JP2002374139A - Balance type lc filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized balance type LC filter with which superior electrical characteristics can be obtained and design changes in the I/O impedance and an attenuation pole is facilitated. SOLUTION: Conductors 3a, 3b, 4a, 4b for resonance coils are electrically connected in series, respectively, through viaholes 29 formed in an insulator sheet 2b, thereby forming coils L1, L2 for resonance, which are arranged in parallel on the same layer and have an electrical path length of λ/2. Conductors 5, 6 for coupling coils are formed in almost rectilinear patterns which are arranged in parallel on the same insulator sheet 2e, and have electrical path length of λ/4. An LC parallel resonator Q1, constituted of the coil L1 for resonance and capacitors C2a, C2b for resonance, and an LC parallel resonator Q2 constituted of the coil L2 for resonance and capacitors C3a, C3b for resonance, are cascaded via coupling coils L3, L4 between resonators, thereby constituting a bandpass filter circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a balanced LC filter, and more particularly, to a balanced LC filter used for a wireless communication device such as a portable telephone or a car telephone.

[0002]

2. Description of the Related Art Generally, in a wireless communication device such as a portable telephone or a car telephone, an input / output balance having a filter function and an impedance conversion function is provided between a mixer stage and a modulation stage of a transmission system circuit. A differential filter called a type filter is used.

Conventionally, as this type of balanced filter, a filter described in Japanese Patent Application Laid-Open No. 11-317603 has been known. The balanced filter is provided between a pair of balanced input terminals and a pair of balanced output terminals in a state where the first filter circuit section and the second filter circuit section are electrically connected to each other by ground. ing. Each of the first and second filter circuit units is configured by cascading two strip line resonators. More specifically, two sets of two strip line type resonators provided on the same insulator layer are provided inside a laminate formed by stacking insulator layers, and the first and second filter circuit units are respectively provided. And The first and second filter circuit units are stacked mirror-symmetrically on different layers of the stack. The stripline type resonator is electrically connected to a balanced input terminal and a balanced output terminal via a coupling capacitor. Then, the strip line of the input side resonator and the strip line of the output side resonator are electromagnetically coupled using the shield electrode.

[0004]

In a conventional balanced filter, a resonator is electrically connected to a balanced input terminal or a balanced output terminal via a coupling capacitor.
Therefore, since the strip line of the resonator is not directly connected to the input / output terminal, there is a problem that the change in the electrical characteristics due to the radiation from the strip line, the lamination displacement of the shield electrode, and the like is large. Furthermore, the Q of the resonator is reduced due to the eddy current loss generated in the shield electrode, which is disadvantageous for miniaturization. In addition, since the design is made with a stripline type resonator, it is necessary to greatly change the line width of the stripline, the distance between the stripline and the shield electrode, etc. in order to change the design of the input / output impedance and attenuation pole. It was not possible to respond flexibly to design changes.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a balanced LC filter which is small in size, has good electrical characteristics, and can be easily changed in input / output impedance and attenuation pole design.

[0006]

In order to achieve the above object, a balanced LC filter according to the present invention comprises:
(A) a pair of balanced input terminals, (b) a pair of balanced output terminals, and (c) at least a pair of coupling coils for electrically coupling between the pair of balanced input terminals and the pair of balanced output terminals. (D) a plurality of Ls electrically cascaded between the pair of balanced input terminals and the pair of balanced output terminals.
(E) the plurality of LC resonators are electrically connected to each other via the pair of coupling coils.

More specifically, (f) a laminate formed by stacking a plurality of insulator layers, a conductor for a resonance coil, a conductor for a coupling coil, and a capacitor conductor, and (g) provided on a surface of the laminate. A pair of balanced input terminals and a pair of balanced output terminals, (h) at least a pair of coupling coils formed of the coupling coil conductor in the laminate, and (i) a resonance coil conductor in the laminate. And (j) the plurality of LC resonators are provided between the pair of balanced input terminals and the pair of balanced output terminals. , And the pair of balanced input terminals and the pair of balanced output terminals are electrically coupled via the pair of coupling coils.

Here, the conductor for the resonance coil is constituted by a spiral pattern provided on the surface of the insulator layer, or is constituted by connecting via holes provided in the insulator layer in the laminating direction. Further, the resonance coil constituting the LC resonator has an electric path length of substantially λ / 2. further,
The pair of coupling coils are arranged symmetrically on the surface of the same insulator layer.

With the above configuration, the resonator is of a lumped constant type, and a small balanced-balanced balanced LC filter can be obtained.

Further, since both ends of the coupling coil and the resonance coil constituting the LC resonator are directly connected to one of the balanced input terminal and the balanced output terminal, the coil is connected to the input / output terminal. And is electrically connected directly to the coil, thereby suppressing radiation from the coil. Furthermore, by not providing a shield electrode on the laminate, eddy current loss generated in the shield electrode is eliminated, and the Q of the coil is improved.

In one of the terminal pairs, one of the balanced input terminal and the balanced output terminal, one of the terminals is opened, so that the other terminal becomes an unbalanced terminal. It can also be used as a filter.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a balanced type L according to the present invention will be described.
An embodiment of the C filter will be described with reference to the accompanying drawings. In the present embodiment, a two-stage balanced LC filter will be described.

As shown in FIG. 1, a balanced LC filter 1 is composed of insulating sheets 2b and 2c provided with resonance coil conductors 3a, 3b, 4a and 4b on their surfaces, and coupling coil conductors 5 and 6, respectively. An insulator sheet 2e provided on the surface;
Capacitor conductors 7 to 28 are respectively constituted by insulating sheets 2 g to 2 m provided on the surface. Insulator sheet 2
Reference numerals a to 2n denote sheets obtained by kneading dielectric powder or magnetic powder together with a binder or the like.

Resonant coil conductors 3a, 3b, 4a, 4b
Are spiral patterns, respectively, and the insulator sheet 2b
Are electrically connected in series via the via holes 29 provided in the first and second coils to form the resonance coils L1 and L2. The resonance coils L1 and L2 are juxtaposed on the same layer, and the electric path length is set to λ / 2 (λ: wavelength at the center frequency). It is needless to say that the resonance coil conductors 3a to 4b do not necessarily have to be in a spiral pattern, but may be in any pattern such as a linear pattern or a meandering pattern.

The coupling coil conductors 5 and 6 have a substantially U-shaped pattern, and the coupling coils L whose straight portions face each other.
3, L4. The coupling coils L3 and L4 are juxtaposed on the same insulator sheet 2e and are arranged line-symmetrically. This is because a line-symmetric shape is preferable in order to maintain balance. The electric path length of each of the coupling coils L3 and L4 is set to λ / 4. The coupling coil conductors 5 and 6 do not necessarily have to have a U-shaped pattern, and the shape is not particularly limited as long as they are line-symmetric. For example, the pattern may be semicircular, U-shaped, V-shaped, or the like.

The capacitor conductors 7, 13, 19 and the capacitor conductors 9, 15, 21 are made of insulating sheets 2g, 2
h, 2i, and 2j, facing the capacitor conductors 11 and 17, respectively, and pole adjusting capacitors C1a and C1b, respectively.
Is composed. The capacitor conductors 8, 14, and 20 and the capacitor conductors 10, 16, and 22 are
g, 2h, 2i, 2j, and the capacitor conductors 12, 1
8 and pole adjusting capacitors C1c,
C1d. The capacitor conductor 23 faces the capacitor conductors 19 and 25 and the capacitor conductors 20 and 26 with the insulator sheets 2k and 21 interposed therebetween, and constitutes resonance capacitors C2a and C2b, respectively. The capacitor conductor 24 faces the capacitor conductors 21 and 27 and the capacitor conductors 22 and 28 with the insulator sheets 2k and 21 interposed therebetween, and constitutes resonance capacitors C3a and C3b, respectively.

Each of the conductors 3a, 3b, 4a, 4b, 5-28 is formed by a method such as a sputtering method, a vapor deposition method, a printing method, and a photolithography method.
It is made of a material such as d, Ag, Pd, and Cu.

The sheets 2a to 2n are stacked and integrally fired to form a rectangular laminate 30 as shown in FIG. The external dimensions of the laminate 30 are, for example, 3.2 mm in length, 1.6 mm in width, and 1.3 m in height.
m. The laminate 30 has six external electrodes 31 to 34,
G1 and G2 are formed. These external electrodes 31 to
34, G1 and G2 are formed by a method such as a sputtering method, an evaporation method, a coating method, and a printing method.
It is made of a material such as Ag, Pd, Cu, and Cu alloy.

The external electrode 31 is electrically connected to one end 5a of the resonance coil conductor 3b and the coupling coil conductor 5, and the capacitor conductors 7, 13, 19, and 25. The external electrode 32 is electrically connected to one end 6a of the resonance coil conductor 3a and the coupling coil conductor 6, and to the capacitor conductors 8, 14, 20, and 26. The external electrodes 31 and 32 are input terminals.

The external electrode 33 is electrically connected to the other end 5b of the resonance coil conductor 4b and the coupling coil conductor 5, and to the capacitor conductors 9, 15, 21, and 27. The external electrode 34 includes the other end 6 b of the resonance coil conductor 4 a and the coupling coil conductor 6, and the capacitor conductor 1.
0,16,22,28. The external electrodes 33 and 34 are output terminals.

The external electrode G1 is electrically connected to the capacitor conductor 23 and functions as a ground terminal. The external electrode G2 is electrically connected to the capacitor conductor 24 and functions as a ground terminal.

FIG. 3A shows an electric equivalent circuit diagram of the balanced LC filter 1 having a laminated structure. The balanced LC filter 1 includes an LC parallel resonator Q1 including a resonance coil L1 and resonance capacitors C2a and C2b, and an LC parallel resonator Q2 including a resonance coil L2 and resonance capacitors C3a and C3b. Coupling coil L
3, and a band-pass filter circuit cascaded through L4. That is, the LC parallel resonators Q1 and Q2 are:
Not connected via a coupling capacitor. A ground terminal G1 is connected to an intermediate connection point between the capacitors C2a and C2b connected in series, and a capacitor C3 connected in series.
A ground terminal G2 is connected to an intermediate connection point between a and C3b. In this way, a so-called branch line type lumped constant circuit is obtained.

By adjusting the inductance values of the resonance coils L1 and L2 of the LC parallel resonators Q1 and Q2 and the capacitance values of the resonance capacitors C2a, C2b, C3a and C3b, the balanced LC filter 1 is formed.
Center frequency and impedance can be adjusted. The electric path length of the resonance coils L1 and L2 is λ / 2.
, The phase difference between the output terminals 33 and 34 is 1
An 80-degree balanced signal can be output stably.

The balanced LC filter 1 having the above-described configuration is composed of two lumped-parameter LC parallel resonators Q1 and Q2.
, And can be reduced in size as compared to a conventional filter that required four resonators. Further, since both ends of all the coils L1 to L4 are electrically connected directly to any one of the input / output terminals 31 to 34, radiation from the coils L1 to L4 is suppressed. Further, since no shield electrode is provided in the laminate 30, eddy current loss generated in the shield electrode is eliminated, and the coils L1 to L4
Can be improved.

The balance type LC filter 1
By using the external electrodes 31 and 32 as a pair of balanced input terminals and the external electrodes 33 and 34 as a pair of balanced output terminals, a balanced-balanced LC filter is obtained. On the other hand, the input-side external electrodes 31 and 32 and the output-side external electrodes 33 and 34 can be used as unbalanced terminals. That is, the external electrodes 31 and 32 (the external electrodes 33 and 3
4) One of the external electrodes is connected to an external unbalanced circuit, and the other external electrode is opened. As a result, the balanced LC filter 1 becomes an unbalanced-balanced or unbalanced-unbalanced LC filter.

For example, as shown in FIG. 3B, the external electrode 31 is used as an unbalanced input terminal, the external electrode 32 is opened, and the external electrodes 33 and 34 are used as a pair of balanced output terminals. The balance type LC filter 1 has an unbalanced
It becomes a balanced LC filter. FIG. 4 is a graph showing the reverse pass characteristic S12, the input reflection characteristic S11, and the output reflection characteristic S22 of the filter 1 at this time. FIG.
4 is a graph showing a transmission characteristic S21 at an external electrode 33 and a transmission characteristic S31 at an external electrode 34. S21 and S31
Overlap with each other (around 1.7 GHz and 2.2
(At around 2.7 GHz), the amplitude difference between the signals output to the external electrodes 33 and 34 is zero. FIG.
4 is a graph showing phase characteristics S21 and S31 of signals output to external electrodes 33 and 34, respectively. S21 and S31
Is 180 degrees.

The balance type LC filter 1 has a balanced-type LC filter 1 by using the external electrodes 31 and 32 as a pair of balanced input terminals and the external electrodes 33 and 34 as a pair of balanced output terminals.
It becomes a balanced LC filter. FIG. 7 is a graph showing the reverse pass characteristic S12, the input reflection characteristic S11, and the output reflection characteristic S22 of the filter 1 at this time. FIG. 8 is a graph showing a transmission characteristic S21 at the external electrode 33 and a transmission characteristic S31 at the external electrode 34. S21 and S31 overlap almost completely, and the amplitude difference is 0 over the entire frequency range. FIG. 9 is a graph showing phase characteristics S21 and S31 of signals output to the external electrodes 33 and 34, respectively. It can be seen that the phase difference between S21 and S31 is 180 degrees.

Further, since the balanced LC filter 1 of this embodiment has the pole adjusting capacitors C1a to C1d, an attenuation pole can be provided at an arbitrary frequency, and the input / output impedance can be easily adjusted. is there. For example, as shown in FIGS. 4 to 6, the LC filter 1 has an attenuation pole A on the lower frequency side than the center frequency, but the capacitance of the pole adjustment capacitors C1a to C1d is reduced to about 1/2. By changing, as shown in FIGS. 10 to 12, the attenuation pole A can be moved to a higher frequency side than the center frequency.

The balanced LC filter according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the invention. For example, as shown in FIG.
a and via holes 4 for inductors respectively provided in 42b
5a, 45b, 46a, 46b are transferred to the insulator sheet 42a.
To 42c in the stacking direction.

Via holes 45a and 45b for inductors,
46a and 46b are insulator sheets 42a to 42, respectively.
The columnar inductors L1 and L2 having a length of substantially λ / 2 (λ: wavelength of the center frequency) are formed by being connected in the stacking direction of c. The inductors L1 and L2 referred to here are mainly connected via holes 45a, 45b, 46a and 46b.
It means that it is composed of For example, the lead conductors 43a to 44b also have an inductance component, and the inductors L1 and L2 are mainly constituted by via holes 45a to 46b, and the via holes 45a to 46b are designed as inductors in an equivalent circuit. The sheet 42b is set thicker than the other sheets. At this time, the thickness of the sheet 42b is
A plurality of sheets having the same sheet thickness as the other sheets 2a, 42a, etc. may be stacked and secured, or may be secured by using one thick sheet.

The axial direction of the inductors L1 and L2 is the sheet 4
Perpendicular to the surfaces 2a-42c. Inductor L
When a current flows through the inductors L1 and L2, a magnetic field circling around a plane perpendicular to the axial direction of the inductors L1 and L2 is generated around each of the inductors L1 and L2. Inductor L1,
One end of each of L2 (via holes 45a, 46a)
Are connected to the lead conductors 43a and 44a. The other ends of the inductors L1 and L2 (via holes 45)
b, 46b) are connected to the lead conductors 43b, 44b.

The balance type LC filter 41 having the above-described configuration can provide the same operation and effect as the filter 1 of the first embodiment.

Further, in the above embodiment, the insulator sheets on which the conductors are formed are stacked and then integrally fired, but the invention is not necessarily limited to this. The sheet may be fired in advance. Further, an LC filter may be manufactured by a manufacturing method described below. After a paste-like insulator material is applied by printing or the like to form an insulator layer, an arbitrary conductor is formed by applying a paste-like conductor material to the surface of the insulator layer. Next, a paste-like insulator material is applied over the conductor. LC having a laminated structure by successively coating in this way
A filter is obtained.

[0034]

As is clear from the above description, according to the present invention, the number of resonators can be reduced, and the balance type L
The size of the C filter can be reduced. Further, since the coil is electrically connected directly to the input / output terminal, radiation from the coil can be suppressed. Furthermore, since no shield electrode is provided on the laminate, eddy current loss occurring in the shield electrode is eliminated, the Q of the coil can be increased, and a high-performance and small-sized balanced LC filter can be obtained.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing an embodiment of a balanced LC filter according to the present invention.

FIG. 2 is a perspective view showing the appearance of the balanced LC filter shown in FIG.

FIG. 3 is an electric equivalent circuit diagram of the balanced LC filter shown in FIG. 2;

FIG. 4 is a graph showing reverse pass characteristics and input / output reflection characteristics when the balanced LC filter shown in FIG. 2 is of an unbalanced-balanced type;

FIG. 5 is a graph showing pass characteristics when the balanced LC filter shown in FIG. 2 is changed to an unbalanced-balanced type;

FIG. 6 is a graph showing phase characteristics when the balanced LC filter shown in FIG. 2 is changed to an unbalanced-balanced type.

FIG. 7 is a graph showing a reverse pass characteristic and an input / output reflection characteristic when the balanced LC filter shown in FIG. 2 is a balanced-balanced type;

FIG. 8 is a graph showing pass characteristics when the balanced LC filter shown in FIG. 2 is a balanced-balanced type.

FIG. 9 is a graph showing phase characteristics when the balanced LC filter shown in FIG. 2 is a balanced-balanced type.

FIG. 10 shows the results when the capacitance of the pole adjusting capacitor of the balanced LC filter shown in FIG. 2 is changed.
5 is a graph showing reverse pass characteristics and input / output reflection characteristics.

FIG. 11 shows the results when the capacitance of the pole adjusting capacitor of the balanced LC filter shown in FIG. 2 is changed.
5 is a graph showing pass characteristics.

FIG. 12 is a graph showing the relationship when the capacitance of the pole adjusting capacitor of the balanced LC filter shown in FIG. 2 is changed.
4 is a graph showing phase characteristics.

FIG. 13 is an exploded perspective view showing another embodiment of the balanced LC filter according to the present invention.

[Description of Signs] 1,41: Balanced LC filter 2a to 2n, 42a to 42c: Insulating sheet 3a, 3b, 4a, 4b: Conductor for resonance coil 5, 6: Conductor for coupling coil 7 to 28: Capacitor conductor 30 laminated body 31, 32 balanced input terminal 33, 34 balanced output terminal 45a, 45b, 46a, 46b via hole L1, L2 resonance coil L3, L4 coupling coil C2a, C2b, C3a, C3b ... resonance Capacitors Q1, Q2 ... LC parallel resonator

 ──────────────────────────────────────────────────の Continued on the front page F term (reference) 5J024 AA01 CA03 CA04 CA09 DA04 DA29 DA32 DA35 EA03 EA06 EA07

Claims (8)

[Claims] A pair of balanced input terminals; a pair of balanced output terminals; at least a pair of coupling coils for electrically coupling between the pair of balanced input terminals and the pair of balanced output terminals; A plurality of LC resonators electrically connected in cascade between the balanced input terminal and the pair of balanced output terminals, wherein the plurality of LC resonators are electrically connected to each other via the pair of coupling coils. A balanced LC filter. 2. The terminal according to claim 1, wherein one of the terminal pair of the balanced input terminal and the balanced output terminal has one terminal in an open state and the other terminal has an unbalanced terminal. 2. The balanced LC filter according to 1. 3. A laminate comprising a plurality of insulator layers, a conductor for a resonance coil, a conductor for a coupling coil, and a capacitor conductor, a pair of balanced input terminals and a pair of balances provided on the surface of the laminate. An output terminal; at least one pair of coupling coils configured with the coupling coil conductor in the laminate; and a plurality of LC resonators configured with the resonance coil conductor and the capacitor conductor in the laminate. The plurality of LC resonators are electrically connected in cascade between the pair of balanced input terminals and the pair of balanced output terminals via the pair of coupling coils, and the pair of balanced input terminals. And the pair of balanced output terminals are electrically coupled via the pair of coupling coils. 4. The balanced LC filter according to claim 3, wherein the resonance coil conductor is formed of a spiral pattern provided on a surface of the insulator layer. 5. The balanced LC filter according to claim 3, wherein the resonance coil conductor is formed by connecting via holes provided in the insulator layer in a stacking direction. 6. The balance according to claim 3, wherein the resonance coil constituting the LC resonator has an electric path length of substantially λ / 2. Type LC filter. 7. Both ends of the coupling coil and the resonance coil constituting the LC resonator are directly connected to one of the balanced input terminal and the balanced output terminal, and The balanced LC filter according to any one of claims 3 to 6, wherein no shield electrode is provided on the body. 8. The balanced LC filter according to claim 3, wherein said pair of coupling coils are arranged line-symmetrically on the surface of the same insulator layer.