Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-08-03
2004-01-13
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S062000, C349S007000
Reexamination Certificate
active
06678023
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projector using a liquid crystal display device. And also, the present invention relates to a liquid crystal projection TV incorporating the liquid crystal projector.
2. Description of the Related Art
In recent years, a technique for manufacturing a semiconductor device in which a semiconductor thin film is formed on an inexpensive glass substrate, such as a thin film transistor (TFT), has been rapidly developed. The reason is that the demand for an active matrix type liquid crystal display device (liquid crystal panel) has been increased.
The active matrix type liquid crystal panel is structured such that a TFT is disposed for each of several tens to several millions pixel regions disposed in matrix, and an electric charge going in and out of each pixel electrode is controlled by the switching function of the TFT.
Above all, a projection type display device using an active matrix type liquid crystal panel, a so-called projector has rapidly broadened the market. The reason is that the liquid crystal projector is superior in color reproducibility, is small, is lightweight, and has low power consumption, as compared with a projector using a CRT.
The liquid crystal projector is classified into a three-panel type and a single panel type by the number of active matrix type liquid crystal panels to be used.
FIG. 16
shows an example of a three-plate type liquid crystal projector. Reference numeral
1601
denotes a light source,
1602
and
1603
denote dichroic mirrors for selectively reflecting light in a wavelength region of R (red) and G (green), respectively. Reference numerals
1604
,
1605
, and
1606
denote total reflection mirrors, and
1607
,
1608
, and
1609
denote transmission type liquid crystal panels corresponding to R, G, and B. Reference numeral
1610
denotes a dichroic prism, and
1611
denotes a projection lens.
In the three-plate type liquid crystal projector, pictures corresponding to the three primary colors of red, green, and blue are displayed on the three black and white display liquid crystal panels
1607
,
1608
, and
1609
, and the liquid crystal panels are illuminated with beams of light of the three primary colors corresponding to the pictures. The obtained pictures of the respective primary color components are synthesized by the dichroic prism
1610
and are projected on a screen. Thus, the three-plate type liquid crystal projector is superior in display properties (resolution, screen illumination, color purity). However, since the liquid crystal panels and optical parts (lenses, mirrors, and the like) for three systems are required, the optical system becomes complicated and miniaturization is difficult. Moreover, since the expensive dichroic prism is required, the cost becomes very high.
On the other hand, in the single plate type liquid crystal projector, by the same system as a conventional direct view type liquid crystal display device using a color filter, the obtained color picture is projected on a screen by a method of driving each of the R, G, and B pixels.
FIG. 17
is a structural view showing a conventional single plate type projector. Reference numeral
1701
denotes a light source,
1702
denotes a condensing lens,
1703
denotes a liquid crystal panel,
1704
denotes a projection lens, and
1705
denotes a screen.
Since the number of optical parts of the single plate type liquid crystal projector is merely ⅓ of those of the foregoing three-plate type liquid crystal projector, the single type liquid crystal projector is superior in cost, size, and the like. However, in the case where the same liquid crystal panel is used for both the three-plate type and the conventional single plate type, while three colors are overlapped on one pixel in the three-plate type, one pixel can be used only as one color pixel in the single plate type, so that the picture quality of the single plate type is inferior to that of the three-plate type. Moreover, in the above single plate type liquid crystal projector, a desired color picture is obtained by making an unnecessary component absorbed by a color filter. Thus, only ⅓ of the white light incident on the liquid crystal panel transmits, so that use efficiency of light is poor.
Although a method of making a light source brighter has been adopted to improve the brightness of the above single plate type liquid crystal projector, there have occurred problems with respect to the heat generation due to light absorption of a color filter and its light resistance.
Then, for the purpose of overcoming the defects of the conventional single plate type liquid crystal projector, a liquid crystal projector using three dichroic mirrors and a microlens array has been devised.
Reference will be made to FIG.
18
.
FIG. 18
is a structural view showing an optical system of the above single plate type liquid crystal projector. Reference numeral
1801
denotes a white light source including a lamp and a reflector. Reference numerals
1802
,
1803
, and
1804
denote dichroic mirrors which reflect light in the wavelength regions of blue, red, or green, respectively. Reference numeral
1805
denotes a microlens array which is constituted by a plurality of microlenses. Reference numeral
1806
denotes a liquid crystal panel, which makes display in a TN (twisted nematic) mode. Incidentally, the liquid crystal panel
1806
operates in a normally white mode in which white display is made when a voltage is not applied. Reference numeral
1807
denotes a field lens,
1808
denotes a projection lens, and
1809
denotes a screen.
The light
1801
source emits the white light having a spectrum of red, green, and blue. The light source
1801
is set so that the parallelity of the emitted white light becomes high. The reflector is used to effectively use the white light emitted from the lamp.
The white light emitted from the light source
1801
is incident on the dichroic mirrors
1802
,
1803
, and
1804
. These three dichroic mirrors are disposed at different angles so that the white light from the light source
1801
is separated into beams of light of three primary colors (red, green, and blue), and these three light beams are incident on the microlens array
1805
at different angles.
The dichroic mirror
1802
reflects only the ray of light in the blue wavelength region and transmits other beams of light. The dichroic mirror
1803
reflects only the ray of light in the red (R) wavelength region among the beams of light having passed through the dichroic mirror
1802
, and transmits other beams of light. The dichroic mirror
1804
reflects the ray of light in the green wavelength region among the beams of light having passed through the dichroic mirrors
1802
and
1803
. By adopting such a structure, it is possible to separate the white light emitted from the light source
1801
into three colors.
Reference will be made to FIG.
19
. As shown in
FIG. 19
, one microlens corresponds to three pixels of the liquid crystal panel
1806
corresponding to the three primary colors of R, G, and B.
The microlens array
1805
distributes the above separated beams of light of the three primary colors to the corresponding pixels and condenses the beams.
Like this, in the single plate type liquid crystal projector having the above structure, after the white light is separated into beams of light of the three primary colors of R, G, and B, the respective beams of light are made incident on an opening portion of the corresponding pixel of the liquid crystal panel by the microlens, so that the light can be used at efficiency not less than three times the foregoing single plate type liquid crystal projector using the color filter.
However, in the liquid crystal projector using this microlens, the light flux condensed to the respective pixels by the microlens diverges in a large angle range after it has passed through the liquid crystal panel. Thus, unless a projection lens with a large aperture is used, the light flux can not be completely use
Hamada Hiroshi
Hirakata Yoshiharu
Mizuguchi Yoshihiro
Naka Shun-ichi
Nishi Takeshi
Robinson Eric J.
Robinson Intellectual Property Law Office P.C.
Semiconductor Energy Laboratory Co,. Ltd.
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