Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
2003-01-06
2004-11-16
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S160000, C315S378000, C345S084000
Reexamination Certificate
active
06819064
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a display system for producing color images by light-modulating (spatially light-modulating) the lights of different color elements obtained through sequential color separation and, more particularly, to a display system which adopts a pulse-width modulation for light modulation.
BACKGROUND OF THE INVENTION
A pulse-width modulating display system is generally provided with a spatial light modulator that generates image lights by partially reflecting or transmitting light from a light source, and sequentially projects the image lights produced by the modulator on a screen to display images. The spatial light modulator generates the image lights on the basis of input image signals from external devices such as PCs and video equipment. The contrast of images displayed on the screen is normally defined by modulating the pulse-width of signals that execute ON/OFF control of the modulator.
There is described an example of the pulse-width modulating display system in Japanese Patent Application laid open No. HEI10-78550. The conventional display system obtains color images by light-modulating the lights of different color elements which have undergone sequential color separation.
FIG. 1
is a block diagram showing the configuration of the conventional display system. With reference to
FIG. 1
, the display system comprises a light source
1
, a color switch filter unit
31
used in the sequential color separation of white light from the light source, a spatial light modulator
2
for sequentially receiving the lights of different color elements obtained by the sequential color separation and generating the image lights of the color elements by partially reflecting the input lights in a prescribed direction, a projection lens
3
for projecting the image lights of the color elements sequentially generated by the spatial light modulator
2
on a screen
4
, and a drive circuit
51
for driving the spatial light modulator
2
and color switch filter unit
31
in synchronism based on an image signal
101
and a frame synchronous signal
102
sent from the outside (e.g. PC).
Examples of the spatial light modulator
2
include a digital micromirror device (DMD) comprised of hundreds of thousand of micro-mirrors whose angles of gradient are adjustable. The micro-mirrors of DMD correspond to, one each, the picture elements (pixels) of images displayed on the screen
4
. Any images can be presented by controlling the angle of each micro-mirror. To be specific, each of the micro-mirrors is selectively adjusted at the first angle for reflecting the light in a direction to avert it from the projection lens
3
or the second angle for reflecting the light to the projection lens
3
, thus creating desired images on the screen
4
. The angle control of the micro-mirrors is executed based on a modulation signal
103
fed from the drive circuit
51
.
The color switch filter unit
31
includes a color wheel
41
provided with plural color filters (Red, Green, Blue) which have different spectral transmittance characteristics and are arranged one by one in the circumferential direction, a motor
11
which supports the center of the color wheel
41
for rotating the wheel
41
in a prescribed direction, a couple of elements (light emitting element
12
and light acceptance element
13
) disposed opposite to each other with the color wheel
41
between them, and a color wheel control circuit
81
for controlling the rotation of the motor
11
.
The color wheel control circuit
81
receives a color wheel phase signal
112
from the light acceptance element
13
as well as a color switch control signal
104
from the drive circuit
51
, and sends a motor control signal
111
to the motor
11
. The color wheel phase signal
112
includes information on the rotation cycle of the color wheel
41
. The information is derived from the timing of the reception of light that the light emitting element
12
emits through a hole made in a prescribed position on the color wheel
41
to the light acceptance element
13
.
The image signal (video signal)
101
fed from the outside consists of image signals relative to respective colors Red, Green and Blue (including intensity information), which are sequentially output with respect to each frame. Besides, frame synchronization is performed based on the frame synchronous signal
102
. The modulation signal
103
is a signal for controlling the angles of the micro-mirrors of the spatial light modulator
2
according to the image signal
101
(image signals for colors R, G and B). That is, the respective micro-mirrors are set at the first angle or the second angle based on the modulation signal
103
. The color switch control signal
104
controls color filter (R, G, B) switching to execute the color separation by the color wheel
41
. The color filters can be switched in timing with the changeover of the image signal
101
based on the frame synchronous signal
102
. The color filter switching is carried out by rotating the color wheel
41
in a light path.
In the following, the image display operation of the above-mentioned conventional display system will be described by taking the case where the image signal (R, G, B)
101
is fed into the drive circuit
51
for example.
The light radiated from the light source
1
enters in the color switch filter unit
31
. When the image signal (Red)
101
is input on this occasion, the drive circuit
51
controls the angles of the micro-mirrors corresponding to the respective pixels in response to the signal (R)
101
. Concretely, the drive circuit
51
feeds the modulation signal
103
with the spatial light modulator
2
to switch the angles of the respective micro-mirrors to the first angle (at which the micro-mirror reflects light to divert it from the projection lens
3
) or the second angle (at which the micro-mirror reflects light toward the projection lens
3
).
In addition, the drive circuit
51
switches the color filters of the color wheel
41
in synchronism with the angle control of the micro-mirrors (spatial light modulation in the spatial light modulator
2
) according to the frame synchronous signal
102
. More specifically, the drive circuit
51
feeds the color wheel control circuit
81
with the color switch control signal
104
to switch the filter set in the light path to the color filter (R) when the image signal (R)
101
is input. The color wheel control circuit
81
sends the motor control signal
111
to the motor
11
based on the color switch control signal
104
and the color wheel phase signal
112
received from the light acceptance element
13
. In response to the motor control signal
111
, the motor
11
rotates the color wheel
41
so that the light radiated from the light source
1
enters the color filter (R).
The light having entered the color filter (R) transmits therethrough and becomes light (R). The light (R) then enters into the spatial light modulator
2
. The light modulator
2
spatially light-modulates the light (R) to generate image light (R). The image light (R) is projected on the screen
4
by the projection lens
3
.
Subsequently, the image signal (Green)
101
is input. With this the drive circuit
51
feeds the spatial light modulator
2
with the modulation signal
103
to execute the angle control of the micro-mirrors according to the image signal (G)
101
. At the same time, the drive circuit
51
feeds the color wheel control circuit
81
with the color switch control signal
104
to switch the filter of the color wheel
41
to the color filter (G). The color wheel control circuit
81
sends the motor control signal
111
to the motor
11
based on the color switch control signal
104
and the color wheel phase signal
112
received from the light acceptance element
13
. In response to the motor control signal
111
, the motor
11
rotates the color wheel
41
so that the light radiated from the light source
1
enters the color filter (G).
The light having entered the color filter (G) transmits therethrough to become l
NEC Viewtechnology Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Tran Chuc
Wong Don
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