Computer graphics processing and selective visual display system – Display driving control circuitry
Reexamination Certificate
2001-07-05
2003-10-14
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Display driving control circuitry
C345S055000, C345S060000, C345S061000, C345S062000, C345S063000, C345S076000, C345S087000, C345S208000, C345S211000, C345S212000, C345S213000, C315S169300, C315S169400
Reexamination Certificate
active
06633285
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a driving circuit to drive a capacitive load with a driving pulse, and a display device using the driving circuit.
BACKGROUND ART
A sustain driver to drive a sustain electrode in a plasma display panel for example is known as a conventional driving circuit to drive a capacitive load.
FIG. 13
is a circuit diagram showing the configuration of a conventional sustain driver. As shown in
FIG. 13
, the sustain driver
400
includes a recovering capacitor C
11
, a recovering coil L
11
, switches SW
11
, SW
12
, SW
21
, and SW
22
, and diodes D
11
and D
12
.
The switch SW
11
is connected between a power supply terminal V
4
and a node N
11
, while the switch SW
12
is connected between the node N
11
and the ground terminal. The power supply terminal V
4
is provided with voltage Vsus. The node N
11
is connected to
480
sustain electrodes for example, and in
FIG. 13
a panel capacitance Cp corresponding to the total capacitance between a plurality of sustain electrodes and the ground terminal is shown.
The recovering capacitor C
11
is connected between a node N
13
and the ground terminal. The switch SW
21
and the diode D
11
are connected in series between the nodes N
13
and N
12
, and the diode D
12
and the switch SW
22
are connected in series between the nodes N
12
and N
13
. The recovering coil L
11
is connected between the nodes N
12
and N
11
.
FIG. 14
is a timing chart for use in illustration of the operation of the sustain driver
400
in
FIG. 13
during a sustain period.
FIG. 14
shows the voltage at the node N
11
and the operation of the switches SW
21
, SW
11
, SW
22
and SW
12
in FIG.
13
.
At first, during the period Ta, the switch SW
21
turns on, and the switch SW
12
turns off. At the time, the switches SW
11
and SW
22
are both off. Thus, LC resonance by the recovering coil L
11
and the panel capacitance Cp causes the voltage at the node N
11
to gradually rise. During the period Tb, the switch SW
21
turns off, and the switch SW
11
turns on. Thus, the voltage at the node N
11
abruptly increases, and the voltage at the node N
11
is fixed at the level of Vsus during the period Tc.
During the period Td, the switch SW
11
turns off, and the switch SW
22
turns on. Thus, the LC resonance by the recovering coil L
11
and the panel capacitance Cp causes the voltage at the node N
11
to gradually decrease. Then, during the period Te, the switch SW
22
turns off, and the switch SW
12
turns on. Thus, the voltage at the node N
11
abruptly drops, and is fixed at the ground potential level. The above operation is repeated during the sustain period, so that a periodic sustain pulse Psu is applied to the plurality of sustain electrodes.
As described above, the rising and falling parts of the sustain pulse Psu consist of the LC resonance part during the periods Ta and Td by the operation of the switch SW
21
or SW
22
and edge parts e
1
and e
2
during the periods Tb and Te by the turn-on operation of the switch SW
11
or SW
12
.
These switches SW
11
, SW
12
, SW
21
and SW
22
are each composed of an FET (field effect transistor) serving as a switching element, and each FET has a drain-source capacitance as a parasitic capacitance, and a line connected to each FET has an inductance component. Therefore, when the switch SW
11
or the like changes from an off state to an on state, LC resonance is generated by the drain-source capacitance and the inductance component of the lines, and the LC resonance causes unwanted electromagnetic wave radiation.
The diodes D
11
and D
12
each have an anode-cathode capacitance as a parasitic capacitance, and a line connected to each diode has an inductance component. Therefore, when the switch SW
11
or the like changes from an off state to an on state, LC resonance is generated by the anode-cathode capacitance and the inductance component of the lines, and the LC resonance causes unwanted electromagnetic wave radiation.
Furthermore, the drain-source capacitance of each FET, the anode-cathode capacitance of each diode and the inductance component of each line are small, so that the LC resonance frequency is high, and the frequency of the resultant electromagnetic wave is also high. Meanwhile, according to the standard for unwanted radiation defined by the Electrical Appliance and Material Control Law (Federal Communications Commission (FCC) in the United States), a limit value is set for an electromagnetic wave having a frequency of 30 MHz or higher. As a result, the radiation of such a high frequency electromagnetic wave could have an electromagnetically adverse effect on other electronic devices, and therefore the radiation of such an unwanted, high frequency electromagnetic wave should be suppressed.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a driving circuit allowing unwanted high frequency electromagnetic wave radiation to be suppressed and a display device using the driving circuit.
A driving circuit according to one aspect of the present invention outputs a driving pulse to drive a capacitive load and includes an electrical circuit connected to a pulse supply path for supplying the driving pulse to the capacitive load, an interconnection portion connected to the electrical circuit and a frequency reducing circuit for reducing the resonance frequency of LC resonance by the parasitic capacitance of the electrical circuit and the inductance component of the interconnection portion.
In the driving circuit, the resonance frequency of the LC resonance by the parasitic capacitance of the electrical circuit connected to the pulse supply path for supplying the driving pulse to the capacitive load and the inductance component of the interconnection portion is reduced, so that the frequency of electromagnetic waves generated by the LC resonance can be reduced, and unwanted high frequency electromagnetic wave radiation can be suppressed.
The electrical circuit preferably includes a switching circuit for applying the driving pulse to the capacitive load.
In this case, the resonance frequency of the LC resonance by the parasitic capacitance of the switching circuit for applying the driving pulse to the capacitive load and the inductance component of the interconnection portion is reduced, so that the frequency of electromagnetic waves generated by the LC resonance can be reduced, and unwanted high frequency electromagnetic wave radiation can be suppressed.
The capacitive load preferably includes a discharge cell having a plurality of electrodes, and the switching circuit preferably includes a sustain pulse switching circuit for applying a sustain pulse to the capacitive load during a sustain period for lighting the discharge cell.
In this case, the resonance frequency of the LC resonance by the parasitic capacitance of the sustain pulse switching circuit for applying a sustain pulse to the capacitive load during a sustain period to light the discharge cell and the inductance component of the interconnection portion is reduced, the frequency of electromagnetic waves generated by the LC resonance during the sustain period can be reduced, and unwanted high frequency electromagnetic wave radiation can be suppressed.
The capacitive load preferably includes a discharge cell having a plurality of electrodes, and the switching circuit preferably includes an initialization pulse switching circuit for applying an initialization pulse to the capacitive load during an initialization period for adjusting wall charges at the electrodes of the discharge cell.
In this case, the resonance frequency of the LC resonance by the parasitic capacitance of the initialization pulse switching circuit for applying an initialization pulse to the capacitive load during an initialization period for adjusting wall charges at the discharge cell and the inductance component of the interconnection portion is reduced, so that in the driving circuit for apply the initialization pulse, the frequency of electromagnetic waves generated by the LC resonance during the sustain period
Hashiguchi Jumpei
Kigo Shigeo
Shoji Hidehiko
Hjerpe Richard
Zamani Ali
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