U.S. patent application number 12/074093 was filed with the patent office on 2009-07-16 for display system comprising a mirror device with micromirrors controlled to operate in intermediate oscillating state.
Invention is credited to Kazuma Arai, Taro Endo, Fusao Ishii, Yoshihiro Maeda.
Application Number | 20090179837 12/074093 |
Document ID | / |
Family ID | 39738596 |
Filed Date | 2009-07-16 |
United States Patent
Application |
20090179837 |
Kind Code |
A1 |
Endo; Taro ; et al. |
July 16, 2009 |
Display system comprising a mirror device with micromirrors
controlled to operate in intermediate oscillating state
Abstract
A display system includes a spatial light modulator for
displaying an image by the modulation state of a plurality of
micromirrors, and a control device for controlling the spatial
light modulator. The control device includes a data conversion
device for converting all or a part of the digital image data input
to the display system into non-binary data, and a
modulation-control device for generating a modulation control
signal for micromirrors depending on the non-binary data, and a
modulation-control device for controlling the spatial light
modulator. The modulation state of the micromirrors by the
modulation control signal includes modulation by oscillation of the
micromirrors. The modulation-control device controls a voltage
value of the modulation control signal to be applied to the driving
electrode of the micromirror such that the amplitude of the
oscillation can be smaller than the maximum amplitude of the
micromirrors in the modulation by the oscillation of the
micromirrors.
Inventors: |
Endo; Taro; (Tokyo, JP)
; Maeda; Yoshihiro; (Tokyo, JP) ; Arai;
Kazuma; (Tokyo, JP) ; Ishii; Fusao; (Menlo
Park, CA) |
Correspondence
Address: |
Bo-In Lin
13445 Mandoli Drive
Los Altos Hills
CA
94022
US
|
Family ID: |
39738596 |
Appl. No.: |
12/074093 |
Filed: |
March 1, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60904565 |
Mar 2, 2007 |
|
|
|
Current U.S.
Class: |
345/84 |
Current CPC
Class: |
H04N 2005/7466 20130101;
G09G 3/346 20130101; G09G 2310/06 20130101; G09G 3/2029 20130101;
H04N 5/7458 20130101; G09G 2320/0266 20130101 |
Class at
Publication: |
345/84 |
International
Class: |
G09G 3/34 20060101
G09G003/34 |
Claims
1. A display system, comprising: a light source; a spatial light
modulator having a plurality of micromirrors and forming an image
to be displayed from a light from said light source; and a control
device controlling said spatial light modulator, wherein said
control device comprising a modulation-control device generating a
modulation control signal for said plurality of micromirrors
depending on a digital image data input to the display system, and
controlling said spatial light modulator; a modulation state of
said micromirrors by said modulation control signal includes
modulation by oscillation of said micromirrors; and said
modulation-control device controls a plurality of voltage value to
be applied to a driving electrode of said micromirror so that said
amplitude of said oscillation can be equal to or smaller than the
maximum amplitude of said micromirrors. wherein a number of said
voltage value is at least three.
2. The display system according to claim 1, wherein said control
device comprises a data conversion device converting a part or all
of said digital image data into a non-binary data; and said
modulation-control device generates a modulation control signal of
said micromirrors depending on said non-binary data, and controls
said spatial light modulator.
3. The display system according to claim 1, wherein said modulation
control signal controls an offset voltage to be applied to said
micromirror.
4. The display system according to claim 3, wherein said offset
voltages are a plurality of different voltage values.
5. The display system according to claim 1, wherein a time duration
for applying said voltage value to a driving electrode is shorter
than a quarter of said oscillation period of said micromirrors.
6. The display system according to claim 1, wherein a time duration
for applying said voltage value to a driving electrode is shorter
than a quarter of a least significant bit (LSB) period for control
of said micromirrors.
7. The display system according to claim 1, wherein said
oscillation having said amplitude includes free oscillation which
decreases its amplitude with time.
8. The display system according to claim 1, wherein a time duration
in which said oscillation is repeated is longer than one
oscillation period of said micromirrors.
9. The display system according to claim 1, wherein a number of
times at which said oscillation of said micromirrors is repeated in
said time duration is two times or more in one frame period of said
digital image data.
10. The display system according to claim 1, wherein said
modulation-control device generates the modulation control signal
to perform modulation by said oscillation of the micromirrors based
on at least 1-bit data other than a most significant bit (MSB) in a
plurality of bits forming said digital image data input to said
display system.
11. The display system according to claim 1, wherein an oscillating
state having an amplitude equal to or smaller than the maximum
amplitude of said micromirrors is controlled to turn from an ON
state of said micromirrors.
12. The display system according to claim 1, wherein an oscillating
state having an amplitude equal to or smaller than the maximum
amplitude of said micromirrors is controlled to turn from an OFF
state of said micromirrors.
13. The display system according to claim 1, wherein an oscillating
state having an amplitude equal to or smaller than the maximum
amplitude of said micromirrors is controlled to turn to an ON state
of said micromirrors.
14. The display system according to claim 1, wherein an oscillating
state having an amplitude equal to or smaller than the maximum
amplitude of said micromirrors is controlled to turn to an OFF
state of said micromirrors.
Description
BACKGROUND
[0001] 1. Field of Invention
[0002] The present invention relates to a display technique, an
efficient technique applied to a display system for representing
gray scale using a display device having a plurality of
micromirrors.
[0003] 2. Prior Art
[0004] As disclosed by the patent document 1, there has been a well
known technique of displaying a projected picture by performing
pulse width modulation (PWM) control based on the digital picture
data using a display device such as a DMD (digital mirror device)
etc. having a plurality of micromirrors.
[0005] That is, optical modulation is performed depending on the
digital picture data by balancing the incoming light from a light
source to each micromirror between two states, that is, an ON state
in which the incoming light is reflected toward a projective
optical system and an OFF state in which the incoming light
deviates from the projective optical system.
[0006] In this case, the brightness of each pixel of a projected
picture depends on the total length of time in which each
micromirror stays in the ON state in each frame period of the
picture. Therefore, there has been the technological problem of an
increasing amount of digital picture data to be processed in one
frame period, and a higher speed of modulation-controlling a mirror
into the ON state in order to represent more delicate gray
scale.
[0007] Therefore, to represent delicate gray scale without
increasing the speed of modulation-controlling a micromirror into
the ON state, it is necessary to increase or decrease the quantity
of light of a light source in addition to the modulation-control by
balancing the micromirror in the DMD as disclosed by the patent
document 2, thereby complicating the controlling operation.
[0008] [Patent Document 1] U.S. Pat. No. 5,287,096
[0009] [Patent Document 2] U.S. Pat. No. 5,589,852
SUMMARY
[0010] An advantage of the present invention is to realize more
delicate gray scale in the picture display using a spatial light
modulation element to display a picture depending on the modulation
state of a plurality of micromirrors without increasing the speed
of modulation-controlling the micromirrors into the ON state.
[0011] Another advantage of the present invention is to realize
more delicate gray scale in the picture display using a spatial
light modulation element to display a picture depending on the
modulation state of a plurality of micromirrors without complicated
control of the quantity of light of a light source or an additional
circuit.
[0012] The present invention provides a display technology for
realizing the intermediate oscillation by applying a plurality of
voltages to a driving electrode of micromirror, or applying an
offset voltage to the potential of the micromirror.
[0013] The first aspect of the present invention is a display
system including: a light source; a spatial light modulation
element having a plurality of micromirrors and forming an image to
be displayed from the light from the light source by modulating the
plurality of micromirrors; and a control device for controlling the
spatial light modulation element. With the configuration, the
control device includes a modulation-control device for generating
a modulation control signal for the plurality of micromirrors
depending on the digital picture data input to the display system,
and controlling the spatial light modulation element; the
modulation state of the micromirrors by the modulation control
signal includes the modulation by the oscillation of the
micromirrors; and the modulation-control device controls a voltage
value of the modulation control signal to be applied to a driving
electrode of the micromirror so that the amplitude of the
oscillation can be equal to or smaller than the maximum amplitude
of the micromirrors in the modulation by the oscillation of the
micromirrors, wherein a number of said voltage value is at least
three.
[0014] The second aspect of the present invention is based on the
display system according to the first aspect. The control device
includes a data conversion device for converting a part or all of
the digital picture data input to the display system into
non-binary data; and the modulation-control device generates a
modulation control signal of the micromirrors depending on the
non-binary data, and controls the spatial light modulation
element.
[0015] The third aspect of the present invention is based on the
display system according to the first aspect. In the display
system, the modulation control signal controls an offset voltage to
be applied to said micromirror.
[0016] The fourth aspect of the present invention is based on the
display system according to the third aspect. In the display
system, the offset voltages are a plurality of different voltage
values.
[0017] The fifth aspect of the present invention is based on the
display system according to the first aspect. In the display
system, a time duration for applying the voltage value to a driving
electrode is shorter than a quarter of the free oscillation period
of the micromirrors.
[0018] The sixth aspect of the present invention is based on the
display system according to the first aspect. In the display
system, a time duration for applying the voltage value to a driving
electrode is shorter than a quarter of a least significant bit
(LSB) period for control of the micromirrors.
[0019] The seventh aspect of the present invention is based on the
display system according to the first aspect. In the display
system, the oscillation having the amplitude includes free
oscillation which decreases its amplitude with time.
[0020] The eighth aspect of the present invention is based on the
display system according to the first aspect. In the display
system, a time duration in which the oscillation is repeated is
longer than one oscillation period of the micromirrors.
[0021] The ninth aspect of the present invention is based on the
display system according to the first aspect. In the display
system, a number of times at which the oscillation of the
micromirrors is repeated in a time duration is two times or more in
one frame period of the digital image data.
[0022] The tenth aspect of the present invention is based on the
display system according to the first aspect. In the display
system, the modulation-control device generates a modulation
control signal to perform modulation by the oscillation of the
micromirrors based on at least 1-bit data other than an MSB in a
plurality of bits forming the digital picture data input to the
display system.
[0023] The eleventh aspect of the present invention is based on the
display system according to the first aspect. In the display
system, an oscillating state having an amplitude equal to or
smaller than the maximum amplitude of the micromirrors is
controlled to turn from an ON state of the micromirrors.
[0024] The twelfth aspect of the present invention is based on the
display system according to the first aspect. In the display
system, an oscillating state having an amplitude equal to or
smaller than the maximum amplitude of the micromirrors is
controlled to turn from an OFF state of the micromirrors.
[0025] The thirteenth aspect of the present invention is based on
the display system according to the first aspect. In the display
system, an oscillating state having an amplitude equal to or
smaller than the maximum amplitude of the micromirrors is
controlled to turn to an ON state of the micromirrors.
[0026] The fourteenth aspect of the present invention is based on
the display system according to the first aspect. In the display
system, an oscillating state having an amplitude equal to or
smaller than the maximum amplitude of the micromirrors is
controlled to turn to an OFF state of the micromirrors.
DRAWINGS
[0027] FIG. 1A shows a prior art illustrating the basic principle
of a projection display using a micromirror device;
[0028] FIG. 1B shows a prior art illustrating the basic principle
of a micromirror device used for a projection display;
[0029] FIG. 1C shows an example of the driving circuit of prior
arts;
[0030] FIG. 1D shows the scheme of binary pulse width modulation
(binary PWM) of conventional digital micromirrors to generate gray
scale;
[0031] FIG. 2 shows the concept of an example of the configuration
of the display system according to an embodiment of the present
invention;
[0032] FIG. 3 is a block diagram showing an example of the
configuration of the spatial light modulation element forming the
display system according to an embodiment of the present
invention;
[0033] FIG. 4A shows the concept of an example of the configuration
of the pixel unit forming the spatial light modulation element
according to an embodiment of the present invention;
[0034] FIG. 4B shows the concept of an example of a variation of
the pixel unit forming the spatial light modulation element
according to an embodiment of the present invention;
[0035] FIG. 5 is a diagram showing an example of the pulse width
modulation (PWM) using binary data;
[0036] FIG. 6 is a diagram showing an example of converting binary
data into non-binary data;
[0037] FIG. 7 is a diagram showing an example of converting a part
of binary data into non-binary data;
[0038] FIG. 8 is a diagram showing an example of converting binary
data into non-binary data in a display system a an embodiment of
the present invention;
[0039] FIG. 9A is an explanatory view showing the ON state of the
micromirrors;
[0040] FIG. 9B is a diagram showing the voltage waveform for
realizing the ON state of the micromirrors;
[0041] FIG. 10A is an explanatory view showing the OFF state of the
micromirrors;
[0042] FIG. 10B is a diagram showing the voltage waveform for
realizing the OFF state of the micromirrors;
[0043] FIG. 11A is an explanatory view showing the oscillating
state of the micromirrors;
[0044] FIG. 11B is a diagram showing the voltage waveform for
realizing the oscillating state of the micromirrors;
[0045] FIG. 12 is a diagram showing an embodiment of the
oscillating state of the micromirrors in the display system
according to an embodiment of the present invention;
[0046] FIG. 13 is a diagram showing an embodiment of the
oscillating state of the micromirrors in the display system
according to an embodiment of the present invention;
[0047] FIG. 14 is a diagram showing the principle of the improved
gray scale by the oscillating state of the micromirrors in the
display system according to an embodiment of the present
invention;
[0048] FIG. 15 is a diagram illustrating the improved gray scale by
a combination of the ON state of the micromirrors and the
oscillating state by the display system according to an embodiment
of the present invention;
[0049] FIG. 16 is a diagram illustrating the improved gray scale by
a combination of the ON state of the micromirrors and the
oscillating state by the display system according to an embodiment
of the present invention;
[0050] FIG. 17 is a diagram illustrating the improved gray scale by
a combination of the ON state of the micromirrors and the
oscillating state by the display system according to an embodiment
of the present invention; and
[0051] FIG. 18 is a diagram illustrating the improved gray scale by
a combination of the ON state of the micromirrors and the
oscillating state by the display system according to an embodiment
of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0052] The embodiments of the present invention are described below
in detail with reference to the attached drawings.
[0053] FIG. 2 shows the concept of an example of the configuration
of the display system according to an embodiment of the present
invention. FIG. 3 is a block diagram showing an example of the
configuration of the spatial light modulation element forming the
display system according to an embodiment of the present invention.
FIGS. 4A and 4B show the concept of an example of the configuration
of a pixel unit 211 forming the spatial light modulation element
according to an embodiment of the present invention.
[0054] A display system 100 according to the embodiments of the
present invention includes a spatial light modulation element 200,
a control device 300, a light source 510, and a projective optical
system 520.
[0055] As shown in FIGS. 3 and 4 etc., the spatial light modulation
element 200 includes a pixel array 210, a column driver 220, a row
driver 230, and an external interface unit 240.
[0056] In the pixel array 210, a plurality of pixel units 211 are
arranged in grid form at each intersection of a bit line 221
vertically extending from the column driver 220 and a word line 231
horizontally extending from the row driver 230.
[0057] As illustrated in FIGS. 9A, 10A, and 11A, each pixel unit
211 is provided with a micromirror 212 supported as freely tilted
on a substrate 214 through a hinge 213.
[0058] On the substrate 214, an OFF electrode 215 and an OFF
stopper 215a, and an ON electrode 216 and an ON stopper 216a are
symmetrically arranged about the hinge 213 provided with a hinge
electrode 213a.
[0059] The OFF electrode 215 pulls the micromirror 212 with a
Coulomb force by applying predetermined potential, and tilts the
micromirror 212 until it touches the OFF stopper 215a. Thus,
incoming light 311 entering the micromirror 212 is reflected toward
the optical path in the OFF position deviated from the optical axis
of a projective optical system 130.
[0060] The ON electrode 216 pulls the micromirror 212 with the
Coulomb force by applying predetermined potential, and tilts the
micromirror 212 until it touches the ON stopper 216a. Thus, the
incoming light 311 entering the micromirror 212 is reflected toward
the optical path in the ON position matching the optical axis.
[0061] An OFF capacitor 215b is connected to the OFF electrode 215,
and the OFF capacitor 215b is connected to a bit line 221-1 through
a gate transistor 215c.
[0062] An ON capacitor 216b is connected to the ON electrode 216.
The ON capacitor 216b is connected to the bit line 221-2 through a
gate transistor 216c.
[0063] The word line 231 controls the opening and closing
operations of the gate transistor 215c and the gate transistor
216c.
[0064] That is, a horizontal row of the pixel unit 211 connected to
any word line 231 is simultaneously selected, and the
charge/discharge of electric charge with respect to the OFF
capacitor 215b and the ON capacitor 216b is controlled by the bit
line 221-1 and the bit line 221-2, thereby individually controlling
the ON/OFF of the micromirror 212 in each pixel unit 211 in the
horizontal row.
[0065] FIG. 4B shows the concept of an example of a variation of
the pixel unit illustrated in FIG. 4A.
[0066] In the pixel unit 211A of an example of a variation shown in
FIG. 4B, the hinge 213 (hinge electrode 213a) that supports the
micromirror 212 is connected to a mirror potential control line 232
so that the potential of the micromirror 212 can be externally
controlled, which is different from the configuration shown in FIG.
4A.
[0067] Therefore, in the pixel unit 211A in a variation example
shown in FIG. 4B, by controlling the combination of the voltage
applied from the bit line 221-1 and the bit line 221-2 to the OFF
electrode 215 and the ON electrode 216 and the voltage level and
the application timing of the voltage applied from the mirror
potential control line 232 to the micromirror 212, the tilt angle
and the tilt speed of the micromirror 212 can be optionally
controlled.
[0068] For example, by maintaining constant timing of applying a
voltage to the OFF electrode 215 and the ON electrode 216, and
changing the value of the voltage applied from the mirror potential
control line 232 to the 215 and the ON electrode 216, and further
to the micromirror 212, the level of the amplitude of the
intermediate oscillation between the ON state and the OFF state of
the micromirror 212 can be changed.
[0069] The external interface unit 240 illustrated in FIG. 3
includes a timing controller 241 and a parallel/serial interface
242. The timing controller 241 selects the pixel unit 211 of the
horizontal row by the word line 231 based on a scanning timing
control signal 432 output from a selector 324.
The parallel/serial interface 242 provides a modulation control
signal 440 for the column driver 220.
[0070] The light source 510 irradiates the spatial light modulation
element 200 with incoming light 511, the light is reflected as
reflected light 512 by each micromirror 212, and the reflected
light 512 in the optical path through the 520 is projected as
projected light 513 on the screen etc. not shown in the attached
drawings.
[0071] As shown in FIG. 2 as a conceptual illustration, the control
device 300 according to the present embodiment for controlling the
spatial light modulation element 200 is provided with a data
splitter 310 and a data converter 320.
[0072] As described later, the control device 300 realizes gray
scale using the ON/OFF state (ON/OFF modulation) and the
oscillating state (oscillation modulation) of the micromirror 212
of the spatial light modulation element 200.
[0073] The data splitter 310 has the function of separating a
binary picture signal 400 of externally input binary data into
separated data 410 for control of the micromirror 212 for ON/OFF
modulation and separated data 420 for control of the micromirror
212 for a modulation state, and the function of outputting a
synchronization signal 430 for control of the data converter
320.
[0074] The data converter 320 includes a first state control unit
321, a second state control unit 322, a timing control unit 323,
and a selector 324.
[0075] The first state control unit 321 has the function of
controlling the micromirror 212 for the ON/OFF state by outputting
non-binary data 411 to the spatial light modulation element 200
through the selector 324 based on the separated data 410.
[0076] The second state control unit 322 has the function of
controlling the micromirror 212 for the oscillating state by
outputting non-binary data 421 to the spatial light modulation
element 200 through the selector 324 based on the separated data
420.
[0077] The timing control unit 323 calculates the time required to
placed the micromirror 212 in the ON state and the time (time
duration) required to placed the micromirror 212 in the oscillating
state in each frame partly forming the binary picture signal 400
with respect to each micromirror 212 configuring a pixel of an
image based on the synchronization signal 430 generated by the
binary picture signal 400, controls the first state control unit
321 and the second state control unit 322, and outputs a control
signal 431 to the selector 324.
[0078] The selector 324 switches the output of the non-binary data
411 or the non-binary data 421 to the spatial light modulation
element 200 according to the control signal 431, thereby switching
the control of the micromirror 212 from the ON/OFF modulation by
the first state control unit 321 (non-binary data 411) to the
oscillation modulation by the second state control unit 322
(non-binary data 421), or from the oscillation modulation to the
ON/OFF modulation.
[0079] Described functions of the data splitter 310, the first
state controller 321, the second state controller 322, the timing
control unit 323 and the selector 324 can be provided with an
integrated processor.
[0080] Described below are the binary data and the non-binary data
with reference to FIGS. 5, 6, 7, and 8.
[0081] As shown in FIG. 5, the N bits of the binary data (binary
picture signal 400) are data having different weights from the LSB
(least significant bit) to the MSB (most significant bit).
[0082] When the gray scale is represented by the control of the
pulse width modulation (PWM), the weight of each bit indicates a
time width for pulse control, that is, the duration of the ON state
of each segment (subframe).
[0083] The example shown in FIG. 6 is an embodiment of converting
all 5 bits of the input binary data into the non-binary data of
"weight"=1.
[0084] The period of a segment (subframe) of the binary data of all
5 bits is determined by the weight (=1) of the LSB, the data is
converted into non-binary data (bit string) for each segment, and
transferred to the spatial light modulation element 200.
[0085] That is, the frequency of the ON state of the interval of
the LSB of the binary data is calculated, and the gray scale is
represented to continue the period of the ON state for the bit
string.
[0086] The example shown in FIG. 7 is an embodiment of converting
the 3 internal bits of the binary data into non-binary data. In
this example, the quantity of light is modulated (ratio of the
quantity of light =1/2) on the lowest order bit of the binary data
using the spatial light modulation element 200 or the light source
510. In this case, the weight of all bits other than the highest
order bit of the binary data is set to 2, and the interval of one
segment is extended, thereby matching the interval of the segment
of the lowest order bit with the intervals of other segments.
[0087] Each pixel element (pixel unit 211) of the spatial light
modulation element 200 is a micromirror 212 controlled in any of
the ON/OFF (positioning) state, the oscillating state, and the
intermediate state.
[0088] As shown in FIG. 8, in the case of the present embodiment,
the ON/OFF (positioning) state is controlled by the non-binary data
411 output from the first state control unit 321, and the
oscillating state is controlled by the non-binary data 421 output
from the second state control unit 322.
[0089] In this case, the quantity of light is modulated by the
spatial light modulation element 200 using the non-binary data 421,
thereby extending the interval of a segment, and moderating the
time request in an arithmetic operation.
[0090] Described below is the basic control of the micromirror 212
of the spatial light modulation element 200 according to the
present embodiment.
[0091] In the following descriptions, Va (1, 0) indicates that a
predetermined voltage Va is applied to the OFF electrode 215, and
not applied to the ON electrode 216.
[0092] Va (0, 1) indicates that no voltage is applied to the OFF
electrode 215, and the voltage Va is applied to the ON electrode
216.
[0093] Va (0, 0) indicates that no variation Va is applied to the
OFF electrode 215 or the ON electrode 216.
[0094] Va (1, 1) indicates that the voltage Va is applied to both
of the OFF electrode 215 and the ON electrode 216.
[0095] FIGS. 9A, 9B, 10A, 10B, 11A, and 11B show basic examples of
the configurations of the pixel unit 211 including the micromirror
212, the hinge 213, the OFF electrode 215, and the ON electrode
216, and the state control of controlling the micromirror 212 in
the ON state and the oscillating state.
[0096] FIG. 9A shows that the micromirror 212 is pulled and tilted
from the neutral position into the ON state by applying the
predetermined voltage Va only to the ON electrode 216 (Va (0, 1)),
and enters the ON state. In the ON state of the micromirror 212,
the reflected light 512 passing through the micromirror 212 is
captured by the projective optical system 520, and projected as the
projected light 513. FIG. 9B shows the quantity of light projected
in the ON state.
[0097] FIG. 10A shows that the micromirror 212 is pulled and tilted
from the neutral position into the OFF state by applying the
predetermined voltage Va only to the OFF electrode 215 (Va (1, 0)),
and enters the OFF state. In the OFF state of the micromirror 212,
the reflected light 512 deviates from the projective optical system
520, and does not become the projected light 513. FIG. 10B shows
the quantity of light projected in the OFF state.
[0098] FIG. 11A shows an example of performing free oscillation at
the maximum amplitude A0 between the tilt position (full ON) in
which the micromirror 212 touches the ON electrode 216 and the tilt
position (full OFF) in which the micromirror 212 touches the OFF
electrode 215 (Va (0, 0)).
[0099] The micromirror 212 is irradiated with the incoming light
511 at a predetermined angle. The quantity of light reflected in
the ON direction and a part of the quantity of light (quantity of
light of the reflected light 512) reflected between the ON
direction and the OFF direction enter the projective optical system
520, and is projected as the luminance (projected light 513) of an
image. FIG. 11B shows the quantity of light projected in the OFF
state.
[0100] That is, in the ON state of the micromirror 212 shown in
FIG. 9A, substantially all of the reflected optical flux travels in
the ON direction in which it is captured by the projective optical
system 520, and projected as the projected light 513.
[0101] In the OFF state of the micromirror 212 shown in FIG. 10A,
the reflected light 512 travels and deviates from the projective
optical system 520 in the OFF direction, and there is no light
projected as the projected light 513.
[0102] In the oscillating state of the micromirror 212 shown in
FIG. 11A, a part of the optical flux of the reflected light 512,
diffracted light, scattered light, etc. are captured by the
projective optical system 520, and projected as the projected light
513.
[0103] In the examples shown in FIGS. 9A, 9B, 10A, 10B, 11A, and
11B, the voltage Va represented by two values, that is, 0 and 1, is
applied to each of the OFF electrode 215 and the ON electrode 216,
but the levels of the Coulomb force generated between the
micromirror 212 and the OFF electrode 215 and the ON electrode 216
can be increased by increasing the levels of the value of Va as
multiple values, thereby controlling the tilt angle of the
micromirror 212 to the subtleties.
[0104] Furthermore, in the examples shown in FIGS. 9A, 9B, 10A,
10B, 11A, and 11B, the micromirror 212 (hinge electrode 213a) is
described as ground potential, but the tilt angle of the
micromirror 212 can be controlled to the subtleties by applying the
offset voltage to the micromirror 212.
[0105] In the case of the present embodiment, as described later,
the amplitude of the tilt displacement of the micromirror 212 is
obtained by generating free oscillation of the amplitude Al and the
amplitude A2 smaller than the maximum amplitude AO between the ON
and the OFF by applying Va (0, 1), Va (1, 0), and Va (0, 0) in
appropriate timing during the tilt displacement of the micromirror
212 between ON and OFF, thereby realizing more subtle gray
scale.
[0106] A method of displaying a picture using the display system
100 is described below.
[0107] When the binary picture signal 400 is input to the control
device 300, it is divided into the separated data 410 and the
separated data 420.
[0108] The first state control unit 321 and the second state
control unit 322 calculate the time duration in which the
micromirror 212 is placed in the ON state in one frame of a picture
with respect to the respectively micromirrors 212 of the spatial
light modulation element 200 forming the pixel of a picture
depending on the separated data 410 and the separated data 420 of
the picture signal, the time duration in which the micromirror 212
is placed in the oscillating state, or the frequency of oscillating
the micromirror 212.
[0109] The first state control unit 321 and the second state
control unit 322 of the control device 300 calculate the time
duration in which the micromirror 212 is placed in the ON state,
the time duration in which the micromirror 212 is placed in the
oscillating state, or the frequency at which the micromirror 212 is
oscillated using the ratio of the quantity of light of the
projected light 513 obtained by the oscillation in the oscillation
time T of a predetermined micromirror 212 and the quantity of light
of the projected light 513 obtained by placing the mirror in the ON
state in the oscillation time T.
[0110] Using the calculated time duration or value of the
frequency, the ON/OFF control and the oscillation-control are
performed on each micromirror 212 forming one frame of a
picture.
[0111] Described below is an example of realizing free oscillation
in the intermediate position between the ON state and the OFF state
in the control device 300 according to the present embodiment.
[0112] FIG. 12 shows an example of performing free oscillation with
an amplitude A smaller than the maximum amplitude AO in the
intermediate state between the ON state and the OFF state from the
OFF state. Described are means for realizing the process. [0113]
The Timing Method [0114] The first method is to control the
micromirror by applying two voltages, zero and Va, to the
electrodes while the micromirror is at GND state or zero volt. As
seen 411 in FIG. 12, the voltage Va(0,1) is applied to the OFF
electrode 215 and the ON electrode 216 of the micromirror 2l2 in
the OFF state. [0115] At time t1a, Va(0,0) is applied to the OFF
electrode 215 and the ON electrode 216 of the micromirror 212,
resulting no Coulomb force between the electrodes and the
micromirror. [0116] By the spring force of the hinge 213, the
micromirror 212, which was pulled to the OFF state, is released to
move toward the ON state. [0117] In the period between t1b and t1c,
Va(0,1) is applied to the OFF electrode 215 and the ON electrode
216 to pull the micromirror 212 toward the OFF state in order to
reduce the speed of the micromirror 212 which is moving toward the
ON state. [0118] At time t1c, before the micromirror 212 is
reaching the ON state, Va(0,0) is applied to the OFF electrode 215
and the ON electrode 216 to set Coulomb force between the
electrodes and the mirror to zero, and the micromirror 212 starts
free oscillation with the amplitude A smaller than the maximum
amplitude A0. [0119] At time t1d, Va(0,1) is applied to the OFF
electrode 215 and the ON electrode 216 of the mircomirror 212, the
oscillation of the micromirror 212 is stopped and the mirror is
placed in the OFF state. [0120] The free oscillation period T2, or
oscillation modulation period, is set to get desirable gray scale
level, from the time required by the number of the free oscillation
cycle calculated by the light intensity obtained by one cycle of
the free oscillation, or from the time calculated by the light
intensity per arbitrary free oscillation period T. [0121] In this
control method, the timing of t1a, t1b and t1c governs the
amplitude A or the initial speed of the free oscillation of the
micromirror 212. [0122] It is understood that the oscillation
amplitude A can be controlled by setting the timing of t1a, t1b and
t1c. [0123] The period between t1a to t1c is shorter than the half
of the free oscillation period of the micromirror 212, and shorter
than the half of the period required by LSB in the PWM control.
Especially, the period between t1a to t1b is shorter than the
quarter of the free oscillation period of the micromirror 212, and
shorter than the quarter of the period required by LSB in the PWM
control. [0124] The time t2a through time t2d and the value of the
voltage Va are determined by the first state control unit 321 and
the second state control unit 322 of the data converter 320. [0125]
In this embodiment, the driving circuit of each electrode is
simplified by making the voltage Va common with the voltage value
for use in the PWM control (ON state control) of the micromirror.
That is, in this case, it is not necessary to have a plurality of
driving voltages. [0126] (2) Multiple Voltage Method [0127] The
acceleration of the micromirror 212 moving between ON state and OFF
state is governed by Coulomb force generated by the voltage applied
to the electrodes and the micromirror 212. [0128] The second method
is to control the micromirror 212 by use of three voltage value 0,
Va and Vb applied to the OFF electrode 215. The micromirror 212 is
set to zero volts or in GND state in this embodiment as well.
[0129] As seen 411 in FIG. 12, the voltage Va(0,1) is applied to
the OFF electrode 215 and the ON electrode 216 of the micromirror
2l2 in the OFF state. [0130] At time t1a, Va(0,0) is applied to the
OFF electrode 215 and the ON electrode 216 of the micromirror 212,
resulting no Coulomb force between the electrodes and the mirror.
By the spring force of the hinge 213, the micromirror 212, which
was pulled to the OFF state, is released to move toward the ON
state. [0131] In the period between t1b and t1c, Vb(0,1) is applied
to the OFF electrode 215 and the ON electrode 216 to pull the
micromirror 212 toward the OFF state in order to reduce the speed
of the micromirror 212 which is moving toward the ON state. [0132]
Vb is greater than Va and thus the force to reduce the speed of the
micromirror 212 is greater. [0133] At time t1c, before the
micromirror 212 is reaching the ON state, Va(0,0) is applied to the
OFF electrode 215 and the ON electrode 216 to set Coulomb force
between the electrodes and the mirror to zero, and the micromirror
212 starts free oscillation with the amplitude A2 smaller than the
maximum amplitude A0. [0134] At time t1d, Va(0,1) is applied to the
OFF electrode 215 and the ON electrode 216 of the micromirror 212,
the oscillation of the micromirror 212 is stopped and the mirror is
placed in the OFF state. [0135] The free oscillation period T2, or
oscillation modulation period, is set to get desirable gray scale
level, from the time required by the number of the free oscillation
cycle calculated by the light intensity obtained by one cycle of
the free oscillation, or from the time calculated by the light
intensity per arbitrary free oscillation period T. [0136] In this
control method, the timing of t1a, t1b and t1c are fixed and the
voltage applied in the period between t1b and t1c governs the
amplitude A2 or the initial speed of the free oscillation of the
micromirror 212. [0137] That is, the amplitude A can be controlled
by the control voltage without changing the timing of t1a, t1b and
t1c. [0138] It should be understood that it is also possible to
obtain the same effect by applying other value than zero volts to
the micromirror 212 although above description mentions the method
applying voltage to the electrodes.
[0139] FIG. 13 shows an example of performing free oscillation in
the intermediate state between the ON state and the OFF state from
the ON state of a mirror. Described below is means for realizing
the oscillation in the control device 300 according to the present
embodiment.
[0140] As seen 412 in FIG. 13, the voltage Va(1,0) is applied to
the OFF electrode 215 and the ON electrode 216 of the micromirror
2l2 in the ON state.
[0141] At time t2a, Va (0, 0) is applied to the OFF electrode 215
and the ON electrode 216 of the micromirror 212, resulting no
Coulomb force between the electrodes and the micromirror.
[0142] By the spring force of the hinge 213, the micromirror 212,
which was pulled to the ON state, is released to move toward the
OFF state.
[0143] In the period between t2b and t2c, Va (1, 0) is applied to
the OFF electrode 215 and the ON electrode 216 to pull the
micromirror 212 toward the ON state in order to reduce the speed of
the micromirror 212 which is moving toward the OFF state.
[0144] At time t2c, before the micromirror 212 is reaching the OFF
state, Va(0,0) is applied to the OFF electrode 215 and the ON
electrode 216 to set Coulomb force between the electrodes and the
mirror to zero, and the micromirror 212 starts free oscillation
with the amplitude A smaller than the maximum amplitude A0.
[0145] At time t2d, Va (0, 1) is applied to the OFF electrode 215
and the ON electrode 216 of the micromirror 212, the oscillation of
the micromirror 212 is stopped and the mirror is placed in the OFF
state.
[0146] The free oscillation period T3, or oscillation modulation
period, is set to get desirable gray scale level, from the time
required by the number of the free oscillation cycle calculated by
the light intensity obtained by one cycle of the free oscillation,
or from the time calculated by the light intensity per arbitrary
free oscillation period T.
[0147] In this control method, the timing of t2a, t2b and t2c
governs the amplitude A or the initial speed of the free
oscillation of the micromirror 212.
[0148] It is understood that the oscillation amplitude A can be
controlled by setting the timing of t2a, t2b and t2c.
[0149] The time t2a through time t2d and the value of the voltage
Va are determined by the first state control unit 321 and the
second state control unit 322 of the data converter 320.
[0150] The method to control the amplitude A, smaller than the
maximum amplitude A0 by controlling the timing has been described.
It is also possible to obtain the same effect by controlling the
voltage applied to the electrodes by three or more voltage value,
or controlling the offset voltage applied to the micromirror, as
described earlier.
[0151] The improved gray scale according to the present embodiment
is realized as illustrated in FIG. 14. That is, FIG. 14 shows an
example of realizing the quantity of light of the projected light
513 obtained in the oscillation time T of the micromirror 212 as
indicating about 1/4 and 1/8 of the quantity of light obtained by
placing the micromirror 212 in the ON state for the same time
duration by the control method shown in FIG. 12.
[0152] That is, the 1/4 of the luminance ratio is realized by
setting the amplitude A of the oscillation of the micromirror 212
as the amplitude Al (for example, 50%) with respect to the maximum
amplitude A0.
[0153] In addition, the 1/8 of the luminance ratio is realized by
setting the amplitude A of the oscillation of the micromirror 212
as the amplitude A2 (for example, 25%) with respect to the maximum
amplitude A0.
[0154] Assuming that the gray scale of 256 levels (8 bits) is
represented by changing the time Ton for control of the ON state in
one frame of a picture to be displayed, the gray scale of 1024
levels (10 bits) can be represented by combining it with the free
oscillation (1st state) of the amplitude A1.
[0155] In addition, by combining the ON state, the amplitude A1
(first oscillating state) and the amplitude A2 (second oscillating
state) as a free oscillation state, the gray scale of 2048 levels
(11 bits) can be generated.
[0156] FIGS. 15, 16, 17, and 18 show examples of realizing 2048
levels (11 bits) by combining the ON state, the amplitude A1, and
the amplitude A2 as free oscillation.
[0157] That is, FIG. 15 shows an example of sequentially and
independently executing the oscillating state of the amplitude A1
and the amplitude A2 after the transfer from the ON state to the
OFF state of the micromirror 212 in one frame of the binary picture
signal 400.
[0158] FIG. 16 shows an example of executing the oscillating state
of the amplitude A1 after continuously generating an oscillating
state of the amplitude A2 after the ON state of the micromirror
212, and temporarily entering the OFF state.
[0159] FIG. 17 shows an example of executing the oscillating state
of the amplitude A1 temporarily through the OFF state after
transferring to the oscillating state of the maximum amplitude A0
after the transfer of the amplitude A2 from the OFF state of the
micromirror 212.
[0160] FIG. 18 shows an example of executing the oscillating state
of the amplitude A2 after temporarily entering the OFF state after
the OFF state. of the amplitude A1 without entering the OFF state
during the ON state of the micromirror 212.
[0161] In any case shown in FIGS. 15 to 18, 2048 levels (11 bits)
of the gray scale can be realized by combining the ON state of the
micromirror 212 with the free oscillation of the amplitude A1 and
the amplitude A2.
[0162] In description above, the free oscillation of the amplitude
A1 and the amplitude A2 are provided within continuous one frame
period. To reduce complication of the operation as controlling
oscillation of the micromirrors, frame period can be divided so
that each oscillation is performed in a separate
period(sub-frame).
[0163] Thus, by controlling the micromirror with the amplitude A of
the oscillation adjusted, the luminance of 1/n (n is an integer) of
the quantity of light Lon obtained by placing the micromirror 212
in the ON state for the same time duration T can be acquired.
[0164] To increase the gray scale of the picture to be displayed by
combining the ON state and the oscillating state of the
micromirror, the mirror can be controlled to obtain the values of
n=1.33, n=2, n=3, n=5, and n=10 as the luminance ratio of the 3/4
of Lon in addition to the above-mentioned value of n.
[0165] The relationship between the luminance Losc obtained by the
oscillation-control in one frame period of picture data and the
time Tosc in which the oscillation-control is performed can be
represented by the following equation.
Losc=Lon.times.(1/n).times.(Tosc/T)
[0166] That is, to realize the same luminance Losc, control can be
performed by increasing the value of the integer n, extending the
modulation time Tosc, or decreasing the value of the integer n to
shorten the modulation time Tosc.
[0167] Thus, the system of projecting a picture to be displayed
using a plurality of spatial light modulation elements can set
substantially equal timing of the control time for each of the
spatial light modulation elements, thereby reducing the motion
artifacts and color artifacts of a picture to be displayed.
[0168] Furthermore, it is possible to oscillation-control the
micromirror such that the luminance of the projected picture
obtained by one oscillation of the micromirror controlled in the
oscillation period T1 of the mirror by a control device can be 1/n
of the luminance Lon2 of the projected picture obtained in the ON
state of the memory controlled in the oscillation period T1.
[0169] In this case, the relationship between the luminance Losc
obtained by the oscillation-control in a frame period of the
picture data and the frequency m at which the oscillation of the
micromirror is performed by the oscillation-control can be
represented by the following equation.
Losc=Lon2.times.(1/n).times.m
[0170] That is, to realize the same luminance Losc, control can be
performed by increasing the value of an integer n to increase the
frequency m at which the oscillation is performed, or decreasing
the value of the integer n to decrease the frequency of the
modulation.
[0171] Thus, the system of projecting a picture to be displayed
using a plurality of spatial light modulation elements can set
substantially equal timing of the control time for each of the
spatial light modulation elements, thereby reducing the motion
artifacts and color artifacts of a picture to be displayed.
[0172] As described above, according to the display system 100 of
the present embodiment, more delicate gray scale can be realized in
the picture display using a spatial light modulation element 200 to
display a picture depending on the modulation state of a plurality
of micromirrors 212 without increasing the amount of data of the
digital picture data (binary picture signal 400).
[0173] In addition, without the necessity to perform complicated
control such as increase/decrease of the quantity of light of the
light source 510 or add an additional circuit, delicate gray scale
can be realized on a picture display using the spatial light
modulation element 200 for displaying a picture in the modulation
state of the plurality of micromirror 212.
[0174] More delicate gray scale can be read in the picture display
using a spatial light modulation element to display a picture
depending on the modulation state of a plurality of micromirrors
without increasing the speed of modulation-controlling the
micromirrors into the ON state.
[0175] In addition, more delicate gray scale can be read in the
picture display using a spatial light modulation element to display
a picture depending on the modulation state of a plurality of
micromirrors without complicated control of, for example, the
quantity of light of a light source or an additional circuit.
[0176] The present invention is not limited to the configurations
according to the above-mentioned embodiments, but various changes
can be bade within the gist of the invention.
* * * * *