Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2002-10-08
2004-08-17
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169300, C345S092000, C345S084000, C345S204000
Reexamination Certificate
active
06777885
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a driver circuit formed on an insulation surface. Further, it also relates to a display device having the driver circuit and a light emitting element provided on the insulation surface. Particularly, the present invention relates to an active matrix display having the driver circuit and a plurality of pixels which are arranged in matrix, and a switching element and a light emitting element are arranged in each pixel.
2. Description of the Related Art
An active matrix display device having a plurality of pixels in which a switching element and a light emitting element are arranged in each pixel, has advantages like superiority in response, operation with a low voltage and a wide view angle. Therefore, the active matrix display device comes under the spotlight as a next generation flat panel display.
Incidentally, the light emitting element means an element of which a luminance is controlled by electric current or voltage. For the light emitting element, electron source elements typified by an OLED (organic light emitting diode) element, a FE (field emission display) element, an MIM (Metal-Insulator-Metal) element and the like may be used.
The light emitting element comprises of an anode, a cathode, and a layer containing an organic compound (hereafter simply referred to as an organic compound layer) and sandwiched between the anode and the cathode. The light emitting element emits light according to a voltage applied between the anode and the cathode. Note that emitting the light emitting element is referred to as driving the light emitting element.
An organic compound layer usually has a lamination structure. A typical lamination structure thereof is one proposed by Tang et al. of Eastman Kodak Company and consisting of a hole-transporting layer, a light emitting layer, and an electron transporting layer. Other examples of the lamination structure include one in which a hole injection layer, a hole transporting layer, a light emitting layer, and an electron transporting layer are layered in order on an anode, and one in which a hole injection layer, a hole transporting layer, a light emitting layer, an electron transporting layer, and an electron injection layer are layered in order on an anode. A light emitting layer may be doped with a fluorescent pigment or the like. A given voltage is applied to the organic compound layer structured as above from a pair of electrodes (an anode and a cathode) to induce recombination of carriers in its light emitting layer. As a result, the light emitting layer emits light.
At this time, the emission luminance of the light emitting element is in proportion to the current flowing between the electrodes (the anode and the cathode). Accordingly, a pixel structure in which a current flowing to the light emitting element of each pixel is controlled by a current (hereafter referred to as control current) input to the pixel portion, is proposed. Such a pixel structure is referred as to current control type pixel.
An example of the structure of the current control type pixel in the active matrix display device is shown with FIG.
7
.
As shown in
FIG. 7
, the current control type pixel comprises of a signal line
701
, a scanning line
702
, a power source line
703
, a wiring
710
, a light emitting element
709
, a switching transistor
704
, a current storage transistor
705
, a current transistor
706
consisting of a current mirror circuit, a driver transistor
707
consisting of a current mirror circuit and using for driving the light emitting element, and a storage capacitor
708
.
Either of a source electrode and a drain electrode of the switching transistor
704
is connected to the signal line
701
, and the other is connected to a drain of the current transistor
706
and either of a source electrode and a drain electrode of the current storage transistor
705
, further, the gate electrode of the switching transistor
704
is connected to the scanning line
702
.
A source electrode of the current transistor
706
is connected to the power source line
703
. A source electrode of the current storage transistor
705
or one side of a drain electrode of the current storage transistor
705
disconnected with the switching transistor
704
is connected to one of electrodes of the storage capacitor
708
, a gate electrode of the current transistor
706
and a gate electrode of the driver transistor
707
.
A side of the storage capacitor
708
disconnected with the current storage transistor
705
is connected to the power source line
703
. A source electrode of the driver transistor
707
is connected to the power source line
703
, while a drain electrode of the driver transistor
707
is connected to one of electrodes of the light emitting element
709
.
Next, a driving method (operation method) in which a video signal is input to the pixel shown in FIG.
7
and the light emitting element emits light, will be described as below. Note that as the video signal input to the pixel, a current (signal current) having a current magnitude corresponding to the luminance represented by the pixel is input. In the pixel shown in
FIG. 7
, the control current which controls the current flowing to the light emitting element in each pixel is identical with the video signal (signal current).
A signal is input to the scanning line
702
, thereby the switching transistor
704
is in state of ON, then, the signal current input from the signal line
701
is input to the pixel. At this time, the current storage transistor
705
is in state of conductive by the signal input to the wiring
710
.
After the signal current is input to the pixel, as time sufficiently goes by, the signal current turns to flow between the source and the drain of the current transistor
706
. At this time, in the storage capacitor
708
, a gate voltage (a voltage between the gate and the source), in order that the current transistor
706
flows a signal current as a drain current, is retained. The signal of the wiring
710
changes thereafter, the current storage transistor
705
becomes in a non-conductive state.
In case that the characteristics of the current transistor
706
and driver transistor
707
are uniform, the drain current of the current transistor
706
is equal to the drain current of the driver transistor
707
. At this time, a current equal to the signal current input from the power source line
703
thorough the driver transistor
707
is input to the light emitting element
709
. After this manner, the light emitting element
709
emits light in a luminance corresponding to the signal current.
Note that even after the signal current is not input to the pixel, the driver transistor
707
flows a current equal to the signal current by the voltage retained in the storage capacitor
708
.
FIG. 8
is a block diagram showing the configuration of an active matrix display device having the current control pixel illustrated in FIG.
7
.
FIG. 8
illustrates a pixel portion
804
, scanning driver circuits
803
a
,
803
b
which input signals to the scanning line of each pixel in the pixel portion
804
, and a signal line driver circuit
802
which input signals to the signal line of each pixel in the pixel portion
804
. The pixel portion
804
and the scanning driver circuits
803
a
,
803
b
are provided on a substrate (hereafter referred to as pixel substrate)
801
having an insulation surface. The signal line driver circuit
802
which are out of a LSI chip
806
and the like, and the LSI chip
806
is attached to the pixel substrate
801
by a TAB
805
.
Note that in the current control pixel shown in
FIG. 7
, the driver circuit input control current is denoted as a control current output circuit. In the configuration of the display device shown in
FIG. 8
, the control current output circuit corresponds to the signal line driver circuit.
Further, a wiring providing control current output from the control current output circuit to the pixel portion is denoted as a control current line.
Alemu Ephrem
Semiconductor Energy Laboratory Co,. Ltd.
Wong Don
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