Laminated filter, duplexer, and mobile communication...

Details Laminated filter, duplexer, and mobile communication... Laminated filter, duplexer, and mobile communication...

2000-07-10

2002-12-10

Nguyen, Patricia (Department: 2817)

Wave transmission lines and networks

Coupling networks

Wave filters including long line elements

C333S219000, C333S134000

Reexamination Certificate

active

06492886

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a laminated filter and a duplexer used mainly for a radio frequency device such as a portable telephone and the like, and a mobile communication apparatus using the same.
BACKGROUND OF THE INVENTION
A laminated filter of the prior art generally comprises dielectric layers
1401
a
,
1401
b
,
1401
c
,
1401
d
and
1401
e
, resonator electrodes
1402
a
and
1402
b
, load capacitor electrodes
1403
a
and
1403
b
, an inter-resonator coupling capacitor electrode
1404
, input/output coupling capacitor electrodes
1405
a
and
1405
b
, and shielding electrodes
1406
a
and
1406
b
, as shown in FIG.
14
A.
Ends of the electrodes
1402
a
and
1402
b
, and the electrodes
1406
a
and
1406
b
are connected to a grounding terminal electrode
1408
a
provided on a side surface of a dielectric, and, ends of the electrodes
1403
a
and
1403
b
, and the electrodes
1406
a
and
1406
b
are connected to a grounding terminal electrode
1408
b
on another side surface of the dielectric. The electrode
1405
a
is connected to an input/output terminal electrode
1407
a
provided on a side surface of the dielectric, and the electrode
1405
b
is connected to another input/output terminal electrode
1407
b
provided on another side surface of the dielectric. The electrodes
1408
a
and
1408
b
are grounded to constitute a structure.
Each of the electrodes in the above-described laminated filter functions as a stripline in a microwave band for which this laminated filter is used, since the electrodes are formed in the dielectric. Therefore, an equivalent circuit of this laminated filter is represented by
FIG. 14B
in the microwave band. In
FIG. 14B
, inductors
1613
and
1615
, respectively, represent inductance components of the electrodes
1403
a
and
1403
b
. An inductor
1606
represents an inductance component of the electrode
1404
. Furthermore, inductors
1603
and
1609
represent inductance components of the electrodes
1405
a
and
1405
b
, respectively.
In the above structure, the electrodes
1402
a
and
1402
b
act as quarter-wave resonators, since they are grounded at one end. Moreover, because the electrode
1404
and the electrodes
1402
a
and
1402
b
, as well as the electrodes
1405
a
and
1405
b
and the electrodes
1402
a
and
1402
b
compose parallel plate capacitors between them, they provide capacitive couplings between input/output terminals and the resonators, and also between the resonators. Furthermore, an attenuation pole (a frequency at which an impedance between the input/output terminals increases) can be formed in a transmission characteristic with an electromagnetic coupling obtained by adjusting widths of and a space between the electrodes
1402
a
and
1402
b
, and a capacitance obtained by adjusting the parallel plate capacitors formed between the electrodes
1404
, and
1402
a
and
1402
b.
As a result, the attenuation pole is formed at one side of a pass band
1701
in the transmission characteristic between the input/output terminals, as shown in
FIG. 14C
, thereby serving as a band-pass filter having an attenuation band
1702
in vicinity of the pass band
1701
.
In addition, a duplexer of the prior art comprises a receiving filter
1501
, a transmission filter
1502
, and a phase-shifting circuit
1503
, as shown in
FIG. 15
, and one end of the receiving filter
1501
serves as a receiving terminal
1510
, and one end of the transmission filter
1502
as a transmission terminal
1511
.
The phase-shifting circuit
1503
comprises an inductor
1504
, another inductor
1505
, a capacitor
1506
, a capacitor
1507
, and another capacitor
1508
. In the duplexer, the capacitor
1506
, the inductor
1504
, and the capacitor
1507
are designed to become equivalent to a transmission line, which is approximately one quarter of a wavelength at a pass band frequency of the transmission filter
1502
. The capacitor
1507
, the inductor
1505
, and the capacitor
1508
are also designed to become equivalent to a transmission line, which is approximately one quarter of a wavelength at a pass band frequency of the receiving filter
1501
.
Of a transmission signal input from the transmission terminal
1511
, only a signal component having the pass band frequency passes through the transmission filter
1502
, and it is fed to the phase-shifting circuit
1503
. The receiving filter
1501
, as observed from a common terminal
1509
, shows high impedance in this case, and thereby the transmission signal is output from the common terminal
1509
without flowing into a path toward the receiving filter
1501
. On the other hand, a receiving signal input from the common terminal
1509
is fed to the phase-shifting circuit
1503
. However, the signal is input only to the receiving filter
1501
without flowing into a path toward the transmission filter
1502
, since an impedance as observed from the common terminal
1509
toward the transmission filter
1502
side is high in this case, and therefore the signal is output to the receiving terminal
1510
only after a signal component having the pass band frequency of the receiving filter
1501
passes through.
Consequently, the transmission signal input from the transmission terminal
1511
is output from the common terminal
1509
via the phase-shifting circuit
1503
without being influenced by the receiving filter
1501
. The receiving signal input from the common terminal
1509
is also output to the receiving terminal
1510
via the phase-shifting circuit
1503
without being influenced by the transmission filter
1502
. Hence, the device functions as a duplexer.
The laminated type filter of the prior art had a problem that it needs to increase a number of resonators in order to gain a magnitude of attenuation, thereby resulting in a large size and an increase of an insertion loss in the pass band.
Moreover, the duplexer of the prior art also had a problem in that it needs a phase-shifting circuit consisting of an inductor and a capacitor of chip components, thereby requiring a large area of mounting surface.
The present invention is intended to address the above problems, and it aims at realizing a laminated filter having a low insertion loss and a high attenuation with a simple structure, and a duplexer of a small size with a small number of components.
SUMMARY OF THE INVENTION
In a laminated filter having a plurality of resonator electrodes, an inter-resonator coupling capacitor electrode for coupling between adjacent resonators, and two input/output coupling capacitor electrodes for coupling between input/output terminals and resonator electrodes, the present invention is to provide a capacitor electrode for electrically connecting one side of the input/output terminals with a portion of the input/output coupling capacitor electrode, wherein the input/output coupling capacitor electrode and the capacitor electrode comprise a parallel circuit.
This composition forms a parallel resonance circuit in one of the input/output terminals, and provides an additional attenuation pole besides another attenuation pole formed with an electromagnetic coupling between the resonators and an inter-resonator capacitance, thereby realizing the laminated filter of a high magnitude of attenuation with the same shape as that of the prior art.
Moreover, in a laminated filter having a pass band in a first band, and an attenuation band in a second band, there is provided a parallel circuit as described above at one side of the input/output terminals, whereby an attenuation pole formed by the parallel circuit is set in the vicinity of the second band. Furthermore, in a laminated filter having an attenuation band in the first band and a pass band in a second band, there is provided a parallel circuit as described above at one side of the input/output terminals, whereby an attenuation pole formed by the parallel circuit is set in the vicinity of the first band. A duplexer of the present invention is composed by connecting these two laminated filters at the input/output termina

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