Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2002-05-23
2003-09-09
Nguyen, Hoang (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169100, C345S055000, C345S077000
Reexamination Certificate
active
06617801
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a drive device that performs light-emitting drive of a light-emitting panel wherein capacitative light-emitting elements such as organic electroluminescent elements are arranged in matrix fashion.
2. Description of the Related Art
In recent years, as display devices have become of large size, thin display devices are being demanded and various types of thin display devices are being put into practice. Organic electroluminescent elements (hereinbelow simply referred to as EL elements) are known as one type of display element employed in such thin display devices.
EL elements are capacitative light-emitting elements that may in electrical terms be equivalently represented by a capacitative constituent C and a diode-characteristic constituent coupled in parallel with this capacitative constituent, as shown in FIG.
1
. When a DC light-emitting drive voltage is applied between the electrodes of the EL element, electrical charge is accumulated on capacitative constituent C and when the barrier voltage or light-emitting threshold voltage that is characteristic of this element is exceeded current starts to flow from the electrode (anode side of the diode constituent E) to the organic functional layer that performs the role of light-emitting layer, thereby causing this to emit light with an intensity proportion to this current.
FIG. 2
of the accompanying drawings is a view showing the voltage V-current I-brightness L characteristic of such an EL element.
As shown in
FIG. 2
, the characteristic of an EL element is similar to that of a diode; at voltages below the light-emitting threshold voltage V
th
, the current I is very small while at voltages at or above the light-emitting threshold value V
th
the current increases abruptly. Also, the brightness L is practically proportional to the current I. That is, if a drive voltage exceeding the light-emitting threshold value voltage V
th
is applied, a light-emitting brightness proportional to the current produced by this drive voltage is presented while if the drive voltage is below the light-emitting threshold voltage V
th
no drive current flows and the light-emitting brightness remains at zero.
FIG. 3
of the accompanying drawings diagrammatically illustrates the construction of an EL display device in which is mounted a light-emitting panel constituted by a matrix arrangement of such EL elements.
In
FIG. 3
, n cathode leads (metallic electrodes) B
1
to B
n
are arranged in parallel in the horizontal direction in light-emitting panel
11
while m anode leads (transparent electrodes) A
1
, to A
m
, are arranged in parallel in the vertical direction, respectively, EL elements E
1,1
to E
m,n
being formed at the intersections (total of n×m intersections). The EL elements E
1,1
to E
m,n
that play the role of pixels are arranged in lattice fashion, corresponding to the positions of intersections of anode leads A
1
to A
m
along the vertical direction and cathode leads B
1
to B
n
along the horizontal direction, with one terminal thereof being connected to the anode lead (anode lead side of diode constituent E of the above equivalent circuit) and their other terminals (cathode lead side of diode constituent E of the above equivalent circuit) being connected with the cathode leads.
Light emission control circuit
12
respectively controls cathode lead scanning circuit
13
and anode lead driver
14
such that an image representing the video data is caused to be displayed in accordance with this input video data. Specifically, light emission control circuit
12
supplies to cathode lead scanning circuit
13
scanning pulse signal SP such as to make the respective EL elements E
1,1
to E
m,n
capable of being driven, one horizontal scanning line at a time. Furthermore, light emission control circuit
12
generates drive pulses having a logic level corresponding to the input video data and supplies these drive pulses to anode lead driver
14
, one horizontal scanning line (GP
1
to GP
m
) at a time. Cathode lead scanning circuit
13
includes scanning switches
5
1
to
5
n
corresponding to the cathode leads B
1
to B
n
that individually determine the voltages of the cathode leads. Scanning switches
5
1
to
5
n
respectively apply earth potential (0 V) to the corresponding cathode lead during the period in which scanning pulse signal SP is applied from light emission control circuit
12
and in periods other than this apply bias potential Vcc (for example 10 V) thereto. The bias potential Vcc is applied in order to prevent crosstalk light emission by EL elements respectively connected to respective cathode leads to which scanning pulse signal SP is not supplied and is normally set at bias potential Vcc=V
F
Anode power source circuit
10
generates a prescribed anode power source voltage V
A
constituting the source of drive current supplied to respective anode leads A
1
to A
m
in order to drive respective EL elements E
1,1
to E
m,n
in accordance with the power source voltage from battery
100
; this is then supplied to anode lead driver
14
. Anode lead driver
14
comprises anode drive switches
6
1
to
6
m
and constant current drivers
2
1
to
2
m
constituting current sources that supply drive current respectively to the EL elements E
1,1
to E
m,n
through anode leads A
1
to A
m
respectively, of light-emitting panel
11
. Constant current drivers
2
1
to
2
m
respectively generate the above drive currents having a prescribed constant current in accordance with anode power source voltage V
A
supplied from anode power source circuit
10
and output these respectively to anode drive switches
6
1
to
6
m
. Anode drive switches
6
connect the output terminal of constant current drivers
2
to anode leads A if the drive pulse GP supplied from light emission control circuit
12
is for example logic level “1” and apply earth potential to the anode leads A if the drive pulse GP is logic level “0”. For example, anode drive switch
6
1
connects the output terminal of constant current driver
2
1
to anode lead A
1
if the drive pulse GP
1
supplied from light emission control circuit
12
is for example logic level “1” and applies earth potential to the anode lead A
1
if the drive pulse GP
1
is logic level “0”. Also, anode drive switch
6
m
connects the output terminal of constant current driver
2
m
to anode lead A
m
if the drive pulse GP
m
supplied from light emission control circuit
12
is for example logic level “1” and applies earth potential to the anode lead A
m
if the drive pulse GP
m
is logic level “0”. The amounts of current supplied by the respective constant current drivers
2
1
to
2
m
are the current amounts necessary to maintain a condition in which an EL element is emitting light with the desired instantaneous brightness (hereinbelow, this condition is called the “steady light emission condition”). Also, when an EL element is in the steady light emission condition, charge is stored on the capacitative constituent C of this EL element, so the voltage across the two terminals of the EL element is a positive voltage V
F
somewhat higher than the light-emitting threshold voltage V
th
(this voltage is called the forward voltage). Consequently, only the EL elements on the cathode lead that is set to earth potential in response to the scanning pulse signal SP emit light in response to the drive current that is supplied from constant current drivers
2
. Of the respective anode drive switches
6
1
to
6
m
, only the anode switches that are supplied with drive pulses of logic level “1” from light emission control circuit
12
apply drive current on the corresponding anode lead. The respective EL elements E
1,1
to E
i,j
that are provided in light-emitting panel
11
are thereby made to assume a light emission condition (light-emitting or non-light-emitting) in response to the input video (image) data.
The condition of the light-emitting panel
11
shown in
FIG. 3
illustrates by way of example a condit
Ishizuka Shinichi
Murakata Masaki
Ochi Hideo
Yoshida Takayoshi
Nguyen Hoang
Pioneer Corporation
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