Inductor devices – Coil or coil turn supports or spacers – Printed circuit-type coil
Reexamination Certificate
1997-03-12
2001-09-04
Mai, Anh (Department: 2832)
Inductor devices
Coil or coil turn supports or spacers
Printed circuit-type coil
C336S232000, C336S223000
Reexamination Certificate
active
06285273
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to laminated balun transformers, and more particularly, to a laminated balun transformer used as a balanced-unbalanced signal converter or phase converter in a radio communication IC chip.
2. Description of the Related Art
A balun transformer converts a balanced signal in a balanced transmission line into an unbalanced signal in an unbalanced transmission line and vice versa. “Balun” is an acronym from BALanced to UNbalanced. A balanced transmission line is provided with a pair of signal paths and a balanced signal transfers, as a voltage difference, between the two signal paths. In a balanced transmission line, since external noise equally affects the two signal paths, the external noise is canceled. Therefore, a balanced transmission line is unsusceptible to external noise. Since a circuit in an analog IC chip is configured with a differential amplifier, input and output terminals for an analog IC chip signal are of a balanced type which input and output signals as voltage differences between the two terminals, in many cases. In contrast, an unbalanced transmission line transfers an unbalanced signal, as a voltage, between one transmission line and the ground (zero voltage). It includes a coaxial line and a microstripline on a substrate.
A balun transformer, in which a winding is wrapped around a magnetic core such as ferrite in a bifilar winding, is conventionally used for a balanced-unbalanced converter in a transmission line of a high-frequency circuit. Such a balun transformer, however, has a large conversion loss in a high-frequency band above the UHF band and is limited as to size reduction.
In such a frequency band, a coaxial balun transformer
51
shown in
FIG. 6
is used. The balun transformer
51
has a center electrode
55
, one end of the center electrode
55
being connected to an input and output terminal
52
a
and the other end being made open. Around the center electrode
55
, two internal electrodes
56
a
and
56
b
are provided so as to electromagnetically couple with the center electrode
55
. The other two input and output terminals
52
b
and
52
c
are connected to the internal ends opposing each other of the two internal electrodes
56
a
and
56
b
through leads
57
a
and
57
b
, respectively. A ground electrode
58
is provided around the two internal electrodes
56
a
and
56
b
with a dielectric member disposed therebetween. Both ends of the ground electrode
58
are connected to the external ends of the internal electrodes
56
a
and
56
b.
Another balun transformer has also been proposed. This balun transformer is a laminated balun transformer
60
shown in FIG.
7
. The balun transformer
60
includes a dielectric layer
61
b
on which a lead electrode
62
is provided, a dielectric layer
61
c
on which a &lgr;/2 stripline
63
is provided, a dielectric layer
61
d
on which &lgr;/4 striplines
64
and
65
are provided, and dielectric layers
61
a
and
61
e
on which ground electrodes
66
and
67
are provided, respectively. The &lgr;/4 striplines
64
and
65
are electromagnetically coupled with the left section
63
a
and the right section
63
b
of the &lgr;/2 stripline
63
, respectively.
Since the balun transformer
51
of
FIG. 6
has a coaxial structure, it is difficult to make it compact. Therefore, it is not suited to units such as mobile radio equipment which require a compact balun transformer.
Although the balun transformer
60
of
FIG. 7
is definitely more compact than the balun transformer
51
having the coaxial structure, since the &lgr;/2 stripline
63
is routed on the dielectric layer
61
c
, the balun transformer
60
occupies a large area on a printed circuit board when it is mounted on the printed circuit board.
To adjust the electric characteristics of the balun transformer
60
, electromagnetic coupling between striplines is adjusted by changing the thickness of a dielectric layer and the width of a stripline. However, there is no other way but to change the width of the &lgr;/4 stripline
64
or the line width of the left-hand section
63
a
of the &lgr;/2 stripline
63
to, for example, independently adjust electromagnetic coupling between the &lgr;/4 stripline
64
and the left-hand section
63
a
of the &lgr;/2 stripline
63
and electromagnetic coupling between the &lgr;/4 stripline
65
and the right-hand section
63
b
of the &lgr;/2 stripline
63
. This is because, when the thickness of the dielectric layer
61
c
disposed between the &lgr;/4 striplines
64
and
65
and the &lgr;/2 stripline
63
is changed, electromagnetic coupling between the &lgr;/4 stripline
65
and the right-hand section
63
b
of the &lgr;/2 stripline
63
is affected. Adjustment by stripline width causes a slight change and it is not easy to adjust electromagnetic coupling between striplines.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a laminated balun transformer which allows easy adjustment of electromagnetic coupling between striplines and which can be made compact.
The foregoing object is achieved in one aspect of the present invention through the provision of a laminated balun transformer including at least two pairs of striplines each stripline of a pair being electromagnetically coupled through a dielectric layer, the pairs of striplines being separated with a dielectric layer interposed between the pairs in a stacked structure.
The foregoing object is achieved in another aspect of the present invention through the provision of a laminated balun transformer including a first dielectric sheet with a first stripline located at one surface thereof, a second dielectric sheet with a second stripline electromagnetically coupled with the first stripline located at one surface thereof, a third dielectric sheet with a third stripline located at one surface thereof, a fourth dielectric sheet with a fourth stripline electromagnetically coupled with the third stripline located at one surface thereof, and an electrically connection electrically connecting the first stripline and the fourth stripline wherein the first, the second, the third, and the fourth dielectric sheets are in a stacked relationship one above another in a laminated structure. The electrical connecting means includes external electrodes provided on side faces of the laminated member and via holes provided inside the laminated member.
According to the present invention, since at least two pairs of striplines electromagnetically coupled with a dielectric layer disposed therebetween are provided, the two pairs of striplines being stacked through a dielectric layer, each stripline being laminated to a dielectric layer without being disposed on the same dielectric layer as another stripline, and a balun transformer having a small area is obtained. In addition, since the thickness of a dielectric layer sandwiched by one pair of electromagnetically coupled striplines can be adjusted independently of the thickness of the dielectric layer sandwiched by the other pair of striplines, a laminated balun transformer in which electromagnetic coupling between striplines can be easily adjusted is obtained.
REFERENCES:
patent: 3483499 (1969-12-01), Lugten
patent: 3833872 (1974-09-01), Marcus et al.
patent: 4342143 (1982-08-01), Jennings
patent: 5184103 (1993-02-01), Gadreau et al.
patent: 5373112 (1994-12-01), Kamimura et al.
patent: 5386206 (1995-01-01), Iwatani et al.
patent: 5497137 (1996-03-01), Fujiki
patent: 5521573 (1996-05-01), I noh et al.
patent: 5834992 (1998-11-01), Kato et al.
patent: 5-82350 (1993-04-01), None
patent: 5-135968 (1993-06-01), None
Burns Doane , Swecker, Mathis LLP
Mai Anh
Murata Manufacturing Co. Ltd.
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