Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
1999-01-13
2002-03-19
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C349S162000, C349S008000
Reexamination Certificate
active
06359668
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the technical field of a display device, and particularly to the technical field of a display device such as a liquid crystal display device or the like which can be used as both a reflective display type utilizing reflection of external light and a transmissive type utilizing transmission of light from a light source, and an electronic apparatus using the display device, such as a portable telephone, a watch, or the like.
BACKGROUND ART
In a conventional reflective display device performing display by using external light, display is made hard to see in dark in accordance with decreases in the quantity of light. On the other hand, in a transmissive display device performing display by using a light source such as a back light or the like, the power consumption is increased by the amount corresponding to the light source regardless of the brightness of place, and particularly it is unsuitable as a portable display device operated by a battery. Therefore, in a transflective display device which can be used as both the reflective and transmissive display devices, mainly in the light, light being incident from the display screen is reflected by a semi-reflecting film provided in the device, and at the same time, the quantity of light emitted from the display screen is controlled for each pixel by using a liquid crystal, an optical element such as a polarized light separator or the like, which are arranged on the optical path, to perform reflective display. On the other hand, mainly in the dark, from the back of the semi-reflecting film, the light is irradiated from the light source, and at the same time, the quantity of light emitted from the display screen is controlled for each pixel by using the above mentioned liquid crystal, the optical element such as a polarized light separator or the like to perform transmissive display.
In a conventional liquid crystal display device utilizing a variable transmission polarization axis optical element making the polarization axis of transmitted light to be rotated, such as a TN (Twisted Nematic) liquid crystal, a STN (Super-Twisted Nematic) liquid crystal or the like, a structure is employed in which the variable transmission polarization axis optical element is held between two polarizers. A polarizer as an example of polarized light separators polarizes incident light by absorbing a polarized light component in a direction different from the polarization axis in a predetermined direction, and thus exhibits poor efficiency of light utilization. Particularly, in the above liquid crystal display device which can be used as both the reflective and transmissive display devices, in reflective display, light is reflected by the semi-reflecting film, thereby further deteriorating the efficiency of light utilization. Therefore, there is the problem of dark display in reflective display.
A conventional transflective display device using a TN liquid crystal panel as variable transmission polarization axis means is described with reference to FIG.
31
.
FIG. 31
is a sectional view of a conventional transflective display device.
In
FIG. 31
, the display device comprises an upper polarizer
5130
, a TN liquid crystal panel
5140
, a lower polarizer
5170
, a transflector
5180
, and a light source
5210
. Although, in
FIG. 31
, the respective portions are shown as separate portions for the sake of clarity, the portions are, in fact, closely arranged. The upper polarizer
5130
and the lower polarizer
5170
are arranged so that the transmission polarization axes thereof are perpendicular to each other in order to perform normally white display.
White display in reflective display is described. The light shown on the optical path
5111
is changed to linearly-polarized light parallel to the drawing by the upper polarizer
5130
, and the polarization axis is twisted for 90° by the TN liquid crystal panel
5140
to produce linearly-polarized light perpendicular to the drawing. The linearly-polarized light is transmitted through the lower polarizer
5170
keeping perpendicular to the drawing, and reflected by the transflector
5180
, with a part transmitted. The reflected light is again transmitted as linearly-polarized light perpendicular to the drawing through the lower polarizer
5170
, and the polarization axis is twisted for 90° by the TN liquid crystal panel
5140
to produce linearly-polarized light parallel to the drawing, which is then emitted from the upper polarizer
5130
.
Since each of the upper polarizer
5130
and the lower polarizer
5170
is a polarized light separator accompanied with absorption respectively, a part of light is absorbed during the transmissions through the upper polarizer
5130
and the lower polarizer
5170
twice for each. Furthermore, some light is transmitted through the transflector
5180
and travels toward the light source
5210
, and is not used for display. As a result, the conventional transflective liquid crystal display device exhibits a low efficiency of light utilization, and thus has the problem of darkening the display screen, particularly, in reflective display.
Therefore, the inventors proposed a transflective display device described in Japanese Patent Application No. 8-245346, which had not been published, as yet, on the priority date of this application, in which the lower polarizer and the transflector, which are on the light source side, are substituted with a reflective polarizer, which is an example of polarized light separators to reflect the light of a linearly-polarized component in a predetermined direction and also to transmit the light of a linearly-polarized component being in the direction perpendicular to the predetermined direction. In this display device, the efficiency of reflection is increased by the polarized light separator to obtain bright display. Also a display device using a reflective polarizer is disclosed in the Published Japanese Translations of PCT International Publication for Patent applications No. 9-506985 (International Publication No. WO/95/17692) and International Publication No. WO/95/27819).
Description will now be made on the transflective display device using the reflective polarizer proposed by the inventors in Japanese Patent Application No. 8-245346, with reference to FIG.
32
.
In
FIG. 32
, the display device comprises the upper polarizer
5130
, an upper glass substrate
5302
, a lower glass substrate
5304
, a polarized light separator
5160
, a transflective light absorption film
5307
, and the light source
5210
. The display device further comprises a TN liquid crystal panel held between the upper glass substrate
5302
and the lower glass substrate
5304
, the TN liquid crystal panel includes a voltage applied region
5110
and a voltage unapplied region
5120
. Particularly, the polarized light separator
5160
comprises a reflective polarizer.
First, white and black display in reflective display is described. The light, which is shown on the optical path
5601
and is incident from the outside of the display device, is changed to linearly-polarized light parallel to the drawing by the upper polarizer
5130
, and then, the polarization direction of it is twisted for 90° by the voltage unapplied region
5120
of the TN liquid crystal panel to produce light of a linearly-polarized component being in the direction perpendicular to the drawing. After that the light is reflected by the polarized light separator
5160
as it is a linearly-polarized component light perpendicular to the drawing, and then the polarization direction is twisted for 90° by the TN liquid crystal panel to produce light of a linearly-polarized component parallel to the drawing, which is then emitted from the upper polarizer
5130
. Therefore, with no voltage applied to the TN liquid crystal panel, white display is obtained. In this way, the light of white display is the light reflected by the polarized light separator
5160
which selectively reflects most of the linearly-polarized light transmitted through the upper polarize
Iijima Chiyoaki
Sakura Seiichi
Tsuchihashi Toshihiko
Harness & Dickey & Pierce P.L.C.
Qi Mike
Sikes William L.
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