Liquid crystal cells – elements and systems – Liquid crystal system – Liquid crystal writing tablet
Reexamination Certificate
1999-06-14
2001-02-20
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal system
Liquid crystal writing tablet
C345S174000
Reexamination Certificate
active
06191828
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a position sensible liquid crystal display (PSLCD) device, and more particularly, to a position sensible liquid crystal display device having the capability of sensing the precise position of a stylus on the display.
2. Discussion of the Related Art
In general, as shown in
FIG. 1
, a liquid crystal display (LCD) device includes an upper plate
3
, a lower plate
1
, and a liquid crystal sealed between the upper and lower plates. The upper plate
3
has a common electrode
6
, a layer of black matrix
4
, and a layer of R (red), G (green), and B (blue) color filers
5
that filter light to generate colors. The lower plate has a plurality of data lines and scanning lines arranged at right angles and at fixed intervals to form a matrix of pixel regions therebetween. Each of the pixel regions has a thin film transistor and a pixel electrode. More particularly, lower plate
1
has thin film transistors
2
disposed thereon at fixed intervals, each with a gate electrode G (corresponding to a scanning line), a source electrode S, and a drain electrode D (corresponding to a data line). Each of the pixel regions has a pixel electrode
2
a
connected to the drain electrode D of the thin film transistor
2
. Black matrix
4
on the upper plate
3
blocks light in sections other than pixel electrodes
2
a,
which corresponds to the R, G, and B color filters
5
. Upon selective application of driving signals from external driving circuits to the scanning lines and the data lines, the LCD device displays an image. Recently, much effort has gone into providing the LCD with a position sensor input device so that the LCD can be used like a note book. That is, a position sensible LCD device is used with a position sensor input device to display letters or graphics written with a stylus on the LCD.
FIGS. 2A and 2B
illustrate layers in a position sensible LCD device, wherein
FIG. 2A
illustrates a PSLCD device having an opaque position sensor input device and
FIG. 2B
illustrates a PSLCD device having a transparent position sensor input device.
The PSLCD device having an opaque position sensor input device includes a PSD (Position Sensor input Device) panel
21
, a back light layer
22
, an LCD panel
23
, and a protective layer
24
arranged in succession. The PSLCD device having a transparent position sensor input device includes a back light layer
22
, an LCD panel
23
, and a PSD panel
21
arranged in succession.
The operation of the aforementioned PSLCD devices will be explained.
FIG. 3
is a block diagram of the modules of a PSLCD system.
A driving pulse circuit
12
alternately provides driving pulses to the PSD panel
21
in X-, and Y-axis directions. LCD driving circuit
13
provides a driving signal to the LCD in PSLCD
11
. Personal computer
14
controls the LCD driving circuit
13
. A stylus
15
is sensed according to capacitive coupling occurring in the PSD. A PSD data processing circuit
16
processes a position signal of the stylus
15
to provide position data. Microcomputer
17
controls the driving pulse generating circuit
12
and transfers the position data from the PSD data processing circuit
16
to the personal computer
14
. Therefore, the personal computer
14
controls the LCD driving circuit
13
so that the personal computer
14
can display the pixel on which the stylus is placed.
The operation principle of the aforementioned PSLCD module will now be explained in more detail.
Under the control of the microcomputer
17
, the driving pulse generating circuit
12
provides driving pulses to X-, and Y-axis of the PSD alternately for sensing the present position of the stylus
15
. The stylus
15
senses a position signal in a potential distribution on the PSD using capacitive coupling and provides the position signal to the PSD data processing circuit
16
. The PSD data processing circuit
16
receives the present X- and Y-axis coordinate data of the stylus and converts the coordinate data into digitized position data. Upon reception of the position data from PSD data processing circuit
16
, the microcomputer
17
analyses the position data to calculate the present position of the stylus
15
and updates personal computer
14
accordingly. Thus, the pixel of the LCD on which the stylus
15
is placed is displayed under the control of the microcomputer
17
.
A conventional PSLCD will be explained with reference to the attached drawing.
FIG. 4
illustrates a perspective view of a disassembled conventional transparent PSLCD.
Referring to
FIG. 4
, the transparent PSLCD includes an LCD panel
31
, a PSD
32
on the LCD panel
31
, and a protective layer
33
. The LCD panel
31
is the conventional LCD shown in FIG.
1
. The PSD
32
is adapted to sense a position of the stylus according to a potential distribution of a driving AC signal, and the protective layer
33
is provided for protecting the PSD from the stylus.
FIG. 5
illustrates a plane view of a configuration of a conventional PSD.
Referring to
FIG. 5
, the conventional PSD includes a tablet
41
(sometimes called “digitizer”), first, second, third and fourth ITO layers
42
,
42
a,
43
and
43
a
on four sides of the tablet
41
. The tablet
41
has a plurality of grids
44
spaced at fixed intervals in X- and Y-axis directions. The grids
44
in the X- and Y-axis directions are formed with transparent electrodes (ITO) having uniform internal resistances and are isolated from one another. Each of the first and second ITO layers
42
and
42
a
applies a driving voltage in the X-axis direction for sensing a position of the stylus. Each of the third and fourth ITO layers
43
and
43
a
applies a driving voltage in Y-axis direction for sensing a position of the stylus. Each of the first, second, third and fourth ITO layers
42
,
42
a,
43
and
43
a
has a switch for selective application of a grounding voltage or a source voltage to the grids in X- and Y-axis directions of the tablet
41
. The switches in the first and second ITO layers
42
and
42
a
are denoted XS
1
and XS
2
, respectively, and the switches in the third and fourth ITO layers
43
and
43
a
are denoted YS
1
and YS
2
, respectively. In the conventional PSD, the first and second ITO layers
42
and
42
a
and the third and fourth ITO layers
43
and
43
a
are alternately applied a source voltage Vcc from driving pulse generating circuit
12
.
When the switches XS
1
and XS
2
are switched on, the switches YS
1
and YS
2
are switched off. If the source voltage is applied to first ITO layer
42
and a ground voltage is applied to the second ITO layer
42
a,
the potential of the grids
44
in the tablet
41
gradually decrease between the first ITO layer
42
and to the second ITO layer
42
a.
This is because, although the X- and Y-axes grids have uniform resistances throughout the tablet, if the source voltage Vcc is applied from one side, there will be a potential difference between a grid
44
next to a source voltage input terminal and a grid
44
farthest from the source voltage input terminal because of a potential difference due to distance. By using the characteristic of the grids having the potential difference, it is possible to detect a position of a particular point if a source voltage and a grounding voltage are selectively applied to the X- and Y-axes directions. That is, after selective application of a source voltage and a grounding voltage, potentials in the X- and Y-axis are detected with a stylus, and the present position of the stylus is derived.
FIG. 6
illustrates a potential distribution on the conventional PSD tablet shown in FIG
5
. A driving voltage is applied to centers of four sides of the conventional PSD. As shown, when a driving voltage is applied to centers of four sides of the conventional PSD, the potential decreases as it goes from the centers to corners of the tablet. This comes from the potential differences caused by distance differences between the grids at the centers which are nearest to voltage input term
Ahm Young Soo
Kim Chee Young
Kim Jun Hee
Dudek James A.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
LG Electronics Inc.
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