Single panel reflective LCD projector by fwg31028

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                               Single panel reflective LCD projector

                                                      Jeffrey A. Shimizu

                      Philips Research, 345 Scarborough Road, Briarcliff Manor, NY 10510


                                                         ABSTRACT

We have constructed a high resolution projection display with a single reflective LCD panel. Reflective technology based on
standard silicon CMOS processing has emerged as a favorable direction for projection displays. Advantages include low
investment and fabrication costs, high resolution capability, and high aperture ratio. As a move towards lower cost and high
performance, we have applied reflective technology to a single panel projection display. The pixel array is SXGA
(1280x1024) and is fabricated in a process with both 5 Volt logic and 15 Volt structures. A thin 1 micron liquid crystal cell
is formed over the array. A fast on time of 0.2 ms is attained with a nematic LC effect. System architecture is based upon a
scrolling color illumination system wherein three color bands are present on the panel at all times. This arrangement avoids
the 2/3 light loss in spectral efficiency present in a more conventional color wheel system. The system demonstrates that
color sequential projection displays are feasible with LCD devices. And this direction holds great promise in a wide variety
of applications including consumer HDTV displays.

Keywords: Single panel, LCD, reflective, projection, display


                                                    1. INTRODUCTION

The past few years have seen rapid advancement in LCD and DMD projection systems. Image quality has dramatically
improved including a steady direction towards higher resolution. These displays have found large acceptance primarily as
means for electronic presentations. Projection technology has the potential to be successfully applied over a wide range of
applications including business presentation, consumer projection television, projection workstation monitors, point of sale
displays, video wall, and electronic cinema. The prime direction for expanding the use of projection is to reduce cost while
maintaining or improving image quality.

An exciting direction that has recently emerged is reflective LCD on silicon substrates.1-3 With this approach the active
matrix is fabricated in a standard silicon semiconductor line. There are many advantages for reflective LCD. The active
area from which the picture information is reflected consists of an array of patterned aluminum mirrors. The reflective
mirrors are formed on top of the array covering the address circuitry and pixel transistors. By contrast a transmissive LCD
experiences competition between the active transmissive area and the area for the circuits and pixel transistor. The
reduction in active area limits the amount of light passed by the LCD. This problem becomes ever greater with the push
towards higher resolution and smaller device size. In addition the high aperture ratio of a reflective device results in better
image quality. Images with reflective devices are smooth and continuous, not interrupted by dark row and column lines.
Additional advantages of reflective devices come from its foundation on silicon substrates. From a circuit point of view
silicon is the best material for the active matrix. The pixel transistors are small and there is great ability to integrate drivers
and other functions on chip. In addition to performance issues, many advantages come from fabrication on existing silicon
lines. The equipment and infrastructure already exists. Developments proceed at a rapid pace governed by a competitive
silicon industry. Displays are made on the same lines as commercial integrated circuits obviating the need for large
investments in dedicated display lines. This opens the opportunity for many companies with direct or even indirect access to
semiconductor lines to enter the display business.

Advantages of reflective LCD technology are many and this has spawned a number of current efforts for both virtual
displays and projection systems.4 In general the demands for projection are greater for both the device and the system. Much
of the projection work exploits high resolution, aiming at XGA and better. They are typically three panel systems with
individual panels for the red, green, and blue portions of the color image.
While the three panel systems are significant, we believe a direction towards single panel presents even greater opportunity.
Single panel brings lower cost and improved image quality. Cost advantage comes from fewer LCD panels, and eliminating
the need for convergence mechanics and adjustments. The benefit to image quality comes from inherent color convergence.
In a three panel system the panels must be placed relative to each other to within a fraction of a pixel. Any misconvergence
results in a loss of picture quality, specifically white field MTF (modulation transfer function). As systems move to greater
resolution this becomes an increasing problem. In principle, three panel systems can be well converged. In practice it is very
difficult to achieve and maintain alignment.

Fast switching speeds are necessary in order to create a single panel color sequential system. Due to the dynamics of the
display the response speed must be an order of magnitude faster than that required for a three panel system. We have
implemented a nematic reflective LC effect with a switching time able to support single panel operation. With a reflective
display light passes the LC layer twice, so the cell gap is half that required for a transmissive cell with the same optical
delay (retardance). Half the gap leads to a factor of four improvement in switching speed. So as circumstance has it,
reflective LCD displays and fast response time form a favorable match.

Armed with a fast LC effect and a high performance silicon process, we proceeded to construct a high resolution reflective
single panel projection display. In the interest of maintaining system light efficiency we implemented a scrolling color
architecture that avoids the 2/3 light loss of a more conventional color wheel system. With a color wheel 2/3 of the light is
lost since only one color is displayed at a time. The scrolling color architecture employs scanning red, green, and blue
illumination stripes.5 Spectral efficiency is maintained as all three colors are on the panel at all times.

The single panel system we constructed is based on an SXGA (1280x1024) pixel array. This high resolution and the
scrolling color architecture present challenges for all elements of the system. The display is truly a systems level
undertaking as characteristics of each element has great influence on the other elements. The following report describes
elements of the liquid crystal, scrolling color architecture, optics, panel, electronics, and the system characteristics. The
resulting SXGA projection display clearly demonstrates that single panel operation is feasible with a reflective LCD device.


                                                   1. LIQUID CRYSTAL

One of the keys to a single panel system is a fast liquid crystal cell. As colors are presented in sequence, the liquid crystal
(LC) must switch fast enough to avoid color contamination. At 60 Hz an individual color time is 5.55 ms. Exact speed
requirement depends on (and influences) the illumination scheme. For a reasonable system we targeted a response time of
less than one millisecond.

Reflective operation requires a different LC effect than the typical 90 degree twisted nematic used in transmissive displays.
Further, LC materials and effects that are fine for three panel may not support single panel operation. One approach
towards fast switching is to use ferro electric LC materials.6 While these materials give more than adequate response time,
they pose many practical difficulties. Ferro electrics have difficulties with gray scale, alignment, and stability that introduce
additional burdens. Thus we have a bias towards nematic effects.

Asymmetry of electrical response is also a factor in LC selection. Response in driving from low to high voltage, the on-time,
is faster than driving from high to low voltage, the off-time. For the on transition the liquid crystal is driven to align with
the applied electric field. For the off transition the liquid crystal relaxes from the driven state to the natural zero field state.
In the color sequential display a given pixel is driven in turn by red, green, and blue. To achieve saturated colors one color
may not leak into the other. To ensure color separation we chose the faster on transition to drive towards black. That is, we
prefer an LC effect that is normally white.

To obtain a fast response a thin cell gap is necessary. The thinner the gap the greater the applied electric field for the same
voltage. In a reflective cell light passes the cell gap twice. Thus to achieve the same birefringence, ∆nd, the cell gap of the
reflective cell is half that of a transmissive cell. Again to minimize cell thickness, a high ∆n material should be chosen. We
have chosen a ∆n = 0.2, with a 1 micron cell gap. This cell gap is very much thinner than the 3-5 microns used in more
conventional liquid crystal cells. A thin cell gap requires greater care in cell fabrication as gap thickness tolerances are
proportionally smaller. This tight tolerance can not be achieved with conventional ball spacers dispersed in the liquid
crystal. To maintain a fine cell gap we use integrated spacers. The spacers are photo lithographically defined posts formed
during the fabrication of the device in the semiconductor fab.

The combination of thin cell and nematic LC effect achieves the switching speed target. A measured curve of LC response
is shown in Figure 1. The plot shows a response time of 0.2 ms for the driven transition to black. Data was taken at 50°  C.
This response data exceeds our requirement for LC speed and supports construction of the single panel projection display.

                                               3.5
                                               3.0
                         Output (arb. units)




                                               2.5
                                               2.0
                                               1.5
                                               1.0
                                               0.5
                                               0.0
                                                     0.0          0.5       1.0      1.5          2.0
                                                                         Time (ms)

Figure 1: Measured response speed of the liquid crystal. Measurements are taken on a 1 micron thick reflective cell driven
to black at a temperature of 50°C.


                                                           2. SCROLLING COLOR ARCHITECTURE

With the scrolling color architecture we aim to gain the advantages of a single panel system without sacrificing system light
efficiency. There are a number of approaches towards single panel displays. In the area of projection, DMD is the most
notable.7 Single panel DMD systems employ a rotating color wheel. This leads to a nominal 2/3 light loss. When one color
is present on the display, the other two colors are lost. This spectral light loss is not present in the scrolling color
architecture.

With the scrolling color system all three colors are present on the panel at all times. White light from the lamp is split into
constituent red, green, and blue beams. The colored beams illuminate the panel as spatially separated stripes of light. A
representation of the illumination pattern is shown in Figure 2. The stripes of light scroll across the display from top to
bottom. As one color scrolls off the bottom of the panel it appears immediately again at the top.

To create the color image the LCD is effectively addressed at three different places simultaneously. Data for a given color,
for example green, is written to a row just after the passing of the previous color, blue (see Figure 2). The (green) band then
illuminates the pixel. The panel is addressed at three places and these address rows shift downward in sync with the
illumination pattern. In practice only one row is active at a time. So the active row jumps around the panel from top, to
center, to bottom. Address then returns to the top and the sequence repeats with each of the row numbers incremented by
one on the next pass.

This novel scrolling color architecture meets the objective of maintaining spectral efficiency. The architecture also has
many implications for the rest of the system including the optics, panel, and electronics. These elements are described in the
following sections.
                                                             Red                       Active Address
                      Colored Stripes                                                      Lines :
                      Scroll Top to                                                         Red
                      Bottom
                                                            Green

                                                                                            Green

                                                             Blue

                                                                                            Blue

                                                            LCD

Figure 2: Schematic of the light pattern present at the LCD panel. Spatially separated bands of red, green, and blue light
scroll down the panel and appear immediately again at the top. Red, green, and blue picture information is written to the
panel in sync with the illumination just after the previous color band.


                                                        3. OPTICS

The scrolling color architecture presents challenges for the optical system. The first challenge is the reduction in system
etendue since a given color covers approximately 1/3 of the panel area. This etendue reduction favors larger panel sizes.
The second challenge is for an efficient color scanner which we implemented with a rotating prism scanner.

As seen in Figure 2, each color illuminates nominally 1/3 of the panel. The optical system is often characterized by the
geometrical quantity etendue which describes the optical size of a light beam. The etendue, E, of an area, A, illuminated at
an F-number, F, is given by,
                                                           E = π A / 4 F2 .                                             (1)
In general etendue is invariant in the optical system. Thus, calculation of the etendue at the panel, for example, can be
translated directly to other places in the system. The etendue parameter is useful in estimating light efficiency in projection
systems.8 For simplicity it is sufficient to say that light collection from a given lamp is a non-linear but monotonic function
of the system etendue. So to achieve a high collection efficiency, a certain system etendue is required.

It is useful to consider the scrolling color system in comparison to a three panel system and a color wheel system. The
scrolling color system has full spectral efficiency so the system may be as bright as a three panel system. However the
etendue is reduced to 1/3. For roughly equivalent brightness, the panel size should be three times larger in area than for a
panel used in a three panel system. But because three panels are required the total area remains the same. In practice the
trade between collection efficiency and panel size favors a smaller panel with some corresponding loss in brightness. And
since lamp collection is not linear with etendue, the loss can be moderate. In comparison to a color wheel system, the
scrolling color architecture has nominally three times the spectral efficiency. To realize the full gain, the panel area must
increase by a factor of three. Given the same panel area, there is a trade between the high spectral efficiency with scrolling
color and the higher collection efficiency with a color wheel. In general this trade favors the scrolling color system unless
the panel size is very small and thus system brightness limited in both cases.

We have constructed a scrolling color system where the scanning action is affected by a rotating square prism. As a prism
rotates, refraction at the faces causes light to translate vertically. Refraction at the prism faces and the corresponding
scanning motion is shown in Figure 3. A rectangular stripe of light is formed just before the scanning prism and is imaged
through this prism onto the LCD panel. Rotation of the prism creates a continuous scan of the stripe from top to bottom. As
a vertex of the prism passes a given point at the input stripe, the light jumps discontinuously from bottom to top. At some
time the stripe may even be split between the top and bottom. In this manner an efficient scanner is created with little loss
or required over scan.
                                        (a)                                      (b)
Figure 3: Scanning action from a rotating prism. Refraction at the prism creates a translation of the input stripe as in (a). As
the vertex passes light jumps instantly from bottom to top. The stripe may even be split between top and bottom as shown in
(b).

The optical path makes use of three scanning prisms, one for each color as shown in Figure 4. The Philips high brightness
UHP lamp is used as the light source. Lens integrator arrays are used to shape and homogenize the distribution to form the
wide illumination stripe. A multiple polarizing beamsplitter component is used for polarization recovery.9 The light path is
split into red, green, and blue paths via dichroic color filters. Each color channel has a rotating prism for scanning. The
three prisms are offset in phase relative to each by 30 degrees, or 1/3 of a complete vertical scan. This phase offset creates
the spatial separation of colors at the panel. Dichroic color filters are used to recombine the colors into a single illumination
beam. The beam then encounters a polarizing beamsplitter, PBS. The PBS directs a polarized beam onto the reflective LCD
panel, which modulates the polarization with the picture information. The reflective LCD in combination with the PBS
directs the picture forward through the projection lens and onto the screen. Of all the components in the system, only the
panel, PBS, and projection lens are in the imaging path. Thus all other components are illumination optics and have
relatively coarse tolerances for fabrication and mechanical placement.
                                                                                        PBS

                                                             Liquid
                                                             Crystal
                                                             Display

                                Scanning Prism
                                                                                        Projection Lens



                  Lamp




                                Lens Arrays
Figure 4: Schematic of the optics in the scrolling color engine. Up to the polarizing beamsplitter (PBS) the components are
illumination optics with relatively coarse tolerances.

One of the key elements in the optical path is the polarizing beamsplitter, PBS. A typical PBS has very good extinction over
a small angular range of about ±1° We desire an angular acceptance on the order of ±12° This wide angular acceptance is
                                    .                                                       .
possible with a trade in extinction. That is the transmission of “p” and the reflection of “s” polarized light is reduced to
achieve wide angle performance. In order to achieve good system contrast, additional polarizing films are required. Due to
the geometry of the PBS interface, the polarization vector passed by the PBS rotates within the illumination cone. This skew
angle problem can be largely compensated for by a quarter wave retarder placed between the PBS and the reflective LCD.10
With this arrangement we have measured basic system contrast of 1300:1 in an F/2.4 illumination cone. In this case the off
state is created with a simple mirror and the on state with a mirror and quarter wave foil. This high contrast confirms a thin
film based PBS can be used successfully in a reflective LCD projection system. Additional properties of the total display
system are presented later in section 6.


                                                         4. REFLECTIVE LCD PANEL

The reflective LCD is the critical element of the system. The panel must meet resolution, speed, and architectural
requirements of the single panel system. To support the LC effect a 15 Volt process is used. Architecture features include
random row address, large storage capacitor, dedicated light shield, and four metal layers.

The fast liquid crystal effect requires ±6 Volts to achieve proper contrast. To support this voltage requirement a 15 Volt
silicon process is necessary. This “medium voltage” capability is obtained through a thicker gate oxide and additional
implants. In addition to the medium voltage devices, the process also supports standard 5 Volt CMOS logic. The logic is
used for fabrication of the row and column drivers.

The layout of the active matrix is shown schematically in Figure 5. The active pixel array consumes the largest portion of
the device. Each pixel contains a pixel switch, storage capacitor, and overlying aluminum mirror electrode. The column
drivers route the image data onto the columns. On this panel we have integrated the digital to analog converter (DAC). This
allows a digital interface which is both lower in cost and less sensitive to noise. Moreover, there is a direct digital mapping
from video frame memory to the pixel array. Image data is grouped into 8 blocks of 160 columns each. The parallel image
data is stored in buffers and transferred to all columns, one a line at a time. Before driving onto the columns data is level
shifted to the required 15 Volts. The row drivers select the active row. In a departure from a simple sequential shift register,
a random access row decoder is used. In the scrolling color architecture, the row sequence jumps down the panel in 1/3
vertical increments. Row sequence data is generated off chip as a row address signal and the corresponding row is activated
by the row driver.

                              Image Data

                                                                                    5V Column Driver and DAC


                                                                                         15V Column Drive


                             RowAdr
                                                          15V Row Enable
                                           Row decoder




                                                                                             Active matrix
                                                                           (of pixel switch + storage C + mirror electrode)




Figure 5: Schematic of the active matrix layout. Features of the panel architecture include 15 Volt drive, a digital interface
with on-chip DAC, and a random access row decoder.

To comfortably meet requirements for speed, light shielding, and mirrors, four layers of metal were used. Single panel data
rates are relatively high. At a white frame rate of 60 Hz an individual line time is about 4 µs. To achieve high data rates
with reasonable margin we use full metal routing for both column and row lines. We use a third layer of metal for a
dedicated light shield. Projection illumination levels at the device are very high and light has the opportunity to leak
through the mirror electrodes or between pixel gaps and reach the underlying silicon. Light reaching the silicon will
generate unwanted charge carriers that tend to destroy the image. To provide the greatest opportunity for light shielding a
dedicated metal layer is used covering the entire circuitry. The light shield is just below the pixel mirror and is interrupted
only near the center of the pixel to allow electrical contact between the pixel electrode and the pixel switch. Light
transmission of this structure has been measured at 10-10. A fourth metal layer is used for the mirror electrode.

To obtain accurate colors, a large pixel storage capacitor is necessary. The active matrix drives charge onto the pixel
electrode. This charge creates a voltage difference relative to the counter electrode. The liquid crystal material itself has a
capacitance that changes with orientation of the molecules. A given charge is deposited at the pixel and then the liquid
crystal orients with the applied electric field. As molecules re-orient, the change in capacitance of the liquid crystal changes
the voltage applied across the gap. This problem is particularly relevant for color sequential where the information at the
pixel changes rapidly, even for static images.11 To counter this problem a large storage capacitor is required. Fortunately
since the pixel transistor and address lines occupy relatively little area there is good opportunity to add a large storage
capacitor.

A cross section of the pixel area is shown schematically in Figure 6. Metals 1 and 2 are used for routing of the row and
column lines respectively. The row line contacts the gate of the pixel switch. When the row is selected, data on the column
line is driven onto the pixel. The transistor drain, storage capacitor, and mirror electrode are in electrical contact. On top of
the structure 1 micron high spacers are fabricated. These spacers define the liquid crystal gap.

                                    LC Spacer
                                                                                         Mirror Metal
                                                                                         Light Shield
                                                                   Storage
                                          Pixel                    Capacitor             Metal 2
                                          Switch
                                                                                         Metal 1



                                                     Substrate


Figure 6: Schematic of the pixel cross section. The pixel uses four levels of metal for rows, columns, light shield, and mirror
electrode. The structure also features a large storage capacitor and integrated liquid crystal spacers.

The active matrix is fabricated on a standard silicon line up to and including the LC spacers. After silicon fabrication, an
alignment layer is added and the device is finished with a liquid crystal cover glass and cell. Despite the relatively large
area for a silicon chip, the process can have a high yield. The actual transistor density is relatively low. Most of the area is
in the pixel array, which has low transistor density and therefore achieves a high yield. This silicon based approach can
achieve maturity quickly and be a flexible, powerful, and low cost way to construct LCD displays.


                                              5. SYSTEM ELECTRONICS

The function of the electronics is to take input video and data graphics and format the signals as appropriate for the liquid
crystal display. Since we want to study operation of the display system, flexible and powerful electronics were constructed.
The system can be adapted, through software control via a PCI interface, to a host computer and reconfigured through
programming of gate array chips on the system boards. With this system various addressing schemes, inversion modes,
frame rates, and data partitioning can be examined.

A block diagram of the electronics architecture is shown in Figure 7. Functionally the system is partitioned into a video
front end, the scrolling color system (SCS) engine, the panel interface, and control with a target computer. Ancillary
function such as scanner control is also provided. Basic function is to accept video data, and re-format as required by the
LCD and single panel data sequencing. Input sources are full bandwidth video or computer data graphics. From either
source the image data is pre-formatted into 8-bit per color R:G:B data at 108 MHz pixel rate. Image data must be written to
a frame memory since read out to the panel is not in sequence or even synchronous to the input image data. The SCS is the
main functional block of the system. It includes the video frame memory and the processing and control necessary to format
the data. Image data paths are internal to the SCS. The PCI bus interface is used for sending configuration and data control
signals from the target computer which hosts system control software incorporating a graphical user interface.



               multi-format          FRONT END
               video source            (VIDEO)                SCS ENGINE         INTERFACE          DISPLAY


                                        DATA
                                       GRAPHICS
                                                    PCI bus
                                   GUI

                                          TARGET              SCANNER
                                         COMPUTER             CONTROL




                                  Network connection with
                                  development environment
Figure 7: Electronics system block diagram. Input video or data graphics image data is stored in the scrolling color system
(SCS) engine. The SCS creates the proper read out sequence and generates control signals for interfacing to the LCD
display.

The heart of the electronics system is the SCS engine. It maintains broad flexibility through software control over a PCI bus
and primary function execution via programmable Altera FPGAs. The function of the SCS centers on the storage of image
data in frame memory and read out as required by the display system. The frame memory stores R:G:B data 8-bits deep in
an array of 1280x1024 pixels. Read out is controlled by a row, column, and color sequencer (RCC) FPGA. With the RCC,
data is read out with a 1/3 panel delay per color. Row address data is also generated. Data from the frame memory passes to
a color processor where gamma and any additional color corrections are applied. Gamma correction refers to the non linear
transfer between data value and light response at the display. Video signals are often pre-distorted assuming a power law
behavior of a CRT display. The LCD transfer characteristics differ from that of a CRT and are accounted for by appropriate
shaping of the applied gamma response curve. A different gamma curve may be applied for all three colors.


                                           6. SYSTEM CHARACTERISTICS

The previous sections described the system elements of liquid crystal, active matrix, optics, and electronics. In this section
the basic characteristics and operation as a display system are presented. The primary goal was to construct a high
resolution single panel reflective LCD projection display.

In support of this work two different devices were made with pixel separations of 15.2 and 20 microns. The SXGA
(1280x1024) active area diagonals are 1.0” and 1.3”, respectively. While there are differences between the two, the basic
constructions are similar. Two device sizes were studied because of light collection considerations, and to examine parallel
approaches. Cost implications, brightness requirements, application, and potential architecture flexibility make both sizes of
interest. Additionally the silicon active matrix comes from different sources. Arrays with the larger 20 micron pixel size
were made by Philips starting first as a subset arrays operating at full bandwidth. Arrays with the 15.2 micron pixel size
were made by National Semiconductor and started with an analog interface. Optical and electronic hardware were
constructed to support both sizes.

Much of the system performance and characteristics are derived from the LCD display device. Although all elements
presented challenges, the device is the critical component in the display. The characteristics of the reflective LCD are
summarized in Table 1.
                  Image Device                          Reflective LCD on Silicon
                  Pixel Array                           1280 x 1024 (SXGA)
                  Silicon Process                       15 Volt plus 5 Volt CMOS logic
                  Liquid Crystal                        Nematic
                  Cell Gap                              1 micron
                  LC Response                           0.2 ms on time at 50°C
                  Active area (diagonal)                1.3” and 1.0”
                  Pixel Size                            20 micron, and 15.2 micron
                  Gray Scale                            Analog voltage ±6 V
                  Frame Rates                           60-90 Hz Capable x 3 per color
Table 1: Basic characteristics of the display device.

Characteristics of the display system are shown in Table 2. The display is based upon the scrolling color architecture. This
approach has the advantage of maintaining spectral efficiency. The architecture forces a trade between device size and light
collection efficiency. At the device sizes chosen, 1.0” and 1.3”, the impact on light efficiency is important. Notice, however,
that the brightness reduction of 75% is not as extreme as the direct reduction in panel area of 59%. System brightness and
impact of panel size is a function of the lamp. Here we use the 120 Watt Philips UHP projection lamp. This lamp is chosen
for its small arc gap, high brightness, and long life. Further reduction in arc gap will both increase system brightness and
reduce the impact of panel size.

                 Architecture                          Single panel - scrolling color
                 Brightness                            600 lm and 450 lm (1.3” and 1.0” device)
                 Contrast                              200:1
                 Lamp                                  120 Watt Philips UHP
                 F-number                              2.4
                 Video Input                           RGB: Computer SXGA or digital video
                 Gray Scale                            8-bit per color internal
                 Gamma response                        Non-linear function via look up table
Table 2: Characteristics of the single panel projection display system.

The system accepts either computer or video input data. A digital interface accepts 8 bit per color RGB data at a pixel
resolution of 1280x1024. System electronics perform the data partitioning and staggered sequential read out of the scrolling
color architecture. Digital gray scale is converted into an analog voltage, which is sampled and stored at the pixel. A non-
linear gray response (gamma) is incorporated through the use of look up tables, which may be different for each color.

The resulting images are impressive. The combination of high aperture ratio and high pixel resolution produces images that
are sharp, detailed, and smooth. The single panel aspect produces perfect color convergence and maintains image quality
out to the corners. Colors are well saturated. Color and brightness uniformity is good at all gray scales. Notice that even if
there are local brightness variations due to the panel, the variations are the same in all three colors so color uniformity is
easier to achieve. The saturated colors and uniformity of field shows the liquid crystal cell is both fast and uniform.

The system constructed demonstrates that a single panel system is possible with a reflective LCD device. The combination
of the two represents an important direction. The system points a way towards large area displays that are high resolution,
have excellent image performance, and are low cost. In a time when digital information and imagery becomes increasingly
important the display can be a catalyst for substantial activity. Indeed, the ability to bring low cost, high performance
displays to mass markets not only makes consumer applications such as HDTV more important and immediate, but can
impact the way we view and interact with information and entertainment.
                                              7. ACKNOWLEDGMENTS

Clearly the construction of a display system involves the efforts of many people across many areas of expertise. In this paper
I represent a group of creative and dedicated individuals. Among those involved I mention the special contribution of a few
individuals. Peter Janssen is the father of the effort and it is through his persistence and talents that we were able to reach
our goals. Gerard Blom managed and shepherded the project allowing others to concentrate on their own tasks. Leaders of
the major tasks were George Melnik, Niek Lambert, John Dean, and Dave Cohen. Jan Peter Stadler dedicated great effort
towards fabrication of the silicon within Philips. National Semiconductor also produced silicon arrays for the project and
proved to be excellent partners. And many thanks go to all those who contributed their talents and hard work to the project.


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