Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-04-22
2002-01-15
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S077000, C345S082000
Reexamination Certificate
active
06339415
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electroluminescent display and its drive method for displaying in color by using elements such as organic electroluminescent elements.
Heretofore, matrix displays are already known wherein light-emitting elements made from a material such as organic electroluminescence are used. Such a conventional matrix display has a matrix (lattice) of a plurality of anode lines and a plurality of cathode lines, and a plurality of light-emitting elements each of which is connected to each of the intersections of the matrix of the anode lines and cathode lines. For display in full color, R (red), G (green), and B (blue) light-emitting elements are arranged in order in such a manner that these three light-emitting elements are formed in one group so as to constitute one pixel. Each light-emitting element to be connected to each intersection can be represented by an electroluminescent element E with the diode properties and the parasitic capacitance C connected in parallel to the electroluminescent element E as shown in
FIG. 1
in the attached drawings.
An example of this type of conventional full-color matrix displays will be described referring to
FIG. 2
to
FIG. 4
in the attached drawings. A
1
to A
768
are anode lines and B
1
to B
64
are cathode lines, so arranged as to intersect each other. Light-emitting elements R, G, and B, which emit red, green, and blue color respectively, are connected to each of the intersections of these anode and cathode lines. These light-emitting elements R, G, and B are arranged respectively in such a regular manner that light-emitting elements of the same color are connected to the same anode line. That is, the layout is constituted in such a manner that the anode line A
1
has 64 light-emitting elements of R connected thereto, the anode line A
2
has 64 light-emitting elements of G connected thereto, and the anode line A
3
has 64 light-emitting elements of B connected thereto. On the other hand, cathode lines have light-emitting elements of R, G, and B connected thereto repeatedly and sequentially. Thus, three light-emitting elements R, G, and B, which are adjacent to each other, form a unit pixel E as a group. As shown in the drawings, 16384 pixels of E
1′1
to E
256′64
are to be arranged in a matrix.
A cathode line scanning circuit
1
comprises scanning switches
5
1
to
5
64
for scanning cathode lines B
1
to B
64
in sequence. Each scanning switch
5
1
to
5
64
is connected at one end thereof to a reverse bias voltage Vcc of a constant-voltage power supply, while the other end thereof is connected to the ground (0 V). This reverse bias voltage Vcc acts to prevent emission of light-emitting elements connected to a cathode line B
1
to B
64
not being scanned.
An anode drive circuit
2
comprises constant-current power supplies
2
1
to
2
768
and drive switches
6
1
to
6
768
for selecting anode lines to be connected to the constant-current power supply
2
1
to
2
768
out of anode lines A
1
to A
768
. Turning any drive switch ON will allow the constant-current power supply
2
1
to
2
768
to be connected to the anode line corresponding to the drive switch.
A anode reset circuit
3
comprises shunt switches
7
1
to
7
768
for connecting the anode lines A
1
to A
768
to the ground (0 V).
A light-emission control circuit
4
is provided for controlling the cathode line scanning circuit
1
, anode drive circuit
2
, and anode reset circuit
3
in response to light-emission data to be input.
Referring to
FIGS. 2
to
4
, the operation of the full-color matrix display will be described. The operation to be described below is an example wherein the cathode line B
1
is scanned to cause a pixel E
1′1
to emit light and then the cathode line B
2
is scanned to cause the pixel E
2′2
to emit light. In addition, for the sake of understanding the explanation, light-emitting elements which are emitting light are shown with diode symbols, while light-emitting elements which are not emitting light are shown with capacitor symbols.
FIG.2
shows the state wherein the pixel E
1′1
is emitting light. In this state, the cathode line B
1
is being scanned with a scanning switch
5
1
switched to the ground potential. Scanning switches
5
2
to
5
64
have been switched to the constant-voltage power supply and thus the cathode lines B
2
to B
64
are subjected to the reverse bias voltage Vcc. On the other hand, the anode lines A
1
to A
3
are connected to the constant-current power supply
2
1
to
2
3
by means of the drive switches
6
1
to
6
3
and the shunt switches
7
1
to
7
3
are made open. Other anode lines A
4
to A
768
are connected to the ground potential by means of the shunt switches
7
4
to
7
768
with the drive switches
6
4
to
6
768
made open.
Thus, in the state shown in
FIG. 2
, only pixel E
1′1
is forward-biased in which a driving current is flowing in the direction shown by the arrow from the constant-current power supply
2
1
, caused to emit light. The parasitic capacitance of the pixel E
1′1
is charged in the forward direction.
In this case, the light-emitting elements R, G, and B in pixels E
1°2
to E
1′64
are connected to the constant-power supplies
2
1
to
2
3
. However, since the cathode lines are connected to the constant-voltage supplies so as to be kept at the reverse bias voltage Vcc, the voltage across the both sides of the light-emitting elements are almost 0V and thus these light-emitting elements do not emit light. In addition, the pixels E
2′1
to E
256′1
are connected at the both sides thereof to the ground potential and thus do not emit light. Furthermore, the pixels E
2′2
to E
256′64
are reverse-biased and thus do not emit light with the parasitic capacitance of the light-emitting elements charged in the reverse direction as shown in the drawing (by hatching the capacitors).
After the cathode line B
1
has been scanned and before the cathode line B
2
is started to be scanned, all the anode lines A
1
to A
768
and cathode lines B
1
to B
64
are once shunted to the ground potential to be reset to 0V. That is, as shown in
FIG. 3
, all the drive switches
6
1
to
6
768
are turned OFF, while all the scanning switches
5
1
to
5
64
and all the shunt switches
7
1
to
7
768
are switched to the ground potential. Since this causes all the anode and cathode lines to become the same potential of 0V, all the charges which were charged in each light-emitting element will be discharged.
Then, as shown in
FIG. 4
, the cathode line B
2
is started to scan. That is, only the scanning switch
5
2
corresponding to the cathode line B
2
is switched to the ground potential with other scanning switches
5
1
,
5
3
to
5
64
connected to the reverse bias voltage Vcc and drive switches
6
4
to
6
6
switched to the constant-current power supply
2
4
to
2
6
. Consequently, the anode lines A
4
to A
6
are driven, shunt switches
7
1
to
7
3
,
7
7
to
7
768
are turned ON, and the anode lines A
1
to A
3
, A
7
to A
768
are turned in the potential thereof to 0V.
As described above, since all the light-emitting elements have zero electric charge in the moment of switching each switch, the anode lines A
4
to A
6
has the potential of Vcc (more accurately 63/64 Vcc). This allows the light-emitting elements of the pixel E
2′2
, which is to emit light subsequently, to be charged at a dash by charging currents from a plurality of paths shown by the arrows in
FIG. 4
, the parasitic capacitance of each light-emitting element is charged instantaneously, and thus these light-emitting elements emit light at predetermined instantaneous luminance.
Concerning the reset operation mentioned above, the present applicant has already proposed the method disclosed in Japanese Patent Application Laid Open No. 9-232074. The reset driving method disclosed in the above patent publication solves the problem that the reverse-direction electric charges of pixels E
2′2
to E
2&prim
Eisen Alexander
Hjerpe Richard
Pioneer Electronic Corporation
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