Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-10-02
2002-12-17
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S077000, C345S034000, C345S035000, C345S036000, C345S045000, C315S169300, C327S108000, C340S870030
Reexamination Certificate
active
06496168
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a display element drive device for driving a single EL display element or a plurality of parallel-connected EL display elements.
FIG. 5
shows the relation between the current density and brightness of an organic EL light emitting element. The coordinates of the current density and brightness are logarithmically represented. Generally, the organic EL light emitting element is a current-driven light emitting element. As shown in
FIG. 5
, the luminance brightness of the organic EL light emitting element is determined according to the current value per unit area, that is, the current density of the light emitting element. It is, therefore, important for uniforming the brightness and improving display quality to set the current density with good accuracy.
FIG. 6
is a circuit block diagram illustrating an example of an organic EL light emitting element of the dot matrix type. As illustrated in
FIG. 6
, in the case of using the EL light emitting elements each having a constant area like those of the dot matrix type, while display rows are selected by sink type row drivers
4
, all pixels can be driven by a single constant current reference source
1
and a plurality of constant current drivers (that is, source type column drivers)
2
a
,
2
b
,
2
c
, . . . ,
2
n
. Incidentally, in
FIG. 6
, reference numeral
3
designates each of the organic EL light emitting elements.
Incidentally, in addition to the dot matrix display apparatus, a fixed segment display apparatus has been generally known. Despite the constraint that a display pattern is fixed, this fixed segment display apparatus has advantages in that the display apparatus of this type can display edge portions of curves more beautifully than the display apparatus of the dot matrix type, and that the EL light emitting elements are easily manufactured because of a small number of steps of a manufacturing process thereof. Thus, the fixed segment display apparatus is effectively used in relatively low cost equipment and in field requiring display quality.
Unlike the dot matrix display apparatus, the areas of individual pictures (or segments) differ from one another in the fixed segment display apparatus. Thus, the current values of the driving currents of individual segments differ from one another. Therefore, a plurality of constant current reference sources are needed for causing the segments to emit light with the same brightness.
FIG. 7
is a circuit block diagram illustrating a conventional fixed segment display apparatus. In this apparatus, a plurality of constant current reference sources
5
a
,
5
b
,
5
c
, . . . ,
5
n
supply constant currents to constant current drivers
6
a
,
6
b
,
6
c
, . . . ,
6
n
, respectively. Thus, each of organic EL light emitting segments
7
a
,
7
b
,
7
c
, . . . ,
7
n
is driven.
Thus, in the fixed segment display apparatus, the display pattern varies with the segments. Further, the number of the segments and the areas of the segments vary with apparatuses to which the display pattern is applied. Therefore, it is not preferable from the viewpoint of standardization of the display apparatus to fix a set value of each of the preliminarily prepared constant current sources
5
a
,
5
b
,
5
c
, . . . ,
5
n
for a drive device consisting of the constant current reference sources
5
a
,
5
b
,
5
c
, . . . ,
5
n
and the current drivers
6
a
,
6
b
,
6
c
, . . . ,
6
n
. Consequently, this conventional display apparatuses have a drawback in that a drive device should be custom-designed for each of the display apparatuses. Moreover, the use of the plurality of constant current reference sources
5
a
,
5
b
,
5
c
, . . . ,
5
n
itself hinders the enhancement of the area efficiency of the circuit.
Incidentally, it is possible to use a constant voltage circuit instead of the drive circuit shown in FIG.
7
and parallel-connect all the organic EL light emitting elements with the constant voltage circuit. In this case, the custom-designed constant current reference sources are unnecessary. Consequently, the area efficiency of the circuit can be enhanced.
However, generally, according to the voltage-current characteristic of the organic EL light emitting element, change in the current increases exponentially with increase in the voltage, as illustrated in FIG.
8
. Thus, in the case of the drive circuit using the constant voltage circuit, even when a small error occurs in the constant voltage, the current density may largely change. Consequently, there is a fear that the brightness of the organic EL light emitting element largely changes, and the display quality is deteriorated. It is, therefore, necessary to precisely adjust the voltage supply. Consequently, the provision of a more complex voltage stabilization circuit is needed. Especially, in the case that organic EL light emitting elements in an automobile instrument panel are driven by being supplied with power from an automobile battery, there is the necessity for applying voltages to drive loads other than a power steering device and a power window device. Thus, there has been a problem of how to achieve the stabilization of a supply voltage.
Additionally, the resistance value of the organic EL light emitting element may change owing to the deterioration thereof and to the influence of the ambient temperature, so that the driving current changes. Consequently, there has been a problem of how to stabilize the brightness of the organic EL light emitting element.
SUMMARY OF THE INVENTION
In view of the problems of the conventional example, in the Japanese Patent Application No. 10-301188, the Applicants of the present application have proposed a display element drive device (namely, a proposed device example), which serves as a display element drive circuit enabled to increase the area efficiency of the circuit, and to be adapted to standardization, and to cause small change in the luminance brightness of display elements when the display elements are supplied with power from an automobile battery that is relatively liable to bring about voltage variation, and to stably maintain the luminance brightness even when the resistance value of the display element changes owing to the deterioration thereof, and to have excellent durability.
In this proposed device example, as illustrated in
FIGS. 9 and 10
, a plurality of fixed segment organic EL display elements
11
a
to
11
n
are parallel-connected to one another, and a stabilization voltage is supplied to the parallel circuit. Thus, the plurality of conventional drive reference sources (namely, the current sources) needed owing to the difference in the area among the segments are omitted. Moreover, the segments are allowed to have the same brightness.
Further, to deal with variation in characteristics and aged deterioration in the voltage-driven case, the device has a current detecting means
31
(a drive state detecting means) for detecting the current value of electric current supplied to one specific organic EL display element (hereunder referred to as “reference organic EL display elements”)
11
z
(reference light emitting element) other than the organic EL display elements
11
a
to
11
n
, and for outputting a current value signal adapted to change according to the electric current value, a voltage control circuit
32
for converting a current value signal, which is received from the current detecting means
31
, into a stabilization voltage adjustment signal, and a stabilization voltage supply circuit
33
for converting a voltage Vin, which is supplied from an astable battery power supply (+B), into a constant stabilization voltage Vout.
Incidentally, the reference organic EL display element
11
z
is connected to the current detecting means
31
, and supplied with electric current from the current detecting means
31
. On the other hand, other organic EL display elements
11
a
, . . . ,
11
n
are supplied with electric current through predetermined switching circuits
15
(
15
a
to
15
n
), as illustrated in FIG.
10
.
Autonetworks Technologies Ltd.
Nguyen Jimmy H.
Shalwala Bipin
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