Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2003-02-10
2004-06-29
Vo, Tuyet T. (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169300, C345S214000, C345S213000, C345S182000, C345S076000
Reexamination Certificate
active
06756738
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an organic EL drive circuit and an organic EL display device using the same and, in particular, the present invention relates to an improvement of an organic EL drive circuit for current-driving a column line (anode side drive line) of each of organic EL elements of an organic EL panel by supplying current, which corresponds to an input digital value and is generated by a D/A converter circuit utilizing a current mirror circuit, to each of terminal pins of the organic EL panel, such that a peak current for driving the organic EL panel can be easily generated by the drive circuit and an area of the drive circuit can be reduced and an organic EL display device using the same organic EL drive circuit.
2. Description of the Prior Art
It has been known that an organic EL display device, which realizes a high luminance display by light generated by itself, is suitable for a display on a small display screen and the organic EL display device has been attracting public attention as the next generation display device to be mounted on a portable telephone set, a DVD player or a PDA (Personal Digital Assistants) such as a portable terminal device, etc.
Known problems of the organic EL display device are that, when it is driven by voltage as in a liquid crystal display device, luminance variation thereof becomes substantial and that, since there is difference in sensitivity between R (red), G (green) and B (blue), a control of luminance of a color display becomes difficult.
In view of these problems, an organic EL display device using current drive circuits has been proposed recently. For example, JPH10-112391A discloses a technique with which the luminance variation problem is solved by employing a current drive system.
An organic EL display panel of an organic EL display device for a portable telephone set, having 396 (132 3) terminal pins for column lines and 162 terminal pins for row lines has been proposed. However, there is a tendency that the number of column lines as well as row lines is further increased.
An output stage of a current drive circuit of such organic EL display panel of the active matrix type or the simple matrix type includes a current source drive circuit, such as an output circuit constructed with a current mirror circuit for each of the terminal pins. A drive stage thereof includes a parallel-driven type current mirror circuit (reference current distribution circuit) having a plurality of output side transistors for each of the terminal pins as disclosed in JP2002-82662 (domestic priority application claiming priorities of JP2001-86967 and JP2001-396219) corresponding to U.S. patent application Ser. No. 10,102,671. In the disclosed drive stage, a plurality of mirror currents are generated correspondingly to the respective terminal pins by branching a reference current generated by the parallel-driven type current mirror circuit to thereby drive the output circuits. Alternatively, the mirror currents distributed to the respective terminal pins are amplified by respective k-time current amplifier circuits, where k is an integer not smaller than 2, and the output circuits are driven with the amplified currents. The drive stage including the k-time amplifier circuits is disclosed in JP2002-33719, in which D/A converter circuits are provided correspondingly to the respective terminal pins. In the disclosed circuit construction, the D/A converter circuit converts display data corresponding to the column side terminal pins into analog data to generate a column side drive currents simultaneously.
In this disclosed construction, a peak current is generated for initially charging an organic EL element having capacitive load characteristics to drive the organic EL element. The peak current may be generated before the drive stage as a reference current, after a D/A converter circuit as described in JP2002-33719 or in a current output stage.
FIG. 5
shows a typical example of the peak current generator circuit for an organic EL display element of an organic EL display panel, which generates the peak current in the current output stage and is disclosed in JPH11-45071A. Further,
FIG. 6
shows another example, which is disclosed in JP2002-33719 and in which the peak current generator circuit is provided after the D/A converter circuit.
The example shown in
FIG. 5
in which the peak current generator circuit is provided in the current output stage will be described first. In the current drive circuit shown in
FIG. 5
, a pulse generator circuit
5
generates a pulse signal
6
synchronized with a drive pulse and the pulse signal
6
is supplied to a switching element
8
of an initial charging circuit
7
b
provided in parallel to a load resistor of a constant current source (current mirror output circuit)
7
a
of a drive circuit
7
. Upon this, the switching element
8
is turned ON and a current flows to an organic EL element
4
through the switching element
8
and a switching transistor
7
c
, which is simultaneously turned ON by the drive pulse, so that the organic EL element
4
is driven. As a result, a large current flows for a constant time from a start time of the driving, which is determined by an ON resistance of the switching element
8
and a junction capacitance of the organic EL element
4
. Therefore, in the initial drive stage, the organic EL element
4
is charged rapidly, so that a luminance of the organic EL element
4
is improved and luminance variation thereof is prevented.
The peak current generator circuit shown in
FIG. 6
includes a column driver
1
of an organic EL drive circuit, a D/A converter circuit
2
and a current mirror type current output circuit
3
.
The current mirror type current output circuit
3
includes a drive stage current mirror circuit
3
a
and an output stage current mirror circuit
3
b.
The drive stage current mirror circuit
3
a
is a peak current generator circuit and includes diode-connected PNP input side transistor Qs and output side transistor Qt. Emitters of these transistors are connected to an input terminal
3
c
of the output stage current mirror circuit
3
b
through a P channel MOS FET Trs and an N channel MOS FET Trt, respectively.
A collector of the input side transistor Qs is connected to an output terminal
2
b
of the D/A converter circuit
2
and a collector of the output side transistor Qt is grounded. An emitter area ratio of the transistor Qs to the transistor Qt is 1:x. Assuming that an output current of the D/A converter circuit
2
is Ia, a drive current generated at the input terminal
3
c
becomes (x+1) Ia. Therefore, the current mirror circuit
3
a
generates drive current (1+x) Ia when the transistor Trt is in ON state. The transistor Trs is a load transistor provided correspondingly to the transistor Trt and has a gate connected to GND. The transistor Trs is provided to balance a drive line. Incidentally, the transistor Trt is turned ON for a constant time in the initial stage of driving by a control signal CONT.
The current mirror circuit
3
a
drives a PNP input side transistor Qx of the output stage current mirror circuit
3
b
through PNP current mirror transistors Qu and Qw, which are provided for base current correction. As a result, current (1+x) Ia flows through the input side transistor Qx for a constant time during which the transistor Trt is turned ON to perform a peak current drive of the organic EL element. Thereafter, the drive current Ta is outputted as a normal drive current. The current (1+x) Ia and the current Ta are amplified to N times by a PNP type output side transistor Qy of the output stage current mirror circuit
3
b
and outputted to one (
9
) of the column side terminal pins of an organic EL panel.
Incidentally, an emitter area ratio of the transistor Qx to the transistor Qy in the output stage current mirror circuit
3
b
is 1:N and emitters of these transistors are connected to not a power source line +VDD but a power source line +Vcc having a volta
Fujisawa Masanori
Maede Jun
Mattingly Stanger & Malur, P.C.
Rohm & Co., Ltd.
Vo Tuyet T.
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