Diplexer circuit, high-frequency circuit and high-frequency module

This application is a 371 national phase of International Application No. PCT/JP 2007/63323 filed Jul. 3, 2007, claiming the priority of Japanese Patent Application No. 2006-183224 filed Jul. 3, 2006; Japanese Patent Application No. 2006-183225 filed Jul. 3, 2006; Japanese Patent Application No. 2006-183226 filed Jul. 3, 2006; and Japanese Patent Application No. 2007-034436 filed Feb. 15, 2007, all of which are hereby incorporated by reference.

The present invention relates to a diplexer circuit used for mobile communications apparatuses such as cell phones, and wireless communications apparatuses between electronic apparatuses, electric apparatuses, etc., a high-frequency circuit, and a high-frequency module having such a high-frequency circuit.

There are various systems using TDMA (time division multiple access) for mobile communications, for instance, EGSM (extended global system for mobile communications) and DCS (digital cellular system) widely used mostly in Europe, PCS (personal communications service) widely used in the U.S., and PDC (personal digital cellular system) used in Japan. Conventionally proposed as small, lightweight, high-frequency circuit devices adapted to pluralities of systems are, for instance, dual-band, high-frequency switch modules for use in mobile communications equipments adapted to two systems of EGSM and DCS, triple-band, high-frequency switch modules for use in mobile communications equipments adapted to three systems of EGSM, DCS and PCS, etc. Wireless LAN data communications according to the IEEE802.11 standard, etc. are widely used at present, and this wireless LAN standard includes pluralities of standards having different frequency bands, etc. Various high-frequency circuits are used in wireless-LAN, multiband communications apparatuses.

When one cell phone is used in pluralities of frequency bands, the cell phone should have a high-frequency switch module comprising a circuit for branching transmission signals and received signals in pluralities of frequency bands transmitted from and received by an antenna, and a switch for switching a transmission path and a reception path. The high-frequency switch module, a key part for multiband, wireless communications, is strongly demanded to be made smaller and higher in performance, and the removal of noises in unnecessary bands is indispensable.

To meet such demand, JP 11-27177 A proposes a high-frequency switch comprising filters whose number is reduced by utilizing floating capacitance generated between an antenna and the ground to remove harmonic distortion generated in a transmission signal from a power amplifier. This high-frequency switch has an attenuation pole in a third-harmonic band by adjusting floating capacitance generated between an antenna terminal, transmission circuit terminals and receiving circuit terminals and the ground, and adjusting the length of transmission lines constituting choke elements to substantially λ/6. Although a specific adjusting method is not described, it is extremely complicated to adjust all of these floating capacitances while adjusting the transmission lines to desired length. Although attenuation should be conducted to a level of about seventh harmonics, for instance, in a GSM system, this method cannot attenuate such high-order harmonics because it uses only an attenuation pole of third harmonics.

JP 2003-69362 A proposes a diplexer comprising a parallel resonance circuit having a resonance frequency equal to the frequency of second harmonics on the side of a lowpass filter terminal to remove second harmonics efficiently. With the parallel resonance circuit connected to common terminal and the lowpass filter terminal, this diplexer efficiently removes harmonics having two times as large frequency as a first frequency on the low-frequency side, while reducing signal loss. Specifically, the lowpass filter circuit in the diplexer comprises two parallel resonance circuits constituted by coils and capacitors, with grounded capacitance connected to a connecting point of these parallel resonance circuits and the lowpass filter terminal. However, two parallel resonance circuits make the diplexer larger with a more complicated circuit structure. Also, a multi-stage lowpass filter provides large insertion loss, deteriorating the characteristics. In addition, because the lowpass filter circuit in this diplexer is designed to attenuate two times as large frequency as the first frequency, or a second frequency, it cannot sufficiently attenuate unnecessary bands other than n-th order harmonics.

When both circuits for EGSM and DCS in different frequency bands of 900 MHz and 1800 MHz, respectively, are used, interference occurs to cause the leakage of signals and the deterioration of isolation characteristics. This problem becomes conspicuous as high-frequency devices are made smaller. Against this backdrop, JP 2001-352202 A proposes a high-frequency switch module handling pluralities of transmission/receiving systems having different passbands, in which one transmission/receiving system and the other transmission/receiving system are disposed in different regions of a laminate in a plane direction. However, their formation in different regions of the laminate in a plane direction does not provide sufficient shielding between one transmission/receiving system and the other transmission/receiving system.

With respect to a lowpass filter used in a high-frequency switch module, JP 2004-328136 A proposes a lowpass filter comprising a series resonance circuit and a parallel resonance circuit connected in series for improving the attenuation characteristics of second and third harmonics in signal waves (fundamental waves), with grounded capacitances connected to both ends of the parallel resonance circuit, and with a phase-adjusting transmission line disposed between the series resonance circuit and the parallel resonance circuit. However, the attenuation characteristics and insertion loss of this lowpass filter are not necessarily sufficient to the demand of higher performance accompanied by increase in the number of bands, etc. Also, when composite filters each comprising a lowpass filter and a notch filter are connected via transmission lines, unnegligible deterioration of characteristics occurs due to electromagnetic interference and parasitic capacitance between circuits, and between filter-constituting transmission lines and capacitances. In addition, composite filters sacrifice the demand of miniaturization to improve characteristics. In the course of increasing the integration of laminate modules, it is difficult to design the arrangement of elements such as inductors, etc. constituting lowpass filters and laminate modules comprising them, which meets the demands of smaller size and higher performance.

Accordingly, the first object of the present invention is to provide a diplexer circuit in which unnecessary bands are reduced while suppressing the increase of insertion loss, without making its circuit more complicated and larger.

The second object of the present invention is to provide a high-frequency circuit comprising such a diplexer circuit.

The third object of the present invention is to provide a high-frequency module having such a high-frequency circuit formed in a multilayer substrate.

The fourth object of the present invention is to provide a high-frequency module in which interference and signal leakage are suppressed between transmission and receiving circuits having different frequency bands without increasing the mounting area.

The fifth object of the present invention is to provide a high-frequency module comprising a lowpass filter having excellent filtering performance, in which inductors and capacitors are easily designed.

The first diplexer circuit of the present invention comprises a common terminal, a low-frequency-side terminal, a high-frequency-side terminal, a low-frequency-side path comprising a low-frequency filter disposed between the common terminal and the low-frequency-side terminal, and a high-frequency-side path comprising a high-frequency filter disposed between the common terminal and the high-frequency-side terminal, the low-frequency filter comprising a first transmission line series-connected to the low-frequency-side path and a capacitor parallel-connected to part of the first transmission line. This diplexer circuit can be miniaturized, because a parallel resonance circuit for suppressing unnecessary bands is constituted by using part of the first transmission line in the low-frequency-side path.

In the above diplexer circuit, it is preferable that the capacitor is parallel-connected to part of the first transmission line on the side of the low-frequency-side terminal to constitute a parallel resonance circuit, and that the other part of the first transmission line constitutes an inductance element. In the first transmission line in the low-frequency filter, a portion constituting an inductance element is disposed on the common terminal side, and a portion constituting the parallel resonance circuit is disposed on the side of the low-frequency-side terminal, to expand the degree of freedom in the arrangement of the parallel resonance circuit. One end of the capacitor may be connected in parallel to part of the first transmission line, and the other end of the capacitor may be connected to another circuit element connected to the low-frequency-side terminal.

The second diplexer circuit of the present invention comprises a common terminal, a low-frequency-side terminal, a high-frequency-side terminal, a low-frequency-side path comprising a low-frequency filter disposed between the common terminal and the low-frequency-side terminal, and a high-frequency-side path comprising a high-frequency filter disposed between the common terminal and the high-frequency-side terminal, parasitic capacitance generated on the side of the common terminal being used as a capacitor for suppressing unnecessary waves. When the common terminal of this diplexer circuit is connected to another circuit element, the above parasitic capacitance functions as a capacitance element, thereby improving design efficiency and the degree of freedom. For instance, when the above common terminal is connected to an antenna, the above parasitic capacitance can be attached to an antenna terminal, thereby suppressing harmonics.

In the above diplexer circuit, the high-frequency filter may comprise a first capacitor connected to the common terminal, the parasitic capacitance being generated on the common terminal side of the first capacitor.

In the above diplexer circuit, one of opposing electrodes constituting the first capacitor, which is connected to the common terminal, is preferably opposing a ground electrode, thereby generating the parasitic capacitance between both electrodes. Utilizing an electrode on the connecting terminal side for one of capacitors constituting the diplexer circuit, which is connected to the common terminal, parasitic capacitance can be generated efficiently with a simple structure, thereby avoiding size increase of the circuit.

In the above diplexer circuit, the high-frequency filter preferably comprises a first capacitor connected to the common terminal, a second capacitor connected between the first capacitor and the high-frequency-side terminal, and a series resonance circuit comprising a third transmission line and a third capacitor between a connecting point of the first capacitor and the second capacitor and the ground, the third transmission line and the first to third capacitors being formed in a laminate comprising dielectric layers provided with electrode patterns, and one of opposing electrodes constituting the first capacitor in the laminate, which is connected to the common terminal, being opposing a ground electrode. Because one of electrodes for capacitors constituting the diplexer circuit, which is connected to the common terminal, is opposing the ground electrode, parasitic capacitance can be generated efficiently, and easily adjusted by changing a ground electrode area, the distance between one of opposing electrodes constituting the first capacitor, which is connected to the common terminal, and the ground electrode, etc.

The first high-frequency circuit of the present invention comprises the first diplexer circuit, and a second transmission line connected to the low-frequency-side terminal, the capacitor being parallel-connected to part of the first transmission line and at least part of the second transmission line. Because a parallel resonance circuit for suppressing unnecessary bands is constituted using the first transmission line and a transmission line of another circuit connected to the low-frequency-side terminal, the diplexer circuit can be made smaller. Also, because the capacitor is bridging the first transmission line and the second transmission line, the arrangement of the capacitor is easy when this high-frequency circuit is formed in a multilayer substrate.

The above high-frequency circuit preferably comprises a switch circuit connected to the low-frequency-side terminal for switching a transmission-side path and a receiving-side path in the low-frequency-side path, the second transmission line being a transmission line disposed in the receiving-side path of the switch circuit. This structure provides a small high-frequency circuit comprising a switch circuit downstream of the diplexer circuit, and suppressing unnecessary bands.

The first high-frequency module of the present invention has the diplexer circuit or the high-frequency circuit formed in a multilayer substrate comprising dielectric layers provided with electrode patterns. This structure provides a small high-frequency circuit suppressing unnecessary bands.

In the above high-frequency module, electrode patterns constituting part of the first transmission line, electrode patterns constituting at least part of the second transmission line, and the capacitor electrode patterns are preferably overlapping in the laminate in a lamination direction. This structure can make the parallel resonance circuit smaller, advantageous in miniaturizing a high-frequency module.

The second high-frequency module of the present invention comprises the second diplexer circuit formed in a multilayer substrate comprising dielectric layers provided with electrode patterns. When the common terminal of this diplexer circuit is connected to another circuit element, the parasitic capacitance functions as a capacitance element, improving the efficiency and degree of freedom of designing a high-frequency module.

The above high-frequency module preferably comprises a first switch circuit for switching a transmission system and a receiving system in the first frequency band branched by the diplexer circuit, and a second switch circuit for switching a transmission system and a receiving system in the second frequency band branched by the diplexer circuit. When the diplexer circuit of the high-frequency antenna switch module having such a structure is connected to an antenna, parasitic capacitance generated in the diplexer circuit can be attached to an antenna terminal, thereby suppressing harmonics.

The third high-frequency module of the present invention is used in a multiband wireless communications apparatus selectively using at least a first frequency band and a second frequency band higher than the first frequency band, comprising a diplexer circuit for branching a first transmission/receiving system in the first frequency band and a second transmission/receiving system in the second frequency band, a first switch circuit connected to the diplexer circuit for switching a transmission system and a receiving system in the first transmission/receiving system, and a second switch circuit connected to the diplexer circuit for switching a transmission system and a receiving system in the second transmission/receiving system; the diplexer circuit and the first and second switch circuits being formed in or on a laminate comprising dielectric layers provided with electrode patterns; among transmission lines for the diplexer circuit and the first and second switch circuits, transmission lines through which signals in the first frequency band pass being formed on one side of a ground electrode formed on a dielectric layer in the laminate in a lamination direction, and transmission lines through which signals in the second frequency band pass being formed on the other side of the ground electrode in a lamination direction.

Because transmission lines through which signals in the first frequency band pass and transmission lines through which signals in the second frequency band pass are separated by the ground electrode in a lamination direction in the diplexer circuit, etc., interference between both transmission and receiving circuits, and the leakage of signals and unnecessary harmonics can be suppressed. Because transmission lines through which signals in the first frequency band pass and transmission lines through which signals in the second frequency band pass are separated in a lamination direction, it is possible to avoid plane size increase for the separation of both circuits.

In addition to those for the first and second frequency bands, transmission and receiving circuits for a third frequency band having a different frequency band, etc. may be added. In this case, both of transmission lines for signals in third and fourth frequency bands are preferably formed on one side of the ground electrode.

In the third high-frequency module, the second frequency band is preferably substantially the same as the frequency band of second harmonics in the first frequency band. When the second frequency band is substantially the same as the frequency band of second harmonics in the first frequency band, the leakage, etc. of unnecessary harmonics in the first frequency band have large influence on signals in the second frequency band. Accordingly, the third high-frequency module having sure shielding between the first frequency band and the second frequency band is particularly effective.

To suppress harmonics, the third high-frequency module preferably comprises a lowpass filter comprising an inductance-constituting transmission line and a capacitor, dielectric layers on which electrode patterns constituting the transmission line are formed and dielectric layers on which electrode patterns constituting the capacitor are formed being separated by a ground electrode in a lamination direction, and no opposing ground electrode being formed on the opposite side of the ground electrode in a lamination direction with respect to the electrode patterns constituting the transmission line. In this case, one side of the ground electrode is an inductance-forming portion, and the other side of the ground electrode is a capacitor-forming portion, in a lamination direction. In this structure, because a ground electrode is disposed between the transmission line and the capacitor, interference is prevented between the transmission line and the capacitor, thereby improving filtering performance, and making the designing of the transmission line and the capacitor easy.

The third high-frequency module preferably does not comprise an opposing ground electrode on the opposite side of the ground electrode in a lamination direction with respect to the electrode patterns constituting the capacitor. This structure can miniaturize the lowpass filter.

The above high-frequency module preferably comprises pluralities of the capacitors. When comprising pluralities of capacitors like a π-type or ladder-type lowpass filter, etc., the close arrangement of capacitors and inductance is likely to cause interference. On the other hand, the formation of pluralities of capacitors on one side of the ground electrode in a lamination direction can effectively suppress interference between inductance-constituting transmission lines and capacitors. Pluralities of inductance-constituting transmission lines may be used like a ladder-type lowpass filter. In this case, the transmission lines are formed on the opposite side of the capacitor with respect to the ground electrode.

In the above high-frequency module, at least one of the capacitors may be connected in parallel to the transmission lines. This structure can also effectively suppress interference between the transmission lines and the capacitors.

FIG. 1 is a view showing an equivalent circuit of the diplexer circuit according to one embodiment of the present invention.

FIG. 2 is a view showing an equivalent circuit of the high-frequency circuit according to another embodiment of the present invention.

FIG. 3 is a view showing an equivalent circuit of the quadband antenna switch circuit of the present invention.

FIG. 4 is a partially developed view showing dielectric layers provided with electrode patterns for constituting the high-frequency module according to one embodiment of the present invention.

FIG. 5 is a graph showing the bandpass characteristics of the high-frequency module according to one embodiment of the present invention.

FIG. 6 is a graph showing the bandpass characteristics of the high-frequency switch module of Comparative Example.

FIG. 7 is a view showing an equivalent circuit of the diplexer circuit according to another embodiment of the present invention.

FIG. 8 is a view showing parasitic capacitance in an equivalent circuit of the diplexer circuit according to another embodiment of the present invention.

FIG. 9 is a schematic cross-sectional view showing part of the high-frequency module laminate according to another embodiment of the present invention.

FIG. 10 is a view showing an equivalent circuit of the quadband antenna switch circuit according to a further embodiment of the present invention.

FIG. 11 is a block diagram showing the high-frequency module according to a still further embodiment of the present invention.

FIG. 12 is a partially developed view showing dielectric layers provided with electrode patterns for constituting the high-frequency module according to a still further embodiment of the present invention.

FIG. 13 is a partially developed view showing dielectric layers provided with electrode patterns for constituting a still further high-frequency switch module of the present invention.

FIG. 14 is a partially developed view showing dielectric layers provided with electrode patterns for constituting the laminated high-frequency module comprising the lowpass filter according to one embodiment of the present invention.

FIG. 15 is a view showing an equivalent circuit of the lowpass filter according to one embodiment of the present invention.

FIG. 16 is a view showing an equivalent circuit of the lowpass filter according to another embodiment of the present invention.

FIG. 17( a ) is a schematic cross-sectional view showing one example of the lowpass filter used in the present invention.

FIG. 17( b ) is a schematic cross-sectional view showing another example of the lowpass filter used in the present invention.

[1] First Embodiment

(A) Diplexer Circuit

FIG. 1 shows an equivalent circuit of the diplexer circuit according to one embodiment of the present invention. The diplexer circuit has a function of passing a transmission signal through a high-frequency-side transmission circuit or a low-frequency-side transmission circuit during transmission, while branching received signals having different frequencies to a high-frequency-side receiving circuit or a low-frequency-side receiving circuit during reception. The diplexer circuit shown in FIG. 1 comprises a common terminal Pc, a low-frequency-side terminal P 1 , a high-frequency-side terminal Ph, a low-frequency filter, and a high-frequency filter, these filters acting to branch a signal path connected to the common terminal Pc to a low-frequency-side path between the common terminal Pc and the low-frequency-side terminal P 1 , and a high-frequency-side path between the common terminal Pc and the high-frequency-side terminal Ph.

The low-frequency filter comprises a first transmission line LL 1 disposed between the common terminal Pc and the low-frequency-side terminal P 1 , and a series resonance circuit comprising a transmission line LL 2 having one end connected between the first transmission line LL 1 and the low-frequency-side terminal P 1 and the other end connected to the ground, and a first capacitor CL 1 . With the resonance frequency of the series resonance circuit of the transmission line LL 2 and the first capacitor CL 1 set equal to the frequency of a high-frequency-side signal, for instance, the high-frequency-side signal can be prevented from entering the low-frequency-side path. In this embodiment, a capacitor C is connected in parallel to part of the first transmission line LL 1 on the side of the low-frequency-side terminal P 1 in the low-frequency filter, thereby constituting a parallel resonance circuit. The remaining part of the first transmission line LL 1 on the side of the common terminal Pc constitutes an inductor. Because part of the first transmission line LL 1 constitutes a parallel resonance circuit with the capacitor C, it is possible to avoid the low-frequency filter circuit from becoming larger by the addition of the parallel resonance circuit. Although the capacitor C is parallel-connected to part of the first transmission line LL 1 in the example shown in FIG. 1 , this structure is not restrictive, but the capacitor C may be parallel-connected to a portion including another circuit element series-connected to the first transmission line LL 1 . Apart from the series resonance circuit and the parallel resonance circuit comprising part of the first transmission line LL 1 and the capacitor C, the structure shown in FIG. 1 is not restrictive, but other structures may be adopted.

The high-frequency filter comprises second and third capacitors CH 4 , CH 5 connected between the common terminal Pc and the high-frequency-side terminal Ph, and a series resonance circuit comprising a transmission line LH 4 and a fourth capacitor CH 6 connected between a connecting point of the second and third capacitors CH 4 , CH 5 and the ground. However, the high-frequency filter is not restricted to this circuit structure, but proper modification can be made.

The diplexer circuit having a structure in which part of the first transmission line LL 1 and the capacitor C are connected in parallel can be formed in a multilayer substrate comprising dielectric layers provided with electrode patterns. For instance, electrode patterns for the capacitor C are formed on adjacent dielectric layers such that they oppose part of electrode patterns for the first transmission line LL 1 formed on dielectric layers, and ends of these electrode patterns are connected to the low-frequency-side terminal P 1 . Part of the first transmission line LL 1 may be wider than the other portion.

(B) High-Frequency Circuit

FIG. 2 shows an equivalent circuit of the high-frequency circuit according to one embodiment of the present invention. This high-frequency circuit comprises a diplexer circuit, a second transmission line Lg 2 in a downstream circuit connected to the low-frequency-side terminal P 1 of the diplexer circuit, and a capacitor C connected in parallel to part of the first transmission line LL 1 on the side of the low-frequency-side terminal P 1 and at least part of the second transmission line Lg 2 on the side of the low-frequency-side terminal P 1 . In the example shown in FIG. 2 , the downstream circuit is a switch circuit (circuit structure will be described below) for switching a transmission-side path and a receiving-side path in the low-frequency-side path. The second transmission line Lg 2 is disposed in the receiving-side path of the switch circuit. FIG. 2 also shows a diode Dg 1 in the switch circuit connected to the low-frequency-side terminal P 1 .

Because the first transmission line LL 1 in the low-frequency filter in the diplexer circuit, the second transmission line Lg 2 in the receiving-side path in the switch circuit, and the capacitor C parallel-connected to them constitute a parallel resonance circuit, the circuit is not made larger. With the resonance frequency of this parallel resonance circuit adjusted to other bands than the frequencies of received signals, wide unnecessary bands can be attenuated. Because the other circuit structure such as a high-frequency filter, etc., may be the same as shown in FIG. 1 , its explanation will be omitted. The capacitor C may be parallel-connected to part or all of the second transmission line Lg 2 .

The high-frequency circuit shown in FIG. 2 can be formed in a multilayer substrate comprising dielectric layers provided with electrode patterns, to constitute a high-frequency module. Examples of the high-frequency module include an antenna switch module for switching a transmission system connected to an antenna and a receiving signal path, a composite module integrally comprising the above antenna switch module and a high-frequency amplifier module comprising a high-frequency amplifier circuit for amplifying a transmitting signal, etc., though not restrictive.

As the high-frequency module according to one embodiment of the present invention, FIG. 3 shows an equivalent circuit of a quadband antenna switch circuit using low-frequency bands comprising a GSM850 band (transmission frequency: 824-849 MHz, and receiving frequency: 869-894 MHz) and an EGSM band (transmission frequency: 880-915 MHz, and receiving frequency: 925-960 MHz), and high-frequency bands comprising a DCS band (transmission frequency: 1710-1785 MHz, and receiving frequency: 1805-1880 MHz) and a PCS band (transmission frequency: 1850-1910 MHz, and receiving frequency: 1930-1990 MHz). This antenna switch circuit comprises a diplexer circuit Dip comprising a low-frequency filter and a high-frequency filter, a first switch circuit SW 1 disposed downstream of the low-frequency filter of the diplexer circuit for switching a transmission terminal Tx-LB and a receiving terminal Rx-LB by voltage supplied from a control terminal Vc, and a second switch circuit SW 2 disposed downstream of the high-frequency filter of the diplexer circuit for switching a transmission terminal Tx-HB and a receiving terminal Rx-HB by voltage supplied from a control terminal Vc. The transmission terminal Tx-LB and the receiving terminal Rx-LB on the low-frequency side are commonly used in GSM and EGSM, and the transmission terminal Tx-HB and the receiving terminal Rx-HB on the high-frequency side are commonly used in DCS and PCS. The receiving terminal Rx-LB on the low-frequency side and the receiving terminal Rx-HB on the high-frequency side are selectively used depending on regions in which mobile terminals comprising this module are used. For instance, Europe uses Rx-LB for EGSM and Rx-HB for DCS, and the U.S. uses Rx-LB for GSM and Rx-HB for PCS. In this case, each transmission/receiving terminal needs a wide band design having the desired characteristics in a low-frequency band of GSM850 and EGSM and a high-frequency band of DCS and PCS. Downstream of the receiving terminal Rx-LB on the low-frequency side and the receiving terminal Rx-HB on the high-frequency side may be a switch circuit (not shown) with four receiving terminals.

The high-frequency switch module is not restricted to quadband, but may be triple- or dual-band. For instance, a first frequency band may be one of GSM 850 and EGSM in the low-frequency band, and a second frequency band may be one of DCS and PCS in the high-frequency band. The high-frequency module is not restricted to communications systems for cell phones, but may be for other communications systems for wireless LAN, etc. The number and arrangement of circuit elements in a filter circuit, a switch circuit, a detection circuit, a balanced-to-unbalanced circuit, etc. used for the high-frequency circuit and the high-frequency module may be changed, if necessary.

In the antenna switch circuit shown in FIG. 3 , the diplexer circuit Dip comprising a low-frequency filter and a high-frequency filter for branching transmission and receiving systems in the first frequency band transmission and receiving systems in the second frequency band comprises a lowpass filter as a low-frequency-side (GSM/EGSM side) filter for passing transmission signals and received signals of GSM and EGSM while attenuating transmission signals and received signals of DCS and PCS, and a highpass filter as a high-frequency-side (DCS/PCS side) filter for passing the transmission signals and received signals of DCS and PCS while attenuating the transmission signals and received signals of GSM and EGSM. The low-frequency filter and the high-frequency filter connected to an antenna terminal Ant, a common terminal, are respectively constituted by transmission lines and capacitors, but may be constituted by a bandpass filter or a notch filter.

In the lowpass filter as a low-frequency-side (GSM/EGSM side) filter, a transmission line LL 1 passes signals in a low-frequency band (GSM and EGSM) with low loss, but has high impedance to signals in a high-frequency band (DCS and PCS), thereby preventing signals in the DCS and PCS band from passing. A transmission line LL 1 preferably has such length that it has high impedance in the frequencies of signals in the DCS and PCS band to prevent the signals in the DCS and PCS band from being transmitted to a GSM path. A transmission line LL 2 and a capacitor CL 1 constitute a series resonance circuit having a resonance frequency in the DCS and PCS band, so that signals in the DCS and PCS band are grounded and thus prevented from entering a low-frequency path. In the highpass filter as a high-frequency-side (DCS/PCS Side) filter, capacitors CH 4 , CH 5 pass signals in the high-frequency band (DCS and PCS) with low loss, but has high impedance to signals in the low-frequency band (GSM and EGSM), thereby preventing signals in the GSM and EGSM band from passing. A transmission line LH 4 and a capacitor CH 4 constitute a series resonance circuit having a resonance frequency in the GSM and EGSM band, so that signals in the GSM and EGSM band are grounded and thus prevented from entering a high-frequency path.

The switch circuit shown in FIG. 3 comprises a first switch circuit SW 1 connected to the diplexer circuit for switching a transmission system (transmission terminal Tx-LB) and a receiving system (receiving terminal Rx-LB) in the first transmission/receiving system, and a second switch circuit SW 2 connected to the diplexer circuit for switching a transmission system (transmission terminal Tx-HB) and a receiving system (receiving terminal Rx-HB) in the second transmission/receiving system. Any of the first and second switch circuits SW 1 , SW 2 comprises switch elements and transmission lines as main elements. The switch elements are preferably PIN diodes, but GaAs switches can be used. Switch circuits comprising PIN diodes are cheaper than those comprising GaAs switches, but the GaAs switches can be operated with lower power consumption than switch circuits comprising the PIN diodes. Accordingly, they are selected to exhibit their advantages.

The first switch circuit SW 1 (upper side in FIG. 3 ) for switching a transmission terminal Tx-LB and a receiving terminal Rx-LB for GSM/EGSM comprises two diodes Dg 1 , Dg 2 and two transmission lines Lg 1 , Lg 2 as main elements. The diode Dg 1 is disposed between the low-frequency filter of the diplexer circuit and the transmission terminal Tx-LB, an anode of the diode Dg 1 being connected to the low-frequency filter of the diplexer circuit, and a cathode of the diode Dg 1 being connected to an L-type lowpass filter LPF 1 constituted by a transmission line LL 3 and capacitors CL 2 , CL 3 . A transmission line Lg 1 is connected between the other end of the transmission line LL 3 constituting the lowpass filter LPF 1 and the ground. Because the lowpass filter LPF 1 suppresses only high-order harmonic distortion contained in a transmission signal input from a power amplifier (not shown) on the GSM/EGSM side, it preferably passes transmitting signals of GSM/EGSM, but sufficiently attenuates two times or more as large frequencies as that of the transmission signal of GSM/EGSM. To sufficiently attenuate only harmonic distortion contained in the transmission signal of GSM/EGSM input from a power amplifier, the inductance-generating transmission line LL 3 and the capacitor CL 3 constitute a parallel resonance circuit having a resonance frequency two or three times the transmission frequency of GSM/EGSM.

Capacitors Cg 6 , Cg 2 , Cg 1 function not only as DC-cutting capacitors for removing a DC component and applying a control DC voltage to a circuit comprising diodes Dg 1 and Dg 2 , but also as part of phase-adjusting circuits. A transmission line Lg 2 is disposed between an anode of the diode Dg 1 and the receiving terminal Rx-LB, the diode Dg 2 is connected between one end of the transmission line Lg 2 and the ground, and the capacitor Cg 1 is connected between an anode of the diode Dg 2 and the ground. A resistor Rg is connected in series between the anode of the diode Dg 2 and a control terminal Vc. A capacitor Cvg connected between the control terminal Vc and the ground prevents noise from entering a control power supply, thereby stabilizing control. Any of transmission lines Lg 1 and Lg 2 is a λ/4 line, preferably having such length as to provide a resonance frequency within a frequency band of a transmission signal of GSM/EGSM. For instance, when their resonance frequencies are substantially equal to an intermediate frequency (869.5 MHz) of a transmission signal of GSM, excellent insertion loss characteristics can be obtained within the desired frequency band.

The second switch circuit SW 2 (lower side in FIG. 3 ) switches a receiving terminal Rx-HB common to DCS and PCS, and a transmission terminal Tx-HB common to DCS and PCS. The second switch circuit SW 2 comprises two diodes Dd 1 and Dd 2 , and two transmission lines Ld 1 and Ld 2 as main elements. The diode Dd 1 is disposed between the high-frequency filter of the diplexer circuit and the transmission terminal Tx-HB, an anode of the diode Dd 1 being connected to the high-frequency filter of the diplexer circuit, and a cathode of the diode Dd 1 being connected to an L-type lowpass filter LPF 2 constituted by a transmission line LH 5 and capacitors CH 7 , CH 8 . A transmission line Ld 1 is connected between the other end of the transmission lines LH 5 constituting the lowpass filter LPF 2 and the ground. Because the lowpass filter LPF 2 suppresses only high-order harmonic distortion contained in a transmission signal input from a power amplifier (not shown) on the side of DCS and PCS, it preferably passes a transmission signal of DCS or PCS, while sufficiently attenuating two times or more as large frequencies as that of the transmission signal of DCS or PCS. To secure isolation between the transmission terminal Tx-HB and the antenna terminal Ant, and between the transmission terminal Tx-HB and the receiving terminal Rx-HB when the diode Dd 1 is in an OFF state, a series circuit of an inductor Ls and a capacitor Cs is connected in parallel to the diode Dd 1 to cancel a capacitance component of the diode in an OFF state.

Any of transmission lines Ld 1 and Ld 2 is a λ/4 line, preferably having such length as to provide a resonance frequency within a frequency band of a transmission signal in the transmission/receiving system of DCS and PCS, particularly having such length that the resonance frequency is an intermediate frequency of the above frequency band. For instance, when the resonance frequency of the transmission lines Ld 1 and Ld 2 is substantially an intermediate frequency (1810 MHz) of transmission signals in the bands of DCS and PCS, excellent electric characteristics can be obtained in each mode, so that two transmission signals can be handled by one circuit. A capacitor Cd 2 functions not only as a DC-cutting capacitor for removing a DC component and applying a control DC voltage to a circuit comprising diodes Dd 1 and Dd 2 , but also as part of a phase-adjusting circuit. The transmission lines Ld 2 has one end connected to the capacitor CH 5 constituting the high-frequency filter of the diplexer circuit, and the other end connected to the grounded diode Dd 2 and capacitor Cd 1 . An anode of the diode Dd 2 is connected to a control terminal Vc via a resistor Rd. A capacitor Cvd stabilizes control by preventing noise from entering the control power supply. A capacitor Cd 5 is a DC-cutting capacitor.

When overcurrent due to static electricity, thunderbolt, etc. flows through the antenna terminal, an inductor L 1 permits the overcurrent to escape to the ground GND, thereby preventing the breakage of the module. An inductor L 2 and Cg 2 , and an inductor L 5 and Cd 2 act as highpass, phase-adjusting circuits for adjusting a connection phase, thereby suppressing harmonics from leaking from the high-frequency amplifier circuit HPA. The relation with antenna-switch-side impedance is adjusted to be conjugated matching in a fundamental wave and non-conjugated matching in unnecessary n-th harmonics. L 3 , C 2 , L 4 and C 1 constitute an LC resonance circuit and an LC highpass circuit, with a resonance point near 250 MHz to attenuate electrostatic pulse, thereby preventing the electrostatic pulse from leaking to the downstream of the receiving terminal to protect a downstream bandpass filter. C 3 is a matching-adjusting capacitor.

(C) High-Frequency Module

FIG. 4 shows a high-frequency module having the antenna switch circuit of FIG. 3 in a multilayer (11-layer) substrate. BOTTOM denotes a rear surface of the multilayer substrate. Each layer has a right-side region 1 of about ⅓ in width in which the antenna switch circuit is formed, and a left-side region 2 of about ⅔ in width in which a high-frequency amplifier circuit (not shown) is formed. The diplexer circuit has the structure shown in FIG. 2 . The high-frequency amplifier circuit is connected, for instance, to the transmission terminal Tx-LB of GSM/EGSM in the antenna switch circuit to send the amplified transmission signal to the antenna switch circuit. It is preferable that the connection of the high-frequency amplifier and the antenna switch circuit is formed on upper-side layers, and that lines for the high-frequency amplifier and lines for the antenna switch circuit are formed on different layers without vertical overlap to avoid interference.

In FIG. 4 , the same symbols are used on electrode patterns corresponding to the transmission lines and capacitors shown in FIGS. 2 and 3 . The second capacitor CH 4 and the third capacitor CH 5 in the high-frequency filter of the diplexer circuit, and the first capacitor CL 1 in the low-frequency filter are formed below the sixth dielectric layer provided with a ground electrode. Electrode patterns for the transmission line LL 2 and the first capacitor CL 1 constituting a series resonance circuit are formed with overlapping in a lamination direction. Similarly, electrode patterns for the transmission line LH 4 and the fourth capacitor CH 6 constituting a series resonance circuit are formed with overlapping in a lamination direction. Electrode patterns for the first transmission line LL 1 in the low-frequency filter are formed on the second to fifth layers, so that a coil is constituted. Also, electrode patterns for the second transmission line Lg 2 in the first switch circuit SW 1 are formed on the fifth and seventh to eleventh layers, so that a coil is constituted.

An end of the electrode pattern of the first transmission line LL 1 formed on the second layer is connected to an electrode pattern of a capacitor C formed on the third layer via a through-hole electrode. The electrode pattern of the capacitor C is opposing an end of the electrode pattern of the second transmission line Lg 2 formed on the fifth layer, to constitute a capacitor. An end of the electrode pattern of the first transmission line LL 1 formed on the second layer and an end of the electrode pattern of the second transmission line Lg 2 formed on the seventh layer are connected to a capacitor Cg 6 mounted on the uppermost layer, via through-hole electrodes. Such arrangement of electrode patterns provides a structure in which the capacitor C is connected in parallel to part of the first transmission line LL 1 and part of the second transmission line Lg 2 . As described above, in the embodiment shown in FIG. 4 , the electrode patterns constituting part of the first transmission line LL 1 , the electrode patterns constituting part of the second transmission line Lg 2 , and the electrode pattern of the capacitor C are overlapping in a lamination direction.

Because the diplexer of the present invention comprises a low-frequency filter comprising a first transmission line series-connected to a low-frequency-side path and a capacitor parallel-connected to part of the first transmission line, it can effectively suppress unnecessary bands with low loss despite its small size. The high-frequency module of the present invention can also be small, and suppress the leakage and interference of signals in transmission and receiving systems having different frequency bands.