U.S. patent application number 13/291867 was filed with the patent office on 2013-05-09 for multiple-linear-array mems display chips.
This patent application is currently assigned to Alces Technology, Inc.. The applicant listed for this patent is David M. Bloom, Matthew A. Leone. Invention is credited to David M. Bloom, Matthew A. Leone.
Application Number | 20130114123 13/291867 |
Document ID | / |
Family ID | 48223496 |
Filed Date | 2013-05-09 |
United States Patent
Application |
20130114123 |
Kind Code |
A1 |
Bloom; David M. ; et
al. |
May 9, 2013 |
MULTIPLE-LINEAR-ARRAY MEMS DISPLAY CHIPS
Abstract
Single-chip, multiple-linear-array MEMS form the basis for
high-resolution, high-frame-rate video displays.
Inventors: |
Bloom; David M.; (Jackson,
WY) ; Leone; Matthew A.; (Jackson, WY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bloom; David M.
Leone; Matthew A. |
Jackson
Jackson |
WY
WY |
US
US |
|
|
Assignee: |
Alces Technology, Inc.
Jackson
WY
|
Family ID: |
48223496 |
Appl. No.: |
13/291867 |
Filed: |
November 8, 2011 |
Current U.S.
Class: |
359/292 ;
359/291 |
Current CPC
Class: |
G02B 26/105 20130101;
G02B 26/0841 20130101 |
Class at
Publication: |
359/292 ;
359/291 |
International
Class: |
G02B 26/00 20060101
G02B026/00 |
Claims
1. A light modulator chip comprising: two linear arrays of
micro-electromechanical light modulator elements integrated on the
chip, the arrays parallel to each other and separated from one
another in a direction perpendicular to the longest array
dimension.
2. The chip of claim 1 where movable elements in each array are
addressed by a single layer of wiring that provides direct
connection to each element.
3. The chip of claim 1 where the arrays are offset from one another
in a direction parallel to the longest array dimension.
4. The chip of claim 1 where the light modulator elements are
reflective micro-electromechanical ribbons comprising silicon
nitride.
5. The system of claim 1 further comprising: a third linear array
of micro-electromechanical light modulator elements integrated on
the chip, the third array parallel to the other two and separated
from the other two in a direction perpendicular to the longest
array dimension.
6. The system of claim 5 further comprising: a fourth linear array
of micro-electromechanical light modulator elements integrated on
the chip, the fourth array parallel to the other three and
separated from the other three in a direction perpendicular to the
longest array dimension.
7. A display system comprising: a first light source that
illuminates a single-chip, multiple-linear-array,
micro-electromechanical light modulator; an optical system that
converts light modulated by the multiple-linear-array light
modulator into multiple line images; and, a scan mechanism that
scans the multiple line images simultaneously to form a
two-dimensional image.
8. The system of claim 7, where the multiple-linear-array,
micro-electromechanical light modulator comprises two, and only
two, linear arrays of micro-electromechanical light modulator
elements integrated on the chip.
9. The system of claim 7, where the multiple-linear-array,
micro-electromechanical light modulator comprises three, and only
three, linear arrays of micro-electromechanical light modulator
elements integrated on the chip.
10. The system of claim 7, where the multiple-linear-array,
micro-electromechanical light modulator comprises four, and only
four, linear arrays of micro-electromechanical light modulator
elements integrated on the chip.
11. The system of claim 7 further comprising a second light source
that illuminates the multiple-linear-array light modulator.
12. The system of claim 11 where the first light source is focused
to a first thin strip of light that illuminates a first array of
the multiple-linear-array light modulator and the second light
source is focused to a second thin strip of light that illuminates
a second array of the multiple-linear-array light modulator.
13. The system of claim 12 where the first and second thin strips
of light have different widths.
14. The system of claim 11 further comprising a third light source
that illuminates the multiple-linear-array light modulator.
15. The system of claim 14 where the first light source is focused
to a first thin strip of light that illuminates a first array of
the multiple-linear-array light modulator, the second light source
is focused to a second thin strip of light that illuminates a
second array of the multiple-linear-array light modulator and the
third light source is focused to a third thin strip of light that
illuminates the second array of the multiple-linear-array light
modulator.
16. The system of claim 15 where the second and third thin strips
of light are separated from one another on the second array.
17. A method of displaying a video image having columns of pixels
comprising: providing a display based on a single-chip,
multiple-linear-array, micro-electromechanical light modulator;
and, (a) configuring a first linear array of the single-chip
modulator to modulate a first color component of a first column of
the video image; (b) configuring a second linear array of the
single-chip modulator to modulate a second color component of the
first column of the video image; (c) configuring the first linear
array of the single-chip modulator to modulate the first color
component of a second column of the video image; (d) configuring
the second linear array of the single-chip modulator to modulate a
third color component of the second column of the video image; and,
(e) for successive columns after the second, alternately
configuring the second linear array of the single-chip modulator to
modulate the second and third color components on a column by
column basis.
18. A method of displaying a video image having columns of pixels
comprising: providing a display based on a single-chip,
multiple-linear-array, micro-electromechanical light modulator;
and, for each frame of video data: (a) configuring a first linear
array of the single-chip modulator to modulate a first color
component of a first column of the video image; (b) configuring a
second linear array of the single-chip modulator to modulate a
second color component of the first column of the video image; (c)
configuring the first linear array of the single-chip modulator to
modulate the first color component of a second column of the video
image; (d) configuring the second linear array of the single-chip
modulator to modulate a third color component of the second column
of the video image; (e) for successive columns after the second,
alternately configuring the second linear array of the single-chip
modulator to modulate the second and third color components on a
column by column basis; and, (f) repeating steps (a) through (e)
with the roles of the second and third color components
reversed.
19. A method of displaying a video image having columns of pixels
comprising: providing a display based on a single-chip,
multiple-linear-array, micro-electromechanical light modulator;
and, for each column of video data: (a) configuring a first linear
array of the single-chip modulator to modulate a first color
component of the column of the video image during a column time;
(b) configuring a second linear array of the single-chip modulator
to modulate a second color component of the column of the video
image during a first part of the column time; and, (c) configuring
the second linear array of the single-chip modulator to modulate a
third color component of the column of the video image during a
second part of the column time.
Description
TECHNICAL FIELD
[0001] The disclosure is generally related to linear-array MEMS
(micro-electromechanical systems) display chips.
BACKGROUND
[0002] Linear arrays of miniature light modulators form the basis
for a broad family of MEMS-based video displays. These displays
form line images that are swept back and forth to "paint"
two-dimensional scenes. FIGS. 1A-1C show display system concepts
for a linear array MEMS display.
[0003] In FIGS. 1A-1C, light source 105 illuminates MEMS linear
array 115 through lens 110. Array 115 is shown schematically, and
enlarged, in inset 120. Elements 116, 117 and 118 are just a few of
the light modulator elements that form the array. Array 115 may
operate in transmission or reflection. For example, one type of
linear array light modulator is formed from thousands of reflective
micro-electromechanical ribbons arranged in a single column.
[0004] Array 115 imparts phase information onto a narrow strip of
light. Optical system 125 then converts the phase information into
amplitude variations to form a line image. Scan mirror 130 scans a
line image 135 across a screen such as screen 140 shown in FIG. 1B.
The line image is scanned fast enough that the scanning motion is
not noticeable to the human eye. Scanned line images on screen 140
provide a full video experience.
[0005] Optical system 125 may take different forms which are
complementary to different methods of encoding phase information
with array 115. Some examples of such optical systems are presented
in U.S. Pat. No. 7,054,051 ("Differential interferometric light
modulator and image display device"), U.S. Pat. No. 7,286,277
("Polarization light modulator") and U.S. Pat. No. 7,940,448
("Display system").
[0006] One of the properties of MEMS light modulators which enables
their use in linear array display systems like that of FIGS. 1A-1C
is their high speed. The two-dimensional image formed on screen 140
is updated many times per second, and each two-dimensional image is
formed by successive line images, each different from the next. A
change from one line image to another requires reconfiguring linear
array elements. The time available to do this is called a "column
time". High resolution video displays put extreme requirements on
MEMS switching speed as the column time available is short.
[0007] Consider, for example, a "4K" video display having 4096
columns by 2160 rows of pixels. If the display operates at 196
frames per second, and is reconfigured to display red, green and
blue information sequentially on a column by column basis, then the
amount of time that the linear array remains in any particular
configuration is only a few hundred nanoseconds.
[0008] As resolution requirements become even greater and the
desired number of frames of video information per second also
increases, the time available to reconfigure a linear array for
each new column (i.e. each new line image) becomes a limiting
factor. Of course, in the example above, one could turn the display
chip on its side and use an array with 4096 elements to generate
2160 columns, but that strategy requires a display chip twice as
long, using up valuable wafer real estate.
[0009] Hence, what are needed are linear-array MEMS display chips
that can provide high-resolution, high-frame rate video.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIGS. 1A-1C show display system concepts for a linear array
MEMS display.
[0011] FIGS. 2A and 2B show display system concepts for a
multiple-linear-array MEMS display.
[0012] FIG. 3 shows a double-linear-array MEMS light modulator
chip.
[0013] FIGS. 4A-4C show MEMS ribbon modulators.
[0014] FIG. 5 shows a single-layer wiring scheme for a
double-linear-array MEMS light modulator chip.
[0015] FIGS. 6A and 6B show along-array offsets for a
double-linear-array MEMS light modulator chip.
[0016] FIG. 7 shows a triple-linear-array MEMS light modulator
chip.
[0017] FIG. 8 shows a quadruple-linear-array MEMS light modulator
chip.
[0018] FIG. 9 shows a single-layer wiring scheme for a
quadruple-linear-array MEMS light modulator chip.
[0019] FIG. 10 illustrates a first timing scheme for sending column
data to a double-linear-array MEMS light modulator chip.
[0020] FIG. 11 illustrates a second timing scheme for sending
column data to a double-linear-array MEMS light modulator chip.
[0021] FIG. 12 illustrates pixel width adjustments.
[0022] FIG. 13 illustrates a third timing scheme for sending column
data to a double-linear-array MEMS light modulator chip.
[0023] FIG. 14 illustrates an illumination scheme for a
double-linear-array MEMS light modulator chip.
DETAILED DESCRIPTION
[0024] Multiple-linear-array MEMS display chips, and methods for
operating them, are described below. Chips that have more than one
linear array light modulator offer a way to build single-chip,
high-resolution display systems. Multiple linear arrays on a single
chip also lead to better optical power handling, higher display
brightness and wider color gamut.
[0025] Double-linear-array chips may be used to improve resolution
in monochrome or full color displays. Along-array offsets between
two arrays may be used to improve resolution in monochrome
displays, for example. When three-color illumination is used, one
array modulates one of the three colors, while the second array
modulates the other two colors. Humans have better visual acuity
at, and are more sensitive to, green than red or blue. Hence a
double-linear-array chip may use one array to modulate green and
the other array to modulate red and blue.
[0026] A triple-linear-array chip provides one array for each of
three illumination colors while a quadruple-linear-array chip may
be illuminated by four colors for a wider color gamut, higher
brightness, or both. Single-level wiring schemes for double-,
triple-, and quadruple-linear-array chips mean that only layout,
rather than process flow, changes are required to transition from
single- to multiple-linear-array chip production.
[0027] Displays based on linear-array light modulators produce line
images. The line images are scanned to produce what appears to
human observers to be two-dimensional images with rows and columns
of pixels. As a line image is scanned from one column position to
the next, the linear array light modulator changes configuration to
create the new column of pixels.
[0028] When line images from two or more linear-array light
modulators are scanned by a single scan mirror, the line images are
separated in the resulting apparent two-dimensional image. A signal
delay may be applied to column data for different colors to
compensate for the spatial separation of arrays on a multi-array
chip. Similarly, when one array modulates two colors, the delay
between the time that the array is configured for the first and
second colors leads to a separation of the corresponding line
images. Separating illumination light on the linear array can
compensate for this effect so that columns of each color are lined
up in a two-dimensional image.
[0029] Various methods for operating multiple-linear-array display
chips offer tradeoffs among resolution and available column time,
among other parameters. In some cases two arrays are used to
modulate three colors, for example. One way to have a single array
modulate both red and blue information is to have the line image
from that array alternate between red and blue columns. This omits
half of the red and blue information from displayed images, but
surprisingly the omission may not be particularly noticeable.
[0030] These and other aspects of multiple-linear-array MEMS
display chips are now discussed in greater detail. FIGS. 2A and 2B
show display system concepts for a multiple-linear-array MEMS
display. FIGS. 2A and 2B are similar to FIGS. 1A-1C except that the
display system of FIGS. 2A and 2B includes a multiple-linear-array
MEMS light modulator chip.
[0031] In FIG. 2A, light source 205 illuminates MEMS
multiple-linear-arrays 215 through lens 210. Optional light source
206 illuminates MEMS multiple-linear-arrays 215 through lens 211.
Additional light sources, not shown, may also illuminate MEMS
multiple-linear-arrays 215. Examples of multiple-linear-arrays 215
are discussed in detail below, especially in connection with FIGS.
3-8. Such arrays may operate in transmission or reflection;
however, most of the discussion is in terms of linear arrays of
reflective MEMS ribbons.
[0032] Multiple-linear-arrays 215 impart phase information onto
narrow strips of light. Optical system 225 then converts the phase
information into amplitude variations to form line images. Scan
mirror 230 scans line images, e.g. 235, 236, across a screen such
as screen 240 shown in FIG. 2B. The line images are scanned fast
enough that the scanning motion is not noticeable to the human eye.
Scanned line images on screen 240 provide a full video
experience.
[0033] Optical system 225 may take different forms which are
complementary to different methods of encoding phase information
with arrays 215. Some examples of such optical systems are
presented in U.S. Pat. No. 7,054,051 ("Differential interferometric
light modulator and image display device"), U.S. Pat. No. 7,286,277
("Polarization light modulator") and U.S. Pat. No. 7,940,448
("Display system").
[0034] Line images 235, 236 from arrays 215 appear separated on
screen 240 by an amount labeled ".delta..times." in the figure. At
any given time line images 235 and 236 represent different columns
of a two-dimensional image that appears on screen 240. Therefore
image data corresponding to a single column of a two-dimensional
image is sent to different linear arrays in a multi-array system at
different times.
[0035] FIG. 3 shows a double-linear-array MEMS light modulator chip
305. Chip 305 includes two linear arrays, 310 and 315, of MEMS
light modulator elements such as elements 321, 322 and 323. The
elements of the arrays may be reflective or transmissive light
modulators such as liquid crystals or MEMS mirrors have either
piston or tilt motion; however, most of the discussion of array
elements is directed toward reflective MEMS ribbons such as those
discussed in connection with FIG. 4 below. Only a few dozen
elements per array are shown in FIG. 3; however, actual arrays may
have as many as several thousand elements.
[0036] In FIG. 3, linear arrays 310 and 315 are separated from one
another by a distance, W, in the y direction, perpendicular to the
longest array dimension. Array separation W is larger than one
pixel and leads to separation between line images scanned from chip
305. This is shown as 5.times. in FIG. 2B. In fact, W=5.times. when
both are measured in image pixels.
[0037] FIGS. 4A-4C show MEMS ribbon modulators that may be used as
the elements of arrays such as 310 and 315. These ribbon modulators
change the phase of light reflected from them depending on voltage
applied between the ribbon and a substrate. FIGS. 4A and 4B show a
MEMS ribbon modulator in relaxed and deflected states,
respectively. FIG. 4C shows a MEMS ribbon structure that does not
deflect even when a voltage is applied to it.
[0038] In FIG. 4A MEMS ribbon 405 is supported at its ends by
support posts 415 over substrate 410. Several processes for
creating MEMS ribbons have been described elsewhere. Typical
ribbons are etched from a layer of silicon nitride and made highly
reflective by coating with aluminum. A typical ribbon may be
between about 50 .mu.m and about 500 .mu.m long, between about 1
.mu.m and about 20 .mu.m wide, and between about 0.05 .mu.m and 2
.mu.m thick although these dimensions may vary significantly.
Arrows 420 represent light reflecting from the surface of ribbon
405.
[0039] FIG. 4B shows the ribbon of FIG. 4A with addition of voltage
source 430 which creates a potential difference between ribbon 405
and substrate 410. A voltage applied between ribbon and substrate
causes the ribbon to deflect toward the substrate by an amount
.DELTA.z, as shown in the figure. The phase of light reflected by
ribbon 405 in its deflected state (FIG. 4B) versus its relaxed
state (FIG. 4A) is given by where .phi. is the phase, .DELTA.z is
the ribbon deflection and .lamda. is the wavelength of light. Phase
modulation caused by ribbon deflection is converted to amplitude
modulation by an optical system such as 225 in FIG. 2A.
[0040] FIG. 4C shows a ribbon similar to that of FIGS. 4A and 4B
with the exception of additional support posts 440. Additional
support posts 440 prevent ribbon 435 from deflecting even when a
voltage is applied between the ribbon and the substrate by voltage
source 430. As discussed below in connection with FIG. 9,
supported, fixed ribbons like 435 in FIG. 4C may be used as
conductors to carry voltages to other ribbons in single-layer
wiring schemes for multiple-linear-array chips.
[0041] FIG. 5 shows a single-layer wiring scheme for a
double-linear-array MEMS light modulator chip. In FIG. 5, linear
array A1 includes ribbons that appear within dashed rectangle 505
while linear array A2 includes ribbons that appear within dashed
rectangle 510. (The spacing between ribbons in the arrays shown in
FIG. 5 is exaggerated for clarity.) Every other ribbon is arrays A1
and A2 is connected to a bias voltage, V.sub.BIAS. The remaining
ribbons are connected to individual signal lines that carry
voltages V.sub.1,0, V.sub.1,1, V.sub.2,0, etc. Here V.sub.x,y is a
signal for ribbon Y in array AX. Each ribbon connected to an
individual signal line can be deflected independently, while those
connected to V.sub.BIAS move together. The single layer wiring
scheme permits fabrication of double-linear-arrays on chips using
processes designed for single linear arrays. Only layout, rather
than process flow, changes are required as all wiring is created in
the same process step. The single layer wiring scheme provides a
direct connection to each passive ribbon without switching or
multiplexing elements.
[0042] FIGS. 6A and 6B show along-array offsets for a
double-linear-array MEMS light modulator chip. In FIG. 6A, arrays
A1 and A2 include ribbons enclosed by dashed rectangles 605 and
610, respectively. In FIG. 6B, arrays A3 and A4 include ribbons
enclosed by dashed rectangles 615 and 620, respectively.
[0043] Arrays A1 and A2 are offset from each other, in the
direction of the longest array dimension, by an amount .DELTA.x
equal to one-half the ribbon pitch, p/2. Arrays A3 and A4 are
offset by one ribbon pitch, p. Along-array offsets such as those
depicted in FIGS. 6A and 6B may be used in some multi-linear-array
chips as a way of increasing image resolution. A pair of offset
arrays can be used to increase the resolution of a single array in
the direction of the longest array dimension by doubling the number
of addressable points in an image.
[0044] FIGS. 7 and 8 show triple- and quadruple-linear array MEMS
light modulator chips, respectively. The chips shown in FIGS. 7 and
8 are similar to the double-linear-array chip of FIG. 3 except for
the increased number of arrays.
[0045] In FIG. 7, triple-linear-array chip 705 includes three
linear arrays, 710, 715 and 720, while in FIG. 8
quadruple-linear-array chip 805 includes four linear arrays, 810,
815, 820 and 825. All of the arrays of the triple- and
quadruple-linear-array chips contain light modulator elements as
discussed in connection with FIG. 3. The elements of the arrays may
be reflective or transmissive light modulators such as liquid
crystals or MEMS mirrors have either piston or tilt motion;
however, most of the discussion of array elements is directed
toward reflective MEMS ribbons such as those discussed in
connection with FIG. 4. Only a few dozen elements per array are
shown; however, actual arrays may have as many as several thousand
elements.
[0046] Triple- and quadruple-linear-array chips may include single
layer wiring schemes which permit their fabrication using processes
designed for single linear arrays. Only layout, rather than process
flow, changes are required. As an example, FIG. 9 shows a
single-layer wiring scheme for a quadruple-linear-array MEMS light
modulator chip.
[0047] In FIG. 9, linear array A1 includes ribbons that appear
within dashed rectangle 905, and linear arrays A2, A3 and A4
include ribbons that appear within dashed rectangles 910, 915 and
920, respectively. (The spacing between ribbons in the arrays shown
in FIG. 9 is exaggerated for clarity.)
[0048] In FIG. 9, unfilled rectangles, such as 930, represent
ribbons that may be deflected by applying a voltage between them
and the chip substrate, as shown, e.g. in FIG. 4B. Shaded
rectangles, such as 925, represent ribbons that do not deflect when
a voltage is applied between them and the chip substrate, as shown,
e.g. in FIG. 4C. The non-deflecting ribbons in arrays A1 and A4 are
used as conductors to carry voltages to deflecting ribbons in
arrays A2 and A3. This means that every other ribbon in each of
arrays A1-A4 can be individually addressed and made to deflect in
response to an applied voltage. These ribbons are connected to
individual signal lines that carry voltages V.sub.1,0, V.sub.1,1,
V.sub.2,0, etc. Here V.sub.x,y is a signal for moveable ribbon Y in
array AX. A single layer wiring scheme for a triple-linear-array
may be realized by deleting either array A2 or A3 from FIG. 9.
[0049] Double-, triple- or quadruple-linear-arrays of MEMS light
modulators may thus be fabricated on a single chip using processes
developed for single linear array chips. Arrays on a single chip
are spaced apart from each other in the y direction (see FIG. 3) by
many pixels, often one hundred or more. The array spacing leads to
spacing between line images that are scanned to form a
two-dimensional image. Effects of this spacing may be compensated
by introducing a delay between array configurations for a single
column in a two-dimensional image. For example if one array on a
chip modulates red line images while another array modulates green
line images, then red and green data for a single column in an
image with red and green components should be modulated at
different times by the two arrays.
[0050] Arrays on a single chip may also be offset from each other
in the x direction (see FIGS. 3, 6A and 6B). Such offsets may be
used to improve image resolution. Whether to offset by one-half or
one ribbon pitch depends on the type of modulation performed by the
arrays and the type of optical system used to convert that
modulation into line images.
[0051] A single chip with multiple-linear-arrays per chip may be
used as part of a high-resolution monochrome or color display.
Choices related to how each array of a multiple-linear-array chip
is used affect the available column time for each array. The
available column time is the length of time during which a linear
array of MEMS modulators is configured for one column of image
data. After one column time, the MEMS linear array is reconfigured
for the next column of image data.
[0052] As an example, if the number of columns to be shown in a
two-dimensional image is multiplied by X, then the available column
time is divided by X. Showing an image with twice as many columns
leaves half the time available to display each one, all other
things being equal. Thus MEMS arrays must work faster to display
images having more columns of image pixels. More rows of image
pixels may be obtained by using linear arrays containing more
modulator elements.
[0053] If the number of frames of image data shown per second is
multiplied by Y, then the available column time is divided by Y.
Frames are still images that form a video when shown in rapid
succession. Image data, such as the location of objects in an
image, may change from frame to frame.
[0054] Available column time is reduced by scanner duty factor. A
scan mirror, such as 230 in FIGS. 2A and 2B, normally requires a
short time to return to a starting position after each scan. Time
used up for this "flyback" reduces the available column time. The
delay between column data sent to different arrays, which is used
to compensate for the arrays' separation in the y direction (e.g. W
in FIG. 3), also reduces the available column time.
[0055] Available column time is reduced by a factor of three when a
single linear array is used to modulate red, green and blue light
sequentially for each column in a color display when compared to
modulating only one color for a monochrome display. Using two,
three or four linear arrays to modulate different colors is a way
to increase the available column time. Multiple-linear-arrays per
chip can make a single-chip, high-resolution, color video display
feasible given limits on the amount of time required to reconfigure
MEMS light modulator elements.
[0056] FIG. 10 illustrates a first timing scheme for sending column
data to a double-linear-array MEMS light modulator chip. In this
"drop" timing scheme one array of a double-linear-array chip
modulates one color while the other array modulates two other
colors. A common example is one array dedicated to green with the
other dedicated to red and blue.
[0057] In FIG. 10, time axis 1005 is marked in units of column
time. The column time is determined by factors such as number of
columns displayed in a two-dimensional video image, number of video
frames per second, scanner flyback time (or duty factor), and array
separation on chip.
[0058] In the timing scheme of FIG. 10, one array of a double-array
chip is dedicated to green. Boxes marked "G1", "G2", etc. represent
green line image data sent to this "green" array that modulates
green light. Image data for the green component of one column of a
two-dimensional video image is represented by "G1". The green array
is configured according to this data during the first column time.
During the second column time, the green array is configured
according to the "G2" data for the green component of the next
column of the video image.
[0059] During column time 1, the other array of the double-array
chip is configured with line image data "R1" which represents the
red component of one column of a two-dimensional video image. The
"red/blue" array is illuminated with red light during this time.
During column time 2, the red/blue array is configured with line
image data "B2" which represents the blue component of the next
column of the two-dimensional video image.
[0060] In the timing scheme of FIG. 10, the green component of
every column in a video image is displayed, but only the red or
blue component of every other column is displayed. The red
component of column 2 and the blue component of column 3 are
dropped, for example. This means that the horizontal resolution of
the red and blue components of the video image is only half that of
the green component. However, human visual acuity is greater for
green than for red or blue, so the perceived image quality may
still be acceptable. When compared to a single array modulating
red, green and blue sequentially for each column, the "drop" timing
scheme of FIG. 10 provides almost three times longer available
column time. For a given MEMS modulator technology, e.g. reflective
ribbon modulators, this leads to the ability to display a higher
resolution or higher frame rate color image with a
double-linear-array chip.
[0061] FIG. 11 illustrates a second timing scheme for sending
column data to a double-linear-array MEMS light modulator chip. In
the scheme represented by FIG. 11, red and blue columns are
interlaced. Each frame of a video image is divided into two fields.
In the first field red and blue columns are shown in order: red,
blue, red, blue. In the second field, the order is reversed: blue,
red, blue, red.
[0062] In FIG. 11, the first of two fields in a video frame is
"FIELD 1" 1105 while the second is "FIELD 2" 1110. Within each
field dark (e.g. 1115) and light (e.g. 1120) stripes represent red
and blue column information, respectively. The order of red and
blue columns is reversed from FIELD 1 to FIELD 2. The timing scheme
of FIG. 11 provides better red/blue horizontal resolution than the
scheme of FIG. 10; however, the available column time is reduced by
a factor of two.
[0063] The drop and interlacing timing schemes of FIGS. 10 and 11
may lead to red or blue flicker in some cases. FIG. 12 illustrates
pixel width adjustments which are one way to make flicker less
noticeable. In FIG. 12, grid 1205 represents six columns of pixels
in a video image. Pixels 1210 and 1215 are shaded for emphasis. The
height of all pixels is the same. The width of green pixels is
shown by "green width". Pixel width adjustments for red or blue
pixels make these pixels wider than the green pixels without
changing the spacing between pixels. Since alternate columns of red
or blue pixels are dropped in the schemes of FIGS. 10 and 11, red
and blue pixels may be made up to twice as wide as green ones. This
is indicated by "red, blue width" and "2.times. green width" which
is the maximum width for a wide red or blue pixel.
[0064] Pixel width adjustments may be made by changing the focus of
illumination light on a linear array of light modulators. Lenses
210 and 211 in FIG. 2A, for example, may be used to make such
adjustments. Pixel width adjustments do not affect the available
column time.
[0065] FIG. 11 illustrated how columns in a video display may be
interlaced by showing red and blue information for different
columns in successive fields of a video frame. Rows may also be
interlaced to increase image resolution. For row interlacing, a
video frame is divided into two fields offset from one another by
half a pixel in the vertical direction, parallel to the columns.
The two fields are displayed sequentially and the available column
time is reduced by a factor of two.
[0066] Row interlacing may be achieved by slightly tilting a scan
mirror (e.g. mirror 230 in FIGS. 2) or a modulator chip from one
field to the next. Row interlacing may be combined with any
combination of the drop, column interlacing or wide pixel
techniques described above.
[0067] FIG. 13 illustrates a third timing scheme for sending column
data to a double-linear-array MEMS light modulator chip. In this
scheme, no color information is dropped, but the column time
available for the red/blue modulator is half that for the green
modulator. FIG. 13 is similar to FIG. 10; time axis 1305 is marked
in units of column time. In FIG. 13, however, a red line image is
displayed for the first half of each green column time and a blue
line image is displayed for the second half. The "red, blue" row in
the figure shows red information for column 2 displayed during the
first half of column time 2 and blue information for column 2
displayed during the second half of column time 2.
[0068] In the timing scheme of FIG. 13, a red line image for each
column is displayed before a blue line image for the same column.
These images will be separated from one another because they are
generated at different times just as line images 235, 236 from
different arrays are separated in FIG. 2B. In the case of the
timing scheme of FIG. 13, called "red/blue sequential" timing,
however, the separation is small, usually just a few pixels.
[0069] FIG. 14 illustrates an illumination scheme for a
double-linear-array MEMS light modulator chip that removes the
red/blue separation when red/blue sequential timing is used. FIG.
14 shows two linear arrays A1 1405 and A2 1410 of a
double-linear-array chip. Similar to the arrays discussed in
connection with, e.g. FIG. 3 above, each array contains as many as
several thousand modulator elements. Array A1 is illuminated with a
thin stripe of green light 1415 while array A2 is illuminated with
a thin stripe of red light 1420 and a thin stripe of blue light
1425.
[0070] The separation between arrays A1 and A2 is W, while the
separation between the red and blue stripes of light is Y. If the
delay between red and blue line images in a red/blue sequential
timing scheme is a certain number of pixels, then the spacing Y
between red and blue illumination stripes on array A2 can be
adjusted by the same number of pixels to superimpose red and blue
line images. The red/blue delay and corresponding spacing Y, may be
less than one pixel size.
[0071] Array A2 may be thought of as two arrays separated by Y with
each array available only half the time. Red/blue sequential timing
with a double-linear-array chip increases the available column time
by about 40% compared to using one array for red, blue and green
sequential column color. Given a fixed MEMS modulator
reconfiguration time, this increase in available column time can be
used to increase the number of columns in a video image, the frame
rate, or both.
[0072] MEMS light modulator chips having multiple linear arrays of
light modulators offer a way to produce high-resolution, high-frame
rate video from a single-chip display system. Various timing
schemes may be used to display three colors using two linear
arrays. Similar methods may be used to display four colors using
three linear arrays, for example. The specific methods used depend
on color and resolution requirements of each potential
application.
[0073] Although many of the examples above are presented in terms
of one array in a double-array chip handling green while the other
handles red and blue, different colors may be assigned to different
arrays. Multiple-linear-array chips may also be used to improve
resolution of monochrome displays.
[0074] The above description of the disclosed embodiments is
provided to enable any person skilled in the art to make or use the
disclosure. Various modifications to these embodiments will be
readily apparent to those skilled in the art, and the principles
defined herein may be applied to other embodiments without
departing from the scope of the disclosure. Thus, the disclosure is
not intended to be limited to the embodiments shown herein but is
to be accorded the widest scope consistent with the principles and
novel features disclosed herein.
* * * * *