Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-08-09
2004-12-07
Liang, Regina (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S080000, C315S169300
Reexamination Certificate
active
06828950
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron display device in which electro luminescence (EL) elements are formed on a substrate, and a method of driving the same. In particular, the present invention relates to an EL display device using semiconductor devices (devices using a semiconductor thin film), and a method of driving the same. The present invention also relates to electronic devices using an EL display device in a display portion.
2. Description of the Related Art
In recent years, EL display devices including EL elements as self light-emitting elements are being actively developed. An EL display device is also called an organic EL display (OELD) or an organic light-emitting diode (OLED).
An EL display device is of a self light-emitting type, unlike a liquid crystal display device. An EL element has a structure in which an EL layer is interposed between a pair of electrodes (anode and cathode), and the EL layer usually has a layered structure. Typically, there is a layered structure “hole transport layer/light-emitting layer/electron transport layer” proposed by Tang of Eastman Kodak. This structure has a very high light-emitting efficiency, and most of the EL display devices that are being studied and developed adopt this structure.
Alternatively, an EL layer may have a structure in which a hole injection layer, a hole transport layer, a light-emitting layer, and an electron transport layer are stacked in this order on an anode or a structure in which a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and electron injection layer are stacked in this order on an anode. A light-emitting layer may be doped with a fluorescent colorant.
In the present specification, all the layers provided between a cathode and an anode are collectively referred to as an “EL layer”. Therefore, the above-mentioned hole injection layer, hole transport layer, light-emitting layer, electron transport layer, electron injection layer, etc. are all included in the EL layer.
A predetermined voltage is applied to an EL layer with the above-mentioned structure through a pair of electrodes, whereby carriers are recombined in a light-emitting layer to emit light. In the present specification, light emission of an EL element is referred to “driving of an EL element”. Furthermore, in the present specification, a light-emitting element composed of an anode, an EL layer, and a cathode is referred to as an “EL element”.
In the present specification, an anode and a cathode of an EL element may be referred to as “both electrodes” of an EL element.
In the present specification, an EL element refers to both an element utilizing light emission (fluorescence) from singlet excitons and an element utilizing light emission (phosphorescence) from triplet excitons.
As a method of driving an EL display device, there is an active matrix system.
FIG. 6
is a block diagram showing an exemplary active matrix type display device. In a pixel portion, source signal lines for receiving a signal from a source signal line driving circuit and gate signal lines for receiving a signal from a gate signal line driving circuit are formed in a matrix. Furthermore, power supply lines are formed in parallel with the source signal lines. In the present specification, the electric potential of the power supply line is referred to as a “power supply potential”.
FIG. 5
shows a structure of a pixel portion of an active matrix type EL display device. Gate signal lines (G
1
to G
y
) for receiving a selection signal from a gate signal line driving circuit are connected to gate electrodes of switching TFTs
301
of respective pixels. Furthermore, one of a source region and a drain region of the switching TFT
301
of each pixel is connected to a source signal line (S
1
to S
x
) for receiving a signal from the source signal line driving circuit, and the other is connected to a gate electrode of an EL driving TFT
302
and one electrode of a capacitor
303
of each pixel. The other electrode of the capacitor
303
is connected to a power supply line (V
1
to V
x
). One of a source region and a drain region of the EL driving TFT
302
of each pixel is connected to the power supply line (V
1
to V
x
), and the other is connected to an EL element
304
of each pixel.
The EL element
304
includes an anode, a cathode, and an EL layer provided between the anode and the cathode. In the case where the anode of the EL element
304
is connected to the source region or the drain region of the EL driving TFT
302
, the anode of the EL element
304
functions as a pixel electrode, and the cathode thereof functions as a counter electrode. On the other hand, in the case where the cathode of the EL element
304
is connected to the source region or the drain region of the EL driving TFT
302
, the cathode of the EL element
304
functions as a pixel electrode and the anode thereof functions as a counter electrode.
In the present specification, the electric potential of a counter electrode is referred to as a “counter potential”. A power source for supplying a counter potential to the counter electrode is referred to as a “counter power source”. The potential difference between the electric potential of the pixel electrode and that of the counter electrode is an EL driving voltage, which is applied to the EL layer.
As a gray-scale display method of the above-mentioned EL display device, there are an analog gray-scale system and a time gray-scale system.
First, an analog gray-scale system of an EL display device will be described.
FIG. 7
shows a timing chart in the case where the display device in
FIG. 5
is driven by the analog gray-scale system. A period, which starts when one gate signal line is selected and finishes when the subsequent gate signal line is selected, is referred to as “one line period (L)”. A period, which starts when one image is selected and finishes when the subsequent image is selected, corresponds to one frame period. In the case of the EL display device in
FIG. 5
, there are y gate signal lines, so that y line periods (L
1
to L
y
) are provided in one frame period.
As a resolution is increased, the number of line periods in one frame period is also increased, which makes it necessary to drive a driving circuit at a high frequency.
The power supply lines (V
1
to V
x
) are kept at a constant potential. The counter potential is also kept constant. The counter potential has a potential difference with respect to the power supply potential to such a degree that an EL element emits light.
In a first line period (L
1
), a selection signal is supplied to a gate signal line G
1
from the gate signal line driving circuit. Then, an analog video signal is successively input to the source signal lines (S
1
to S
x
). All the switching TFTs
301
connected to the gate signal line G
1
are turned on, so that the analog video signals input to the source signal lines S
1
to S
x
are input to the gate electrodes of the EL driving TFTs
302
through the switching TFTs
301
.
The switching TFT
301
is turned on, and the analog video signal input to the pixels becomes a gate voltage of the EL driving TFT
302
. At this time, a drain current is determined with respect to a gate voltage in one-to-one correspondence, in accordance with Id-Vg characteristics of the EL driving TFT
302
. More specifically, the electric potential of the drain region (EL driving potential in an ON state) is determined so as to correspond to the voltage of the analog video signal input to the gate electrode of the EL driving TFT
302
. Then, a predetermined drain current flows through the EL element, and the EL element emits light in a light emission amount corresponding to the current amount.
When the above-mentioned operation is repeated and an input of the analog video signals to the source signal lines (S
1
to S
x
) is completed, the first line period (L
1
) is completed. A combination of a period, which finishes when the input of the analog video signals to the s
Dinh Duc Q
Liang Regina
Semiconductor Energy Laboratory Co,. Ltd.
LandOfFree
Display device and method of driving the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Display device and method of driving the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Display device and method of driving the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3310158