Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-09-20
2004-06-15
Liang, Regina (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S211000, C315S169300
Reexamination Certificate
active
06750833
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a driving circuit for an active matrix type display using an electro-optical element, such as an organic electroluminescence element (hereinafter referred to as “organic electroluminescence element”), and the like. The invention further relates to a driving method of electronic device and an electronic apparatus, and to the electronic device. More particularly, the present invention relates to a driving circuit having a function for applying reverse bias to an electro-optical element to suppress the deterioration thereof, to a driving method of electronic device and an electronic apparatus, and to the electronic device.
2. Description of Related Art
It is known that a display can be realized by arranging a plurality of pixels in matrix that include an organic electroluminescence element that is one of electro-optical elements. In such a display, the organic electroluminescence element is arranged such that a laminated organic thin film including a light emitting layer is interposed between a cathode formed of a metal electrode, for example, Mg, Ag, Al, Li, and the like and an anode formed of a transparent electrode composed of ITO (indium tin oxide).
FIG. 8
shows an ordinary arrangement of a driving circuit for an active matrix type display using an organic electroluminescence element. In this figure, the organic electroluminescence element is shown as a diode
10
. Further, the driving circuit
1
is composed of two transistors Tr
1
and Tr
2
each composed of a thin film transistor (TFT) and a capacitance element
2
for accumulating electric charge.
Herein both the transistors Tr
1
and Tr
2
are p-channel type TFTs. The transistor Tr
1
can be controlled to be turned on and off according to the electric charge accumulated in the capacitance element
2
in the figure. The capacitance element
2
is charged by a data line V
DATA
through the transistor Tr
2
that is turned on by setting a selection potential V
SEL
to a low level. When the transistor Tr
1
is turned on, a current flows to the organic electroluminescence element
10
through the transistor Tr
1
. The continuous flow of the current to the organic electroluminescence element
10
permits the element to emit light continuously.
FIG. 9
shows a brief timing chart for the circuit of FIG.
8
. As shown in
FIG. 9
, when data is to be written, the transistor Tr
2
is turned on by setting the selection potential V
SEL
to the low level, whereby the capacitance element
2
is charged. This charge period is a writing period T
W
in the figure. An actual display period follows the writing period T
W
. In this period, the transistor Tr
1
is turned on by the electric charge accumulated in the capacitance element
2
. This period is shown as a display period T
H
in the figure.
FIG. 10
shows another arrangement of the driving circuit for the organic electroluminescence element. The driving circuit shown in the figure is written in the literature “The Impact of Transient Response of Organic Light Organic Light Emitting Diodes on the Design of Active Matrix OLED Displays” (1998 IEEE IEDM 98-875). In
FIG. 10
, reference numeral Tr
1
denotes a driving transistor, reference numeral Tr
2
denotes a charge controlling transistor, reference numeral Tr
3
denotes a first selection transistor, and reference numeral Tr
4
denotes a second selection transistor that is turned off during the charge period of a capacitance element
2
.
As is well known, the characteristics of transistors are dispersed even if they have the same standard. Accordingly, even if the same voltage is applied to the gates of transistors, a current having a given value does not always flow through the transistors, which may cause irregular luminance and the like. In contrast, in this driving circuit, electric charge is accumulated in the capacitance element
2
based on an amount of current according to a data signal output from a current source
4
. Thus, the emitting state of organic electroluminescence can be controlled based on the amount of current according to data.
Herein all the transistors Tr
1
to Tr
4
are P-channel type MOS transistors. The transistors Tr
2
and TR
3
are turned on by setting a selection potential V
SEL
to a low level, which causes electric charge having a value according to the output from the current source
4
to be accumulated in the capacitance element
2
. Then, after the selection potential V
SEL
goes to a high level and the transistors Tr
2
and Tr
3
are turned off, the transistor Tr
1
is turned on by the electric charge accumulated in the capacitance element
2
and the transistor Tr
4
is turned on by a data holding control signal V
gp
so that a current flows to the organic electroluminescence element
10
.
FIG. 11
shows a brief timing chart as to the circuit of
FIG. 10
, As shown in
FIG. 11
, when data is to be written by the current source
4
, the transistors Tr
2
and Tr
3
are turned on by setting the selection potential V
SEL
to the a low level, thereby charging the capacitance element
2
. This charging period is a writing period T
W
in FIG.
11
. An actual display period follows the write period T
W
. During the period in which the data holding control signal V
gp
is set to the low level, the transistor Tr
1
is turned on, and this turned-on period is a display period T
H
.
FIG. 12
shows still another arrangement of the driving circuit for the organic electroluminescence element. The driving circuit shown in the figure is the circuit disclosed in Japanese Unexamined Patent Application Publication No. 11-272233. In this figure, the driving circuit includes a transistor Tr
1
for supplying a current from a power supply to an organic electroluminescence element
10
when it is turned on, a capacitance element
2
for accumulating electric charge for maintaining the transistor Tr
1
in the turned-on state, and a charge controlling transistor Tr
5
for controlling the charge of the capacitance element
2
according to an external signal. Note that when the organic electroluminescence element
10
is to emit, a potential V
rscan
is maintained to a low level to turn off a charge controlling transistor Tr
7
. With this operation, no reset signal V
rsig
is output. Note that reference numeral Tr
6
denotes an adjustment transistor.
The transistor Tr
5
is turned on, and the capacitance element
2
is charged by a data line V
DATA
through a transistor Tr
6
. Then, the conductance between the source and the drain of the transistor Tr
1
is controlled according the charged level of the capacitance element
2
, and a current flows to the organic electroluminescence element
10
. That is, as shown in
FIG. 13
, when a potential V
scan
is set to a high level to turn on the transistor Tr
5
, the capacitance element
2
is charged through the transistor Tr
6
. The conductance between the source and the drain of the transistor Tr
1
is controlled according the charged level of the capacitance element
2
, and a current flows to the organic electroluminescence element
10
. The organic electroluminescence element
10
emits.
SUMMARY OF THE INVENTION
Incidentally, it is known that application of reverse bias to an organic electroluminescence element is an effective means to increase the life thereof. This increase of life is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 11-8064.
However, in the method of the publication, additional power supplies such as a negative power source, and the like must be newly prepared to apply reverse bias to the organic electroluminescence element, and the organic electroluminescence element must be controlled so as to permit the reverse bias to be applied thereto.
Accordingly, an object of the present invention is to provide a driving circuit for an active matrix type display capable of applying reverse bias to an electro-optical element such as an organic electroluminescence element, and the like without almost increasing power consumption and cost, to provide a driving met
Dinh Duc Q
Liang Regina
Oliff & Berridg,e PLC
Seiko Epson Corporation
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