Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-08-07
2003-04-08
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S082000
Reexamination Certificate
active
06545651
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a driving circuit for organic thin film EL elements which utilizes an electro luminescence (EL) phenomenon of organic thin films, and more specifically a driving circuit for organic thin EL films which is to be used for displaying characters and figures by driving a matrix of EL elements.
2. Description of the Prior Art
There is known a fact that when a certain organic thin film which is interposed between an anode and a cathode is electrically energized, positive holes and electrons poured from the respective electrodes recombine with each other in the organic film, whereby a luminescent phenomenon takes place due to energies produced by the recombination. This phenomenon is referred to as an organic thin film EL. Since an organic thin film EL element has merit that it can be driven with a DC voltage on the order of several to ten-odd volts, emits rays at a higher efficiency, and is thinner and lighter in weight than other display devices, researches are now being made vigorously for application to various kinds of light-emitting devices.
Though the EL phenomenon can take place even when an organic thin film which is capable of transmitting light (hereinafter referred to as an organic light-emitting thin film layer) is composed of a single layer, it is necessary for obtaining high luminance at a low voltage to pour a carrier from each electrode into the organic light-emitting thin film layer with an enhanced efficiency. Accordingly, there have been proposed laminated structures wherein additional carrier pouring layers or carrier transport layers are interposed between electrodes and organic light-emitting thin film layer for lowering energy barriers between the electrodes and the organic light-emitting thin film layers, thereby facilitating to shift carriers into the organic light-emitting thin film layers. For example, Japanese Patent Application Laid-Open No. 57-51781 proposes a structure which is composed of an anode/an organic positive hole transport layer/an organic light-emitting thin film layer/a cathode and Japanese Patent Application Laid-Open No. 6-314594 proposes a structure which is composed of an anode/a plurality of organic positive hole pouring transport layer/an organic light-emitting thin film layer/a plurality of organic electron pouring transport layer/a cathode. The laminating sequence may be reversed.
FIG. 5
shows a sectional view of an organic thin film EL element having a general laminated structure which is composed of an anode/an organic positive hole transport layer/a light-emitting thin film layer/a cathode formed on a support substrate, and means for applying a voltage to this element.
Materials which are used for composing the organic thin film EL element will be described with reference to FIG.
5
. Speaking of electrodes first, at least one of the cathode and anode must be transparent since light must he taken out of the organic light-emitting thin film layer. In most cases, a thin film of indium-tin oxide (ITO) or a thin film of gold is used as an anode
31
. On the other hand, a material which has a small work function is selected for a cathode
34
for the purpose of lowering a pouring barrier to electrons and a film of a metal such as magnesium, aluminium, indium or an alloy thereof is used as the cathode
34
. Aromatic amine class 3, a polyphyrine derivative or the like is used as an organic positive hole transport layer
32
and 8-hydroxyquinoline metal complex, a butadiene derivative, a benzoxadole derivative or the like is used as an organic light-emitting thin layer
33
. In case of a structure which has an organic electron transport layer, a naphthalimide derivative, a perylene tetracarbonate di-imide derivative, quinacridon derivative or the like is additionally used though the organic thin film EL element shown in
FIG. 5
does not use such a substance. The electrodes and the organic thin film layers are formed on a support substrate made of a glass or resin material by a dry film forming method such as vacuum deposition or sputtering or by a wet film forming method such as spin coating or dipping by gradually laminating the material mentioned above from a solution in which the material mentioned above is dissolved or dispersed. When a transparent electrode (the anode
31
in this case) is formed as a first layer, a support substrate
30
must also be made of a transparent substance.
When a voltage is applied to an EL element which is composed as described above, it exhibits a voltage-current characteristic like that of a diode as shown in FIG.
6
. It is therefore general to drive the element with a current.
As devices to which organic thin film EL elements having structures and electric characteristics like those described above are applied, there have conventionally been proposed planar surface light-transmitting type organic thin film EL displays which drive matrices of organic thin film EL elements exemplified above as unit picture elements arranged in two dimensions on planar surfaces of support substrates. Japanese Patent Application Laid-Open No. 7-36410 discloses an example (conventional example 1) of such a device. Referring to
FIG. 7
which illustrates a theoretical circuit of a driving circuit of a conventional example 1 proposed by this Japanese patent, a display panel
10
is driven by an X driver
12
and a Y driver
14
. A matrix of the display panel
10
is composed of signal electrodes
16
-
0
,
16
-
1
,
16
-
2
, . . . from the X driver
12
and scanning electrodes
18
-
0
,
18
-
1
, . . . from the Y driver
14
. A light-emitting element
20
is connected to each intersection of the matrix. The X driver
12
comprises constant-voltage power sources
22
-
0
,
22
-
1
,
22
-
2
, . . . which receive a driving pulse signal
26
together with a power source voltage (=+V) from a control computer
24
and output a constant current for igniting the light-emitting elements to the signal electrodes
16
-
0
,
16
-
1
,
16
-
2
, . . . . Further, the Y driver
14
comprises switch elements
28
-
0
,
28
-
1
, . . . which are turned on and off by a control signal
29
from the control computer
24
to connect and disconnect the scanning electrodes
18
-
0
,
18
-
1
, . . . to and from ground, thereby driving a matrix.
FIG. 11
illustrates a more concrete composition of the circuit shown in
FIG. 7
described above.
In
FIG. 11
, a video signal is supplied to a shift register
38
used as a memory by way of an A/D converter
36
which comprises a plurality of flip-flop circuits (hereafter referred to as FFs)
44
through
44
. Signals from the FFs in the shift register
38
are supplied to PWM modulators
48
through
48
by way of FFs
46
through
46
in an X driver
40
. Signals (analog signals indicating pulse widths corresponding to luminance data) from the PWM modulators
48
through
48
are supplied to signal electrodes A
0
, A
1
, A
2
, A
3
, . . . , whereas signals from FFs
50
through
50
in a Y driver
34
are supplied to scanning electrodes K
0
, K
1
, K
2
, K
3
, . . . , whereby a matrix of a display panel
30
is composed of the signal electrodes A
0
, A
1
, A
2
, A
3
, . . . and the scanning electrodes K
0
, K
1
, K
2
, K
3
, . . . . Light emitting elements
52
through
52
are connected to the signal electrodes A
0
, A
1
, A
2
, A
3
, . . . and the scanning electrodes K
0
, K
1
, K
2
, K
3
, . . . at intersections between the signal electrodes A
0
, A
1
, A
2
, A
3
, . . . and the scanning electrodes K
0
, K
1
, K
2
, K
3
, . . .
A timing generator
42
which is used as a controller receives a horizontal synchronizing signal and a vertical synchronizing signal, and outputs signals SCLK, LCLK, FPUL and FCLK. The signal SCLK is supplied to the A/D converter
36
and the FFs
44
through
44
in the shift register
38
, the signal LCLK is supplied to the FFs
46
through
46
in the X driver
40
, and the signals FPUL and FCLK are supplied to the FFs
50
through
50
in the Y driver
34
.
Describing with r
Kawashima Shingo
Nishigaki Eitaro
Hjerpe Richard
Michael Best & Friedrich LLC
Nguyen Francis
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