Patent Publication Number: US-7224240-B2

Title: Balanced high-frequency filter, antenna duplexer, balanced high-frequency circuit and communication apparatus

Description:
This application is a continuation-In-Part of U.S. patent application Ser. No 10/390,287, filed Mar. 17, 2003 now U.S. Pat. No. 6,900,705. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a balanced high-frequency filter, an antenna duplexer, a balanced high-frequency circuit and a communication apparatus. 
     2. Related Art of the Invention 
     In recent years, with the development of mobile communications, there have been expectations for improvements in performance and reductions in size of devices to be used for mobile communication. As a filter for use in a radio frequency (RF) stage, surface acoustic wave filters have been widely used. Also, in recent years, there have been expectations for filters using film bulk acoustic resonators (FBAR). Balancing of such filters and semiconductor elements used in RF stages has been pursued for the purpose of improving noise characteristics, for example, in terms of crosstalk between devices and there is a demand for improved balance characteristics. 
     A conventional balanced high-frequency device is described below.  FIG. 28  shows a configuration of a conventional balanced high-frequency device  2801 . The balanced high-frequency device  2801  is constituted by an input terminal IN serving as a unbalanced input/output terminal and output terminals OUT 1  and OUT 2  serving as balanced input/output terminals. 
     Moreover, in the case of a balanced high-frequency device, impedance matching is necessary.  FIGS. 29(   a ) and  29 ( b ) shows configurations of conventional balanced high-frequency devices respectively having a matching circuit. In  FIG. 29(   a ), a balanced high-frequency device  2901  is constituted by an input terminal IN serving as an unbalanced input/output terminal and output terminals OUT 1  and OUT 2  serving as balanced input/output terminals. Moreover, a matching circuit  2902  is connected between the output terminals OUT 1  and OUT 2 . Moreover, in  FIG. 29(   b ), a balanced high-frequency device  2903  is constituted by an input terminal IN serving as an unbalanced input/output terminal and output terminals OUT 1  and OUT 2  serving as balanced input/output terminals. Furthermore, matching circuits  2904  and  2905  are connected between the output terminals OUT 1  and OUT 2  and ground planes respectively. This type of the matching circuit is used to match a balanced high-frequency device with the characteristic impedance of a balanced input/output terminal. 
     As an example of the above balanced high-frequency device, a conventional surface acoustic wave filter is described below.  FIG. 30  shows a block diagram of an surface acoustic wave filter  3001  having a balanced input/output terminal. In  FIG. 30 , the surface acoustic wave filter  3001  is constituted on a piezoelectric substrate  3002  by first, second, and third inter-digital transducer electrodes (hereafter respectively referred to as IDT electrode)  3003 ,  3004 , and  3005  and first and second reflector electrodes  3006  and  3007 . One-hand electrode finger of the first IDT electrode  3003  is connected to an output terminal OUT 1  and the other-hand electrode finger of the first IDT electrode  3003  is connected to an output terminal OUT 2 . Moreover, one-hand electrode fingers of the second and third IDT electrodes  3004  and  3005  are connected to an input terminal IN and the other-hand electrode fingers of the electrodes  3004  and  3005  are grounded. By using the above configuration, it is possible to realize an surface acoustic wave filter having an unbalanced-balanced input/output terminal. Moreover, in the case of the surface acoustic wave filter in  FIG. 30 , impedances of the input and output terminals are respectively designed as 50 Ω. 
     Moreover, a conventional surface acoustic wave filter is described below as an example of a balanced high-frequency device having a matching circuit.  FIG. 31  shows a block diagram of surface acoustic wave filter  3101  having a matching circuit. In  FIG. 31 , the surface acoustic wave filter  3101  is constituted on a piezoelectric substrate  3102  by first, second, and third inter-digital transducer electrodes (hereafter respectively referred to as IDT electrode)  3103 ,  3104 , and  3105  and first and second reflector electrodes  3106  and  3107 . The first IDT electrode  3103  is divided into two divided IDT electrodes. One electrode finger of a first divided IDT electrode  3108  is connected to an output terminal OUT 1 , one electrode finger of a second divided IDT electrode  3109  is connected to an output terminal OUT 2 , and the other-hand electrode fingers of the first and second divided IDT electrodes are electrically connected. Moreover, one-hand electrode fingers of the second and third IDT electrodes  3104  and  3105  are connected to an input terminal IN and the other-hand electrode fingers of the electrodes  3104  and  3105  are grounded. Furthermore, an inductor  3110  is connected between output terminals as a matching circuit. By using the above configuration, it is possible to realize surface acoustic wave filter having an unbalanced-balanced input/output terminal. Furthermore, in the case of the surface acoustic wave filter in  FIG. 31 , impedances of input and output terminals are designed as 50 Ω for the input side and as 150 Ω for the output side. Therefore, the filter has an impedance conversion function. 
       FIGS. 32(   a ) to  32 ( c ) show characteristic diagrams of a conventional surface acoustic wave filter of a 900-MHz band shown in  FIG. 30 . In  FIGS. 32(   a ) to  32 ( c ),  FIG. 32(   a ) shows a passing characteristic,  FIG. 32(   b ) shows an amplitude balance-characteristic in a pass band (from 925 up to 960 MHz), and  FIG. 32(   c ) shows a phase balance-characteristic in a pass band. From  FIG. 32 , it is found that the amplitude balance-characteristic greatly deteriorates from −0.67 dB to +0.77 dB and the phase balance-characteristic greatly deteriorates from −6.3° to +9.4° in each pass band. 
     In this case, the amplitude balance-characteristic denotes the difference between the signal amplitude of the input terminal IN and output terminal OUT 1  and the signal amplitude of the input terminal IN and output terminal OUT 2 . When the difference becomes zero, the balance-characteristic does not deteriorate. Moreover, the phase balance-characteristic denotes a shift of the difference between the signal phase of the input terminal IN and output terminal OUT 1  and the signal phase of the input terminal IN and output terminal OUT 2  from 180°. When the difference becomes zero, the balance-characteristic does not deteriorate. 
     With the above-described balanced high-frequency device and the surface acoustic wave filter described as an example of the balanced high-frequency device, however, there has been a problem that a deterioration in balance characteristics considered one of important electrical characteristics of the device is large. 
     Also, the balanced high-frequency device in the conventional art is a phase-shifting circuit used to improve the balance characteristics by considering the characteristics in the pass band, and the characteristics outside the pass band have not been taken into consideration. In a case where a balanced high-frequency element provided as the balanced high-frequency device is connected to the input side of a semiconductor device, not only the characteristics in the pass band but also the characteristics outside the pass band are important. In a case where a balanced high-frequency element is used for a receiving filter in particular, characteristics in a transmission frequency band are important as well as those in a reception frequency band. With the conventional balanced high-frequency device, however, there is a problem that the amount of leakage of common-mode signal components to the balanced output terminals is large. 
     SUMMARY OF THE INVENTION 
     In view of the above-described problems of the conventional art, an object of the present invention is to provide a balanced high-frequency filter and an antenna duplexer having reduced common-mode signal components in a transmission frequency band. Another object of the present invention is to provide a balanced high-frequency circuit and a communication apparatus using such a balanced high-frequency filter or an antenna duplexer. Still another object of the present invention is to provide a balanced high-frequency circuit in which common-mode signal components in a transmission frequency band are reduced. 
     In order to achieve the above object, the 1 st  aspect of the present invention is a balanced high-frequency filter comprising: 
     a balanced high-frequency element having at least one balanced terminal; and 
     a phase-shifting circuit, 
     wherein the phase-shifting circuit is a series resonance circuit which is electrically connected between the balanced terminals and which resonates with common-mode signal components at a predetermined frequency; 
     a resonance frequency of the series resonance circuit is set in a second frequency band; 
     a first frequency band is a pass band of the balanced high-frequency element; and 
     the second frequency band is an attenuation band of the balanced high-frequency element. 
     The 2 nd  aspect of the present invention is the balanced high-frequency filter according to the 1 st  aspect of the present invention, wherein the first frequency band is a reception frequency band, and the second frequency band is a transmission frequency band. 
     The 3 rd  aspect of the present invention is the balanced high-frequency filter according to the 1 st  or the 2 nd  aspect of the present invention, wherein the phase-shifting circuit has a transmission line which has a length equal to about ½ of a wavelength in the second frequency band; and 
     the phase-shifting circuit is connected between the balanced terminals. 
     The 4 th  aspect of the present invention is the balanced high-frequency filter according to the 3 rd  aspect of the present invention, wherein the phase-shifting circuit has at least two transmission lines; 
     one of the transmission lines has a length equal to about ½ of a wavelength in the second frequency band; 
     the other of the transmission lines differs in length from said one of the transmission lines; and 
     the phase-shifting circuit is connected between the balanced terminals. 
     The 5 th  aspect of the present invention is the balanced high-frequency filter according to the 1 st  or the 2 nd  aspect of the present invention, wherein the phase-shifting circuit has at least first, second and third impedance elements; 
     the first impedance element and the second impedance element are connected in series between the balanced terminals; 
     a connection point between the first impedance element and the second impedance element is grounded through the third impedance element; 
     the first impedance element and the third impedance element form a series resonance circuit; and 
     the second impedance element and the third impedance element form a series resonance circuit. 
     The 6 th  aspect of the present invention is the balanced high-frequency filter according to the 5 th  aspect of the present invention, wherein each of the first and second impedance elements is a capacitor, and the third impedance element is an inductor. 
     The 7 th  aspect of the present invention is the balanced high-frequency filter according to the 5 th  aspect of the present invention, wherein each of the first and second impedance elements is an inductor, and the third impedance element is a capacitor. 
     The 8 th  aspect of the present invention is the balanced high-frequency filter according to the 6 th  or the 7 th  aspect of the present invention, wherein the impedance of each of the first and second impedance elements in the first frequency band is set so that a value of the first or second impedance element normalized on a characteristic impedance value of one of the balanced terminals is equal to or larger than 3. 
     The 9 th  aspect of the present invention is the balanced high-frequency filter according to the 1 st  or the 2 nd  aspect of the present invention, wherein the balanced high-frequency element is constituted by a surface acoustic wave filter. 
     The 10 th  aspect of the present invention is the balanced high-frequency filter according to the 1 st  or the 2 nd  aspect of the present invention, wherein the balanced high-frequency element is constituted by a filter using an FBAR. 
     The 11 th  aspect of the present invention is the balanced high-frequency filter according to the 1 st  or the 2 nd  aspect of the present invention, wherein the balanced high-frequency filter is connected to an input side of a low-noise amplifier having balanced terminals. 
     The 12 th  aspect of the present invention is the balanced high-frequency filter according to the 1 st  or the 2 nd  aspect of the present invention, wherein the balanced high-frequency filter is connected to an input side of a mixer having balanced terminals. 
     The 13 th  aspect of the present invention is an antenna duplexer comprising the balanced high-frequency filter according to the 1 st  or the 2 nd  aspect of the present invention. 
     The 14 th  aspect of the present invention is an antenna duplexer according to the 13 th  aspect of the present invention, wherein the balanced high-frequency filter is a receiving filter in the antenna duplexer; 
     the first frequency band is a reception frequency band in the antenna duplexer; and 
     the second frequency band is a transmission frequency band in the antenna duplexer. 
     The 15 th  aspect of the present invention is an antenna duplexer according to the 14 th  aspect of the present invention, wherein the antenna duplexer is connected to an input side of a low-noise amplifier having balanced terminals. 
     The 16 th  aspect of the present invention is a balanced high-frequency circuit comprising: 
     a low-noise amplifier having balanced terminals; 
     a mixer having balanced terminals; and 
     a phase-shifting circuit, 
     wherein the phase-shifting circuit is a series resonance circuit which is electrically connected between the balanced terminals connecting the low-noise amplifier and the mixer to each other, and which resonates with common-mode signal components at a predetermined frequency; 
     a resonance frequency of the series resonance circuit is set in a second frequency band; 
     a first frequency band is the frequency band of desired waves; and 
     the second frequency band is the frequency band of interference waves. 
     The 17 th  aspect of the present invention is the balanced high-frequency circuit according to the 16 th  aspect of the present invention, wherein the first frequency band is a reception frequency band, and the second frequency band is a transmission frequency band. 
     The 18 th  aspect of the present invention is the balanced high-frequency circuit according to the 16 th  or the 17 th  aspect of the present invention, wherein the phase-shifting circuit has a transmission line which has a length equal to about ½ of a wavelength in the second frequency band; and 
     the phase-shifting circuit is connected between the balanced terminals. 
     The 19 th  aspect of the present invention is the balanced high-frequency circuit according to the 16 th  or the 17 th  aspect of the present invention, wherein the phase-shifting circuit has at least first, second and third impedance elements; 
     the first impedance element and the second impedance element are connected in series between the balanced terminals; 
     a connection point between the first impedance element and the second impedance element is grounded through the third impedance element; 
     the first impedance element and the third impedance element form a series resonance circuit; and 
     the second impedance element and the third impedance element form a series resonance circuit. 
     The 20 th  aspect of the present invention is the balanced high-frequency circuit according to the 19 th  aspect of the present invention, wherein each of the first and second impedance elements is a capacitor, and the third impedance element is an inductor. 
     The 21 st  aspect of the present invention is the balanced high-frequency circuit according to the 19 th  aspect of the present invention, wherein each of the first and second impedance elements is an inductor, and the third impedance element is a capacitor. 
     The 22 nd  aspect of the present invention is the balanced high-frequency circuit according to the 20 th  or the 21 st  aspect of the present invention, wherein the impedance of each of the first and second impedance elements in the first frequency band is set so that a value of the first or second impedance element normalized on a characteristic impedance value of one of the balanced terminals is equal to or larger than 3. 
     The 23 rd  aspect of the present invention is a balanced high-frequency circuit comprising: 
     a circuit board having balanced lines; and 
     a phase-shifting circuit, 
     wherein the phase-shifting circuit is mounted on the circuit board; 
     the phase-shifting circuit is a series resonance circuit which is electrically connected between the balanced terminals, and which resonates with common-mode signal components at a predetermined frequency; 
     a resonance frequency of the series resonance circuit is set in a second frequency band; 
     a first frequency band is the frequency band of desired waves; and 
     the second frequency band is the frequency band of interference waves. 
     The 24 th  aspect of the present invention is the balanced high-frequency circuit according to the 23 rd  aspect of the present invention, wherein the first frequency band is a reception frequency band, and the second frequency band is a transmission frequency band. 
     The 25 th  aspect of the present invention is the balanced high-frequency circuit according to the 23 rd  or the 24 th  aspect of the present invention, wherein the phase-shifting circuit has a transmission line, the transmission line has a length equal to about ½ of a wavelength in the first frequency band; and 
     the phase-shifting circuit is connected between the balanced terminals. 
     The 26 th  aspect of the present invention is the balanced high-frequency circuit according to the 23 rd  or the 24 th  aspect of the present invention, wherein the phase-shifting circuit has at least first, second and third impedance elements; 
     the first impedance element and the second impedance element are connected in series between the balanced terminals; 
     a connection point between the first impedance element and the second impedance element is grounded through the third impedance element; 
     the first impedance element and the third impedance element form a series resonance circuit; and 
     the second impedance element and the third impedance element form a series resonance circuit. 
     The 27 th  aspect of the present invention is the balanced high-frequency circuit according to the 26 th  aspect of the present invention, wherein each of the first and second impedance elements is a capacitor, and the third impedance element is an inductor. 
     The 28 th  aspect of the present invention is the balanced high-frequency circuit according to the 26 th  aspect of the present invention, wherein each of the first and second impedance elements is an inductor, and the third impedance element is a capacitor. 
     The 29 th  aspect of the present invention is the balanced high-frequency circuit according to the 27 th  or the 28 th  aspect of the present invention, wherein the impedance of each of the first and second impedance elements in the first frequency band is set so that a value of the first or second impedance element normalized on a characteristic impedance value of one of the balanced terminals is equal to or larger than 3. 
     The 30 th  aspect of the present invention is q communication apparatus using the balanced high-frequency filter according to the 1 st  or the 2 nd  aspect of the present invention. 
     The 31 st  aspect of the present invention is a communication apparatus using the antenna duplexer according to the 13 th  aspect of the present invention. 
     The 32 nd  aspect of the present invention is a communication apparatus using the antenna duplexer according to the 14 th  aspect of the present invention. 
     The 33 rd  aspect of the present invention is a communication apparatus using the balanced high-frequency circuit according to the 16 th  or the 17 th  aspect of the present invention. 
     The 34 th  aspect of the present invention is a communication apparatus using the balanced high-frequency circuit according to the 23 rd  or the 24 th  aspect of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a balanced high-frequency device in the embodiment 1 of the present invention. 
         FIG. 2  is an illustration for explaining the analysis of a balance-characteristic deterioration cause of a conventional surface acoustic wave filter. 
         FIGS. 3(   a ) and  3 ( b ) are characteristic diagrams of the balance-characteristic analysis of a conventional surface acoustic wave filter, in which  FIG. 3(   a ) is an amplitude balance-characteristic diagram and  FIG. 3(   b ) is a phase balance-characteristic diagram. 
         FIG. 4  is an illustration for explaining operations of the balanced high-frequency device in the embodiment 1 of the present invention. 
         FIG. 5  is a block diagram of the balanced high-frequency device in the embodiment 2 of the present invention. 
         FIG. 6  is a block diagram of the balanced high-frequency device in the embodiment 3 of the present invention. 
         FIGS. 7(   a ) to  7  ( c ) are illustrations for explaining operations of the balanced high-frequency device in the embodiment 3 of the present invention. 
         FIG. 8  is a block diagram of the balanced high-frequency device in the embodiment 4 of the present invention. 
         FIG. 9(   a ) is an illustration for explaining operations of the balanced high-frequency device in the embodiment 4 of the present invention,  FIG. 9(   b ) is an illustration showing an equivalent circuit of a phase circuit on differential-mode signal components in the embodiment 4 of the present invention, and  FIG. 9(   c ) is an illustration showing an equivalent circuit of a phase circuit on common-mode signal components in the embodiment 4 of the present invention. 
         FIG. 10(   a ) is an illustration for explaining operations of the balanced high-frequency device in the embodiment 4 of the present invention,  FIG. 10(   b ) is an illustration showing an equivalent circuit of a phase circuit on differential-mode signal components in the embodiment 4 of the present invention, and  FIG. 10(   c ) is an illustration showing an equivalent circuit of a phase circuit on common-mode signal components in the embodiment 4 of the present invention. 
         FIG. 11  is a block diagram of the balanced high-frequency device in the embodiment 5 of the present invention. 
         FIG. 12(   a ) is an illustration for explaining operations of the balanced high-frequency device in the embodiment 5 of the present invention,  FIG. 12(   b ) is an illustration showing an equivalent circuit of a phase circuit on differential-mode signal components in the embodiment 5 of the present invention, and  FIG. 12(   c ) is an illustration showing an equivalent circuit of a phase circuit on common-mode signal components in the embodiment 5 of the present invention. 
         FIG. 13(   a ) is an illustration for explaining operations of the balanced high-frequency device in the embodiment 5 of the present invention,  FIG. 13(   b ) is an illustration showing an equivalent circuit of a phase circuit on differential mode signal components in the embodiment 5 of the present invention, and  FIG. 13(   c ) is an illustration showing an equivalent circuit of a phase circuit on common-mode signal components in the embodiment 5 of the present invention. 
         FIG. 14  is a block diagram of the balanced high-frequency device in the embodiment 6 of the present invention. 
         FIG. 15(   a ) is a passing characteristic diagram of a balanced high-frequency device when using the phase circuit  603 ,  FIG. 15(   b ) is an amplitude balance-characteristic diagram of a balanced high-frequency device when using the phase circuit  603 , and  FIG. 15(   c ) is a phase balance-characteristic diagram of a balanced high-frequency device when using the phase circuit  603 . 
         FIG. 16(   a ) is an amplitude balance-characteristic diagram of a balanced high-frequency device when using the phase circuit  603  and  FIG. 16(   b ) is a phase balance-characteristic diagram of a balanced high-frequency device when using the phase circuit  603 . 
         FIG. 17(   a ) is a passing characteristic diagram of a balanced high-frequency device when using the phase circuit  901 ,  FIG. 17(   b ) is an amplitude balance-characteristic diagram of a balanced high-frequency device when using the phase circuit  901 , and  FIG. 17(   c ) is a phase balance-characteristic diagram of a balanced high-frequency device when using the phase circuit  901 . 
         FIG. 18(   a ) is an amplitude balance-characteristic diagram of a balanced high-frequency device when using the phase circuit  901  and  FIG. 18(   b ) is a phase balance-characteristic diagram of a balanced high-frequency device when using the phase circuit  901 . 
         FIG. 19(   a ) is a passing characteristic diagram of a balanced high-frequency device when using the phase circuit  1001 ,  FIG. 19(   b ) is an amplitude balance-characteristic diagram of a balanced high-frequency device when using the phase circuit  1001 , and  FIG. 19(   c ) is a phase balance-characteristic diagram of a balanced high-frequency device when using the phase circuit  1001 . 
         FIG. 20(   a ) is an amplitude balance-characteristic diagram of a balanced high-frequency device when using the phase circuit  1001  and  FIG. 20(   b ) is a phase balance-characteristic diagram of a balanced high-frequency device when using the phase circuit  1001 . 
         FIG. 21(   a ) is an impedance characteristic diagram when using the phase circuit  601  and  FIG. 21(   b ) is an impedance characteristic diagram when using the phase circuit  2201 . 
         FIG. 22  is a block diagram in which a matching circuit is included in a phase circuit. 
         FIG. 23(   a ) is a block diagram of a balanced high-frequency device in the embodiment 7 of the present invention and  FIG. 23(   b ) is a block diagram of a balanced high-frequency device having a phase circuit including a matching circuit. 
         FIG. 24  is a block diagram of a balanced high-frequency device in the embodiment 8 of the present invention. 
         FIG. 25  is a block diagram of a balanced high-frequency device in the embodiment 9 of the present invention. 
         FIG. 26  is a block diagram of a balanced high-frequency device in the embodiment 10 of the present invention. 
         FIG. 27  is a block diagram of a balanced high-frequency circuit in the embodiment 11 of the present invention. 
         FIG. 28  is a block diagram of a conventional balanced high-frequency device. 
         FIG. 29(   a ) and  29 ( b ) are block diagrams including a matching circuit of a conventional balanced high-frequency device, in which  FIG. 29(   a ) is a block diagram when the matching circuit is constituted by one impedance element and  FIG. 29(   b ) is a block diagram when the matching circuit is constituted by two impedance elements. 
         FIG. 30  is a block diagram of a conventional surface acoustic wave filter. 
         FIG. 31  is a block diagram including a matching circuit of a conventional surface acoustic wave filter. 
         FIG. 32(   a ) is a passing characteristic diagram of a conventional surface acoustic wave filter,  FIG. 32(   b ) is an amplitude characteristic diagram of a conventional surface acoustic wave filter, and  FIG. 32(   c ) is a phase balance-characteristic diagram of a conventional surface acoustic wave filter. 
         FIG. 33  is a diagram showing the configuration of a balanced high-frequency filter in embodiment 12 of the present invention. 
         FIG. 34(   a ) is a diagram showing a characteristic of common-mode signal components in the balanced high-frequency filter in embodiment 12 of the present invention. 
         FIG. 34(   b ) is a diagram showing a characteristic of common-mode signal components in a conventional balanced high-frequency device. 
         FIG. 35(   a ) is a diagram showing a passing characteristic of the balanced high-frequency filter in embodiment 12 of the present invention. 
         FIG. 35(   b ) is a diagram showing an amplitude balance characteristic of the balanced high-frequency filter in embodiment 12 of the present invention. 
         FIG. 35(   c ) is a diagram showing a phase balance characteristic of the balanced high-frequency filter in embodiment 12 of the present invention. 
         FIG. 36  is a diagram showing the configuration of FBAR in embodiment 12 of the present invention. 
         FIG. 37  is a diagram showing another configuration of balanced high-frequency filter in embodiment 12 of the present invention. 
         FIG. 38(   a ) is a diagram showing the configuration of connections in the balanced high-frequency filter in embodiment 12 of the present invention. 
         FIG. 38(   b ) is a diagram showing the configuration of different connections in the balanced high-frequency filter in embodiment 12 of the present invention. 
         FIG. 39  is a diagram showing the configuration of a balanced high-frequency filter in embodiment 13 of the present invention. 
         FIG. 40(   a ) is a diagram showing a characteristic of common-mode signal components in the balanced high-frequency filter in embodiment 13 of the present invention. 
         FIG. 40(   b ) is a diagram showing a characteristic of common-mode signal components in a conventional balanced high-frequency device. 
         FIG. 41(   a ) is a diagram showing a passing characteristic of the balanced high-frequency filter in embodiment 13 of the present invention. 
         FIG. 41(   b ) is a diagram showing an amplitude balance characteristic of the balanced high-frequency filter in embodiment 13 of the present invention. 
         FIG. 41(   c ) is a diagram showing a phase balance characteristic of the balanced high-frequency filter in embodiment 13 of the present invention. 
         FIG. 42  is a diagram showing another configuration of phase-shifting circuit in embodiment 13 of the present invention. 
         FIG. 43(   a ) is a diagram showing the relationship between loss and a normalized impedance in the case of use of the phase-shifting circuit shown in  FIG. 39 . 
         FIG. 43(   b ) is a diagram showing the relationship between loss and a normalized impedance in the case of use of the phase-shifting circuit shown in  FIG. 42 . 
         FIG. 44  is a diagram showing the configuration of an antenna duplexer in embodiment 14 of the present invention. 
         FIG. 45  is a diagram showing another configuration of antenna duplexer in embodiment 14 of the present invention. 
         FIG. 46(   a ) is a diagram showing the configuration of a balanced high-frequency circuit in embodiment 15 of the present invention. 
         FIG. 46(   b ) is a diagram showing another configuration of balanced high-frequency circuit in embodiment 15 of the present invention. 
         FIG. 47  is a diagram showing the configuration of a balanced high-frequency circuit in embodiment 16 of the present invention. 
         FIG. 48  is a diagram showing another configuration of balanced high-frequency circuit in embodiment 16 of the present invention. 
         FIG. 49  is a diagram showing a characteristic of common-mode signal components in the balanced high-frequency device shown in  FIG. 30 . 
     
    
    
     DESCRIPTION OF SYMBOLS 
     
         
           101  Balanced high-frequency device 
           102  Balanced device 
           103  Phase circuit 
           201  Surface acoustic wave filter 
           202  Ideal surface acoustic wave filter 
           203 ,  204  Capacity component 
           501  Balanced high-frequency device 
           502  Balanced device 
           503 ,  504  Phase circuit 
           601  Balanced high-frequency device 
           602  Balanced device 
           603  Phase circuit 
           604  Transmission line 
           801  Balanced high-frequency device 
           802  Balanced device 
           803  Phase circuit 
           804 ,  805 ,  806  Impedance element 
           901  Phase circuit 
           902 ,  903  Capacitor 
           904  Inductor 
           905  Virtual ground point 
           1001  Phase circuit 
           1002 ,  1003  Capacitor 
           1004  Capacitor 
           1005  Virtual ground point 
           1101  Balanced high-frequency device 
           1102  Balanced device 
           1103  Phase circuit 
           1104 ,  1105 ,  1106  Impedance element 
           1201  Phase circuit 
           1202 ,  1203  Inductor 
           1204  Capacitor 
           1205  Connection point 
           1301  Phase circuit 
           1302 ,  1303  Capacitor 
           1304  Inductor 
           1305  Connection point 
           1401  Balanced high-frequency device 
           1402  Surface acoustic wave filter 
           1403  Phase circuit 
           1404  Piezoelectric substrate 
           1405  First IDT electrode 
           1406  Second IDT electrode 
           1407  Third IDT electrode 
           1408  First reflector electrode 
           1409  Second reflector electrode 
           1601 ,  1801 ,  2001  Maximum value of amplitude balance-characteristic deterioration of conventional surface acoustic wave filter 
           1602 ,  1802 ,  2002  Minimum value of amplitude balance-characteristic deterioration of conventional surface acoustic wave filter 
           1603 ,  1803 ,  2003  Maximum value of phase balance-characteristic deterioration of conventional surface acoustic wave filter 
           1604 ,  1804 ,  2004  Minimum value of phase balance-characteristic deterioration of conventional surface acoustic wave filter 
           2101 ,  2102  Region showing vicinity of band pass frequency 
           2201  Phase circuit 
           2202  Capacitor 
           2301  Balanced high-frequency device 
           2302  Phase circuit 
           2304 ,  2305  Capacitor 
           2306  Inductor 
           2307  Inductor serving as matching circuit 
           2308  Virtual ground point 
           2309  Combined inductor 
           2401  Balanced high-frequency device 
           2402  Surface acoustic wave filter 
           2403  Phase circuit 
           2404  Piezoelectric substrate 
           2405  First IDT electrode 
           2406  Second IDT electrode 
           2407  Third IDT electrode 
           2408  First reflector electrode 
           2409  Second reflector electrode 
           2410  First divided IDT electrode 
           2411  Second divided IDT electrode 
           2501  Balanced high-frequency device 
           2502  Surface acoustic wave filter 
           2503  Phase circuit 
           2504  Piezoelectric substrate 
           2505  First IDT electrode 
           2506  Second IDT electrode 
           2507  Third IDT electrode 
           2508  First reflector electrode 
           2509  Second reflector electrode 
           2601  Balanced high-frequency device 
           2602  Semiconductor device 
           2603  Phase circuit 
           2604   a ,  2604   b ,  2605   a ,  2605   b  Bipolar transistor  2606   a ,  2606   b  Inductor 
           2607  DC-cut capacitor 
           2608  Bypass capacitor 
           2609   a ,  2609   b  DC-cut capacitor 
           2610 ,  2611  Bias circuit 
           2612   a ,  2612   b  Choke inductor 
           2701  Balanced high-frequency circuit 
           2702  Transmitting amplifier 
           2703  Transmitting filter 
           2704  Switch 
           2705  Antenna 
           2706  Receiving filter 
           2707  Receiving amplifier 
           2708 ,  2709  Balanced transmission line 
           2801 ,  2901  Balanced high-frequency device 
           2902 ,  2904 ,  2905  Matching circuit 
           2903  Balanced high-frequency device 
           3001  Surface acoustic wave filter 
           3002  Piezoelectric substrate 
           3003  First IDT electrode 
           3004  Second IDT electrode 
           3005  Third IDT electrode 
           3006  First reflector electrode 
           3007  Second reflector electrode 
           3101  Surface acoustic wave filter 
           3102  Piezoelectric substrate 
           3103  First IDT electrode 
           3104  Second IDT electrode 
           3105  Third IDT electrode 
           3106  First reflector electrode 
           3107  Second reflector electrode 
           3108  First divided IDT electrode 
           3109  Second divided IDT electrode 
           3110  Inductor 
           5101  Balanced high-frequency filter (device) 
           5102  Balanced high-frequency element 
           5103  Phase-shifting circuit 
           5104  Transmission line 
           5401  FBAR 
           5402  Substrate 
           5403  Lower electrode 
           5404  Piezoelectric thin film 
           5405  Upper electrode 
           5406  Cavity 
           5501  Balanced high-frequency filter 
           5502  Balanced high-frequency element 
           5503  Phase-shifting circuit 
           5504  Transmission line 
           5505  Transmission line 
           5601  Low noise amplifier 
           5602  Mixer 
           5701  Balanced high-frequency filter 
           5702  Balanced high-frequency element 
           5703  Phase-shifting circuit 
           5704 ,  5705  Capacitor 
           5706  Inductor 
           5707  Connection point 
           6001  Phase-shifting circuit 
           6002 ,  903  Inductor 
           6004  Capacitor 
           6005  Connection point 
           6201  Antenna duplexer 
           6202  Transmitting filter 
           6203  Receiving filter 
           6204  Phase-shifting circuit 
           6401  Balanced high-frequency circuit 
           6402  Low-noise amplifier 
           6403  Mixer 
           6404  Phase-shifting circuit 
           6501  Balanced high-frequency circuit 
           6502  Circuit board 
           6503  Transmitting amplifier 
           6504  Transmitting filter 
           6504  Switch 
           6506  Receiving filter 
           6507  Low-noise amplifier 
           6508  Mixer 
           6509  Phase-shifting circuit 
           6601  Balanced high-frequency circuit 
           6602  Antenna duplexer 
           6603  Transmitting filter 
           6604  Receiving filter 
       
    
     PREFERRED EMBODIMENTS OF THE INVENTION 
     Embodiments of the present invention are described below by referring to the accompanying drawings. 
     (Embodiment 1) 
     A balanced high-frequency device of embodiment 1 of the present invention is described below by referring to the accompanying drawings.  FIG. 1  shows a configuration of a balanced high-frequency device  101  of the embodiment 1 of the present invention. In  FIG. 1 , the balanced high-frequency device  101  is constituted by a balanced device  102  and a phase circuit  103 . Moreover, in the case of a balanced device  102 , the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal and the output-side terminals are output terminals OUT 1  and OUT 2  serving as balanced input/output terminals. Furthermore, a phase circuit  103  is connected between the output terminals. By using the above configuration, it is possible to realize a balanced high-frequency device having an unbalanced-balanced input/output terminal. 
     First, a balance-characteristic deterioration cause of the balanced high-frequency device is studied by using surface acoustic wave filter. The conventional surface acoustic wave filter  201  shown in  FIG. 30  has a problem that a balance-characteristic deteriorates. In this case, the balance-characteristic is analyzed by the configuration shown in  FIG. 2 . In  FIG. 2 , the surface acoustic wave filter  201  is constituted by an ideal surface acoustic wave filter  202  whose balance-characteristic is not deteriorated and capacitive components  203  and  204 . Combination by the parasitic component of the surface acoustic wave filter  201  is assumed by connecting the capacitive components  203  and  204  between the input side and output side of the ideal surface acoustic wave filter  202 . 
       FIGS. 3(   a ) and  3 ( b ) show filter characteristics when setting these capacitive components  203  and  204  to substantially 0.1 pF in which  FIG. 3(   a ) shows an amplitude balance-characteristic in a pass band and  FIG. 3(   b ) shows a phase balance-characteristic in a pass band. A result of analyzing the balance-characteristic in  FIG. 3  very well coincides with the measured characteristic of the conventional surface acoustic wave filter shown in  FIG. 32  as a trend of balance-characteristic deterioration. Therefore, combination of the input terminal and output terminal of a balanced device is considered as a main factor of balance-characteristic deterioration. 
     Operations of the balanced high-frequency device of the embodiment 1 of the present invention are described below by referring to the accompanying drawings.  FIG. 4  shows the outline of operations of the balanced high-frequency device  101  of the embodiment 1 of the present invention. Combination due to a parasitic component between an input terminal and an output terminal is estimated as a main factor of deterioration of the balance-characteristic of the balanced high-frequency device  101 . It is considered that the above mentioned can be explained by showing a signal component flowing through balanced input and output terminals by an common-mode signal component and a differential-mode signal component. Here, common-mode signal component means common-mode signal component, and differential-mode signal component means opposite-phase signal component. That is, a signal component i input from the input terminal IN is differentially output as differential-mode signal components id 1  and id 2  by the balanced device  102 . However, the combination by a parasitic component is not made differential by the output terminal OUT 1  or OUT 2  but it is superimposed as common-mode signal components ic 1  and ic 2  and the common-mode signal components ic 1  and ic 2  cause the balance-characteristic to deteriorate. 
     Therefore, in the case of an embodiment of the present invention, it is possible to reduce the common-mode components ic 1  and ic 2  when the phase circuit  103  operates as a resonant circuit at a predetermined frequency to make impedances of the common-mode signal components ic 1  and ic 2  when viewing the output-terminal side from the balanced device  102  lower than impedances of the differential-mode signal components id 1  and id 2  when viewing the output-terminal side from the balanced device  102 . 
     As described above, the balanced high-frequency device  101  of the present invention realizes a balanced high-frequency device excellent in balance-characteristic by reducing the common-mode signal components ic 1  and ic 2  by the phase circuit  103 . 
     In the case of this embodiment, it is described that the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal, the output-side terminals are output terminals OUT 1  and OUT 2  serving as balanced input/output terminals, and the phase circuit  103  is connected between the output terminals. However, this embodiment is not restricted to the above case. It is also allowed that the input-side terminal is an input terminal serving as a balanced input/output terminal, the output-side terminal is an output terminal serving as an unbalanced input/output terminal, and the phase circuit  103  is connected between input terminals. 
     (Embodiment 2) 
     A balanced high-frequency device of embodiment 2 of the present invention is described below by referring to the accompanying drawings.  FIG. 5  shows a configuration of a balanced high-frequency device  501  of the embodiment 2 of the present invention. In  FIG. 5 , the balanced high-frequency device  501  is constituted by a balanced device  502  and phase circuits  503  and  504 . Moreover, in the case of the balanced device  502 , the input-side terminal is an input terminal IN serving as a balanced input/output terminal and the output-side terminals are output terminals OUT 1  and OUT 2  serving as balanced input/output terminals. By using the above configuration, it is possible to realize a balanced high-frequency device having balanced-unbalanced input and output terminals. 
     Also in the case of the balanced high-frequency device  501  of the present invention, it is possible to realize a balanced high-frequency device excellent in balance-characteristic because the phase circuit  503  operates as a resonant circuit at a predetermined frequency and makes impedances of common-mode signal components ic 1  and ic 2  when viewing the input-terminal side from the balanced device  502  lower than those of differential-mode signal components id 1  and id 2  when viewing the input-terminal side from the balanced device  502  and the phase circuit  504  operates as a resonant circuit at a predetermined frequency and makes impedances of the common-mode signal components ic 1  and ic 2  when viewing the output-terminal side from the balanced device  502  lower than those of the differential-mode signal components id 1  and id 2  when viewing the output-terminal side from the balanced device  502  and thereby, reduces the common-mode signal components ic 1  and ic 2 . 
     (Embodiment 3) 
     A balanced high-frequency device of embodiment 3 of the present invention is described below by referring to the accompanying drawings. A more specific circuit configuration is shown below as a phase circuit.  FIG. 6  shows a configuration of a balanced high-frequency device  601  of the embodiment 2 of the present invention. In  FIG. 6 , the balanced high-frequency device  601  is constituted by a balanced device  602  and a phase circuit  603 . Moreover, in the case of the balanced device  602 , the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal and output-side terminals are output terminals OUT 1  and OUT 2  serving as balanced input/output terminals. Furthermore, the phase circuit  603  is constituted by a transmission line  604  and set between output terminals. The transmission line  604  has a length of λ/2 (in this case, λ denotes a wavelength) which corresponds to a phase shift of 180°. Furthermore, in this case, λ is equal to a frequency in a pass band or nearby the pass band. By using the above configuration, it is possible to realize a balanced high-frequency device having an unbalanced-balanced input/output terminal. 
     Operations of the balanced high-frequency device  601  are described by referring to the accompanying drawings. As shown in  FIG. 7(   a ), when a signal component i is input to the balanced device  602  from the input terminal IN, common-mode signal components ic 1  and ic 2  and differential-mode signal components id 1  and id 2  are output from the balanced device. A transmission line  604  set between output terminals performs operations different from each other for the common-mode signal components ic 1  and ic 2  and differential-mode signal components id 1  and id 2 . That is, as shown in  FIG. 7(   b ), for the common-mode signal components ic 1  and ic 2 , a configuration is realized in which a opened λ/4 line is connected to the output terminals OUT 1  and OUT 2  respectively and operates as a series resonant circuit, impedances of the output terminals to a ground plane almost becomes short, and the common-mode signal component ic 1  or ic 2  is not propagated to the output terminal OUT 1  or OUT 2 . 
     Moreover, for the differential-mode signal components id 1  and id 2 , a configuration is realized in which shorted λ/4 line is connected to the output terminals OUT 1  and OUT 2  respectively because a virtual setting plane is formed at the middle point of the transmission line  604 , operates as a parallel resonant circuit, and impedances of the output terminals to ground planes almost become open, and thereby the differential-mode signal components id 1  and id 2  are propagated to the output terminals OUT 1  and OUT 2 . 
     As described above, the balanced high-frequency device of the embodiment 3 of the present invention makes it possible to reduce common-mode signal components by using the transmission line  604  as a phase circuit and thus, it is possible to realize a balanced high-frequency device excellent in balance-characteristic. 
     In the case of this embodiment, the phase circuit is constituted by the transmission line. However, the configuration of the phase circuit is not restricted to the above configuration. By using a configuration operating as a phase circuit, the same advantage as the present invention can be obtained. 
     Moreover, it is allowed that a phase circuit is formed on a circuit substrate by using a transmission line and a chip component or integrated on a substrate with a balanced device mounted or in a package. Furthermore, it is allowed to form a part of the phase circuit in a laminated device constituted by forming electrode patterns on a plurality of dielectric layers and laminating the dielectric layers. Furthermore, by constituting the laminated device so as to have another circuit function and integrating the laminated device with a balanced high-frequency device of the present invention as a composite device, it is possible to realize a multifunctional compact balanced high-frequency device. 
     In the case of this embodiment, an input terminal is described as the unbalanced type and an output terminal is described as the balanced type. However, it is allowed that an input terminal is the balanced type and an output terminal is the unbalanced type. Moreover, it is allowed that both input terminal and output terminal are the balanced type. 
     (Embodiment 4) 
     A balanced high-frequency device of embodiment 4 of the present invention is described below by referring to the accompanying drawings. A more specific circuit configuration is shown below as a phase circuit.  FIG. 8  shows a configuration of a balanced high-frequency device of the embodiment 4 of the present invention. In  FIG. 8 , the balanced high-frequency device  801  is constituted by a balanced device  802  and a phase circuit  803 . In the case of the balanced device  802 , the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal and output-side terminals are output terminals OUT 1  and OUT 2  serving as balanced input/output terminals. 
     The phase circuit  803  is constituted by impedance elements  804 ,  805 , and  806 . In this case, the output terminals OUT 1  and OUT 2  are grounded through impedance elements  804  and  805 , the impedance element  806  is connected between the output terminals, and the phase circuit  803  is also connected between the output terminals. In this case, the impedance elements  804  and  805  substantially have the same impedance and the imaginary part of the impedance of the impedance element  806  is reverse to that of the impedances of the impedance elements  804  and  805  in polarity. By using the above configuration, a balanced high-frequency device having unbalanced-balanced input and output terminals can be obtained. 
     Then, operations of the balanced high-frequency device of the embodiment 4 of the present invention are described below by using a specific impedance element.  FIGS. 9(   a ) and  9 ( b ) are illustrations for explaining operations of the balanced high-frequency device of the embodiment 4 of the present invention. As shown in  FIG. 9(   a ), a phase circuit  901  is constituted by capacitors  902  and  903  and an inductor  904 . As shown in  FIG. 9(   a ), when a signal component i is input to the balanced device  802  from the input terminal IN, common-mode signal components ic 1  and ic 2  and differential-mode signal components id 1  and id 2  are output from the balanced device. In this case, the inductor  904  connected between output terminals forms a virtual ground point  905  on the differential-mode signal components id 1  and id 2 . 
       FIG. 9(   b ) shows the equivalent circuit of the phase circuit  901  on the differential-mode signal components id 1  and id 2 . Because the inductor  904  forms the virtual ground point  905  on the differential-mode signal components id 1  and id 2 , the capacitor  902  and a part of the inductor  904  form a parallel resonant circuit to a ground plane at the output terminal OUT 1  and the capacitor  903  and a part of the inductor  904  form a parallel resonant circuit to a ground plane at the output terminal OUT 2 . By designing parallel resonant frequencies of the parallel resonant circuits so as to be kept in a pass band or nearby the pass band, impedances of the differential-mode signal components id 1  and id 2  at a predetermined frequency to a ground plane approach infinity and transferred to the output terminals without being shorted to a ground plane. That is, on the differential-mode signal components, operations substantially same as those shown in  FIG. 7(   c ) are executed.  FIG. 9(   c ) shows the equivalent circuit of the phase circuit  901  on the common-mode signal components ic 1  and ic 2 . OUT 1  and OUT 2  have almost equal potentials on the common-mode signal components, the inductance  904  does not form a virtual ground point on the common-mode signal components ic 1  and ic 2 , and OUT 1  and OUT 2  are substantially open. In this case, a part of the inductor  904  denotes a range up to the virtual ground point  905  {refer to  FIG. 9(   b )}. 
     Thus, by designing impedances of the capacitors  902  and  903  serving as impedance elements arranged between the balanced input/output terminals OUT 1  and OUT 2  and ground planes to sufficiently small values, the common-mode signal components ic 1  and ic 2  are shorted to ground planes and therefore, they are not transferred to the balanced input/output terminals. 
     Moreover, it is allowed that the phase circuit of the embodiment 4 of the present invention has the configuration shown in  FIG. 10 .  FIGS. 10(   a ) to  10 ( c ) are illustrations for explaining operations of the balanced high-frequency device of the embodiment 4 of the present invention. As shown in  FIG. 10(   a ), a phase circuit  1001  is constituted by inductors  1002  and  1003  and a capacitor  1004 . As shown in  FIG. 10(   a ), when a signal component i is input to a balanced device  802  from an input terminal IN, common-mode signal components ic 1  and ic 2  and differential-mode signal components id 1  and id 2  are output from the balanced device. In this case, the capacitor  1004  connected between output terminals forms a virtual ground point  1005  on differential-mode signal components id 1  and id 2 . 
       FIG. 10(   b ) shows the equivalent circuit of the phase circuit  1001  on the differential-mode signal components id 1  and id 2 . As shown in  FIG. 10(   b ), because the capacitor  1004  forms a virtual ground point  1005  on the differential-mode signal components id 1  and id 2 , the inductor  1002  and a part of the capacitor  1004  form a parallel resonant circuit to a ground plane at the output terminal OUT 1  and the inductor  1003  and a part of the capacitor  1004  form a parallel resonant circuit to a ground plane at the output terminal OUT 2 . Therefore, by designing parallel resonant frequencies of the parallel resonant circuits so that they are kept in a pass band or nearby the pass band, impedances of the differential-mode signal components id 1  and id 2  at desired frequencies to a ground plane approach infinity and the components are transferred to the output terminals without being shorted to ground planes. That is, operations substantially same as those shown in  FIG. 7(   c ) are executed on the differential-mode signal components id 1  and id 2 .  FIG. 10(   c ) shows the equivalent circuit of the phase circuit  1001  on the common-mode signal components ic 1  and ic 2 . OUT 1  and OUT 2  have almost equal potential on the common-mode signal components, the capacitor  1004  does not form a virtual ground point on the common-mode signal component ic 1  or ic 2 , and OUT 1  and OUT 2  substantially become open. In this case, a part of the capacitor  1004  denotes a range up to the virtual ground point (refer to  FIG. 10(   b )). 
     Therefore, by designing impedances of the inductors  1002  and  1003  serving as impedance elements arranged between the balanced input/output terminals OUT 1  and OUT 2  and ground planes to sufficiently small values, the common-mode signal components ic 1  and ic 2  are shorted to ground planes and therefore, they are not transferred to the balanced input terminals. 
     As described above, in the case of the balanced high-frequency device of the embodiment 4 of the present invention, it is possible to reduce common-mode signal components by using three impedance elements as phase circuits and thus, realize a balanced high-frequency device excellent in balance-characteristic. 
     In the case of this embodiment, the numbers of and configurations of inductors and capacitors serving as impedance elements constituting a phase circuit are not restricted to the above case. Moreover, though device values of the impedance elements  804  and  805  are substantially equal to each other, it is not always necessary that they are equal to each other. They are optimally selected in accordance with a circuit configuration. By using a configuration operating as a phase circuit, the same advantage as the present invention can be obtained. 
     Moreover, it is allowed that a phase circuit is formed on a circuit substrate by using a transmission line and a chip component or integrated on a substrate with a balanced device mounted or in a package. Furthermore, it is allowed to form a part of the phase circuit in a laminated device constituted by forming electrode patterns on a plurality of dielectric layers and laminating the dielectric layers. Furthermore, by constituting the laminated device so as to have another circuit function and integrating the laminated device with a balanced high-frequency device of the present invention as a composite device, it is possible to realize a multifunctional compact balanced high-frequency device. 
     Furthermore, in the case of this embodiment, it is described that an input terminal is the unbalanced type and an output terminal is the balanced type. However, it is allowed that the input terminal is the balanced type and the output terminal is the unbalanced type. Furthermore, it is allowed that both the input terminal and output terminal are the balanced type. 
     (Embodiment 5) 
     A balanced high-frequency device of embodiment 5 of the present invention is described below by referring to the accompanying drawings. A more specific circuit configuration is shown below as a phase circuit.  FIG. 11  shows a configuration of a balanced high-frequency device  1101  of the embodiment 5 of the present invention. In  FIG. 11 , the balanced high-frequency device  1101  is constituted by a balanced device  1102  and a phase circuit  1103 . Moreover, in the case of the balanced device  1102 , the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal and output-side terminals are output terminals OUT 1  and OUT 2  serving as balanced terminals. 
     The phase circuit  1103  is constituted by impedance elements  1104 ,  1105 , and  1106 . The impedance elements  1104  and  1105  are connected between the output terminals in series and the middle point  1107  between the impedance elements  1104  and  1105  is grounded through the impedance element  1106  and the phase circuit  1103  is connected between the output terminals. In this case, the imaginary part of the impedance of the impedance element  1106  is opposite to imaginary parts of impedances of the impedance elements  1104  and  1105  in polarity. Moreover, the impedance elements  1104  and  1105  have the substantially same value. By using the above configuration, it is possible to obtain a balanced high-frequency device having an unbalanced-balanced input/output terminal. 
     Then, operations of a balanced high-frequency device of the present invention are described below by using a specific impedance element.  FIGS. 12(   a ) to  12 ( c ) are illustrations for explaining operations of the balanced high-frequency device of the present invention. As shown in  FIG. 12(   a ), a phase circuit  1201  is constituted by inductors  1202  and  1203  and a capacitor  1204 . As shown in  FIG. 12(   a ), when a signal component i is input from an input terminal IN to the balanced device  1102 , common-mode signal components ic 1  and ic 2  and differential-mode signal components id 1  and id 2  are output from the balanced device  1102 .  FIG. 12(   b ) shows the equivalent circuit of the phase circuit  1201  on the differential-mode signal components. As shown in  FIG. 12(   b ), the connection point  1205  between the inductors  1202  and  1203  serves as a virtual ground point on the differential-mode signal components id 1  and id 2 . Therefore, by sufficiently increasing values of the inductors  1202  and  1203 , it is possible to increase an impedance to a ground plane and the differential-mode signal components id 1  and id 2  are transferred to output terminals OUT 1  and OUT 2 . 
     Moreover,  FIG. 12(   c ) shows the equivalent circuit of the phase circuit  1201  on common-mode signal components. As shown in  FIG. 12(   c ), the connection point  1205  between the inductors  1202  and  1203  does not serve as a virtual ground point on the common-mode signal components ic 1  and ic 2 . Therefore, by designing the inductor  1202  and a part of the capacitor  1204  and the inductor  1203  and a part of the capacitor  1204  so that they form a series resonant circuit at a predetermined frequency, common-mode signal components are shorted to ground planes and therefore, they are not transferred to the output terminal OUT 1  or OUT 2 . In this case, a part of the capacitor  1204  denotes one hand equivalently becoming parallel connection (refer to  FIG. 12(   c )). 
     Furthermore, it is allowed that a phase circuit of the present invention has the configuration shown in  FIGS. 13(   a ) to  13 ( c ).  FIGS. 13(   a ) to  13 ( c ) are illustrations for explaining operations of the balanced high-frequency device of the present invention. As shown in  FIG. 13(   a ), a phase circuit  1301  is constituted by capacitors  1302  and  1303  and an inductor  1304 . As shown in  FIG. 13(   a ), when a signal component i is input from an input terminal IN to the balanced device  1102 , common-mode signal components ic 1  and ic 2  and differential-mode signal components id 1  and id 2  are output from the balanced device  1102 .  FIG. 13(   b ) shows the equivalent circuit of the phase circuit  1301  on the differential-mode signal components id 1  and id 2 . As shown in  FIG. 13(   b ), the connection point  1305  between the capacitors  1302  and  1303  serves as a virtual ground point on the differential-mode signal components id 1  and id 2 . Therefore, by sufficiently decreasing values of the capacitors  1302  and  1303 , it is possible to increase an impedance to a ground plane and the differential-mode signal components are transferred to the output terminals OUT 1  and OUT 2 . 
       FIG. 13(   c ) shows the equivalent circuit of the phase circuit  1301  on the common-mode signal components ic 1  and ic 2 . As shown in  FIG. 13(   c ), the connection point  1305  between the capacitors  1302  and  1303  does not serve as a virtual ground point on the common-mode signal components ic 1  and ic 2 . Therefore, by designing the capacity  1302  and a part of the inductor  1304  and the capacitor  1303  and a part of the inductor  1304  so that they respectively form a series resonant circuit at a predetermined frequency, common-mode signal components are shorted to ground planes and therefore, they are not transferred to the output terminal OUT 1  or OUT 2 . In this case, a part of the inductor  1304  denotes one hand equivalently becoming parallel connection (refer to  FIG. 13(   c )). 
     As described above, the balanced high-frequency device of the embodiment 5 of the present invention can reduce common-mode signal components by using three impedance elements as phase circuits and therefore, it is possible to realize a balanced high-frequency device excellent in balance-characteristic. 
     Moreover, in the case of this embodiment, the numbers of and configurations of inductors and capacitors serving as impedance element constituting a phase circuit are not restricted to the above case. Furthermore, though devices values of the impedance elements  1104  and  1105  are substantially equal to each other, it is not always necessary that the values are equal to each other but the values are optimally selected in accordance with a circuit configuration. Therefore, by using a configuration operating as a phase circuit, the same advantage as the present invention can be obtained. 
     Furthermore, it is allowed that a phase circuit is formed on a circuit substrate by using a transmission line and a chip component or formed on a substrate with a balanced device mounted or in a substrate. Furthermore, it is allowed to form a part of the phase circuit in a laminated device constituted by forming electrode patterns on a plurality of dielectric layers and laminating the dielectric layers. Furthermore, by constituting the laminated device so as to have another circuit function and integrating the laminated device with a balanced high-frequency device of the present invention as a composite device, it is possible to realize a multifunctional compact balanced high-frequency device. 
     In the case of this embodiment, it is described that an input terminal is the unbalanced type and an output terminal is the balanced type. However, it is also allowed that the input terminal is the balanced type and the output terminal is the unbalanced type. Furthermore, it is allowed that both the input terminal and output terminal are the balanced type. 
     (Embodiment 6) 
     Then, a balanced high-frequency device of embodiment 6 of the present invention is described below by referring to the accompanying drawings. A specific configuration of the balanced high-frequency device is described below on a case of using surface acoustic wave filter as balanced device.  FIG. 14  shows a configuration of a balanced device of the present invention. In  FIG. 14 , a balanced high-frequency device  1401  is constituted by a surface acoustic wave filter  1402  and a phase circuit  1403  respectively serving as a balanced device. Moreover, in the case of the surface acoustic wave filter  1402 , the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal and output-side terminals are output terminals OUT 1  and OUT 2  serving as balanced input/output terminals. Moreover, the phase circuit  1403  is connected between the output terminals. 
     The surface acoustic wave filter  1402  is constituted on a piezoelectric substrate  1404  by first, second, and third inter-digital transducer electrodes (hereafter respectively referred to as IDT electrode)  1405 ,  1406 , and  1407  and first and second reflector electrodes  1408  and  1409 . One-hand electrode finger of the first IDT electrode  1405  is connected to the output terminal OUT 1  and the other-hand electrode finger of the first IDT electrode  1405  is connected to the output terminal OUT 2 . Moreover, one-hand electrode fingers of the second and third IDT electrodes  1406  and  1407  are connected to the input terminal IN and the other-hand electrode fingers of them are grounded. By using the above configuration, it is possible to obtain a balanced high-frequency device having an unbalanced-balanced input/output terminal. 
     Then, specific characteristics of the balanced high-frequency device of this embodiment are described below.  FIGS. 15(   a ) to  15 ( c ) show characteristics of the balanced high-frequency device  1401  when using the phase circuit  603  shown in  FIG. 6  as the phase circuit  1403 . In this case, the transmission line  604  constituting the phase circuit  603  has substantially a length of λ/2 which corresponds to a phase shift of 180°.  FIG. 15(   a ) shows a passing characteristic,  FIG. 15(   b ) shows amplitude balance-characteristic of a pass band, and  FIG. 15(   c ) shows a phase balance-characteristic of a pass band. The balance-characteristics in  FIGS. 15(   b ) and  15 ( c ) are greatly improved compared to conventional characteristics shown in  FIG. 31  and are almost close to an ideal characteristic. Moreover, in the case of the passing characteristic, the attenuation at the high pass-band side is improved by approx. 5 dB. 
     Then, a case of changing the length of the transmission line  604  is evaluated.  FIGS. 16(   a ) and  16 ( b ) show balance-characteristics when changing the length of the transmission line  604 .  FIG. 16(   a ) shows amplitude balance-characteristics and  FIG. 16(   b ) shows phase balance-characteristics. Moreover, symbols  1601  and  1602  denote the maximum value and minimum value of deteriorations in the amplitude balance-characteristic in a pass band of the surface acoustic wave filter of this embodiment. Symbols  1603  and  1604  denote the maximum value and minimum value of deteriorations in the phase balance-characteristics in the bass band of the surface acoustic wave filter of this embodiment. Furthermore, broken lines show the maximum value and minimum value of deteriorations in the balance-characteristics of a conventional surface acoustic wave filter. From  FIGS. 16(   a ) and  16 ( b ), it is found that the balance-characteristics are improved when the transmission line length ranges substantially between λ/4 and 3λ/4. Moreover, it is found that a more preferable balance-characteristic is obtained when the amplitude balance-characteristic ranges between substantially −5 dB and +5 dB and the phase balance-characteristic ranges between substantially −0.5° and +0.5° by keeping a phase angle in substantially the range between 3λ/8 and 5λ/8. 
     Then, characteristics when using a phase circuit of another configuration are shown.  FIGS. 17(   a ) to  17 ( c ) show characteristics of the balanced high-frequency device  1401  when using the phase circuit  901  shown in  FIG. 9  as the phase circuit  1403 . In this case, capacitances Cg1 and Cg2 of the capacitors  902  and  903  are substantially equal to each other so that impedances of the capacitors  902  and  903  respectively become 3 Ω at the frequency in a pass band. Moreover, the inductance Lb of the inductor  904  is designed so that parallel resonant frequencies between Cg1 and Lb/2 and between Cg2 and Lb/2 are kept in a pass band. 
       FIG. 17(   a ) shows a passing characteristic,  FIG. 17(   b ) shows an amplitude balance-characteristic of a pass band, and  FIG. 17(   c ) shows a phase balance-characteristic of a pass band. The balance-characteristics are greatly improved compared to those shown in  FIG. 31  and are almost close to an ideal state. Moreover, in the case of the passing characteristics, the attenuation at the high pass-band side is improved by approx. 5 dB. 
     Then, a case in which impedances of the capacitors  902  and  903  are changed is evaluated.  FIGS. 18(   a ) and  18 ( b ) show balance-characteristics to normalized impedances obtained by dividing impedances of the capacitors  902  and  903  by the characteristic impedance of a terminal. In this case, because the characteristic impedance of a balanced output terminal is equal to substantially 50 Ω, it is assumed that the characteristic impedance of each terminal is equal to substantially 25 Ω.  FIG. 18(   a ) shows amplitude balance-characteristics and  FIG. 18(   b ) shows phase balance-characteristics. Moreover, symbols  1801  and  1802  denote the maximum value and minimum value of deteriorations in the amplitude balance-characteristics in the pass band of the surface acoustic wave filter of this embodiment and  1803  and  1804  denote the maximum value and minimum value of deteriorations in the phase balance-characteristics in the pass band of the surface acoustic wave filter of this embodiment. From  FIGS. 18(   a ) and  18 ( b ), it is found that the balance-characteristics are improved when normalized impedances are equal to or less than 2. 
     Then, characteristics when using a phase circuit of another configuration are described below.  FIGS. 19(   a ) to  19 ( c ) show characteristics of the balanced high-frequency device  1401  when using the phase circuit  1001  shown in  FIG. 10  as the phase circuit  1403 . In this case, inductance values Lg1 and Lg2 of the inductors  1002  and  1003  are substantially equal to each other and the inductors  1002  and  1003  are designed so that impedances of the inductors are respectively equal to substantially 3 Ω at the frequency in a pass band. Moreover, the capacitance Cb of the capacitor  1004  is designed so that parallel resonant frequencies between Lg1 and 2Cb and between Lg2 and 2Cb are kept in a pass band. 
       FIG. 19(   a ) shows a passing characteristic,  FIG. 19(   b ) shows an amplitude balance-characteristic of a pass band, and  FIG. 19(   c ) shows a phase balance-characteristic of a pass band. The balance-characteristics are greatly improved compared to conventional characteristics shown in  FIG. 31  and are almost close to an ideal state. Moreover, in the case of the passing characteristic, the attenuation at the high pass band side is improved by approx. 5 dB. 
     Then, a case is evaluated in which impedances of the inductors  1002  and  1003  are changed.  FIGS. 20(   a ) and  20 ( b ) show balance-characteristics to normalized impedances obtained by dividing the impedances of the inductors  1002  and  1003  by the characteristic impedance of a terminal. In this case, because the characteristic impedance of a balanced output terminal is substantially equal to 50 Ω, the characteristic impedance of each terminal is set to substantially 25 Ω.  FIG. 20(   a ) shows amplitude balance-characteristics and  FIG. 20(   b ) shows phase balance-characteristics. Moreover, symbols  2001  and  2002  denote the maximum value and minimum value of deteriorations in the amplitude balance-characteristics in the pass band of the surface acoustic wave filter of this embodiment and  2003  and  2004  denote the maximum value and minimum value of deteriorations in the phase balance-characteristics in the bass band of the surface acoustic wave filter of this embodiment. 
     From  FIG. 20 , it is found that the phase balance-characteristics are improved when the normalized impedance is substantially 2 or less. Moreover, the amplitude balance-characteristics are improved when the normalized impedance is substantially 0.5 or less. Therefore, it is preferable to keep the normalized impedance at substantially 2 or less. More preferably, by preferably keeping the normalized impedance at substantially 0.5 or less, it is possible to improve the balance-characteristics. 
     As described above, in the case of the balanced high-frequency device  1401  of the embodiment 6 of the present invention, it is possible to reduce common-mode components by using three impedance elements as phase circuits and thereby realize a balanced high-frequency device excellent in balance-characteristic. 
     Moreover, though this embodiment is described by using a transmission line as a phase circuit, it is preferable that the transmission line substantially has a length of λ/2. This is because the phase circuit more frequently operates as an inductor or capacitor as the transmission-line length is shifted from λ/2 and the impedance of the pass-band frequency  2102  when viewing a balanced device from the output-terminal side is shifted from a matching state. For example, when the length of a transmission line is equal to 3λ/8, the impedance of the passing band  2101  becomes inductive as shown in  FIG. 21(   a ). In this case, as shown in  FIG. 22 , it is only necessary to connect the transmission line  604  as a phase circuit and a capacitor  2202  serving as a matching circuit between output terminals of a phase circuit  2201  in parallel. As shown in  FIG. 21(   b ), by using the above configuration, the impedance of a pass-band vicinity  2102  when viewing a balanced device from the output-terminal side becomes the center of Smith chart and it is possible to realize impedance matching. Thus, it is allowed to constitute a phase circuit so as to include a matching circuit for performing impedance matching. 
     Moreover, the fact that the length of a transmission line is equal to 3λ/8 is equivalent to the fact that the phase angle is 135° and approaches 180° by adding the above matching circuit and the length of the transmission line substantially approaches λ/2. Therefore, by adding the matching circuit, it is possible to decrease the length of the transmission line and downsize the configuration. 
     In the case of this embodiment, the phase circuit is constituted by using the transmission line or three impedance elements. However, the configuration of a phase circuit is not restricted to the above case. Moreover, the numbers of and configurations of inductors and capacitors serving as impedance elements are not restricted to the above case. By using a configuration operating as a phase circuit, the same advantage as the present invention can be obtained. 
     Moreover, it is allowed to form a phase circuit on a circuit substrate by using a transmission line and a chip component. It is also allowed to constitute a phase circuit on a substrate with a balanced device mounted or in a package. Moreover, it is allowed to form a part of a phase circuit in a laminated device constituted by forming electrode patterns on a plurality of dielectric layers and laminating the dielectric layers. Furthermore, by constituting the laminated device so as to have another circuit function and integrating a balanced high-frequency device of the present invention with the laminated device as a composite device, it is possible to realize a multifunctional compact balanced high-frequency device. 
     Though it is described that an input terminal is the unbalanced type and an output terminal is the balanced type in the case of this embodiment, it is allowed that the input terminal is the balanced type and the output terminal is the unbalanced type or both the input terminal and output terminal are the balanced type. 
     (Embodiment 7) 
     A balanced high-frequency device of embodiment 7 of the present invention is described below by referring to the accompanying drawings. A specific configuration when a matching circuit is included in a phase circuit is described below.  FIG. 23(   a ) shows a configuration of the balanced high-frequency device of the embodiment 7 of the present invention. In  FIG. 23(   a ), a balanced high-frequency device  2301  is constituted by a balanced device  2302  and a phase circuit  2303 . Moreover, in the balanced device  2302 , the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal and output-side terminals are output terminals OUT 1  and OUT 2  serving as balanced input/output terminals. Moreover, the phase circuit  2303  is connected between the output terminals. 
     The phase circuit  2303  is constituted by capacitors  2304  and  2305  and an inductor  2306  serving as impedance elements and an inductor  2307  serving as a matching circuit. In this case, the output terminals OUT 1  and OUT 2  are grounded through the capacitors  2304  and  2305  respectively, the inductor  2306  is connected between the output terminals, and the phase circuit  2303  is connected between the output terminals. Moreover, the inductor  2307  serving as a matching circuit is included in the phase circuit  2303 . 
     The inductor  2306  forms a virtual ground point  2308  on a differential-mode signal component. Therefore, the capacitor  2304  and a part of the inductor  2306  form a parallel resonant circuit to a ground plane at the output terminal OUT 1  and the capacitor  2304  and a part of the inductor  2306  form a parallel resonant circuit to a ground plane at the output terminal OUT 2 . By designing parallel resonant frequencies of the parallel resonant circuits so that they are kept in a passing band or nearby the passing band, the impedance of a differential-mode signal component at a predetermined frequency approaches infinity to a ground plane and transferred to an output terminal without being shorted to the ground plane. That is, operations substantially same as those shown in  FIG. 7(   c ) are executed on the differential-mode signal component. 
     Moreover, the inductor  2306  does not form a virtual ground point on common-mode signal component. Therefore, by designing impedances of the capacitors  2304  and  2305  serving as impedance elements arranged between the balanced input/output terminals OUT 1  and OUT 2  and ground planes to sufficiently small values, the common-mode signal component is shorted to a ground plane and thereby, it is not transferred to a balanced input/output terminal. 
     As described above, in the case of the phase circuit  2303  of this embodiment, a resonant circuit at a predetermined frequency is constituted by the capacitors  2304  and  2305  and the inductor  2306  and the inductor  2307  serving as a matching circuit is included. Also in this case, common-mode signal components are reduced and it is possible to realize a balanced high-frequency device having excellent balance-characteristics. 
     Moreover, it is possible to incorporate the inductor  2307  into the inductor  2306 . That is, it is enough to use a combined inductance  2309  of the inductors  2306  and  2307 . In this case, because the inductors  2306  and  2307  are connected in parallel, the expression Lt=(Lb×Lm)/(Lb+Lm) is effectuated when assuming inductances of the inductors  2306  and  2307  and combined inductor  2309  as Lb, Lm, and Lt respectively. Thus, it is possible to decrease values of the inductances. Moreover, it is possible to decrease the number of devices and downsize a circuit configuration. 
     In this case, however, the meaning of a predetermined frequency differs. That is, when assuming capacitances of the capacitors  2304  and  2305  as Cg1 and Cg2, parallel resonant frequencies f 1  and f 2  of differential-mode signal components at each output terminal in a matching state formed by the capacitors  2304  and  2305  and inductor  2306  become f 1 =1/{2π×√(Lb/2)×√(Cg1)} and f 2 =1/{2π×√(Lb/2)×√(Cg2)}. In this case, by including the inductor  2307  serving a matching circuit, the whole parallel resonant frequencies f 1 t and f 2 t become f 1 t=1/{2π√(Lt/2)×√(Cg1)}and f 2 t=1/{2π×√(Lt/2)×√(Cg2)} and thus, they are apparently shifted from predetermined frequencies. 
     That is, the whole parallel resonant frequency of the phase circuit  2303  is shifted from a pass band or the vicinity of the pass band by a value equivalent to the inductor Lm. However, the effect that common-mode signal component can be reduced is the same when the capacitor  2304  and a part of the inductor  2306  form a parallel resonant circuit to a ground plane at the output terminal OUT 1  and the capacitor  2305  and a part of the inductor  2306  form a parallel resonant circuit to a ground plane in a matching state and the impedance to ground planes of the capacitors  2304  and  2305  are sufficiently small. In this case, a part of the inductor  2306  denotes a range up to a virtual ground plane. 
     However, the circuit configuration of this embodiment is not restricted to the above case. As long as operations of a matching circuit and operations of a resonant circuit are substantially the same as the case of the present invention, it is possible to realize a balanced high-frequency device having excellent balance-characteristics similarly to the case of the present invention. 
     Moreover, though values Cg1 and Cg2 of capacitors serving as impedance elements are assumed to be substantially the same and values Lg1 and Lg2 of inductors serving as impedance elements are assumed to be substantially the same, it is not always necessary that these values are the same but they are optimally selected in accordance with a circuit configuration. 
     (Embodiment 8) 
     A balanced high-frequency device of embodiment 8 of the present invention is described below by referring to the accompanying drawings. Specific characteristics of the balanced high-frequency device are described below on a case of using an surface acoustic wave filter as a balanced device.  FIG. 24  shows a configuration of a balanced high-frequency device  2401  of the present invention. In  FIG. 24 , the balanced high-frequency device  2401  is constituted by surface acoustic wave filter  2402  serving as a balanced device and a phase circuit  2403 . Moreover, in the case of the surface acoustic wave filter  2402 , the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal and output-side terminals are output terminals OUT 1  and OUT 2  serving as balanced input/output terminals. Moreover, the phase circuit  2403  is connected between the output terminals. 
     The surface acoustic wave filter  2402  is formed on a piezoelectric substrate  2404  by first, second, and third inter-digital transducer electrodes (hereafter respectively referred to as IDT electrode)  2405 ,  2406 , and  2407  and first and second reflector electrodes  2408  and  2409 . The first IDT electrode  2405  is divided into two divided IDT electrodes and one-hand electrode fingers of the first and second divided IDT electrodes  2410  and  2411  are connected to the output terminals OUT 1  and OUT 2 . The other-hand electrode fingers of the first and second divided IDT electrodes  2410  and  2411  are electrically connected and virtually grounded. Moreover, one-hand electrode fingers of the second and third IDT electrodes  2406  and  2407  are connected to the input terminal IN and the other-hand electrode fingers of them are grounded. By using the above configuration, it is possible to obtain a balanced high-frequency device having an unbalance-balanced input/output terminal. 
     Also in the case of the balanced high-frequency device  2401  of the embodiment 8 of the present invention, it is possible to reduce common-mode signal components by using the phase circuit  2403  and realize a balanced high-frequency device excellent in balance-characteristic. 
     In the case of this embodiment, it is also allowed to constitute a phase circuit by using a transmission line or three impedance elements. Moreover, a configuration of the phase circuit is not restricted to the above one. By using a configuration operating as a phase circuit, the same advantage as the present invention can be obtained. Moreover, the numbers of and configurations of inductors and capacitors serving as impedance elements are not restricted to the above mentioned. By using a configuration operating as a phase circuit, the same advantage as the present invention is obtained. 
     Moreover, it is allowed to form a phase circuit on a circuit substrate by using a transmission line and a chip component or form the phase circuit on a substrate with a balanced device mounted or in a package. Furthermore, it is allowed to form a part of the phase circuit in a laminated device constituted by forming electrode patterns on a plurality of dielectric layers and laminating the dielectric layers. Furthermore, by constituting the laminated device so as to have another circuit function and integrating the laminated device with a balanced high-frequency device of the present invention as a composite device, it is possible to realize a multifunctional compact balanced high-frequency device. 
     Though it is described that an input terminal is the unbalanced type and an output terminal is the balanced type in the case of this embodiment, it is allowed that the input terminal is the balanced type and the output terminal is the unbalanced type. Moreover, it is allowed that both the input and output terminals are the balanced type. 
     (Embodiment 9) 
     A balanced high-frequency device of embodiment 9 of the present invention is described below by referring to the accompanying drawings. Specific characteristics of the balanced high-frequency device are described below on a case of using surface acoustic wave filter as a balanced device.  FIG. 25  shows a configuration of a balanced high-frequency device  2501  of the embodiment 9 of the present invention. In  FIG. 25 , the balanced high-frequency device  2501  is constituted by an surface acoustic wave filter  2502  serving as a balanced device and a phase circuit  2503 . Moreover, in the case of the surface acoustic wave filter  2502 , the input-side terminal is an input terminal IN serving as an unbalanced input/output terminal and output-side terminals are output terminals OUT 1  and OUT 2  serving as balanced terminals. Furthermore, the phase circuit  2503  is connected between the output terminals. 
     The surface acoustic wave filter  2502  is formed on a piezoelectric substrate  2504  by first, second, and third inter-digital transducer electrodes (hereafter respectively referred to as IDT electrode)  2505 ,  2506 , and  2507  and first and second reflector electrodes  2508  and  2509 . One-hand electrode finger of the first IDT electrode is connected to the input terminal IN and the other-hand electrode finger of it is grounded. One-hand electrode fingers of the second and third IDT electrodes  2506  and  2507  are connected to the output terminals OUT 1  and OUT 2  and the other-hand electrode fingers of them are grounded. By using the above configuration, a balanced high-frequency device having an unbalanced-balanced input/output terminal is obtained. 
     Also in the case of the balanced high-frequency device  2501  of the present invention, it is possible to reduce common-mode signal components by using the phase circuit  2503  and therefore, realize a balanced high-frequency device excellent in balance-characteristic. 
     In the case of this embodiment, a phase circuit is provided by using a transmission line or three impedance elements. Moreover, a configuration of the phase circuit is not restricted to the above case. By using a configuration operating as a phase circuit, the same advantage as the present invention is obtained. Furthermore, the numbers of and configurations of inductors and capacitors serving as impedance elements are not restricted to the above case. By using a configuration operating as a phase circuit, the same advantage as the present invention is obtained. 
     Furthermore, a phase circuit may be formed on a circuit substrate by using a transmission line or a chip component or integrate the phase circuit on a substrate with a balanced device mounted or in a package. Furthermore, a part of the phase circuit may be formed in a laminated device constituted by forming electrode patterns on a plurality of dielectric layers and laminating the dielectric layers. Furthermore, by forming the laminated device so as to have another circuit function and integrating a balanced high-frequency device of the present invention with the laminated device as a composite device, it is possible to realize a multifunctional compact balanced high-frequency device. 
     Though it is described that an input terminal is the unbalanced type and an output terminal is the balanced type in the case of this embodiment, the input terminal may be the balanced type and the output terminal the unbalanced type. Moreover, both the input and output terminals may be the balanced type. 
     (Embodiment 10) 
     A balanced high-frequency device of embodiment 10 of the present invention is described below by referring to the accompanying drawings.  FIG. 26  shows a configuration of a balanced high-frequency device  2601  of the embodiment 10 of the present invention. For  FIG. 26 , a specific configuration of the balanced high-frequency device is described on a case of using a semiconductor device as the balanced device. In  FIG. 26 , the balanced high-frequency device  2601  is constituted by a semiconductor device  2602  serving as a balanced device and phase circuits  2603  and  2608 . Moreover, in the case of the semiconductor device  2602 , input-side terminals are input terminals IN 1  and IN 2  serving as balanced input/output terminals and output-side terminals are output terminals OUT 1  and OUT 2  serving as balanced terminals. Furthermore, the phase circuit  2603  is connected between the input terminals and the phase circuit  2608  is connected between the output terminals. 
     Then, a configuration of the semiconductor device  2602  is described below. Symbols  2604   a ,  2604   b ,  2605   a , and  2605   b  denote bipolar transistors and  2606   a  and  2606   b  denote inductors. The input terminal IN 1  is connected to the base of the bipolar transistor  2604   a  through a DC-cut capacitor  2607   a  and the input terminal IN 2  is connected to the base of the bipolar transistor  2604   b  through a DC-cut capacitor  2607   b . Collectors of the bipolar transistors  2604   a  and  2604   b  are connected to emitters of the bipolar transistors  2605   a  and  2605   b  respectively and collectors of the bipolar transistors  2605   a  and  2605   b  are connected to the output terminals OUT 1  and OUT 2  through DC-cut capacitors  2609   a  and  2609   b  respectively. Emitters of the bipolar transistors  2604   a  and  2604   b  are grounded through the inductors  2606   a  and  2606   b  respectively. A bias circuit  2610  supplies a bias current to bases of the bipolar transistors  2604   a  and  2604   b . A bias circuit  2611  supplies a bias current to bases of the bipolar transistors  2605   a  and  2605   b . A power-source voltage Vcc is supplied to collectors of the bipolar transistors  2605   a  and  2605   b  through choke inductors  2912   a  and  2912   b  respectively. By using the above configuration, a balanced semiconductor device operates as an amplifier. 
     Also in the case of the balanced high-frequency device  2601  of the embodiment 10 of the present invention, it is possible to reduce common-mode signal components by using the phase circuits  2603  and  2608  and therefore, realize a balanced high-frequency device excellent in balance-characteristic. 
     In this embodiment, a phase circuit may be formed by using a transmission line or three impedance elements. Moreover, a configuration of the phase circuit is not restricted to the above case. By using a configuration operating as a phase circuit, the same advantage as the present invention is obtained. Furthermore, the numbers of and configurations of inductors and capacitors serving as impedance elements are not restricted to the above case. By using a configuration operating as a phase circuit, the same advantage as the present invention is obtained. 
     A phase circuit on a circuit may be formed on a circuit substrate by using a transmission line or a chip component or integrate the phase circuit on a substrate with a balanced device mounted or in a package. Moreover, a part of the phase circuit may be formed in a laminated device by forming electrode patterns on a plurality of dielectric layers and laminating the dielectric layers. 
     Furthermore, by forming the laminated device so as to have another circuit function and integrating a balanced high-frequency device of the present invention with the laminated device as a composite device, it is possible to realize a multifunctional compact balanced high-frequency device. 
     Furthermore, in the case of this embodiment, it is described that input and output terminals are the balanced type. However, either of the input and output terminals may be the unbalanced type and the other of them is the balanced type. 
     Furthermore, in the case of this embodiment, a semiconductor device is formed by four bipolar transistors. However, a configuration of the semiconductor device is not restricted to the above case. 
     Furthermore, for this embodiment, a case is described in which the semiconductor device  2602  is an amplifier. However, the semiconductor device  2602  is not restricted to an amplifier. The semiconductor device  2602  may be a mixer or oscillator. In short, the semiconductor device  2602  is permitted as long as it is a semiconductor device having a balanced terminal. 
     (Embodiment 11) 
     A balanced high-frequency circuit of embodiment 11 of the present invention is described below by referring to the accompanying drawings.  FIG. 27  is a block diagram of a balanced high-frequency circuit  2701  using a balanced device of the present invention. In  FIG. 27 , an output signal output from a transmitting circuit is transmitted from an antenna  2705  through a transmitting amplifier  2702 , a transmitting filter  2703  and a switch  2704 . Moreover, an input signal received through the antenna  2705  is input to a receiving circuit through the switch  2704 , a receiving filter  2706 , and a receiving amplifier  2707 . In this case, because the transmitting amplifier  2702  is the balanced type and the switch  2704  is the unbalanced type, the transmitting filter  2703  is constituted so as to have an unbalanced-balanced input/output terminal. Furthermore, because the receiving amplifier  2707  is the balanced type and the switch  2704  is the unbalanced type, the receiving filter  2706  is constituted so as to have an unbalanced-balanced input/output terminal. 
     By applying a balanced device of the present invention to the transmitting filter  2703  or receiving filter  2706  of the balanced high-frequency circuit  2701  and a balanced high-frequency device of the present invention to the transmitting amplifier  2702  or receiving amplifier  2707 , it is possible to prevent modulation accuracy deterioration at the time of transmission due to deterioration of a balance-characteristic and sensitivity deterioration at the time of reception due to deterioration of a balance-characteristic and realize a high-performance balanced high-frequency circuit. 
     Moreover, when the switch  2704  is the balanced type and the transmitting amplifier  2702  or receiving amplifier  2707  is the unbalanced type, the same advantage is obtained by replacing balanced-type and unbalanced-type input/output terminals of the transmitting filter  2703  or receiving filter  1006  with each other. 
     Though means of switching transmission and reception is described by using the switch  2704  in the case of the balanced high-frequency circuit  2701 , the means may use a duplexer. 
     Moreover, a phase circuit of the present invention may be formed on a circuit substrate in the case of the balanced high-frequency circuit of this embodiment. For example, in  FIG. 27 , by forming the phase circuit between balanced transmission lines  2708  and  2709  on the circuit substrate, it is possible to prevent balance-characteristic deterioration due to the crosstalk of common-mode signal components and realize an excellent balanced high-frequency circuit. 
     Furthermore, embodiments of the present invention are described by using surface acoustic wave filter or semiconductor device as a balanced high-frequency device. However, the present invention can be applied not only to the above case but also to another device which balance-operates. 
     Furthermore, on a device for handling a high-frequency signal, parasitic components increase as a frequency rises, common-mode signal component increase due to crosstalk, and deterioration of balance-characteristics increases. Therefore, advantages of a balanced high-frequency device of the present invention increase as a frequency rises and it is possible to downsize a transmission line and an impedance element for forming a phase circuit. 
     As described above, the present invention makes it possible to provide a balanced high-frequency device having preferable balance-characteristics, balanced high-frequency circuit, phase circuit, and balance-characteristics improving method. 
     (Embodiment 12) 
       FIG. 33  is a diagram showing the configuration of a balanced high-frequency filter in embodiment 12 of the present invention. Referring to  FIG. 33 , the balanced high-frequency filter  5101  is constituted by a balanced high-frequency element  5102  and a phase-shifting circuit  5103 . The phase-shifting circuit  5103  is constituted by a transmission line  5104  and placed between output terminals. The length of the transmission line  5104  is λ T /2 (λ T  is the wavelength at a frequency in a transmission frequency band). In this embodiment, a transmission frequency band (880 to 915 MHz) used in a global system for mobile communication (GSM system) is used. 
       FIGS. 34(   a ) shows a characteristic of common-mode signal components in the transmission frequency band in a case where the length λ T  corresponds to 904 MHz and where a surface acoustic wave filter having a characteristic shown in  FIG. 30  is used as the balanced high-frequency element. According to  FIG. 34(   a ), the common mode signal component characteristic is markedly improved in comparison with a characteristic in the conventional art shown in  FIG. 49 .  FIG. 34(   b ) shows a characteristic of common-mode signal components in the transmission frequency band in a case where the arrangement shown in  FIG. 30  is used and where the length of the transmission line is λ R  corresponding to 942.5 MHz in a reception frequency band. According to  FIG. 34 , the characteristic of common-mode signal components is improved in comparison with the conventional art when the length of the transmission line is λ T /2. 
       FIGS. 35(   a ),  35 ( b ), and  35 ( c ) show characteristics of the balanced high-frequency device  5101 .  FIG. 35(   a ) shows a passing characteristic,  FIG. 35(   b ) an amplitude balance characteristic in a pass band,  FIG. 35(   c ) a phase balance characteristic in the pass band. In  FIG. 35(   a ), Tx is the transmission frequency band used in the GSM system and Rx is the reception frequency band used in the GSM system. The passing characteristic is a characteristic of differential-mode signal components in a balanced terminal, and the pass band is the reception frequency band Rx. According to  FIGS. 35(   b ) and  35 ( c ), the balance characteristics are markedly improved in comparison with the characteristics in the case of the conventional art shown in  FIG. 32(   a ) to  32 ( c ). In the balanced high-frequency filter of the present invention arranged as described above, the length of the transmission line provided as a phase-shifting circuit is λ T /2 and the corresponding frequency is set in a transmission frequency band, thereby reducing common-mode signal components in the transmission frequency band without deteriorating the passing characteristics and the balance characteristics in the reception frequency band. Thus, a balanced high-frequency filter having improved characteristics in a pass band and outside the pass band can be realized. 
     While this embodiment has been described by way of example with respect to a case where the balanced high-frequency element constituting the balanced high-frequency filter is a surface acoustic wave filter, this arrangement is not exclusively used. According to the present invention, the same effect can also be obtained by using any balanced high-frequency element if common-mode signal components in a transmission frequency band output from a balanced high-frequency element are reduced by a phase-shifting circuit, and if the balanced high-frequency element has balanced terminals. 
     The balanced high-frequency element may be a filter using an FBAR.  FIG. 36  shows the configuration of an FBAR. Referring to  FIG. 36 , the FBAR  5401  includes a lower electrode  5403 , a piezoelectric thin film  5404  and an upper electrode  5405  formed on a substrate  5402 . A cavity  5406  is provided in the substrate  5402  below the lower electrode, thereby realizing an energy confinement type of resonator. The lower electrode  5403  and the upper electrode  5405  correspond to the input and output electrode of the FBAR single unit. Si, sapphire or the like is used for the substrate  5402 . Al, Mo, Au, Cu, Ti or the like is used for the lower electrode  5403  and the upper electrode  5405 . In addition, AlN, ZnO or the like is used for the piezoelectric thin film  5404 . The FBAR is thus formed. A balanced high-frequency filter formed by applying a ladder filter or a mode-coupling filter using this FBAR to the balanced high-frequency element of the present invention can have the same advantage of the balanced high-frequency filter of the present invention. The construction of the FBAR is not limited to that described above. For example, an FBAR using an acoustic mirror may be used. 
     While this embodiment has been described with respect to a case where one transmission line is provided as a phase-shifting circuit, a combination of a plurality of transmission lines may be used.  FIG. 37  shows another configuration of high-frequency filter in embodiment 12 of the present invention. Referring to  FIG. 37 , the high-frequency filter  5501  is constituted by a balanced high-frequency element  5502  and a phase-shifting circuit  5503 . The phase-shifting circuit  5503  is constituted by transmission lines  5504  and  5505  and placed between output terminals. The length of the transmission line  5504  is λ T /2 (λ T  is the wavelength at a frequency in a transmission frequency band), while the length of the transmission line  5504  is λ/2. A length corresponding to a frequency different from the transmission frequency band may be selected as λ to improve the characteristics of common-mode signal components at frequencies outside the transmission frequency band. For example, if λ corresponds to a frequency in a reception frequency band, i.e., a pass band, the passing characteristic can be further improved. If λ corresponds to a frequency in a transmission frequency band of another system, interference waves of common-mode signal components coming from the another system by crosstalk or the like can be reduced. Thus, common-mode signal components of a plurality of systems can be reduced by selecting settings of the number of lengths λ and frequencies. 
     The balanced high-frequency filter of the present invention is used by being connected to a low-noise amplifier or a mixer.  FIG. 38(   a ) is a diagram showing the configuration of a balanced high-frequency filter  5101  and a low-noise amplifier  5601 . A phase-shifting circuit  5103  is connected between balanced terminals through which the balanced high-frequency filter  5101  and the low-noise amplifier  5601  are connected to each other. This arrangement ensures that common-mode signal components in a transmission frequency band can be reduced; saturation and distortion in the low-noise amplifier can be reduced; and a communication apparatus having higher sensitivity can be implemented.  FIG. 38(   b ) is a diagram showing the configuration of a balanced high-frequency filter  5101 , a low-noise amplifier  5601  and a mixer  5602 . A phase-shifting circuit  5103  is connected between balanced terminals through which the low-noise amplifier  5601  and the mixer  5602  are connected to each other. This arrangement ensures that common-mode signal components in a transmission frequency band can be reduced; distortion in the mixer can be reduced; and a communication apparatus having higher sensitivity can be implemented. 
     The first frequency band of the present invention corresponds to the reception frequency band in this embodiment, and the second frequency band of the present invention corresponds to the transmission frequency band in this embodiment. Also, in this embodiment, the first frequency band is a pass band, while the second frequency band is an attenuation band. 
     (Embodiment 13) 
     The configuration of a balanced high-frequency filter of the present invention is described below with reference to the drawings. 
       FIG. 39  is a diagram showing the configuration of a balanced high-frequency filter  5701  in embodiment 13 of the present invention. Referring to  FIG. 39 , the balanced high-frequency filter  5701  is constituted by a balanced high-frequency element  5702  and a phase-shifting circuit  5703 . In the balanced high-frequency element  5702 , a terminal on the input side is an input terminal IN serving as an unbalanced input/output terminal, and terminals on the output side are output terminals OUT 1  and OUT 2  serving as balanced terminals. 
     The phase-shifting circuit  5703  is constituted by capacitors  5704  and  5705  and an inductor  5706  provided as impedance elements. The capacitors  5704  and  5705  are connected in series between the output terminals, and a connection point  5707  between the capacitors  5704  and  5705  is grounded through the inductor  5706 . Thus, the phase-shifting circuit  5703  is connected between the output terminals. 
     In the phase-shifting circuit shown in  FIG. 39 , the connection point  5707  between the capacitors  5704  and  5705  is a virtual ground point with respect to differential-mode signal components corresponding to the passing characteristic of the balanced high-frequency filter. Therefore, the impedance to the ground plane can be increased by setting the value of the capacitors  5702  and  5703  sufficiently small to enable the differential-mode signal components to be transferred to the output terminals OUT 1  and OUT 2  without being grounded. The connection point  5707  between the capacitors  5704  and  5705  is not a virtual ground point with respect to common-mode signal components. The capacitor  5704  and part of the inductor  5706  and the capacitor  5705  and part of the inductor  5706  form series resonance circuits at a predetermined frequency. In the phase-shifting circuit  5703 , if the capacitance of the capacitors is C and the inductance of the inductor is L/2, the resonance frequency of the series resonance circuits with respect to common-mode signal components is f T =1/(2π×(LC) 1/2 ). The common-mode signal components in this frequency band are shorted to the ground plane. 
       FIG. 40(   a ) shows a characteristic of common-mode signal components in a transmission frequency band in a case where the resonance frequency f T  of the series resonance circuits is set to 904 MHz in the transmission frequency band, and where the surface acoustic wave filter  3001  having the configuration shown in  FIG. 30  is used as the balanced high-frequency element.  FIG. 49  shows a characteristic of common-mode signal components in the transmission frequency band (880 to 915 MHz) in the surface acoustic wave filter  3001 . The characteristic of common-mode signal components is referred to herein as leakage of common-mode signal components from the input side to the output side of the balanced high-frequency element. According to  FIG. 40(   a ), the characteristic of common-mode signal components is markedly reduced relative to the characteristic shown in  FIG. 49 .  FIG. 40(   b ) shows a characteristic of common-mode signal components in a transmission frequency band in a case where the resonance frequency of the series resonance circuits is set to 951 MHz in a reception frequency band. Thus, the resonance frequency of the series resonance circuits is set within a transmission frequency band to improve the characteristic of common-mode signal components in comparison with that in the conventional art. 
       FIGS. 41(   a ),  41 ( b ), and  41 ( c ) show characteristics of the balanced high-frequency filter  5701 .  FIG. 41(   a ) shows a passing characteristic,  FIG. 41(   b ) an amplitude balance characteristic in a pass band,  FIG. 41(   c ) a phase balance characteristic in the pass band. In  FIG. 41(   a ), Tx is the transmission frequency band used in the GSM system and Rx is the reception frequency band used in the GSM system. The passing characteristic is a characteristic of differential-mode signal components in a balanced terminal, and the pass band is the reception frequency band Rx. According to  FIGS. 41(   b ) and  41 ( c ), the balance characteristics are markedly improved in comparison with the characteristics in the case of the conventional art shown in  FIG. 32(   a ) to  32 ( c ). 
     In the balanced high-frequency filter of the present invention arranged as described above, the phase-shifting circuit is constituted by three impedance elements and the frequency of the series resonance circuits formed with respect to common-mode signal components is set within a transmission frequency band, thereby reducing common-mode signal components in the transmission frequency band. Thus, a balanced high-frequency filter having improved characteristics in a pass band and outside the pass band can be realized. 
     The phase-shifting circuit in this embodiment may alternatively have a circuit configuration such as shown in  FIG. 42 . Referring to  FIG. 42 , a phase-shifting circuit  6001  is constituted by inductors  6002  and  6003  and a capacitor  6004  provided as impedance elements. The inductors  6002  and  6003  are connected in series between the output terminals. A connection point  6005  between the inductors  6002  and  6003  is grounded through the capacitor  6004 . Thus, the phase-shifting circuit  6001  is connected between the output terminals. 
     In the phase-shifting circuit shown in  FIG. 42 , the connection point  6005  between the inductors  6002  and  6003  is a virtual ground point with respect to differential-mode signal components corresponding to the passing characteristic of the balanced high-frequency filter. Therefore, the impedance to the ground plane can be increased by setting the value of the inductors  6002  and  6003  sufficiently large to enable the differential-mode signal components to be transferred to the output terminals OUT 1  and OUT 2  without being grounded. The connection point  6005  between the inductors  6002  and  6003  is not a virtual ground point with respect to common-mode signal components. The inductor  6002  and part of the capacitor  6004  and the inductor  6002  and part of the capacitor  6004  form series resonance circuits at a predetermined frequency. In the phase-shifting circuit  6001 , if the inductance of the inductors is L and the capacitance of the capacitor is 2×C, the resonance frequency of the series resonance circuits with respect to common-mode signal components is f T 32 1/(2π×(LC) 1/2 ). The common-mode signal components in this frequency band are shorted to the ground plane. 
     If in the phase-shifting circuit  5703  the capacitance of the capacitors is increased, the impedance with respect to differential-mode signal components is reduced and the differential-mode signal components are shorted. A filter loss results in such a case. The passing characteristic of the filter when the impedance of the capacitors  5704  and  5705  was changed was evaluated.  FIG. 43(   a ) shows the value of loss with respect to a normalized impedance, obtained by dividing the impedance of the capacitors  5702  and  5703  in the reception frequency band by the characteristic impedance at the terminal. In this embodiment, the characteristic impedance of the balanced output terminals is 50Ω. Therefore the characteristic impedance of each terminal is 25Ω. As shown in  FIG. 43(   a ), the loss is exacerbated in a region where the normalized impedance is lower than 3. The characteristics shown in  FIGS. 40 and 41  are characteristics when the normalized impedance is 6.8. 
     If in the phase-shifting circuit  6001  the inductance of the inductors is decreased, the impedance with respect to differential-mode signal components is reduced and the differential-mode signal components are shorted. A filter loss results in such a case. The passing characteristic of the filter when the impedance of the inductors  6002  and  6003  was changed was evaluated.  FIG. 43(   b ) shows the value of loss with respect to a normalized impedance, obtained by dividing the impedance of the inductors  6002  and  6003  in the reception frequency band by the characteristic impedance at the terminal. In this embodiment, the characteristic impedance of the balanced output terminals is 50Ω. Therefore the characteristic impedance of each terminal is 25Ω. As shown in  FIG. 43(   b ), the loss is exacerbated in a region where the normalized impedance is lower than 3. 
     From the above, it is preferable to set the normalized impedance in the pass band to 3 or higher. 
     While this embodiment has been described by way of example with respect to a case where the balanced high-frequency element constituting the balanced high-frequency filter is a surface acoustic filter, this arrangement is not exclusively used. According to the present invention, the same effect can also be obtained by using any balanced high-frequency element if common-mode signal components in a transmission frequency band output from a balanced high-frequency element are reduced by a phase-shifting circuit, and if the balanced high-frequency element has balanced terminals. For example, the balanced high-frequency element may be a filter using an FBAR. 
     The phase-shifting circuit in this embodiment may also include a matching circuit with respect to differential-mode signal components. 
     Also, the phase-shifting circuit in this embodiment may be applied to an arrangement such as shown in  FIG. 38 . Also in such a case, the same effect of reducing common-mode signal components to improve the characteristics of a low-noise amplifier or a mixer is obtained and a communication apparatus having improved sensitivity can be implemented. 
     The first frequency band of the present invention corresponds to the reception frequency band in this embodiment, and the second frequency band of the present invention corresponds to the transmission frequency band in this embodiment. Also, in this embodiment, the first frequency band is a pass band, while the second frequency band is an attenuation band. 
     (Embodiment 14) 
     The configuration of an antenna duplexer is described below with reference to the drawings. 
       FIG. 44  is a diagram showing the configuration of an antenna duplexer in embodiment 14 of the present invention. Referring to  FIG. 44 , the antenna duplexer  6201  is constituted by a transmitting filter  6202 , a receiving filter  6203  and a phase-shifting circuit  6204 . The receiving filter  6203  has balanced terminals on the output side. The phase-shifting circuit  6204  is connected between the balanced terminals. The phase-shifting circuit  6204  has the same configuration as that shown in  FIG. 33 . The phase-shifting circuit  6204  is constituted by a transmission line  5104  and placed between the output terminals. The length of the transmission line  5104  is λ T /2 (λ T  is the wavelength at a frequency in a transmission frequency band). 
     The antenna duplexer of the present invention arranged as described above is capable of reducing the amount of leakage of common-mode signal components in a transmission frequency band from the receiving filter  6203 . 
     While this embodiment has been described with respect to a case where one transmission line is provided as a phase-shifting circuit, a combination of a plurality of transmission lines may be used. 
     A phase-shifting circuit  5703  having the same configuration as that shown in  FIG. 39  may be used as the phase-shifting circuit  6204 , as shown in  FIG. 45 . Also in such a case, the amount of leakage of common-mode signal components in a transmission frequency band from the receiving filter  6203  can be reduced by setting within the transmission frequency band the resonance frequency of the series resonance circuits formed in the phase-shifting circuit  5703 . The phase-shifting circuit  6001  shown in  FIG. 42  may also be used as the phase-shifting circuit  6204 . In a case where the phase-shifting circuit is formed by using impedance elements as in the phase-shifting circuit  6001 , it is preferable to set the normalized impedance to the virtual ground plane with respect to differential-mode signal components to 3 or higher. 
     In this embodiment, the configurations of the transmitting filter  6202  and the receiving filter  6203  are not particularly specified. A surface acoustic wave filter or an FBAR may be used for these filters. 
     The phase-shifting circuit in this embodiment may include a matching circuit with respect to differential-mode signal components. 
     The first frequency band of the present invention corresponds to the reception frequency band in this embodiment, and the second frequency band of the present invention corresponds to the transmission frequency band in this embodiment. Also, in this embodiment, the first frequency band is a desired frequency band, while the second frequency band is the frequency band of interference waves. 
     If the antenna duplexer is connected to a low-noise amplifier, saturation and distortion in the low-noise amplifier due to common-mode signal components in a transmission frequency band can be limited and a communication apparatus having higher sensitivity can be implemented. 
     (Embodiment 15) 
     The configuration of a balanced high-frequency circuit of the present invention is described below with reference to the drawings. 
       FIG. 46  is a diagram showing the configuration of a balanced high-frequency circuit in embodiment 15 of the present invention. Referring to  FIG. 46 , the balanced high-frequency circuit  6401  is constituted by a low-noise amplifier  6402 , a mixer  6403  and a phase-shifting circuit  6404 . The low-noise amplifier  6402  has balanced terminals on the output side. The mixer  6403  connected to the low-noise amplifier  6402  has balanced terminals on the input side. The phase-shifting circuit  6404  is connected between these balanced terminals. The phase-shifting circuit  6404  has the same configuration as that shown in  FIG. 33 . The phase-shifting circuit  6404  is constituted by a transmission line  5104  and placed between the output terminals. The length of the transmission line  5104  is λ T /2 (λ T  is the wavelength at a frequency in a transmission frequency band). 
     The balanced high-frequency circuit of the present invention arranged as described above is capable of reducing the amount of leakage of common-mode signal components in a transmission frequency band from the low-noise amplifier  6402  and limiting saturation of common-mode signal components in the transmission frequency band in the mixer  6403 , and a communication apparatus having higher sensitivity can be implemented. 
     While this embodiment has been described with respect to a case where one transmission line is provided as a phase-shifting circuit, a combination of a plurality of transmission lines may be used. 
     A phase-shifting circuit  5703  having the same configuration as that shown in  FIG. 39  may be used as the phase-shifting circuit  6402 , as shown in  FIG. 46(   b ). Also in such a case, the amount of leakage of common-mode signal components in a transmission frequency band from the low-noise amplifier  6402  can be reduced by setting within the transmission frequency band the resonance frequency of the series resonance circuits formed in the phase-shifting circuit  5703 . The phase-shifting circuit  6001  shown in  FIG. 42  may also be used as the phase-shifting circuit  6402 . In a case where the phase-shifting circuit is formed by using impedance elements as in the phase-shifting circuit  6001 , it is preferable to set the normalized impedance to the virtual ground plane with respect to differential-mode signal components to 3 or higher. 
     The phase-shifting circuit in this embodiment may include a matching circuit for matching with the low-noise amplifier and the mixer with respect to differential-mode signal components. 
     The first frequency band of the present invention corresponds to the reception frequency band in this embodiment, and the second frequency band of the present invention corresponds to the transmission frequency band in this embodiment. Also, in this embodiment, the first frequency band is a desired frequency band, while the second frequency band is the frequency band of interference waves. 
     (Embodiment 16) 
     The configuration of a balanced high-frequency circuit of the present invention is described below with reference to the drawings. 
       FIG. 47  is a diagram showing the configuration of a balanced high-frequency circuit in embodiment 16 of the present invention. Referring to  FIG. 47 , the balanced high-frequency circuit  6501  is constituted by a transmitting amplifier  6503 , a transmitting filter  6504 , a switch  6505 , a receiving filter  6506 , a low-noise amplifier  6507 , a mixer  6508  and a phase-shifting circuit  6509 , implemented on a circuit board  6502 . A signal output from the transmitting circuit to be transmitted is output to an antenna terminal ANT via the transmitting amplifier  6502 , the transmitting filter  6503  and the switch  6504 . The balanced high-frequency circuit  6501  thus arranged is used mainly for a communication device in a time division transmitting and receiving system. A received signal input through the antenna terminal ANT is input to the receiving circuit via the switch  6504 , the receiving filter  6506 , the receiving amplifier  6507  and the mixer  6508 . The receiving amplifier  6507  is of a balanced type while the switch  6504  is of an unbalanced type. Therefore the receiving filter  6506  is arranged to have unbalanced-balanced input/output terminals. The phase-shifting circuit  6509  has the same configuration as that shown in  FIG. 33 . The phase-shifting circuit  6509  is constituted by a transmission line  5104  and placed between the output terminals. The length of the transmission line  5104  is λ T /2 (λ T  is the wavelength at a frequency in a transmission frequency band). 
     The balanced high-frequency circuit of the present invention arranged as described above is capable of reducing the amount of leakage of common-mode signal components in a transmission frequency band from the low-noise amplifier  6402  and limiting saturation of common-mode signal components in the transmission frequency band in the low-noise amplifier  6507 . 
     While this embodiment has been described with respect to a case where one transmission line is provided as a phase-shifting circuit, a combination of a plurality of transmission lines may be used. 
     A phase-shifting circuit  5703  having the same configuration as that shown in  FIG. 39  may be used as the phase-shifting circuit  6509 . Also in such a case, the amount of leakage of common-mode signal components in a transmission frequency band from the low-noise amplifier  6502  can be reduced by setting within the transmission frequency band the resonance frequency of the series resonance circuits formed in the phase-shifting circuit  5703 . The phase-shifting circuit  6001  shown in  FIG. 42  may also be used as the phase-shifting circuit  6509 . In a case where the phase-shifting circuit is formed by using impedance elements as in the phase-shifting circuit  6001 , it is preferable to set the normalized impedance to the virtual ground plane with respect to differential-mode signal components to 3 or higher. 
     While the phase-shifting circuit is placed on the input side of the low-noise amplifier  6506  in this embodiment, it may alternatively be placed between the low-noise amplifier  6506  and the mixer  6507  to further reduce the amount of leakage of common-mode signal components in the transmission frequency band and limit saturation of the mixer. 
     The phase-shifting circuit in this embodiment may include a matching circuit with respect to differential-mode signal components. 
     While the balanced high-frequency circuit  6501  using the switch  6505  as a means of switching between transmission and reception has been described, a balanced high-frequency circuit  6601  using an antenna duplexer  6602  as shown in  FIG. 48  may be provided. The balanced high-frequency circuit  6601  using the antenna duplexer  6602  constituted by a transmitting filter  6603  and a receiving filter  6604  is used mainly for a communication apparatus in a system capable of simultaneously performing transmitting and receiving. 
     While the phase-shifting circuit of the present invention is formed on the circuit board for the balanced high-frequency circuit, it may alternatively be incorporated in the receiving filter  6506 , the low-noise amplifier  6507 , the mixer  6508  or the antenna duplexer  6602 . 
     The configurations of the transmitting filter  6504  and the receiving filter  6506  and the configurations of the transmitting filter  6603  and the receiving filter  6604  constituting the antenna duplexer  6602  are not particularly specified. A surface acoustic wave filter or an FBAR may be used for each of these filters. 
     The phase-shifting circuit in this embodiment may include a matching circuit with respect to differential-mode signal components. 
     The first frequency band of the present invention corresponds to the reception frequency band in this embodiment, and the second frequency band of the present invention corresponds to the transmission frequency band in this embodiment. Also, in this embodiment, the first frequency band is a desired frequency band, while the second frequency band is the frequency band of interference waves. 
     In this embodiment, if the balanced high-frequency circuit is applied to a communication apparatus, the communication apparatus can be implemented so as to be capable of suppressing transmission interference waves due to common-mode signal components and have higher sensitivity. 
     While in this embodiment the length of the transmission line provided as a phase-shifting circuit is λ T /2 (λ T  is the wavelength at a frequency in a transmission frequency band), a setting of a resonance frequency in a transmission frequency band may suffice and a slight error in setting the length of the transmission line may be tolerated. 
     Each of the balanced high-frequency filter, the antenna duplexer and the balanced high-frequency circuit in accordance with the present invention is useful as a high-frequency device capable of reducing common-mode signal components, and can be applied to use in a high-frequency module or a communication device. 
     According to the present invention, a balanced high-frequency filter and an antenna duplexer in which common-mode signal components in a transmission frequency band are reduced can be implemented. Also, a balanced high-frequency circuit and a communication apparatus using such a balanced high-frequency filter or antenna duplexer can be provided. A balanced high-frequency circuit in which common-mode signal components in a transmission frequency band are reduced can be provided.