Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2000-01-06
2002-04-23
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169300, C345S101000
Reexamination Certificate
active
06376994
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for driving a light emitting device and, more particularly, to a driving apparatus for an EL device.
FIELD OF THE INVENTION
Attention is paid to an EL (electroluminescence) display as a display apparatus which can be substituted for a liquid crystal display and in which a low electric power consumption, a high display quality, and a thin size can be realized. The EL display has an organic compound in which excellent light emitting performance can be expected and is used as a light emitting layer of an EL device that is used in the EL display. The device has a high efficiency and a long service life which can endure a practical use.
A full-color image display can be accomplished by selecting an organic material which can perform a light emission of red (R), green (G), or blue (B) (i.e., a first, a second, or a third primary color) as an emitting material which is applied to the light emitting layer (RGB method). It can be also accomplished by a CCM (Color Changing Mediums) method using a color converting layer for each of the RGB colors as disclosed in “Nikkei Electronics”, Vol. 1.29 (No. 654), pp. 99-103, 1996, or the like.
The organic EL device (hereinafter, simply referred to as an EL device) can be expressed by an electrical equivalent circuit as shown in FIG.
1
.
As will be understood from
FIG. 1
, the EL device can be expressed by a configuration comprising a capacitive component C and a component E having diode characteristics connected in parallel with the capacitive component. Generally, the EL device is a capacitive light emitting device.
When a light emission driving voltage is applied to the EL device, charges corresponding to a capacitance first flow to an electrode as a displacement current and are accumulated. When the voltage exceeds a certain voltage (light emission threshold voltage) that is peculiar to the device, a forward current starts to flow from an anode into an organic layer serving as a light emitting layer and light emission occurs at an intensity that is proportional to the driving current.
FIGS. 2
to
4
show light emitting characteristics (L-I, I-V, and L-V characteristics: where “L”, “I”, and “V” denotes a light emission luminance, a driving current, and a driving voltage, respectively) of the EL device. When the driving voltage exceeding the light emission threshold value is applied to the EL device, light emission occurs at a luminance that is proportional to the driving current in accordance with the driving voltage. When the applied driving voltage is equal to or lower than the light emission threshold value, no driving current flows and the light emission luminance is also almost equal to zero.
As a method of driving a color panel using the EL device, it is known that a simple matrix driving method can be applied. A driving method of performing a resetting operation to discharge accumulated charges in each EL device arranged in a matrix form just before scanning lines are switched (hereinafter, referred to as a reset driving method) has been disclosed in Japanese Laid-Open Patent Publication (Kokai) No.H09-199136 (1997) by the same applicant as that of the present invention. The reset driving method will now be described with reference to
FIGS. 5
to
8
.
EL devices E
1,1
to E
n,m
serving as pixels are arranged in a matrix form. One end (anode side of the diode component E of the equivalent circuit) of each EL device is connected to an anode line and the other end (cathode side of the diode component E) is connected to a cathode line at each intersecting position between anode lines A
1
to A
n
arranged along the vertical direction and cathode lines B
1
to B
m
arranged along the horizontal direction, respectively.
A cathode line scanning circuit
1
and an anode line driving circuit
2
are provided as light emission driving means for the EL device. The cathode line scanning circuit
1
has a function to individually decide an electric potential of each cathode line in order to select a cathode line to be scanned. In more detail, scan switches
5
1
to
5
m
corresponding to the cathode lines B
1
to B
m
connect either a reverse bias voltage V
B
(for example, 10V) or a ground potential (0V) to the corresponding cathode lines.
The anode line driving circuit
2
has a function to individually supply a driving current through each anode line. In more detail, current sources
2
1
to
2
n
are provided in correspondence to the anode lines A
1
to A
n
. Currents which are generated in the current sources flow individually to the anode lines A
1
to A
n
through drive switches
6
1
to
6
n
.
The anode lines A
1
to A
n
are also connected to an anode resetting circuit
3
. The anode resetting circuit
3
has shunt switches
7
1
to
7
n
each provided every anode line. When the shunt switch is turned on, the corresponding anode line is connected to the ground potential.
Each of the cathode line scanning circuit
1
, the anode line driving circuit
2
and the anode resetting circuit
3
is controlled by a light emission control circuit
4
. The light emission control circuit
4
controls each circuit in order to display an image carried by image data in accordance with an image data signal supplied from an image data generating system (not shown).
That is, the light emission control circuit
4
generates a scanning line selection control signal to the cathode line scanning circuit
1
, selects any of the cathode lines B
1
to B
m
corresponding to a horizontal scanning period of the image data, and connects it to the ground potential. The control circuit
4
switches the scan switches
5
1
to
5
m
so that the reverse bias voltage V
B
is applied to the other cathode lines. The scan switches
5
1
to
5
m
are, therefore, subjected to a switching control according to what in called a-line-at-a-time scanning such that they are sequentially switched to the ground potential every horizontal scanning period. The cathode line connected to the ground potential acts as a scanning line for enabling the EL devices connected to the cathode line to perform a light emission.
The anode line driving circuit
2
performs a light emission control to the scanning line that is being scanned. The light emission control circuit
4
generates a drive control signal (driving pulse) indicating a result of a discrimination with respect to which one of the EL devices connected to the scanning line is allowed to perform the light emission at which timing for which duration in accordance with image information of the image data. The light emission control circuit
4
supplies the generated control signal to the anode line driving circuit
2
.
The anode line driving circuit
2
controls the on/off operations of the drive switches
6
1
to
6
n
in response to the control signal and supplies the driving current to the EL device in accordance with the pixel information through the anode lines A
1
to A
n
. The EL device to which the driving current is supplied, thus, performs a light emission according to the pixel information.
The anode resetting circuit
3
is provided to perform the resetting operation. The resetting operation is performed in response to the reset control signal from the light emission control circuit
4
. The anode resetting circuit
3
turns on any of the shunt switches
7
1
to
7
n
corresponding to the reset target anode line indicated by the reset control signal and turns off the other switches. The operation of a reset driving method based on the above configuration will now be described.
An operation flow will be explained as an example hereinbelow where after the cathode line B
1
is scanned and the EL devices E
1,1
and E
2,1
are allowed to emit the light, the scan is shifted to the cathode line B
2
and the EL devices E
2,2
and E
3,2
are allowed to emit the light. For simplicity of explanation, the EL device which performs the light emission is shown by a diode symbol and the EL device which does not perform the light emission is shown by a capacitor symbol.
Ochi Hideo
Okuda Yoshiyuki
Tsuchida Masami
Pioneer Corporation
Sughrue & Mion, PLLC
Vu David
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