Television – Video display – Projection device
Reexamination Certificate
1998-01-22
2001-09-18
Eisenzopf, Reinhard J. (Department: 2614)
Television
Video display
Projection device
C348S756000, C348S751000, C348S761000, C348S790000, C348S791000
Reexamination Certificate
active
06292234
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection type color liquid crystal (LC) display apparatus for projecting an image onto a screen.
2. Description of the Related Art
Image display apparatuses are available which display an image on a cathode ray tube (CRT) display and project the image on the CRT display onto a screen. In recent years, however, projection type color LC display apparatuses (which incorporate LC display devices) have been proposed to replace such projection type display apparatuses. There is a class of projection type color LC display apparatuses called a “single plate type” (e.g., as disclosed in Japanese Laid-open Publication No.4-60538) which incorporate a single LC display device. Single plate type projection type color LC display apparatuses are known as especially suitable for use in systems with small dimensions due to their relatively simple optical systems.
A single plate-type projection type color LC display apparatus is illustrated in FIG.
11
. As shown in
FIG. 11
, light from a incandescent light source
101
is reflected from a mirror
102
(shaped as an ellipsoid of revolution), which is disposed in such a manner that its first focal point coincides with the location of the light source
101
, and converges onto the second focal point of the mirror
102
.
The light converged at the second focal point of the mirror
102
is passed through an integrator
103
(which is located near the second focal point of the mirror
102
), whereby it becomes uniform in terms of its angular distribution, i.e., dispersed. This light is further collimated by means of a condenser lens
104
. The collimated light is separated by dichroic mirrors
105
R,
105
G, and
105
B (having selective reflectivity for red, green, and blue, respectively) into respective components of three primary colors, i.e., red (R), green (G), and blue (B). These light beams of three colors enter respective picture elements of a LC display device
106
corresponding to R, G, and B.
The LC display device
106
includes: a LC panel
107
for modulating its incident light in accordance with an image signal; a microlens array
108
for converging the light beams of three colors onto the respective picture elements of the LC display panel
107
corresponding to R, G, and B; a polarizing plate
109
disposed on the side of the microlens array
108
from which the light enters (defined as the “incident side”); and a polarizing plate
110
disposed on the side of the LC panel
107
from which the light goes out (defined as the “outgoing side”).
FIG. 12
illustrates the configuration of the LC panel
107
, which includes a LC layer
113
interposed between a pair of opposing substrates
111
and
112
. A plurality of pixel electrodes
115
are disposed in a matrix shape on the surface of the substrate
111
. A thin film transistor (TFT)
116
and a storage capacitance
117
are provided corresponding to each pixel electrode
115
for driving the pixel electrode
115
. One pixel is defined by a corresponding set of a pixel electrode
115
, a TFT
116
, and a storage capacitance
117
.
Signal lines
118
are provided on the surface of the substrate
111
corresponding to respective columns of pixel electrodes
115
, whereas gate lines
119
are provided corresponding to respective rows of pixel electrodes
115
. A gate of each TFT
116
is coupled to a corresponding gate line
119
; a source of the TFT
116
is coupled to a corresponding signal line
118
; and a drain of the TFT
116
is coupled to a pixel electrode
115
and one of the electrodes of the storage capacitance
117
. The other electrode of the storage capacitance
117
is set at a potential which is at the same level as that of a counter electrode
121
. The substrate
111
thus constructed is commonly referred to as an “active matrix substrate”.
On the counter substrate
112
opposing the active matrix substrate
111
, a counter electrode
121
and a light shielding layer
122
are layered in this order. In positions of the light shielding layer
122
corresponding to the respective pixel electrodes
115
, aperture regions
123
exist. The LC molecules in the LC layer
113
may take, for example, a twisted nematic orientation state.
FIG. 13
illustrates a cross section of the LC panel
107
and the microlens array
108
. As seen from
FIG. 13
, the microlens array
108
includes microlenses
124
of a hexagonal shape wherein the outer peripheries of individual spherical lenses are merged with one another. Such a microlens array
108
can be produced by an ion exchange method.
The microlenses
124
are located relative to the picture elements
125
as shown in FIG.
14
. Specifically, on the LC panel
107
, repetitive sets of picture elements
125
of R, G, and B (arranged in this order) are provided in each horizontal line of the display. Furthermore, with respect to any two adjoining horizontal lines, each picture element
125
in the upper (lower) horizontal row is offset from the corresponding element
125
in the lower (upper) horizontal row by substantially half of the pitch of the picture elements
125
. The microlenses
124
are disposed so that the optical axis of each microlens
124
coincides with the center of the “green” picture element
125
G of the corresponding set of picture elements
125
R,
125
G, and
125
B.
The light beams of R, G, and B entering the microlenses
124
thus disposed are converged to form convergence spots that fall within the aperture regions
123
of the picture elements
125
of the corresponding colors.
Referring back to
FIG. 14
, among the components of the light beams R, G, and B which have been reflected from the dichroic mirrors
105
R,
105
G, and
105
B at their respective angles, only the P-polarization component passes through the polarizing plate
109
, while the S-polarization component is absorbed by the polarizing plate
109
.
The P-polarization component of the green light beam enters a microlens
124
along the direction of the normal axis of the microlens
124
(hereinafter referred to as the “normal direction”), so as to be converged on the aperture region
123
of the corresponding green picture element
125
G. The P-polarization components of the red and blue light beams enter the microlens
124
at an angle &thgr;(in opposite directions) with respect to the normal direction, so as to be respectively converged on the aperture regions
123
of the red and blue picture elements
125
R and
125
B flanking the green picture element
125
G.
Thus, in the illustrated projection type color LC display apparatus, light beams of R, G, and B are respectively converged onto the corresponding picture elements
125
R,
125
G, and
125
B of the LC display device
106
. The light beams which have passed through the respective picture elements
125
are further projected onto a screen
128
via a field lens
126
and a projection lens
127
, whereby color display is effected.
If the collimated light from the condenser lens
104
has a poor degree of parallelism in the above-described conventional color LC display apparatus, a portion of the collimated light may not be properly converged through the microlens array
108
to stay within the aperture region
123
(FIG.
12
), and hence intercepted by the light shielding layer
122
, i.e., not transmitted through the LC display device
106
. As a result, the display images becomes darker.
The above-mentioned problem might appear to be overcome by simply optimizing the parallelism of the collimated light. However, such an approach has the following problems.
Since the parallelism of a collimated light beam generally decreases as the diameter of the collimated light beam decreases, the diameter of the collimated light beam must be maximized. However, there is an upper limit to the diameter of the collimated light beam. The reason is that an excessively large diameter of the collimated light beam causes peripheral portions of the collimated light beam to fall outside the dichroic mirrors
105
R,
105
Miyake Takahiro
Ueda Kazuhiko
Eisenzopf Reinhard J.
Lo Linus H
Nixon & Vanderhye PC
Sharp Kabushiki Kaisha
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