Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-06-13
2003-07-22
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S096000, C349S113000, C349S114000, C349S117000
Reexamination Certificate
active
06597418
ABSTRACT:
This application claims the benefit of Korean Patent Application No. P00-32588, filed on Jun. 14, 2000, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a liquid crystal display device, and more particularly, to a transparent reflective liquid crystal display that is capable of improving a light efficiency and a color purity.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) of active matrix driving system uses thin film transistors (TFT's) as switching devices to display a natural moving picture. Since such a liquid crystal display can be made into a smaller-size device than a CRT (cathode ray tube), it is commercially available as a monitor in portable devices, such as portable televisions, laptop personal computers, and the like.
Such a LCD requires a separate light source because it is not a self-emitting device. The LCD can be largely classified into a transmissive type and a reflective type depending on a type of light source. The transmissive LCD has a backlight unit installed opposite the rear substrate of two transparent substrates into which a liquid crystal is injected, to transmit light being input from the backlight unit to a screen. On the other hand, the reflective LCD has a reflective surface formed on the rear substrate of two transparent substrates into which a liquid crystal is injected, to reflect an external light or a separate auxiliary light incident the rear substrate via the front substrate to a screen.
Recent investigations have been made to study a transparent reflective LCD capable of having the advantages of both the transmissive type and the reflective type.
Referring to
FIG. 1
, the conventional transparent reflective LCD includes a front substrate
108
and a rear substrate
104
having a liquid crystal
106
injected therebetween, a &lgr;/4 plate
109
and a linear polarizer
110
disposed on the front surface of the front substrate
108
, an absorptive color filter
107
installed between the front substrate
108
and the liquid crystal
106
, a &lgr;/4 plate
103
and a linear polarizer
102
disposed on the rear surface of the rear substrate
104
, and a metal reflecting plate
105
installed between the rear substrate
104
and the liquid crystal
106
. Holes
105
a
are defined in the metal reflecting plate
105
at a desired interval.
An external light is converted into a specific linear-polarized light by means of the linear polarizer
110
and thereafter is converted into a circular-polarized light by means of the &lgr;/4 plate
109
to be incident to the metal reflecting plate
105
via the absorptive color filter
107
and the liquid crystal
106
. The external light being incident to the metal reflecting plate
105
retrogresses a light path to go toward the display screen. At this time, the absorptive color filter
107
transmits only a visible light having a specific wavelength band and absorbs a light beam having other wavelength bands. A light input from the backlight unit
101
is converted into a specific linear-polarized light by means of the linear polarizer
102
, is then converted into a circular-polarized light by means of the &lgr;/4 plate
103
to traverse the rear substrate
104
, and thereafter is incident to the metal reflecting plate
105
. Light from the backlight unit
101
incident the metal reflecting plate
105
in this manner also is incident the liquid crystal
106
via a hole
105
a
of the metal reflecting plate
105
, and then goes toward the display screen via the liquid crystal
106
.
However, the conventional transparent reflective LCD has a drawback in that a light irradiated from the backlight unit
101
has a large light loss due to the linear polarizer
102
at the rear substrate side. Consequently, a light absorption ratio of the linear polarizer
102
is about 55% or more. Also, only a portion of the light passing through the linear polarizer
102
goes toward the display screen via the hole
105
a
of the metal reflecting plate
105
. At this time, since light reflects from the metal reflecting plate
105
without passing through the hole
105
a
and retrogresses a light path incident to the linear polarizer
102
in a changed polarization state, most reflective light is absorbed by the linear polarizer
102
. In the case of displaying a picture or an image using the transmissive type, a light efficiency is deteriorated because only a slight portion of a light generated from the backlight unit
101
is utilized for a display light. Furthermore, the conventional transparent reflective LCD has a problem in that it is difficult to obtain acceptable color purity.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a transparent reflective liquid crystal display that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
In one aspect of the present invention, a transparent reflective liquid crystal display is provided with a structure adapted for improving light efficiency.
In another aspect of the present invention, a transparent reflective liquid crystal display is provided with a structure that provides adequate color purity.
In order to achieve these and other objects of the invention, a transparent reflective liquid crystal display device according to an embodiment of the present invention includes a first circular polarizer for transmitting a circular-polarized light input from a backlight unit having a first direction while reflecting a circular-polarized light having a second direction contrary to the first direction. A second circular polarizer is arranged in opposition to the first circular polarizer and transmits circular-polarized light having the second direction while reflecting the circular-polarized light having the first direction. Such an arrangement that includes a pair circular polarizers can improve the ratio of light reaching a display screen from a backlight unit to the light emitted from a backlight unit.
To provide increased color purity, a circular-polarizing color filter is provided at one side of the second circular polarizer for extracting a circular-polarized light having a specific visible light wavelength band in the circular-polarized light having the first direction, and a reflecting member is arranged in opposition to the second circular polarizer to reflect light from an external source. The reflecting member has a hole formed in opposition to the circular-polarizing color filter to transmit the circular-polarized light having the specific visible light wavelength band via the hole.
A transparent reflective liquid crystal display device according to another embodiment of the present invention includes a circular polarizer for transmitting a circular-polarized light having a first direction input from the backlight unit while reflecting a circular-polarized light having a second direction contrary to the first direction. A &lgr;/4 plate is arranged in opposition to the circular polarizer for converting a circular-polarized light input from the circular polarizer into a linear-polarized light having a specific direction.
To improve color purity, a first circular-polarizing color filter is provided for reflecting a circular-polarized light having a specific visible light wavelength band in a circular-polarized light from an external light source, and a light-absorbing member is provided at a rear side of the circular-polarizing color filter for absorbing light that transmits through the circular-polarizing color filter. Between the first &lgr;/4 plate and the light-absorbing member, a reflecting member may be provided for reflecting light, and a second circular-polarizing color filter for transmitting a circular-polarized light having a specific visible light band in the circular-polarized light input from the circular polarizer may be provided in a hole passing through the first circular-polarizing color filter, the light-absorbing member, the reflecting member, and/or the &lgr;/4 plate.
Kim Yong Beom
Moon Jong Weon
Chowdhury Tarifur R.
LG. Philips LCD Co. Ltd.
Morgan & Lewis & Bockius, LLP
LandOfFree
Transparent reflective liquid crystal display does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Transparent reflective liquid crystal display, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transparent reflective liquid crystal display will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3027035