Monolithic LC resonator and monolithic LC filter

Abstract: Inductor patterns (24a, 24b) are electrically connected through long via-holes (23) formed in sheets (14, 15), respectively. The long via-holes are arranged along the right-, left-edges of the inductor patterns, respectively. The inductor patterns (24a, 24b) and the long via-holes (23) form an inductor (L1) having a tubular structure with a rectangular cross section and filled with an insulator therein. A capacitor pattern (25) is opposed to the open ends of the inductor patterns through the sheets, respectively, to form a capacitor (C1). That is, the capacitor pattern (25) is laminated inside of the tubular structure of the inductor. The capacitor and the inductor having the tubular structure form an LC parallel resonance circuit.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monolithic LC resonator and a monolithic LC filter, and more particularly to a monolithic LC resonator and a monolithic LC filter suitable for use in a high frequency wave band. 2. Description of the Related Art EP-A-926 933 and US-A-5 404 118 disclose LC filters with multilayered inductors. FIGS. 13 and 14 show an example of a conventional monolithic LC resonator. As shown in FIG. 13, an LC resonator 100 comprises a ceramic sheet 104 having a capacitor pattern 112 formed on the upper face thereof, a ceramic sheet 105 having an inductor pattern 111 formed on the upper face thereof, a ceramic sheet 106 having an input capacitor pattern 115 and an output capacitor pattern 116 formed on the upper face thereof, ceramic sheets 102 and 108 having shield electrodes 113 and 114 formed on the upper faces thereof, respectively, and so forth. The ceramic sheets 101 to 108 are stacked, and fired to form a laminate 110 shown in FIG. 14. On the laminate 110, an input terminal 121, an output terminal 122, and ground terminals 123 and 124 are formed. To the input terminal 121, the input capacitor pattern 115 is connected. To the output terminal 122, the output capacitor pattern 116 is connected. To the ground terminal 123, the lead-out portion of the inductor pattern 111, and one end of each shield electrode 113 and 114 is connected. To the ground terminal 124, the lead-out portion of the capacitor pattern 112, and the other ends of the shield electrodes 113 and 114 are connected. In the above-described LC resonator 100, an inductor comprising the inductor pattern 111, and a capacitor comprising the capacitor pattern 112 opposed to the open end of the inductor pattern 111 form an LC parallel resonance circuit. The LC parallel resonance circuit is electrically connected to the input terminal 121 via a coupling capacitor comprising the inductor pattern 111 and the input capacitor pattern 115 opposed to each other. Similarly, the LC parallel resonance circuit is electrically connected to the output terminal 122 via a coupling capacitor comprising the inductor pattern 111 and the output capacitor pattern 116 opposed to each other. The characteristics of the LC resonator depend on the Q value of the inductor in the resonance circuit. The Q value of the inductor is expressed as Q = 2πf 0 L/R, in which L is the inductance of the inductor, R is the resistance of the inductor, and f 0 is the resonance frequency. As seen in this formula, the Q value of the inductor can be increased by decreasing the resistance R of the inductor. The resistance R is inversely proportional to the cross section of the inductor pattern 111. Hence, the Q value can be increased by increasing the cross section S of the inductor pattern 111. However, in the case where the thickness of the inductor pattern 111 is increased in order to increase the cross section S of the inductor pattern 111, arises the problem that the internal strain of the laminate 110 is enlarged when the ceramic sheets 101 to 108 are integrally fired, resulting in delamination and so forth. Further, a magnetic field generated in the periphery of the inductor pattern 111 is concentrated on the edge of the inductor pattern 111, causing a large eddy current loss. Moreover, in the conventional LC resonator 100, the magnetic field generated in the periphery of the inductor pattern 111 is interrupted by the capacitor pattern 112. Thus, there arises the problem that the inductance L of the inductor is low. As described above, with the conventional LC resonator 100, it is difficult to attain a high Q value, since the resistance R of the inductor pattern 111 constituting the LC resonance circuit is large, and moreover, the inductance L is low. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a monolithic LC resonator and a monolithic LC filter each including an inductor having a high Q value. To achieve the above object, according to the present invention, a monolithic LC resonator includes a laminated body including an insulation layer, an inductor pattern, and a capacitor pattern laminated together, an LC resonance circuit in the laminated body, which includes an inductor defined by the inductor pattern, and a capacitor defined such that the capacitor pattern is opposed to the inductor pattern with the insulation layer being sandwiched between the capacitor pattern and the inductor pattern. In the monolithic LC resonator, the inductor of the LC resonance circuit has a tubular structure defined by at least two inductor patterns electrically connected through via-holes provided in the insulation layer, and the capacitor pattern is located inside of the tubular structure of the inductor. Further, according to the present invention, a monolithic LC filter includes a laminated body including plural insulation layers, plural inductor patterns, and plural capacitor patterns laminated together, plural LC resonators in the laminated body, which include the plural inductors defined by the inductor patterns, and the plural capacitors defined such that the capacitor patterns are opposed to the inductor patterns with the insulation layers being sandwiched between the capacitor patterns and the inductor patterns. In the monolithic LC filter, the inductor of each LC resonator has a tubular structure defined by at least two inductor patterns electrically connected through via-holes provided in the insulation layer, and at least one of the capacitor pattern and a coupling capacitor pattern for capacitance-coupling the LC resonators is located inside of the tubular structure of said inductor. The inductor has the plural tubular structure. The surface area of the inductor can be increased without increasing the thickness of the inductor pattern. In general, high frequency current has the properties that it flows so as to be concentrated onto the surface of a conductor, due to the skin effect. Accordingly, the whole of the inductor, of which the surface area is increased, can be effectively used as a path for high frequency current. Accordingly, the resistance of the inductor is decreased as compared with that of a conventional inductor, and the Q value of the inductor is enhanced. Further, with high frequency current flowing through the inductor, a magnetic field is generated in the outer periphery of tubular structure, not inside of the tubular structure. Thus, the capacitor pattern and the coupling capacitor pattern for capacitance-coupling the resonators, arranged inside of the inductor having the tubular structure, scarcely interrupt the magnetic field of the inductor. Further, since the inductor has the tubular structure, the concentration of a magnetic field, generated in the periphery of the inductor, onto the edges of the inductor pattern is reduced. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded perspective view showing the configuration of a monolithic LC resonator according to an embodiment of the present invention; FIG. 2 is a perspective view showing the appearance of the monolithic LC resonator of FIG. 1; FIG. 3 is a schematic cross sectional view of the monolithic LC resonator of FIG. 2; FIG. 4 is an electric equivalent circuit diagram of the monolithic LC resonator of FIG. 2; FIG. 5 is an exploded perspective view showing the configuration of a monolithic LC filter according to an embodiment of the present invention; FIG. 6 is a perspective view showing the appearance of the monolithic LC filter of FIG. 5; FIG. 7 is a schematic cross sectional view of the monolithic LC filter of FIG. 6; FIG. 8 is an electric equivalent circuit diagram of the monolithic LC filter of FIG. 6; FIG. 9 is an exploded perspective view showing the configuration of a monolithic LC filter according to another embodiment of the present invention; FIG. 10 is an electric equivalent circuit diagram of the monolithic LC filter of FIG. 8; FIG. 11 is a plan view showing a modification example of the via-hole; FIG. 12 is a plan view of a further modification example of the via-hole; FIG. 13 is an exploded perspective view of a conventional monolithic LC resonator; and FIG. 14 is a perspective view showing the appearance of the monolithic LC resonator of FIG. 13. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the monolithic LC resonator and the monolithic LC filter of the present invention will be described with reference to the accompanying drawings. [First Embodiment] FIG. 1 shows the configuration of a monolithic LC resonator 1. FIGS. 2 and 4 are a perspective appearance view of the LC resonator 1 and an electric equivalent circuit diagram thereof, respectively. The LC resonator 1 includes an LC parallel resonance circuit R1 including an inductor L1 and a capacitor C1. The LC parallel resonance circuit R1 is electrically connected between an input terminal 2 and an output terminal 3 via coupling capacitors Cs1 and Cs2, respectively. As shown in FIG. 1, the resonator 1 comprises insulation sheets 14 and 16 having inductor patterns 24a and 24b provided thereon, respectively, an insulation sheet 15 having a capacitor pattern 25 provided thereon, an insulation sheet 17 having an input lead-out pattern 22 and an output lead-out pattern 23 provided thereon, insulation sheets 12 and 19 having shield patterns 26 and 27 provided thereon, respectively, and so forth. The insulation sheets 11 to 19 are produced by kneading dielectric powder or magnetic powder together with a binder or the like, and forming into sheets, respectively. The patterns 22 to 27 are made of Ag, Pd, Cu, Ni, Au, Ag-Pd, or the like, and are formed by printing or the like, respectively. The linear inductor patterns 24a and 24b each having a constant width are provided in the centers of the sheets 14 and 16. One end of each linear inductor pattern 24a and 24b is exposed onto the front-side of the corresponding sheets 14 and 16 respectively, as viewed in FIG. 1. The inductor patterns 24a and 24b are electrically connected to each other through long via-holes 33 provided in the sheets 14 and 15. The long via-holes 33 are disposed along the right-, left-edges as viewed in FIG. 1 of the inductor patterns 24a and 24b. The inductor patterns 24a and 24b, and the long via-holes 33 define an inductor L1 having a tubular structure with a rectangular cross section and filled with an insulator therein, as shown in the cross sectional view of FIG. 3. The capacitor pattern 25 is provided in the center and rear as viewed in FIG. 1 of the sheet 15, and between the long via-holes 33 thereof. One end of the pattern 25 is exposed onto the rear side of the sheet 15. The capacitor pattern 25 is opposed to the open ends of the inductor patterns 24a and 24b via the sheets 14 and 15, respectively, to define a capacitor C1. That is, the capacitor pattern 25 is located inside of the tubular structure of the inductor L1. The capacitor C 1 and the tubular structure inductor L1 define the LC parallel resonance circuit R1. The input, output capacitor patterns 22 and 23 are provided on the right- and left-sides of the sheet 17, respectively. One end of the input capacitor pattern 22 is exposed onto the left-side of the sheet 17, and the other end of the input capacitor pattern 22 is opposed to the inductor pattern 24b with the sheet 16 being sandwiched between them to define the coupling capacitor Cs1. One end of the output capacitor pattern 23 is exposed onto the right-side of the sheet 17, and the other end of the output capacitor pattern 23 is opposed to the inductor pattern 24b with the sheet 16 being sandwiched between them to define the coupling capacitor Cs2. The shield patterns 26 and 27 each having a wide area are disposed so as to sandwich the patterns 22, 23, 24a, 24b, and 25. The shield patterns 26 and 27 are exposed to the front and rear sides of the sheets 12 and 19, respectively. The respective sheets 11 to 19 having the above-described configurations are sequentially stacked, joined under pressure, as shown in FIG. 1, and fired integrally to produce a laminated body 21 shown in FIG. 2. On the right-, left-end faces of the laminate 21, an input electrode 2 and an output electrode 3 are provided, respectively. Ground electrodes 4 and 5 are provided on the front-, back-faces of the laminated body 21. To the input electrode 2, the one end of the input capacitor pattern 22 is connected, and to the output electrode 3, the one end of the output capacitor pattern 23 is connected. To the ground electrode 4, one end of each shield pattern 26 and 27, and one end of each inductor pattern 24a and 24b are connected. To the ground electrode 5, the other ends of the shield patterns 26 and 27, and one end of the capacitor pattern 25 are connected. In the monolithic resonator 1, the inductor L1 has the tubular structure defined by the inductor patterns 24a and 24b, and the long via-holes 33. The surface area of the inductor L1 is increased without increasing the thickness of the inductor patterns 24a and 24b, and the long via-holes 33, as shown in FIG. 3. Generally, high frequency current has the properties that it flows so as to concentrate onto the surface of a conductor, due to the skin effect. Accordingly, the whole of the inductor L1 having the wider surface area can be advantageously used as a path for the high frequency current. Thus, the resistance of the inductor L1 is reduced as compared with that of a conventional inductor, so that the Q value of the inductor L1 can be enhanced. When high frequency current flows through the inductor L1, a magnetic field is generated in the outer periphery of the tubular structure, and is not generated inside of the tubular structure. Accordingly, the capacitor pattern 25 disposed inside of the inductor L1 having the tubular structure scarcely interrupts the magnetic field of the inductor L1. Further, the inductor L1 has the tubular structure, and thereby, the concentration of the magnetic field, generated in the periphery of the inductor L1, on the edges of the inductor patterns 24a and 24b are reduced. As' a result, a monolithic LC resonator 1 having a high Q value and excellent characteristics can be provided. [Second Embodiment] FIG. 5 shows the configuration of a monolithic LC filter 41. FIGS. 6 and 8 are a perspective appearance view and an electric equivalent circuit diagram of the LC filter 41. In the second embodiment, a band-pass filter as an example is described. Needless to say, the LC filter of the present invention may be a band-elimination filter or the like. The LC filter 41 is a three-stage LC band-pass filter. An LC resonator Q1 in the first (initial) stage, an LC resonator Q2 in the second stage, and an LC resonator Q3 in the third (final) stage are longitudinally connected via coupling capacitors Cs1 and Cs2, respectively. As shown in FIG. 5, the LC filter 41 comprises insulation sheets 54 and 56 having inductor patterns 61a, 62a, 63a; 61b, 62b, and 63b provided thereon, respectively, an insulation sheet 55 having capacitor patterns 65, 66, 67 and long via-holes 68 provided thereon, respectively, insulation sheets 53 and 57 having coupling capacitor patterns 76a, 77a; 76b, and 77b provided thereon, insulation sheets 51 and 59 having shield patterns 78a and 78b provided thereon respectively, and so forth. The linear inductor patterns 61a and 61b are provided in the left position on the left sides of the sheets 54 and 56, respectively. One end of each linear inductor pattern 61a and 61 b is exposed onto the front side of corresponding sheets 54 and 56, respectively. The inductor patterns 61 a and 61 b are electrically connected to each other through long via-holes 68 provided in the sheets 54 and 55. The long via-holes 68 are arranged to be connected to the right-, left-edges of the inductor pattern 61a and 61b, respectively. The inductor patterns 61a and 61b, and the long via-holes 68 define an inductor L1 having a tubular structure with a rectangular cross section and filled with an insulator therein as shown in the cross sectional view of FIG. 7. The input lead-out patterns 71a and 71b extended from the centers of the inductor patterns 61 a and 61 b are exposed onto the left-sides of the sheets 54 and 56, respectively. The linear inductor patterns 62a and 62b are formed in the centers of the sheets 54 and 56. One end of each linear inductor pattern 62a and 62b is exposed onto the front side of corresponding sheets 54 and 56, respectively. The inductor patterns 62a and 62b are electrically connected to each other through long via-holes 68 provided in the sheets 54 and 55, respectively. The inductor patterns 62a and 62b, and the long via-holes 68 define an inductor L2 having a tubular structure with a rectangular cross section, as shown in the cross sectional view of FIG. 7. The linear inductor patterns 63a and 63b are provided in the right position of the sheets 54 and 56, respectively. One end of each linear inductor pattern 63a and 63b is exposed onto the front side of corresponding sheets 54 and 56, respectively. The inductor patterns 63a and 63b are electrically connected to each other through long via-holes 68 provided in the sheets 54 and 55. The inductor patterns 63a and 63b, and the long via-holes 68 define an inductor L3 having a tubular structure with a rectangular cross section, as shown in FIG. 7. The output lead-out patterns 73a and 73b extended from the centers of the inductor patterns 63a and 63b are exposed onto the right-sides of the sheets 54 and 56. The capacitor patterns 65, 66, and 67 are provided in the right rear, the center rear, and the left rear positions of the sheet 55, respectively. Further, each of the capacitor patterns 65, 66, and 67 is located between long via-holes 68. One end of each capacitor pattern 65, 66, and 67 is exposed on the rear side of the sheet 55. The capacitor pattern 65 is opposed to the open ends of the respective inductor patterns 61a and 61 b via the sheets 54 and 55, to define a capacitor C1. Similarly, the capacitor patterns 66 and 67 are opposed to the open ends of the inductor patterns 62a and 62b and those of the inductor patterns 63a and 63b via sheets 54 and 55 to define capacitors C2 and C3, respectively. That is, the capacitor patterns 65, 66, and 67 are located inside of the tubular structures of the inductors L1, L2, and L3, respectively. The capacitor C1 and the tubular structure inductor L1 define an LC parallel resonance circuit, that is, define a first stage LC resonator Q1. The capacitor C2 and the tubular structure inductor L2 define an LC parallel resonance circuit, that is, define a second stage LC resonator Q2. The capacitor C3 and the tubular structure inductor L3 define an LC parallel resonance circuit, that is, define a third stage LC resonator Q3. The coupling capacitors 76a, 76b, 77a, and 77b are arranged in the rear of the sheets 53 and 57, respectively. The coupling capacitor patterns 76a and 76b are opposed to the inductor patterns 61a, 62a; 61b, and 62b to define a coupling capacitor Cs1. The coupling capacitor pattern 77a and 77b are opposed to the inductor patterns 62a, 63a; 62b, and 63b to define a coupling capacitor Cs2. The respective sheets 50 to 59 having the above-described configurations are sequentially stacked, as shown in FIG. 5, joined under pressure, and fired integrally to produce a laminated body 60 shown in FIG. 6. On the right-, left-end faces of the laminated body 60, an input electrode 42 and an output electrode 43 are formed, respectively. Ground electrodes 44 and 45 are formed on the front-, back-side faces of the laminate 60. To the input electrode 42, the input lead-out patterns 71 a and 71b are connected. To the output electrode 43, the output lead-out patterns 73a and 73b are connected. To the ground electrode 44, one end of each shield pattern 78a and 78b, and one end of each inductor pattern 61a to 63b are connected, respectively. To the ground electrode 45, the other ends of the shield patterns 78a and 78b, and one end of each capacitor pattern 65 to 67 are connected, respectively. In the monolithic LC filter 41, the inductors L1 to L3 of the respective LC resonators Q 1 to Q3 have a tubular structure. With this configuration, the skin effect for high frequency currents can be effectively utilized, and moreover, the capacitor patterns 65 to 67 scarcely interrupt magnetic fields generated by the inductors L1 to L3. Hence, the inductors L1 to L3 can attain a high Q value, respectively, and thereby, the LC filter 41 has excellent band-pass filter characteristics. [Third Embodiment] As shown in FIG. 9, a monolithic LC filter 81 according to the third embodiment is the same as the LC filter 41 of the second embodiment except that three insulation sheets 53a, 55a, and 57a are used instead of the insulation sheets 53, 55, and 57. On the upper surfaces of the insulation sheets 53a and 57a, capacitor patterns 65a to 67a, and 65b to 67b are provided, respectively. On the upper surface of the insulation sheet 55a, coupling capacitor patterns 76 and 77 are formed. Of the six long via-holes 68 provided in each of the sheets 54 and 55a, the inner four long via-holes 68 are shorter than the two outer long via-holes 68 to avoid short-circuiting with the coupling capacitor patterns 76 and 77. In this embodiment, parts corresponding to those of FIGS. 5 to 8 are designated by the same reference numerals, and the duplicated description is omitted. In the monolithic LC filter 81, the inductors L1 to L3 of the respective LC resonators Q1 to Q3 have a tubular structure. Accordingly, the skin effect for high frequency currents can be effectively utilized. As seen in FIG. 10, both ends of each of the coupling capacitor patterns 76 and 77 are arranged within the tubular structure of the respective inductors L1 to L3. With this configuration, the coupling capacitor patterns 76 and 77 are suppressed from causing the interruption of magnetic fields of the inductors L1 to L3. Thus, the inductors L1 to L3 can attain a high Q value, respectively. Accordingly, the LC filter 81 has excellent band-pass filter characteristics. [Other Embodiments] The present invention is not restricted to the above-described embodiments. Various changes and modifications can be made in the invention without departing from the scope thereof. For example, in the inductors according to the above embodiments, each tubular structure having a rectangular cross section is composed of two inductor patterns and two long via-holes. The number and shape of inductor patterns, and those of via-holes are optional. For example, in the first embodiment, as shown in FIG. 11, a long via-hole 33 may extend along the three sides of the inductor pattern 24a. Further, as shown in FIG. 12, plural via-holes 33 may be arranged along the three sides of the inductor pattern 24a. Moreover, the number of LC filter stages (the number of resonators) is optional. Further, in the above-described embodiments, the insulation sheets having the patterns provided thereon are stacked, and fired so as to be integrated. The present invention is not restricted to this example. As an insulation sheet, a sheet fired previously may be employed. Further, the following production method may be employed to define the LC resonator and the LC filter. After an insulation layer is formed from a paste insulation material by a printing method or the like, a paste conductive pattern material is coated on the surface of an insulation layer to form an optional pattern. Subsequently, the paste insulation material is coated so as to cover the pattern, whereby an insulation layer containing the pattern therein is formed. Similarly, the above-described coating is repeated thereon to define an LC resonator or an LC filter each having a lamination structure. As seen in the above-description, according to the present invention, the inductor defines the tubular structure. Accordingly, the surface area of the inductor can be increased without increasing the thickness of the inductor pattern. The whole of the inductor having the increased surface area can be effectively used as a path for high frequency current. Thus, the resistance of the inductor can be reduced as compared with that of a conventional inductor, and the Q value of the inductor can be enhanced. Further, with high frequency currents flowing through the inductor, magnetic fields are generated in the outer periphery of the tubular structure, not inside of the tubular structure. Accordingly, the capacitor pattern disposed inside of the inductor having the tubular structure and the coupling capacitor pattern for capacitance-coupling the resonators scarcely interrupt the magnetic field of the inductor. Further, since the inductor consists of the tubular structure, the concentration of a magnetic field, generated in the periphery of the inductor, onto the edges of the inductor pattern can be relaxed. As a result, a monolithic LC resonator and a monolithic LC filter each having a high Q value and good highfrequency characteristics can be provided.

Claims: A monolithic LC resonator (1) comprising: a laminated body (21) including an insulation layer (14), an inductor pattern (24a), and a capacitor pattern (25) laminated together, and an LC resonance circuit (R1) in the laminated body, which includes an inductor (L1) defined by the inductor pattern, and a capacitor (C1) defined such that the capacitor pattern is opposed to the inductor pattern with the insulation layer being sandwiched between the capacitor pattern and the inductor pattern, characterised in that said inductor (L1) of the LC resonance circuit has a tubular structure defined by at least two inductor patterns (24a, 24b) electrically connected through via-holes (33) provided in the insulation layer (14), and the capacitor pattern (25) is located inside of the tubular structure of said inductor. A monolithic LC filter (41) comprising: a laminated body (60) including plural insulation layers, plural inductor patterns (61a, 62a, 63a, 61b, 62b, 63b), and plural capacitor patterns (65, 66, 67) laminated together, and plural LC resonators (Q1, Q2, Q3) in the laminated body, including plural inductors (L1, L2, L3) defined by the inductor patterns, and plural capacitors (C1, C2, C3) defined such that the capacitor patterns are opposed to the inductor patterns with the insulation layers being sandwiched between the capacitor patterns and the inductor patterns, characterised in that the inductor (L1) of each LC resonator has a tubular structure defined by at least two inductor patterns (61a, 61b) electrically connected through via-holes (68) provided in the insulation layer (54, 55), and at least one of the capacitor patterns (65, 66, 67) and a coupling capacitor pattern for capacitance-coupling the LC resonators is located inside of the tubular structure of said inductor.

Inventors: KATO NOBORU, MATSUMURA SADAYUKI, NOMURA HIROKO, KATO, NOBORU, MATSUMURA, SADAYUKI, NOMURA, HIROKO
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 2000
Main classification: H01P1
IPC codes: H01F27, H01P1, H03H7, H01F17