Three-terminal variable inductor

Details Three-terminal variable inductor Three-terminal variable inductor

2001-04-06

2002-12-24

Donovan, Lincoln (Department: 2832)

Inductor devices

Coil or coil turn supports or spacers

Printed circuit-type coil

C336S223000, C336S232000

Reexamination Certificate

active

06498556

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to three-terminal variable inductors, and more particularly, to a three-terminal inductor for use in, for example, mobile communication devices.
2. Description of the Related Art
It is becoming more and more critical that current electronic devices have smaller sizes, and especially for mobile communication devices such as cellular phones and automobile phones, components incorporated therein must be severely restricted in size. In addition, as the operating frequency becomes higher, the circuit and components defining circuits in such devices become more complex, and the components tolerate less variations. Conventionally, in manufacturing a circuit having a center tap connected to the electric center of a coil, a pair of coil components
101
and
102
are mounted on a printed circuit board
106
, and are electrically connected to each other via electrodes
103
and
104
and a center tap electrode
105
provided on the printed circuit board
106
, as shown in FIG.
9
. As methods of changing the values of inductance of the coil components
101
and
102
, it has been proposed, for example, that the coil components
101
and
102
be replaced by other two coil components having different values of inductance which are balanced in advance, or variable coils be used as the coil components
101
and
102
and the values of inductance thereof be changed while maintaining the balance of the inductance values.
In accordance with these methods, however, due to component variations or displacements during mounting, the inductance values of the coil components
101
and
102
may not be well balanced. It may also occur that the center tap electrode is connected off the electric center of the coil defined by the coil components
101
and
102
. In addition, because the two coil components
101
and
102
are electrically connected via the center tap electrode
105
provided on the printed circuit board
106
, a considerable area is occupied on the printed circuit board
106
.
Furthermore, as for the method which changes the inductance values by replacing the coil components
101
and
102
with other two coil components, the complex work of removing the coil components has inhibited automation and mass production. Similarly, as for the method which uses variable coils as the coil components
101
and
102
to change the inductance values of the coil components
101
and
102
, the complex work of adjusting the inductance values while maintaining the balance therebetween has also inhibited automation and mass production.
In order to overcome these problems, a three-terminal variable inductor
110
shown in
FIG. 10
has been proposed. In the three-terminal variable inductor
110
, a pair of spiral coil electrodes
112
and
113
having identical dimensions are disposed on the top surface of an insulative substrate
111
. The spiral coil electrodes
112
and
113
are electrically connected to trimming electrodes
116
a
to
116
d
via openings provided on an insulating protective film
115
. The trimming electrodes
116
a
to
116
d
are connected to a center tap electrode
117
, thereby being electrically connected to a common terminal electrode
122
. One end of the coil electrode
112
and one end of the coil electrode
113
are electrically connected to a terminal electrode
120
and a terminal electrode
121
, respectively.
In order to adjust the value of inductance of the three-terminal variable inductor
110
, the trimming electrodes
116
a
to
116
d
are cut one by one as desired, for example, by irradiating laser beams on the three-terminal variable inductor
110
. Accordingly, the value of inductance between the terminal electrode
120
and the common terminal electrode
122
and the value of inductance between the terminal electrode
121
and the common terminal electrode
122
can be changed in steps while maintaining the balance therebetween.
In the three-terminal variable inductor
110
, however, because the trimming electrodes
116
a
to
116
d
are arranged to partially overlap the spiral coil electrodes
112
and
113
, stray capacitance between the trimming electrodes
116
a
to
116
d
and the spiral coil electrodes
112
and
113
is large. Therefore, the three-terminal variable inductor
110
has a low self resonance frequency and fails to provide favorable frequency characteristics at higher frequencies. In addition, the trimming electrodes
116
a
to
116
d
shield magnetic fields generated by the spiral coil electrodes
112
and
113
, resulting in inadequate Q characteristics of the three-terminal variable inductor
110
.
SUMMARY OF THE INVENTION
In order to solve the problems described above, preferred embodiments of the present invention provide a three-terminal variable inductor which is very small, minimizes the occupied area on a printed circuit board when mounted thereon, achieves stable adjustment of inductance values while maintaining a good balance, and which achieves excellent characteristics.
According to a preferred embodiment of the present invention, a three-terminal variable inductor includes a first terminal electrode, a second terminal electrode, a third terminal electrode, a first spiral coil electrode electrically connected between the first terminal electrode and the third terminal electrode, an inner end portion thereof being associated with the first terminal electrode and an outer portion thereof being associated with the third terminal electrode, a second spiral coil electrode electrically connected between the second terminal electrode and the third terminal electrode, an inner end portion thereof being associated with the second terminal electrode and an outer portion thereof being associated with the third terminal electrode, and at least one trimming electrode arranged so as not to cross any portion of the first spiral coil electrode and the second spiral coil electrode, between the outer portion of the first spiral coil electrode and the outer portion of the second spiral coil electrode, the outer portions being disposed in proximity to each other, the at least one trimming electrode electrically connecting the first spiral coil electrode and the second spiral coil electrode.
In accordance with the unique construction of the preferred embodiment of the present invention described above, by trimming the at least one trimming electrode, the value of inductance between the first terminal electrode and the second terminal electrode can be changed without disturbing the balance of the inductance value between the first terminal electrode and the third terminal electrode and the inductance value between the second terminal electrode and the third terminal electrode. In addition, since the trimming electrode is arranged so as not to cross any portion of the first spiral coil electrode and the second spiral coil electrode, the three-terminal variable inductor has a small stray capacitance between the trimming electrode and the first and second spiral coil electrodes and therefore has a high self resonance frequency, thus exhibiting favorable frequency characteristics at high frequency bands. Furthermore, since the trimming electrode does not block magnetic fields generated by the first and the second spiral coil electrodes, Q characteristics are greatly improved.
The three-terminal variable inductor may further include a plurality of trimming electrodes, and a center tap electrode electrically connected to the third terminal electrode is disposed between the outer portion of the first spiral coil electrode and the outer portion of the second spiral coil electrode, the outer portions being disposed in proximity to each other, the plurality of trimming electrodes being electrically connected to the center tap electrode.
In accordance with the above-described unique construction, by trimming the at least one trimming electrode, the value of inductance between the first and second terminal electrodes, the value of inductance between the first and thi

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