Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-03-25
2003-01-14
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S115000
Reexamination Certificate
active
06507380
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a display device particularly to a display device and such as a liquid crystal display device which is equipped with a polarized light separator, such as a polarizer or a reflective polarizer, and which can serve as both a reflective type device that displays by reflecting external light and a transmissive type device that displays by allowing light from a light source to be transmitted and, further, to an electronic apparatus such as a portable telephone and a watch using such a display device.
BACKGROUND ART
Conventionally, in the case of a reflective type device, which displays by using external light, the display becomes rather hard to see in a dark place as the quantity of light decreases. On the other hand, in the case of a transmissive type device, which displays by using a light source, such as a backlight, the power consumption is rather large due to the light source regardless of whether the device is used in a light place or a dark place. In particular, it is not suitable for a portable display device or the like of the type which is operated by a battery. In view of this, a transflective display device, which can serve as both a reflective type and a transmissive type device, effects reflective type display, mainly in a light place, by controlling the quantity of light emitted from the display screen for each pixel by means of optical elements, such as liquid crystal and a polarized light separator arranged in the optical path thereof while reflecting external light entering from the display screen by a transflective film provided in the device. On the other hand, it effects transmissive type display, mainly in a dark place, by controlling the quantity of light emitted from the display screen for each pixel by means of the above-mentioned optical elements such as liquid crystal and the polarized light separator while applying light from a built-in light source, such as backlight, from behind the above-mentioned transflective film.
A liquid crystal display device which is thus capable of being used as both a reflective type and a transmissive type device and which utilizes a variable transmission polarization axis optical element that rotates the polarization axis of transmission light of a conventional TN (Twisted Nematic) liquid crystal or STN (Super-Twisted Nematic), adopts a construction in which this variable transmission polarization axis optical element is placed between two polarizers.
In the case of the above-described reflective type display, in the construction equipped with these two polarizers, when external light impinges upon the display screen, only a polarized light component in a specific direction is transmitted through the first polarizer on the display screen side of the liquid crystal, and the other polarized light component is absorbed by this first polarizer. The direction of polarization of the light transmitted through the first polarizer is selectively varied in accordance with the orientation of the liquid crystal, which varies depending on the voltage applied to the liquid crystal, and the light impinges upon the second polarizer on the other side of the liquid crystal. For example, in a normally white mode, this external light behaves as follows with respect to each pixel: (i) when no voltage is applied to the liquid crystal, the light emitted from this liquid crystal is transmitted through the second polarizer and is further reflected by a reflection plate on the back side thereof, and then transmitted again through the second polarizer, the liquid crystal and the first polarizer to be emitted from the display screen of the liquid crystal display device as display light; and (ii) when a voltage is applied to the liquid crystal, the light emitted from this liquid crystal is absorbed by the second polarizer and no display light is eventually emitted from the display screen.
In this way, reflective type display is effected by controlling the quantity of display light emitted from the display screen for each pixel using the liquid crystal, polarizer or the like arranged in the optical path of external light while reflecting the external light impinging from the display surface by a reflection film provided inside the device.
In the case of the above mentioned transmissive type display, in the construction in which these two polarizers are provided, when light from a light source is emitted from behind the liquid crystal as seen from the display screen, only a polarized light component in a specific direction is transmitted through the second polarizer on the back side of the liquid crystal, and the other polarized light component is absorbed by this second polarizer. The direction of polarization of the light transmitted through the second polarizer is selectively varied in accordance with the orientation of the liquid crystal depending on the voltage applied to the liquid crystal, and the light impinges upon the first polarizer on the display screen side of the liquid crystal. This light from the light source behaves, for example, in normally white mode, as follows with respect to each pixel: (i) when no voltage is applied to the liquid crystal, the light emitted from this liquid crystal is transmitted through the first polarizer, and emitted from the display screen of the liquid crystal display device as display light, and (ii) when a voltage is applied to the liquid crystal, the light emitted from this liquid crystal is absorbed by the first polarizer and no display light is emitted from the display screen.
In this way, the transmissive type display is effected by controlling the quantity of light emitted from the display screen for each pixel using the liquid crystal, polarizer or the like arranged in the optical path of the light from the light source.
DISCLOSURE OF INVENTION
However, a polarizer, which is an example of the polarized light separator, effects polarization by absorbing the polarized light component which is in a direction different from a specific polarization axis direction of the incident light, so that the efficiency in the utilization of light is rather poor. Thus, in reflective type display and transmissive type display, which are effected, as described above, with two polarizers arranged on either side of the liquid crystal, the display is rather dark. If an attempt is made to brighten the display by simply replacing the polarizers by some other polarized light separation means, the contrast in display, which is regarded as important as the brightness of display, deteriorates.
The present invention has been made in view of the above problem. It is an object of the present invention to provide a display device of the type which can display high contrast and bright display at the reflective display and the transmissive display and an electronic apparatus using this display device in a display device utilizing a variable transmission polarization axis variable optical element such as liquid crystal.
The above object of the present invention is achieved by a display device comprising: variable transmission polarization axis means capable of varying a transmission polarization axis; first polarized light separating means which is arranged on one side of the variable transmission polarization axis means and which allows light that is a linear polarized light component in a first direction to be transmitted and reflects or absorbs light that is a linear polarized light component in a predetermined direction different from the first direction; second polarized light separating means which is arranged on the other side of the variable transmission polarization axis means and which allows light that is a linear polarized light component in a second direction to be transmitted and reflects light that is a linear polarized light component in a predetermined direction different from the second direction; a polarizer arranged on the opposite side of the variable transmission polarization axis means with respect to the second polarized light separating means; and a light source w
Harness & Dickey & Pierce P.L.C.
Seiko Epson Corporation
Ton Toan
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