Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
2000-06-29
2004-09-28
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
Reexamination Certificate
active
06798468
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a display device and an electronic apparatus. More particularly, the present invention relates to a transflective display device having two modes of display.
DISCUSSION
Since a conventional display device employing TN (Twisted Nematic) liquid crystal or STN (Super-Twisted Nematic) liquid crystal adopts the structure of a liquid-crystal display panel sandwiched between two polarizers, the utilization of light is poor. A transflective display device in particular suffers dark display during a reflective display mode.
Referring to
FIG. 14
, a conventional transflective liquid-crystal display device using a TN liquid-crystal display panel is now discussed. Referring to
FIG. 14
, there are shown an upper polarizer
130
, a TN liquid-crystal display panel
140
, a lower polarizer
170
, a transflective plate
180
, and a light source
210
. Although
FIG. 14
shows the components spaced apart from each other, they actually closely adhere to one another.
Discussed now is how white color is presented during a reflective display mode. A light ray
111
is linearly polarized in a direction parallel with the page bearing
FIG. 14
by the upper polarizer
130
, is twisted in a polarization direction 90° by the TN liquid-crystal display panel
140
, becoming a light ray linearly polarized in a direction perpendicular to the page, and is then transmitted through the lower polarizer
170
. Part of the light ray transmitted through the lower polarizer
170
is reflected by the transflective plate
180
, and is again transmitted through the lower polarizer
170
. The light ray is then twisted in a polarization direction 90° by the TN liquid-crystal display panel
140
and is thus linearly polarized in a direction parallel with the page, and is then transmitted through the upper polarizer
130
.
Because of its light absorbing feature, the lower polarizer
170
partly absorbs the light ray. This lowers the utilization of light, presenting a dark display during the reflective display mode.
In an effort to resolve this problem, we have proposed a transflective display device (see Japanese Patent Application No. 8-245346) in which the lower polarizer
170
is replaced with a reflective polarizer that reflects a light ray component linearly polarized in a predetermined direction while transmitting a light ray component linearly polarized in a direction perpendicular to the predetermined direction. Referring to
FIG. 15
, the transflective display device using this reflective polarizer is now discussed.
Referring to
FIG. 15
, there are shown a non-voltage applied area
605
of the TN liquid-crystal display panel and a voltage applied area
606
of the TN liquid-crystal display panel. There are also shown the upper polarizer
130
, an upper glass substrate
302
, a lower glass substrate
304
, a reflective polarizer
160
, a transmissive-absorbent layer
307
, and a lighting apparatus
210
.
The principle of the reflective display mode is now discussed. A light ray
601
, which is linearly polarized in a direction parallel with the page by the upper polarizer
130
, is twisted in a polarization direction
900
by the non-voltage applied area
605
of the TN liquid-crystal display panel, thereby becoming a light ray linearly polarized in a direction perpendicular to the page. The light ray is then reflected by the reflective polarizer
160
, and is twisted in a polarization direction 90° by the non-voltage applied area
605
of the TN liquid-crystal display panel, thereby becoming a light ray linearly polarized in a direction parallel with the page. The light ray is then transmitted through the upper polarizer
130
. When no voltage is applied to the TN liquid-crystal panel, a white display is thus presented.
On the other hand, a light ray
603
, which is linearly polarized in a direction parallel with the page by the upper polarizer
130
, is transmitted through the voltage applied area
606
of the TN liquid-crystal display panel without any change in a polarization direction, and is transmitted through the reflective polarizer
160
. The light ray is then absorbed by the transmissive-absorbent layer
307
. A black display is thus presented when a voltage is applied to the TN liquid-crystal display panel.
During the transmissive display mode, a light ray
602
emitted from the lighting apparatus
210
passes through an aperture formed in the transmissive-absorbent layer
307
, and is linearly polarized in a direction parallel with the page by the reflective polarizer
160
. The light ray is then twisted in a polarization direction 90° by the non-voltage applied area
605
of the TN liquid-crystal display panel, thereby becoming a light ray linearly polarized in a direction perpendicular to the page, and is absorbed by the upper polarizer
130
. A black display is thus presented when no voltage is applied to the TN liquid-crystal display panel.
A light ray
604
emitted from the lighting apparatus
210
passes through an aperture formed in the transmissive-absorbent layer
307
, and is linearly polarized in a direction parallel with the page by the reflective polarizer
160
. The light ray is then transmitted through the voltage applied area
606
of the TN liquid-crystal display panel with no change in a polarization direction, and is transmitted through the upper polarizer
130
. A white display is thus presented when a voltage is applied to the TN liquid-crystal display panel.
In the transflective display device using such a reflective polarizer, a positive-negative relationship is reversed between the display in the reflective display mode and the display in the transmissive display mode. For this reason, a user has difficulty watching a display with the lighting apparatus
210
lit under an external light, and the display under such conditions is not adequate depending on the purpose of use.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a display device that is free from a positive-negative reversal between the reflective display mode and the transmissive display mode. It is another object of the present invention to provide an electronic apparatus employing such a display device.
The above and other objects are provided by a display device includes a reflective polarizer beneath a liquid-crystal display panel, and a light diffusing plate and a lighting apparatus disposed beneath the reflective polarizer. In a reflective display mode, the display device presents a specular display resulting from a light ray reflected by the reflective polarizer and a diffusion display resulting from a diffused light. In a transmissive display mode, the display device presents a dark display and a diffusion display caused by the light diffusing plate.
The present invention works on the above principle, and comprises polarization axis varying means, first polarizing splitter means disposed on one side of the polarization axis varying means which transmits a light ray component linearly polarized in a first direction while reflecting or absorbing a light ray component linearly polarized in a predetermined direction different from the first direction, second polarizing splitter means disposed on the other side of the polarization axis varying means which reflects a light ray component linearly polarized in a second direction while transmitting a light ray component linearly polarized in a predetermined direction different from the second direction, lighting means disposed on the side of the second polarizing splitter means opposite to the polarization axis varying means, and light diffusing means disposed between the second polarizing splitter means and the lighting means which diffuses and reflects a light ray coming in from the second polarizing splitter means, while transmitting a light ray coming from the lighting means toward the second polarizing splitter means.
REFERENCES:
patent: 4678285 (1987-07-01), Ohta et al.
patent: RE33987 (1992-07-01), Suzawa
patent: 5339179 (1994-08-01), Rudisill et al.
patent: 5479279 (199
Akkapeddi P. R.
Harness & Dickey & Pierce P.L.C.
Kim Robert H.
Seiko Epson Corporation
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