariser. They may also be made from plastics materials, and there is also the possibility of low cost reel-to-reel processing in the manufacture of such displays.
If costs are to be kept as low as possible, passive addressing schemes are employed. The most simple configuration of display device is a segmented reflective display, and there are a number of applications where this type of display is sufficient. A segmented reflective electrophoretic display has low power consumption, good brightness and is also bistable in operation, and therefore able to display information even when the display is turned off.
However, improved performance and versatility is provided using a matrix addressing scheme. Active matrix addressing schemes are generally required when bright full colour displays with high resolution greyscale are required. Such devices are being developed for signage and billboard display applications, and as (pixellated) light sources in electronic window and ambient lighting applications. Colours can be implemented using colour filters and the display pixels then function simply as greyscale devices or else colour subtractive particles may be used (CMYK).
Of particular interest for this invention is an electrophoretic display device which uses so-called "in plane switching". This type of device uses selective movement of the particles selectively laterally in the display material layer. When the particles are moved towards lateral electrodes, an opening appears between the electrodes, through which an underlying surface can be seen. This provides the transmissive mode of operation required for the functionality of the device explained above.
The in-plane electrodes may all be provided on one substrate, or else both substrates may be provided with electrodes, although this raises costs due to alignment needs.
When the particles are randomly dispersed, they block the passage of light to the underlying surface and the particle colour is seen. The particles may be coloured and the underlying surface black or white, or else the particles can be black or white, and the underlying surface coloured.
In this example, the underlying surface will for example comprise an LCD panel which is turned off, and this will typically take the form of a black screen. The in-plane switching device can thus be adapted for transmissive operation, or transflective operation. In particular, the movement of colour subtractive particles creates a passageway for light, so that both reflective and transmissive operation can be implemented through the material. This means the device can also operate with backlight illumination rather than only with reflective operation.
This therefore gives an additional mode of operation in which the first display panel 12 functions as a backlight for a transmissive mode of operation of the second panel 14. This can provide a way of displaying an image using an emitting rather than reflecting mode with low power consumption. As mentioned above, the second display panel 14 may have low refresh rate, so that this may be suitable for slowly changing images. This provides a lower power way of displaying an image in a light emitting mode than simply using the first display panel 12. In particular, the power consumption associated with the refreshing of the first display panel 12 is avoided, as it is simply used as a backlight. The two display outputs can be combined to define the overall output image.
Thus, the first display panel 12 can be used for the motion parts of an image whereas the second display panel 14 can be used for static parts of an image. For example, the second display panel 14 can define a decorative frame for an image displayed by the first panel 12. Alternatively, the second display panel 14 can be used for static parts of an image such as an on-screen menu, whereas the video content is displayed by the first display panel 12. In these examples, the second display panel is driven to the transparent mode in the areas where it is not used for providing the static image.
As mentioned above, the first display panel 12 may comprises an electroluminescent display device. This type of device can provide all of the functions outlined above, as full colour high speed light emitting displays can be formed using this technology. However, they can be made transparent, which provides an additional window mode of operation for the device of the invention. In this mode, both displays are set to transparent, and the device can function as a window with a built in display function. This may be of interest for shop frontage, offices, shops, vehicles etc. The two different types of display panel required to implement the display device of the invention are readily available, and for this reason, a detailed description has not been given of the actual display technology.
A controller is required to synchronise the operation of the two display panels (including the backlight). This is shown schematically as 18 in Figure 1. The implementation of the controller 18 will be routine to those skilled in the art. In the simplest implementation, the second display panel is simply driven to the transmissive state whenever the first display panel is in use, and the second display panel is driven to display a static image whenever the first display panel is not in use. The slightly more complicated modes of operation described above require different parts of the two display outputs to be synchronised to provide a desired combined effect, but the implementation of this will be routine to those skilled in the art. For this reason, the controller required to oversee the operation of the two display panels has not been described in detail.
The invention may find applications in LCD TV screens and LCD monitors, but also for small screens such as mobile phone screens. In all cases, the appearance of the screen when turned off can display an image of the user's choice. The invention can also be applied to signage applications, and enables a single sign design to have the ability to display full video or bistable static images, and maintain the respective benefits of each display mode as desired. A transparent implementation also enables window applications, such as shop windows, windscreens (functioning as an integrated head up display), offices etc. to be used. Various modifications will be apparent to those skilled in the art.

Claims

CLAIMS:
1. A display device (10), comprising: a first, light emitting display panel (12); a second, bistable display panel (14) provided on top of the first display panel, wherein the device is operable in first and second modes, a first mode in which the second display panel (14) is in a transparent mode to allow viewing of a display output from the underlying first display panel (12), and a second mode in which the second display panel (14) is in a reflective display mode to provide a reflective display output and the first display panel is turned off.
2. A device as claimed in claim 1, further operable in a third mode in which the first display panel (12) functions as a backlight for a transmissive mode of operation of the second panel (14).
3. A device as claimed in claim 1 or 2, further operable in a fourth mode in which the second display panel (14) provides a frame image to supplement the output of the first display panel (12).
4. A device as claimed in any preceding claim, wherein the first display panel (12) comprises a colour video display panel.
5. A device as claimed in claim 4, wherein the first display panel (12) comprises an LCD panel.
6. A device as claimed in claim 4, wherein the first display panel (12) comprises an electroluminescent display panel.
7. A device as claimed in claim 6, further operable in a fifth mode in which the first and second display panels (12,14) are in transparent modes.
8. A device as claimed in any preceding claim, wherein the second display panel (14) comprises an electrophoretic display panel.
9. A device as claimed in claim 8, wherein the second display panel (14) comprises an in-plane switching electrophoretic display panel.
10. A method of controlling a display device, comprising: in a first mode of operation, controlling a first light emitting display panel (12) to provide a video output and controlling a second display panel (14) on top of the first display panel to be in a transparent mode to allow viewing of the display output from the underlying first display panel (12); and in a second mode of operation, switching off the first display panel (12) and controlling the second display panel to be in a reflective bistable display mode to provide a reflective display output.
11. A display controller for controlling a display device, adapted to: in a first mode of operation, control a first light emitting display panel (12) to provide a video output and control a second display panel (14) on top of the first display panel to be in a transparent mode to allow viewing of the display output from the underlying first display panel, and in a second mode of operation, switch off the first display panel (12) and control the second display panel (14) to be in a reflective bistable display mode to provide a reflective display output.
PCT/IB2007/052829 2006-07-25 2007-07-16 Display device WO2008012727A1 (en)

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