JP4710174B2 - Balanced LC filter - Google Patents

Description

[0001]
BACKGROUND 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 mobile phone or a car phone.
[0002]
[Prior art]
Generally, in a wireless communication device such as a mobile phone or a car phone, it is called an input / output balanced (balanced) filter having a filter function and an impedance conversion function between a mixer stage and a modulation stage of a transmission system circuit. A differential filter is used.
[0003]
Conventionally, as this type of balanced filter, one described in JP-A-11-317603 has been known. This balanced filter is provided between the pair of balanced input terminals and the pair of balanced output terminals in a state where the first filter circuit unit and the second filter circuit unit are electrically connected to each other through the ground. ing. Each of the first and second filter circuit units is configured by cascading two stripline resonators. More specifically, two sets of two stripline resonators provided on the same insulator layer are provided in the laminate formed by stacking the insulator layers, and the first and second filter circuit portions are respectively provided. And The first and second filter circuit units are laminated mirror-symmetrically on different layers of the laminate. The stripline resonator is electrically connected to a balanced input terminal or a balanced output terminal via a coupling capacitor. 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]
[Problems to be solved by the invention]
Incidentally, 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 terminals, there is a problem that the electrical characteristics change greatly due to radiation from the strip line, misalignment of the shield electrode, and the like. Further, the Q of the resonator is lowered due to eddy current loss generated in the shield electrode, which is disadvantageous for miniaturization. In addition, because it is designed with a stripline type resonator, when changing the design of input / output impedance and attenuation pole, it is necessary to change the line width of the stripline and the interval between the stripline and the shield electrode, It was not possible to respond flexibly to design changes.
[0005]
SUMMARY OF THE INVENTION An object of the present invention is to provide a balanced LC filter that is small and has good electrical characteristics, and that allows easy design changes of input / output impedance and attenuation pole.
[0006]
[Means and Actions for Solving the Problems]
In order to achieve the above object, the balanced LC filter according to the present invention includes:
(A) a pair of balanced input terminals;
(B) a pair of balanced output terminals;
(C) at least a pair of coupling coils for electrically coupling the pair of balanced input terminals and the pair of balanced output terminals;
(D) a plurality of LC parallel resonators electrically connected in cascade between the pair of balanced input terminals and the pair of balanced output terminals;
(E) a pair of pole adjusting capacitors electrically connecting each of the pair of balanced input terminals and the pair of balanced output terminals;
With
(F) The capacitance portion of the plurality of LC parallel resonators is configured by connecting two capacitors in series and grounding an intermediate connection point of the two capacitors,
( G ) The plurality of LC parallel resonators are electrically connected to each other via the pair of coupling coils.
[0007]
More specifically,
( H ) a laminate formed by stacking a plurality of insulator layers, a resonant coil conductor, a coupling coil conductor and a capacitor conductor;
( I ) a pair of balanced input terminals and a pair of balanced output terminals provided on the surface of the laminate;
( J ) at least a pair of coupling coils configured with the coupling coil conductor in the laminate;
( K ) a plurality of LC parallel resonators configured with the resonance coil conductor and the capacitor conductor in the laminate;
( L ) a pair of pole adjusting capacitors constituted by capacitor conductors;
With
( M ) The plurality of LC parallel resonators are electrically connected in cascade via the pair of coupling coils between the pair of balanced input terminals and the pair of balanced output terminals, and The balanced input terminal and the pair of balanced output terminals are electrically coupled via the pair of coupling coils,
(N) The capacitance portion of the plurality of LC parallel resonators is configured by connecting two capacitors in series and grounding an intermediate connection point between the two capacitors.
( O ) The pair of pole adjusting capacitors electrically connect the pair of balanced input terminals and the pair of balanced output terminals, respectively.
[0008]
Here, the resonance coil conductor is configured by a spiral pattern provided on the surface of the insulator layer, or via holes provided in the insulator layer are connected in the stacking direction . Et al is a pair of coupling coils are disposed symmetrically on the surface of the same insulator layer.
[0009]
With the above configuration, the resonator becomes a lumped constant type, and a small balanced-balanced balanced LC filter can be obtained.
[0010]
Furthermore, 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 electrically connected to the input / output terminal. Directly connected to the coil, radiation from the coil is suppressed. Furthermore, by not providing a shield electrode in the laminate, eddy current loss generated in the shield electrode is eliminated and the Q of the coil is improved.
[0011]
Also, in one of the pair of balanced input terminals and balanced output terminals, when one terminal is opened, the other terminal becomes an unbalanced terminal, and an unbalanced-balanced balanced LC filter can be obtained. Can be used.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a balanced LC filter according to the present invention will be described below with reference to the accompanying drawings. In the present embodiment, a two-stage balanced LC filter will be described.
[0013]
As shown in FIG. 1, the balanced LC filter 1 is provided with insulator sheets 2b and 2c having resonance coil conductors 3a, 3b, 4a and 4b on the surface, and coupling coil conductors 5 and 6 on the surface. Insulator sheet 2e, and insulator sheets 2g to 2m provided with capacitor conductors 7 to 28 on the surface, respectively. The insulator sheets 2a to 2n are formed by kneading dielectric powder or magnetic powder together with a binder or the like into a sheet shape.
[0014]
The resonant coil conductors 3a, 3b, 4a, 4b are spiral patterns, and are electrically connected in series via via holes 29 provided in the insulator sheet 2b to constitute the resonant coils L1, L2. Yes. The resonance coils L1 and L2 are juxtaposed on the same layer, and the electric path length is set to λ / 2 (λ: wavelength of the center frequency). Needless to say, the resonant coil conductors 3a to 4b do not necessarily have a spiral pattern, and may have an arbitrary pattern such as a straight line or a meandering pattern.
[0015]
The coupling coil conductors 5 and 6 are substantially U-shaped patterns, and constitute coupling coils L3 and L4 whose linear portions are opposed to each other. The coupling coils L3 and L4 are juxtaposed on the same insulator sheet 2e and arranged in line symmetry. This is because a line-symmetric shape is preferable in order to maintain the balance. The electrical path lengths of the coupling coils L3 and L4 are set to λ / 4. The coupling coil conductors 5 and 6 do not necessarily have a U-shaped pattern, and the shape is not particularly limited as long as it is line symmetric. For example, it may be a semicircular, U-shaped or V-shaped pattern.
[0016]
Capacitor conductors 7, 13, 19 and capacitor conductors 9, 15, 21 oppose capacitor conductors 11, 17 with insulator sheets 2g, 2h, 2i, 2j interposed therebetween, and constitute pole adjusting capacitors C1a, C1b, respectively. ing. Capacitor conductors 8, 14, 20 and capacitor conductors 10, 16, 22 are opposed to capacitor conductors 12, 18 across insulator sheets 2g, 2h, 2i, 2j, and constitute pole adjusting capacitors C1c, C1d, respectively. ing. The capacitor conductor 23 faces the capacitor conductors 19 and 25 and the capacitor conductors 20 and 26 with the insulator sheets 2k and 2l 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 2l interposed therebetween, and constitutes resonance capacitors C3a and C3b, respectively.
[0017]
Each of the conductors 3a, 3b, 4a, 4b, and 5-28 is formed by a method such as sputtering, vapor deposition, printing, or photolithography, and is made of a material such as Ag-Pd, Ag, Pd, or Cu.
[0018]
The sheets 2a to 2n are stacked and integrally fired to form a rectangular laminate 30 as shown in FIG. The outer dimensions of the laminate 30 are, for example, a length of 3.2 mm, a width of 1.6 mm, and a height of 1.3 mm. Six external electrodes 31 to 34, G1, and G2 are formed on the laminate 30. These external electrodes 31 to 34, G1, and G2 are formed by a method such as sputtering, vapor deposition, coating, or printing, and are made of a material such as Ag—Pd, Ag, Pd, Cu, or Cu alloy.
[0019]
The external electrode 31 is electrically connected to the resonance coil conductor 3 b and the one end 5 a of the coupling coil conductor 5 and the capacitor conductors 7, 13, 19, and 25. The external electrode 32 is electrically connected to the resonance coil conductor 3 a and the one end 6 a of the coupling coil conductor 6 and the capacitor conductors 8, 14, 20, and 26. The external electrodes 31 and 32 are input terminals.
[0020]
The external electrode 33 is electrically connected to the resonance coil conductor 4 b and the other end 5 b of the coupling coil conductor 5 and the capacitor conductors 9, 15, 21, 27. The external electrode 34 is electrically connected to the resonance coil conductor 4 a and the other end 6 b of the coupling coil conductor 6 and the capacitor conductors 10, 16, 22, and 28. The external electrodes 33 and 34 are output terminals.
[0021]
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.
[0022]
FIG. 3A shows an electrical 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. It has a band-pass filter circuit that is connected in cascade through inter-coupling coils L3 and L4. That is, the LC parallel resonators Q1 and Q2 are not connected via the coupling capacitor. A ground terminal G1 is connected to an intermediate connection point between the capacitors C2a and C2b connected in series, and a ground terminal G2 is connected to an intermediate connection point between the capacitors C3a and C3b connected in series. In this way, a so-called branch line type lumped constant circuit is obtained.
[0023]
The center frequency and impedance of the balanced LC filter 1 are adjusted 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. It can be performed. Further, since the electrical path length of the resonance coils L1, L2 is set to λ / 2, a balanced signal having a phase difference of 180 degrees can be stably output between the output terminals 33, 34.
[0024]
The balanced LC filter 1 having the above configuration is composed of two lumped-constant LC parallel resonators Q1 and Q2, and is smaller than a conventional filter that requires four resonators. Is possible. Moreover, 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. Furthermore, since no shield electrode is provided in the laminate 30, eddy current loss generated in the shield electrode is eliminated, and the Q of the coils L1 to L4 can be improved.
[0025]
And this balance type LC filter 1 makes the external electrodes 31 and 32 function as a pair of balanced input terminals and the external electrodes 33 and 34 function as a pair of balanced output terminals. Become. On the other hand, the input side external electrodes 31 and 32 and the output side external electrodes 33 and 34 can also be used as unbalanced terminals. That is, one of the external electrodes 31 and 32 (external electrodes 33 and 34) is connected to the 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.
[0026]
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 filter 1 is an unbalanced-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. 5 is a graph showing the transmission characteristic S21 at the external electrode 33 and the transmission characteristic S31 at the external electrode 34. In the frequency region where S21 and S31 overlap (near 1.7 GHz and around 2.2 to 2.7 GHz), the amplitude difference between the signals output to the external electrodes 33 and 34 is zero. FIG. 6 is a graph showing the phase characteristics S21 and S31 of the 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.
[0027]
In addition, 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, the balanced LC filter 1 becomes a balanced-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 the transmission characteristic S21 at the external electrode 33 and the transmission characteristic S31 at the external electrode 34. S21 and S31 are almost completely overlapped, and the amplitude difference is 0 over the entire frequency region. FIG. 9 is a graph showing the phase characteristics S21 and S31 of the 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.
[0028]
Furthermore, since the balanced LC filter 1 of this embodiment includes the pole adjustment capacitors C1a to C1d, an attenuation pole can be provided at an arbitrary frequency, and the input / output impedance can be easily adjusted. 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 adjusting capacitors C1a to C1d is about ½. By changing, as shown in FIGS. 10 to 12, the attenuation pole A can be moved to the high frequency side from the center frequency.
[0029]
The balanced LC filter according to the present invention is not limited to the above embodiment, and can be variously modified within the scope of the gist. For example, as shown in FIG. 13, the resonant coil conductor is formed by connecting inductor via holes 45a, 45b, 46a, and 46b provided in the insulating sheets 42a and 42b, respectively, in the stacking direction of the insulating sheets 42a to 42c. It may be configured.
[0030]
The inductor via holes 45a, 45b, 46a, 46b are connected in the stacking direction of the insulating sheets 42a-42c, respectively, and columnar inductors L1, L2 having a length of λ / 2 (λ: wavelength of the center frequency) are substantially connected. Constitute. The inductors L1 and L2 referred to here mean that they are mainly constituted by via holes 45a, 45b, 46a, and 46b connected to each other. For example, the lead conductors 43a to 44b also have an inductance component, and the inductors L1 and L2 are mainly composed of 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 to be thicker than other sheets. At this time, the thickness of the sheet 42b may be secured by stacking a plurality of sheets having the same sheet thickness as the other sheets 2a and 42a, or may be secured by using one thick sheet.
[0031]
The axial directions of the inductors L1 and L2 are perpendicular to the surfaces of the sheets 42a to 42c. When a current flows through the inductors L1 and L2, a magnetic field that circulates in a plane perpendicular to the axial direction of the inductors L1 and L2 is generated around each of the inductors L1 and L2. One end (via hole 45a, 46a) of each of the inductors L1, L2 is connected to the lead conductors 43a, 44a. The other ends (via holes 45b, 46b) of the inductors L1, L2 are connected to lead conductors 43b, 44b.
[0032]
The balanced LC filter 41 having the above configuration can achieve the same effects as the filter 1 of the first embodiment.
[0033]
Further, in the above-described embodiment, the insulating sheets on which the conductors are formed are stacked and then fired integrally. However, the embodiment is not necessarily limited thereto. A sheet fired in advance may be used. Moreover, you may manufacture LC filter with the manufacturing method demonstrated below. After an insulating layer is formed by applying a paste-like insulator material by means such as printing, a paste-like conductor material is applied to the surface of the insulator layer to form an arbitrary conductor. Next, a paste-like insulator material is applied over the conductor. In this way, an LC filter having a laminated structure can be obtained by repeatedly applying in order.
[0034]
【The invention's effect】
As is clear from the above description, according to the present invention, the number of resonators can be suppressed, and the balanced LC filter can be downsized. 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 in the laminate, eddy current loss generated in the shield electrode is eliminated, the coil Q 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 an appearance of the balanced LC filter shown in FIG.
3 is an electrical equivalent circuit diagram of the balanced LC filter shown in FIG.
4 is a graph showing reverse pass characteristics and input / output reflection characteristics when the balanced LC filter shown in FIG. 2 is unbalanced-balanced.
FIG. 5 is a graph showing pass characteristics when the balanced LC filter shown in FIG. 2 is set to an unbalanced-balanced type.
6 is a graph showing phase characteristics when the balanced LC filter shown in FIG. 2 is set to an unbalanced-balanced type.
FIG. 7 is a graph showing reverse pass characteristics and input / output reflection characteristics when the balanced LC filter shown in FIG. 2 is balanced-balanced.
FIG. 8 is a graph showing pass characteristics when the balanced LC filter shown in FIG. 2 is balanced-balanced.
FIG. 9 is a graph showing phase characteristics when the balanced LC filter shown in FIG. 2 is balanced-balanced.
10 is a graph showing reverse pass characteristics and input / output reflection characteristics when the capacitance of the pole adjustment capacitor of the balanced LC filter shown in FIG. 2 is changed.
11 is a graph showing pass characteristics when the capacitance of the pole adjustment capacitor of the balanced LC filter shown in FIG. 2 is changed.
12 is a graph showing phase characteristics when the capacitance of the pole adjusting capacitor of the balanced LC filter shown in FIG. 2 is changed.
FIG. 13 is an exploded perspective view showing another embodiment of a balanced LC filter according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,41 ... Balance type LC filter 2a-2n, 42a-42c ... Insulator sheet | seat 3a, 3b, 4a, 4b ... Resonance coil conductor 5, 6 ... Coupling coil conductor 7-28 ... Capacitor conductor 30 ... Laminate 31 32 ... balanced input terminals 33, 34 ... balanced output terminals 45a, 45b, 46a, 46b ... via holes L1, L2 ... resonance coils L3, L4 ... coupling coils C2a, C2b, C3a, C3b ... resonance capacitors Q1, Q2 ... LC parallel resonator

Claims (9)

A pair of balanced input terminals;
A pair of balanced output terminals;
At least a pair of coupling coils for electrically coupling the pair of balanced input terminals and the pair of balanced output terminals;
A plurality of LC parallel resonators electrically connected in cascade between the pair of balanced input terminals and the pair of balanced output terminals;
A pair of pole adjusting capacitors electrically connecting each of the pair of balanced input terminals and the pair of balanced output terminals;
With
The capacitance portion of the plurality of LC parallel resonators is configured by connecting two capacitors in series and grounding an intermediate connection point of the two capacitors,
The plurality of LC parallel resonators are electrically connected to each other via the pair of coupling coils;
A balanced LC filter characterized by the above.   2. The balance according to claim 1, wherein in one of the balanced input terminal and the balanced output terminal, one terminal is in an open state and the other terminal is an unbalanced terminal. Type LC filter. One LC parallel resonator is connected between one of the balanced input terminals and one of the coupling coils, and between the other balanced input terminal and the other of the coupling coils,
The other LC parallel resonator is connected between one of the balanced output terminals and one of the coupling coils, and between the other balanced output terminal and the other of the coupling coils,
The balanced LC filter according to claim 1, wherein: A laminate formed by stacking a plurality of insulator layers, a resonant coil conductor, a coupling coil conductor, and a capacitor conductor;
A pair of balanced input terminals and a pair of balanced output terminals provided on the surface of the laminate;
At least a pair of coupling coils configured with the coupling coil conductor in the laminate;
A plurality of LC parallel resonators configured with the resonant coil conductor and the capacitor conductor in the laminate;
A pair of pole adjusting capacitors configured by a capacitor conductor;
With
The LC parallel resonators are electrically connected in cascade via the pair of coupling coils 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,
The capacitance portion of the plurality of LC parallel resonators is configured by connecting two capacitors in series and grounding an intermediate connection point of the two capacitors,
The pair of pole adjusting capacitors respectively electrically connect the pair of balanced input terminals and the pair of balanced output terminals;
A balanced LC filter characterized by the above.   5. The balanced LC filter according to claim 4, wherein the resonance coil conductor is formed of a spiral pattern provided on a surface of the insulator layer. 6.   5. The balanced LC filter according to claim 4, wherein the resonance coil conductor is configured by connecting via holes provided in the insulator layer in a stacking direction. 6.   Both ends of the coupling coil and the resonance coil constituting the LC parallel resonator are directly connected to any one of the balanced input terminal and the balanced output terminal, and a shield electrode is provided on the laminate. The balanced LC filter according to claim 4, wherein the balanced LC filter is not provided.   The balanced LC filter according to any one of claims 4 to 7, wherein the pair of coupling coils are arranged line-symmetrically on the surface of the same insulator layer. One LC parallel resonator is connected between one of the balanced input terminals and one of the coupling coils, and between the other balanced input terminal and the other of the coupling coils,
The other LC parallel resonator is connected between one of the balanced output terminals and one of the coupling coils, and between the other balanced output terminal and the other of the coupling coils,
The balanced LC filter according to claim 4, wherein:

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