Display device and electronic equipment employing the same

Details Display device and electronic equipment employing the same Display device and electronic equipment employing the same

2002-07-22

2004-07-27

Hjerpe, Richard (Department: 2674)

Computer graphics processing and selective visual display system

Plural physical display element control system

Display elements arranged in matrix

C345S089000, C345S090000, C345S096000, C345S099000, C345S103000, C345S100000, C349S009000, C349S057000, C349S121000, C349S117000, C349S104000

Reexamination Certificate

active

06768481

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a technical field of display devices and, more particularly, to a display device such as a liquid crystal display that is equipped with a polarized light separator such as a polarizer or a reflective polarizer and that can be used as a reflective type in which external light is reflected to perform display and also as a transmissive type in which the light of a light source is transmitted to perform display, a driving method for the same, and electronic equipment such as a portable telephone, a watch, and a portable information terminal that employ the same.
BACKGROUND ART
Hitherto, in the case of a reflective type display device that makes use of external light to carry out display, the display becomes difficult to view as the quantity of light decreases in a dark place. On the other hand, a transmissive type display device that makes use of a backlight or other light source to carry out display consumes more electric power because of the light source regardless of whether the location where it is placed is bright or dark, and it is therefore not suited for a portable display device or the like operated on batteries in particular. Hence, a transflective type display device that can be used as the reflective type and also as the transmissive type is adapted to reflect external light entering through a display screen by a semi-reflective film provided therein while controlling the quantity of light outgoing from the display screen for each pixel by employing an optical element such as a liquid crystal or a polarized light separator disposed on an optical path thereof whereby to perform reflective display mainly for a bright place. On the other hand, mainly for a dark place, the transflective type display device is adapted to apply light source light by employing a built-in light source such as a backlight from the rear side of the foregoing semi-reflective film while controlling the quantity of light outgoing from the display screen for each pixel by employing an optical element such as a liquid crystal or a polarized light separator thereby to perform transmissive display.
A conventional liquid crystal display device that utilizes a variable transmission polarization axis optical element such as a TN (Twisted Nematic) liquid crystal, STN (Super-Twisted Nematic) liquid crystal or the like in which the polarization axis of transmitted light is rotated employs a structure wherein the variable transmission polarization axis optical element is sandwiched between two polarizers. The polarizer, which is an example of a polarized light separator, effects polarization by absorbing polarized light components in a different direction from that of a particular polarization axis direction from incident light, leading to a poor utilization factor of light. Especially in the case of the liquid crystal display device that can be used as the reflective type and also as the transmissive type described above, since light is reflected by the semi-reflective film for the reflective display, the utilization factor of light is worse. This poses a problem of dark display when the reflective display is carried out.
Referring to
FIG. 33
, a conventional transflective type display device employing a TN liquid crystal panel as the variable transmission polarization axis means will be described.
FIG. 33
is a sectional view showing the conventional transflective type display device.
In
FIG. 33
, the display device is provided with an upper polarizer
205
, an upper glass substrate
206
, a TN liquid crystal layer that includes a voltage applied region
207
and a voltage non-applied region
208
, a lower glass plate
209
, a lower polarizer
210
, a transflective plate
211
, and a light source
212
. As the transflective plate
211
, an Al (aluminum) plate formed to be thin, for example, is used. Alternatively, the transflective plate
211
may be configured by providing a reflective plate with an opening. In
FIG. 33
, the respective components are shown as if they were separated for the sake of clarity; however, they are actually disposed in close contact to each other. Further, it is assumed that the upper polarizer
205
and the lower polarizer
210
are arranged such that the transmissive polarization axes are mutually orthogonalized to effect display in a normally white mode.
First, white display in the reflective display will be discussed. A light indicated on an optical path
201
is converted by the upper polarizer
205
into a linearly polarized light, which is directed parallel to a paper surface, twisted by 90 degrees in the direction of polarization in the voltage non-applied region
208
of the TN liquid crystal layer into a linearly polarized light perpendicular to the paper surface, transmitted as the linearly polarized light perpendicular to the paper surface through the lower polarizer
210
, and reflected by the transflective plate
211
, a part thereof being transmitted. The reflected light is transmitted again through the lower polarizer
210
as the linearly polarized light perpendicular to the paper surface, and twisted in the voltage non-applied region
208
of the TN liquid crystal layer by 90 degrees in the direction of polarization to become a linearly polarized light parallel to the paper surface, then it exits the upper polarizer
205
. Thus, the white display is effected when no voltage is applied. In contrast to this, a light indicated by an optical path
203
is converted by the upper polarizer
205
into a linearly polarized light ray parallel to the paper surface, transmitted as the linearly polarized light parallel to the paper surface without being changed in the direction of polarization in the voltage applied region
207
of the TN liquid crystal layer, and absorbed by the lower polarizer
210
, thus effecting black display.
The white display and the black display in the case of a transmissive display operation will now be described. A part of a light that is emitted from a light source
212
and that is indicated on an optical path
202
is transmitted through a transflective plate
211
, converted on the lower polarizer
210
into a linearly polarized light perpendicular to the paper surface, twisted by 90 degrees in the direction of polarization in the voltage non-applied region of the TN liquid crystal layer to become a linearly polarized light parallel to the paper surface, and transmitted through the upper polarizer
205
as the linearly polarized light parallel to the paper surface, thus effecting the white display. In contrast to this, a part of a light that is emitted from the light source
212
and indicated on an optical path
204
is transmitted through the transflective plate
211
, converted by the lower polarizer
210
into a linearly polarized light perpendicular to the paper surface, transmitted without being changed in the direction of polarization in the voltage applied region
207
of the TN liquid crystal layer, and absorbed by the upper polarizer
205
, thus effecting black display.
As set forth above, the upper polarizer
205
and the lower polarizer
210
are both polarized light separators that involve the absorption; therefore, especially in the case of the reflective display, the light is partly absorbed when it is transmitted twice through the upper polarizer
205
and the lower polarizer
210
. Furthermore, some of the light is transmitted through the transflective plate
211
to the light source
212
side and therefore not used for the display. As a result, the conventional transflective type liquid crystal display device has been posing a problem of a poor light utilization factor that causes a dark display screen especially in the case of the reflective display mode.
To solve the aforesaid problem, in Japanese Patent Application No. 8-245346 that was not yet laid open to the public on the priority date of the application concerned, we have proposed a transflective type display device that employs a reflective polarizer, which is an example of a polarized light separator for r

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