Abstract:
The invention relates to a microdisplay system that utilizes a small high resolution active matrix liquid crystal display with an illumination system and a magnifying optical system to provide a hand held communication display device. The system can employ an LED illumination system and cellular communication or processor circuits within a compact housing to provide communication devices such as pagers, telephones, televisions, and hand held computer devices with a compact high resolution video display.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Flat-panel displays are being developed which utilize liquid crystals or electroluminescent materials to produce high quality images. These displays are expected to supplant cathode ray tube (CRT) technology and provide a more highly defined television picture or computer monitor image. The most promising route to large scale high quality liquid crystal displays (LCDs), for example, is the active-matrix approach in which thin-film transistors (TFTs) are co-located with LCD pixels. The primary advantage of the active matrix approach using TFTs is the elimination of cross-talk between pixels, and the excellent grey scale that can be attained with TFT-compatible LCDs.  
           [0002]    Flat panel displays employing LCDs generally include five different layers: a white light source, a first polarizing filter that is mounted on one side of a circuit panel on which the TFTs are arrayed to form pixels, a filter plate containing at least three primary colors arranged into pixels, and finally a second polarizing filter. A volume between the circuit panel and the filter plate is filled with a liquid crystal material. This material will allow transmission of light in the material when an electric field is applied across the material between the circuit panel and a ground affixed to the filter plate. Thus, when a particular pixel of the display is turned on by the TFTs, the liquid crystal material rotates polarized light being transmitted through the material so that the light will pass through the second polarizing filter.  
           [0003]    The primary approach to TFT formation over the large areas required for flat panel displays has involved the use of amorphous silicon, which has previously been developed for large-area photovoltaic devices. Although the TFT approach has proven to be feasible, the use of amorphous silicon compromises certain aspects of the panel performance. For example, amorphous silicon TFTs lack the frequency response needed for high performance displays due to the low electron mobility inherent in amorphous material. Thus the use of amorphous silicon limits display speed, and is also unsuitable for the fast logic needed to drive the display.  
           [0004]    As the display resolution increases, the required clock rate to drive the pixels also increases. In addition, the advent of colored displays places additional speed requirements on the display panel. To produce a sequential color display, the display panel is triple scanned, once for each primary color. For example, to produce color frames at 20 Hz, the active matrix must be driven at a frequency of 60 Hz. In brighter ambient light conditions, the active matrix may need to be driven at 180 Hz to produce a 60 Hz color image. At over 60 Hz, visible flicker is reduced.  
           [0005]    Owing to the limitations of amorphous silicon, other alternative materials include polycrystalline silicon, or laser recrystallized silicon. These materials are limited as they use silicon that is already on glass, which generally restricts further circuit processing to low temperatures.  
           [0006]    Integrated circuits for displays, such as, the above referred color sequential display, are becoming more and more complex. For example, the color sequential display is designed for displaying High Definition Television (HDTV) formats requiring a 1280-by-1024 pixel array with a pixel pitch, or the distance between lines connecting adjacent columns or rows of pixel electrodes, being in the range of 15-55 microns, and fabricated on a single five-inch wafer.  
         SUMMARY OF THE INVENTION  
         [0007]    In accordance with the invention, the cost and complexity of high resolution displays is significantly reduced by fabricating multiple integrated displays of reduced size on a single wafer and then dicing the wafer to produce a plurality of display devices.  
           [0008]    The displays are then assembled with appropriate magnifying optics to form a portable display system of low cost and reduced size. Included in the optics is a magnification system which compensates for the small image size by magnifying and projecting the image at an appropriate distance for viewing.  
           [0009]    In preferred embodiments, the microdisplay, because of its small size and weight, can be used as a hand-held communication system such as a pager, a wireless mobile telephone, or alternatively, as a head-mounted display. The display can provide a visual display suitable for data, graphics or video and accommodate standard television or high definition television signals. The system can optionally include circuitry for cellular reception and transmission of facsimile communications, can be-voice activated, can include a mouse operated function, provide internet access, and can have a keyboard or touch pad for numeric or alphabetic entry. The telephone or hand-held unit can be equiped with a camera or solid state imaging sensor so that images can be generated and transmitted to a remote location and/or viewed on the display. Also the telephone user can call to access a particular computer at a remote location, present the computer screen on the micro display, access specific files in the computer memory and download data from the file into a memory within the telephone or a modular memory and display unit connected to the telephone. The telephone can be connected to a local computer or display and the data from the file can be loaded into the local memory.  
           [0010]    In a preferred embodiment of the invention, a light emitting diode (LED) device is used to illuminate the display. For transmission displays the LED device operates as a backlight and can include a diffuser. An LED device can also be used as a light source for a reflective display in another preferred embodiment of the invention. The displays are preferably liquid crystal displays using a nematic liquid crystal material. Consequently, controlling the time domain is not necessary to obtain grey scale.  
           [0011]    For the purposes of this application, a microdisplay is defined as a display having at least 75,000 pixel electrodes and an active area of less than 158 mm 2 , where the active area of the display is the area of the active matrix circuit that generates an image, including all of the pixel electrodes but not including the driver electronics and the border area for bonding and sealing of the liquid crystal display. For example, the array can be at least 320×240, 640×480 or higher. A preferred embodiment of the microdisplay has an active area of 100 mm 2  or less, and is preferably in the range between 5 mm 2  and 80 mm 2 . The pixel pitch for these displays is in the range of 5-30 microns and preferably in the range between 5 and 18 microns. By utilizing pixel pitches of less than 18 microns smaller high resolution displays are now possible.  
           [0012]    For displays of this size and resolution to be read by a user at distances of less than 10 inches (25.4 cm) there are specific lighting and magnification requirements. For a 0.25 inch (6.35 mm) diagonal display, for example, the LED device preferably includes a plurality of LEDS coupled to a diffuser. The lens used to magnify the display image has a field of view in the range of 10-60 degrees, and preferably at least about 16 degrees-22 degrees, an ERD in the range of of about 25 mm-100 mm and an object distance of between about 1.5 and 5 feet (152.4 cm). A color field sequentially operated LED backlight system can use a plurality of LEDS with a two or four sided reflector assembly to concentrate the light through the-liquid crystal display. A preferred embodiment can use at least two LEDs, or as many as six or more of each color, to provide the desired brightness level. Alternatively the LEDs can be arranged around the periphery of a transmissive display and directed down into a conical reflector that directs the backlighting through the display in concentrated form.  
           [0013]    The display can be operated using a color sequential system as described in U.S. patent application Ser. No. 08/216,817, “Color Sequential Display Panels” filed on Mar. 23, 1994, the entire contents of which is incorporated herein by reference, discloses an active matrix display in which the control electronics is integrated with the active matrix circuitry using single crystal silicon technology. The control electronics provides compressed video information to produce a color image for data, a still image or a video image such as a television image on the display.  
           [0014]    The microdisplays described herein can be used in head mounted displays, including color sequential systems as described in greater detail in U.S. application Ser. No. 08/410,124 filed on Mar. 23, 1995, the entire contents of which is incorporated herein by reference. Further details regarding the drive electronics suitable for a microdisplay can be found in U.S. Ser. No. 08/106,416 filed on Aug. 13, 1993, the entire contents of which is incorporated herein by reference. A preferred embodiment of the display control circuit utilizes an “under scanning” feature in which selected pixels are rapidly turned on and off to enhance edge definition and emulate a higher resolution display. The display control circuit can also utilize a panning capability so that a small portion of a displayed image can be selected, by mouse operation for example, and presented using the entire microdisplay image area thereby allowing the user to perceive smaller displayed features. This can also be used to view selected portions of a high resolution image, such as a portion of a 640×480 image on a 320×240 microdisplay. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The above and other objects and features of the invention will be better understood and appreciated by those skilled in the art in view of the description of the preferred embodiments given below in conjunction with the accompanying drawings, in which:  
         [0016]    [0016]FIG. 1 is a perspective view of a single wafer having a plurality of display devices formed thereon in accordance with the invention.  
         [0017]    [0017]FIG. 2 is a schematic illustration of a die for an integrated active matrix panel display which includes optional control signal circuitry therein.  
         [0018]    [0018]FIGS. 3A and 3B are exploded views of a video display device and pager in accordance with a preferred embodiment of the invention.  
         [0019]    FIGS.  4 A- 4 I are exterior views of hand-held imaging devices in accordance with the invention.  
         [0020]    [0020]FIG. 5A is a side view of a lens suitable for magnifying a microdisplay in accordance with the invention.  
         [0021]    [0021]FIG. 5B is a side view of a multi element lens providing an increased field of view.  
         [0022]    [0022]FIG. 5C is a cross-sectional view of a display assembly with a fixed lens.  
         [0023]    [0023]FIG. 5D is a schematic view of an LED backlighting system for a liquid crystal display in accordance with the invention.  
         [0024]    [0024]FIG. 6 is an optical diagram of a lighting system for a reflective liquid crystal display.  
         [0025]    FIGS.  7 A- 7 C illustrates preferred LED backlighting systems for a transmission type display.  
         [0026]    [0026]FIG. 8 is a perspective view of a preferred embodiment mobile telephone having a display device in accordance with the invention.  
         [0027]    FIGS.  9 A- 9 J are illustrations of further preferred embodiments of a telephone microdisplay system in accordance with the invention.  
         [0028]    FIGS.  10 A- 10 C are side cross-sectional, front, and front cross-sectional views of a hand held rear projection display system in accordance with the invention.  
         [0029]    FIGS.  11 A- 11 B illustrate a body worn, hand operated display system in accordance with the invention.  
         [0030]    [0030]FIG. 12A is a perspective view of a head-mounted display system of the invention.  
         [0031]    [0031]FIG. 12B is a partial schematic perspective view of the system of FIG. 12A emphasizing additional features of the invention.  
         [0032]    [0032]FIG. 12C is a schematic perspective of the system of FIG. 12A which emphasizes certain aspects of the invention.  
         [0033]    [0033]FIG. 12D is a schematic perspective view of the headband and pads of FIG. 12C.  
         [0034]    [0034]FIG. 12E is a partial schematic side view of the system of FIG. 12A.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]    High Resolution Active Matrix MicroDisplay  
         [0036]    A preferred embodiment of the invention utilizes a process of making a plurality of flat panel displays  10  in which a large number of active matrix arrays  14  are fabricated on a single wafer  12  as illustrated in connection with FIG. 1. The number of displays fabricated on a single wafer depends upon the size of the wafer and the size of each display. A preferred embodiment of the invention, for example, uses a high resolution display having an imaging area of the display with a diagonal of 0.5 inches (12.7 mm) or less. For a four inch wafer, forty separate displays can be fabricated on a single four inch wafer. Where each display has a diagonal of about 0.25 inches (6.35 mm), 80 displays can be fabricated on a single wafer, over 120 displays can be fabricated on a five inch wafer, and 400 displays can be fabricated on an 8 inch wafer.  
         [0037]    By fabricating a large number of small high resolution displays on a single wafer the manufacturing yield can be substantially increased and the cost per display can be substantially reduced.  
         [0038]    To obtain monochrome resolutions of at least 75,000 pixels (e.g. a 320×240 array) suitable for displaying an NTSC television signal on a 0.25 inch diagonal display the pixel electrodes are preferably on the order of about 15 microns in width or less. To obtain a monochrome resolution of at least 300,000 pixels (e.g. 640×480 array) on a 0.25 inch diagonal display the pixel electrodes preferably have a width of about 8-10 microns.  
         [0039]    These small high resolution displays require magnification such that when held in a user&#39;s hand within the range of 0.5 inches to 10 inches of the user&#39;s eye, a clear image is provided.  
         [0040]    Referring now to FIG. 2, an integrated circuit active matrix display die is shown schematically which has been diced from a single wafer along with selected number of replicated circuits. Incorporated into the circuit  100  are scanner circuits  42   a ,  42   b ,  42   c ,  42   d , along with pixie driven circuits  44   a ,  44   b ,  44   c ,  44   d , select scanner circuits  46   a ,  46   b  and a display matrix circuit  90 .  
         [0041]    Further details regarding the fabrication of each die on a wafer can use the methods described in U.S. Pat. No. 5,256,562, the contents of which incorporated herein its entirety by reference.  
         [0042]    By fabricating a selected number of circuits  100  on a single wafer, the circuit yield from a single wafer is greatly enhanced at the expense of reduced display area. However, this area disadvantage is overcome by magnifying and projecting the display image as will be described herein.  
         [0043]    A video signal bus  35 - 1  through  35 - 16  carries analog video signals from digital to analog amplifiers (not shown) to column drivers  44   a - d . Because signal interference and signal loss can occur as the analog video signal cross each signal line in the signal bus  35 , the channels of video signals are arranged to reduce interference. As illustrated, there are four column drivers  44   a - 44   d , two column drivers  44   a , 44   b  at the top of the active matrix circuit  90  and two column drivers  44   c , 44   d  at the bottom of the active matrix circuit region  90 . Each channel is allocated to one of the column drivers  44  such that each column driver  44  receives video from four channels. The top column drivers  44   a , 44   b  receive video from the channels that drive the odd-numbered pixel columns and the bottom column drivers  44   c , 44   d  receive video from the channels that drive the even-numbered columns. As shown, no video signal has to cross the path of more than one other video signal.  
         [0044]    The illustrated arrangement of column drivers is particularly suited for edge-to-center and center-to-edge video writing, although the data can also be written from left-to-right or right-to-left. It should be understood that more or less than four column drivers  44  can be employed in preferred embodiments of the invention. For applications having resolutions of 320×240 or 640×480 it is desirable to use single column and row drivers to drive the display. For high speed, high definition displays more can be used to improve performance.  
         [0045]    The data scanners  42   a - d  are responsive to a pixel data signal  142  and a pixel clock signal  143  from a control signal generator (not shown). The data scanners  42   a - d  can use a shift register array to store data for each scan. An odd shift register array can be used to store data to odd column pixels and an even shift register array can be used to store data to even column pixels. As illustrated, there are left and right odd data scanners  42   a , 42   b  and left and right even data scanners  42   c , 42   d.    
         [0046]    The column drivers  44  selected by the data scanner  42  transmit video data to a selected column of C pixels in the active matrix circuit  90 . The select scanner  46  controlled by a control signal generator determines by control lines which pixels accept this column data.  
         [0047]    To reduce signal loss across the active matrix region  90 , the select lines are driven from both sides by select scanners  46   a  and  b . As viewed in FIG. 2, a left select scanner  46   a  and right select scanner  46   b  are connected to the select data line  146  and the select clock line  147 . A third enabling line  148  can also be used for specific applications. The left select scanner  46   a  provides a select line signal at the end of the select line nearest the lowest-valued pixel column (C 1 ) and right select scanner  46   b  provides a select line signal at the end of the select line nearest the highest-valued pixel column (C N ) Thus, an identical select line signal is supplied at both ends of the select line.  
         [0048]    Although static shift registers can be used, the shift registers of the data scanner  42  and the select scanners  46  are preferably implemented as dynamic shift registers. The dynamic shift registers rely on capacitor storage without leakage. However, dynamic shift registers are susceptible to leakage, especially when they are exposed to light. Hence, light shields are needed to protect the scanners  42 , 46  from exposure to light. Similarly, light shields are also used to protect the transmission gates  44  and pixel columns C 1 -C N .  
         [0049]    For further information regarding the input signals to the circuit  100 , reference is made to the above-cited U.S. patents and applications.  
         [0050]    In a preferred embodiment of the invention, the panel drive circuitry of FIG. 2 is fabricated as an integrated circuit along with the active matrix circuit  90 . The integrated circuitry is preferably fabricated in single crystal silicon having a silicon-on-insulator (SOI) structure using the fabrication and transfer procedures described previously in the aforementioned U.S. Pat. No. 5,256,562. By fabricating the row and column drive circuitry  42 , 44 , 46  as well as the scanners in single crystal with the active matrix circuit  90 , the size of the display panel is not constrained by the connecting pins for the various discrete components. The integrated fabrication also increases the operating speed of the display relative to displays constructed from discrete components. Furthermore, the drive circuitry can be optimized to increase display performance. For example, it is easier to construct a small 1280 H×1024V display panel with dual select scanners through integrated fabrication than it is using discrete components.  
         [0051]    The pixel electrodes in a preferred embodiment are between 60 and 250 microns square. Consequently, a 1280 H×1024V active matrix with the control system can be fabricated such that there are at least 40 such integrated circuits on a five inch wafer, for example, A preferred embodiment in the form of a stand-alone video display device  20  featuring a liquid crystal display incorporating the actual matrix display circuit  100  will now be described in connection with the exploded views of FIGS. 3A and 3B.  
         [0052]    In FIG. 3A, a portable imaging device such as a paper is illustrated having a housing including a top  40  and a bottom  44  with a door  50  for access to a battery  48 . The battery  48  provides power to the circuit board  42 , the display  24  and the backlight  22 . The pager can be operated by controls  38  or push buttons accessible through one of the housing surfaces that actuate display functions. An optical system  20  is positioned within the housing and includes a backlight  22 , preferably an LED backlight, a transmission liquid crystal display  24 , a focusing mechanism including a knob  28  that the user rotates to move the tunnel  30  relative to the optic slide  26 , a lens assembly  32 , and a cover glass  34 .  
         [0053]    Preferred embodiment of hand held display devices are illustrated in connection with FIGS.  4 A- 4 I. FIG. 4A is a perspective view of a preferred embodiment of a pager system  150  having two display viewing areas  152  and  154  within a housing  155 . Viewing area  152  has a lens through which the user views a microdisplay as described previously. A second flat panel display without magnification is viewed by the user at  154 . The second display is a simple low resolution numeric and/or alphabetic display to read telephone numbers or scrolled numbers or messages. The microdisplay magnification can be adjusted at switch  158 . The displays are operated by switches  156 ,  157 . As seen in the rear view of FIG. 4B, the rear surface  162  of housing  155  is thicker in that portion containing the microdisplay and the battery. The sideview of the housing  155  shown in FIG. 4C illustrates a clip  160  that is used to fasten the device to the clothing of the user. The clip  160  is attached to the bottom surface  164  of the housing  155 .  
         [0054]    Another preferred embodiment of a hand-held viewing device  170  is illustrated in the perspective view of FIG. 4E. A first display is seen through lens  172  with magnification being adjusted by knob  174 . A second display  180  as described above is positioned on the same side of the device  170  as the lens  172  for ease of viewing. The displays are operated by switch  176  and buttons or control elements  178 . A top view is illustrated in FIG. 4F showing ridges  184  that accommodate the fingers of the user and the second display switch  182 , which is shown more clearly in the side view of FIG. 46.  
         [0055]    Rear and bottom views of device  170  show rear  188  and bottom  186  sides in FIGS. 4H and 4I, respectively.  
         [0056]    A lens  65  suitable for magnifying the image of a microdisplay for viewing by a user is illustrated in the example of FIG. 5A.  
         [0057]    For a 0.25 inch diagonal microdisplay, the outer diameter  64  of the lens can be about 30.4 mm, the thickness  70  of the lens at the optical axis  67  can be about 8 mm, the inner surface  60  that receives light from the display has a curved diameter of about 21.6 mm, and the viewing surface  61  has a diameter of  68  of about 22.4. The peripheral edge  69  used to hold the lens in the assembly can have a thickness  66  of about 2 mm and a radius  71  of about 4 mm. The lens  65  can be made of glass or a plastic material such as acrylic. This particular example of such a lens has a 16 degree field of view and an ERD of 25. The lens assembly can include an automatic focusing system, or a lens system that collapses in size when not in use.  
         [0058]    Another preferred embodiment for providing a color display can use a diffraction optical system such as those described in application U.S. Ser. No. 08/565,058 filed on Nov. 30, 1995, the entire contents of which is incorporated herein by reference.  
         [0059]    Another preferred embodiment of a 1.25 inch diameter lens system  52  with a larger field of view is illustrated in FIG. 5B. Three lens elements  51 ,  53  and  55  enlarge the image on the display  54 .  
         [0060]    The lens  65  of FIG. 5A can be used in the alternative display assembly of  80  of FIG. 5C. In this embodiment, the display  82  is positioned between the backlight housing  84 , containing LED  86 , and the lens housing  88  that holds the lens  65  in a fixed position relative to the display  82 .  
         [0061]    A microdisplay system  300  utilizing a folded optical path is illustrated in connection with FIG. 5D. In this embodiment, an LED array  302 , or other light source, illuminates the display within housing  304 . The display  306  directs an image along a first optical path  312  that is reflected by mirror  308  along a second other path  314  through the lens  310  as described previously.  
         [0062]    Lighting System for Reflective Liquid Crystal Display  
         [0063]    The details of a lighting system  102  for a reflective micro, display of the invention will now be described in connection with FIG. 6. Illumination for a reflective LCD system  500  based upon the active matrix circuit described heretofore in connection with FIG. 2 is provided by an array of Light Emitting Diodes (LED(s))  501  disposed adjacent light-diffuser  505  which uniformly transmits the source LED light to a linear polarizer  502 .  
         [0064]    The linear polarized light  516  from polarizer  502  is passed to a polarizing beamsplitter or prism  508  which is reflected by beam splitter  508  and is incident on specularly reflective LCD  506  to provide the requisite illumination. The light incident on LCD  506  is selectively reflected to generate an image that is rotated by ¼ wave plate  504  so that it is transmitted through splitter  508  and through lens  510  to the observer  512 .  
         [0065]    Shown in FIGS.  7 A- 7 C are preferred embodiments of an LED backlighting system utilizing a diffuser for a transmission display in accordance with the invention. In a first embodiment of an LED illumination system  400  shown in FIG. 7A, blue (B) 402 , green (G) 404 , and red (R) 406  LEDs are optically coupled to a flat diffuser element  408  around the periphery of an illumination area of  410  that is positioned adjacent the display active or viewing area. For a display having a diagonal of 6.35 mm, the side of  412  of the viewing area  410  can be about 3.81 mm in size, and the length  414  of the viewing area can be about 5.08 mm. The diffuser  408  can be a plastic material such as acrylic and the back of the diffuser can be coated with a reflective material to improve light output of the device.  
         [0066]    In another embodiment of an LED display illumination system  420  as shown in FIG. 7B, the LED&#39;s  422  are coupled in pattern to the edge of the diffuser  408 . The LEDs  422  are actuated in sequence  407  to provide color sequential operation with fewer LEDs.  
         [0067]    In the system  430  of FIG. 7C, the display  432  is coupled to an angled diffuser  436  at interface  440 . The linear array of LEDs  434  are coupled at one end of the diffuser and a reflective back surface is designed to evenly distribute light as it is directed through the interface.  
         [0068]    Illustrated in connection with FIG. 8 is a cellular telephone  200  having a magnified microdisplay in accordance with the invention. The display can be included in a base portion  210  of a “flip-phone” along with keypad  218  and microphone  220 . The speaker  206 , or the display or a second display as well as additional circuitry can be included in second portion  208  that rotates relative to the base  210 . An antenna  204  can telescope out of the base for improved wireless reception. A battery is housed at  212 . A lens  202  can be viewed by the user while holding the speaker to his or her ear thus enabling both viewing and voice transmission at the same time. The display can be turned on or off at switch  216  to save battery life when the display is not in use. The magnification can be adjusted at knob  214 .  
         [0069]    Additionally, a small camera  215  such as a charge coupled device (CCD) or other solid state imaging sensor can be mounted on a telescoping element to provide an imaging or video-conferencing capability. The camera can be pivoted so that the user can point and hold the camera in any selected direction. The image generated can be seen on the display and/or transmitted to a remote location, selected buttons or touch pad keys  218  can be used as a mouse control for the display.  
         [0070]    Alternatively, the display can be formed in a modular component that snaps onto the base portion of a standard telephone and couples to a display circuit port in the base section of the telephone. This is illustrated in-the preferred embodiments of FIGS.  9 A- 9 J.  
         [0071]    [0071]FIG. 9A shows a telephone  250  having standard features such as a display  252  and a port  254  for external communications. The modular display unit  260  shown in FIG. 9B is configured to dock with the telephone  250  wherein the connector  268  is inserted into port  254  and latch  264  connects to the top of the base section of telephone  250  thereby connecting the micro display within display subhousing  262  to the receiver within the telephone  250 . The subhousing  262  pivots relative to main housing  270  to allow viewing of the display through lens  267  during use of the telephone  250 . In this embodiment, telescoping camera  215  can extend from subhousing  262 . Base  270  includes a second battery, drive electronics for the LED backlit LCD display on activation switch  266 . FIG. 9C is a sideview of telephone  250  showing the battery housing  250  on the opposite side from the speaker  206 . Back panel  258  is shown in the rear view of FIG. 9D along with second battery contacts  256  exposed thereon. When the telephone  250  is docked in unit  260 , the surface  258  abuts surface  265  and connectors  264  are positioned against contacts  256  such that the telephone can be powered by the second battery in housing  270 .  
         [0072]    [0072]FIGS. 9E, 9F and  9 G illustrate top front and side views of unit  260  where the subhousing is shown in both its storage position  274  and its viewing position  272 . FIGS. 9H and 9I show back and second side views of unit  260  and illustrate battery access panel  275 , focus know  276  and control buttons  278  that are exposed on the side of housing  270  when the sub-housing  262  is rotated to the viewing position  272 .  
         [0073]    In the embodiment  280  shown in FIG. 9J the telephone  284  is shown docked with housing  286 . However in this embodiment, the display is mounted withing a pivoting unit  282 . The user can swing unit  282  along arc  292  to expose viewing lens  288 . The user can also swing the display around a second orthogonal axis  294  at joint  298  so that the display rotates into a variety of viewing positions relative to hinge section  290 .  
         [0074]    [0074]FIGS. 10A, 10B and  10 C show side cross-sectional, front and front cross-sectional views of a hand-held rear projection system  320  using a microdisplay. The system  320  includes a microdisplay and backlight assembly  330 , a projection lens system  326 , a reflective screen  328  and optional retractable sun screens  324 . The device has a thickness  322  of less than 2 inches, preferably about 1 inch, a height  336  of less than 8 inches, preferably about 5-6 inches and a display diagnoal  334  of 4 inches or less, preferably about 3 inches. This provides a system volume that is preferably less than about 40 inches. The rear reflective screen  328  is shown in the front view of FIG. 10C at  338  and are surrounded on 3 sides by retractable shades  332  ( 324 ). The handle portion can include speakers  338  and an earphone jack  325 .  
         [0075]    A body worn hand-held display system is shown in FIGS. 11A and 11B. The hand-held unit  350  includes a microdisplay viewed through port  352  that is controlled by control element  356  and connected by cable  354  to a body worn communications pod  340 .  
         [0076]    Head Mounted Display System  
         [0077]    In yet another embodiment of the invention shown in FIG. 12A, the HDTV color active matrix display, as described in connection with FIG. 2, is provided with suitable optics and incorporated into a housing  860  and pivotally attached to a headband frame  861  to provide a novel head mounted display system  864 . In general, the system  864  is comprised of a unique headband frame  861  and adjustable strap  862  for attaching the system to the user&#39;s head, a side-mounted speaker system  866  connected-by cable  868  to electronics console  870  attached to the front of the frame  862 , a microphone  872  rotatably suspended from speaker frame  874 , and the aforementioned display housing  860  dependent from console  870  and electronically connected thereto by cable  876 .  
         [0078]    Not shown in FIG. 12A is a headband system comprised of two or more pads  180 A,  180 B, as shown in FIGS.  12 B- 12 E.  
         [0079]    To allow for the broadest range of head sizes, the headband frame  861  utilizes two contoured foam pads  880 A and  880 B, angled, and spaced apart such that both small and large forehead curvature are accommodated. Each foam pad also has two primary contact areas  881  and  883 , that act in the same way. When combined with a strap  862  placed below the ball formed at the rear of the head, the net effect is that the headband frame  861  is securely located on the wearer&#39;s forehead  887  whether child or adult.  
         [0080]    When the electronics are used, there is some heat being generated in the main housing or console  870 . Prior art headbands used wide forehead pads which effectively trapped this heat at the wearer&#39;s brow. This proved to be quite uncomfortable after extended wear.  
         [0081]    The foam pads  880 A and  880 B displace the headband frame  861  from the user&#39;s forehead  887  leaving a gap therebetween which serves as a warm air vent  875  to dissipate warm air generated by the electronics in console  870 .  
         [0082]    This new embodiment provides a “chimney-like effect” that effectively vents the warm air away from the wearer&#39;s face. The foam pads are removably attached, as by Velcro® type fasteners, and covered with terrycloth  861  for improved comfort. Optional additional vents  871  are provided in the console  870 .  
         [0083]    Equivalents  
         [0084]    While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.