Wave transmission lines and networks – Coupling networks – Frequency domain filters utilizing only lumped parameters
Reexamination Certificate
2000-05-19
2002-07-02
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Coupling networks
Frequency domain filters utilizing only lumped parameters
C333S177000
Reexamination Certificate
active
06414568
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to band pass filters, and more particularly, the present invention relates to band pass filters included in mobile communication devices such as cellular phones, and various electronic apparatuses.
2. Description of the Related Art
In general, this kind of band pass filter has a plurality of LC resonators, which perform a mutual inductive coupling, which is the so-called “M” coupling, and a capacitive coupling between the LC resonators.
FIG. 8
shows an electric equivalent circuit diagram of a two-stage band pass filter having two LC resonators. In this band pass filter, an LC resonator
1
is connected to an input terminal IN via a coupling capacitor C
5
, and an LC resonator
2
is connected to an output terminal OUT via a coupling capacitor C
6
. The LC resonator
1
is defined by a parallel circuit including an inductor L
1
and a capacitor C
1
. The LC resonator
2
is defined by a parallel circuit including an inductor L
2
and a capacitor C
2
. The LC resonator
1
and the resonator
2
achieve a mutual inductive coupling between the LC resonators
1
,
2
.
FIG. 9
shows the detailed structure of a conventional band pass filter
80
having the above equivalent circuit, and
FIG. 10
shows an example of the appearance of the conventional band pass filter
80
. As shown in
FIG. 9
, the band pass filter
80
includes a ceramic sheet
63
having an input lead pattern
73
and an output lead pattern
74
disposed on a surface thereof, a ceramic sheet
64
having inductor patterns
69
and
70
disposed on a surface thereof, a ceramic sheet
65
having capacitor patterns
71
and
72
disposed on a surface thereof, a ceramic sheet
61
having a shield electrode
75
disposed on a surface thereof, a ceramic sheet
67
having a shield electrode
76
disposed on a surface thereof.
The inductor L
1
is defined by the inductor pattern
69
, and the inductor L
2
is defined by the inductor pattern
70
. The capacitor C
1
is defined by the capacitor pattern
71
and an open end
69
b
of the inductor pattern
69
, which opposes the capacitor pattern
71
. The capacitor C
2
is defined by the capacitor pattern
72
and an open end
70
b
of the inductor pattern
70
, which opposes the capacitor pattern
72
. The coupling capacitor C
5
is defined by the inductor pattern
69
and the input lead pattern
73
. The coupling capacitor C
6
is defined by the inductor pattern
70
and the output lead pattern
74
.
Lead portions
69
a
and
70
a
of the inductor patterns
69
and
70
respectively provided on the surface of the ceramic sheet
64
are exposed at the front and back surfaces of the ceramic sheet
64
. In addition, the capacitor patterns
71
and
72
respectively provided on the surface of the ceramic sheet
65
are exposed at the back and front surfaces of the ceramic sheet
65
. That is, the inductor pattern
69
of the LC resonator
1
and the inductor pattern
70
of the LC resonator
2
are arranged opposite to each other, and the capacitor pattern
71
of the LC resonator
1
and the capacitor pattern
72
of the LC resonator
2
are arranged opposite to each other. As a result, the LC resonator
1
and the LC resonator
2
perform an interdigital coupling between the LC resonators
1
,
2
.
As shown in
FIG. 10
, an input terminal IN, an output terminal OUT, and ground terminals G
1
and G
2
are provided on a laminated body
78
defined by laminating the ceramic sheets
61
to
68
. The input terminal IN is connected to the input lead pattern
73
, and the output terminal OUT is connected to the output lead pattern
74
. The ground terminal G
1
is connected to the lead portion
69
a
of the inductor pattern
69
, the lead portion
72
a
of the capacitor pattern
72
, ends
75
a
of the shield electrode
75
, and ends
76
a
of the shield electrode
76
. The ground terminal G
2
is connected to the lead portion
70
a
of the inductor pattern
70
, the lead portion
71
a
of the capacitor pattern
71
, the other ends
75
b
of the shield electrode
75
, and the other ends
76
b
of the shield electrode
76
.
In the conventional band pass filter
80
, the inductor patterns
69
and
70
are located on the same ceramic sheet
64
, and the capacitor patterns
71
and
72
are located on the same ceramic sheet
65
. The inductor patterns
69
and
70
extend to the mutually opposing sides of the ceramic sheet
64
, and the lead portions
69
a
and
70
a
are exposed at the respective opposite sides. Similarly, the capacitor patterns
71
and
72
also extend to the mutually opposing surfaces of the ceramic sheet
65
, and the lead portions
71
a
and
72
a
are exposed at the respective opposite sides.
With this arrangement, for example, as shown in
FIG. 11
, when the sheets
61
to
68
are laminated, if the sheets
64
deviate from the sheet
65
in a direction A, an area in which the capacitor pattern
71
and the open end
69
b
of the inductor pattern
69
defining the capacitor C
1
face each other decreases, whereas, in contrast, an area in which the capacitor pattern
72
and the open end
70
b
of the inductor pattern
70
defining the capacitor C
2
face each other increases. As a result, since the resonant frequency of the LC resonator
1
shifts in a direction opposite to a direction in which the resonant frequency of the LC resonator
2
shifts, the characteristics of the band pass filter are deteriorated.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a band pass filter in which the resonant frequencies of the LC resonators shift in the same direction when laminated layers deviate from each other.
One preferred embodiment of the present invention provides a band pass filter including a laminated body having a laminated body of a plurality of insulation layers, a plurality of inductor patterns, and a plurality of capacitor patterns; a plurality of inductors provided inside of the laminated body by the plurality of inductor patterns; and a plurality of capacitors provided inside of the laminated body by disposing the capacitor patterns to be opposed to the inductor patterns such that a plurality of LC resonators are formed thereby. In this band pass filter, the capacitor pattern of a first LC resonator of at least one pair of the adjacent LC resonators and the inductor pattern of a second LC resonator of the pair of the LC resonators are disposed on a surface of a first insulation layer, whereas the inductor pattern of the first LC resonator of the pair of the LC resonators and the capacitor pattern of the second LC resonator of the pair of the LC resonators are disposed on a surface of a second insulation layer. On each of the first and second insulation layers, the capacitor pattern and the inductor pattern extend to the same side of the insulation layer so as to be exposed.
With the above arrangement, the inductor patterns of at least one pair of the adjacent LC resonators are arranged in a direction opposite to each other, and the capacitor patterns thereof are also arranged in a direction opposite to each other. As a result, the adjacent LC resonators are interdigitally coupled. In addition, since the capacitor pattern and the inductor pattern on each insulation layer extend to the same side of the insulation layer so as to be exposed, even though the laminated sheets deviate and are located at different positions, the amounts of changes in areas in which the capacitor patterns and the inductor patterns defining each of the capacitors of the adjacent LC resonators face each other are substantially equal. This allows the resonant frequencies of the LC resonators to shift in the same direction, with the result that the characteristics of the band pass filter are stabilized.
Furthermore, at least three insulation layers having the inductor patterns and the capacitor patterns disposed thereon are preferably laminated so as to increase the capacitance of the capacitor in each LC resonator. In
Kato Noboru
Matsumura Sadayuki
Sasamura Miki
Bettendorf Justin P.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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