Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
1999-09-24
2001-05-08
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C340S457100, C345S076000, C345S214000
Reexamination Certificate
active
06229267
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image display apparatus and a method for driving the apparatus and, more particularly, to a display apparatus having capacitive light-emitting devices, such as organic electroluminescence devices, and the method for driving the apparatus.
2. Description of the Related Art
An electroluminescence display panel which has a plurality of organic electroluminescence devices arranged in a matrix form is receiving great attention as a display which can have lower power consumption and high display quality and can be suitable for thin-profile display apparatus. As shown in
FIG. 1
, the organic electroluminescence device has at least a single organic function layer
102
, comprised of an electron-transport layer, a light-emitting layer, hole-transport layer, etc., and a metal electrode
103
, both formed on a transparent substrate
100
like a glass plate on which a transparent electrode
101
is formed. As a positive voltage is applied to the anode of the transparent electrode
101
and a negative voltage to the cathode of the metal electrode
103
, i.e., as a DC voltage is applied between the transparent electrode
101
and the metal electrode
103
, the organic function layer
102
emits light. With the organic function layer formed of an organic compound which can be expected to have an excellent emission characteristic, the electroluminescence display can be used practically.
An organic electroluminescence device (hereinafter also referred to as “EL device”) can be expressed as an electrically equivalent circuit as shown in FIG.
2
. As apparent from the circuit diagram, the device can be replaced with a capacitive component C and a component E with a diode characteristic that is coupled in parallel to the capacitive component C. The EL device is thus a capacitive light-emitting device. When a DC drive voltage is applied between the electrodes of the EL device, charges are stored in the capacitive component C. When the drive voltage exceeds the barrier voltage or emission threshold value inherent to the device, a current starts flowing into the organic function layer that has the light-emitting layer from one of the electrodes (the anode side of the diode component E) and light is emitted with the intensity proportional to the current.
The voltage V v.s. current I v.s. luminance L characteristic of the device is similar to the diode characteristic such that the current I is very small for the voltage equal to or lower than the emission threshold value Vth but abruptly increases when the voltage becomes greater than the emission threshold value Vth, as shown in FIG.
3
. The current I is approximately proportional to the luminance L. Such a device provides a luminance proportional to the current that accords to the drive voltage when the drive voltage above the emission threshold value Vth is applied to the device, but it has substantially no drive current flowing when the applied drive voltage is lower than the emission threshold value Vth, so that the luminance stays substantially equal to zero.
Passive matrix driving can be used to drive a display panel which uses a plurality of such EL devices.
FIG. 4
exemplifies the structure of a passive matrix display panel. An N number of cathode lines (metal electrodes) B
1
to B
n
are laid horizontally, and an M number of anode lines (transparent electrodes) A
1
to A
m
are laid in parallel vertically to cathode lines B
1
-B
n
, with light-emitting layers of EL devices E
1,1
to E
m,n
placed at (a total of n×m) intersections between the anode lines A
1
-A
m
and the cathode lines B
1
-B
n
. The devices E
1,1
to E
m,n
which serve as pixels are arranged in a grid pattern, and have their one ends (each of which corresponds to the anode of the diode component E in the aforementioned equivalent circuit) connected to the anode lines A
1
-A
m
at the respective intersections between the vertical anode lines A
1
-A
m
and the horizontal cathode lines B
1
-B
n
and the other ends (each of which corresponds to the cathode of the diode component E in the equivalent circuit) connected to the cathode lines B
1
-B
n
. The cathode lines B
1
-B
n
are connected to, and driven by, a cathode-line scan circuit
1
, while the anode lines A
1
-A
m
are connected to, and driven by, an anode-line driver
2
.
The cathode-line scan circuit
1
has scan switches
5
1
to
5
n
which are associated with the cathode lines B
1
-B
n
and respectively determine the potentials of the cathode lines B
1
-B
n
. Each of the scan switches
5
1
-
5
n
connects either a reverse bias voltage V
CC
(e.g., 10 V), which is a power supply voltage, or a ground potential (0 V) to the associated cathode line.
The anode-line driver
2
has current sources (e.g., constant current sources)
2
1
to
2
m
and drive switches
6
1
to
6
m
, which are associated with the anode lines A
1
-A
m
and supply the drive current to the respective devices via the respective anode lines. The anode-line driver
2
performs ON/OFF control on the drive switches
6
1
-
6
m
to let the current flow through the respective anode lines A
1
-A
m
individually. It is typical to use current sources as the drive sources instead of voltage sources like constant voltage sources for reasons such as the aforementioned current v.s. luminance characteristic being stable with respect to a temperature variation whereas the voltage v.s. luminance characteristic is not. The amount of the current to be supplied from each of the current sources
2
1
-
2
m
is set to the amount that is necessary to keep the associated device emitting light at the desired instantaneous luminance (hereinafter this state will be called “steady emission state”). As electrical charges are being stored in the capacitive component C in the device while the device is in the steady emission state, the voltage across the device becomes a specified value Ve (hereinafter called “specified emission voltage”).
The anode lines A
1
-A
m
are also connected to an anode-line resetting circuit
3
, which has shunt switches
7
1
-
7
m
provided for the respective anode lines. As each shunt switch is selected, the anode-line resetting circuit
3
sets the associated anode line to the ground potential.
The cathode-line scan circuit
1
, the anode-line driver
2
and the anode-line resetting circuit
3
are connected to an emission controller
4
.
In accordance with image data supplied from an image data generating system (not shown), the emission controller
4
controls the cathode-line scan circuit
1
, the anode-line driver
2
and the anode-line resetting circuit
3
to display images carried by the image data. The emission controller
4
controls switching of the scan switches
5
1
-
5
n
to send a scan-line selection control signal to the cathode-line scan circuit
1
, select one of the cathode lines that corresponds to the horizontal scan period of the image data, connect the selected cathode line to the ground and apply the reverse bias voltage V
CC
to the other cathode lines. The reverse bias voltage V
CC
is applied by a constant voltage source to be connected to each cathode line in order to prevent cross-talk emission from the devices connected at the intersections of the driven anode lines and the cathode lines which are not selected for scanning. The reverse bias voltage V
CC
is generally set equal to the specified emission voltage Ve. As the scan switches
5
1
-
5
n
are sequentially switched to the ground potential every horizontal scan period, the cathode line which has been switched to the ground potential serves as a scan line which permits the devices connected to the cathode line to emit light.
The anode-line driver
2
performs drive control on the selected scan line. The emission controller
4
generates drive control signals (drive pulses) indicating which device connected to the scan line should be enabled to emit light at what timing and for how long, in accordance with pixel information specified by the image data, and sends the driv
Okuda Yoshiyuki
Ushigusa Yoshihiro
Pioneer Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
Tran Chuc D
Wong Don
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