Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
1999-05-05
2001-04-24
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S193000
Reexamination Certificate
active
06222426
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a branching filter that uses an surface acoustic wave (SAW) resonance type filter used for compact mobile communication equipment for portable telephones and the like.
2. Description of Related Art
In recent years, advances have been made in the development of terminals for compact, light mobile communication equipment such as portable telephones. RF (Radio Frequency) filters are incorporated into these terminals. Surface acoustic wave (SAW) resonance type filters are used for this RF filter.
Accompanying the development of these terminals is a demand for the parts to be made more compact and to have higher performance. Therefore, there is also a demand for more compact, higher performance SAW resonance filters (also called SAW elements).
FIG. 9
is a block diagram of a structural example of a conventional portable telephone branch filter.
The branch filter
10
shown in
FIG. 9
comprises an antenna (ANT) terminal
11
, an LC chip
12
, a transmission filter
13
, an Rx-branching filter circuit strip line
14
, a receiving filter
15
, a transmission (Tx) terminal
16
, and a receiving (Rx) terminal
17
. The LC chip
12
is provided between the ANT terminal
11
and ground. The transmission filter
13
is connected between ANT terminal
11
and Tx terminal
16
, and the series circuit of the Rx-branching filter circuit strip line
14
and the receiving filter
15
are connected in this sequence between the ANT terminal
11
and the receiving terminal
17
.
FIG. 10
is a circuit structural figure of the specific circuit structure of the branching filter shown in FIG.
9
. Reference number
11
is the ANT terminal,
2
,
3
, and
4
are branching filter circuit strip lines (inductance) (equivalent to
14
in FIG.
9
),
13
is the transmission filter,
15
is the receiving filter,
16
is the transmission (Tx) terminal, and
17
is the receiving (Rx) terminal.
Conventionally, with this type of portable telephone branching filter, the transmission and receiving filters were each composed using dielectric resonators.
FIGS. 11 and 12
show a portable telephone branching filter and mounting aspect, respectively.
FIG. 11
is a schematic perspective view of the front surface, and
FIG. 12
is a schematic perspective view of the back surface.
As is clear from the structural examples shown in
FIGS. 11 and 12
, chips
13
and
15
of the transmission and receiving filters are incorporated into on-board substrate
9
. Branching filter circuit strip lines
2
,
3
, and
4
are provided as structural elements on this on-board substrate
9
. As is also clear from
FIG. 12
, this on-board substrate
9
comprises an insulation substrate
9
a
such as a resin substrate, low temperature sinter substrate, or aluminum substrate, a metallized conductive coating pattern
9
b
provided thereon, and an insulation pattern
9
c
formed by exposing substrate
9
a
. Branching filter circuit strip lines
2
,
3
, and
4
are formed in continuum with conductive coating pattern
9
b.
With this type of portable telephone branching filter, each chip of the transmission filter
13
and the receiving filter
15
is provided divided on separate piezoelectric substrates. Then, these two piezoelectric substrates are individually incorporated into one on-board substrate
9
, offering the merit of excellent insulation characteristics for both filters.
However, besides the piezoelectric substrate on which are provided the chips of these transmission and receiving filters
13
and
15
, an on-board substrate
9
with a space for incorporating the Rx-branching filter circuit strip line
14
and the LC chip
12
(thus, branching filter circuit strip lines
2
,
3
, and
4
shown in
FIG. 11
) is needed, so the on-board substrate becomes large, and the connecting wiring for the branching filter structure becomes long. Because of this, the structure of this on-board substrate
9
becomes complex, and the area occupied by the connecting wiring increases. This inhibits making the on-board substrate and thus the branching filter more compact.
On the other hand, a branching filter has been developed that uses a SAW resonator for the transmission filter and receiving filter (Japanese Patent Laid-open No. 6-97761). For the branching filter that uses a SAW resonance type filter disclosed in this publication, the transmission and receiving filters comprise ladder-type resonator filters with a structure similar to a serial arm SAW resonator and a parallel arm SAW resonator. With this conventional branching filter, it is possible to make the branching filter more compact to some degree, but the problem of insulation between filters has not been looked into yet.
FIG. 13
is a schematic perspective view showing a structural example of the branching filter disclosed in this Japanese Patent Laid-open No. 6-97761. This branching filter has a structure with which the structural elements are incorporated into package
20
. Specifically, inside a package construction
21
A is provided a ground layer
21
B, an impedance matching element
22
, a phase adjustment element
23
, a trap circuit
24
, a transmission SAW filter element
25
, and a receiving SAW filter element
26
.
In this way, the conventional branching filter disclosed in Japanese Patent Laid-open No. 6-97761 is structured to house in a single package
20
the transmission SAW filter element
25
, the receiving SAW filter element
26
, an LC chip, and an Rx-branching filter circuit strip line.
However, in this case, particularly because the transmission SAW filter element
25
, the receiving SAW filter element
26
, the LC chip (phase adjustment element
23
), and the Rx-branching filter circuit strip line (impedance matching element
22
) are housed within the same package
20
, there are problems including a degradation of the insulation characteristics between the transmission area and receiving area, and a degradation of the branching filter characteristics as an interaction works between the connecting wires.
SUMMARY OF THE INVENTION
Thus, an object of the present invention is to provide a branching filter that uses a SAW resonance type filter that is capable of being made more compact as well as having a higher performance level.
Another object of the present invention is to provide branching filter that uses a SAW resonance type filter with a structure with which the transmission SAW filter and receiving SAW filter can be placed in one chip.
To achieve these objects, the branching filter of the present invention comprises the unique structure described below. Specifically, the branching filter of the present invention comprises a SAW resonator. The SAW resonator comprises a transmission SAW filter linked between an antenna terminal and transmission terminal, a receiving SAW filter with different bandpass characteristics from the above-mentioned transmission SAW filter linked between the above-mentioned antenna terminal and receiving terminal, and a composite circuit of a frequency adjusting LC circuit and branching filter circuit (also called a strip line for a branching filter circuit) linked between the above-mentioned antenna terminal and the above-mentioned transmission and receiving SAW filters. Also, with the present invention, this branching filter circuit is composed from a serial arm SAW resonator. Specifically, all or part of this branching filter circuit is structured as a serial arm SAW resonator.
For a preferred embodiment of the present invention, it is desirable to have a structure, between the antenna terminal and transmission SAW filter, with a frequency adjusting LC circuit connected to the antenna terminal and a Tx-branching filter circuit strip line connected as a branching filter circuit between the above-mentioned LC circuit and transmission SAW filter for the composite circuit. It is also acceptable to have a structure with only a frequency adjusting LC circuit connected between the antenna terminal and transmission SAW filter for the composite circuit.
For
Fujita Yoshiaki
Komazaki Tomokazu
Shimamura Hajime
Burdett James R.
Frank Robert J.
Oki Electric Industry Co. Ltd.
Pascal Robert
Summons Barbara
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