Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-03-23
2001-06-12
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S077000, C345S080000, C345S090000, C345S092000, C345S093000, C345S204000, C345S205000, C345S214000, C315S169300
Reexamination Certificate
active
06246384
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a drive circuit for an electroluminescence (hereinafter referred to as EL) display apparatus comprising an electroluminescence device and thin-film transistors (hereinafter referred to as TFT).
2. Description of the Prior Art
In recent years, EL display apparatuses using EL devices have gained attention as display apparatuses to replace CRTs and LCDS.
Furthermore, display apparatuses using TFTs as the switching devices for driving the EL device are being researched and developed.
FIG. 1
shows a circuit diagram of an organic EL display apparatus of the prior art.
According to the same diagram, a display pixel
1
of the organic EL display apparatus of the prior art comprises a first TFT
100
, a second TFT
200
, a holding capacitor
300
, and an organic EL device
400
.
A gate signal line G, which supplies a gate signal, and a drain signal line D, which supplies a drain signal, cross, and in the vicinity of the intersection of both signal lines G and D there are provided the organic EL device
400
and the TFTs
100
,
200
for driving the organic EL device
400
.
First, the first TFT
100
comprises a gate electrode
110
, which is connected to the gate signal line G and supplied with the gate signal, a drain electrode
120
, which is connected to the drain signal line D and supplied with the drain signal, and a source electrode
130
, which is connected to a gate electrode
210
of the second TFT
200
and to the holding capacitor
300
.
Next, the second TFT
200
comprises the gate electrode
210
, which is connected to the source electrode
130
of the first TFT
100
, a source electrode
220
, which is connected to an anode
410
of the organic EL device
400
, and a drain electrode
230
, which is connected to a driving power supply
500
for supplying power to the organic EL device
400
so as to drive the organic EL device
400
.
Furthermore, the organic EL device
400
comprises the anode
410
, which is connected to the source electrode
220
of the second TFT
200
, a cathode
420
, which is connected to a common power supply terminal
600
, and a light emitting device layer
430
, which is sandwiched between the anode
410
and the cathode
420
.
When the gate signal from the gate signal line G is supplied to the gate electrode
110
of the first TFT
100
, the first TFT
100
turns on and the drain signal that was supplied from the drain signal line D is applied to the gate electrode
210
of the second TFT
200
and to the holding capacitor
300
. As a result, the second TFT
200
turns on and a current flows, corresponding to the gate voltage of the second TFT
200
, from the driving power supply
500
to the organic EL device
400
so that the light emitting device layer
430
of the organic EL device
400
emits light.
The organic EL device
400
is deposited in a sequence of the anode
410
formed from a transparent electrode, such as indium tin oxide (ITO), a first hole transport layer formed from 4,4′-bis(3-methylphenylphenylamino)biphenyl (MTDATA), a second hole transport layer formed from 4,4′,4″-tris(3-methylphenylphenylamino)triphenylanine (TPD), a light emitting layer formed from 10-benzo[h]beryllium-benzoquinolinol complex (Bebq
2
) including a Quinacridone derivative, the light emitting device layer
430
formed from various electron transport layers formed from Bebq
2
, and the cathode
420
formed from a magnesium-indium alloy.
In the organic EL device, holes injected from the anode and electrons injected from the cathode are recombined within the light emitting layer so as to excite the organic molecules forming the light emitting layer and generate an exciton. In the process where the exciton deactivates, light is released from the light emitting layer. This release of light to the outside from the transparent anode through the transparent insulating substrate results in light being emitted.
On the other hand, it is necessary for the EL device in each display pixel to emit the same quantity of light so that a uniform and stable display is obtained at the surface of the EL display apparatus. However, since the characteristic of each second TFT
200
that is provided in each display pixel is not uniform, the currents supplied to the EL devices by the drive circuit for the EL display apparatus in the prior art cannot be kept uniform, thus resulting in a problem where the non-uniform currents appear as an uneven display among the display pixels.
Namely, the size of each second TFT varies, due to deviations in mask patterns during the manufacture of the TFTs and so forth, so that the current flowing to each drain varies even though the same gate voltage is applied to each second TFT. Therefore, the current supplied to the EL device differs with each display pixel and appears as an uneven display.
SUMMARY OF THE INVENTION
In view of the shortcomings of the above-mentioned prior art, it is therefore an object of the present invention to provide an EL display apparatus, in particular a drive circuit for the EL device, designed to improve the uniformity of light emission among display pixels and to easily enable the current supply to the EL device to be controlled.
The electroluminescence display apparatus of the present invention for performing display operations by an electroluminescence device, which comprises an anode and a cathode, emitting light, comprises: a first thin-film transistor, of which a source electrode is connected to a holding capacitor, a drain electrode is connected to a drain signal line, and a gate electrode is connected to a gate signal line; a second thin-film transistor, of which the drain electrode is connected to a driving power supply of the above-mentioned electroluminescence device, and the gate electrode is connected to the source electrode of the above-mentioned first thin-film transistor; a third transistor and a fourth transistor, which are connected between the source electrode of the above-mentioned second thin-film transistor and the anode of the above-mentioned electroluminescence device, for being switched in accordance with a predetermined external signal that is applied to respective gate electrodes; and a charging capacitor, which is connected between the above-mentioned third thin-film transistor and fourth thin-film transistor.
The electroluminescence display apparatus for performing display operations by causing the electroluminescence device, which comprises the anode and cathode, to emit light, comprises: the first thin-film transistor, of which the source electrode is connected to the holding capacitor, the drain electrode is connected to the drain signal line, and the gate electrode is connected to the gate signal line; the second thin-film transistor, of which the drain electrode is connected to the driving power supply of the above-mentioned electroluminescence device, and the gate electrode is connected to the source electrode of the above-mentioned first thin-film transistor; a first diode and a second diode, which are connected in series in a forward direction toward the anode of the above-mentioned luminescence device from the above-mentioned second thin-film transistor between the source electrode of the second thin-film transistor and the anode of the electroluminescence device; and a charging capacitor, which is connected between the above-mentioned first diode and the above-mentioned second diode. The driving power supply generates an output, the voltage of which changes periodically.
The electroluminescence display apparatus for performing display operations by causing the electroluminescence device, which comprises the anode and cathode, to emit light, comprises: a first switching device for receiving a display signal in accordance with a selection signal; the holding capacitor, which is connected to the first switching device, for holding the received display signal for a fixed period; a second switching device, which is connected between the holding capacitor and the first swit
Cantor & Colburn LLP
Kovalick Vincent E.
Sanyo Electric Co,. Ltd.
Shalwala Bipin
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