HK1222033B - Display assembly including two superposed display devices - Google Patents

Description

Display assembly comprising two stacked display devices

Technical Field

The present invention relates to a display assembly comprising two superimposed display devices. More particularly, the present invention relates to such a display assembly for accommodation in a portable object such as a wristwatch.

Background Art

The readability of information displayed by active digital display devices, such as liquid crystal displays (LCDs) or organic light-emitting diode (OLED) displays, is highly dependent on ambient lighting conditions. For some digital display devices, displayed information can be read well in brightly lit environments but becomes difficult to read in the dark. Conversely, other types of digital display devices offer good quality in low light or darkness but are virtually unusable in broad daylight.

For example, consider a transflective liquid crystal display cell—that is, a liquid crystal cell capable of displaying information that is visible in full sunlight by means of reflection phenomena and, through transmission using a backlight, also visible at night. Such transflective liquid crystal display cells are optimized to provide the best possible reflection of sunlight and, therefore, ensure good readability of the displayed information in bright conditions. However, to achieve the best possible reflection of sunlight for such transflective liquid crystal display cells, their transmission efficiency is significantly limited. Consequently, when the backlight is activated to allow the displayed information to be read in low light, the vast majority of the light generated by the backlight is lost through absorption phenomena. Consequently, energy efficiency is low. Furthermore, the optical quality of the information displayed by the liquid crystal cell is highly dependent on the viewing angle.

Regarding emissive display devices, such as organic light-emitting diode display devices, these devices have optical qualities that are superior to those of liquid crystal display units because the optical quality does not depend on the viewing angle. However, these high-quality emissive display devices do not allow for reflective operating modes. Therefore, the information they display is easy to read indoors or in the dark, but becomes difficult to read once outdoors. In order to overcome this problem, it is necessary to increase the amount of current supplied to the emissive display device to ensure a minimum level of readability. In addition, even under normal conditions of use, these emissive display devices use more current than reflective liquid crystal display units. Their power consumption makes it impossible to keep them permanently turned on, for example, in a watch, the only source of energy for which is a battery that typically needs to last for more than a year.

Summary of the Invention

It is an object of the present invention to overcome the above-mentioned problems and others by providing a display assembly for a portable object, such as a wristwatch, that operates properly both in brightly lit environments and in dark environments.

To this end, the present invention relates to a display assembly for a portable object, which includes a first reflective display device located on the observer side, which can be switched between a transparent state when it is not working and a reflective state when it is enabled, and a second emissive display device is arranged below the first reflective display device.

According to a supplementary feature of the invention, the reflective display device is incorporated into the emissive display device.

According to another feature of the invention, the reflective display device is bonded to the emissive display device by means of an adhesive film or a liquid adhesive layer.

As a result of these features, the present invention provides a display assembly for a portable object, such as a wristwatch, that operates optimally regardless of ambient lighting conditions. In bright sunlight, information is preferably displayed by a reflective display. Indeed, a reflective display that utilizes sunlight to display information is highly energy efficient. Therefore, it can remain permanently on and provide excellent readability of the information. Conversely, in low light or darkness, information is displayed by an emissive display. This emissive display uses more current than a reflective display, but the information displayed by it is visible at night or in darkness, thanks to its excellent optical properties that are particularly independent of viewing angle.

According to a first variant embodiment of the invention, the first display device comprises a reflective liquid crystal display unit and the second display device comprises an emissive organic light emitting diode display unit.

According to a second variant embodiment of the present invention, the first display device comprises a reflective liquid crystal display unit, and the second display device comprises a transmissive liquid crystal display unit, with a backlight device arranged therebelow.

As a result of these other characteristics, the present invention provides a display assembly that allows information to be permanently displayed in a simple, readable manner with low power consumption. In particular, the present invention provides a display assembly that allows a large amount of information to be displayed that is visible even in darkness.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will emerge more clearly from the following detailed description of several exemplary embodiments of the display assembly according to the invention, which examples are given by way of non-limiting examples only, with reference to the accompanying drawings, in which:

- FIG. 1 is a cross-sectional view of a first embodiment of a display assembly according to the present invention, the display assembly comprising a reflective liquid crystal display unit coupled to an organic light emitting diode display unit.

2A to 2D schematically illustrate operating modes of the display assembly shown in FIG. 1 according to whether the liquid crystal display unit and the organic light emitting diode display unit are enabled or disabled.

3 is a cross-sectional view of a variant embodiment of the display assembly according to the present invention shown in FIG. 1 , wherein a single-polarization liquid crystal display unit is combined with an organic light emitting diode display unit.

4A to 4D schematically illustrate the operating modes of the display assembly shown in FIG. 3 according to whether the single-polarization liquid crystal display unit and the organic light emitting diode display unit are enabled or disabled.

- Figure 5 is a cross-sectional view of a second embodiment of a display assembly according to the invention comprising a reflective liquid crystal display unit coupled to a backlit transmissive liquid crystal display unit.

DETAILED DESCRIPTION

The present invention stems from the following general inventive concept: to provide a display assembly that can display information in a readable manner both in bright sunlight and in dim light or darkness, while optimizing power consumption. To achieve this goal, the present invention teaches combining a display device with an emissive display device, wherein the display device is configured to switch between a transparent, inoperative state and an operational state in which it reflects ambient light. Reflective displays are typically liquid crystal display units, while emissive displays are typically transmissive liquid crystal display units or organic light-emitting display units associated with a backlight. For displaying information in bright sunlight, a reflective display device is preferably used, as it can display information clearly and readable by reflecting sunlight while consuming less power. For displaying information in dim light or darkness, an emissive display device is preferably used. Due to their excellent optical properties, particularly in terms of contrast and color reproduction, such emissive displays enable the display of large amounts of information in an extremely easy-to-read manner. In particular, the readability of the displayed information is independent of the viewing angle. Furthermore, the power consumption of such an emissive display device can be significantly reduced while ensuring good readability of the displayed information, regardless of dim light or darkness. Therefore, a display assembly is provided comprising a reflective display device which is placed on the top of a stack and which is capable of permanently displaying information with extremely low energy consumption, and an emissive display device which is placed at the bottom of the stack and which is capable of displaying information on demand in a very easy-to-read manner in low light or darkness.

1 is a cross-sectional view of a first embodiment of a display assembly according to the present invention. The display assembly, generally indicated by the general reference numeral 1, comprises a first reflective display device 2 located on the side of an observer 4 and a second emissive display device 6 arranged below the first reflective display device 2.

According to the present invention, a first reflective display device 2, which is reflective in a first switching state and transparent in a second switching state, includes a liquid crystal display unit 8. The liquid crystal display unit 8 includes, in a non-limiting manner, a front substrate 10 located on the side of the observer 4 and a rear substrate 12 extending parallel to and away from the front substrate 10. The two front substrates 10 and the rear substrate 12 are made of a transparent material such as glass or plastic. The two front substrates 10 and the rear substrate 12 are joined to each other by a sealing frame 14, which defines a closed space for accommodating liquid crystals 16. The optical properties of the liquid crystals 16 are modified by applying appropriate voltages at specific intersections between a transparent electrode 18 provided on the lower surface of the front substrate 10 and a transparent counter electrode 20 provided on the upper surface of the rear substrate 12. The electrodes 18 and the counter electrode 20 are made of a transparent conductive material such as indium-zinc oxide or indium-tin oxide, also known as ITO.

In the context of the present invention, any liquid crystal phase can be envisaged, such as twisted nematic (TN), super twisted nematic (STN) or vertical alignment (VA). Likewise, all addressing schemes can be envisaged, such as direct addressing, active matrix addressing or passive matrix multiplexing addressing.

The absorbing polarizer 22 is bonded to the upper surface of the front substrate 10 via an adhesive layer 24. The adhesive layer 24 can be formed of an adhesive film or a liquid adhesive layer. The adhesive used to bond the absorbing polarizer 22 to the liquid crystal display element 8 can be transparent or slightly diffuse, depending on whether specular reflection or diffuse reflection is required. The absorbing polarizer 22 can be, for example, an iodine-based polarizer or a dye-based polarizer.

Reflective polarizer 26 is bonded to the lower surface of rear substrate 12 via adhesive layer 28. Adhesive layer 28 may be transparent or slightly diffusive, depending on whether specular or diffuse reflection is desired. Reflective polarizer 26 may be a wire grid polarizer. Alternatively, it may be a polarizer composed of a series of birefringent layers that induce polarized reflection or transmission through constructive or destructive interference, such as a dual brightness enhancement film (DBEF) or APF polarizer sold by a US company.

Similarly, according to the present invention, the second emissive display device 6 includes an emissive display unit 30 having an organic light emitting diode, which will be referred to as an "OLED" hereinafter. The OLED display unit 30 includes a transparent substrate 32 made of glass or plastic material and an encapsulation cover 34 extending parallel to and away from the substrate 32. The substrate 32 and the encapsulation cover 34 are joined to each other by a sealing frame 36, which defines a closed space isolated from air and moisture to accommodate a stack of light emitting layers, generally indicated by the reference numeral 38. An upper transparent electrode 40, for example, made of indium-tin oxide or ITO, and a lower reflective electrode 42 are constructed on both sides of the stack of light emitting layers 38, wherein the lower reflective electrode 42 is made of a material such as aluminum or silver, calcium, or a metal alloy of aluminum or silver with calcium, lithium or magnesium.

The liquid crystal display unit 8 is arranged above the OLED unit 30 relative to the observer 4. Preferably, the liquid crystal display unit 8 is bonded to the OLED unit 30 by means of a transparent adhesive layer 44 formed of an adhesive film or a liquid adhesive layer. It is preferable to bond the liquid crystal display unit 8 to the OLED unit 30 to avoid the problem of stray reflection between the two units, which will degrade the optical quality of the display assembly 1 according to the present invention.

A circular polarizer 46, consisting of an absorbing polarizer 48 and a quarter-wave plate 50, is inserted between the liquid crystal display unit 8 and the OLED unit 30. The purpose of this circular polarizer 46 is to absorb ambient light and thus give the OLED unit 30 a black appearance when the OLED unit 30 is turned off. The quarter-wave plate 50 is fixed to the substrate 32 by means of an adhesive layer 51.

According to a supplementary feature of the present invention, the transmission axis of reflective polarizer 26 of liquid crystal display unit 8 is oriented parallel to the transmission axis of absorptive polarizer 48 of circular polarizer 46 of OLED display unit 30. Thus, when liquid crystal display unit 8 is in transmissive mode, linearly polarized light emitted by OLED display unit 30 passes through liquid crystal display unit 8. Conversely, ambient light that reaches the OLED display unit by passing through liquid crystal display unit 8 is circularly polarized by circular polarizer 46. This light is then reflected by lower reflective electrode 42, which causes the direction of rotation of the circular polarization to reverse and the circular polarizer 46 to absorb the light. Consequently, the display assembly 1 according to the present invention appears black to observer 4.

Figures 2A to 2D schematically illustrate the operating modes of the display assembly 1 according to the present invention, depending on whether the liquid crystal display cell 8 or the OLED display cell 30 is in use. Hereinafter, it will be assumed that the liquid crystal display cell 8 is a twisted nematic cell. This example is provided solely as a non-limiting illustration, as it is easier to describe the operation of the display assembly 1 according to the present invention when the liquid crystal display cell 8 is of the twisted nematic type. However, it should be understood that the liquid crystal display cell 8 may be of other types, such as super twisted nematic or vertical alignment.

More specifically, in FIG2A , both the liquid crystal display unit 8 and the OLED display unit 30 are turned off. Therefore, the liquid crystal display unit 8 is transparent. Ambient light, indicated by reference numeral 52, is linearly polarized by the absorptive polarizer 22. Ambient light 52 then undergoes a 90° rotation as it passes through the liquid crystal display unit 8. Because the transmission axis of the reflective polarizer 26 extends perpendicular to the transmission axis of the absorptive polarizer 22, the reflective polarizer 26 allows the ambient light 52 to pass through without modification, and the ambient light 52 propagates toward the OLED display unit 30. Before penetrating the OLED display unit 30, the ambient light 52 is circularly polarized by the circular polarizer 46. Ultimately, the ambient light 52 passes through the OLED display unit 30, where it is reflected onto the lower reflective electrode 42. After reflection from the lower reflective electrode 42, the rotational direction of the circular polarization of the light is reversed, causing the light to be absorbed by the circular polarizer 46. Consequently, the display assembly 1 appears black to the observer 4.

2B, the liquid crystal display unit 8 is deactivated, while the OLED display unit 30 is activated. Therefore, the liquid crystal display unit 8 is transparent and lets the light emitted from the OLED display unit 30 pass therethrough.

More specifically, ambient light 52, linearly polarized by absorptive polarizer 22, undergoes a 90° rotation as it passes through reflective liquid crystal display unit 8 and is then transmitted unchanged by reflective polarizer 26, whose transmission axis is perpendicular to that of absorptive polarizer 22. Ambient light 52 is then circularly polarized by circular polarizer 46, which transmits the light without absorption, given that the transmission axis of absorptive polarizer 48 is oriented parallel to that of reflective polarizer 26. Ultimately, ambient light 52 passes through OLED display unit 30. Within OLED display unit 30, ambient light 52 is reflected by transparent lower electrode 42. Upon reflection, the direction of rotation of the light's circular polarization is reversed, causing it to be absorbed by circular polarizer 46 when it passes through it again. Furthermore, half of the light emitted from the OLED display unit 30 is absorbed by the absorptive polarizer 48, while the other half of the light, which is linearly polarized, first passes through the reflective polarizer 26 without modification because the transmission axis of the reflective polarizer 26 is oriented parallel to the transmission axis of the absorptive polarizer 48, which is a component of the circular polarizer 46. Upon passing through the liquid crystal display unit 8, the polarized light undergoes a 90° rotation, so that its polarization direction ultimately becomes parallel to the transmission axis of the absorptive polarizer 22, and the polarized light passes through the absorptive polarizer 22 without being absorbed. As a result, the displayed information glows against a dark background.

2C , the liquid crystal display unit 8 is enabled in reflective mode and the OLED display unit 30 is turned off. Thus, the liquid crystal display unit 8 reflects ambient light 52, causing the information it displays to glow against the dark background provided by the OLED display unit 30. The contrast between the illuminated pixels of the liquid crystal display unit 8 and the dark background of the OLED display unit 30 enables the information to be displayed in a very easy to read manner.

More specifically, in the unswitched region of the liquid crystal display cell 8, ambient light 52 linearly polarized by the absorptive polarizer 22 undergoes a 90° rotation as it passes through the liquid crystal display cell 8 and is then transmitted unchanged by the reflective polarizer 26, whose transmission axis is perpendicular to that of the absorptive polarizer 22. The ambient light 52 is then circularly polarized by the circular polarizer 46, which transmits the light without absorption, given that the transmission axis of the absorptive polarizer 48 is oriented parallel to that of the reflective polarizer 26. Ultimately, the ambient light 52 passes through the OLED display cell 30, where it is reflected by the lower transparent electrode 42. At this point, the direction of rotation of the circular polarization is reversed, so that when the light passes through the circular polarizer 46 again, it is absorbed by the latter. Furthermore, in the switched region of the liquid crystal display cell 8, after being linearly polarized by the absorptive polarizer 22, the ambient light 52 passes through the liquid crystal display cell 8 without modification, so that the polarization direction of the ambient light 52 is perpendicular to the transmission axis of the reflective polarizer 26 and therefore parallel to the reflection axis of the polarizer 26. Therefore, the ambient light 52 is reflected by the reflective polarizer 26 in the direction of the liquid crystal display cell 8. In the switched region of the liquid crystal display cell 8, when the ambient light 52 passes through the liquid crystal display cell 8 again, the liquid crystal molecules do not modify the polarization direction of the ambient light 52, so that the ambient light 52 is not absorbed by the absorptive polarizer 22 on its return journey, which makes the reflective mode of the display assembly 1 possible.

In FIG2D , the liquid crystal display unit 8 is enabled in reflective mode and the OLED display unit 30 is turned on. In this case, light emitted by the OLED display unit 30 is absorbed by the absorptive polarizer 22 in the active area of the liquid crystal display unit 8 displaying information. More specifically, ambient light 52 is linearly polarized by the absorptive polarizer 22 and then passes through the switched area of the liquid crystal display unit 8 without being altered. Because the transmission axis of the absorptive polarizer 22 is perpendicular to the transmission axis of the reflective polarizer 26, the ambient light 52 is reflected by the reflective polarizer 26 and then passes through the switched area of the liquid crystal display unit 8 again without being altered. Finally, the ambient light 52 passes through the absorptive polarizer 22 without being absorbed and is perceived by the observer 4, allowing the liquid crystal display unit 8 to display information in reflective mode. As for the remaining ambient light 52, it is linearly polarized by the absorptive polarizer 22 and then passes through the non-switched area of the liquid crystal display unit 8. As it passes through, the polarization direction of ambient light 52 rotates 90°, so that when the light exits liquid crystal display cell 8, its polarization direction is parallel to the transmission axis of reflective polarizer 26. This light then passes through reflective polarizer 26 without modification and is then circularly polarized by circular polarizer 46. Ambient light 52 then penetrates OLED display cell 30, where it is reflected by transparent lower electrode 42. At this point, the rotation direction of the circular polarization is reversed, so that when the light passes through circular polarizer 46 again, it is absorbed by the latter. In addition, half of the light emitted from OLED display cell 30 is absorbed by absorptive polarizer 48, while the other half of the light emitted from OLED display cell 30 passes through absorptive polarizer 48 and becomes linearly polarized, and then passes through reflective polarizer 26 without modification because the transmission axis of reflective polarizer 26 is parallel to the transmission axis of absorptive polarizer 48. In the enabled areas of the liquid crystal display cell 8, light passes through without modification, so that it is absorbed by the absorptive polarizer 22, because its polarization direction is perpendicular to the transmission axis of the absorptive polarizer 22. However, in the inactive areas of the liquid crystal display cell 8, the polarization direction of the light is rotated by 90°, so that this portion of light passes through the absorptive polarizer 22 without being absorbed and can be perceived by the observer 4.

FIG3 is a cross-sectional view of a variant embodiment of the display assembly 1 according to the present invention shown in FIG1 . The display assembly shown in FIG3 , generally designated by the general reference numeral 100, includes a liquid crystal display unit 102 disposed above an OLED display unit 104. The liquid crystal display unit 102 is a single polarizer unit whose liquid crystals are arranged vertically. The liquid crystal display unit 102 includes a front substrate 106 disposed on the side of the observer 4 and a rear substrate 108 extending parallel to and away from the front substrate 106. The front substrate 106 and the rear substrate 108 are joined to each other by a sealing frame 110 that defines a closed space for accommodating the vertically aligned liquid crystals 112. A transparent electrode 114 is disposed on the lower surface of the front substrate 106, while a transparent counter electrode 116 is disposed on the upper surface of the rear substrate 108.

The OLED display unit 104 includes a transparent substrate 118 made of glass or plastic, and an encapsulation cover 120 extending parallel to and away from the substrate 118. The substrate 118 and the encapsulation cover 120 are joined to each other by a sealing frame 122, which defines a sealed space isolated from air and moisture to accommodate a stack of layers consisting of a light-emitting layer 124. A transparent upper electrode 126 and a lower reflective electrode 128 are formed on both sides of the stack of light-emitting layers 124.

The liquid crystal display unit 102 is disposed above the OLED display unit 104 relative to the observer 4. Preferably, the liquid crystal display unit 102 is bonded to the OLED display unit 104 by means of an adhesive layer 130 formed of an adhesive film or a liquid adhesive layer. The adhesive used to bond the liquid crystal display unit 102 to the OLED display unit 104 can be transparent or slightly diffuse, depending on whether specular reflection or diffuse reflection is required.

Finally, the circular polarizer 132 composed of the absorbing polarizer 134 and the quarter-wave plate 136 is bonded to the liquid crystal display unit 102 by means of a transparent adhesive layer 138 .

Generally speaking, ambient light becomes circularly polarized when passing through the assembly consisting of the absorptive polarizer 134 and the quarter-wave plate 136. When not in operation, the liquid crystal does not alter the polarization of light. Therefore, circularly polarized light propagates through the liquid crystal display unit 102 and the OLED display unit 104 and is reflected onto the lower reflective electrode 128. Upon reflection from the lower reflective electrode 128, the direction of rotation of the light's circular polarization is reversed, causing it to be absorbed by the circular polarizer 132 upon passing through it again. Consequently, the display assembly 100 appears black.

When an electric field is applied to selected electrodes of the liquid crystal display unit 102, the liquid crystal is reoriented and changes the polarization of the light so that the circular polarization becomes linear polarization when reflected onto the lower reflective electrode 128 of the OLED display unit 104. The light reflected by the lower reflective electrode 128 is therefore not absorbed by the absorptive polarizer 134 on its return trip and enables the reflective mode of the display assembly 100.

Figures 4A to 4D schematically illustrate the operating modes of the display assembly 100 shown in Figure 3, depending on whether the liquid crystal display unit 102 or the OLED display unit 104 is in use. More specifically, in Figure 4A, both the liquid crystal display unit 102 and the OLED display unit 104 are turned off. Therefore, the liquid crystal display unit 102 is transparent and does not change the polarization of the ambient light 52. After being circularly polarized by the circular polarizer 132, the ambient light 52 passes through the liquid crystal display unit 102 and the OLED display unit 104 without being changed, and then reflects onto the lower reflective electrode 128. When reflected onto the lower reflective electrode 128, the rotation direction of the circular polarization of the light is reversed, so that when the light passes through the circular polarizer 132 again, it is absorbed. As a result, the display assembly 100 appears black.

In FIG4B , the liquid crystal display unit 102 is deactivated, while the OLED display unit 104 is activated. After being circularly polarized by the circular polarizer 132, ambient light 52 passes through the liquid crystal display unit 102 and the OLED display unit 104 without modification, and is then reflected by the lower reflective electrode 128. At this point, the direction of rotation of the circular polarization of the light is reversed, so that when the light passes through the circular polarizer 132 again, it is absorbed by the latter. Conversely, the light emitted by the OLED display unit 104 passes through the liquid crystal display unit 102 and the circular polarizer 132, making it perceptible to the observer 4. As a result, the information displayed by the OLED display unit 104 is displayed on a dark background.

In FIG4C , the liquid crystal display unit 102 is enabled, while the OLED display unit 104 is disabled. In the unswitched regions of the liquid crystal display unit 102, ambient light 52 is circularly polarized by the circular polarizer 132, then passes through the liquid crystal display unit 102 and the OLED display unit 104 without modification, and is then reflected by the lower reflective electrode 128. At this point, the direction of rotation of the circular polarization is reversed, so that when the light passes through the circular polarizer 132 again, it is absorbed by the latter. In the switched regions of the liquid crystal display unit 102, the liquid crystal molecules modify the circular polarization of the ambient light 52, so that when the ambient light 52 is reflected on the lower reflective electrode 128 of the OLED display unit 104, the circular polarization becomes linearly polarized. The light reflected by the lower reflective electrode 128 is therefore not absorbed by the absorptive polarizer 134 on its return trip, which enables the reflective mode of the display assembly 100.

In FIG4D , both the liquid crystal display unit 102 and the OLED display unit 104 are enabled. In the switched region of the liquid crystal display unit 102, ambient light 52 reflected by the lower reflective electrode 128 is not absorbed by the absorptive polarizer 134 and is visible to the viewer 4, allowing the liquid crystal display unit 102 to display information in the reflective mode. In addition, light emitted by the OLED display unit 104 passes through the liquid crystal display unit 102 and the circular polarizer 132, making it visible to the viewer 4.

It is important to note that other alignment modes of the liquid crystal molecules are also conceivable in order to produce the display component 100 according to the invention shown in FIG. 3 , such as twisted nematic or super twisted nematic modes.

5 is a cross-sectional view of a second embodiment of a display assembly according to the present invention. The display assembly, generally indicated by the general reference numeral 200, comprises a first reflective display device 202 located on the side of the observer 4 and a second emissive display device 204 arranged below the first reflective display device 202.

According to the present invention, the first reflective display device 202, which is reflective in a first switching state and transmissive in a second switching state, comprises an upper liquid crystal display unit 206. All liquid crystal phases are conceivable, such as twisted nematic, super twisted nematic or homeotropic alignment. Likewise, all addressing schemes are conceivable, such as direct addressing, active matrix addressing or passive matrix multiplexing addressing.

The upper liquid crystal display unit 206 includes a front substrate 208 positioned on the side facing the viewer 4, and a rear substrate 210 extending parallel to and away from the front substrate 208. Both the front substrate 208 and the rear substrate 210 are made of a transparent material such as glass or plastic. They are bonded to each other via a sealing frame 212, which defines a closed space for containing liquid crystals 214. The optical properties of the liquid crystals are altered by applying appropriate voltages to specific intersections between electrodes 216 disposed on the lower surface of the front substrate 208 and counter electrodes 218 disposed on the upper surface of the rear substrate 210. The electrodes 216 and counter electrodes 218 are made of transparent conductive materials such as indium tin oxide or indium zinc oxide.

The absorptive polarizer 220 is bonded to the upper surface of the front substrate 208 by means of a transparent adhesive layer 222. The transparent adhesive layer 222 can be formed by an adhesive film or a liquid adhesive layer. The absorptive polarizer 220 can be, for example, an iodine-based polarizer or a dye-based polarizer. The reflective polarizer 224 is bonded to the lower surface of the rear substrate 210 by means of an adhesive layer 226. The adhesive layer 226 can be transparent or slightly diffuse, depending on whether specular reflection or diffuse reflection is required. The reflective polarizer 224 can be a wire grid polarizer. It can also be a double brightness enhancement film (DBEF) or an APF type polarizer. These polarizers are all sold by American companies.

Furthermore, according to the present invention, the second emissive display device 204 includes a lower transmissive liquid crystal display unit 228 associated with the backlight device 230. The lower liquid crystal display unit 228 can be switched between a transmissive mode and an absorptive mode. All liquid crystal phases are conceivable, such as twisted nematic, super twisted nematic, or vertical alignment. Similarly, all types of addressing are conceivable, such as direct addressing, active or passive matrix addressing. The lower liquid crystal display unit 228 is optimized to allow the maximum amount of light from the backlight device 230 to pass through in the transmissive mode, while blocking as much light as possible in the absorptive state, thereby providing excellent contrast.

More specifically, the lower liquid crystal display unit 228 includes a front substrate 232 disposed on the side of the observer 4 and a rear substrate 234 extending parallel to and away from the front substrate 232. The two front substrates 232 and the rear substrate 234 are made of a transparent material such as glass or plastic. They are joined to each other by a sealing frame 236 that defines a closed space for accommodating the liquid crystal 238. Electrodes 240 are provided on the lower surface of the front substrate 232, and a counter electrode 242 is provided on the upper surface of the rear substrate 234. These electrodes 240 and the counter electrode 242 are made of a transparent conductive material such as indium tin oxide (ITO).

The absorbing polarizer 244 is bonded to the upper surface of the front substrate 232 by means of a transparent adhesive layer 246. The transparent adhesive layer 246 can be formed of an adhesive film or a liquid adhesive layer. The absorbing polarizer 248 is bonded to the lower surface of the rear substrate 234 by means of a transparent adhesive layer 250.

According to the present invention, the upper liquid crystal display unit 206 is disposed above the lower liquid crystal display unit 228. Preferably, the upper liquid crystal display unit 206 is bonded to the lower liquid crystal display unit 228 via a transparent adhesive layer 252. Thus, the problem of stray reflections between the two display units, which would reduce the optical quality of the display assembly 200, is avoided.

Finally, a backlight assembly 230 is positioned below the lower liquid crystal display unit 228. The backlight assembly 230 includes a light guide 254 into which light emitted by one or more light sources 256 is directed. The light guide 254 is positioned between a reflective film 260 positioned below the light guide 254 and a (brightness enhancement) film or a combination of films 258, such as a BEF (brightness enhancement film) type prismatic film and/or a diffuser film, or a DBEF (double brightness enhancement film) or an APF type reflective polarizer. Due to the reflective film 260 and the extraction structure provided in the upper surface of the light guide 254, the light emitted by the light sources 256 and directed into the light guide 254 is extracted upward from the light guide 254 and passes sequentially through the lower liquid crystal display unit 228 and the upper liquid crystal display unit 206.

According to one feature of the present invention, the transmission axis of the reflective polarizer 224 of the upper liquid crystal display unit 206 is parallel to the transmission axis of the absorptive polarizer 244 of the lower liquid crystal display unit 228. According to one variation, the absorptive polarizer 244 of the lower liquid crystal display unit 228 can be omitted, which allows for savings in terms of space and manufacturing costs. However, the use of the absorptive polarizer 244 has the advantage of ensuring improved display contrast in the emissive mode.

It goes without saying that the invention is not limited to the embodiments that have just been described and that a person skilled in the art may envisage various simple changes and variants without departing from the scope of the invention as defined by the appended claims.

Parts List:

1 Display Components

2. First reflective display device

4 Observers

6 Second Emission Display Device

8 LCD unit

10 Front base plate

12 rear substrate

14 Sealing frame

16 LCD

18 Transparent Electrode

20 Transparent counter electrode

22 Absorption polarizer

24 Adhesive layer

26 Reflective Polarizer

28 Adhesive layer

30 Transmitter Display Unit

32 substrate

34 Package cover

36 Sealing frame

38 Luminescent Layer

40 Upper transparent electrode

42 lower reflective electrode

44 transparent adhesive layer

46 Circular Polarizer

48 Absorption Polarizer

50 Quarter Wave Plate

51 adhesive layer

52 Ambient Light

100 display components

102 LCD unit

104 OLED display units

106 front base plate

108 rear substrate

110 Sealing Frame

112 LCD

114 transparent electrode

116 Transparent Counter Electrode

118 substrate

120 package cover

122 Sealing Frame

124 Luminescent Layer

126 Upper transparent electrode

128 lower reflective electrode

130 adhesive layer

132 Circular Polarizer

134 Absorption Polarizer

136 Quarter Wave Plate

138 adhesive layer

200 display components

202 first reflective display device

204 Second emission display device

206 Upper LCD unit

208 front base plate

210 rear substrate

212 Sealed Frame

214 LCD

216 electrodes

218 counter electrode

220 Absorption Polarizer

222 transparent adhesive layer

224 Reflective Polarizer

226 adhesive layer

228 lower LCD unit

230 Backlight

232 front base plate

234 rear substrate

236 Sealed Frame

238 LCD

240 electrodes

242 counter electrode

244 Absorption Polarizer

246 transparent adhesive layer

248 Absorption Polarizer

250 transparent adhesive layer

252 transparent adhesive layer

254 Light Guide

256 light sources

258 Brightness Enhancement Film

260 reflective film

Claims (5)

1. A display assembly for a portable object, the display assembly (1) comprising a first reflective display device (2) located on the side of an observer (4) and a second emitting display device (6) disposed below the first reflective display device (2), the first reflective display device being switchable between a transparent state when not in operation and a reflective state when in operation, and a circular polarizer (46) composed of an absorptive polarizer (48) and a quarter-wave plate (50). The first reflective display device (2) includes a liquid crystal display unit (8) configured to switch between a reflective state and a transparent state. The first reflective display device is a twisted nematic, super-twisted nematic, or vertically aligned liquid crystal display unit. The second emitting display device (6) includes an emitting organic light-emitting diode display unit (30) configured to switch between an enabled state and an inactive state. The emitting organic light-emitting diode display unit emits light in its enabled state and does not emit light in its inactive state. The liquid crystal display unit (8) is disposed between the upper absorptive polarizer (22) and the lower reflective polarizer (26), and the circular polarizer (46) is disposed between the lower reflective polarizer (26) and the emitting organic light-emitting diode display unit (30), thereby increasing the contrast between the liquid crystal display unit in the reflective state and the emitting organic light-emitting diode display unit in the non-working state, and increasing the contrast between the emitting organic light-emitting diode display unit in the enabled state and the emitting organic light-emitting diode display unit in the non-working state. 2. The display assembly according to claim 1, wherein the first reflective display device (2) is bonded to the second emitting display device (6) by means of an adhesive layer (44). 3. The display component according to claim 2, wherein the adhesive layer (44) is formed of an adhesive film or a liquid adhesive layer. 4. The display assembly according to any one of claims 1 to 3, characterized in that the lower reflective polarizer (26) and the absorptive polarizer (48) both have transmission axes, and these transmission axes are parallel to each other. 5. A display assembly for a portable object, the display assembly (100) comprising a first reflective display device (102) located on the side of an observer (4) and a second emitting display device (104) disposed below the first reflective display device (102), the first reflective display device being switchable between a transparent state when not in operation and a reflective state when in operation, and a circular polarizer (132) composed of an absorptive polarizer (134) and a quarter-wave plate (136). The first reflective display device (102) includes a liquid crystal display unit configured to switch between a reflective state and a transparent state. The first reflective display device is a twisted nematic, super-twisted nematic, or vertically aligned liquid crystal display unit. The second emitting display device (104) includes an emitting organic light-emitting diode (OLED) display unit configured to switch between an enabled state and an inactive state. The OLED display unit emits light in its enabled state and does not emit light in its inactive state. The circular polarizer (132) is disposed on the front surface of the liquid crystal display unit, thereby increasing the contrast between the liquid crystal display unit in the reflective state and the emitting organic light-emitting diode display unit in the non-operating state, and increasing the contrast between the emitting organic light-emitting diode display unit in the enabled state and the emitting organic light-emitting diode display unit in the non-operating state. The emitting organic light-emitting diode display unit (104) includes a lower reflective electrode (128).