Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-06-23
2001-12-04
Wu, Xiao (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S087000, C345S099000
Reexamination Certificate
active
06326942
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical spatial modulation device for modulating radiated light in accordance with information representing an image to be displayed for each pixel and an image display apparatus employing the optical spatial modulation device.
A liquid crystal display device is known as an optical spatial modulation device for modulating radiated light in accordance with information representing an image to be displayed for each pixel. There has been widely used a ordinary liquid crystal display device of a type wherein the intensity of light is modulated by putting an array of so-called twisted nematic liquid crystals, that is, liquid crystals used in a twisted nematic operating mode, in continuously varying states. A twisted nematic liquid crystal is referred to hereafter simply as a TN liquid crystal.
With regard to such liquid crystal materials and liquid crystal display devices, there have been published an article with a title “New Technology Seen from Patent Information: 13 Liquid Crystal,” authored by Yoko Watanabe, Pages 26 to 31, Volume 92, a July 1995 issue of “Inventions”, a monthly magazine published by Japan Institute of Invention and Innovation, an article with a title “New Technology Seen from Patent Information: 26 Liquid Crystal Display Device,” authored by Takashi Hinatsu, Pages 62 to 69, Volume 92, an August 1996 issue of “Inventions”, a monthly magazine published by Japan Institute of Invention and Innovation and a book with a title “Liquid Crystal Device Handbook,” issued by the 142
nd
Committee of the Japan Society for the Promotion of Science and published by the Nikkan Kogyo Newspaper.
However, the TN liquid crystal has a problem of a slow response speed, making it desirable to develop an optical spatial modulation device that is capable of operating at a high speed. As a liquid crystal material for light modulation that is capable of operating at a high speed, for example, there are a ferroelectric liquid crystal referred to hereafter as an FLC and a non-ferroelectric inductive liquid crystal. An FLC has a state storing characteristic. In general, as a state, there may be only 2 values. Thus, with an optical spatial modulation device using such a material for light modulation, continuous light modulation can not be carried out. That is to say, such a device is capable of operating by merely changing from an on state to an off state or vice versa.
In addition, as a liquid crystal material for light modulation having a state storing characteristic, there are also a cholesteric liquid crystal or a kailar nematic liquid crystal operating in a phase transition mode and a polymer liquid crystal which carries out write and erase operations between isotropic and glass phases. Other liquid crystal materials that can be used as a material for light modulation include a polymer diffusion liquid crystal which is referred to hereafter as a PDLC.
When displaying a multi-tone image by means of an optical spatial modulation device using such a material for light modulation, a pulse width modulation (PWM) technique is typically adopted in order to make use an afterglow characteristic of the human eye. To put it in detail, when displaying a multi-tone image by means of such an optical spatial modulation device, light is switched from an on state to an off state and vice versa at a high speed with controlled timing so that the multi-tone image is displayed and projected on a human eye.
The following is a description of an image display apparatus employing such an optical spatial modulation device.
FIG. 22
is a conceptual diagram showing the image display apparatus. As shown in the figure, a light generated by a light source
101
is radiated to an optical spatial modulation device
103
by a radiation optical system
102
. The light modulated by the optical spatial modulation device
103
is then projected on a screen
105
by a projection optical system
104
. As a result, an image is displayed on the screen
105
.
FIG. 23
is a diagram showing a squint view of disassembled components of an enlarged portion of the optical spatial modulation device
103
mentioned above. As shown in the figure, the optical spatial modulation device
103
comprises a driving layer
106
, a reflection layer
107
, a modulation layer
108
and a common electrode
109
. It should be noted that, if the modulation layer
108
is implemented by a crystal, an orientation layer is provided between the common electrode
109
and the crystal and another orientation layer is provided between the crystal and the reflection layer
107
.
In an operation to drive this optical spatial modulation device
103
, first of all, data coming from a data line
111
is written into each memory cell
112
at a point of intersection of a scanning line
110
and the data line
111
created on the driving layer
106
. Each of the memory cells
112
corresponds to a pixel.
Next, electric fields are applied to the electrically charged modulation layer
108
provided between reflection pads
113
created on the reflection layer
107
and the common electrode
109
in accordance with pieces of data recorded in the memory cells
112
so as to reflect the respective pixels. The modulation layer is implemented typically by an FLC. As a result, areas of the modulation layer
108
are put in either a light passing state or a light shielding state in dependence on pixels facing the areas.
Then, some of the light radiated to the optical spatial modulation device
103
passing through the modulation layer
108
is reflected by the reflection pads
113
on the reflection layer
107
and output by way of the reflection layer
108
as shown in FIG.
22
. That is to say, only some of the light radiated to the optical spatial modulation device
103
that manages to pass through the modulation layer
108
is reflected. As a result, light is modulated for each pixel.
In order to continuously change a displayed image in this image display apparatus, the radiation of a light from the light source
101
is halted each time the image is changed and then the state of the modulation layer
108
is changed with respect to all the pixels. Then, at a point of time the operation to change the state of the modulation layer
108
with respect to all the pixels is completed, the radiation of the light from the light source
101
is resumed. As a result, lights modulated for the pixels are sequentially projected on the screen
105
. Thus, while the state of the modulation layer
108
of the optical spatial modulation device
103
employed in the image display apparatus is being changed, the light source
101
is turned off. As the operation to change the state of the modulation layer
108
is completed, a light is radiated from the light source
101
to the optical spatial modulation device
103
.
It should be noted that, since the FLC normally has a state storing characteristic, once an electric field is applied to put the FLC in a desired state, residual electric charge remains in the FLC. It is thus necessary to apply an electric field to the FLC in the opposite direction in order to neutralize the residual electric charge. As a technique for neutralizing residual electric charge, among other methods, a 2-field technique is known. In the 2-field technique, pieces of pixel data of a desired image are written into the memory cells
112
in order to apply electric fields to the modulation layer
108
in accordance with the pieces of pixel data to display the desired image. Then, pieces of pixel data for inverting the pieces of pixel data of the displayed image are written into the memory cells
112
in order to apply electric fields to the modulation layer
108
in accordance with the pieces of pixel data newly written into the memory cells
112
. That is to say, according to this 2-field technique, residual electric charge is neutralized by alternately applying electric fields to the modulation layer
108
in opposite directions for a display of 1 picture.
The image display apparatus like the one
Kananen Ronald P.
Rader Fishman & Grauer
Sony Corporation
Wu Xiao
LandOfFree
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