Flat panel monitor combining direct view with overhead projection capability

A back-lit flat panel display subsystem for direct viewing as a monitor and having overhead projection capability. The display subsystem contains a removable door assembly which provides for back-lighting when configured for direct viewing. When the door assembly is removed, the active matrix LCD is semi-transparent and can be placed over (viewing surface down) the imaging screen of an overhead projector such that the LCD color image can be thus projected. The lamps that provide the back-lighting remain within the display subsystem when the door is removed so as to not disturb the power supply lines to the lamps and a unique optical junction is provided between the lamps and a light pipe within the door. The display subsystem contains a sensor detecting door presence and simultaneously shuts off the lamps and reverses the display image (to right to left) upon door removal and turns on the lamps upon door insertion and displays the image from left to right. Within the display, a conductive (grounded) anti-reflective coating is used on the flat panel display to reduce electronic emissions. The system is also portable and can operate as a stand alone peripheral or integrated within a computer system board.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the field of information display 
technology for electronic devices. Specifically, the present invention 
relates to a display component capable of use within a computer system. 
2. Prior Art 
Flat panel displays or liquid crystal displays (LCDs) are popular display 
devices for conveying information generated by a computer system. The 
decreased weight and size of a flat panel display greatly increases its 
versatility over a cathode ray tube (CRT) display. High quality flat panel 
displays are typically back-lit. That is, a source of illumination is 
placed behind the LCD layers so that visualization of the resultant image 
is made much easier. However, providing a back-lit screen generally makes 
the display screen non-transparent. It is desired, then, to provide a LCD 
screen having the high quality image generation characteristics of a 
back-lit LCD, yet offering a transparent LCD screen. The present invention 
provides such advantageous capability. 
During meetings and lectures, overhead projection units or "projectors" are 
often used to project transparent slides, foils or "overheads" onto a 
screen or wall. The projection and resultant enlargement of these images 
onto the screen allows image presentation to a large audience. With the 
introduction of computer systems that offer a wide range of software, 
including graphics packages and slide presentation capabilities, it would 
be advantageous to allow the graphic image output of a computer system to 
be projected and enlarged onto a screen for audience presentation. The 
present invention offers such advantageous capability. 
Further, some back-lit LCD screens utilize light extraction patterns. These 
screens have lamps along the edges of a light pipe and depend on an 
extraction pattern to distribute the light intensity. The light extraction 
patterns of the prior art are uni-directional in that the dots vary in 
size only in one direction, depending on their distance from the lamp in 
that dimension only. As a result, in prior art back-lit displays that 
utilize light extraction patterns, edges and corners are often darker and 
the overall image is not uniformly bright. This condition requires that 
lights longer than the active area be used to account for the 
nonuniformity. It would be advantageous to provide acceptable uniform 
illumination of the LCD screen using lights of lower intensity (and 
shorter length) for power conservation. The present invention provides 
such advantageous functionality. 
Accordingly, it is an object of the present invention to improve the 
versatility of a flat panel display screen. It is an object of the present 
invention to provide an improved flat panel display screen that can be 
used with an overhead projector. It is also an object of the present 
invention to provide a direct view flat panel display screen that is 
back-lit that can also be used with an overhead projector to project and 
enlarge a resultant display image. It is yet an other object of the 
present invention to provide such capability in a portable computer system 
or a display subsystem wherein the back-lighting components of the display 
subsystem are removable, thus exposing a transparent LCD screen for use in 
combination with the overhead projector. It is yet another object of the 
present invention to provide a removable door assembly as discussed above 
wherein the illumination sources remain within the display subsystem unit 
when the door assembly is removed. These, and other objects of the present 
invention not specifically mentioned above, will become clearer within 
discussions of the present invention herein. 
SUMMARY OF THE INVENTION 
A back-lit flat panel display subsystem is described for direct viewing as 
a monitor and having overhead projection capability. The display subsystem 
contains a removable door assembly which provides for back-lighting when 
configured for direct viewing. When the door assembly is removed, the 
active matrix LCD is semi-transparent and can be placed over (viewing 
surface down) the imaging screen of an overhead projector such that the 
LCD color image can be thus projected. The lamps that provide the 
back-lighting remain within the display subsystem when the door is removed 
so as to not disturb the power supply lines to the lamps and a unique 
optical junction is provided between the lamps and a light pipe within the 
door. The display subsystem contains a sensor detecting door presence and 
simultaneously shuts off the lamps and reverses the display image (to 
right to left) upon door removal and turns on the lamps upon door 
insertion and displays the image from left to right. Within the display, a 
conductive (grounded) anti-reflective coating is used on the flat panel 
display to reduce electronic emissions. The system is also portable and 
can operate as a stand alone peripheral or integrated within a computer 
system board. 
Specifically, embodiments of the present invention include a display 
subsystem for displaying video information, the display subsystem 
including: (a) a display assembly for rendering the video information, the 
display assembly comprising: (i) a flat panel display matrix having a 
first surface for viewing during direct monitoring and an opposite surface 
for viewing during overhead projection monitoring; (ii) a light source 
positioned adjacent to the flat panel display matrix for providing 
back-light for the flat panel display matrix; (iii) a sensor for detecting 
when a removable door is inserted into or removed from the display 
assembly and for generating a control signal indicative thereof; (b) the 
removable door assembly adapted for insertion into and removal from the 
display assembly and comprising a light pipe for optically coupling with 
the light source for uniformly illuminating the flat panel display matrix 
with the back-light; and (c) a control circuit responsive to the sensor 
for turning the light source on and providing the video information to the 
flat panel display matrix in a first direction when the control signal is 
at a first state and for turning the light source off and providing the 
video information to the flat panel display matrix in a second direction 
when the control signal is at a second state wherein the flat panel 
display matrix generates an image from left to right, for the direct 
monitoring, when the video information is provided thereto in the first 
direction and wherein the flat panel display matrix generates an image 
from right to left, for the overhead projection monitoring, when the video 
information is provided thereto in the second direction. The present 
invention also includes a method for same. 
The present invention also includes a multi-layer flat panel display screen 
comprising: (a) a rear polarizer for polarizing incident light; (b) a back 
glass structure disposed adjacent to the rear polarizer; (c) a thin film 
matrix for selectively polarizing light emitted through the rear 
polarizer, the thin film matrix comprising: (i) a transistor layer having 
a two-dimensional matrix of individually addressable transistors; (ii) a 
color filter layer; and (iii) a liquid crystal layer disposed between the 
transistor layer and the color filter layer; (d) a front glass structure 
disposed adjacent to the thin film matrix; (e) a front polarizer for 
polarizing light emitted through the thin film matrix; and (f) an 
anti-reflective and conductive layer for increasing light intensity and 
for reducing electromagnetic emissions, the anti-reflective and conductive 
layer composed of alternating layers of a dielectric layer and a 
transparent conductive layer, wherein the transparent conductive layers 
are grounded wherein the anti-reflective and conductive layer is disposed 
on the front polarizer. 
Embodiments of the present invention also include an optical junction 
formed between a permanently housed light source within a display assembly 
and a removable light pipe when inserted into the display assembly. The 
optical junction is formed from a reflective film attached along the long 
axis of the light source and extends past a side of the light source to 
cover a gap between the light source and the light pipe. Another 
reflective strip is placed along and extends past an edge of the light 
pipe to bridge the gap. The reflective material is used to reflect stray 
light into the light pipe. 
Embodiments of the present invention also include a display subsystem for 
displaying video information, the display subsystem comprising: (a) a 
display assembly comprising: (i) a flat panel display matrix having a 
first surface for viewing during direct monitoring and an opposite surface 
for viewing during overhead projection monitoring; (ii) a light source 
positioned adjacent to the flat panel display matrix for providing 
back-light for the flat panel display matrix; (iii) a sensor for detecting 
when a removable door is inserted into or removed from the display 
assembly and for generating a control signal indicative thereof; (b) the 
removable door assembly adapted for insertion into and removal from the 
display assembly and comprising a light pipe for optically coupling with 
the light source for illuminating the flat panel display matrix with the 
back-light and wherein the light source remains secured within the display 
assembly upon removal of the removable door assembly so that a power 
supply line to the light source is not disturbed upon removal of the 
removable door assembly and further comprising a control circuit 
responsive to the sensor for turning the light source on when the control 
signal is at a first state and for turning the light source off when the 
control signal is at a second state.

DETAILED DESCRIPTION OF THE INVENTION 
In the following detailed description of the present invention numerous 
specific details are set forth in order to provide a thorough 
understanding of the present invention. However, it will be obvious to one 
skilled in the art that the present invention may be practiced without 
these specific details. In other instances well-known methods, procedures, 
components, and circuits have not been described in detail as not to 
unnecessarily obscure the present invention. 
The present invention includes embodiments directed at an improved flat 
panel display subsystem that can be adapted for integration with or within 
a computer system. The high resolution color flat panel display has a 
back-lighting door assembly ("back-lighting assembly") for direct viewing. 
This door assembly can be removed to expose the transparent active LCD 
display screen. Once removed, the transparent active LCD display screen 
can be positioned on top of an overhead projector in order to project the 
displayed image in an enlarged fashion onto a receiving screen. 
With reference to FIG. 1A, a perspective view of the display subsystem of 
the present invention is illustrated with the display side facing outward. 
This is the direct viewing configuration. Direction arrow 20' indicates 
the viewing direction. Light enters along "A" for projection viewing and 
along "B" for direct viewing. The display subsystem comprises three major 
assemblies. The base assembly 12 which is coupled to a display assembly 10 
via a hinge in order to allow the display assembly 10 to adjust to 
different angles for direct monitoring or allows the display assembly to 
lay flat for overhead projection configurations and for storage and 
transportation (as will be shown in FIG. 1C). The base assembly 12 
supports the display 10 for direct viewing configurations and also 
contains several electronic circuit systems for providing the display unit 
with power, audio information, and video information. 
The display assembly 10 contains two stereo speakers 8a and 8b as well as 
an active matrix LCD color screen 20. Although many different resolutions 
can be utilized within the scope of the present invention, an embodiment 
of the present invention utilizes an LCD screen 20 having 1024 pixels by 
768 pixels by RGB color and utilizes amorphous silicon thin film 
transistors (TFT). The LCD screen 20 is composed of color TFT-LCD panel, 
driver ICs, control circuitry, and power supply circuitry all contained in 
a rigid bezel. LCD screen 20 is capable of displaying 4096 true colors 
without frame rate modulation in text or graphics mode. An exemplary LCD 
screen 20 can be obtained by Mitsubishi Electronics as part number 
AA12XA4D-NDES, however, various flat panel LCD screens and screen 
technologies can be used within the scope of the present invention with 
proper configuration. 
As shown in FIG. 1A, the display assembly 10 is back-lit via a separate 
assembly or removable door assembly 14. In this view the door is partially 
removed from the display assembly 10. The door assembly 14 is removed so 
that the display 20 can become transparent for overhead projection 
configurations. While inserted, the door assembly 14 provides 
back-lighting for the LCD screen 20 for direct viewing configurations. 
Although a number of lamps can be utilized, one embodiment utilizes four 
cold cathode fluorescent (CCF) tubes which are located within the display 
assembly 10 to illuminate along the top and bottom edges of a light pipe 
located within the door assembly 14 (as will be discussed further below) 
when the door assembly 14 is inserted within the display assembly 10. It 
is appreciated that the high voltage CCF tubes are not removed from the 
display assembly 10 when the door assembly 14 is removed as to not break 
the high voltage connection that supplies power to the CCF tubes. Also 
shown is a snap fit clip 34 which is used to secure the door assembly 14 
to the display assembly 10. 
FIG. 1B illustrates the back side of the display subsystem (e.g., along 
"B") with the door assembly 14 completely removed to expose inner 
components of the display assembly 10. In this view, with the door 
assembly 14 removed, the back side of the LCD screen 20 is exposed. 
Located on the base assembly 12 are inputs for AC power 44 and an 
audio/video input connector 48. Power supplied to the subsystem, backlight 
brightness and audio volume are controlled by the computer system's 
software through the audio/video input connector 48. In an alternative 
embodiment, in addition to computer control these features can be manually 
adjusted. For instance, also located on the display subsystem can be 
(optionally) a power on switch 2a, a brightness adjustment knob 2b and a 
volume adjustment knob 3c for the stereo speakers 8a and 8b. The 
audio/video input connector 48 is coupled to the digital audio/video 
output of a computer system. Under one embodiment of the present 
invention, the computer system is capable of transmitting (UNIX) 
compatible digital audio/video output signals. 
Located within the display assembly 10 are two lamp assemblies or housings. 
One lamp housing 40 is shown. Each lamp housing contains a pair of CCF 
lamps 52. There is a pair, as shown, on the bottom of the display assembly 
in lamp housing 40 and also a pair (obscured) of lamps on the top edge. 
Each pair of CCF lamps is mounted within its respective lamp housing using 
two rubber shock mounts, as shown, 50a and 50b to secure lamps 52. An 
identical configuration is employed for the top lamp housing (obscured). A 
reflective film 42 is applied to the inner portions of the lamp housings 
and this tape extends outside, beyond the positions of the lamps 52, for 
providing an optical coupling with components of the door assembly 14 when 
inserted. The same is true for the upper lamp housing. 
Also shown in FIG. 1B are two receiving holes 32 located on the right and 
left sides of the display assembly 10. These receiving holes 32 fasten to 
corresponding latches (34 not shown) located on the door assembly 14. 
There is also a recess associated with these latch holes 32 for removal of 
the door assembly 14. Also located within this region of the display 
assembly 10 is a magnetic reed switch 22 that is responsive to the 
presence of a magnet 140 (not shown) that is located along the mating edge 
of the door assembly 14. Using this switch 22, the display subsystem 
determines whether or not the door assembly 14 is inserted or removed from 
the display assembly 10 and responds accordingly. 
It is appreciated that the reed switch 22 and sensor, in lieu of being 
magnetically operated, can also be implemented using and optical sensor 
(or switch, such as using a LED or fiber-optic device) or a mechanical 
sensor (or switch, such as a toggle or spring switch). 
There are also two notches 95a and 95b located on the top of the display 
assembly 10. These notches 95a and 95b are for mating with corresponding 
latches located on an overhead projector of the present invention for 
securing the display subsystem properly over an illuminating screen of the 
projector. When used in a projector configuration, the display subsystem 
is extended so that the base assembly 12 and the display assembly 10 are 
flat and the facing side of the display subsystem, as shown in FIG. 1B, is 
placed facing down on top of the illuminating screen of the projector. In 
this way, light is projected through the back side of the LCD screen 20. 
FIG. 1C illustrates the present invention display subsystem in its flat 
configuration for storage or for use with an overhead projector. The base 
assembly 12 and the display assembly 10 are extended within a similar 
spatial plane. Alternatively, the base can be folded down toward the 
overhead projector for added stability as shown. As shown by direction 
20', the viewing side of the LCD screen is facing downward. This is the 
overhead projection configuration. The back side 14 of the display 
assembly (e.g., where the door assembly 12 is inserted) is facing upward. 
Therefore, light passes through the LCD screen 20 in one direction for 
direct viewing (e.g., back-lit viewing) and through the opposite direction 
when used for overhead projection. This is done, as will be explained 
further below, because the transistor layers of the LCD screen 20 are 
exposed at the rear end 14 and illumination energy from the overhead 
projector could cause them to malfunction or become destroyed if 
illuminated from the rear 14. Also at issue are considerations having to 
do with the collumnation angle of the light coming from the overhead 
projector. This is covered further below with respect to FIG. 8C. 
FIG. 2 illustrates a corner view of a fully assembled door assembly 14 of 
the present invention. The facing side 68 of the door assembly 14, as 
shown, is inserted into the display assembly 10. In the configuration as 
shown in FIG. 2, the left illustrated side of the door assembly 14 is 
inserted at the top of the display assembly 10. The door assembly 14 
consists of a rigid back material 70 (in one embodiment is rigid plastic) 
upon which is mounted an acrylic light pipe 56 which is planar having 
approximate dimensions to illuminate the LCD display screen 20 and is 
approximately 5-6 mm thick in one embodiment. As shown in FIG. 2, the 
light housings located on the top and bottom of the display assembly 10 
mate with the left and right sides of the door assembly 14 (in the 
orientation of FIG. 2). The light pipe 56 distributes light from these 
edges throughout the active area of the LCD display 20 to illuminate the 
image. Located between the light pipe 56 and the back 70 is a rear 
reflector layer 120 (not shown in FIG. 2). Located on the surface of the 
light pipe 56 is a bi-directional light extraction pattern 60 (to be 
described in more detail to follow). 
Placed on top of the light pipe 56 are several textured film layers 58 that 
are used to increase the intensity of light that is seen by a viewer 
through the LCD screen 20 and to provide other functions as will be 
described. The layers 58 and the light pipe 56 and other components as 
described above are mounted to the door back 70 with a pair of clamps 38a 
and 38b that each have a very small lip 64 (approximately 1-1.5 mm or 
less) for grabbing and holding the film and light pipe layers. The lip 64 
is small because the gap between the opening in the display assembly 10 
(that receives the door assembly 14) and the active display area of the 
LCD screen 20 is very small. The clamps 38a and 38b are fastened to the 
back 70 via two screws each, however, a variety of mounting techniques can 
be employed. 
Referring to FIG. 2, located behind one of the clamps (here shown as 38b) 
is positioned a magnet 140. The clamp 38b is made from a non-magnetic 
metal as to not interfere with the interaction between the magnet 140 and 
the reed switch 22. When the door assembly 14 is inserted into the 
receiving hole of the display assembly 10, the magnet 140 aligns with the 
reed switch 22 to indicate the position of the door assembly 14. Also 
located on the outside edge of each clamp 38a and 38b, are two latches 34 
for mating with receiving holes 32 located on the top of the display 
assembly 10. These holes 32 and clamps 38a and 38b secure the door 
assembly 14 to the display assembly 10. As shown, surface 68 is inserted 
into the display assembly 10 for back-lighting. 
FIG. 6 illustrates the component layers that form the door assembly 14 in 
more detail. The back cover 70 is shown and the position of the magnet 
actuator 140 is shown mounted within the door back 70. Mounted along the 
top and bottom edges of the door back 70 are two shutoff reflectors 110. 
These reflectors 110 are used in combination with the reflective film 42 
of the lamp housings 40 to create an optical junction or interface between 
the light pipe 56 and the lamps 52. Positioned in between the light pipe 
56 and the back 70 is a rear reflector layer 120 made from a polyester 
reflective (e.g., white) material in one embodiment of the present 
invention. The purpose of this reflector is to reflect light that is 
extracted by the light extraction pattern 60 placed on the light pipe 56. 
The reflector 120 redirects all the light that is extracted to the rear 
and redirects it to the front of the display. Located on the edges of the 
light pipe 56 that do not mate with a lamp housing are two edge reflectors 
130 and these are made, in one embodiment, from a polyester/silver 
material. These serve to redirect any light escaping to the edges back 
into the active area. 
The dot pattern 60 is a light extraction pattern applied on the surface of 
the light pipe 56 that faces the rear reflector 110. This pattern, 
according to the present invention, is bi-directional in that the size of 
the light extractors varies in two dimensions to account for decreases in 
light intensity in both of these dimensions. This will be discussed in 
more detail with reference to FIG. 13. As shown in FIG. 6, the light 
extraction pattern can be an ultraviolet curable white screen printable 
material and is applied directly to the surface of the light pipe 56. As 
is known with light extraction patterns and light tubes, the extraction 
pattern functions to alter the angle of light traveling within the light 
pipe so that the light is scattered and will exit (e.g., become extracted) 
from the light pipe rather than become reflected within the light pipe. 
Any light incident upon any inside surface of the light pipe will pass 
through that surface if its incident angle is less than the Brewster 
angle. If its incident angel is greater than the Brewster angle (420) it 
will be reflected and remain within the light pipe to be rescattered again 
by the extraction dot pattern. The two edges and the rear of the light 
pipe are reflectorized so as to allow the light to be extracted only to 
the front (viewer) surface. When the door assembly 14 is assembled and 
inserted into the display assembly 10, the minimum raw surface brightness 
is approximately 3700 Cd/m.sup.2. 
The layers 58 as described with respect to FIG. 2 are shown in more detail 
in FIG. 6. Placed on top of the light tube 56 is an omni-directional light 
gain diffuser 58a for increasing the amount of light incident along the 
angle of a viewer and in one embodiment is manufactured from a 
polycarbonate material and is approximately 5-10 mils thick. On top of the 
light gain diffuser 58a is a diffuser layer 58b for diffusing the light. 
This layer 58b in one embodiment of the present invention is composed of a 
polycarbonate material and is approximately 5 mils thick. Its surface is 
of a roughened texture to insure a non-wetting contact to the rear of the 
brightness enhancement film BEF (58c) film. On top of layer 58b is a 
brightness enhancement film BEF (58c) that is composed of a polycarbonate 
material and is approximately 10 mils thick in one embodiment. Lastly, a 
BEF protector layer 58d is placed over the BEF layer 58c for protection of 
the layers underneath, especially the micron-sized peaks of the BEF rib 
structure (to protect the micron-sized tips of the BEF which are very 
fragile). In one embodiment, layer 58d is composed of a polycarbonate 
material and is approximately 20 mils thick. 
These layers as shown in FIG. 6 are secured to the back 70 via stainless 
steel "L" shaped clamps 38a and 38b which are screwed into place. It is 
appreciated that the lip 64 of each clamp is very thin (approximately 
1-1.5 mm). When assembled, the top and bottom edges of the light pipe 56 
of the door assembly 14 are exposed for receiving light from the lamp 
housings 40 of the display assembly 10. The viewing direction 20' for 
direct monitoring is also shown in FIG. 6. 
It is appreciated that the door assembly 14 does not contain the lamp 
housings 40. This feature of the door assembly 14 is advantageous because 
the lamp housings 40 remain within the display assembly 10 when the door 
is removed. By leaving the lamp housings 40 within the display assembly 
10, the high voltage interconnection required to energize the lamps is not 
disturbed, thus increasing the operational life of the display subsystem 
and reducing user exposure to the high voltage elements. 
FIG. 3A is a perspective view of a lamp housing 40 which is mounted within 
the display assembly 10. The housing in one embodiment of the present 
invention contains an outer plastic case 45 and the lamps 52 are inserted 
within a receiving channel of the case 45. The lamps are held in place 
with two elastometric shock mounts 50a and 50b as discussed before. In one 
embodiment, each lamp is 250 mm long and 3.0 mm in diameter. Within a 
given lamp pair 52, in one embodiment, the lamps are coupled in series. 
Reflective film 42 is placed within the channel and extends outward onto 
the exterior lip of the plastic case 45. The reflective film 42 and the 
shutoff reflectors 110 create an optical junction that is used to 
efficiently trap light from the lamp housings 40 within the light pipe 56. 
A cable 76 and connector 77 are used to supply the lamps 52 with a high 
voltage signal (approximately 1200 volts to initially strike the lamps, 
500 volts to sustain). Recesses 70a, 70b and 70c are used to secure the 
lamp housing 40 to a metal containing structure 80 (shown in FIG. 4). 
Extended rods 72a and 72b are used to position the lamp housing within the 
metal containing structure for proper tolerance. The lamp housings 40 are 
secured to the display assembly 10 via small screws inserted in holes 74a 
and 74b, however, a number of different mounting techniques (e.g., snap 
fit, heat staking, etc.) can be used. 
FIG. 3B is a cross-sectional view of the lamp housing 40 containing a shock 
mount 51a. The lamps 52 are shown protruding through the rubber shock 
mount 51a which contains a small tongue 51' which is inserted into a small 
receiving hole or gap 53 within the housing case 45. The same is true for 
shock mount 51b. 
FIG. 4 is a perspective illustration of the back side of a portion of the 
display module assembly 10 with the outer case removed and the door 
assembly 14 removed. The top of FIG. 4 corresponds to the top of the 
display assembly 10. As shown, the back side of the LCD screen 20 is 
facing upward. The lamp housings 40 are both surrounded by a protective 
metal structure 80 (bezel) which also houses the reed switch 22 and also 
channels voltage supply cables 76 from both lamp housings 40. The 
structure 80 also supports the LCD screen 20. Gap 84 illustrates the small 
distance between the edge of the structure 80 and the start of the active 
LCD display 20 region. For this reason, the lip 64 on clamps 38a and 38b 
are very small as to not obstruct illumination of the edge portions of the 
image. It is appreciated that the gap 84 should not be enlarged since it 
is desired to maximize the display active area as a ratio of the total 
size of the module. The gap 150 (FIG. 7) that is minimized is that space 
between the low lamp housings 52 (FIG. 7) and the entry face of the light 
pipe 56 (FIG. 7). 
It is appreciated that the display assembly 10 in one embodiment of the 
present invention also contains inverter circuits required for energizing 
the lamps 52. This is in order to maximum power efficiency by keeping the 
lamp wires as short as possible to reduce capacitance coupling. However, 
in alternative embodiments, these circuits can also be located in the base 
assembly 12. 
FIG. 5 illustrates the components of the lamp housings 40 in more detail. 
The plastic case 45 is inserted inside the insulated shield 80 and the 
reflective film 42 (curved) is inserted into the inside channel of the 
case 45. The function of the insulated shield 80 is to block stray 
electrical emissions (EMI) coming from the display driver PCB located, in 
one embodiment, beneath the lamp housing assembly. The lamps 52 supported 
by the shock mounts 50a and 50b are inserted into the case 45 and are 
therefore surrounded by the reflective film 42. A portion of the 
reflective film 42 extends outside of the channel of the case 45 onto the 
lip 45a. Cable 76 and connector 77 extend outside. This is true for both 
lamp housings 40. 
FIG. 7 illustrates the optical junction created by the present invention 
between the lamp housing (in this case the plastic case 45) and the door 
assembly 14 when inserted into the display assembly 10. The viewing angle 
for direct monitoring is shown by 20'. There is only a very small gap 150 
between the end of the lamps 52 and the start of the light pipe 56. On the 
top of this gap 150, a portion 42a of the reflective film 42 overlaps the 
gap to provide reflection of light that would otherwise stray outside of 
the light pipe 56. This reflective film 42a directs this light back into 
the light pipe. On the bottom of this gap 150, as shown by FIG. 7, the 
shutoff reflector 110 extends over the edge of the door 14 in order to 
bridge the gap 110. Therefore, the gap 150a between the end of the shutoff 
reflector 110 and the edge of the lamps 52 is smaller than gap 150. This 
gap 150a is on the order of 0.25 mm. It is appreciated that the present 
invention advantageously provides a portion of the shutoff reflector to 
extend beyond the edge of the door 14 to decrease the size of gap 150a; in 
this manner more light is reflected back into the light pipe 56. 
It is understood that gap 150 is present since the door assembly 14 is 
removable. The present invention minimizes this gap 150, the distance 
between the start of the light pipe 56 and the end of the lamps 52. The 
present invention further bridges the gap 150 by overhanging the shutoff 
reflector 110 from the edge of the light pipe 56 thus making a smaller gap 
150a. 
The combination of the shutoff reflectors 110 and the reflective film 42 
(especially the film 42 over the lip 45a) create an optical junction that 
prevents light from permanently escaping out of the light pipe 56. As 
light is emitted from the lamps 52, those waves that enter under the 
Brewster angle (approximately 42 degrees) will be reflected within the 
light pipe 56 and will be carried down the pipe and extracted by pattern 
60. Those waves (1) incident upon the light pipe at a higher angle (and 
hence reflected away) or those (2) waves incident directly on the 
reflectors, will be reflected by the reflectors 110 and 42 back into the 
light pipe 56 to increase light intensity for viewing. In other words, any 
light incident on the surface of the light pipe at greater than the 
Brewster angle (42 degree) is reflected off its surface to be re-reflected 
by the films until a percentage of the light rays enter the light pipe. 
The reflective surfaces 110 and 42 are needed most at the edges of the 
light pipe near the lamps 52 because at this close angle, most of the 
light emitted is incident on the light pipe at angles greater than the 
Brewster angle and therefore needs to be reflected back into the light 
pipe 56. Therefore, since the light pipe 56 is removable from the lamp 
housings 40, it is appreciated that the placement of the shutoff 
reflectors 110 along the edge of the light pipe 56 is important to 
maintain the optical junction necessary to reflect light energy that is 
incident along an angle greater the Brewster angle. It is appreciated also 
that the active area of the LCD screen 20 begins approximately at line 56' 
which is at a distance wherein light enters under the Brewster angle and 
is reflected within the light pipe 56 until extracted by pattern 60. 
Therefore, the optical junction (as shown in FIG. 7) created by reflectors 
42 and 110 over the edge of the light pipe 56 closest to the lamps 52 
reflects light that is incident on the light pipe 56 at angles greater 
than the Brewster angle and therefore needs to be reflected back into the 
light pipe 56. Any light escaping from the light pipe in that area is also 
redirected back into the light pipe. Since the door assembly 14, including 
the light pipe is removable, the shutoff reflectors 110 are mounted on the 
edges of the door assembly 14. Such configuration is required according to 
the present invention since the lamps 52 remain housed within the display 
assembly 10 upon removal of the door assembly 14. 
Under the present invention, when the door assembly 14 is removed and 
inserted back, the optical junction as shown in FIG. 7 is disturbed during 
the removal. However, the high voltage connections between the lamps 52 
and their power supply are never disturbed by the removal since the lamps 
52 remain in the display assembly 10. This reduces exposure of the user to 
high voltage circuits and increases the operational lifetime of the 
display subsystem. 
FIG. 8A illustrates a combination 300 including the display subsystem of 
the present invention (including base assembly 12 and display assembly 10) 
positioned over an overhead projector 305 of the present invention. In 
this embodiment of the present invention, the display subsystem can be a 
stand alone peripheral that is for coupling with a computer system. The 
display subsystem is in the overhead projection configuration and is 
placed on top of the projector 305. Although the display subsystem of the 
present invention may be used with a variety of well-known and 
commercially available overhead projectors, the projector 305 is 
particularly adapted for the display subsystem. This projector 305 is 
available from DUKANE, a corporation of Illinois, under model number 28A 
681. This projector 305 generates 8000 lumens through screen 315. This 
amount of light intensity is utilized to take advantage of the color 
properties of the display subsystem. The light is of high intensity in 
order that the colors projected can be of high saturation while not 
depriving the user of the sufficient brightness to view the screen 360. It 
is appreciated that there is a trade off between color saturation and 
brightness in this invention. 
On the left and right sides of the display screen 315 are mounted tracks 
370a and 370b over which the display assembly 10 of the display subsystem 
is mounted such that the LCD screen 20 is placed over the screen 315 with 
the viewing side facing down (as shown by arrow 20'). An image director 
320 then transfers the image from the LCD screen 20 to a receiving screen 
360 (as is well-known with overhead projectors). Two clips 325a and 325b 
are secured to the overhead projector 305 and mate with holes 95a and 95b 
(FIG. 1B) to secure the display assembly 10 in proper position on the 
projector 305. The display subsystem is placed such that it rests over the 
tracks 370a and 370b and the holes 95a and 95b are inserted into the clips 
370a and 370b and the viewing side of the screen 20 is facing downward. 
Also shown in FIG. 8A is a fan inlet strip 322 and a fan 310. The fan 310 
cools an internal lamp within the projector 305 and additionally acts to 
create air flow down through the inlet strip 322 in order to cool the 
display screen 20 as will be discussed further below. Alternatively, a 
pair of fans can be used to cool the lamps and the display separately. 
FIG. 8B illustrates a front view down on the projector 305 with the display 
subsystem removed. FIG. 8B illustrates that when the display assembly 10 
is positioned over tracks 370a and 370b, a channel is formed along the 
inside surfaces of the tracks 370a and 370b, the top surface of screen 315 
and the viewing surface of the display screen 20. In this configuration, 
the fan 310 causes air to flow from the cool side (e.g., the top of the 
screen 20) and down through the air inlet strip 322. This air flow is used 
to cool the LCD screen 20 so that the color filters and other elements of 
LCD screen 20 are not damaged from the heat radiated from screen 315 when 
the projector 305 is turned on and the liquid crystal material is kept 
within its proper operating temperature. It is important that this cooling 
function take place when the display subsystem is used with projector 305 
due to the high intensity (e.g., 8000 lumens) screen 315. It is 
appreciated that such air flow may not be required when the display 
subsystem is used with other, conventional overhead projectors of lower 
light intensity. 
FIG. 8C illustrates another advantage obtained by the present invention in 
placing the display subsystem face down on the projector 305. FIG. 8C 
illustrates a side view of the projector 305 and subsystem 10 arrangement. 
An integral optical element of the overhead projector 305 is a fresnel 
lens 357 located immediately below the projector stage glass (see element 
315 of FIG. 8A). This lens concentrates light received from the projection 
lamps and focuses it through the image residing within the LCD plate 20 
onto the projection lens head 320. In doing so, the light is taken from a 
large area and focused onto a small area creating an optical condition 
known as a collumnation angle. 
This collumnation angle 359 can be as acute as 21 degrees or more. 
Therefore, in order to view the image in the LCD screen 20 completely, all 
the light along this path (as shown) should be free of obstruction. By the 
nature of the construction of the display subsystem, the LCD screen 20 
resides to the front or top of the case 10 in order to be best seen in the 
direct view mode. However, the back light is contained in a rather deep 
cavity in the rear. If one were to place the subsystem 10 over the 
projection 305 with the back of this cavity down against the stage 315, 
the close proximity of the sides of the backlight cavity would be within 
this 21 degree collumnation angle and would obscure the edges of the 
image. As a result, the present invention configuration places the display 
face down on the stage 315 in order to reverse the effects of the 
collumnation angle. The data reversal feature of the present invention 
then compensates for this configuration so that the image is viewed in the 
proper orientation. 
FIG. 9A illustrates the various material layers used in the present 
invention combining the LCD display 20 and the door assembly 14. As 
previously discussed, the door assembly 14 is composed of the back cover 
70, rear reflector 120, light pipe 56 (with extraction pattern 60), and 
top layers 58. Although not part of the door assembly 14, the lamp pairs 
52 are shown. Door assembly 14 is shown in its orientation when inserted 
into the display assembly 20. 
FIG. 9A also illustrates the layers of the LCD screen 20. It is appreciated 
that a number of different LCD screen technologies can be advantageously 
used within the scope of the present invention and the particular 
technology shown in FIG. 9A is exemplary only. LCD screen 20 is composed 
of a rear polarizer 410a, a back supporting glass 415a, an active 
transistor layer or (TFT layer) 417, a liquid crystal layer 420, a color 
filter layer 419, a front supporting glass layer 415b, and a front 
polarizer 410b. As will be discussed further with respect to FIG. 9B, an 
additional layer is applied to the front polarizer. As shown in FIG. 9A, 
the viewing side of the LCD screen 20 is facing outward. It is appreciated 
that when used with the overhead projector 305, one reason the LCD screen 
20 is not placed with the rear polarizer 410a side facing the screen 315 
is that the light intensity from the screen 315 could damage the thin film 
transistor layer 417. This layer 417 has more protection when the color 
filter layer 419 is placed facing screen 315 in the overhead projection 
configuration. 
FIG. 9B illustrates the layers that are placed on top of the front 
polarizer layer 410b of the LCD display screen 20. An adhesive 450 is used 
to secure the front polarizer 410b to the front glass layer 415b. An 
antiglare layer (which can be composed of polymethyl metharcylate or PMMA) 
455 is applied on top of the front polarizer layer 410b. A very thin 
(several hundred A.degree.) composite layer 480 of antireflective ITC 
(AR/ITO) is applied on top of the antiglare layer 455. This layer 480 is 
composed of alternating layers of ITO 435 (composed of In.sub.2 O.sub.3 
/SnO) and dielectric material layers 430. This is also referred to as CHEA 
(conductive high efficiency anti-reflection). Exemplary dielectric 
materials are TiO.sub.2 or SiO.sub.2. The ITO layer 435 is conductive and 
an exemplary mixture is approximately 95% In and 5% SnO. The ITO layers 
435 are electrically grounded. Layer 480 performs dual functions as an 
antireflective layer (making the image brighter by approximately 4-5 
percent per side which is in effect 10%) and as a conductor. 
As shown in FIG. 9B, there is a similar structure applied to the back 
surface of the rear polarizer 410a, except that layer 453 is a clear PMMA 
layer. The ITO layers 435 of the composite layer attached to layer 453 are 
also electrically grounded. 
FIG. 9C is an electrical diagram of the grounding of layers 480 of the LCD 
screen 20 in the present invention. This is done in order to reduce 
electromagnetic emissions from the display assembly 20 of the present 
invention. 
FIG. 10 is a logical block diagram of electronics of the display subsystem 
of the present invention. Although some electrical components are shown 
(in dashed lines) to be associated with the base assembly 12 or the 
display assembly 10, it is appreciated that their locations are exemplary. 
Apart from the LCD screen 20, the actual location of the circuits could be 
in either the display assembly 10 or the base assembly 12. 
Within the base assembly, as shown in FIG. 10, are a power supply unit 537 
for coupling with an alternating current source 44. This power supply 537 
supplies power via line 525 to an audio board 535 and a video board 530. 
The audio board 535 is coupled to the video board via bus 545. Audio and 
video information are sent to the display subsystem via input interconnect 
48. It is appreciated that a variety of audio/video information transfer 
formats and standards can be used within the scope of the present 
invention, including an IBM compatible standard, a UNIX standard, or Apple 
Computer Macintosh.TM. standard. 
Video board 530 is coupled to a bus 515 for communicating and controlling 
elements of the display assembly 20. It is appreciated that portions of 
bus 515 are composed of flex circuits so that base assembly 12 and display 
assembly 10 can move freely about their common hinge. Among other signals, 
this bus 515 carries power, control signals and audio and video data 
signals. The video board 530 is coupled to supply audio signals over bus 
515 to stereo speakers 8a and 8b. Video board 530 also supplies a control 
signal and power over line 515 to a circuit block of inverters 539 which 
contain transformers to supply high voltage required to illuminate lamps 
52 and also contain a switch circuit for turning the lamps 52 off. Lamps 
52 are coupled to the inverter logic 539 via power bus 510 (high voltage 
bus). Bus 515 is also coupled to reed switch 22 which carries a digital 
signal indicating when the door assembly 14 is inserted into the display 
assembly 10 or not present. 
Although both analog and digital data interconnects (e.g., for video and 
audio data from a host computer system) are within the scope of the 
present invention, in one embodiment of the present invention, the display 
subsystem utilizes a digital interface to the host computer system over 
interconnect 48. An adapter is present (in the host computer system) to 
grab the video pixel stream before it is converted to analog (to drive a 
CRT monitor) and to send the digital video data to the video board 530 of 
the display subsystem. The result is a crisp digital representation of the 
pixels in the frame buffer of the host computer system. 
In the case of an exemplary host computer system (such as Indy.TM. 
available from Silicon Graphics of Mountain View, Calif.), there is a 
connector on the host computer system's graphics card which gives access 
to the digital pixel stream. A secondary card is installed (the adapter) 
and the video board 530 of the display subsystem of the present invention 
is coupled to that secondary card. The adapter converts the fast TTL 
signals (e.g., up to 110 MHz) to ECL such that the digital data can be 
transmitted over a long cable without degradation. The video board 530 
converts this data back to CMOS to drive the LCD display 20. An exemplary 
interconnect 48 uses a 68 position connector to carry 24 differential 
pairs for each pixel (hence 24 bit color is available) in addition to the 
required horizontal and vertical synchronization signals. 
The adapter also provides a means for the host computer system and display 
subsystem of the present invention to send and receive control signals via 
I.sup.2 C interface. Using the exemplary host computer system, Indy.TM., 
the I.sup.2 C interface is connected to the display control bus (DCB). The 
adapter also provides a pass-through circuit for line level stereo audio 
information from the host computer system to the speakers in the display 
subsystem. 
Bus 515 of FIG. 10 is coupled to supply video information to column driver 
circuits 501. The column driver circuits 501 control information flow to 
the columns of each of the rows of transistors (within the TFT layer 417) 
of the LCD screen 20 to generate an image in the well-known fashion. 
(There are also separate row driver circuits that are not illustrated but 
operate in the well-known fashion.) 
Refer to FIG. 10 and FIG. 12. The present invention performs two functions 
simultaneously when the door assembly 14 is removed from the display 
assembly 10 as shown by the flow diagram of FIG. 12 as process steps 654 
and 656. The reed switch decision block is shown as block 652. Upon 
removal, the reed switch 22 broadcasts a signal over bus 515 which is 
intercepted by the video board 530. The video board 530 generates a 
control signal to the inverters 539 (over bus 515) causing the inverters 
539 to cut off power to the lamps 52 to reduce power and reduce risk of 
injury when the door assembly 14 is removed. Also, a control signal is 
also sent over bus 515 to the column driver circuits 501 causing the 
column driver circuits 501 to reverse the direction of the stream of video 
information filled to the columns of layer 417 for the overhead projector 
configuration. This is done row by row to immediately reverse (left to 
right) the image displayed on LCD screen 20. Image reversal is required 
since the LCD screen 20 is viewed from opposite sides for when in direct 
monitoring versus overhead projection viewing. 
Upon insertion of the door assembly 14 back into the display assembly 10, 
the reed switch 22 generates a signal over bus 515 indicating the presence 
of the door assembly 10 and the video board 530 generates a signal to the 
inverters over bus 515 to energize the lamps 52 and also generates a 
signal (515b shown in FIG. 11) to the row circuits 501 to reverse the 
information flow to LCD screen 20 for the direct viewing configuration. 
This is illustrated in FIG. 12 as process steps 658 and 660. It is 
appreciated that a number of different logic circuits can be used within 
the video board 530 to perform the above process, including a state 
machine or application specific integrated circuit (ASIC). 
In the preferred embodiment of the present invention, power is controlled 
to the display subsystem via software control. A computer system, via a 
processor, a memory (RAM and ROM), and an I/O device (all coupled to a 
common communication bus) controls power supply 537 to control power 
distribution over bus 525. In an alternative embodiment, the optional 
power on knob 2a is coupled to the power supply 537 to control power 
distribution over bus 525. In the preferred embodiment of the present 
invention brightness and volume are also computer controlled as discussed 
above. In an alternative embodiment, the optional brightness knob 2b is 
coupled to control the voltage supplied by the inverters 539 to the lamps 
52 over bus 510. In an alternative embodiment, the optional volume knob 2c 
can be coupled either to the audio board 535 or to the speakers 8a and 8b 
for volume adjustments. 
FIG. 11 is a logical block diagram of the circuitry within the column 
driver circuits 501 that control the reversal of the image data sent to 
the LCD screen 20 for between (1) direct viewing configuration and (2) 
overhead projection configuration. For each row of pixels (0 to n) of the 
LCD screen 20, there is a separate video input feed line 515a(0-n). These 
feed lines 515a(0-n) each couple to a separate multiplexing circuit of 
610(0-n). The select lines for all of the multiplexing circuits 610(0-n) 
are coupled to control line 515b. When the reed switch 22 indicates that 
the door assembly 14 is within the display assembly 10, then the select 
line 515b asserts a signal to cause the data from the respective video in 
lines 515a(0-n) to be fed to the respective lines 612(0-n). These lines 
612(0-n) are used by the column driver circuits 501 to send video 
information to the columns of the particular row (0-n). In this 
configuration, the columns of each row are filled from left (e.g., first) 
to right (e.g., last). This is used for direct monitoring configurations 
(e.g., back-lit). 
When the reed switch 22 indicates that the door assembly 14 is removed from 
the display assembly 10, then the select line 515b asserts a signal to 
cause the data from the respective video in lines 515a(0-n) to be fed to 
the respective lines 614(0-n). In this configuration, the columns of each 
row are filled from right (e.g. last) to left (e.g., first). This is used 
for overhead projection monitoring configurations. It is appreciated that 
the signal used to control the voltage supplied from the inverters 539 to 
the lamps 52 can be the select signal 515b or a derivation therefrom. 
FIG. 13A illustrates the RGB information flow to the LCD screen 20 for a 
direct viewing configuration with the columns of each row being filled 
from left to right. In FIG. 13A, the LCD screen 20 is shown with the 
direct viewing side facing outward. In this exemplary screen there are n 
rows and x columns, each pixel described by (n, x). The data is filled for 
each row starting with column 1 and ending with column x. FIG. 13B 
illustrates the RGB information flow to the LCD screen 20 for an overhead 
projection viewing configuration with the columns of each row being filled 
from right to left. In FIG. 13B, the LCD screen 20 is shown with the 
direct viewing side facing outward. In this configuration, the data is 
filled for each row starting with column x and ending with column 1. The 
image is effectively reversed or "mirror imaged" under control of the 
select line 515b. 
FIG. 14 illustrates an exemplary rendition of the light extraction pattern 
60 utilized by the present invention which is applied to the light pipe 
56. In the configuration of FIG. 14, the lamps 52 are oriented 
horizontally on the bottom and on the top to illuminate toward the center 
of the pattern 60. The light extraction pattern of the present invention 
utilizes differently sized dots along the pattern to cause light in the 
light pipe 56, adjacent to the dot, to alter its direction of travel. In 
particular, the light's direction that reflects off of a particular dot 
will radiate out of the light pipe 56 (e.g., it becomes extracted and is 
projected through the LCD display 20) unless it is extracted at an angle 
exceeding the Brewster angle where upon it is re-reflected within the 
light pipe to be extracted again by other dots. Since the light intensity 
is larger closer to the lamps 52, the dots nearer to each lamp are 
smaller. FIG. 14 shows that the dots grow larger as the distance away from 
a particular lamp 52 increases along the X direction. 
However, since the lamps 52 are not placed along the left or right edges of 
the pattern, the extraction dots of pattern 60 are larger along these 
edges. These dots along the left and right edges grow progressively 
smaller (along the Y direction) the closer they become to the center of a 
lamp. Therefore, the extraction pattern 60 of the present invention is 
bi-directional in that the sizes of the dots vary in both the X and Y 
direction depending on the configuration of the lamps 52. Additionally, 
since lamps 52 do not extend completely to the corners, the light 
extraction dots here are larger and vary in the X and Y direction. 
Additionally, the lamps are not uniform across their lit area. For 
example, the 1.5 cm lengths (in one embodiment) at the ends of each lamp 
are only about 50% as bright as the center section. 
By varying the sizes of the dots of the light extraction pattern 60 in a 
bi-directional format, the present invention light extraction pattern is 
able to increase the brightness of the overall image within LCD screen 20 
and also provide greater uniform brightness over the image. The present 
invention light extraction pattern 60 effectively provides uniform light 
intensity even around the corners of the display and along the edges of 
the display that do not have corresponding lamps. It is appreciated that 
the dots do not necessarily have to be circular, but can be of a number of 
different geometries within the scope of the present invention (e.g., 
square, triangular or other polygonal shape). 
The preferred embodiment of the present invention, a display subsystem 
using a back-lit flat panel display for direct viewing and also with a 
removable back-lit door assembly for viewing with an overhead projection 
unit, is thus described. While the present invention has been described in 
particular embodiments, it should be appreciated that the present 
invention should not be construed as limited by such embodiments, but 
rather construed according to the below claims.