Liquid crystal cells – elements and systems – Liquid crystal optical element – Liquid crystal sensors
Reexamination Certificate
2002-06-11
2004-02-10
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal optical element
Liquid crystal sensors
C349S096000, C349S200000, C349S201000, C349S199000, C340S815570
Reexamination Certificate
active
06690449
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of liquid crystal displays (LCD's). Specifically, embodiments of the present invention relate to an LCD power loss indication.
BACKGROUND OF THE INVENTION
Portable electronic devices, such as telephones, calculators, personal digital assistants, handheld computer systems or two-way radios are frequently equipped with LCD display screens. These devices are generally powered using either rechargeable or disposable batteries. There are many other similar types of electronic devices that have a battery and an LCD screen. Video game systems, pagers, GPS's, watches, clocks, and other such devices are examples of other types of electronic devices in common use that may contain a battery and an LCD display screen.
Many of these devices have displays and/or alarms to apprise a user when the battery power is low. One conventional approach to apprising a user of low battery power is by use of a display that is illustrated in
FIGS. 1A-1D
.
FIG. 1A
illustrates an LCD display screen
100
a
showing a fully charged battery as exemplified by the image of a battery having three areas indicated to represent full power.
FIG. 1B
illustrates an LCD display screen
100
b
showing a partially charged battery as exemplified by the battery image having two areas indicated and one area appearing blank, signifying a lack of charge. Likewise,
FIG. 1C
illustrates an LCD screen
100
c
showing a low battery charge as exemplified by only one area indicated and the remaining area blank.
FIG. 1D
is an illustration of an LCD screen
100
d
that is inoperable, according to the prior art. The inoperability may be the result of a dead or missing battery, or it may be the result of a faulty device. If there is a dead battery or one that is not present, there is no electricity to light the indicator on the display or to sound an alarm. Thus, there is no apparent way to determine whether the screen is not showing a display because of a lack of power or because either the screen or the device containing the screen is broken.
FIG. 2A
is an exploded diagram of a non-energized LCD display in accordance with prior art. The LCD is composed of a series of layers, beginning with a mirrored substrate
201
upon which is layered a continuous polarizing filter
202
with a specific orientation. Upon the polarizing filter is a semi-continuous electrode layer
203
that has spaces corresponding to the locations of connectors on electrode layer
207
. Liquid crystal layer
205
is layered between alignment gratings
204
and
206
, together with which, in a nonenergized state, it rotates the plane of polarization of light through a ninety degree angle as represented by arrow
210
.
Referring still to
FIG. 2A
, discontinuous electrode layer
207
has electrodes in the contour of an image, such as shown in
FIGS. 1A-1C
, to be displayed when the LCD is energized. There are connectors running from the image to the edge of electrode layer
207
that are mimicked by the spaces in electrode layer
203
below so that they will not be displayed in an energized state. Above discontinuous electrode layer
207
is another continuous polarizing filter layer
208
that has a plane of polarization oriented at 90 degrees from that of continuous polarizing filter layer
202
. Next is a layer of glass
209
at the top surface of the LCD display.
Light passing into the LCD display of
FIG. 2A
strikes the first polarizing filter
208
and is polarized. The polarized light then passes through the liquid crystal and alignment grating layers, where the molecules in the layers change the light's plane of vibration to match their own angle. When the light reaches the far side of these layers, it has been rotated ninety degrees and is matched up with the continuous polarizing filter layer
202
, so it will pass through and reflect off the mirrored surface of the substrate. The reflected light passes back up through the layer stack, is again rotated by the liquid crystal layer, and is able to pass through both polarizing layers, out of the display and into the eye of an observer, thus appearing transparent on the display.
FIG. 2B
is an exploded diagram of an energized LCD display in accordance with prior art. In this case electrode layers
207
and
203
are energized and have common-plane energized electrodes in the contour of the image
212
. The liquid crystal molecules untwist, as indicated by arrow
211
, between the common plane of energized electrodes and the polarized light in that region is blocked by polarizing filter
202
. This causes the LCD to display the image as a dark area on a bright background.
While the prior art displays a depletion of the battery charge and an approaching loss of power, when the power is completely depleted or missing, it shows no indication at all. Thus, a user does not know whether the battery is dead or missing, or whether the device is in some way defective.
SUMMARY OF THE INVENTION
A device and method for indicating a power loss in an LCD is disclosed. In one embodiment, the device provides a display that indicates an absence of power to the LCD. The device includes a continuous polarizing filter layer disposed within a display area that makes up a portion of the total display area of the LCD. A layer of liquid crystals is disposed between alignment gratings and coupled to the continuous polarizing filter layer. In one embodiment a discontinuous polarizing filter layer is optically coupled to the layer of liquid crystals. The discontinuous polarizing filter layer has a plane of polarization aligned with the plane of polarization of the continuous polarizing filter, and the discontinuous polarizing filter layer comprises a contour within the display area conforming to an image, wherein the image is displayed in the absence of an electric field.
REFERENCES:
patent: 5673028 (1997-09-01), Levy
Cawte Andrew
Inglis Edward
Cisco Technology Inc.
Di Grazio Jeanne A.
Kim Robert H.
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