Computer graphics processing and selective visual display system – Display driving control circuitry
Reexamination Certificate
2001-05-02
2004-03-02
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Display driving control circuitry
Reexamination Certificate
active
06700568
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a method for driving capacitive display device such as an inorganic EL display device and a simple matrix type liquid crystal display device or the like.
2. Description of the Related Art
Recently, a variety of plane display devices have been developed. In various kinds of the plane display devices, even when the materials for display elements and the voltage values applied to display panels are different from each other, the structures of the periphery voltage applying circuits and the periphery control circuits are similar to each other. Therefore, hereinafter, although a description will be made while taking an inorganic EL display device as an example in which a phenomenon of electroluminescence (hereinafter, referred to as “EL” for short) is utilized, it is noted that the invention is not limited thereto.
FIG. 7
illustrates a basic structure of an inorganic EL display panel. In the inorganic EL display panel, disposed parallelly on an electrical insulating substrate such as a glass substrate
1
is a ribbon-like first electrode group
2
, laminated thereon is a dielectric material
3
, further laminated thereon is an EL layer
4
, still further laminated thereon is a dielectric material
5
so as to form a three-layered structure. On the three-layered structure, disposed parallelly is a ribbon-like second electrode group
6
that extends in the direction crossing at right angles to the first electrode group
2
so as to form inorganic EL elements at the crossing portions between the first electrode group
2
and the second electrode group
6
. The inorganic EL elements are formed in a space where the ribbon-like electrodes of the first electrode group
2
face the ribbon-like electrodes of the second electrode group
6
, and between the electrodes at both sides are interposed a three-layered dielectric material layer comprised of dielectric material
3
,
5
and an EL layer
4
. Accordingly, the inorganic EL elements are capacitive and are possible to be handled as capacitors in an electrical aspect. In a simple matrix type liquid crystal display panel also, since between the electrodes are interposed an electrical insulating liquid crystal layer, the same as the inorganic EL element, the liquid crystal display element is possible to be handled as a capacitor.
FIG. 8
shows an example of relationship between an impressed voltage applied to an inorganic EL element and a light-emitting luminance thereof. The inorganic EL element emits light when a voltage is applied of which absolute value is larger than a light emitting start voltage of approximately 180V. The light-emitting voltage at which a sufficient luminance is obtained is approximately 230V. Further, in the inorganic EL element, since the characteristic thereof may be changed when a voltage of an identical polarity is applied for a long period of time, it is necessary to carry out an alternating current drive in which positive voltage and negative voltage are applied alternately. Consequently, for an inorganic EL element having a character as shown in
FIG. 8
, it is necessary to drive the same by means of a relatively high voltage of approximately ±200V.
In an inorganic EL display panel having a basic structure as shown in
FIG. 7
, one of the first electrode group
2
and the second electrode group
6
of the inorganic EL elements is determined as a data-side electrode; the another is determined as a scan-side electrode. The inorganic EL elements formed at the crossing portions between the data-side electrodes and the scan-side electrodes constitute pixels respectively. Accordingly, in an inorganic EL display panel as shown in
FIG. 7
, the pixels are arrayed in a matrix configuration.
Conventionally, in a display device in which inorganic EL elements having a basic structure as shown in
FIG. 7
are used, a scan-side drive IC is provided as a drive circuit of the scan-side electrodes; a data-side drive IC is provided as a drive circuit of the data-side electrodes. The scan-side drive IC includes a switching element for applying negative voltage to the data-side electrodes and a switching element for applying positive voltage thereto. The data-side drive IC is comprised of a structure in which a switching element for charging the EL layer
4
with modulating voltage, a switching element for discharging the same and diodes disposed in an inverse direction of the current of the respective switching elements are connected with each other. At the data-side, in accordance with display data, a modulating drive is made using the charging or discharging switching element while at the scan-side, the field that provides positive voltage and the field that provides negative voltage are repeated alternately to carry out, what is called, a field inverting drive in order to apply well-symmetric alternating pulses to the EL layer
4
providing a highly reliable display.
Furthermore, in a modulating system drive circuit for carrying out modulating drive in accordance with the display data, it is possible to use a driving element comprised of a double-well structured IC that has been recently developed. The modulating voltage applied from the data-side in accordance with the display data is modulated into a positive or negative voltage whereby a driving method is made possible in which the voltage that has the same absolute value is applied in both cases where a negative voltage or a positive voltage is applied to the data-side electrode as the driving voltage of the scan-side electrode. By virtue of a bipolar drive as described above, it is made possible to apply a better-symmetric alternating pulse voltage to the inorganic EL element.
FIG. 9
shows an equivalent circuit as a conventional modulating system drive circuit in which an inorganic EL element as shown in
FIG. 7
is handled as just a capacitor having a capacity C as a capacitive display element
10
. The capacitive display element
10
is driven by being charged/discharged at a voltage of +V
M
from a positive power supply
11
or at a voltage of −V
M
from a negative power supply
12
. Current i that flows while charging/discharging the capacitive display element
10
from the positive power supply
11
or the negative power supply
12
flows also through a resistance
13
residing in the wirings or the like. The modulating system drive circuit may be represented as switches
21
,
22
that switch the positive power supply
11
or the negative power supply
12
to apply a voltage to the capacitive display element
10
.
FIG. 10
shows a driving voltage waveform in the equivalent circuit in FIG.
9
. Now, assuming that a switch
21
represented with SW
P
is ON; a switch
22
represented with SW
N
is OFF, and the capacitive display element
10
is charged at a voltage V
M
. At this time, it is understandable that the potential level at the positive electrode of the capacitive display element
10
is +½ V
M
, and the potential level at the negative electrode is −½ V
M
. Now, a consideration will be given about a case where, from a state in which the capacitive display element
10
is charged with the switch
21
closed and the switch
22
opened, the same is charged at a voltage V
M
in inverted polarity by switching the switch
21
SW
P
to OFF; the switch
22
SW
N
to ON. The polarity of both electrodes of the capacitive display element
10
is inverted respectively, and electric power is consumed at a resistance
13
by the current i that flows at this time accompanying with the shift of the electric charge.
First, in case where a capacity C charged at a voltage &agr; V
M
is charged at a voltage &bgr; V
M
, the electric energy consumed at a resistance R is calculated by Expression 1 as below. Herein, &agr; and &bgr; are random values, respectively within −1≦&agr;≦1, −1≦&bgr;≦1. At this time, the following Expression 1 is obtained.
Ri
+
1
C
∫
i
ⅆ
t
=
β
V
M
(
1
)
When curren
Bell Paul A.
Saras Steven
Sharp Kabushiki Kaisha
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