Noise filter array

A noise filter array includes filter elements including an LC parallel resonant circuit and an LC series resonant circuit each of which includes a coil and a capacitor provided in proximity in an array and integrally provided with one another. The LC series resonant circuits include ground capacitors having signal-side electrodes. Inductance adjustment conductors are connected to signal-side electrodes of the capacitors defining the respective filter elements, and a ground electrode of the capacitors is commonly arranged so as to oppose the signal-side electrodes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a noise filter array in which multiple filter elements are integrally provided with one another. Each filter element includes an LC parallel resonant circuit and an LC series resonant circuit each including a coil and a capacitor.

2. Description of the Related Art

Since various communication methods (for example, Global System for Mobile Communications (GSM), Digital Cellular System (DCS), and Personal Communications service (PCS)) are used for mobile phones, some conventional mobile phones use multiple communication bands. In such a case, in order to prevent the reception sensitivity within each communication band from being degraded, it is necessary to effectively suppress noise within each communication band.

In the noise suppression within communication bands near, for example, about 900 MHz and near about 1.8 GHz, noise filters are required to achieve attenuation over a wide range across the communication bands. In order to achieve such wide attenuation characteristics in filters, an inductance can be applied to grounded capacitors to define double-resonance filters.

In the related art, a double-resonance filter element shown inFIG. 10is known (see, for example, Japanese Unexamined Patent Application Publication No. 9-266430). The double-resonance filter element inFIG. 10includes an LC parallel resonant circuit PR in which a stray capacitor C1is provided in parallel with a coil L1provided on a signal line and an LC series resonant circuit SR in which a capacitor C2is serially connected to a coil L2between the signal line and the ground.

Although such a double-resonance filter element in the related art provides attenuation over a wide bandwidth, specifically, although such a double-resonance filter element can suppress the noise within each communication band near about 900 MHz or near about 1.8 GHz in the above example of the mobile phones, in practice, it is difficult to effectively suppress the noises within the communication bands using only one double-resonance filter element in a mobile phone using multiple communication bands.

Accordingly, multiple double-resonance filter elements corresponding to the multiple communication bands can be provided, and these filter elements can be integrally provided with one another to configure a noise filter array. The noise filter array in which the multiple double-resonance filter elements are integrally provided with one another has an array configuration as shown inFIG. 11. The array configuration inFIG. 11is represented as an equivalent circuit. Four filter elements are provided in the exemplary noise filter array shown inFIG. 11.

In the array configuration shown inFIG. 11, since all of the portions corresponding to LC series resonant circuits surrounded by broken lines are grounded, the capacitors and the coils may be shared to provide a simple configuration. In such a case, for example, a noise filter array has a configuration shown inFIG. 12.

Specifically, in the noise filter array inFIG. 12, the signal-side electrodes of ground capacitors C12to C42including the LC series resonant circuits in the filter elements are provided for the respective filter elements while the capacitors C12to C42have a ground-side electrode commonly provided for the signal-side electrodes and one coil L0is connected to the ground-side electrodes.

However, since only one coil L0is commonly used in the LC series resonant circuits in the filter elements in the noise filter array having the configuration shown inFIG. 12, it is difficult to individually adjust the inductances of the LC series resonant circuits for each communication band. Consequently, there is a problem in that it is not possible to appropriately accommodate cases in which the filter elements are provided to suppress noises having different frequencies.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of the present invention provide a noise filter array capable of individually adjusting the inductances of LC series resonant circuits in multiple filter elements and capable of effectively suppressing the noises within multiple communication bands without requiring a complicated configuration.

A noise filter array according to a preferred embodiment of the present invention includes a plurality of filter elements arranged in an array and integrally provided with one another. Each filter element includes an LC parallel resonant circuit and an LC series resonant circuit each including a coil and a capacitor. The noise filter array includes an inductance adjustment conductor that is connected to the signal-side electrode of a ground capacitor of each LC series resonant circuit and the capacitors include a ground electrode that is commonly arranged for the signal-side electrodes so as to oppose the signal-side electrodes.

Preferably, the inductances of the inductance adjustment conductors are individually set in accordance with a signal frequency within a communication band.

Preferably, each of the inductance adjustment conductors has one of a meander shape, a spiral shape, or a coil shape.

Preferably, each of the inductance adjustment conductors is connected to the signal-side electrode of the capacitor through a via hole.

Preferably, the inductance adjustment conductor and the signal-side electrode of the capacitor, which define the LC series resonant circuit, are integrally provided on substantially the same plane.

According to a preferred embodiment of the present invention, the noise filter array preferably has a layered configuration in which the filter elements are provided on both sides in the layering direction of the ground electrode, which is commonly provided for the signal-side electrodes of the capacitors.

According to another preferred embodiment of the present invention, the noise filter array preferably has a layered configuration in which two elements among the filter elements are provided on one side of the ground electrode of the capacitors in the layering direction and two elements among the filter elements are provided on the other side of the ground electrode of the capacitors in the layering direction.

According to another preferred embodiment of the present invention, the noise filter array preferably has a layered configuration in which the filter elements are provided on only one side of the ground electrode of the capacitors in the layering direction.

The locations of the conductors of the coil defining the LC parallel resonant circuit and the LC series resonant circuit are shifted so that the conductors are not overlapped with one another in the thickness direction.

A noise filter array according to another preferred embodiment of the present invention includes a plurality of filter elements provided in an array and integrally provided with one another. Each filter element includes a coil in which a plurality of insulating layers having coil conductors provided thereon are layered and a capacitor in which an insulating layer having a signal-side electrode provided thereon and an insulating layer having a ground electrode formed thereon are layered. The coil is arranged in proximity to the capacitor in the layering direction and the coil is electrically connected to the capacitor. In the noise filter array, the plurality of filter elements are arranged along the layering direction and the plurality of filter elements arranged along the layering direction are overlapped with one another such that the coils are adjacent to one another and the capacitors are arranged on at least one external side in the layering direction so as not to be sandwiched between the coils.

Preferably, an even number of the filter elements are arranged along the layering direction, approximately half of the filter elements are arranged in the upper side in the layering direction and approximately the other half of the filter elements are arranged in the lower side in the layering direction so as to have a substantially symmetrical configuration in the layering direction.

Preferably, the capacitors of the filter elements along the layering direction are collectively arranged on one side of the coils in the layering direction.

Preferably, the ground electrodes of the capacitors are shared between the filter elements and are arranged so as to cover an area in which the coils are provided.

Preferably, of adjacent coils of each filter element, the coil near the capacitors is configured so as to have a winding length of the coil conductors greater than that of the other coil.

Preferably, the capacitors are arranged outside in the layering direction at a mounting surface side.

Preferably, a directional identification mark is preferably provided on the outermost insulating layer in the layering direction.

According to a preferred embodiment of the present invention, it is possible to easily provide the noise filter array in which the multiple LC parallel resonant circuits and the multiple LC series resonant circuits each including a coil and a capacitor are integrally provided with one another without requiring a complicated configuration. In addition, when each filter element includes the LC parallel resonant circuit and the LC series resonant circuit and the LC series resonant circuit includes a ground capacitor and an inductance adjustment conductor, it is possible to easily provide the noise filter array that includes the multiple double-resonance filter elements.

Furthermore, since the inductance adjustment conductor is connected to the signal-side electrode of the ground capacitor defining each filter element, the inductances of the series resonant circuits can be adjusted for each filter element. Accordingly, the use of the noise filter according to a preferred embodiment of the present invention enables the noise within each communication band to be effectively suppressed, for example, even when one mobile phone uses multiple communication bands.

When the inductances of the inductance adjustment conductors are individually set in accordance with the signal frequency of the communication band, the noise included in a signal within each communication band can be effectively suppressed.

Configuring each of the inductance adjustment conductors in one of a meander shape, a spiral shape, or a coil shape as in the noise filter array according to a preferred embodiment of the present invention described above, enables the inductances to be easily adjusted. In addition, it is possible to reduce the variation in plating thickness of the formed conductors when the inductance adjustment conductors are formed by plating.

When each of the inductance adjustment conductors is connected to the signal-side electrode of the capacitor through the via hole, multiple inductance adjustment conductors may be layered, as required. Accordingly, it is possible to increase the inductances of the LC series resonant circuits and to decrease the frequency of the resonant circuits.

When the inductance adjustment conductor and the signal-side electrode of the capacitor, which define the LC series resonant circuit, are integrally provided on substantially the same plane, it is possible to connect the inductance adjustment conductor to the signal-side electrode of the capacitor without the via hole. Consequently, it is possible to decrease the required number of insulating sheets so as to reduce the cost.

When the noise filter array has a layered configuration in which the filter elements are provided on both sides in the layering direction of the ground electrode, which is commonly provided for the signal-side electrodes, it is possible to suppress the magnetic effect between the upper filter elements and the lower filter elements with the ground electrode sandwiched therebetween to reduce a variation in the response point of each filter element.

When two elements among the filter elements are provided on one side of the ground electrode of the capacitors in the layering direction and two elements among the filter elements are provided on the other side of the ground electrode of the capacitors in the layering direction, the noise filter array can be configured to include the four elements.

When the number of filter elements is relatively small, the filter elements may be provided on only one side in the layering direction of the ground electrode commonly provided for the signal-side electrodes. With this configuration, it is possible to decrease the thickness of the components of the noise filter.

When the locations of conductors of the coil defining the LC parallel resonant circuit and the LC series resonant circuit are shifted so that the conductors are not overlapped with one another in the thickness direction, the thickness of the components of the noise filter is made substantially uniform. As a result, the internal stress during manufacturing is reduced and it is possible to prevent the occurrence of cracks between the conductors on adjacent layers, thus improving the yield of the product.

In the noise filter array according to a preferred embodiment of the present invention, the multiple filter elements arranged along the layering direction are overlapped with one another such that the coils are adjacent to one another and the capacitors are arranged on at least one external side in the layering direction so as not to be sandwiched between the coils. Accordingly, gas from a binder can be easily discharged during degreasing and firing of the capacitors, and therefore, delamination can be effectively prevented. Delamination is a phenomenon in which the insulating sheets are separated from one another. In addition, since the capacitors are provided outside the coils, an occurrence of breakage of the coils can be suppressed or prevented even if a crack occurs due to shock, for example, when the circuit board on which the noise filter array is mounted is dropped.

When an even number of the filter elements are arranged along the layering direction, substantially half of the filter elements are arranged in the upper side in the layering direction, and substantially the other half of the filter elements are arranged in the lower side in the layering direction so as to achieve a substantially symmetrical configuration in the layering direction, the variation in characteristics between the filter elements is reduced, thus reducing the variation in insertion loss characteristics.

When the capacitors of the filter elements along the layering direction are collectively arranged on one side of the coils, the discharge of the gas from the binder in the firing of the capacitors is facilitated so as to prevent delamination. In addition, the breakage of the coils can be suppressed or prevented even if a crack occurs due to, for example, shock after the mounting of the noise filter array.

When the ground electrodes of the capacitors are shared between the filter elements and are arranged so as to cover the area in which the coils are provided, the stray capacitance between the coils and the external electrodes toward the ground can be suppressed, thus reducing the variation in the IL characteristics.

When, of adjacent coils of each filter element, the coil near the capacitors is arranged so as to have a winding length of the coil conductors greater than that of the other coil, the variation in the inductance can be reduced between the filter elements even when the capacitors are collectively arranged on one side of the coils.

One side of the coils on which the capacitors are collectively arranged can be set as the mounting surface side to avoid an occurrence of a fatal error, such as the breakage of the coils, even if a crack occurs due to, for example, shock.

The directional identification mark is preferably provided on the outermost insulating layer in the layering direction because the mounting surface on which the capacitors are provided can be easily identified, for example, when the capacitors are collectively arranged on one side of the coils.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

First Preferred Embodiment

FIG. 1is a perspective view showing a noise filter array according to a first preferred embodiment of the present invention.FIG. 2is an exploded perspective view of the noise filter array.FIG. 3is an electrical equivalent circuit diagram of the noise filter array.FIG. 4is an electrical equivalent circuit diagram resulting from a rearrangement of the electrical equivalent circuit diagram inFIG. 3so that the electrical equivalent circuit diagram corresponds to the exploded perspective view inFIG. 2. The noise filter array of the first preferred embodiment will now be described with reference toFIGS. 1 to 4.

The noise filter array of the first preferred embodiment preferably has a substantially rectangular parallelepiped multilayer body1in which substantially rectangular insulating sheets preferably made of a ceramic dielectric material, such as barium titanate, for example, or a ceramic magnetic material, such as ferrite, for example, are layered and are integrally fired. External electrodes2are provided on the side surfaces of the multilayer body1. The external electrodes2provided on the front and rear surfaces along the longer sides are preferably input terminals in1to in4and output terminals out1to out4. The external electrodes2on the left-side and right-side surfaces along the shorter sides are preferably ground terminals GND1and GND2.

In addition, a directional identification mark3is provided at a location displaced from the approximate center of the top surface of the multilayer body1.

In the multilayer body1, four double-resonance filter elements F1to F4, for example, are integrally provided with one another so as to correspond to the four input terminals in1to in4and the four output terminals out1to out4. Two elements in the filter elements F1to F4are arranged on one side of the multilayer body1in the thickness direction (i.e., the layering direction) and the remaining two elements in the filter elements F1to F4are arranged on the other side thereof in the thickness direction (the layering direction) with a ground-side electrode9described below sandwiched between the two elements on one side and the two elements on the other side. In other words, two filter elements F2and F3are provided in parallel in the direction substantially perpendicular to the thickness direction above the ground electrode9and the remaining two filter elements F1and F4are provided in parallel in the direction substantially perpendicular to the thickness direction below the ground electrode9.

In each of the LC parallel resonant circuits PR1to PR4, a plurality of insulating sheets6on which spiral coil conductors5are provided are stacked. The LC parallel resonant circuits PR1to PR4include substantially helical coils L11to and stray capacitors C11to C41, respectively. The coils L11to L41are formed by electrically connecting the coil conductors5on the layers via via holes7. The stray capacitors C11to C41are provided by the stray capacitances that inherently accompany the formation of the coils. One sides of the coil conductors5defining the coils L11to L41are connected to the external electrodes2defining the input terminals in1to in4, and the other sides of the coil conductors5defining the coils L11to L41are connected to the external electrodes2defining the output terminals out1to out4of the multilayer body1.

The locations of the respective coil conductors5defining the coils L11to L41of the LC parallel resonant circuits PR1to PR4are shifted so that the coil conductors5are not overlapped with one another in the thickness direction. Accordingly, the thickness of the multilayer body1is substantially uniform. As a result, the internal stress during the manufacture of the multilayer body1is reduced and it is possible to prevent an occurrence of a crack between the coil conductors5on adjacent layers, thus improving the yield of the product.

In contrast, the LC series resonant circuits SR1to SR4include inductance adjustment conductors L12to L42defining inductance coils and ground capacitors C12to C42, respectively. The inductance adjustment conductors L12to L42and the ground capacitors C12to C42are provided on the insulating sheets6.

Each of the inductance adjustment conductors L12to L42preferably has a substantial meander shape, such that the inductance adjustment conductors L12to L42have different lengths for the filter elements F1to F4in order to achieve a desired inductance in each of the filter elements F1to F4. The shape of the inductance adjustment conductors L12to L42is not limited to the meander shape. Alternatively, each of the inductance adjustment conductors L12to L42may have a substantial spiral shape or in a substantial coil shape.

One end of each of the inductance adjustment conductors L12to L42extends out toward the distal end of the insulating sheet6to be connected to the external electrode2forming each of the output terminals out1to out4. The other end of each of the inductance adjustment conductors L12to L42is electrically connected to a signal-side electrode8of each of the ground capacitors C12to C42through the via hole7.

In contrast, the ground capacitors C12to C42are arranged such that the signal-side electrodes8provided on the insulating sheets6oppose the ground electrode9provided on the insulating sheet6via the insulating sheets6. The signal-side electrodes8are provided for the respective inductance adjustment conductors L12to L42whereas the ground electrode9is commonly provided for the signal-side electrodes8so as to oppose the signal-side electrodes8.

The signal-side electrodes8are electrically connected to the inductance adjustment conductors L12to L42through the via holes7as described above. The ground electrode9extends out toward the left-side and right-side ends of the insulating sheet6to be connected to the external electrodes2forming the ground terminals GND1and GND2.

The directional identification mark3is provided to identify the mounting direction of the noise filter array on a circuit board and is electrically connected to the coil conductors5through the via hole7. The directional identification mark3is electrically connected to the coil conductors5in order to ensure the plating adherence when the directional identification mark3is formed by electroplating.

The noise filter array of the first preferred embodiment includes stray capacitance adjustment conductors11to adjust the stray capacitances of the stray capacitors C11to C41defining the respective LC parallel resonant circuits PR1to PR4. The stray capacitance adjustment conductors11are provided on the insulating sheets6arranged between the respective inductance adjustment conductors L12to L42and the signal-side electrodes8of the respective capacitors C12to C42.

In the manufacture of the noise filter array having the above-described configuration, a conductive paste preferably including Ag, Pd, Cu, Au, or their alloy as a conductive component, for example, is applied to each insulating sheet6by, for example, screen printing to form the coil conductors5, the inductance adjustment conductors L12to L42, the signal-side electrodes8and the ground electrode9of the ground capacitors C12to C42, the stray capacitance adjustment conductors11, and the directional identification mark3on the insulating sheets6. The via holes7are formed by forming through holes preferably using, for example, laser beams and filling the through holes with the conductive paste preferably including Ag, Pd, Cu, Au, or their alloy as a conductive component, for example.

The insulating sheets6on which the conductors, the electrodes, the via holes, and other elements are formed in the manner shown inFIG. 2are layered and are subjected to pressure bonding to manufacture the multilayer body1. Then, after the external electrodes2defining the input terminals in1to in4, the output terminals out1to out4, and the ground terminals GND1and GND2are formed on the side surfaces of the multilayer body1, the multilayer body1is fired. After the multilayer body1is fired, the surface of each of the external electrodes2is preferably plated with Ni or Sn, for example. As a result, the substantially rectangular parallelepiped noise filter array having the configuration shown inFIG. 1is manufactured.

As described above, the inductance adjustment conductors L12to L42are provided in the LC series resonant circuits SR1to SR4in the double-resonance filter elements F1to F4, respectively, in the noise filter array of the first preferred embodiment. Accordingly, the shape of the conductors L12to L42can be changed in the manufacture of the noise filter array to finely adjust the inductances of the filter elements F1to F4individually. As a result, it is possible to easily adjust the frequency of each of the filter elements F1to F4.

Consequently, it is possible to effectively suppress the noise within each communication band even when one mobile phone uses multiple communication bands.

Since the ground electrode9of the capacitors C12to C42is commonly provided for the signal-side electrodes8in the noise filter array of the first preferred embodiment, the inductances can be adjusted regardless of the distance from the capacitors C12to C42to the ground terminals GND1and GND2.

In addition, the two filter elements F2and F3are arranged on one side of the ground electrode9of the capacitors C12to C42in the thickness direction (the layering direction) and the remaining two filter elements F1and F4are arranged on the other side of the ground electrode9of the capacitors C12to C42in the thickness direction (the layering direction) in the noise filter array of the first preferred embodiment. Accordingly, a magnetic effect is unlikely to occur between the upper filter elements F2and F3and the lower filter elements F1and F4with the ground electrode9sandwiched therebetween.

FIG. 5is a characteristics diagram showing examples of the results of a measurement of the insertion loss characteristics with adjustment of the inductance (equivalent series inductance: ESL) by the inductance adjustment conductors L12to L42and without adjustment of the inductance (ESL) thereby.

As shown inFIG. 5, the insertion of the inductance adjustment conductors L12to L42enables the series resonant (second resonant) frequency of each filter element to be adjusted to a desired frequency (about 2 GHz in this example).

FIG. 6is a characteristics diagram showing the results of a measurement of the insertion loss characteristics when the series resonant (second resonant) frequency near 1,800 MHz for the upper filter elements F2and F3is different from that for the lower filter elements F1and F4with the ground electrode9sandwiched between the upper filter elements F2and F3and the lower filter elements F1and F4. The two filter elements F2and F3horizontally arranged in parallel inFIGS. 2 and 4are adjusted in advance so as to have substantially the same inductance, and the two filter elements F1and F4horizontally arranged in parallel inFIGS. 2 and 4are adjusted in advance so as to have substantially the same inductance. Accordingly, two lines including a solid line (F2and F3) and a broken line (F1and F4) are shown in the diagram inFIG. 6.

As shown inFIG. 6, it is possible to easily adjust the inductances with the inductance adjustment conductors L12to L42having different shapes even if the filter elements F1to F4are configured to suppress noises of different frequencies.

Second Preferred Embodiment

FIG. 7is an exploded perspective view of a noise filter array according to a second preferred embodiment of the present invention. The components inFIG. 7having the same reference numerals as those inFIGS. 1 to 4show the same components as in the configuration of the first preferred embodiment or show the corresponding components of the first preferred embodiment.

In the noise filter array of the second preferred embodiment, the inductance adjustment conductors L12to L42are configured so as to have approximately the same shape so that the LC series resonant circuits SR1to SR4in the filter elements F1to F4have substantially the same inductance. Also in the second preferred embodiment, the two filter elements F2and F3are integrally provided on one side of the ground electrode9in the thickness direction (the layering direction) and the remaining two filter elements F1and F4are integrally provided on the other side of the ground electrode9in the thickness direction (the layering direction), as in the first preferred embodiment.

Since the inductance adjustment conductors L12to L42are also provided in the respective filter elements F1to F4in the noise filter array of the second preferred embodiment, the shape of the inductance adjustment conductors L12to L42can be changed in the manufacture of the noise filter array to individually adjust the inductances of the LC series resonant circuits SR1to SR4in the filter elements F1to F4. In other words, the resonance points of the filter elements, which are shifted due to magnetic coupling between the filter elements F2and F3or between the filter elements F1and F4, can be finely adjusted for each filter element, so that variations in characteristics between the filter elements F1to F4are reduced.

FIG. 8is a characteristics diagram showing the results of a measurement of the insertion loss characteristics of the filter elements when the inductance adjustment conductors L12to L42provided in the respective filter elements F1to F4are adjusted so as to have substantially the same inductance.

As shown inFIG. 8, when the inductances of the LC series resonant circuits SR1to SR4in the filter elements F1to F4are individually adjusted, the filter elements F1to F4have approximately the same insertion loss. Accordingly, the characteristics of the filter elements F1to F4are represented by one solid line inFIG. 8. This shows that there is no substantial difference in the characteristics of the series resonant (second resonant) frequency between the filter elements.

Since the remaining configuration, advantages, and effects are similar to those in the first preferred embodiment shown inFIGS. 1 to 4, a detailed description of them is omitted herein.

Third Preferred Embodiment

FIG. 9is an exploded perspective view of a noise filter array according to a third preferred embodiment of the present invention. The components inFIG. 9having the same reference numerals as inFIGS. 1 to 4show the same components as in the configuration of the first preferred embodiment or show the corresponding components of the first preferred embodiment.

In the noise filter array of the third preferred embodiment, the inductance adjustment conductors L12and L42and the signal-side electrodes8of the capacitors C12and C42, which define the respective LC series resonant circuits SR1and SR4, are integrally provided on substantially the same plane, that is, on a single insulating sheet6, and the inductance adjustment conductors L22and L32and the signal-side electrodes8of the capacitors C22and C32, which define the respective LC series resonant circuits SR2and SR3, are integrally provided on substantially the same plane, that is, on a single insulating sheet6. In the noise filter array of the third preferred embodiment, the two filter elements F2and F3are integrally provided on one side of the ground electrode9in the thickness direction (the layering direction) and the remaining two filter elements F1and F4are integrally provided on the other side of the ground electrode9in the thickness direction (the layering direction), as in the first preferred embodiment.

Integrally providing the inductance adjustment conductors L12and L42and the signal-side electrodes8of the capacitors on one insulating sheet6in advance and integrally providing the inductance adjustment conductors L22and L32and the signal-side electrodes8of the capacitors on one insulating sheet6in advance as in the third preferred embodiment enables the inductance adjustment conductors L12to L42to be connected to the signal-side electrodes8without the via holes7, so that the number of the used insulating sheets6can be decreased so as to reduce the cost.

Since the remaining configuration, advantages, and effects are similar to those in the first preferred embodiment shown inFIGS. 1 to 4, a detailed description of them is omitted herein in order to avoid the duplication.

Although the two filter elements F2and F3are preferably arranged on one side of the ground electrode9in the thickness direction (the layering direction) and the remaining two filter elements F1and F4are preferably arranged on the other side of the ground electrode9in the thickness direction (the layering direction) in the first to third preferred embodiments, the filter elements may be provided only on one side of the ground electrode9in the thickness direction (layering direction), if needed. This can decrease the overall thickness of the noise filter array.

Although the inductance adjustment conductors L12and L42are preferably provided on one insulating sheet6and the inductance adjustment conductors L22and L32are preferably provided on one insulating sheet6in the first to third preferred embodiments, the noise filter array may be configured such that the inductance adjustment conductors L12to L42have helical shapes across at least two of the plurality of insulating sheets6and the inductance adjustment conductors L12to L42are connected to one another through the via holes7. With such a configuration, since the inductances of the LC series resonant circuits SR1to SR4can be increased, the frequencies of the LC series resonant circuits SR1to SR4can be further decreased.

Fourth Preferred Embodiment

FIG. 13is a perspective view a noise filter array according to a fourth preferred embodiment of the present invention.FIG. 14is an exploded perspective view of the noise filter array.FIG. 15is an electrical equivalent circuit diagram of the noise filter array.

The noise filter array of the fourth preferred embodiment preferably has a substantially rectangular parallelepiped multilayer body1in which substantially rectangular insulating sheets preferably made of a ceramic dielectric material, such as barium titanate, or a ceramic magnetic material, such as ferrite, for example, are layered and are integrally fired. External electrodes2are provided on the side surfaces of the multilayer body1. Of the external electrodes2provided on the front and rear surfaces along the longer sides, the external electrodes2on one surface define input terminals in1to in4of signals and the external electrodes2on the other surface define output terminals out1to out4of signals. The external electrodes2on the left-side and right-side surfaces along the shorter sides define ground terminals GND1and GND2.

A directional identification mark3is preferably arranged at a location slightly displaced from the approximate center of the top surface of the multilayer body1. The directional identification mark3is provided to identify the mounting direction of the noise filter array on a circuit board.

In the multilayer body1, four filter elements F1to F4, for example, are integrally provided with one another so as to correspond to the four input terminals in1to in4and the four output terminals out1to out4. Specifically, the two filter elements F1and F2are arranged in proximity in the layering direction and the two filter elements F3and F4are arranged in proximity in the layering direction. The two filter elements F1and F4are provided in parallel in the direction substantially perpendicular to the thickness direction and the two filter elements F2and F3are provided in parallel in the direction substantially perpendicular to the thickness direction.

The filter elements F1to F4include coils L1to L4and capacitors C1to C4, respectively, each defining an LC filter. Each of the coils L1to L4have a substantially helical shape by layering multiple insulating sheets (insulating layers)6on which spiral coil conductors5are provided and electrically connecting the coil conductors5on the layers via via holes7. Of the coils defining the filter elements F1and F2and the filter elements F4and F3provided in the layering direction, the coils L1and L2are overlapped with each other so as to be adjacent to each other with insulating sheets6sandwiched therebetween and the coils L4and L3are overlapped with each other so as to be adjacent to each other with insulating sheets6sandwiched therebetween.

The capacitors C1to C4defining the filter elements F1to F4are arranged above and below the coils L1to L4in the layering direction with insulating sheets6sandwiched between the capacitors C1to C4and the filter elements F1to F4. Each of the capacitors C1to C4is configured such that the insulating sheets6on which signal-side electrodes8are provided and the insulating sheets6on which ground electrodes9are provided are alternately arranged in the layering direction. The ground electrodes9are commonly provided for the double-resonance filter elements F1to F4. Accordingly, the noise filter array of the fourth preferred embodiment has a substantially symmetrical configuration in the layering direction.

First ends a1to a4of the coil conductors5defining the coils L1to L4are connected to the external electrodes2composing the input terminals in1to in4of the multilayer body1, respectively, and second ends b1to b4of the coil conductors5are connected to the external electrodes2defining the output terminals out1to out4of the multilayer body1, respectively.

In addition, first ends e1to e4of the signal-side electrodes8defining the capacitors C1to C4are connected to the external electrodes2defining the output terminals out1to out4of the multilayer body1, respectively. Furthermore, first ends d1of the ground electrodes9are connected to the external electrode2defining one ground terminal GND1of the multilayer body1, and the second ends d2of the ground electrodes9are connected to the external electrode2defining the other ground terminal GND2of the multilayer body1.

Accordingly, although the capacitors C1to C4are provided in the respective filter elements F1to F4in the electrical equivalent circuit diagram shown inFIG. 15, the six capacitors electrically connected to one another in parallel define one capacitor for each of the filter elements F1to F4in the actual noise filter array shown inFIG. 14.

During the manufacture of the noise filter array having the above-described configuration, the coil conductors5, the signal-side electrodes8and the ground electrodes9of the ground capacitors C12to C42, and the directional identification mark3are formed on the insulating sheets6. The coil conductors5, the signal-side electrodes8and the ground electrodes9of the ground capacitors C12to C42, and the directional identification mark3are formed by applying a conductive paste preferably including Ag, Pd, Cu, Au, or their alloy as a conductive component, for example, by screen printing, for example. The via holes7are preferably formed by forming through holes using, for example, laser beams and filling the through holes with the conductive paste preferably including Ag, Pd, Cu, Au, or their alloy as a conductive component, for example.

The insulating sheets6on which the conductors, the electrodes, the via holes, and other elements are formed in the manner shown inFIG. 14are layered and are subjected to pressure bonding to manufacture the multilayer body1. Then, after the external electrodes2defining the input terminals in1to in4, the output terminals out1to out4, and the ground terminals GND1and GND2are formed on the side surfaces of the multilayer body1, the multilayer body1is fired. After the multilayer body1is fired, the surface of each of the external electrodes2is preferably plated with Ni or Sn, for example. As a result, the substantially rectangular parallelepiped noise filter array having the configuration shown inFIG. 13is manufactured.

As described above, the capacitors C1to C4including the ground electrodes9and the signal-side electrodes8having larger electrode areas are arranged on the upper and lower external sides of the coils L1and L2, which are adjacent to each other in the layering direction, and the coils L4and L3, which are adjacent to each other in the layering direction, in the noise filter array of the fourth preferred embodiment. Accordingly, gas from the binder can be easily discharged during degreasing and firing of the capacitors C1to C4. Therefore, delamination can be effectively prevented. Delamination is a phenomenon in which the insulating sheets6separate from one another.

In addition, since the capacitors C1to C4are provided outside the coils L1to L4, the distance from the bottom surface of the multilayer body1to the coils L1to L4is increased and an occurrence of breakage of the coils L1to L4can be prevented or suppressed even if a crack occurs due to shock, for example, when the circuit board on which the noise filter array is mounted is dropped or bent. Furthermore, since the noise filter array has a substantially symmetrical configuration in the layering direction, in which the filter elements F1and F4are arranged in the upper direction and the filter elements F2and F3are arranged in the lower direction, variations in the characteristics between the filter elements F1to F4is reduced and variations in the insertion loss characteristics can also be reduced.

FIGS. 16A and 16Bare characteristics diagrams showing the results of a measurement of the insertion loss characteristics of the filter elements F1and F2, respectively, in the noise filter array according to the fourth preferred embodiment.FIGS. 17A and 17Bare characteristics diagrams showing the results of a measurement of the insertion loss characteristics of the filter elements F3and F4, respectively, in the noise filter array according to the fourth preferred embodiment.

FIGS. 16A and 16BandFIGS. 17A and 17Bshow that the filter elements F1to F4have approximately the same insertion loss characteristics.

The rate at which delamination occurs in the firing in the noise filter array of the fourth preferred embodiment and in a noise filter array having a configuration shown inFIG. 18(hereinafter referred to as a comparative example) were examined. The results of the comparison are shown in Table 1.

In addition, the results of the examination of the inductances (L values) of the filter elements F1to F4in the noise filter array of the fourth preferred embodiment and in the comparative example are shown in Table 2. The results of the examination of the electrostatic capacitances of the filter elements F1to F4in the noise filter array of the fourth preferred embodiment and in the comparative example are shown in Table 3.

TABLE 2Inductance of each filter element (nH)F1F2F3F4Fourth136133132137embodimentComparative139135136138example

TABLE 3Electrostatic capacitance of each filter element (pF)F1F2F3F4Fourth82838281embodimentComparative81828183example

The noise filter array in the comparative example inFIG. 18is configured such that the capacitors C1to C4are arranged inside the upper coils L1and L4and the lower coils L2and L3in the layering direction. The number of the layered insulating sheets6on which the signal-side electrodes8are provided is equal to four in the fourth preferred embodiment and the number of the layered insulating sheets6on which the signal-side electrodes8are formed is equal to three in the comparative example, which is one less than that in the fourth preferred embodiment. In contrast, the number of capacitors along the layering direction, arranged of the signal-side electrodes8and the ground electrodes9, is equal to six in both of the examples.

As shown in Table 1, the rate of occurrence of delamination in the fourth preferred embodiment is 0% because the capacitors C1to C4having a greater electrode area are arranged outside the coils L1to L4. In contrast, the rate of occurrence of delamination in the comparative example is relatively high because the capacitors C1to C4are arranged inside the coils L1to L4. Accordingly, the noise filter array of the fourth preferred embodiment is superior to the one in the comparative example.

Tables 2 and 3 show that the filter elements F1to F4have approximately the same inductance and electrostatic capacitance in the fourth preferred embodiment and in the comparative example and the variation between the elements is relatively small.

Fifth Preferred Embodiment

FIG. 19is an exploded perspective view of a noise filter array according to a fifth preferred embodiment of the present invention. The components inFIG. 19having the same reference numerals as inFIG. 14show the same components as in the configuration of the fourth preferred embodiment or show the corresponding components of the fourth preferred embodiment.

In the noise filter array of the fifth preferred embodiment, the four filter elements F1to F4, for example, are integrally provided with one another. The noise filter array of the fifth preferred embodiment is similar to the noise filter array of the fourth preferred embodiment in that the two filter elements F1and F2are arranged in proximity in the layering direction, the two filter elements F3and F4are arranged in proximity in the layering direction, the two filter elements F1and F4are provided in parallel in the direction substantially perpendicular to the thickness direction, and the two filter elements F2and F3are provided in parallel in the direction substantially perpendicular to the thickness direction.

The noise filter array of the fifth preferred embodiment differs significantly from the noise filter array of the fourth preferred embodiment in that the capacitors C1to C4in the filter elements F1to F4are collectively arranged on one side (the lower side inFIG. 19) of the coils L1to L4in the layering direction.

In addition, of the coils L1to L4, the number of the layered insulating sheets6on which the coil conductors5are provided in the coils L2and L3near the capacitors C1to C4is greater than that in the coils L1and L4, which are provided above the coils L2and L3. As a result, the coils L2and L3near the capacitors C1to C4are configured such that the winding length of the coil conductors5is greater than that in the upper coils L1and L4.

This configuration is preferably used because the upper and lower coils have approximately the same inductance and the variations in the characteristics between the filter elements F1to F4are reduced. Specifically, since no electrode for capacitor formation interrupting the magnetic flux is provided for the upper coils L1and L4, the coils L1and L4have higher inductances than those of the lower coils L2and L3. Accordingly, the increase in the winding length of the coil conductors5in the lower coils L2and L3has the advantage in that the upper coils have approximately the same inductance as that of the lower coils and the variations in the characteristics between the filter elements F1to F4are reduced.

First ends a1to a4of the coil conductors5defining the coils L1to L4are connected to the external electrodes2defining the input terminals in1to in4of the multilayer body1, respectively, and the second ends b1to b4of the coil conductors5are connected to the external electrodes2defining the output terminals out1to out4of the multilayer body1, respectively.

In addition, first ends e1to e4of the signal-side electrodes8defining the capacitors C1to C4are connected to the external electrodes2defining the output terminals out1to out4of the multilayer body1, respectively. Furthermore, first ends d1of the ground electrodes9are connected to the external electrode2defining one ground terminal GND1of the multilayer body1, and the second ends d2of the ground electrodes9are connected to the external electrode2defining the other ground terminal GND2of the multilayer body1.

Accordingly, the ground electrodes9of the capacitors C1to C4are commonly provided for the filter elements F1to F4and are arranged so as to cover the area in which the coils L1to L4are provided in the fifth preferred embodiment. Consequently, the stray capacitance between the coils L1to L4and the external electrodes2at the ground side is suppressed, such that the variations in the IL characteristics can be reduced.

In addition, in the noise filter array of the fifth preferred embodiment, since the capacitors C1to C4having greater electrode areas are arranged on one side of the coils L1to L4and L3in the layering direction, gas from the binder can be easily discharged during degreasing and firing of the capacitors C1to C4and, therefore, delamination is effectively prevented.

In addition, since the capacitors C1to C4are provided outside the coils L1to L4, the distance from the bottom surface of the multilayer body1to the coils L1to L4is increased, provided that the surface of the multilayer body1on which the capacitors C1to C4are provided is the mounting surface, and an occurrence of breakage of the coils L1to L4can be prevented even if a crack occurs due to shock, for example, when the circuit board on which the noise filter array is mounted is dropped or bent. It is particularly preferable to provide the directional identification mark3on a surface of the multilayer body1in the configuration of the fifth preferred embodiment because the mounting surface on which the capacitors C1to C4are provided can be easily identified.

The results of an examination of the rate of occurrence of the delamination in the firing in the noise filter array of the fifth preferred embodiment are shown in Table 4. In addition, the results of an examination of the inductances (L values) of the filter elements F1to F4in the noise filter array of the fifth preferred embodiment is shown in Table 5. The results of an examination of the electrostatic capacitances of the filter elements F1to F4in the noise filter array of the fifth preferred embodiment is shown in Table 6.

TABLE 5Inductance of each filter element (nH)F1F2F3F4Fifth150142144151embodiment

TABLE 6Electrostatic capacitance of each filter element (pF)F1F2F3F4Fifth79848380embodiment

As shown in Table 4, the rate of occurrence of delamination in the fifth preferred embodiment is 0% because the capacitors C1to C4having a greater electrode area are arranged outside the coils L1to L4. Tables 5 and 6 shows that the filter elements F1to F4have approximately the same inductance and electrostatic capacitance and the variation between the elements is relatively small.

Since the remaining configuration, advantages, and effects are similar to those in the fourth preferred embodiment shown inFIGS. 13 to 15, a detailed description of them is omitted herein in order to avoid the duplication.

Although the noise filter arrays including the four filter elements F1to F4are described in the first to fifth preferred embodiments, the present invention is not limited to this configuration and is widely applicable to any noise filter array including a plurality of filter elements.

In addition, the situation in which the individual components shown inFIGS. 1 and 13are separately produced are described in the first to fifth preferred embodiments. However, in mass production, after a mother multilayer body in which multiple multilayer bodies are integrated with one another is manufactured, the mother multilayer body may be cut so that the multilayer body1shown inFIG. 1or13is obtained to manufacture the individual elements.

In addition, the insulating sheets6on which the coil conductors5, the signal-side electrodes8, the ground electrodes9, the via holes7, and other elements are provided are layered and, then, the insulating sheets6are integrally fired in the first to fifth preferred embodiments described above. However, the insulating sheets6that are fired in advance may be layered and subjected to pressure bonding to manufacture the multilayer body1.

Furthermore, the formation of the insulating layers by applying an insulating material and the formation of the conductors by applying a conductive material may be sequentially repeated for recoating to manufacture the noise filter array having a layered configuration. For example, a paste insulating material is preferably applied by printing, for example, to form the insulating layers, a paste conductive material is applied on the insulating layers to form the coil conductors5, the signal-side electrodes8, and the ground electrodes9, the via holes7are formed if needed, and a paste insulating material is applied on the coil conductors5, the signal-side electrodes8, and the ground electrodes9to form the insulating layers.

Although the filter elements F1to F4include the LC parallel resonant circuits PR1to PR4and the LC series resonant circuits SR1to SR4, respectively, in the noise filter arrays of the first to third preferred embodiments and the filter elements F1to F4include the LC filters in the noise filter arrays of the fourth and fifth preferred embodiments, the present invention is not restricted to these configurations. For example, preferred embodiments of the present invention are applicable to a noise filter array in which multiple π-shaped filter elements, T-shaped filter element, or LCR ladder filter elements, for example, each including a resistor R are provided in proximity in an array form to be integrally provided with one another.

The present invention is not restricted to the above-described preferred embodiments in other points and various applications and modifications may occur insofar as they are within the scope of the invention.

According to preferred embodiments of the present invention, it is possible to obtain a noise filter array having small variations in characteristics between multiple filter elements with a simple configuration.

Accordingly, it is possible to use the noise filter array of preferred embodiments of the present invention in a wide variety of applications, such as a noise filter to suppress the noise within each communication band in one mobile phone using multiple communication bands.