Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-07-24
2004-03-16
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S077000, C315S169300
Reexamination Certificate
active
06707438
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a driving apparatus for a multi-color light-emitting display panel that uses capacitive light-emitting elements such as organic electroluminescence elements and a drive method for the same.
2. Description of the Related Art
In recent years, with the trend of increasing the size of display devices, thinner display devices have been required, and a variety of thin display devices have been brought into practical use. An electroluminescence display comprising a plurality of organic electroluminescence elements arranged in a matrix has drawn attention as one of the thin display devices.
As shown in
FIG. 1
, the organic electroluminescence element comprises at least one layer of an organic functional layer
102
, made up of an electron transport layer, a light-emitting layer, a hole transport layer or the like, and a metallic electrode
103
, stacked on a transparent substrate
100
of a glass plate or the like on which a transparent electrode
101
is formed. The organic functional layer
102
emits light by applying a positive voltage to the anode of the transparent electrode
101
and a negative voltage to the cathode of the metallic electrode
103
, that is, by applying a current across the transparent electrode and the metallic electrode. The electroluminescence display is practicable by using, as the organic functional layer, an organic compound that can be expected to provide good light emission characteristics.
The organic electroluminescence element (hereinafter simply referred to as an EL element) can be represented electrically by an equivalent circuit as shown in FIG.
2
. As can be seen from the drawing, the EL element can be replaced by a capacitance component C and a diode characteristic component E that is connected in parallel to the capacitance component. Therefore, the EL element can be considered a capacitive light-emitting element. In the EL element, when a DC light emission drive voltage is applied across the electrodes, electric charge is stored in the capacitance component C. When a barrier voltage or light emission threshold voltage, which corresponds to the element, is exceeded thereafter, a current starts to flow from the electrode (the anode of the diode component E) to the organic functional layer which serves as a light-emitting layer to allow the EL element to emit light at an intensity in proportion to the current.
As shown in
FIG. 3
, the characteristic of voltage V—current I—luminosity L of such an EL element is very similar to that of a diode, where the current I is extremely small at voltages not larger than the light emission threshold voltage Vth and suddenly increases at voltages equal to or larger than the light emission threshold voltage Vth. In addition, the current I is generally proportional to the luminosity L. In the EL element, when a drive voltage larger than the light emission threshold voltage Vth is applied to the EL element, the element emits light at luminosity proportional to the current corresponding to the drive voltage. On the other hand, when the drive voltage applied thereto is equal to or smaller than the light emission threshold voltage Vth, no drive current flows and the luminosity of light emission remains zero.
As a method for driving a light-emitting display panel that employs such EL elements, known is a simple matrix drive method.
FIG. 4
shows the configuration of an example of a drive apparatus that uses the simple matrix drive method for a multi-color light-emitting display panel. In the light-emitting display panel, n cathode lines (metallic electrodes) B
1
, . . . , B
n
are provided in the horizontal direction and 3 m anode lines (transparent electrodes) A
1R
, A
1G
, A
1B
, . . . , A
mR
, A
mG
, A
mB
are provided in the vertical direction. EL elements E
1R, 1
, E
1G, 1
, E
1B, 1
, E
mR, n
, E
mG, n
, E
mB, n
are formed at the respective intersections (a total of n×3 m). The EL elements E
1R, 1
, E
mR, n
emit red light; the EL elements E
1G, 1
, . . . , E
mG, n
emit green light; and EL elements E
1B, 1
, . . . , E
mB, n
emit blue light. Three EL elements (for example, E
1R, 1
, E
1G, 1
, E
1B, 1
) of each of three primary colors of red, green, and blue, consecutive in each of the cathode lines, form one pixel. The EL elements E
1R, 1
, E
1G, 1
, E
1B, 1
, . . . , E
mR, n
, E
mG, n
, E
mB, n
are arranged in the shape of lattice with one end thereof (the anode line side of the diode component E in the aforementioned equivalent circuit) connected to the anode lines and the other end thereof (the cathode side of the diode component E in the aforementioned equivalent circuit) connected to the cathode lines, corresponding to the intersections of the anode lines A
1R
, A
1G
, A
1B
, . . . , A
mR
, A
mG
, A
mB
, which are directed along the vertical direction, and the cathode lines B
1
, . . . , B
n
, which are directed along the horizontal direction. The cathode lines are connected to a cathode line scanning circuit
1
, while the anode lines are connected to an anode line drive circuit
2
and an anode line reset circuit
3
.
The cathode line scanning circuit
1
has scanning switches
5
1
, . . . ,
5
n
, corresponding to the cathode lines B
1
, . . . , B
n
, for determining individually the electric potential of each of the cathode lines, each relaying and supplying either one of a positive potential Vcc which serves as a reverse bias voltage or the ground potential (0V) to a corresponding cathode line.
The anode line drive circuit
2
has current sources
2
1R
,
2
1G
,
2
1B
, . . . ,
2
mR
,
2
mG
,
2
mB
, (for example, constant current sources), corresponding to the anode lines A
1R
, A
1G
, A
1B
, . . . , A
mR
, A
mG
, A
mB
, for supplying drive currents to individual EL elements through the respective anode lines, and drive switches
6
1R
,
6
1G
,
6
1B
, . . . ,
6
mR
,
6
mG
,
6
mB
. The anode line drive circuit
2
performs on/off control to allow the drive switches to supply currents to individual anode lines. Voltage sources such as constant voltage sources can be used as the drive sources. However, current sources (current circuits that are controlled to provide a desired amount of supply current) are generally used due to a fact that the aforementioned current—luminosity characteristic is stable against a variation in temperature, whereas the voltage—luminosity characteristic is unstable against a variation in temperature. The amount of supply current of the current sources
2
1R
,
2
1G
,
2
1B
, . . . ,
2
mR
,
2
mG
,
2
mB
is an amount of current required for the EL elements to sustain a state of emitting light at desired instantaneous luminosity (hereinafter, this state is referred to as the steady light emitting state). In addition, the aforementioned capacitance component C of the EL element is charged with electric charge corresponding to the amount of supply current when the EL element is under a light-emitting state. Accordingly, the voltage across the EL element becomes a specified value Ve (hereinafter, this is referred to as the light emission regulating voltage).
The anode line reset circuit
3
has shunt switches
7
1R
,
7
1G
,
7
1B
, . . . ,
7
mR
,
7
mG
,
7
mB
, which are provided for each of the anode lines. The shunt switches are selected to set the cathode lines to the ground potential.
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
to display, in accordance with image data supplied from an image data generation system (not shown), the image to be served by the image data. The light emission control circuit
4
generates a scanning line select control signal for the cathode line scanning circuit
1
to select one cathode line from the cathode lines B
1
, . . . , B
n
, corresponding to a horizontal scan
Ishizuka Shinichi
Ochi Hideo
Sakamoto Tsuyoshi
Morgan & Lewis & Bockius, LLP
Osorio Ricardo
Pioneer Corporation
Shalwala Bipin
LandOfFree
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