Patent Publication Number: US-6985712-B2

Title: RF device and communication apparatus using the same

Description:
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 in  FIG. 18  to be used with one cellular phone. With reference to drawings, a first conventional RF device will be described below. 
     FIG. 19  is a cross-sectional view of the first conventional RF device. In  FIG. 19 , reference numeral  1101  denotes a low temperature cofired ceramic body with a low relative dielectric constant. Reference numeral  1102  denotes a multilayered wiring conductor for constituting part of an RF circuit. Reference numeral  1103  denotes an interlayer via hole and reference numeral  1104  denotes a discrete component, such as a discrete resistor, a discrete capacitor, a discrete inductor and a packaged semiconductor. 
     FIG. 20  is 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 diplexer  1201  that connects a transmitting/receiving switching circuit  1202  and a transmitting/receiving switching circuit  1203  to an antenna (ANT). 
   An operation of the first conventional RF device arranged as described above will be described. 
   The multilayered wiring conductor  1102  electrically interconnects a plurality of discrete components  1104  and, in a substrate  1101  made 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 components  1104 , and the RF circuit serves as an RF device such as an RF multilayered switch. 
   The diplexer  1201  directly connected to the antenna terminal (ANT) branches a signal received through the antenna terminal (ANT) to the transmitting/receiving switching circuits  1202  and  1203 . The duplexer  1204  is connected to the transmitting/receiving switching circuit  1203 . The transmitting/receiving switching circuit  1202  has a transmitting terminal Tx 1  for EGSM transmitting and a receiving terminal Rx 1  for EGSM receiving. The transmitting/receiving switching circuit  1203  has a transmitting terminal Tx 2  for DCS transmitting and a receiving terminal Rx 2  for DCS receiving. The duplexer  1204  has a transmitting terminal Tx 3  for UMTS transmitting and a receiving terminal Rx 3  for UMTS receiving. 
   The receiving terminal Rx 2  is connected to the antenna via a diode  1205 , which is in the off state during transmission using the transmitting terminal Tx 2 . 
   Transmission line  1206   a  and  1206   b  for electrical length correction, a transmitting filter  1207  and a receiving filter  1208 , which are required for duplex transmission, are connected between the transmitting terminal Tx 3  and the receiving terminal Rx 3 . 
   Now, a second conventional RF device will be described as another example of the send/receive switching circuit directly connected to the antenna. 
     FIG. 21  is an exploded perspective view of the second conventional RF device. The RF device has six dielectric substrates with high relative dielectric constant  1301   a  to  1301   f . The dielectric substrate  1301   b  having a shielding electrode  1302   a  formed on the upper surface thereof, the dielectric substrate  1301   c  having an inter-stage coupling electrode  1303  formed on the upper surface thereof, the dielectric substrate  1301   d  having resonator electrodes  1304   a  and  1304   b  formed on the upper surface thereof, the dielectric substrate  1301   e  having input/output coupling capacitor electrodes  1305   a  and  1305   b  formed on the upper surface thereof, and the dielectric substrate  1301   f  having a shielding electrode  1302   b  formed on the upper surface thereof are stacked. 
   End face electrodes  1306   a  and  1306   b , which are connected to the shielding electrodes  1302   a  and  1302  to 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 electrode  1307  which is connected to the ground facing the shielding electrodes  1302   a  and  1302   b  and a common open end of the microstrip resonator electrodes  1304   a  and  1304   b . An end face electrode  1308 , which is provided on the front of the stacked dielectric substrates, is connected to short-circuit ends of the resonator electrodes  1304   a  and  1304   b  and to the shielding electrodes  1302   a  and  1302   b . End face electrodes  1309   a  and  1309   b  at the left and right sides of the stacked dielectric substrates are connected to the input/output coupling electrodes  1305   a  and  1305   b  to constitute input/output terminals. 
     FIG. 22  is a circuit diagram of the second conventional RF device. The input/output coupling electrode  1305   a  and the resonator electrode  1304   a  constitute an input/output coupling capacitor  1401   a , and the input/output coupling electrode  1305   b  and the resonator electrode  1304   b  constitute an input/output coupling capacitor  1401   b . In addition, the input/output coupling electrode  1305   a  and the inter-stage coupling electrode  1303  constitute an inter-stage coupling capacitor  1402   a , and the input/output coupling electrode  1305   b  and the inter-stage coupling electrode  1303  constitute an inter-stage coupling capacitor  1402   b . These components constitute a two-stage band-pass filter shown in  FIG. 22 . 
     FIG. 23  is a block diagram of an antenna duplexer  1503 , which is the second conventional RF device, comprising a transmitting filter  1501 , a receiving filter  1502 , 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 filter  1206  and the receiving filter  1027  are 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 substrate  1101  made 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 substrate  1101  with 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. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an RF device according to an embodiment 1 of this invention. 
       FIG. 2  is a perspective view of the RF device according to the embodiment 1 of this invention. 
       FIG. 3  is a perspective view of the RF device according to the embodiment 1 of this invention. 
       FIG. 4  is a perspective view of the RF device according to the embodiment 1 of this invention. 
       FIG. 5  is a cross-sectional view of the RF device taken along a line A–A′ in  FIG. 1 . 
       FIG. 6  is a block diagram of the RF device according to the embodiment 1 of this invention. 
       FIG. 7  is an equivalent circuit diagram of the RF device according to the embodiment 1 of this invention. 
       FIG. 8  is a perspective view of the RF device according to the embodiment 1 of this invention. 
       FIG. 9  is an equivalent circuit diagram of the RF device according to an embodiment 2 of this invention. 
       FIG. 10  illustrates a switch circuit, including a PIN diode, of the RF device according to the embodiment 2 of this invention. 
       FIG. 11  is a partial perspective view of the RF device according to the embodiment 2 of this invention. 
       FIGS. 12   a  and  12   b  are graphs showing a transfer characteristic of the RF device according to the embodiment 2 of this invention. 
       FIG. 13  shows a configuration of the RF device including a FET according to the embodiment 2 of this invention. 
       FIG. 14  is a perspective view of the RF device according to the embodiment 1 of this invention. 
       FIG. 15  is a perspective view of the RF device according to the embodiment 1 of this invention. 
       FIG. 16  is a perspective view of the RF device according to the embodiment 1 of this invention. 
       FIG. 17  is a perspective view of the RF device according to the embodiment 1 of this invention. 
       FIG. 18  shows frequencies of a plurality of systems for which a first conventional RF device operates. 
       FIG. 19  is a cross-sectional view of the first conventional RF device. 
       FIG. 20  is a circuit diagram of the first conventional RF device. 
       FIG. 21  is an exploded perspective view of a second conventional RF device. 
       FIG. 22  is a circuit diagram of the second conventional RF device. 
       FIG. 23  is a block diagram of a duplexer of the second conventional RF device. 
   

   DESCRIPTION OF SYMBOLS 
   
       
         101  Low temperature cofired ceramic with low dielectric constant 
         102   a ,  102   b  SAW filter 
         103   a ,  103   b ,  103   c ,  103   d ,  103   e  PIN diode 
         104  Discrete inductor 
         105  Discrete capacitor 
         106  Ceramic with high dielectric constant 
         107  Metal foil resonator 
         108  Thermosetting resin 
         109  Upper external electrode 
         201  Multilayered wiring conductor 
         202  Interlayer via hole 
         203  Bottom surface terminal electrode (LGA) 
         301 ,  302  Switch circuit 
         303  Diplexer 
         304 ,  305  Internal terminal 
         306  Antenna terminal 
         307   a ,  307   b  LPF 
         308  Duplexer 
         401  Control terminal 
         402  Resistor 
         403  Control terminal 
         404  Resistor 
         405  Control terminal 
         406  Resistor 
         407  Transmitting filter 
         408  Receiving filter 
         409  Transmission line 
         410  Transmission line 
         411   a ,  411   b  Quarter-wavelength tip-short-circuited resonator 
         412  Inter-stage coupling capacitor 
         413   a ,  413   b  Input/output coupling capacitor 
         414   a ,  414   b  Quarter-wavelength tip-short-circuited resonator 
         415  Inter-stage coupling capacitor 
         416   a ,  416   b  Input/output coupling capacitor 
         501 ,  505  Resonator 
         506 ,  507  Series capacitor 
         508 ,  509  Ground capacitor 
         510 ,  512  Coupling inductor 
         513 ,  514  Coupling capacitor 
         515 ,  516  Bypass capacitor 
         517  Capacitor for matching between terminals 
         518  Inductor for matching between terminals 
         519 ,  520 ,  521 ,  522 ,  523  Switch 
         524 ,  525 ,  526 ,  527 ,  528  Switch coupling capacitor 
         529  Antenna terminal 
         530  Transmitting terminal 
         531  Receiving terminal 
         601  PIN diode 
         602  Coupling capacitor 
         603  Choke coil 
         604  Bypass capacitor 
         605  Resistor 
         606  Control terminal 
         701  Metal foil resonator 
         702  Low temperature cofired ceramic with low dielectric constant 
         703  Ceramic with high dielectric constant 
         704  Thermosetting resin 
         901  Field effect transistor (FET) 
         902  Bypass capacitor 
         903  Control terminal 
         1101  Low temperature cofired ceramic body with low dielectric constant 
         1102  Multilayered wiring conductor 
         1103  Interlayer via hole 
         1104  Discrete component 
         1201  Diplexer 
         1202  Send/receive switching circuit 
         1203  Send/receive switching circuit 
         1204  Duplexer 
         1205  Diode 
         1206   a ,  1206   b  Transmission line 
         1207  Transmitting filter 
         1208  Receiving filter 
         1301   a ,  1301   e  Dielectric substrate with high dielectric constant 
         1302   a ,  1302   b  Shielding electrode 
         1303  Inter-stage coupling electrode 
         1304   a ,  1304   b  Microstrip resonator electrode 
         1305   a ,  1305   b  Input/output coupling electrode 
         1306   a ,  1306   b  End face electrode 
         1307  End face electrode 
         1308  End face electrode 
         1309   a ,  1309   b  Input/output terminal 
         1401   a ,  1401   e  Input/output coupling capacitor 
         1402   a ,  1402   b  Inter-stage coupling capacitor 
     
  
   PREFERRED EMBODIMENTS OF THE INVENTION 
   Now, an RF device according to this invention will be described with reference to the drawings. 
   (Embodiment 1) 
     FIG. 1  is a perspective view of an RF device according to an embodiment 1 of this invention. A substrate  101  is 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 numerals  102   a  and  102   b  denote a SAW filter, reference numerals  103   a  to  103   e  denote a PIN diode, which is one example of a semiconductor device according to this invention, reference numeral  104  denotes a discrete inductor, reference numeral  105  denotes a discrete capacitor, and a substrate  106  is 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 resonator  107  is one example of a part of a resonator according to this invention. Reference numeral  108  denotes a thermosetting resin and reference numeral  109  denotes an upper surface external electrode. 
     FIG. 5  is a cross-sectional view of the RF device shown in  FIG. 1  taken along a line A–A′. Reference numeral  201  denotes a multilayered wiring conductor, reference numeral  202  denotes an interlayer via hole, and reference numeral  203  denotes a bottom surface terminal electrode (LGA: Land Grid Array). 
     FIG. 6  is a block diagram of the RF device according to the embodiment 1 of this invention. Reference numerals  301  and  302  denote a switching circuit (send/receive switching circuit). Reference numeral  303  denotes a diplexer, and specifically, reference numeral  303   a  denotes a low pass filter (LPF) and reference numeral  303   b  denotes a high pass filter (HPF) Reference numerals  304  and  305  denote an internal terminal, reference numeral  306  denotes an antenna terminal, reference numerals  307   a  and  307   b  denote an LPF, and reference numeral  308  denotes a duplexer (Dup). 
     FIG. 7  is an equivalent circuit diagram of the RF device according to the embodiment 1 of this invention. Reference numeral  401  denotes a control terminal, reference numeral  402  denotes a resistor, reference numeral  403  denotes a control terminal, reference numeral  404  denotes a resistor, reference numeral  405  denotes a control terminal, reference numeral  406  denotes a resistor, reference numeral  407  denotes a transmitting filter, reference numeral  408  denotes a receiving filter, reference numerals  409  and  410  denote a transmission line, reference numerals  411   a  and  411   b  denote a quarter-wavelength tip-short-circuited resonator, reference numeral  412  denotes an inter-stage coupling capacitor, reference numerals  413   a  and  413   b  denote an input/output coupling capacitor, reference numeral  414   a  and  414   b  denote a quarter-wavelength tip-short-circuited resonator, reference numeral  415  denotes an inter-stage coupling capacitor, and reference numerals  416   a  and  416   b  denote an input/output coupling capacitor. 
   In the substrate  101  made of a low temperature cofired ceramic with low dielectric constant, the multilayered wiring conductor  201  made of copper or silver, which is one example of the multilayered wiring pattern according to this invention, forms strip lines including the transmission lines  409 ,  410  with an impedance determined by thickness, width and length of the multilayered wiring conductor  201  and the dielectric constant of the substrate  101 . In addition, the multilayered wiring conductors  201  disposed in different two layers form a capacitor in the substrate  101 , the capacitor having an impedance determined by an overlapping area of the multi layered wiring conductors  201 , the dielectric constant of the low temperature cofired ceramic with low dielectric constant sandwiched between the multilayered wiring conductors  201  or the like. 
   Since the substrate  101  made of the low temperature cofired ceramic with low dielectric constant is interposed between the multilayered wiring conductors  201  and the metal foil resonators  107 , capacitors including the inter-stage coupling capacitors  412 ,  415  and the input/output coupling capacitors  413   a ,  413   b ,  416   a  and  416   b  are formed. In addition, in the substrate  101 , the multilayered wiring conductor  201  forms an inductor having an impedance determined by width and length of the line of the multilayered wiring conductor  201  and the dielectric constant of the low temperature cofired ceramic with low dielectric constant. 
   The multilayered wiring conductors  201  are electrically connected to each other via the interlayer via hole  202  formed at a desired position between the multilayered wiring conductors  201 . A pattern of the multilayered wiring conductor  201  in each layer is formed by screen printing or another method. The interlayer via hole  202  is formed by punching a hole in the dielectric sheet constituting the substrate  101  and filling the hole with a conductive paste by printing or another method. External connection terminals including the antenna terminal  306 , transmitting terminals Tx 1 , Tx 2  and Tx 3 , receiving terminals Rx 1 , Rx 2  and Rx 3  and control terminals  401 ,  403  and  405  are formed in the form of the bottom surface terminal electrode  203  disposed on the bottom surface of the substrate  101  via the strip line, the interlayer via hole  202  or the like. 
   On the upper surface of the substrate  101  made of the low temperature cofired ceramic with low dielectric constant, the substrate  106 , 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 substrate  101  is disposed. Between the substrates  101  and  106 , there is sandwiched a plurality of metal foil resonators  107  mainly 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 resonators  107  are filled with the thermosetting resin  108 , whereby the substrates  101  and  106  are interconnected and integrated. 
   The electrode  109 , which is drawn to the upper surface of the substrate  101  via the interlayer via hole  202 , is formed on the upper surface of the substrate  101  in a region where the metal foil resonator  107  and the substrate  106  are not formed. Devices which are difficult to form in the substrate  101 , such as the two SAW filters  102 , the five PIN diodes  103  and the discrete components including the discrete inductor  104  and the discrete capacitor  105 , are mounted and electrically connected to the internal circuit in the stack assembly via the respective upper surface external electrodes  109  formed on the upper surface of the stack assembly. 
   As described above, in the circuit shown in  FIG. 7 , the duplexer  308  is shown as an example of a second high frequency circuit according to this invention, and the part other than the duplexer  308  is shown as an example of a first high frequency circuit according to this invention. 
     FIG. 8  shows an arrangement of electrodes  1413   a ,  1413   b ,  1416   a ,  1416   b ,  1412  and  1415 , each of which constitutes a part of the input/output coupling capacitors  413   a ,  413   b ,  416   a  and  416   b  and inter-stage coupling capacitors  412  and  415 , when forming the transmitting filter  407  and the receiving filter  408  from the substrate  106 , the metal foil resonator  107  and the multilayered wiring conductor in the substrate  101 . 
   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)  301  and  302  and the diplexer  303 . 
   The diplexer  303  has the LPF  303   a  that is connected between the internal terminal  304  and the antenna terminal  306  to be connected to the antenna (ANT) and passes therethrough the first frequency band (EGSM), and the HPF  303   b  that is connected between the internal terminal  305  and the antenna terminal  306  and passes therethrough the second frequency band (EGSM) and the third frequency band (UMTS). 
   The switch circuit  301  is switching means that is connected to the internal terminal  304  and switches between the transmitting terminal Tx 1  and receiving terminal Rx 1  for the first frequency band (EGSM) branched by the LPF  303   a  under the control of the control terminal  401 . The LPF  307   a  for reducing a harmonic distortion caused by amplification when transmitting via the transmitting terminal Tx 1  is inserted between the switch circuit  301  and the transmitting terminal Tx 1 . In addition, the SAW filter  102   a  for reducing an undesired frequency component of a signal inputted through the antenna ANT when receiving via the receiving terminal Rx 1  is inserted between the switch circuit  301  and the receiving terminal Rx 1 . 
   The switch circuit  302  is switching means that is connected to the internal terminal  305  and switches among the transmitting terminal Tx 2  and receiving terminal Rx 2  for the second frequency band (DCS) branched by the HPF  303   b  and the duplexer  308  for the third frequency band (UMTS) under the control of the control terminals  403  and  405 . The low pass filter (LPF)  307   b  for reducing a harmonic distortion caused by amplification when transmitting via the transmitting terminal Tx 2  is inserted between the switch circuit  302  and the transmitting terminal Tx 2 . In addition, the SAW filter  102   b  for reducing an undesired frequency component of a signal inputted through the antenna ANT when receiving via the receiving terminal Rx 2  is inserted between the switch circuit  302  and the receiving terminal Rx 2 . The duplexer  308  is means of branching a signal in the third frequency band (UMTS) received via the switch circuit  302  to the transmitting terminal Tx 3  and receiving terminal Rx 3  for 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 Tx 1 , Tx 2  and the receiving terminals Rx 1 , Rx 2  is 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 Tx 3  and the receiving terminal Rx 3  are provided via the duplexer  308 . 
   The duplexer  308  is composed of the transmitting filter  407 , the receiving filter  408  and the transmission lines  409 ,  410  having an optimum electrical length and connected to the filters. For example, the transmitting filter  407  is a two-stage band pass filter (BPS) composed of the two quarter-wavelength tip-short-circuited resonators  411   a  and  411   b , the inter-stage coupling capacitor  412  disposed therebetween, and the input/output coupling capacitors  413   a  and  413   b  disposed at the input side and output side thereof. 
   Similarly, the receiving filter  408  is a two-stage BPS composed of the two quarter-wavelength tip-short-circuited resonators  414   a  and  414   b , the inter-stage coupling capacitor  415 , and the input/output coupling capacitors  416   a  and  416   b . Here, the quarter-wavelength tip-short-circuited resonator  411   a ,  411   b ,  414   a  and  414   b  constituting the transmitting filter  407  and the receiving filter  408  shown in  FIG. 7  are equivalent to the metal foil resonators  107  shown in  FIG. 1 . 
   The inter-stage coupling capacitors  412  and  415  and the input/output coupling capacitors  413   a ,  413   b ,  416   a  and  416   b  constituting the transmitting filter  407  and the receiving filter  408  are each composed of the multilayered wiring conductor  201  in the substrate  101  and the metal foil resonator  107 . Devices which are difficult to form in the substrate  101 , such as the diodes  103   a  to  103   e , and SAW filters  102   a  and  102   b , are mounted on the substrate  101 , and the strip lines, capacitors and inductors, which can be formed in the substrate  101 , are formed in the substrate  101 , whereby the complicated RF device can be made compact. 
   In addition, since the metal foil resonator  107 , 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 resonator  107 , there is provided the substrate  106  made of a high temperature cofired ceramic with high dielectric constant, which has a higher dielectric loss Qd, rather than the substrate  101  made 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 duplexer  308  or filters  407 ,  408  composed of the substrates  101  and  106  with different dielectric constants and areas and the metal foil resonator  107  formed therebetween, the multilayered RF switches composed of the external components, such as the PIN diodes, formed in the substrate  101  made 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 filter  407  and the receiving filter  408  constituting the duplexer  308  are 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 substrate  106  made of the high temperature cofired ceramic with high dielectric constant. 
   In the above description, the metal foil resonator  107  is used as an example of the resonator electrode according to this invention. However, instead of the metal foil resonator  107 , a printed electrode formed by screen printing or the like can also enhance the dielectric loss Qd due to the substrate  106  made 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 substrate  106  made of the high temperature cofired ceramic with high dielectric constant is provided on the upper surface of the metal foil resonator  107  to enhance the dielectric loss Qd. However, the substrate  106  may be made of the low temperature cofired ceramic with high dielectric constant to enable an electrode to be formed in the substrate  106  by screen printing or the like as in the case of the substrate  101 . 
     FIG. 14  shows an arrangement example in such a case. The substrate  106  shown in  FIG. 14  is composed of stacked substrates  106   a ,  106   b  and  106   c  each made of the low temperature cofired ceramic with high dielectric constant. On a surface of the substrate  106   b , there is formed a ground electrode  106   g . On a surface of the substrate  106   a , there are formed by screen printing input/output coupling capacitors  413   a ,  413   b ,  416   a  and  416   b  and electrodes  1413   a ,  1413   b ,  1416   a ,  1416   b ,  1412  and  1415 , each of which constitutes a part of the inter-stage coupling capacitors  412  and  415 . In this case, the input/output coupling capacitors  413   a ,  413   b ,  416   a  and  416   b  and the inter-stage coupling capacitors  412  and  415 , 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 substrate  106  made 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 capacitors  413   a ,  413   b ,  416   a  and  416   b  and the inter-stage coupling capacitors  412  and  415 . 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 capacitors  412  and  415  and input/output coupling capacitors  413   a ,  413   b ,  416   a  and  416   b  can be enhanced, so that the filters  407  and  408  can be reduced in loss. 
   In  FIG. 14 , the substrate  106  is shown to be composed of three layers having the electrodes printed thereon, and the substrate  101  is 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 resonators  411   a ,  411   b ,  414   a  and  414   b ) may be formed in the substrate  106  made of a ceramic with high dielectric constant.  FIG. 15  shows 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 substrate  106 , rather than on the surface or in the substrate  106 .  FIG. 16  shows an arrangement in such an example, in which the tip-short-circuited resonators  411   a ,  411   b ,  414   a  and  414   b  are disposed in the substrate  101 . The substrate  101  shown in  FIG. 16  is composed of stacked substrates  101   a ,  101   b ,  101   c  and  101   d  each made of the low temperature cofired ceramic with low dielectric constant. Also in the case where the tip-short-circuited resonators  411   a ,  411   b ,  414   a  and  414   b  are disposed in the substrate  101  and are not in contact with the substrate  106  in this way, if the substrate  101   a  is thin so that the resonators can be affected by the substrate  106 , the same effect as described above can be attained even though the resonator electrodes are disposed in the vicinity of the substrate  106 . 
   In the above description, the tip-short-circuited resonator electrodes  411   a ,  411   b ,  414   a  and  414   b  serve 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 circuit  301  for switching between the transmitting terminal Tx 1  and receiving terminal Rx 1  for the first frequency band (EGSM) and the switch circuit  302  for switching among the transmitting terminal Tx 2 , receiving terminal Rx 2  for the second frequency band (DCS) and the duplexer  308  for 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 substrate  101  made 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 substrate  106 , 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, substrate  106 ) and the second high frequency circuit for a higher frequency band may be formed in the first substrate (for example, substrate  101 ). 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. 
   (Embodiment 2) 
   Now, an RF device according to a second embodiment of this invention will be described with reference to the drawings. 
     FIG. 9  is a circuit diagram of the RF device according to the embodiment 2 of this invention. In  FIG. 9 , reference numerals  501  to  505  denote a metal foil resonator serving as the quarter-wavelength tip-short-circuited resonator, reference numerals  506 ,  507  denote a series capacitor, reference numerals  508 ,  509  denote a ground capacitor, reference numerals  510  to  512  denote a coupling inductor, reference numerals  513 ,  154  denote a coupling capacitor, reference numerals  515 ,  516  denote a bypass capacitor, reference numeral  517  denotes a capacitor for matching between terminals, reference numeral  518  denotes an inductor for matching between terminals, reference numerals  519  to  523  denotes a switch, reference numerals  524  to  528  denote a switch coupling capacitor, reference numeral  529  denotes an antenna terminal, reference numeral  530  denotes a transmitting terminal, and reference numeral  531  denotes a receiving terminal. 
   The series capacitors  506  and  507  are connected to open ends of the resonators  501  and  502 , respectively, and the resonators  501  and  502  are connected to each other by the inductor  510 , thereby forming a transmitting filter  540 . The coupling inductor  510  has the ground capacitors  508  and  509  connected to the ends thereof for suppressing harmonics. On the other hand, the resonators  503 ,  504  and  505  are coupled with each other by the capacitors  513  and  514 . The input/output coupling inductors  511  and  512  are connected to open ends of the resonators  503  and  505 , respectively, whereby a receiving band pass filter  541  is formed In addition, the bypass capacitor  515  bridging the coupling elements  511  and  513  and the bypass capacitor  516  bridging the coupling elements  512  and  514  provide an attenuation pole at a frequency higher than the pass band. 
   An output terminal of the transmitting filter  540  and an input terminal of the receiving band pass filter  541  are connected to the antenna terminal  529  via the series inductor  518  and the parallel capacitor  517  both for matching between terminals. The switches  519 ,  520 ,  521 ,  522  and  523  are connected to open ends of the resonators  501 ,  502 ,  503 ,  504  and  505  via the switch coupling capacitors  524 ,  525 ,  526 ,  527  and  528 , respectively. The other ends of the switches are all grounded. In this way, the transmitting filter  540 , the receiving band pass filter  541 , the transmitting terminal  530 , the receiving terminal  531  and the antenna terminal  529  constitute the RF device. 
     FIG. 10  shows a specific circuit arrangement of the switches  519  to  523  including a PIN diode. Reference numeral  601  denotes a PIN diode. The PIN diode  601  is serially connected to a coupling capacitor  602  for blocking a direct current (equivalent to the capacitors  524  to  528  in  FIG. 9 ) to form a frequency shift circuit. A control terminal  606  is connected to the connection between the PIN diode  601  and the coupling capacitor  602  via a resistor  605 , a bypass capacitor  604  and a choke coil  603 . A shift voltage is applied to the control terminal  606  to control the switching among bands. 
   That is, the shift voltage applied to the control terminal  606  is intended to turn on or off the PIN diode  601 . If a certain positive voltage (shift voltage) higher than a bias voltage applied to a cathode of the PIN diode  601  is applied to the control terminal  606 , a resistance of the PIN diode  601  in the forward direction becomes quite low, so that a current flows in the forward direction, and thus, the PIN diode  601  is turned on. The resistor  605  is to control the current value of the PIN diode  601  when 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 terminal  606 , the resistance of the PIN diode  601  in the forward direction becomes quite high, so that no current flows in the forward direction, and thus, the PIN diode  601  is turned off. 
     FIG. 11  is a partial perspective view of the RF device according to the embodiment 2 of this invention, in which the same parts as in  FIG. 10  are assigned the same reference numerals. Reference numeral  701  denotes a metal foil resonator, reference numeral  702  denotes a substrate made of a ceramic with low dielectric constant, which is an example of the first substrate according to this invention, reference numeral  703  denotes a substrate made of a ceramic with high dielectric constant, which is an example of the second substrate according to this invention, and reference numeral  704  denotes a thermosetting resin. 
   A plurality of metal foil resonators  701  are equivalent to the resonators  501  to  505 , and the metal foil resonators  701  are interposed between a lower substrate  702  and an upper substrate  703 . Spaces between the metal foil resonators  701  are filled with the thermosetting resin  704 , which interconnects and integrates the substrates  702  and  703 . The components constituting the RF device according to the second embodiment of this invention except for the resonators  501  to  505 , such as capacitors, inductors and switches, are mounted on the substrate  702  made of the ceramic with low dielectric constant. 
   That is, the high frequency circuit is formed in or on a surface of the substrate  702  except for a part of the filter (that is, the metal foil resonators), and the metal foil resonators  701 , each of which is an example of at least part of the filter according to this invention, are formed on a surface of the substrate  703 . 
     FIGS. 12   a  and  12   b  show transfer characteristics of the RF device according to the embodiment 2 of this invention.  FIG. 12(   a ) shows a transfer characteristic of the transmitting filter  540  composed of the transmission line from the transmitting terminal  530  to the antenna terminal  529 , the resonators  501  and  502  connected to the transmission line via the series capacitors  506  and  507 , respectively, and the inter-stage coupling inductor  510 . The coupling inductor  510 , the series inductor  518  connected to the output terminal of the transmitting filter  540 , and the ground capacitors  508 ,  509  and  517  provide a low pass characteristic to suppress harmonics in a transmitting band. 
   The inductor  518  and capacitor  517  serve also to adjust the impedances of the transmitting filter  540  and receiving band pass filter  541  to prevent the filters from affecting each other in their respective frequency bands at the antenna terminal  529 . Since the impedances of the transmitting filter  540  and the receiving band pass filter  541  are adjusted in this way, the transmitting filter  540  exhibits 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 terminal  530  to the antenna terminal  529  with little attenuation of the sent signal. 
   On the other hand, the transmitting filter  540  exhibits 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 terminal  529  is directed toward the receiving band pass filter  541 . 
     FIG. 12(   b ) shows a transfer characteristic of the receiving band pass filter  541  composed of the transmission line from the antenna terminal  529  to the receiving terminal  531 , the grounded resonators  503 ,  504  and  505 , the inter-stage coupling capacitors  513  and  514 , and the input/output coupling inductors  511  and  512 . The impedance characteristic of the receiving band pass filter  541  and the impedances of the capacitors  515  and  516  used in the bypass circuit provide an attenuation pole as shown in  FIG. 12(   b ). 
   In the circuit arrangement shown in  FIG. 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 filter  541  becomes capacitive, that is, a transmitting frequency higher than a center frequency of the receiving band pass filter  541 . 
   The receiving band pass filter  541  exhibits a low insertion loss for the received signal in the receiving frequency band and can transmit the received signal from the antenna terminal  529  to the receiving terminal  531  with little attenuation of the received signal. On the other hand, the receiving band pass filter  541  exhibits 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 filter  540  is directed toward the antenna terminal  529 . 
   In addition, to the open ends of the resonators  501 ,  502 ,  503 ,  504  and  505 , there are connected frequency shift circuits composed of series connections of the switch coupling capacitors  524 ,  525 ,  526 ,  527  and  528  for blocking a direct current and the switches  519 ,  520 ,  521 ,  522  and  523  each having one end grounded, respectively. 
   That is, a resonance frequency of the resonators  501  to  505  is 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 switches  519  to  523  are in the on state or off state. If any of the switches  519  to  523  is 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 filter  540  and the center frequency and pass band of the receiving band pass filter  541  are shifted to a lower frequency. On the other hand, if any of the switches  519  to  523  is 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 filter  540  and the pass band of the receiving band pass filter  541  are shifted to a higher frequency. In other words, the blocking band of the transmitting filter  540  and the pass band of the receiving band pass filter  541  can be shifted synchronously by operating switches  519  to  523  in this way. 
     FIG. 12  shows relationships between the transfer characteristics of the transmitting filter  540  and receiving band pass filter  541  configured as described above and the on or off state of the switches  519  to  523  in a frequency region from 800 to 1000 MHz. Reference numeral  801  in  FIG. 12(   a ) and reference numeral  803  in  FIG. 12(   b ) designate the transfer characteristic in the case where all of the switches  519  to  523  are turned on, and reference numeral  802  in  FIG. 12(   a ) and reference numeral  804  in  FIG. 12(   b ) designate the transfer characteristic in the case where all of the switches  519  to  523  are turned off. In this way, by switching of the switches  519  to  523 , 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 switches  519  to  523 . For example,  FIG. 13  shows a case where a field effect transistor (FET)  901  serves as the switches  519  to  523 . A gate electrode of the FET  901  is connected to a control terminal  903  via a bypass capacitor  902 . Since the FET  901  is 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 FET  901  can reduce current consumption. Besides, if a varactor diode serves as the switches  519  to  523 , 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 filter  540  and the pass band of the receiving band pass filter  541  of 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 filter  540  is arranged on the transmitting side and the receiving band pass filter  541  is 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 devices  501 ,  502  and the impedance varying devices  519 ,  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 resonators  501  to  505  are composed of electrodes in the substrate  702  made 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 in  FIGS. 13 to 16 ). That is, the substrate  702  may be equivalent to the substrate  101  and the substrate  703  may be equivalent to the substrate  106 . 
   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 in  FIGS. 1 and 11 , and may be those shown in  FIGS. 2 ,  3  and  4 . 
   In the case where the two substrates  106  are disposed on the substrate  101  with spaced apart from each other as shown in  FIG. 2 , if the transmitting filter  407  is constituted by one of the substrates  106  and the substrate  101  and the receiving filter  408  is constituted by the other of the substrates  106  and the substrate  101 , the transmitting filter  407  and the receiving filter  408  can 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 substrate  101  or  702  made of a ceramic with low dielectric constant and the substrate  106  or  703  made of a ceramic with high dielectric constant overlaid thereon. However, the substrate  101  or  702  and the substrate  106  or  703  may be arranged side by side. 
     FIG. 17  shows an arrangement in which the substrates  101  and  106  are arranged side by side and a high frequency circuit formed on or in the substrate  101  and a high frequency circuit formed in the substrate  106  are connected to each other through the wiring pattern  201 . 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.