Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-03-02
2003-04-22
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S076000, C345S084000
Reexamination Certificate
active
06552703
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a display apparatus using capacitive light emitting devices such as organic electroluminescence devices or the like and its driving method.
2. Description of the Related Art
As a display in which an electric power consumption is low and a display quality is high and, further, a thin size can be realized, an electroluminescence display constructed by arranging a plurality of organic electroluminescence devices in a matrix shape is highlighted. As shown in
FIG. 1
, the organic electroluminescence device is constructed in a manner such that an organic function layer
102
of at least one layer consisting of an electron transporting layer, a light emitting layer, a hole transporting layer, or the like and a metal electrode
103
are laminated on a transparent substrate
100
made of a glass substrate or the like on which a transparent electrode
101
is formed. When a plus voltage is applied to an anode of the transparent electrode
101
and a minus voltage is applied to a cathode of the metal electrode
103
, namely, when a direct current is applied across the transparent electrode and the metal electrode, the organic function layer
102
emits light. An organic compound in which good light emitting characteristics can be expected is used as an organic function layer, thereby enabling the electroluminescence display to endure a practical use.
The organic electroluminescence device (hereinafter, simply referred to as a device) can be electrically expressed by an equivalent circuit as shown in FIG.
2
. As will be understood from the diagram, the device can be replaced with a construction comprising a capacitance component C and a component E of characteristics of a diode connected in parallel to the capacitance component. The organic electroluminescence device is, therefore, regarded as a capacitive light emitting device. According to the organic electroluminescence device, when a DC light emission driving voltage is applied across the electrodes, charges are stored in the capacitance component C. Subsequently, when the applied voltage exceeds a barrier voltage or a light emission threshold voltage that is peculiar to the device, a current starts on flowing to the organic function layer serving as a light emitting layer from the electrode (anode side of the diode component E) and the device emits the light at an intensity which is proportional to the current.
The characteristics of a voltage V—a current I—a luminance L of the device are similar to those of the diode as shown in FIG.
3
. When the device is supplied with a voltage of a light emission threshold value Vth or less, the current I is extremely small. When the voltage exceeds the light emission threshold value Vth, the current I suddenly increases. The current I is almost proportional to the luminance L. According to the device, if a driving voltage exceeding the light emission threshold value Vth is applied to the device, the light emission luminance proportional to the current according to the driving voltage is provided. If the driving voltage applied is equal to or less than the light emission threshold value Vth, no driving current flows and the light emission luminance is equal to zero.
A simple matrix driving system can be applied as a driving method of a display panel using a plurality of organic electroluminescence devices.
FIG. 4
shows a structure of an example of a simple matrix display panel. n cathode lines (metal electrodes) B
1
to B
n
are extended and provided in parallel in the lateral direction and m anode lines (transparent electrodes) A
1
to A
m
are extended and provided in parallel in the vertical direction. Light emitting layers of organic electroluminescence devices E
1,1
to E
m,n
are sandwiched in (total n×m) crossing portions of the cathode lines and the anode lines. The devices E
1,1
to E
m,n
serving as pixels are arranged in a lattice shape. In correspondence to each crossing position of the anode lines A
1
to A
m
in the vertical direction and the cathode lines B
1
to B
n
in the horizontal direction, one end (anode line side of the diode component E of the equivalent circuit) is connected to the anode line and the other end (cathode line side of the diode component E of the equivalent circuit) is connected to the cathode line. The cathode lines are connected to a cathode line scanning circuit
1
. The anode lines are connected to an anode line driving circuit
2
.
The cathode line scanning circuit
1
has scan switches
5
1
to
5
n
corresponding to the cathode lines B
1
to B
n
in which an electric potential of each cathode line is individually determined. Each scan switch applies either an inverse bias potential V
cc
(for example, 10V) which is obtained from a power voltage or a ground potential (0V) to the corresponding cathode line.
The anode line driving circuit
2
has current sources
2
1
to
2
m
(for example, constant current sources) and drive switches
6
1
to
6
m
corresponding to the anode lines A
1
to A
m
for individually supplying a driving current to each device through each anode line and is constructed in a manner such that the drive switch is on/off controlled so as to individually supply a current to each anode line. A voltage source such as a constant voltage source can be also used as a driving source. A current source (power supplying circuit whose supply current amount is controlled so as to have a desired value) is generally used because of reasons such that voltage—luminance characteristics are unstable for a temperature change although the current—luminance characteristics are stable for a temperature change and the like. The supply current amount of each of the current sources
2
1
to
2
m
is set to a current amount that is necessary to maintain a state where the device emits the light at a desired instantaneous luminance (hereinafter, the state is referred to as a stationary light emitting state). When the device is in the stationary light emitting state, the charges corresponding to the supply current amount are stored in the capacitance component C of the device. Thus, a voltage across the device is equal to a specified value V
e
(hereinafter, referred to as a specified light emission voltage) corresponding to the instantaneous luminance.
The anode lines are also connected to an anode line resetting circuit
3
. The anode line resetting circuit
3
has shunt switches
7
1
to
7
m
provided every anode line. When the shunt switch is selected, the corresponding anode line is set to a ground potential.
The cathode line scanning circuit
1
, anode line driving circuit
2
, and anode line resetting circuit
3
are connected to a light emission control circuit
4
.
The light emission control circuit
4
controls the cathode line scanning circuit
1
, anode line driving circuit
2
, and anode line resetting circuit
3
in accordance with image data supplied from an image data generating system (not shown) so as to display an image shown by the image data. The light emission control circuit
4
generates a scanning line selection control signal to the cathode line scanning circuit
1
and controls so as to switch the scan switches
5
1
to
5
n
in a manner such that one of the cathode lines corresponding to a horizontal scanning period of the image data is selected and set to the ground potential and the inverse bias potential V
cc
is applied to the other cathode lines. The inverse bias potential V
cc
is applied by the constant voltage source connected to the cathode line in order to prevent that the device connected to the crossing point of the anode line which is at present being driven and the cathode line in which a scan selection is not performed emits light due to crosstalk. The inverse bias potential V
cc
is generally set so that V
cc
=specified light emission voltage V
e
. Since the scan switches
5
1
to
5
n
are sequentially switched to the ground potential every horizontal scanning period, the cathode line set to the ground potential functi
Dinh Duc Q.
Hjerpe Richard
Morgan & Lewis & Bockius, LLP
Pioneer Corporation
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