RF device and communication apparatus using the same

An RF device includes a first substrate having a lower relative dielectric constant, a first RF circuit for a lower frequency band provided in the first substrate, a second substrate having a higher relative dielectric constant larger than the lower relative dielectric constant, and a second RF circuit for a higher frequency band having a part of the second RF circuit sandwiched between the first substrate and the second substrate. The first RF circuit and the second RF circuit are connected to each other and the second substrate is partially overlaid on the first substrate. A semiconductor device or passive device is provided on a region in the surface of the first substrate on which the second substrate is not overlaid, and a multilayered wiring pattern made of copper or silver is formed in the first substrate to form the first RF circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an RF device mainly used in a high frequency radio apparatus, such as a cellular phone.

2. Related Art of the Invention

Recently, as mobile communication users have been increased and a system therefor has become global, an RF device has become a focus of attention that enables the EGSM, DCS and UMTS systems provided for respective frequencies shown inFIG. 18to be used with one cellular phone. With reference to drawings, a first conventional RF device will be described below.

FIG. 19is a cross-sectional view of the first conventional RF device. InFIG. 19, reference numeral1101denotes a low temperature cofired ceramic body with a low relative dielectric constant. Reference numeral1102denotes a multilayered wiring conductor for constituting part of an RF circuit. Reference numeral1103denotes an interlayer via hole and reference numeral1104denotes a discrete component, such as a discrete resistor, a discrete capacitor, a discrete inductor and a packaged semiconductor.

FIG. 20is a circuit diagram of the first conventional RF device. The RF device is one provided for triple bands (EGSM, DCS and UMTS described above) comprising a diplexer1201that connects a transmitting/receiving switching circuit1202and a transmitting/receiving switching circuit1203to an antenna (ANT).

An operation of the first conventional RF device arranged as described above will be described.

The multilayered wiring conductor1102electrically interconnects a plurality of discrete components1104and, in a substrate1101made of a low temperature cofired ceramic, forms a capacitor formed in the substrate and an inductor formed in the substrate. Such capacitor and inductor constitute an RF circuit in conjunction with the discrete components1104, and the RF circuit serves as an RF device such as an RF multilayered switch.

The diplexer1201directly connected to the antenna terminal (ANT) branches a signal received through the antenna terminal (ANT) to the transmitting/receiving switching circuits1202and1203. The duplexer1204is connected to the transmitting/receiving switching circuit1203. The transmitting/receiving switching circuit1202has a transmitting terminal Tx1for EGSM transmitting and a receiving terminal Rx1for EGSM receiving. The transmitting/receiving switching circuit1203has a transmitting terminal Tx2for DCS transmitting and a receiving terminal Rx2for DCS receiving. The duplexer1204has a transmitting terminal Tx3for UMTS transmitting and a receiving terminal Rx3for UMTS receiving.

The receiving terminal Rx2is connected to the antenna via a diode1205, which is in the off state during transmission using the transmitting terminal Tx2.

Transmission line1206aand1206bfor electrical length correction, a transmitting filter1207and a receiving filter1208, which are required for duplex transmission, are connected between the transmitting terminal Tx3and the receiving terminal Rx3.

Now, a second conventional RF device will be described as another example of the send/receive switching circuit directly connected to the antenna.

FIG. 21is an exploded perspective view of the second conventional RF device. The RF device has six dielectric substrates with high relative dielectric constant1301ato1301f. The dielectric substrate1301bhaving a shielding electrode1302aformed on the upper surface thereof, the dielectric substrate1301chaving an inter-stage coupling electrode1303formed on the upper surface thereof, the dielectric substrate1301dhaving resonator electrodes1304aand1304bformed on the upper surface thereof, the dielectric substrate1301ehaving input/output coupling capacitor electrodes1305aand1305bformed on the upper surface thereof, and the dielectric substrate1301fhaving a shielding electrode1302bformed on the upper surface thereof are stacked.

End face electrodes1306aand1306b, which are connected to the shielding electrodes1302aand1302to form ground terminals, are provided at the left and right sides of the stacked dielectric substrates. On the rear of the stacked dielectric substrates, there is provided an end face electrode1307which is connected to the ground facing the shielding electrodes1302aand1302band a common open end of the microstrip resonator electrodes1304aand1304b. An end face electrode1308, which is provided on the front of the stacked dielectric substrates, is connected to short-circuit ends of the resonator electrodes1304aand1304band to the shielding electrodes1302aand1302b. End face electrodes1309aand1309bat the left and right sides of the stacked dielectric substrates are connected to the input/output coupling electrodes1305aand1305bto constitute input/output terminals.

FIG. 22is a circuit diagram of the second conventional RF device. The input/output coupling electrode1305aand the resonator electrode1304aconstitute an input/output coupling capacitor1401a, and the input/output coupling electrode1305band the resonator electrode1304bconstitute an input/output coupling capacitor1401b. In addition, the input/output coupling electrode1305aand the inter-stage coupling electrode1303constitute an inter-stage coupling capacitor1402a, and the input/output coupling electrode1305band the inter-stage coupling electrode1303constitute an inter-stage coupling capacitor1402b. These components constitute a two-stage band-pass filter shown inFIG. 22.

FIG. 23is a block diagram of an antenna duplexer1503, which is the second conventional RF device, comprising a transmitting filter1501, a receiving filter1502, the filters being constituted by the band-pass filter, and a matching circuit provided therebetween.

However, the first conventional RF device configured as described above, the transmitting filter1206and the receiving filter1027are composed of an inductor or capacitor with a low Quality factor, and therefore, have a high loss as a filter. Furthermore, the microstrip resonator structure for increasing the Quality factor has a problem in that the RF device including the substrate1101made of a low temperature cofired ceramic with low relative dielectric constant becomes quite large because the size of the resonator is inversely proportional to the frequency and the square root of the relative dielectric constant.

Even with the microstrip resonator structure, since it is also affected by the substrate1101with low relative dielectric constant, the Quality factor cannot be increased sufficiently, and for example, a circuit provided for the CDMA mode still has a problem of the filter loss.

In the second conventional RF device configured as described above, if a line is provided thereon or therein, the impedance of the line is increased because the substrates constituting the RF multilayered device are made of a low temperature cofired ceramic with high relative dielectric constant, and thus, it is quite difficult to form a complicated circuit in each substrate. In addition, it is also quite difficult to implement a discrete component, such as a discrete resistor, a discrete capacitor, a discrete inductor and a packaged semiconductor, on the second conventional RF device, because the line impedance of the discrete component itself is increased.

SUMMARY OF THE INVENTION

In view of the above described problems, an object of this invention is to provide an RF device having a low filter loss and not suffering from a problem about a line impedance, or a compact RF device not suffering from a problem about a line impedance.

One aspect of the present invention is an RF device, comprising:

a first substrate made of a material with a lower relative dielectric constant and having a high frequency circuit formed therein or on a surface thereof; and

a second substrate made of a material with a higher relative dielectric constant,

wherein at least a part of a filter is provided in, on a surface of or in the vicinity of said second substrate and connected to said high frequency circuit, and

said high frequency circuit is composed of an element other than said part of the filter.

Another aspect of the present invention is the RF device, wherein said at least a part of the filter forms a high frequency circuit for a CDMA mode.

Still another aspect of the present invention is the RF device, wherein said second substrate is partially overlaid on said first substrate, a semiconductor device or passive device is provided on a region in the surface of said first substrate on which said second substrate is not overlaid, and a multilayered wiring pattern made of copper or silver is formed in said first substrate, whereby said high frequency circuit is formed.

Yet still another aspect of the present invention is the RF device, wherein said semiconductor device includes any one of a PIN diode device, a GaAs semiconductor device, a field effect transistor (FET) device and a varactor diode device, and switching among a plurality of frequency bands is realized by an operation of any one of said devices.

Still yet another aspect of the present invention is an RF device, comprising:

a first substrate made of a material with a lower relative dielectric constant and having a first high frequency circuit for a lower frequency band formed therein or on a surface thereof; and

a second substrate made of a material with a higher relative dielectric constant,

wherein at least a part of a filter of a second high frequency circuit for a higher frequency band is provided in, on a surface of or in the vicinity of said second substrate, and said first high frequency circuit and said second high frequency circuit are connected to each other.

A further aspect of the present invention is the RF device, wherein said second substrate is overlaid on said first substrate, and said part of the filter is sandwiched between said first substrate and said second substrate.

A still further aspect of the present invention is the RF device, wherein said second substrate is partially overlaid on said first substrate, a semiconductor device or passive device is provided on a region in the surface of said first substrate on which said second substrate is not overlaid, and a multilayered wiring pattern made of copper or silver is formed in said first substrate, whereby said first high frequency circuit is formed.

A yet further aspect of the present invention is the RF device, wherein said second substrate comprises a plurality of substrates disposed on said first substrate with spaced apart from each other, one of said plurality of substrates constitutes a transmitting filter, and another of said plurality of substrates constitutes a receiving filter.

A still yet further aspect of the present invention is the RF device, wherein said lower frequency band is a frequency band for a TDMA mode, and said higher frequency band is a frequency band for a CDMA mode.

An additional aspect of the present invention is the RF device, wherein each of said first and second substrates is composed of a multilayered and integrally molded ceramic.

A still additional aspect of the present invention is the RF device, wherein said first substrate is made of a low temperature cofired ceramic and said second substrate is made of a high temperature cofired ceramic.

A yet additional aspect of the present invention is the RF device, wherein a part of said filter is a resonator electrode, and said resonator electrode is constituted by a metal foil.

A still yet additional aspect of the present invention is the RF device, wherein the RF device is integrated by filling a space defined by said first substrate, said second substrate and said resonator electrode with a thermosetting resin.

A supplementary aspect of the present invention is the RF device, wherein said semiconductor device includes any one of a PIN diode device, a GaAs semiconductor device, a field effect transistor (FET) device and a varactor diode device, and switching between said first high frequency circuit and said second high frequency circuit is realized by an operation of any one of said devices.

A still supplementary aspect of the present invention is the RF device, wherein whole or a part of said second substrate is covered with a shielding electrode.

A yet supplementary aspect of the present invention is the RF device, wherein said passive device includes a SAW filter with an electrode hermetically sealed.

A still yet supplementary aspect of the present invention is a communication apparatus, comprising the RF device, a transmitting circuit, a receiving circuit and an antenna which are connected to said RF device.

DESCRIPTION OF SYMBOLS

PREFERRED EMBODIMENTS OF THE INVENTION

Now, an RF device according to this invention will be described with reference to the drawings.

FIG. 1is a perspective view of an RF device according to an embodiment 1 of this invention. A substrate101is an example of a first substrate according to this invention, which is made of a low temperature cofired ceramic with low dielectric constant (hereinafter, “low dielectric constant” means a lower relative dielectric constant) Reference numerals102aand102bdenote a SAW filter, reference numerals103ato103edenote a PIN diode, which is one example of a semiconductor device according to this invention, reference numeral104denotes a discrete inductor, reference numeral105denotes a discrete capacitor, and a substrate106is an example of a second substrate according to this invention, which is made of a high temperature cofired ceramic with high dielectric constant (hereinafter, “high dielectric constant” means a higher relative dielectric constant). A metal foil resonator107is one example of a part of a resonator according to this invention. Reference numeral108denotes a thermosetting resin and reference numeral109denotes an upper surface external electrode.

FIG. 5is a cross-sectional view of the RF device shown inFIG. 1taken along a line A–A′. Reference numeral201denotes a multilayered wiring conductor, reference numeral202denotes an interlayer via hole, and reference numeral203denotes a bottom surface terminal electrode (LGA: Land Grid Array).

FIG. 6is a block diagram of the RF device according to the embodiment 1 of this invention. Reference numerals301and302denote a switching circuit (send/receive switching circuit). Reference numeral303denotes a diplexer, and specifically, reference numeral303adenotes a low pass filter (LPF) and reference numeral303bdenotes a high pass filter (HPF) Reference numerals304and305denote an internal terminal, reference numeral306denotes an antenna terminal, reference numerals307aand307bdenote an LPF, and reference numeral308denotes a duplexer (Dup).

FIG. 7is an equivalent circuit diagram of the RF device according to the embodiment 1 of this invention. Reference numeral401denotes a control terminal, reference numeral402denotes a resistor, reference numeral403denotes a control terminal, reference numeral404denotes a resistor, reference numeral405denotes a control terminal, reference numeral406denotes a resistor, reference numeral407denotes a transmitting filter, reference numeral408denotes a receiving filter, reference numerals409and410denote a transmission line, reference numerals411aand411bdenote a quarter-wavelength tip-short-circuited resonator, reference numeral412denotes an inter-stage coupling capacitor, reference numerals413aand413bdenote an input/output coupling capacitor, reference numeral414aand414bdenote a quarter-wavelength tip-short-circuited resonator, reference numeral415denotes an inter-stage coupling capacitor, and reference numerals416aand416bdenote an input/output coupling capacitor.

In the substrate101made of a low temperature cofired ceramic with low dielectric constant, the multilayered wiring conductor201made of copper or silver, which is one example of the multilayered wiring pattern according to this invention, forms strip lines including the transmission lines409,410with an impedance determined by thickness, width and length of the multilayered wiring conductor201and the dielectric constant of the substrate101. In addition, the multilayered wiring conductors201disposed in different two layers form a capacitor in the substrate101, the capacitor having an impedance determined by an overlapping area of the multi layered wiring conductors201, the dielectric constant of the low temperature cofired ceramic with low dielectric constant sandwiched between the multilayered wiring conductors201or the like.

Since the substrate101made of the low temperature cofired ceramic with low dielectric constant is interposed between the multilayered wiring conductors201and the metal foil resonators107, capacitors including the inter-stage coupling capacitors412,415and the input/output coupling capacitors413a,413b,416aand416bare formed. In addition, in the substrate101, the multilayered wiring conductor201forms an inductor having an impedance determined by width and length of the line of the multilayered wiring conductor201and the dielectric constant of the low temperature cofired ceramic with low dielectric constant.

The multilayered wiring conductors201are electrically connected to each other via the interlayer via hole202formed at a desired position between the multilayered wiring conductors201. A pattern of the multilayered wiring conductor201in each layer is formed by screen printing or another method. The interlayer via hole202is formed by punching a hole in the dielectric sheet constituting the substrate101and filling the hole with a conductive paste by printing or another method. External connection terminals including the antenna terminal306, transmitting terminals Tx1, Tx2and Tx3, receiving terminals Rx1, Rx2and Rx3and control terminals401,403and405are formed in the form of the bottom surface terminal electrode203disposed on the bottom surface of the substrate101via the strip line, the interlayer via hole202or the like.

On the upper surface of the substrate101made of the low temperature cofired ceramic with low dielectric constant, the substrate106, which is one example of the second substrate according to this invention, made of a high temperature cofired ceramic with high dielectric constant and having a smaller area than the substrate101is disposed. Between the substrates101and106, there is sandwiched a plurality of metal foil resonators107mainly made of gold, silver or copper, each of which is one example of a resonator electrode which is apart of the resonator according to this invention. Spaces between the metal foil resonators107are filled with the thermosetting resin108, whereby the substrates101and106are interconnected and integrated.

The electrode109, which is drawn to the upper surface of the substrate101via the interlayer via hole202, is formed on the upper surface of the substrate101in a region where the metal foil resonator107and the substrate106are not formed. Devices which are difficult to form in the substrate101, such as the two SAW filters102, the five PIN diodes103and the discrete components including the discrete inductor104and the discrete capacitor105, are mounted and electrically connected to the internal circuit in the stack assembly via the respective upper surface external electrodes109formed on the upper surface of the stack assembly.

As described above, in the circuit shown inFIG. 7, the duplexer308is shown as an example of a second high frequency circuit according to this invention, and the part other than the duplexer308is shown as an example of a first high frequency circuit according to this invention.

FIG. 8shows an arrangement of electrodes1413a,1413b,1416a,1416b,1412and1415, each of which constitutes a part of the input/output coupling capacitors413a,413b,416aand416band inter-stage coupling capacitors412and415, when forming the transmitting filter407and the receiving filter408from the substrate106, the metal foil resonator107and the multilayered wiring conductor in the substrate101.

Now, a circuit configuration of the RF device according to the embodiment 1 of this invention will be described.

The RF device according to the embodiment 1 of this invention is an RF device provided for triple bands having a filtering capability of passing therethrough transmitting frequency bands and receiving frequency bands of a first frequency band (EGSM), a second frequency band (DCS) and a third frequency band (UMTS), the first and second frequency bands being examples of a lower frequency band of this invention, and the third frequency band being an example of a higher frequency band of this invention. The RF device comprises the switch circuits (send/receive switching circuits)301and302and the diplexer303.

The diplexer303has the LPF303athat is connected between the internal terminal304and the antenna terminal306to be connected to the antenna (ANT) and passes therethrough the first frequency band (EGSM), and the HPF303bthat is connected between the internal terminal305and the antenna terminal306and passes therethrough the second frequency band (EGSM) and the third frequency band (UMTS).

The switch circuit301is switching means that is connected to the internal terminal304and switches between the transmitting terminal Tx1and receiving terminal Rx1for the first frequency band (EGSM) branched by the LPF303aunder the control of the control terminal401. The LPF307afor reducing a harmonic distortion caused by amplification when transmitting via the transmitting terminal Tx1is inserted between the switch circuit301and the transmitting terminal Tx1. In addition, the SAW filter102afor reducing an undesired frequency component of a signal inputted through the antenna ANT when receiving via the receiving terminal Rx1is inserted between the switch circuit301and the receiving terminal Rx1.

The switch circuit302is switching means that is connected to the internal terminal305and switches among the transmitting terminal Tx2and receiving terminal Rx2for the second frequency band (DCS) branched by the HPF303band the duplexer308for the third frequency band (UMTS) under the control of the control terminals403and405. The low pass filter (LPF)307bfor reducing a harmonic distortion caused by amplification when transmitting via the transmitting terminal Tx2is inserted between the switch circuit302and the transmitting terminal Tx2. In addition, the SAW filter102bfor reducing an undesired frequency component of a signal inputted through the antenna ANT when receiving via the receiving terminal Rx2is inserted between the switch circuit302and the receiving terminal Rx2. The duplexer308is means of branching a signal in the third frequency band (UMTS) received via the switch circuit302to the transmitting terminal Tx3and receiving terminal Rx3for the third frequency band (UMTS).

A communication mode for the first frequency band (EGSM) and the second frequency band (DCS) is the TDMA (Time Division Multiple Access) mode. One example of the lower frequency band according to this invention is a frequency band for the TDMA mode. In this case, switching between the transmitting terminals Tx1, Tx2and the receiving terminals Rx1, Rx2is accomplished by means of an external diode. A communication mode for the third frequency band (UMTS) is the CDMA (Code Division Multiple Access) mode. One example of the higher frequency band according to this invention is a frequency band for the CDMA mode. The transmitting terminal Tx3and the receiving terminal Rx3are provided via the duplexer308.

The duplexer308is composed of the transmitting filter407, the receiving filter408and the transmission lines409,410having an optimum electrical length and connected to the filters. For example, the transmitting filter407is a two-stage band pass filter (BPS) composed of the two quarter-wavelength tip-short-circuited resonators411aand411b, the inter-stage coupling capacitor412disposed therebetween, and the input/output coupling capacitors413aand413bdisposed at the input side and output side thereof.

Similarly, the receiving filter408is a two-stage BPS composed of the two quarter-wavelength tip-short-circuited resonators414aand414b, the inter-stage coupling capacitor415, and the input/output coupling capacitors416aand416b. Here, the quarter-wavelength tip-short-circuited resonator411a,411b,414aand414bconstituting the transmitting filter407and the receiving filter408shown inFIG. 7are equivalent to the metal foil resonators107shown inFIG. 1.

The inter-stage coupling capacitors412and415and the input/output coupling capacitors413a,413b,416aand416bconstituting the transmitting filter407and the receiving filter408are each composed of the multilayered wiring conductor201in the substrate101and the metal foil resonator107. Devices which are difficult to form in the substrate101, such as the diodes103ato103e, and SAW filters102aand102b, are mounted on the substrate101, and the strip lines, capacitors and inductors, which can be formed in the substrate101, are formed in the substrate101, whereby the complicated RF device can be made compact.

In addition, since the metal foil resonator107, which has high conductivity and less irregularity, is used as the resonator, a Quality factor Qc associated with a conductor loss is enhanced. Therefore, a filter or duplexer having a high Quality factor representing the performance of the filter and low loss can be realized. The Quality factor is expressed by the following formula 1 using the Quality factor Qc associated with the conductor loss, a Quality factor Qd associated with a dielectric loss and a Quality factor Qr associated with a radiation loss.
1/Q=1/Qc+1/Qd+1/Qr(Formula 1)

Furthermore, according to the embodiment 1, on the upper surface of the metal foil resonator107, there is provided the substrate106made of a high temperature cofired ceramic with high dielectric constant, which has a higher dielectric loss Qd, rather than the substrate101made of the low temperature cofired ceramic with low dielectric constant. Thus, the Quality factor of the resonator can be further enhanced. In addition, as the dielectric constant is increased, the length of the resonator can be reduced. Thus, the size of the RF device can be reduced compared to the case where it is formed using only the ceramic with low dielectric constant. Thus, a filter or duplexer having low loss and reduced size can be realized.

As described above, the duplexer308or filters407,408composed of the substrates101and106with different dielectric constants and areas and the metal foil resonator107formed therebetween, the multilayered RF switches composed of the external components, such as the PIN diodes, formed in the substrate101made of the low temperature cofired ceramic with low dielectric constant and on the upper surface thereof, and the like are integrated, whereby the compact RF device with low loss capable of supporting the different communication modes, that is, the TDMA and CDMA modes can be realized.

In the description of this embodiment, the transmitting filter407and the receiving filter408constituting the duplexer308are the two-stage BPFs. However, the filters maybe an LPF or band elimination filter (BEF). Furthermore, the number of stages is not limited to two, and may be changed appropriately for a desired characteristic.

In addition, shielding can be enhanced by providing a ground electrode GND on the whole or part of the surface of the substrate106made of the high temperature cofired ceramic with high dielectric constant.

In the above description, the metal foil resonator107is used as an example of the resonator electrode according to this invention. However, instead of the metal foil resonator107, a printed electrode formed by screen printing or the like can also enhance the dielectric loss Qd due to the substrate106made of the high temperature cofired ceramic with high dielectric constant, and thus, a filter or duplexer with low loss can be realized.

In the above description, the substrate106made of the high temperature cofired ceramic with high dielectric constant is provided on the upper surface of the metal foil resonator107to enhance the dielectric loss Qd. However, the substrate106may be made of the low temperature cofired ceramic with high dielectric constant to enable an electrode to be formed in the substrate106by screen printing or the like as in the case of the substrate101.

FIG. 14shows an arrangement example in such a case. The substrate106shown inFIG. 14is composed of stacked substrates106a,106band106ceach made of the low temperature cofired ceramic with high dielectric constant. On a surface of the substrate106b, there is formed a ground electrode106g. On a surface of the substrate106a, there are formed by screen printing input/output coupling capacitors413a,413b,416aand416band electrodes1413a,1413b,1416a,1416b,1412and1415, each of which constitutes a part of the inter-stage coupling capacitors412and415. In this case, the input/output coupling capacitors413a,413b,416aand416band the inter-stage coupling capacitors412and415, each of which is an example of a part of the filter according to this invention, are formed on a surface of or in the substrate106made of the low temperature cofired ceramic with high dielectric constant. In the RF device thus configured, the low temperature cofired ceramic with high dielectric constant serves as the dielectric of the input/output coupling capacitors413a,413b,416aand416band the inter-stage coupling capacitors412and415. Therefore, the size of the capacitors can be reduced, so that the whole size of the RF device can be reduced.

In addition, in this case, the Quality factors of the inter-stage coupling capacitors412and415and input/output coupling capacitors413a,413b,416aand416bcan be enhanced, so that the filters407and408can be reduced in loss.

InFIG. 14, the substrate106is shown to be composed of three layers having the electrodes printed thereon, and the substrate101is shown to be composed of four layers having the electrodes printed thereon. However, regardless of the number of the layers having the electrodes printed thereon, the same effect can be attained.

In addition, the resonator electrodes (that is, the tip-short-circuited resonators411a,411b,414aand414b) may be formed in the substrate106made of a ceramic with high dielectric constant.FIG. 15shows an arrangement example in such a case. Such an arrangement also can attain the same effect as described above.

Furthermore, the resonator electrodes may be disposed in the vicinity of the substrate106, rather than on the surface or in the substrate106.FIG. 16shows an arrangement in such an example, in which the tip-short-circuited resonators411a,411b,414aand414bare disposed in the substrate101. The substrate101shown inFIG. 16is composed of stacked substrates101a,101b,101cand101deach made of the low temperature cofired ceramic with low dielectric constant. Also in the case where the tip-short-circuited resonators411a,411b,414aand414bare disposed in the substrate101and are not in contact with the substrate106in this way, if the substrate101ais thin so that the resonators can be affected by the substrate106, the same effect as described above can be attained even though the resonator electrodes are disposed in the vicinity of the substrate106.

In the above description, the tip-short-circuited resonator electrodes411a,411b,414aand414bserve as the resonator electrodes. Of course, however, a tip-opened half-wavelength resonator may attain the same effect.

In the above description, the PIN diodes are used in the switch circuit301for switching between the transmitting terminal Tx1and receiving terminal Rx1for the first frequency band (EGSM) and the switch circuit302for switching among the transmitting terminal Tx2, receiving terminal Rx2for the second frequency band (DCS) and the duplexer308for the third frequency band (UMTS). Of course, however, a switching device, such as a GaAs semiconductor, a field effect transistor and a varactor diode, may attain the same effect.

Furthermore, in this embodiment, the RF device provided for triple bands for three systems, that is, EGSM, DCS and UMTS systems has been described. However, it is obvious that this invention is not limited thereto and this invention includes any arrangement in which the substrate101made of a material with a lower dielectric constant having a first high frequency circuit for a lower frequency band formed therein or on a surface thereof and at least part of a resonator of a second high frequency circuit for a higher frequency band are provided on a surface of the substrate106, and the first and second high frequency circuits are connected to each other.

Furthermore, in the description of the embodiment 1, the first high frequency circuit for a lower frequency band is formed in the first substrate and the second high frequency circuit for a higher frequency band is formed in the second substrate. However, as far as no problem of the line impedance arises, the first high frequency circuit for a lower frequency band may be formed in the second substrate (for example, substrate106) and the second high frequency circuit for a higher frequency band may be formed in the first substrate (for example, substrate101). In this case, each component of the first high frequency circuit formed in the second substrate can provide a high Quality factor, and thus, if the first high frequency circuit constitutes a filter, the loss thereof can be reduced.

In addition, the first to third frequency bands should not be limited to those described above. For example, the third frequency band may be a frequency band (800 MHz band) provided for the CDMA-One (R) mode, and the first and second frequency bands may be provided for the PDC mode and the PHS mode, respectively. That is, if the third frequency band is lower than the first or second frequency band, the same effect can be attained. Here, of course, the first to third frequency bands may be provided for modes other than those described above.

Now, an RF device according to a second embodiment of this invention will be described with reference to the drawings.

FIG. 9is a circuit diagram of the RF device according to the embodiment 2 of this invention. InFIG. 9, reference numerals501to505denote a metal foil resonator serving as the quarter-wavelength tip-short-circuited resonator, reference numerals506,507denote a series capacitor, reference numerals508,509denote a ground capacitor, reference numerals510to512denote a coupling inductor, reference numerals513,154denote a coupling capacitor, reference numerals515,516denote a bypass capacitor, reference numeral517denotes a capacitor for matching between terminals, reference numeral518denotes an inductor for matching between terminals, reference numerals519to523denotes a switch, reference numerals524to528denote a switch coupling capacitor, reference numeral529denotes an antenna terminal, reference numeral530denotes a transmitting terminal, and reference numeral531denotes a receiving terminal.

The series capacitors506and507are connected to open ends of the resonators501and502, respectively, and the resonators501and502are connected to each other by the inductor510, thereby forming a transmitting filter540. The coupling inductor510has the ground capacitors508and509connected to the ends thereof for suppressing harmonics. On the other hand, the resonators503,504and505are coupled with each other by the capacitors513and514. The input/output coupling inductors511and512are connected to open ends of the resonators503and505, respectively, whereby a receiving band pass filter541is formed In addition, the bypass capacitor515bridging the coupling elements511and513and the bypass capacitor516bridging the coupling elements512and514provide an attenuation pole at a frequency higher than the pass band.

An output terminal of the transmitting filter540and an input terminal of the receiving band pass filter541are connected to the antenna terminal529via the series inductor518and the parallel capacitor517both for matching between terminals. The switches519,520,521,522and523are connected to open ends of the resonators501,502,503,504and505via the switch coupling capacitors524,525,526,527and528, respectively. The other ends of the switches are all grounded. In this way, the transmitting filter540, the receiving band pass filter541, the transmitting terminal530, the receiving terminal531and the antenna terminal529constitute the RF device.

FIG. 10shows a specific circuit arrangement of the switches519to523including a PIN diode. Reference numeral601denotes a PIN diode. The PIN diode601is serially connected to a coupling capacitor602for blocking a direct current (equivalent to the capacitors524to528inFIG. 9) to form a frequency shift circuit. A control terminal606is connected to the connection between the PIN diode601and the coupling capacitor602via a resistor605, a bypass capacitor604and a choke coil603. A shift voltage is applied to the control terminal606to control the switching among bands.

That is, the shift voltage applied to the control terminal606is intended to turn on or off the PIN diode601. If a certain positive voltage (shift voltage) higher than a bias voltage applied to a cathode of the PIN diode601is applied to the control terminal606, a resistance of the PIN diode601in the forward direction becomes quite low, so that a current flows in the forward direction, and thus, the PIN diode601is turned on. The resistor605is to control the current value of the PIN diode601when it is in the on state. To the contrary, if a voltage of 0 volts or a reverse bias voltage is applied to the control terminal606, the resistance of the PIN diode601in the forward direction becomes quite high, so that no current flows in the forward direction, and thus, the PIN diode601is turned off.

FIG. 11is a partial perspective view of the RF device according to the embodiment 2 of this invention, in which the same parts as inFIG. 10are assigned the same reference numerals. Reference numeral701denotes a metal foil resonator, reference numeral702denotes a substrate made of a ceramic with low dielectric constant, which is an example of the first substrate according to this invention, reference numeral703denotes a substrate made of a ceramic with high dielectric constant, which is an example of the second substrate according to this invention, and reference numeral704denotes a thermosetting resin.

A plurality of metal foil resonators701are equivalent to the resonators501to505, and the metal foil resonators701are interposed between a lower substrate702and an upper substrate703. Spaces between the metal foil resonators701are filled with the thermosetting resin704, which interconnects and integrates the substrates702and703. The components constituting the RF device according to the second embodiment of this invention except for the resonators501to505, such as capacitors, inductors and switches, are mounted on the substrate702made of the ceramic with low dielectric constant.

That is, the high frequency circuit is formed in or on a surface of the substrate702except for a part of the filter (that is, the metal foil resonators), and the metal foil resonators701, each of which is an example of at least part of the filter according to this invention, are formed on a surface of the substrate703.

FIGS. 12aand12bshow transfer characteristics of the RF device according to the embodiment 2 of this invention.FIG. 12(a) shows a transfer characteristic of the transmitting filter540composed of the transmission line from the transmitting terminal530to the antenna terminal529, the resonators501and502connected to the transmission line via the series capacitors506and507, respectively, and the inter-stage coupling inductor510. The coupling inductor510, the series inductor518connected to the output terminal of the transmitting filter540, and the ground capacitors508,509and517provide a low pass characteristic to suppress harmonics in a transmitting band.

The inductor518and capacitor517serve also to adjust the impedances of the transmitting filter540and receiving band pass filter541to prevent the filters from affecting each other in their respective frequency bands at the antenna terminal529. Since the impedances of the transmitting filter540and the receiving band pass filter541are adjusted in this way, the transmitting filter540exhibits a low insertion loss for the sent signal in the transmitting frequency band, which is the pass band, and therefore, can transmit the sent signal from the transmitting terminal530to the antenna terminal529with little attenuation of the sent signal.

On the other hand, the transmitting filter540exhibits a high insertion loss for the received signal in the receiving frequency band, and therefore, reflects most of the input signal in the receiving frequency band. Thus, the received signal inputted through the antenna terminal529is directed toward the receiving band pass filter541.

FIG. 12(b) shows a transfer characteristic of the receiving band pass filter541composed of the transmission line from the antenna terminal529to the receiving terminal531, the grounded resonators503,504and505, the inter-stage coupling capacitors513and514, and the input/output coupling inductors511and512. The impedance characteristic of the receiving band pass filter541and the impedances of the capacitors515and516used in the bypass circuit provide an attenuation pole as shown inFIG. 12(b).

In the circuit arrangement shown inFIG. 9, since the inductors are used for coupling of the input and the output, the impedance of the bypass circuit is equivalently inductive, and the attenuation pole appears in a region in the vicinity of a frequency where the impedance of the receiving band pass filter541becomes capacitive, that is, a transmitting frequency higher than a center frequency of the receiving band pass filter541.

The receiving band pass filter541exhibits a low insertion loss for the received signal in the receiving frequency band and can transmit the received signal from the antenna terminal529to the receiving terminal531with little attenuation of the received signal. On the other hand, the receiving band pass filter541exhibits a high insertion loss for the sent signal in the transmitting frequency band and therefore, reflects most of the input signal in the transmitting frequency band. Thus, the sent signal from the transmitting filter540is directed toward the antenna terminal529.

In addition, to the open ends of the resonators501,502,503,504and505, there are connected frequency shift circuits composed of series connections of the switch coupling capacitors524,525,526,527and528for blocking a direct current and the switches519,520,521,522and523each having one end grounded, respectively.

That is, a resonance frequency of the resonators501to505is determined by a capacitance component and inductance component of the respective resonators and a capacitance of their respective frequency shift circuits at the time when their respective switches519to523are in the on state or off state. If any of the switches519to523is turned on, the capacitance component of the frequency shift circuit is increased, and accordingly, the resonance frequency of the resonator is reduced. As a result, the blocking band of the transmitting filter540and the center frequency and pass band of the receiving band pass filter541are shifted to a lower frequency. On the other hand, if any of the switches519to523is turned off, the capacitance component of the frequency shift circuit is reduced, and accordingly, the resonance frequency of the resonator is increased. As a result, the blocking band of the transmitting filter540and the pass band of the receiving band pass filter541are shifted to a higher frequency. In other words, the blocking band of the transmitting filter540and the pass band of the receiving band pass filter541can be shifted synchronously by operating switches519to523in this way.

FIG. 12shows relationships between the transfer characteristics of the transmitting filter540and receiving band pass filter541configured as described above and the on or off state of the switches519to523in a frequency region from 800 to 1000 MHz. Reference numeral801inFIG. 12(a) and reference numeral803inFIG. 12(b) designate the transfer characteristic in the case where all of the switches519to523are turned on, and reference numeral802inFIG. 12(a) and reference numeral804inFIG. 12(b) designate the transfer characteristic in the case where all of the switches519to523are turned off. In this way, by switching of the switches519to523, the send-side blocking frequency band and the receive-side frequency pass band of the RF device are changed synchronously.

Besides the PIN diode described above, a transistor may serve as the switches519to523. For example,FIG. 13shows a case where a field effect transistor (FET)901serves as the switches519to523. A gate electrode of the FET901is connected to a control terminal903via a bypass capacitor902. Since the FET901is a voltage control device, no current is consumed when the device is turned on, unlike the case of the PIN diode. Thus, using such a FET901can reduce current consumption. Besides, if a varactor diode serves as the switches519to523, the send-side blocking band and the receive-side pass band can be change continuously.

As described above, according to this embodiment, the blocking band of the transmitting filter540and the pass band of the receiving band pass filter541of the RF device can be controlled synchronously by the current or voltage applied thereto externally. Therefore, even if a certain wide band is required, an attenuation can be provided without increasing the number of the stages of each filter. In addition, since the number of the stages is small, the loss is reduced. As a result, the RF device itself can be downsized.

In addition, since the metal foil resonator is used as the resonator, the Quality factor of the resonator is enhanced. And, since the substrate made of the high temperature cofired ceramic with high dielectric constant having a good high frequency characteristic is overlaid on the upper surface of the metal foil resonator, the Quality factor of the resonator is further enhanced. As a result, each of the filters can be reduced in loss.

In the above description, the transmitting filter540is arranged on the transmitting side and the receiving band pass filter541is arranged on the receiving side. However, such an arrangement of the transmitting filter and receiving filter is obviously susceptible to various modifications, such as using a low pass filter, and of course, the modifications are included in this invention.

Besides, while the resonator devices501,502and the impedance varying devices519,520, which are connected to each other in parallel by the capacitors, may be connected to each other by inductors.

This invention is the most effective if it is applied to a communication apparatus for a system with wide transmitting pass band and receiving pass band and a narrow interval between the transmitting pass band and the receiving pass band, such as PCS, EGSM, and CDMA in Japan. However, a system other than those described above may be contemplated.

For example, in another system, the transmitting pass band and the receiving pass band are each divided, with bandwidths thereof corresponding to each other, into two bands, that is, a transmitting Low band and a transmitting High band, and a receiving Low band and a receiving High band, respectively. For the respective two divisional bands, a control signal is used to switch between the transmitting band and the receiving band synchronously, with the transmitting Low band being associated with the receiving Low band and the transmitting High band being associated with the receiving High band. This is equivalent to widening the interval between the transmitting frequency and the receiving frequency during operation of the system, and thus, an attenuation can be ensured without increasing the number of the stages of each filter. Here, in this system, by selecting the band including the channel to be used by the control signal, whole of the transmitting pass band and receiving pass band can be covered. In addition, of course, the arrangement according to this invention can be applied to other systems including TDMA and CDMA.

In addition, since some or all of the capacitors and inductors except for the resonators501to505are composed of electrodes in the substrate702made of the ceramic with low dielectric constant, downsizing can be realized.

The configuration of each substrate in the RF device according to this embodiment may be the same as that according to the embodiment 1 (shown inFIGS. 13 to 16). That is, the substrate702may be equivalent to the substrate101and the substrate703may be equivalent to the substrate106.

The RF device according to this embodiment has been described so far to operate while supporting only one system in the description. However, it may operate while supporting a plurality of systems.

The configuration of the RF device described so far, in which one substrate made of a ceramic with high dielectric constant is overlaid on another substrate made of a ceramic with low dielectric constant, is not limited to those shown inFIGS. 1 and 11, and may be those shown inFIGS. 2,3and4.

In the case where the two substrates106are disposed on the substrate101with spaced apart from each other as shown inFIG. 2, if the transmitting filter407is constituted by one of the substrates106and the substrate101and the receiving filter408is constituted by the other of the substrates106and the substrate101, the transmitting filter407and the receiving filter408can be prevented from interfering with each other, and therefore, a high performance RF device can be provided.

In the above description, the RF device according to this invention has been described to be composed of the substrate101or702made of a ceramic with low dielectric constant and the substrate106or703made of a ceramic with high dielectric constant overlaid thereon. However, the substrate101or702and the substrate106or703may be arranged side by side.

FIG. 17shows an arrangement in which the substrates101and106are arranged side by side and a high frequency circuit formed on or in the substrate101and a high frequency circuit formed in the substrate106are connected to each other through the wiring pattern201. In such a case, the same effect as described above can be attained.

As described above, according to this invention, the metal foil is used for the resonator constituting the duplexer and a ceramic with high dielectric constant having a good material characteristic is provided on the upper surface of the resonator, whereby the resonator with low loss can be provided. Furthermore, external components arranged in or on the upper surface of the low temperature cofired ceramic with low dielectric constant constitute multilayered switches for a plurality of systems, and the duplexer is formed on the upper surface thereof, whereby a compact RF device with low loss provided also for the TDMA and CDMA can be provided.

According to this invention, an RF device having a low filter loss and not suffering from a problem about a line impedance, or a compact RF device not suffering from a problem about a line impedance can be provided.