Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-01-07
2003-07-01
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S077000
Reexamination Certificate
active
06587087
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a method and apparatus for driving an image display panel, and more particularly to a method and apparatus for driving a display using capacitive light-emitting elements such as organic electroluminescence elements or the like.
2. Description of Related Art
An electroluminescence display comprised of a plurality of organic electroluminescence elements arranged in a matrix has drawn attention as a display which provides for low power consumption, high display quality, and reduced thickness. As illustrated in
FIG. 1
, such an organic electroluminescence element has a transparent substrate
100
such as a glass plate on which a transparent electrode
101
is formed; at least one organic functional layer
102
including an electron transport layer, a light emitting layer, a hole transport layer and so on laminated on the transparent electrode
101
; and a metal electrode
103
laminated on the organic functional layer
102
. The transparent electrode
101
serving as an anode is applied with a plus voltage, while the metal electrode
103
serving as a cathode is applied with a minus voltage, i.e., a direct current is applied across the transparent electrode and the metal electrode, to cause the organic functional layer
102
to emit light. By using an organic compound possibly expected to exhibit satisfactory light emitting characteristics for the organic functional layer, the electroluminescence display has become good enough to be fit for practical use.
The organic electroluminescence element (hereinafter simply called the “element” as well) may be electrically represented as an equivalent circuit as illustrated in FIG.
2
. As can be seen from the figure, the element can be replaced with a circuit configuration composed of a capacitive component C and a component E of a diode characteristic coupled in parallel with the capacitive component. Thus, the organic electroluminescence element can be regarded as a capacitive light-emitting element. As the organic electroluminescence element is applied with a direct current light-emission driving voltage across the electrodes, a charge is accumulated in the capacitive element C. Subsequently, when the applied voltage exceeds a barrier voltage or a light emission threshold voltage inherent to the element, a current begins flowing from one electrode (on the anode side of the diode component E) to the organic functional layer which carries the light emitting layer so that light is emitted therefrom at an intensity proportional to this current.
The Voltage V—Current I—Luminance L characteristic of such an element is similar to the characteristic of a diode, as illustrated in FIG.
3
. Specifically, the current I is extremely small at a light emission threshold Vth or lower, and abruptly increases as the voltage increases to the light emission threshold Vth or higher. The current is substantially proportional to the luminance. Such an element, when applied with a driving voltage exceeding the light emission threshold Vth, exhibits a light emission luminance in proportion to a current corresponding to the applied driving voltage. On the other hand, the light emission luminance remains equal to zero when the driving voltage applied to the element is at the light emission threshold Vth or lower which does not cause the driving current to flow into the light emitting layer.
As a method of driving a display panel using a plurality of organic electroluminescence elements as described above, a simple matrix driving mode may,be applied.
FIG. 4
illustrates the structure of an exemplary simple matrix display panel. As can be seen, n cathode lines (metal electrodes) B
1
-B
n
are arranged extending in parallel in the horizontal direction, and m anode lines (transparent electrodes) A
1
-A
m
are arranged extending in parallel in the vertical direction. At each of intersections of the cathode lines and the anode lines (a total of n×m locations), a light emitting layer of an organic electroluminescence element E
1,1
-E
m,n
is sandwiched between associated cathode line and anode line. The elements E
1,1
-E
m,n
carrying pixels are arranged in matrix, and each element has one end connected to an anode line (on the anode line side of the diode component E in the aforementioned equivalent circuit) and the other end connected to a cathode line (on the cathode line side of the diode component E in the aforementioned equivalent circuit) corresponding to the intersections of the anode lines A
1
-A
m
along the vertical direction and the cathode lines B
1
-B
n
along the horizontal direction. The cathode lines are connected to a cathode line scanning circuit
1
and driven thereby, while the anode lines are connected to an anode line driving circuit
2
and driven thereby.
The cathode line scanning circuit
1
has scanning switches
5
1
-
5
n
corresponding to the cathode lines B
1
-B
n
for individually determining potentials thereon. Each of the scanning switches
5
1
-
5
n
connects a corresponding cathode line either to a reverse bias voltage V
CC
(for example, ten volts) derived from a power supply voltage or to a ground potential (zero volt).
The anode drive circuit
2
has current sources
2
1
-
2
m
(for example, regulated current sources) corresponding to the anode lines A
1
-A
m
for individually supplying the elements with driving currents through respective anode lines, and drive switches
6
1
-
6
n
which are adapted to individually control on and off the currents flowing into the anode lines. While voltage sources such as regulated voltage sources could be used for the drive sources, current sources (power supply circuit controlled to supply a desired amount of current) are generally used for several reasons including the fact that the aforementioned current-luminance characteristic remains stable against temperature changes, whereas the voltage-luminance characteristic is unstable against temperature changes. The current sources
2
1
-
2
m
supply the associated elements with such amounts of currents that are required to maintain the respective elements to emit light at desired instantaneous luminance (hereinafter this state is called the “steady light emitting state”). Also, When an element is in the steady light emitting state, the aforementioned capacitive element C is charged with a charge corresponding to the amount of supplied current, so that the voltage across both terminals of the element is at a regulated value Ve (hereinafter, this value is called the “light emission regulating voltage”) corresponding to the instantaneous luminance.
The anode lines are also connected to an anode line reset circuit
3
. The anode line reset circuit
3
has shunt switches
7
1
-
7
m
, disposed one for each anode line. Anode lines are connected to the ground potential, when associated shunt switches are selected.
The cathode line scanning circuit
1
, the anode line drive circuit
2
and the anode line reset circuit
3
are connected to a light emission control circuit
4
.
The light emission control circuit
4
controls the cathode line scanning circuit
1
, the anode line drive circuit
2
and the anode line reset circuit
3
in accordance to the image data supplied from an image data generating system, not shown, so as to display an image represented by image data. The light emission control circuit
4
generates a scanning line selection control signal for controlling the cathode line scanning circuit
1
to switch the scanning switch
5
1
-
5
n
such that any of the cathode lines corresponding to a horizontal scanning period of the image data is selected and set at the ground potential, and the remaining cathode lines are applied with the reverse bias voltage V
CC
. The reverse bias voltage V
CC
is applied by regulated voltage sources connected to cathode lines in order to prevent crosstalk light emission from occurring in elements connected to intersections of a driven anode line and cathode lines which are not selected for scanning. The revers
Anyaso Uchendu O.
Pioneer Corporation
Saras Steven
Sughrue & Mion, PLLC
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