Laminated filter, duplexer, and mobile communication apparatus using the same

[0002] The present invention relates to a laminated filter and a duplexer used mainly for a radio frequency device such as a portable telephone and the like, and a mobile communication apparatus using the same.

[0003] A laminated filter of the prior art generally comprises dielectric layers 1401a, 1401b, 1401c, 1401dand 1401e, resonator electrodes 1402aand 1402b, load capacitor electrodes 1403aand 1403b, an inter-resonator coupling capacitor electrode 1404, input/output coupling capacitor electrodes 1405aand 1405b, and shielding electrodes 1406aand 1406b, as shown in FIG. 14A.

[0004] Ends of the electrodes 1402aand 1402b, and the electrodes 1406aand 1406bare connected to a grounding terminal electrode 1408aprovided on a side surface of a dielectric, and, ends of the electrodes 1403aand 1403b, and the electrodes 1406aand 1406bare connected to a grounding terminal electrode 1408bon another side surface of the dielectric. The electrode 1405ais connected to an input/output terminal electrode 1407aprovided on a side surface of the dielectric, and the electrode 1405bis connected to another input/output terminal electrode 1407bprovided on another side surface of the dielectric. The electrodes 1408aand 1408bare grounded to constitute a structure.

[0005] Each of the electrodes in the above-described laminated filter functions as a stripline in a microwave band for which this laminated filter is used, since the electrodes are formed in the dielectric. Therefore, an equivalent circuit of this laminated filter is represented by FIG. 14B in the microwave band. In FIG. 14B, inductors 1613 and 1615, respectively, represent inductance components of the electrodes 1403aand 1403b. An inductor 1606 represents an inductance component of the electrode 1404. Furthermore, inductors 1603 and 1609 represent inductance components of the electrodes 1405aand 1405b, respectively.

[0006] In the above structure, the electrodes 1402aand 1402bact as quarter-wave resonators, since they are grounded at one end. Moreover, because the electrode 1404 and the electrodes 1402aand 1402b, as well as the electrodes 1405aand 1405band the electrodes 1402aand 1402bcompose parallel plate capacitors between them, they provide capacitive couplings between input/output terminals and the resonators, and also between the resonators. Furthermore, an attenuation pole (a frequency at which an impedance between the input/output terminals increases) can be formed in a transmission characteristic with an electromagnetic coupling obtained by adjusting widths of and a space between the electrodes 1402aand 1402b, and a capacitance obtained by adjusting the parallel plate capacitors formed between the electrodes 1404, and 1402aand 1402b.

[0007] As a result, the attenuation pole is formed at one side of a pass band 1701 in the transmission characteristic between the input/output terminals, as shown in FIG. 14C, thereby serving as a band-pass filter having an attenuation band 1702 in vicinity of the pass band 1701.

[0008] In addition, a duplexer of the prior art comprises a receiving filter 1501, a transmission filter 1502, and a phase-shifting circuit 1503, as shown in FIG. 15, and one end of the receiving filter 1501 serves as a receiving terminal 1510, and one end of the transmission filter 1502 as a transmission terminal 1511.

[0009] The phase-shifting circuit 1503 comprises an inductor 1504, another inductor 1505, a capacitor 1506, a capacitor 1507, and another capacitor 1508. In the duplexer, the capacitor 1506, the inductor 1504, and the capacitor 1507 are designed to become equivalent to a transmission line, which is approximately one quarter of a wavelength at a pass band frequency of the transmission filter 1502. The capacitor 1507, the inductor 1505, and the capacitor 1508 are also designed to become equivalent to a transmission line, which is approximately one quarter of a wavelength at a pass band frequency of the receiving filter 1501.

[0010] Of a transmission signal input from the transmission terminal 1511, only a signal component having the pass band frequency passes through the transmission filter 1502, and it is fed to the phase-shifting circuit 1503. The receiving filter 1501, as observed from a common terminal 1509, shows high impedance in this case, and thereby the transmission signal is output from the common terminal 1509 without flowing into a path toward the receiving filter 1501. On the other hand, a receiving signal input from the common terminal 1509 is fed to the phase-shifting circuit 1503. However, the signal is input only to the receiving filter 1501 without flowing into a path toward the transmission filter 1502, since an impedance as observed from the common terminal 1509 toward the transmission filter 1502 side is high in this case, and therefore the signal is output to the receiving terminal 1510 only after a signal component having the pass band frequency of the receiving filter 1501 passes through.

[0011] Consequently, the transmission signal input from the transmission terminal 1511 is output from the common terminal 1509 via the phase-shifting circuit 1503 without being influenced by the receiving filter 1501. The receiving signal input from the common terminal 1509 is also output to the receiving terminal 1510 via the phase-shifting circuit 1503 without being influenced by the transmission filter 1502. Hence, the device functions as a duplexer.

[0012] The laminated type filter of the prior art had a problem that it needs to increase a number of resonators in order to gain a magnitude of attenuation, thereby resulting in a large size and an increase of an insertion loss in the pass band.

[0013] Moreover, the duplexer of the prior art also had a problem in that it needs a phase-shifting circuit consisting of an inductor and a capacitor of chip components, thereby requiring a large area of mounting surface.

[0014] The present invention is intended to address the above problems, and it aims at realizing a laminated filter having a low insertion loss and a high attenuation with a simple structure, and a duplexer of a small size with a small number of components.

[0015] In a laminated filter having a plurality of resonator electrodes, an inter-resonator coupling capacitor electrode for coupling between adjacent resonators, and two input/output coupling capacitor electrodes for coupling between input/output terminals and resonator electrodes, the present invention is to provide a capacitor electrode for electrically connecting one side of the input/output terminals with a portion of the input/output coupling capacitor electrode, wherein the input/output coupling capacitor electrode and the capacitor electrode comprise a parallel circuit.

[0016] This composition forms a parallel resonance circuit in one of the input/output terminals, and provides an additional attenuation pole besides another attenuation pole formed with an electromagnetic coupling between the resonators and an inter-resonator capacitance, thereby realizing the laminated filter of a high magnitude of attenuation with the same shape as that of the prior art.

[0017] Moreover, in a laminated filter having a pass band in a first band, and an attenuation band in a second band, there is provided a parallel circuit as described above at one side of the input/output terminals, whereby an attenuation pole formed by the parallel circuit is set in the vicinity of the second band. Furthermore, in a laminated filter having an attenuation band in the first band and a pass band in a second band, there is provided a parallel circuit as described above at one side of the input/output terminals, whereby an attenuation pole formed by the parallel circuit is set in the vicinity of the first band. A duplexer of the present invention is composed by connecting these two laminated filters at the input/output terminals where the parallel circuits are provided, and using the connected point as a common terminal.

[0018] With the described structure, the duplexer can be realized without using a phase-shifting circuit, since majority of a signal component passing through either one of the laminated filters is input to the common terminal because the parallel circuit of the other laminated filter provides a high impedance.

[0019] FIG. 1A is an exploded perspective view of a laminated filter of a first exemplary embodiment of the present invention;

[0020] FIG. 1B is an equivalent circuit diagram of the laminated filter of the first exemplary embodiment of this invention, at frequencies in the vicinity of a pass band thereof;

[0021] FIG. 1C is a frequency characteristic of the laminated filter of the first exemplary embodiment of this invention;

[0022] FIG. 1D is an impedance characteristic of the laminated filter of the first exemplary embodiment of this invention;

[0023] FIG. 2 is an exploded perspective view depicting another structural example of the laminated filter of the first exemplary embodiment of this invention;

[0024] FIG. 3 is an exploded perspective view of yet another structural example of the laminated filter of the first exemplary embodiment of this invention;

[0025] FIG. 4 is an exploded perspective view of a laminated filter of a second exemplary embodiment of this invention;

[0026] FIG. 5 is an exploded perspective view of another structural example of the laminated filter of the second exemplary embodiment of this invention;

[0027] FIG. 6 is an exploded perspective view of still another structural example of the laminated filter of the second exemplary embodiment of this invention;

[0028] FIG. 7 is an exploded perspective view of a laminated filter of a third exemplary embodiment of this invention;

[0029] FIG. 8 is an exploded perspective view of another structural example of the laminated filter of the third exemplary embodiment of this invention;

[0030] FIG. 9 is an exploded perspective view of still another structural example of the laminated filter of the third exemplary embodiment of this invention;

[0031] FIG. 10 is an exploded perspective view of a laminated filter of a fourth exemplary embodiment of this invention;

[0032] FIG. 11 is an exploded perspective view of another structural example of the laminated filter of the fourth exemplary embodiment of this invention;

[0033] FIG. 12 is an exploded perspective view of still another structural example of the laminated filter of the fourth exemplary embodiment of this invention;

[0034] FIG. 13 is an exploded perspective view of a duplexer of a fifth exemplary embodiment of this invention;

[0035] FIG. 14A is an exploded perspective view of a laminated filter of the prior art;

[0036] FIG. 14B is an equivalent circuit diagram of the laminated filter of the prior art, in vicinity of a pass band thereof;

[0037] FIG. 14C is a frequency characteristic of the laminated filter of the prior art; and

[0038] FIG. 15 is circuit diagram of a duplexer of the prior art.

[0039] Exemplary embodiments of the present invention will be described hereinafter with reference to FIG. 1 through FIG. 13.

[0040] FIG. 1A is an exploded perspective view of a laminated filter of a first exemplary embodiment of the present invention.

[0041] In FIG. 1A, the laminated filter comprises: dielectric layers 101a, 101b, 101c, 101d, 10le and 101f; resonator electrodes 102aand 102b; load capacitor electrodes 103aand 103b; an inter-resonator coupling capacitor electrode 104; input/output coupling capacitor electrodes 105aand 105b; a capacitor electrode 106; and shielding electrodes 107aand 107b, and it has an integrated configuration. One ends of the electrodes 102aand 102b, and the electrodes 107aand 107bare connected to a grounding terminal electrode 109aprovided on a side surface of a dielectric. One ends of the electrodes 103aand 103b, and the electrodes 107aand 107bare connected to another grounding terminal electrode 109bprovided on another side surface of the dielectric. One ends of the electrode 105aand the electrode 106 are connected to an input/output terminal electrode 108aprovided on one side surface of the dielectric, the electrode 105bis connected to another input/output terminal electrode 108bprovided on another side surface of the dielectric, and the grounding terminal electrodes 109aand 109bare grounded, to constitute a structure.

[0042] The operation of the laminated filter constructed above will be described below.

[0043] Each of the electrodes in the above laminated filter functions as a stripline in a microwave band for which this laminated filter is used, since they are formed in the dielectric. Therefore, an equivalent circuit of this laminated filter can be shown as described in FIG. 1B in the microwave frequency band. In FIG. 1B, inductors 1813 and 1815, respectively, represent inductance components of the electrodes 103aand 103b. An inductor 1806 represents an inductance component of the electrode 104. Furthermore, inductors 1803 and 1809 represent inductance components of the electrodes 105aand 105b, respectively.

[0044] In the above structure, the electrodes 102aand 102bfunction as quarter-wave resonators, since they are grounded via the grounding terminal electrode 109a.

[0045] The electrodes 103aand 103btogether with the electrodes 102aand 102bcomprise parallel plate capacitors via the dielectric layer 101d, since they are arranged in such a manner that portions of them overlap with open ends of their respective electrodes 102aand 102b. These capacitors function as loading capacitors for adjusting resonance frequencies of resonators, since the electrodes 103aand 103bare grounded via the grounding terminal electrode 109b.

[0046] The electrode 104 comprise parallel plate capacitors with the electrodes 102aand 102bvia the dielectric layer 101d, since it is arranged in an overlapping position with the electrodes 102aand 102b. These capacitors function as inter-resonator coupling capacitors.

[0047] The electrodes 105aand 105btogether with the electrodes 102aand 102bcomprise parallel plate capacitors via the dielectric layer 101d, since they are arranged in a manner that portions of them overlap with portions of their respective electrodes 102aand 102b. These capacitors function as input/output coupling capacitors.

[0048] As described above, this laminated body constitutes a tri-plate structure sandwiched between the shielding electrodes on top and bottom, and it functions as a two resonator mono-polar type band pass filter (Band Pass Filter, which will be hereinafter referred to as “BPF”) of a capacitive coupling type, having one attenuation pole formed by an electromagnetic coupling between the two resonators and the inter-resonator coupling capacitor.

[0049] Further, the capacitor electrode 106 formed on an upper surface the dielectric layer 101cis so arranged that one end of it is connected to the input/output terminal electrode 108a, and the other end overlaps with a portion of the electrode 105a. With this structure, the electrode 105aand the electrode 106 form a parallel plate capacitor via the dielectric layer 101c, and this capacitor comprise a parallel circuit with the electrode 105a. The electrode 106 has an inductance component 1810, and the parallel plate capacitor is represented by a capacitor 1811 in FIG. 1B.

[0050] If an inductance “L” and a capacitance “C” are adjusted to satisfy the following simultaneous equations, the parallel circuit can possess a resonance point at a frequency of “ω”, without interfering with an impedance of the original BPF in vicinity of its pass band:

[0051] 1/(j·ω₀·L₀)=j·ω₀·C+1/(j·₀·L) ω·²=1/(L·C)  (equations 1)

[0052] where L0 represents an inductance of the electrode 105abefore the electrode 106 is inserted, ω0 a pass band frequency of the BPF, L an inductance of the electrode 105aafter the electrode 106 is inserted, C a capacitance of the parallel plate capacitor formed between the electrode 105aand the electrode 106, and ω a frequency of the newly formed attenuation pole.

[0053] Accordingly, the laminated filter has a parallel resonance circuit in the input/output terminal, thereby gaining a passing characteristic as shown in FIG. 1C, wherein one attenuation pole is newly added while maintaining the original filtering property.

[0054] According to the above-described structure, this exemplary embodiment having the same shape as that of the prior art, functions as a BPF that can achieve a high magnitude of attenuation.

[0055] In this exemplary embodiment, the capacitor electrode 106 is arranged in such a manner that one end of it is connected to the input/output terminal electrode and the other end overlaps with the input/output coupling capacitor electrode. However, a parallel plate capacitor may be formed by branching off a transmission line electrode 210 from the electrode 105a, as shown in FIG. 2, and arranging it in a manner that a portion of it overlaps with a capacitor electrode 211 connecting the electrode 108a. Accuracy in designing the BPF and the newly formed attenuation pole can be improved in this case, since it reduces a disorder in impedance of the input/output coupling capacitor electrode.

[0056] In addition, another electrode 106 may be formed on a rear surface of the dielectric layer 101dso as to sandwich the electrode 105aor the electrode 210 between a top and a bottom of it, by taking advantage of the laminated structure of this exemplary embodiment. This improves flexibility in designing the parallel resonance circuit, since it can increase a capacitance of the parallel plate capacitor with a same area.

[0057] In the BPF of this exemplary embodiment, the attenuation pole by the parallel circuit can be set anywhere near a first band, when the first band and a second band are designed respectively as an attenuation band and a pass band. A laminated type BPF of the prior art structure has an attenuation pole formed by an electromagnetic coupling between resonators and an inter-resonator coupling capacitor. It therefore has one attenuation pole in the attenuation band, if it employs two resonators. Since there can be composed two attenuation poles in the case of this exemplary embodiment, it can achieve not only an increase in magnitude of attenuation in the attenuation band, but also an expansion in bandwidth of the attenuation band at the same time.

[0058] Although the parallel circuit is provided in this exemplary embodiment only in a portion formed by one of the input/output coupling capacitor electrodes, 105a, and the electrode 106, another parallel circuit may be formed with the other input/output coupling capacitor electrode 105bby providing another electrode 312, as shown in FIG. 3. In this case, there is an effect of providing two additional attenuation poles. Because these two attenuation poles can be provided independently with respect to each other, various designs can be made possible such as setting them at both sides of the pass band, converging them in the attenuation band, and the like.

[0059] In this exemplary embodiment, although there is no other end surface electrode on the side surfaces where the electrodes 108aand 108bare formed, additional grounding terminal electrodes may be provided at both sides of the electrodes 108aand 108b, to make connections with the upper and the lower shielding electrodes for grounding. This improves the grounding of the laminated body, and improves the BPF characteristic.

[0060] Although there are many ways and methods of forming individual electrodes in the present exemplary embodiment, the above effectiveness of this invention is not influenced by the forming methods. Likewise, there are various kinds of materials adaptable for the electrodes and the dielectric bodies of this exemplary embodiment, and the effectiveness of this invention is not determined by any particular material.

[0061] The laminated filter of the present invention, if employed in a mobile communication apparatus, can suppress a large part of spurious signals while maintaining the same size, and thereby a mobile communication apparatus of superior performance can be constructed.

[0062] FIG. 4 is an exploded perspective view of a laminated filter of a second exemplary embodiment of the present invention.

[0063] In FIG. 4, the laminated filter having an integrated configuration comprises: dielectric layers 401a, 401b, 401c, 401d, 401eand 401f; resonator electrodes 402aand 402b; input-to-output terminal transmission line electrodes 403a, 403band 403c; filtering capacitor electrodes 404a, and 404b; a capacitor electrode 405; and shielding electrodes 406aand 406b. One ends of the electrodes 402aand 402b, and the electrodes 406aand 406bare connected to a grounding terminal electrode 408aprovided on a side surface of a dielectric. The other ends of the electrodes 402aand 402bare connected, respectively, to frequency adjusting terminal electrodes 409aand 409bprovided on a side surface of the dielectric. One end of the electrode 403ais connected to an input/output terminal electrode 407aprovided on a side surface of the dielectric. The other end of the electrode 403aand one end of the electrode 403bare connected to the electrode 404a. The other end of the electrode 403band one end of the electrode 403care connected to the electrode 404b. The other end of the electrode 403cand one end of the electrode 405 are connected to an electrode 407b. The electrodes 406aand 406bare connected to another electrode 408b, and these grounding terminal electrodes 408aand 408bare grounded, to comprise a filter structure.

[0064] The operation of the laminated filter constructed above will be described below.

[0065] The electrodes 402aand 402bact as quarter-wave resonators, since they are grounded via the electrode 408a. The electrodes 404aand 404bare arranged in such positions as to overlap with parts of the electrodes 402aand 402b, respectively, to form parallel plate capacitors with the electrodes 402aand 402bvia the dielectric layer 401d. Therefore, the two resonators are in series connection to the transmission lines between the input/output terminals via the capacitors. As a result, the filter of this exemplary embodiment functions as a two resonator notch filter (Band Elimination Filter, hereinafter referred to as “BEF”) which provides a high magnitude of attenuation at resonance frequencies of the series resonance circuits comprising the electrodes 402aand 402b.

[0066] Moreover, the electrodes 403a, 403band 403c, i.e. transmission lines between the input/output terminals, function as coupling elements between two resonators, and to external distributed constant lines, by way of adjusting lengths and line widths of the electrodes. Accordingly, this laminated body constitutes a tri-plate structure sandwiched between the shielding electrodes on top and bottom, and the two resonators are connected in parallel via the transmission line, thereby functioning as a two resonator BEF having the electrodes 407aand 407bserving as terminals.

[0067] Further, the capacitor electrode 405 formed on an upper surface of the dielectric layer 401cis so arranged that one end of it is connected to the electrode 407b, and the other end overlaps with a portion of the electrode 403c. With this structure, the electrode 403cand the electrode 405 form a parallel plate capacitor via the dielectric layer 401c, to comprise a parallel circuit between the electrode 405 and the electrode 403c.

[0068] If an inductance “L” and a capacitance “C” are adjusted to satisfy the following simultaneous equations, the parallel circuit can possess a resonance point at a frequency of “ω”, without interfering with an impedance of the original BEF in vicinity of its pass band:

[0069] 1/(j·ω₀·L₀)=j·₀C+1/(j·ω₀·L) ω²=1/(L·C)  (equations 2)

[0070] where L0 represents an inductance of the electrode 403cbefore the electrode 405 is inserted, ω0 a pass band frequency of the BEF, L an inductance of the electrode 403cafter the electrode 405 is inserted, C a capacitance of the parallel plate capacitor formed between the electrode 403cand the electrode 405, and ω a frequency of a newly formed attenuation pole.

[0071] Accordingly, the laminated filter has a parallel resonance circuit between the input/output terminals, thereby gaining a passing characteristic having a new addition of attenuation pole while also maintaining the original filtering property.

[0072] According to the above-described structure, this exemplary embodiment having the same shape as that of the prior art, functions as a BEF that can achieve a high magnitude of attenuation.

[0073] In this exemplary embodiment, the capacitor electrode 405 is arranged in such a manner that one end of it is connected to the electrode 407band the other end overlaps with the electrode 403c. However, a parallel plate capacitor may be formed by branching off a transmission line electrode 510 from the electrode 403c, as shown in FIG. 5, and arranging it in a manner that a portion of it overlaps with an electrode 511. Accuracy in designing the BEF and the newly formed attenuation pole can be improved in this case, since it reduces a disorder in impedance of the electrode 403c.

[0074] In addition, two capacitor electrodes may be formed to sandwich the electrode 403cor the electrode 510 between a top and a bottom of it, in the like manner as the first exemplary embodiment. This improves flexibility in designing the parallel resonance circuit, since it can increase a capacitance of the parallel plate capacitor with a same area.

[0075] In the BEF of this exemplary embodiment, the attenuation pole by the parallel circuit may be set anywhere near a second band, when a first band and the second band are designed respectively as a pass band and an attenuation band. A laminated type BEF of the prior art can have attenuation poles formed in number equal to a number of the resonators. It therefore has two attenuation poles in the attenuation band, if it employs two resonators. However, there can be three attenuation poles in the case of this exemplary embodiment, and it can thereby achieve an increase in magnitude of attenuation and also an expansion in bandwidth of the attenuation band at the same time.

[0076] In this exemplary embodiment, although the parallel circuit is formed only in one of the electrodes, 403c, another parallel circuit may include the other electrode 403a, as shown in FIG. 6. In this case, there is an effect of providing two additional attenuation poles. Because these two attenuation poles are provided independently with respect to each other, various designs can be made possible such as setting them at both sides of the pass band, converging them in the attenuation band, and so on.

[0077] In this exemplary embodiment, although there is no other end surface electrode on the side surfaces where the input/output terminal electrodes are formed, additional grounding terminal electrodes may be provided at both sides of the terminal electrodes, to make connections with the upper and lower shielding electrodes for grounding. This enhances the grounding of the laminated body, and improves the BEF characteristic.

[0078] FIG. 7 is an exploded perspective view of a laminated filter of a third exemplary embodiment of the present invention.

[0079] In FIG. 7, the laminated filter having an integrated configuration comprises: dielectric layers 701a, 701b, 701c, 701d, 701eand 701f; capacitor electrodes 702aand 702b; transmission line electrodes 703aand 703b; a capacitor electrode 704; and shielding electrodes 705aand 705b. One end of the electrode 702aand the electrodes 705aand 705bare connected to a grounding terminal electrode 707aprovided on a side surface of a dielectric. One end of the electrode 703ais connected to an input/output terminal electrode 706aprovided on a side surface of the dielectric. The other end of the electrode 703aand one end of the electrodes 703bare connected to one end of the electrode 702b. The other end of the electrode 703band one end of the electrode 704 are connected to an input/output terminal electrode 706bprovided on another side surface of the dielectric. The electrodes 705aand 705bare connected with an electrode 707b, and the electrodes 707aand 707bare grounded, to constitute a filter structure.

[0080] The laminated filter constructed as above operates in a manner, which will be described hereinafter.

[0081] The electrodes 702aand 702bare arranged in a manner that portions of them overlap with each other, to form a parallel plate capacitor via the dielectric layer 701d. Also, the electrodes 703aand 703bfunction as inductors between the input/output terminals, and the above capacitor functions as a capacitor disposed between transmission lines connecting the input/output terminals and a ground. Therefore, this laminated body comprises a tri-plate structure sandwiched between the shielding electrodes on top and bottom, and functions as a T-type three element low pass filter (Low Pass Filter, hereinafter referred to as “LPF”) having the electrodes 706aand 706bserving as terminals.

[0082] Further, the capacitor electrode 704 formed on an upper surface of the dielectric layer 701cis arranged so that one end of it is connected to the electrode 706b, and the other end overlaps with a portion of the electrode 703b. With this structure, the electrode 703band the electrode 704 form a parallel plate capacitor via the dielectric layer 701c, to comprise a parallel circuit between the electrode 704 and the electrode 703b. If an inductance “L” and a capacitance “C” are adjusted to satisfy the following simultaneous equations, the parallel circuit can possess a resonance point at a frequency of “ω”, without interfering with an impedance of the original LPF in vicinity of its pass band:

[0083] 1/(j·ω₀·L₀)=j·ω₀·C+1/(j·ω₀·L) ω·²=1/(L·C)  (equations 3)

[0084] where L0 represents an inductance of the electrode 703bbefore the electrode 704 is inserted, ω0 a pass band frequency of the LPF, L an inductance of the electrode 703bafter the electrode 704 is inserted, C a capacitance of the capacitor formed between the electrode 703band the electrode 704, and ω a frequency of a newly formed attenuation pole.

[0085] Accordingly, this laminated body comprises the tri-plate structure sandwiched between the shielding electrodes on top and bottom, thereby gaining a passing characteristic having a new addition of attenuation pole while also maintaining the original filtering property.

[0086] According to the above-described structure, this exemplary embodiment having the same shape as that of the prior art, functions as an LPF that can achieve a high magnitude of attenuation.

[0087] In this exemplary embodiment, the capacitor electrode 704 is arranged in such a manner that one end of it is connected to the electrode 706band the other end overlaps with the electrode 703b. However, a parallel plate capacitor may be formed by branching off a transmission line electrode 808 from the electrode 703b, as shown in FIG. 8, and arranging it in a manner that a portion of it overlaps with a capacitor electrode 809 connected to the input/output terminal electrode 706b. Accuracy in designing the LPF and the newly formed attenuation pole can be improved in this case, since it reduces a disorder in impedance of the filtering transmission line electrodes for the filter.

[0088] In addition, two capacitor electrodes may be formed to sandwich the electrode 703bor the electrode 808 between a top and a bottom thereof, in the like manner as the first exemplary embodiment. This improves flexibility in designing the parallel resonance circuit, since it can increase a capacitance of the parallel plate capacitor with a same area.

[0089] In this exemplary embodiment, although the parallel circuit is formed only in one of the electrodes, 703b, another parallel circuit may include the other electrode 703a, as shown in FIG. 9. In this case, there is an effect of providing two additional attenuation poles. Because these two attenuation poles are provided independently with respect to each other, various settings can be made possible.

[0090] In this exemplary embodiment, although there is no other end surface electrode on the side surfaces where the input/output terminal electrodes are formed, additional grounding terminal electrodes may be provided at both sides of the terminal electrodes, to make connections with the upper and lower shielding electrodes for grounding. This enhances the grounding of the laminated body, and improves the LPF characteristic.

[0091] FIG. 10 is an exploded perspective view of a laminated filter of a fourth exemplary embodiment of the present invention.

[0092] In FIG. 10, the laminated filter having an integrated configuration comprises: dielectric layers 1001a, 1001b, 1001c, 1001d, 100le and 1001f; input/output terminal transmission line electrodes 1002a, 1002band 1002c; a filtering transmission line electrode 1003; a capacitor electrode 1004; and shielding electrodes 1005aand 1005b. The electrodes 1002aand 1002care formed on an upper surface of the dielectric layer 1001d. The electrodes 1002band 1003 are formed on an upper surface of the dielectric layer 1001e. One end of the electrode 1002aand one end of the electrode 1004 are connected to an input/output terminal electrode 1006aprovided on a side surface of a dielectric. The other end of the electrode 1002aand one end of the electrode 1002bare so arranged that portions of them overlap with each other via the dielectric layer 1001d. The other end of the electrode 1002band one end of the electrode 1002care also arranged so that portions of them overlap with each other via the dielectric layer 1001d. The other end of the electrode 1002cis connected to another input/output terminal electrode 1006bprovided on a side surface of the dielectric. The transmission line electrode 1003 branched off from the electrode 1002b, the electrodes 1005aand 1005bare connected to a grounding terminal electrode 1007aprovided on a side surface of the dielectric. The grounding electrodes 1007aand 1007bare grounded, to comprise a filter structure.

[0093] The operation of the laminated filter constructed above will be described below.

[0094] The electrodes 1002aand 1002bare arranged in a manner that portions of them overlap with each other, to form a parallel plate capacitor via the dielectric layer 1Old. The electrodes 1002band 1002care also arranged in a manner that portions of them overlap with each other, to form another parallel plate capacitor via the dielectric layer 1001d. Therefore, these two capacitors are in series connection between the input/output terminals. In addition, the electrode 1003 functions as an inductor between a connecting point of the two capacitors and the ground. Thus, the laminated body of this embodiment comprises a tri-plate structure sandwiched between the shielding electrodes on top and bottom, and it functions as a T-type three element high pass filter (High Pass Filter, which will be hereinafter referred to as “HPF”) having the electrodes 1006aand 1006bserving as terminals.

[0095] The capacitor electrode 1004 formed on an upper surface of the dielectric layer 1001cis arranged so that one end of it is connected to the electrode 1006a, and the other end overlaps with a portion of the electrode 1002a. With this structure, the electrode 1002aand the electrode 1004 form a capacitor via the dielectric layer 1001c, and this capacitor comprises a parallel circuit with the electrode 1002a. If an inductance “L” and a capacitance “C” are adjusted to satisfy the following simultaneous equations, the parallel circuit can possess a resonance point at a frequency of “ω”, without interfering with an impedance of the original HPF in vicinity of its pass band:

[0096] 1/(j·ω₀·L₀)=j·ω₀·C+1/(j·ω₀·L) ω·²=1/(L·C)  (equations 4)

[0097] where L0 represents an inductance of the electrode 1002abefore the electrode 1004 is inserted, ω a pass band frequency of the HPF, L an inductance of the electrode 1002aafter the electrode 1004 is inserted, C a capacitance of the capacitor formed between the electrode 1002aand the electrode 1004, and w a frequency of a newly formed attenuation pole.

[0098] Accordingly, the filter of this exemplary embodiment has a parallel resonance circuit in the input/output terminal, thereby gaining a passing characteristic having a new addition of attenuation pole while also maintaining the original filtering property. According to the above-described structure, this exemplary embodiment having the same shape as that of the prior art, functions as an HPF that can achieve a high magnitude of attenuation.

[0099] In this exemplary embodiment, the electrode 1004 is arranged in such a manner that one end of it is connected to the electrode 1006aand the other end overlaps with the electrode 1002a. However, a capacitor may be formed by branching off a transmission line electrode 1108 from the electrode 1002a, as shown in FIG. 11, and arranging it in a manner that a portion of it overlaps with a capacitor electrode 1109 connected to the electrode 1006a. Accuracy in designing the HPF and the newly formed attenuation pole can be improved in this case, since it reduces a disorder in impedance of the electrode 1002a.

[0100] In addition, two capacitor electrodes may be formed to sandwich the electrode 1002aor the electrode 1108 between a top and a bottom of it, in the like manner as the first exemplary embodiment. This improves flexibility in designing the parallel resonance circuit, since it can increase a capacitance of the parallel plate capacitor with a same surface area.

[0101] In this exemplary embodiment, although the parallel circuit is formed only with the electrode 1002aconnecting with one of the electrodes, 1006a, another parallel circuit may include the electrode 1002cconnecting with the other electrode 1006b, as shown in FIG. 12. In this case, there is an effect of providing two additional attenuation poles. Because these two attenuation poles are provided independently with respect to each other, various designs can be made possible.

[0102] In this exemplary embodiment, although there is no other end surface electrode on the side surfaces where the input/output terminal electrodes are formed, additional grounding terminal electrodes may be provided at both sides of the terminal electrodes, to make connections with the upper and lower shielding electrodes for grounding. This enhances the grounding of the laminated body, and improves the HPF characteristic.

[0103] FIG. 13 is an exploded perspective view of a duplexer of a fifth exemplary embodiment of the present invention.

[0104] In FIG. 13, the duplexer having an integrated configuration comprises: dielectric layers 1301a, 1301b, 1301c, 1301d, 1301eand 1301f; resonator electrodes 1302a, 1302b, 1302cand 1302d; input-to-output transmission line electrodes 1303a, 1303band 1303c; filtering capacitor electrodes 1304aand 1304b; a transmission line electrode 1305; load capacitor electrodes 1306aand 1306b; an inter-resonator coupling capacitor electrode 1307; input/output coupling capacitor electrodes 1308aand 1308b; a transmission line electrode 1309; a capacitor electrode 1310, another capacitor electrode 1311; and shielding electrodes 1312aand 1312b. One ends of the electrodes 1302a, 1302b, 1302cand 1302d, and the electrodes 1312aand 1312bare connected to a grounding terminal electrode 1314aprovided on a side surface of a dielectric. The other ends of the electrodes 1302aand 1302bare connected respectively to frequency adjusting terminal electrodes 1315aand 1315bprovided on another side surface of the dielectric. One ends of the electrodes 1306aand 1306b, and the electrodes 1312aand 1312bare connected to another grounding terminal electrode 1314cprovided on another side surface of the dielectric. One end of the electrode 1303ais connected to an input/output terminal electrode 1313aprovided on a side surface of the dielectric, and the other end of the electrode 1303ais connected to one end of the electrode 1303band the electrode 1304a. The other end of the electrode 1303band one end of the electrode 1303care connected to the electrode 1304b. The other end of the electrode 1303c, one end of the electrode 1310, one end of the electrode 1308a, and one end of the electrode 1311 are connected to a common terminal electrode 1316 provided on a side surface of the dielectric. One end of the electrode 1308bis connected to an electrode 1313b. The electrodes 1312aand 1312bare connected to an electrode 1314b, and the electrodes 1314a, 1314b, and 1314care grounded.

[0105] The operation of the duplexer constructed above will be described below.

[0106] The electrodes 1302aand 1302bact as quarter-wave resonators, since they are grounded via the electrode 1314a. The electrodes 1304aand 1304bare arranged in positions to overlap respectively with portions of the electrodes 1302aand 1302b, to form capacitors via the dielectric layer 1301d. Therefore, the two resonators are in series connection to the input-to-output terminal transmission lines 1303a, 1303band 1303cvia the capacitors, and thereby they function as two sets of BEF which provide a high magnitude of attenuation at resonance frequencies of the series resonance circuits comprising the electrodes 1302aand 1302b. Furthermore, the transmission lines 1303a, 1303band 1303cfunction as coupling elements between two resonators, and also with an external distributed constant lines, by way of adjusting lengths and line widths of the transmission lines 1303a, 1303band 1303c. Accordingly, the two resonators are in parallel connection via the transmission lines, thereby functioning as a two resonator BEF having the electrode 1313aand the common terminal electrode 1316 serving as input/output terminals.

[0107] In addition, the electrodes 1302cand 1302dact as quarter-wave resonators, as they are grounded via the electrode 1314a. The electrodes 1306aand 1306bcomprise capacitors via the dielectric layer 1301d, since they are arranged in such positions that portions of them overlap with open ends of the respective electrodes 1302cand 1302d. These capacitors function as loading capacitors for adjusting resonance frequencies of the resonators, since the electrodes 1306aand 1306bare grounded via the grounding terminal electrode 1314c. The electrode 1307 comprises capacitors with the electrodes 1302cand 1302dvia the dielectric layer 1301d, since it is arranged in a position that portions of it overlap with the electrodes 1302cand 1302d. These two capacitors function as inter-resonator coupling capacitors. The electrodes 1308aand 1308bcomprise capacitors via the dielectric layer 1301d, since they are arranged in such positions that portions of them overlap with potions of the respective electrodes 1302cand 1302d, and these capacitors function as input/output coupling capacitors. Accordingly, the laminated body of this exemplary embodiment comprises a tri-plate structure sandwiched between the shielding electrodes on top and bottom, and it functions as a two resonator mono-polar type BPF of capacitive coupling type having one attenuation pole formed by an electromagnetic coupling between the two resonators and the inter-resonator coupling capacitors.

[0108] Furthermore, the transmission line electrode 1305 is branched off from the electrode 1303c, and it is arranged so that a portion of it overlaps with the electrode 1310. With this arrangement, the electrode 1305 and the electrode 1310 form a capacitor via the dielectric layer 1301 c, and constitute a parallel circuit with the electrode 1303c.

[0109] In addition, the electrode 1309 is also branched off from the electrode 1308a, and it is arranged so that a portion of it overlaps with the electrode 1311. With this arrangement, the electrode 1309 and the electrode 1311 form a capacitor via the dielectric layer 1301c, and comprise a parallel circuit with the electrode 1308a.

[0110] In this embodiment, each of the electrodes of this laminated filter is designed in such a manner that a pass band and an attenuation band of the above-said BEF, respectively, become a first band and a second band, and an attenuation band and a pass band of the above-said BPF respectively become the first band and the second band. An inductance “Lt” and a capacitance “Ct” are further adjusted so as to satisfy the following simultaneous equations:

[0111] 1/(j·ω1·Lt0)=j·ω1·Ct+1/(j·ω1·Lt) ω₂²=1/(Lt·Ct)  (equations 5)

[0112] where ω1 represents a frequency in the first band, ω₂a frequency in the second band, Lt0 an inductance of the electrode 1303cbefore the electrodes 1305 and 1310 are inserted, Lt an inductance of the electrode 1303cafter the electrodes 1305 and 1310 are inserted, and Ct a capacitance of the capacitor formed between the electrodes 1305 and 1310.

[0113] In this embodiment, the BEF shows a passing characteristic having an additional attenuation pole in the vicinity of the second band while maintaining its original filter characteristic, since it has a parallel resonance circuit between the input/output terminals because it is provided with a resonance point in the second band without causing a disorder to an impedance in the first band.

[0114] In addition, an inductance “Lr” and a capacitance “Cr” are adjusted to satisfy the following simultaneous equations:

[0115] 1/(j·ω2·Lr0)=j·ω2·Cr+1/(j·ω2·Lr) ω₁²=1/(Lr·Cr)  (equation 6)

[0116] where Lr0 represents an inductance of the electrode 1308cbefore the electrodes 1309 and 1311 are inserted, Lr an inductance of the electrode 1308cafter the electrodes 1309 and 1311 are inserted, and Cr a capacitance of the parallel plate capacitor formed between the electrodes 1309 and 1311. With this structure, the BPF shows a passing characteristic having an additional attenuation pole near the first band while maintaining its original filter characteristic, since it has a parallel resonance circuit between the input/output terminals because it is provided with a resonance point in the first band without causing a disorder to an impedance in the second band.

[0117] When electrodes are individually set under the above conditions, a signal input to the electrode 1313ais routed through the BEF, but only a signal component of the first band passes through, and is output from the electrode 1316. However, the signal does not flow from the electrode 1316 toward the BPF side, since the parallel circuit formed by the electrode 1308a, the electrode 1309, and the electrode 1311 provides a high impedance in the first band in light of the radio frequencies. Also, a signal in the second band input to the electrode 1316 does not flow toward the BEF side, since the parallel circuit formed by the electrode 1303a, the electrode 1305, and the electrode 1310 provides a high impedance in the second band in light of the radio frequencies. Hence, a majority of it flows into the BPF side, and only a signal component of the second band is output from the electrode 1313b.

[0118] With the structure described above, the duplexer of this exemplary embodiment comprising a single element can separate signals of the first band and signals of the second band without using a phase-shifting circuit. As a result, this duplexer can be useful for a system having a channel requiring a low loss in the first band and a high attenuation in the second band, and another channel needing a high attenuation at both sides of the second band.

[0119] In the present exemplary embodiment, although the duplexer comprises a single element using a laminated body, it is not necessarily comprised of a single element. It may comprise two elements using a BEF provided with a pass band in the first band and an attenuation band in the second band as described in the second exemplary embodiment, and a BPF provided with an attenuation band in the first band and a pass band in the second band as described in the first exemplary embodiment, wherein the two elements are connected together at each side of their input/output terminal electrodes where a parallel circuit is formed. This structure improves an efficiency of mounting on a substrate.

[0120] Although the duplexer of this exemplary embodiment comprises of the BEF provided with a pass band in the first band and an attenuation band in the second band, and the BPF provided with an attenuation band in the first band and a pass band in the second band, it may comprise a BPF provided with a pass band in the first band and an attenuation band in the second band as described in the first exemplary embodiment, and a BEF provided with an attenuation band in the first band and a pass band in the second band as described in the second exemplary embodiment. In this case, it functions as a duplexer useful for a system having a channel requiring a high attenuation at both sides of the first band, and another channel needing a high attenuation in the first band and a low loss in the second band.

[0121] Furthermore, the duplexer may be a structure using a BPF provided with a pass band in the first band and an attenuation band in the second band as described in the first exemplary embodiment, and a BEF provided with an attenuation band in the first band and a pass band in the second band as described in the second exemplary embodiment, wherein the two filters are connected together at each side of their input/output terminal electrodes where a parallel circuit is formed. The duplexer may also comprise a BPF provided with a pass band in the first band and an attenuation band in the second band as described in the first exemplary embodiment, and another BPF provided with an attenuation band in the first band and a pass band in the second band as also described in the first exemplary embodiment. In this case, it functions as a duplexer useful for a system having a channel requiring a high attenuation at both sides of the first band, and another channel requiring a high attenuation at both sides of the second band.

[0122] Besides, the duplexer may be a structure comprising a BPF provided with a pass band in the first band and an attenuation band in the second band as described in the first exemplary embodiment, and another BPF provided with an attenuation band in the first band and a pass band in the second band as also described in the first exemplary embodiment, wherein the two filters are connected together at each side of their input/output terminal electrodes where a parallel circuit is formed.

[0123] Moreover, the duplexer may also comprise a BEF provided with a pass band in the first band and an attenuation band in the second band as described in the second exemplary embodiment, and another BEF provided with an attenuation band in the first band and a pass band in the second band as described also in the second exemplary embodiment. In this case, it functions as a duplexer useful for a system having a channel requiring a low loss in the first band and a high attenuation in the second band, and another channel needing a high attenuation in the first band and a low loss in the second band.

[0124] Also, the duplexer may comprise a structure using individually a BEF provided with a pass band in the first band and an attenuation band in the second band as described in the second exemplary embodiment, and another BEF provided with an attenuation band in the first band and a pass band in the second band as described also in the second exemplary embodiment, wherein the two filters are connected together at each side of their input/output terminal electrodes where a parallel circuit is formed.

[0125] Also, the duplexer may comprise an LPF provided with a pass band in the first band and an attenuation band in the second band as described in the third exemplary embodiment, and a BPF provided with an attenuation band in the first band and a pass band in the second band as described also in the first exemplary embodiment. In this case, it functions as a duplexer useful for a system having a channel requiring a low loss in the first band and another channel needing a high attenuation at both sides of the second band.

[0126] Further, the duplexer may be constructed comprising individually an LPF provided with a pass band in the first band and an attenuation band in the second band as described in the third exemplary embodiment, and a BPF provided with an attenuation band in the first band and a pass band in the second band as described in the first exemplary embodiment, wherein the two filters are connected together at each side of their input/output terminal electrodes where a parallel circuit is formed.

[0127] Furthermore, the duplexer may comprise a BPF provided with a pass band in the first band and an attenuation band in the second band as described in the first exemplary embodiment, and an HPF provided with an attenuation band in the first band and a pass band in the second band as described in the fourth exemplary embodiment. In this case, it functions as a duplexer useful for a system having a channel requiring a high attenuation at both sides of the first band and another channel needing a low loss in the second band.

[0128] Moreover, the duplexer may be constructed comprising individually a BPF provided with a pass band in the first band and an attenuation band in the second band as described in the first exemplary embodiment, and an HPF provided with an attenuation band in the first band and a pass band in the second band as described in the fourth exemplary embodiment, wherein the two filters are connected together at each side of their input/output terminal electrodes where a parallel circuit is formed.

[0129] Also, the duplexer may comprise a BEF provided with a pass band in the first band and an attenuation band in the second band as described in the second exemplary embodiment, and an HPF provided with an attenuation band in the first band and a pass band in the second band as described in the fourth exemplary embodiment. In this case, it functions as a duplexer useful for a system having a channel requiring a low loss in the first band and a high attenuation in the second band, and another channel needing a low loss in the second band.

[0130] In addition, the duplexer may comprise a BEF provided with a pass band in the first band and an attenuation band in the second band as described in the second exemplary embodiment, and an HPF provided with an attenuation band in the first band and a pass band in the second band as described in the fourth exemplary embodiment, wherein the two filters are connected together at each side of their input/output terminal electrodes where a parallel circuit is formed.

[0131] Also, the duplexer may comprise an LPF provided with a pass band in the first band and an attenuation band in the second band as described in the third exemplary embodiment, and a BEF provided with an attenuation band in the first band and a pass band in the second band as described in the second exemplary embodiment. In this case, it functions as a duplexer useful for a system having a channel requiring a low loss in the first band, and another channel needing a high attenuation in the first band and a low loss in the second band.

[0132] Moreover, the above duplexer may comprise an LPF provided with a pass band in the first band and an attenuation band in the second band as described in the third exemplary embodiment, and a BEF provided with an attenuation band in the first band and a pass band in the second band as described in the second exemplary embodiment, wherein the two filters are connected together at each side of their input/output terminal electrodes where a parallel circuit is formed.

[0133] Furthermore, the duplexer may comprise an LPF provided with a pass band in the first band and an attenuation band in the second band as described in the third exemplary embodiment, and an HPF provided with an attenuation band in the first band and a pass band in the second band as described in the fourth exemplary embodiment. In this case, it functions as a duplexer useful for a system having a channel requiring a low loss in the first band, and another channel needing a low loss in the second band.

[0134] Also, the above duplexer may comprise an LPF provided with a pass band in the first band and an attenuation band in the second band as described in the third exemplary embodiment, and an HPF provided with an attenuation band in the first band and a pass band in the second band as described in the fourth exemplary embodiment, wherein the two filters are connected together at each side of their input/output terminal electrodes where a parallel circuit is formed.

[0135] In addition, since the phase-shifting circuit that had been needed in the past can be eliminated in a mobile communication apparatus by employing a duplexer of this invention, the mobile communication apparatus can be constructed smaller in size.

[0136] As has been described, the present invention can realize a laminated filter of a high magnitude of attenuation with a same size as before. In addition, it can also realize a duplexer without using the phase-shifting circuit.