Abstract:
The present invention has for its object to provide a matching circuit with multiband capability which can be reduced in size, even if the number of handled frequency bands rises. The matching circuit of the present invention comprises a load having frequency-dependent characteristics, a first matching block connected with one end to the load with frequency-dependent characteristics, and a second matching block formed by lumped elements connected in series to the first matching block. And then, when a certain frequency band is used, matching is obtained with the series impedance of the first matching block and the second matching block. When a separate frequency band is used, a π-type circuit is constituted by connecting auxiliary matching blocks to both sides of the second matching block. Next, at the same frequency, by taking the combined impedance of this π-type circuit and a load whose characteristics do not depend on the frequency to be Z 0 , the influence of the second matching block is removed.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional and claims the benefit of priority under 35 U.S.C. § 120 from U.S. application Ser. No. 11/434,889, filed May 17, 2006, the entire content of which is incorporated herein by reference, and claims the benefit of priority under 35 U.S.C. § 119 os Japanese Patent Application No. 2005-148621, filed May 20, 2005. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention pertains to a matching circuit handling multiple bands which, in a plurality of frequency bands, establishes matching between circuits having different impedances. It pertains to matching circuits built into small-sized multiband power amplifiers which amplify, with high efficiency, signals in a plurality of frequency bands used e.g. in mobile communications and satellite communications. 
         [0004]    2. Description of Related Art 
         [0005]    Accompanying the diversification of services offered by means of radio communications, conversion to multiband capability for processing signals in a plurality of frequency bands is required of radio equipment. As an indispensable device included in radio equipment, there is the power amplifier. In order to carry out efficient amplification, there is a need to obtain impedance matching between the amplification element and its peripheral circuits, so a matching circuit is used. As an example of a conventional multiband power amplifier, technology as shown in Reference 1 (NTT DoCoMo Technical Journal, Vol. 10, No. 1: “Mobile Handsets”) is disclosed. 
         [0006]    The configuration of the 800 MHz/2 GHz band power amplifier shown in Reference 1 is shown in  FIG. 1 , and the operation thereof will be explained. The transmitted signal coming from the transmitter is input into the single pole terminal of an input switch  150 , a Single Pole Double Throw (SPDT) switch. Next, the transmitted signal, by being switched by input switch  150 , is input into an 800 MHz band amplifier  151  connected to a double throw terminal of input switch  150 , or a 2 GHz band amplifier  152 . The output signals of 800 MHz band amplifier  151  and 2 GHz band amplifier  152  are switched by an output switch  153 , a Single Pole Double Throw switch, and supplied to an antenna. 
         [0007]    In  FIG. 2 , the configuration of 800 MHz band amplifier  151  and 2 GHz band amplifier  152  is shown. Each amplifier is configured with a series connection of an input matching circuit  160 , an amplification element  161 , and an output matching circuit  162 . Input matching circuit  160  obtains matching between a signal source  163 , whose output impedance does not depend on the frequency, and amplification element  161 . Output matching circuit  162  obtains matching between the output impedance of amplification element  161  and a load  164 . 
         [0008]    Since the input impedance of amplification element  161  constituting each amplifier varies with frequency, input matching circuit  160  and output matching circuit  162  are different depending on the operation frequencies, even if the same amplification element  161  is used. Accordingly, as shown in  FIG. 1 , separate amplifiers  151 ,  152  handling each frequency band have been necessary. Consequently, there has been the problem that the total circuit area of the transmitter became larger as the operating frequency bands rose. 
         [0009]    In order not to increase the circuit area of an amplifier, the method of designing matching circuits for wideband operation can also be considered. However, compared to matching circuits designed for narrowband operation, the result is that there occurs a reduction in gain and efficiency. Accordingly, with respect to these problems, the applicant of the present application first proposed, in Reference 2 (International Publication No. WO 2004/082138 Pamphlet), a matching circuit which can handle the conversion to multiband capability. The input matching circuit of the amplifier disclosed in Reference 2 is shown in  FIG. 3 . E.g., the FET (Field Effect Transistor) input impedance can be expressed as a load  170  (impedance Z L (f)) having frequency-dependent characteristics. A first terminal P 1  to which this load  170  is connected has a main matching block  171  connected to it. The other end (point A) of main matching block  171  is connected to one end of a delay circuit  172  having a certain reactance value. The other end (point B) of delay circuit  172  is connected to a signal source  173  having an impedance Z 0  (below, the impedance not changing with frequency is called Z 0 ). 
         [0010]    Main matching block  171  is designed to match the impedance Z L (f 1 ) of load  170  with the impedance Z 0  of signal source  173 , in frequency band f 1 . In other words, main matching block  171  becomes a matching circuit with respect to frequency f 1 . Delay circuit  172  is constituted by a distributed-parameter element, the characteristic impedance of which is given, as is well known, by the relationship shown in Eq. 1. 
         [0000]        Z 0=√{square root over ( L/C )}  (1) 
         [0011]    Here, L is the inductance of the distributed-parameter element and C is the capacitance of the distributed-parameter element. Consequently, by taking the characteristic impedance of delay circuit  172  to be Z 0 , matching is obtained in frequency band f 1  between signal source  173  and load  170 . 
         [0012]    When operating in a frequency band f 2 , different from frequency band f 1  (e.g. when frequency band f 2  is lower than frequency band f 1 ), the impedance of load  170  changes to Z L (f 2 ). Also, since main matching block  171  is a matching circuit with respect to frequency f 1 , matching between signal source  173  and load  170  is not obtained at frequency f 2 . Accordingly, an auxiliary matching block  175  is connected via switch element  174  to point B. And then, when operating in frequency band f 2 , switch element  174  is taken to be in a conducting state. By choosing a configuration like this, it is possible, whichever is the value of the impedance estimated from point A toward the side of load  170 , to make the impedance Z 0 , seen from point B toward the side of delay circuit  172 . Here, the delay value of delay circuit  172  is set to the delay value required to match at point B in frequency band f 2 . 
         [0013]    With the same approach as for the matching circuit shown in  FIG. 3 , an example where the number of frequency bands which can be handled has been increased to three is shown in  FIG. 4 . By the fact that the number of frequency bands has increased from two to three, the system increases by one additional set, the set of delay circuit  180 , switch element  181 , and auxiliary matching block  182 . In a third frequency band f 3 , the impedance Z L (f 3 ) of load  170  is regulated by means of delay circuit  180  and auxiliary matching block  182  so that the impedance seen from point C toward the side of delay circuit  180  becomes Z 0 . Further, since the characteristic impedances of the delay circuits are fixed and do not depend on the frequency, it is possible to obtain matching between signal source  173  and load  170  in each frequency band if switch element  174  and switch element  181  are chosen to be in a non-conducting state in the case of frequency band f 1 , switch element  174  is chosen to be in a conducting state for in the case of frequency band f 2 , and switch element  181  is chosen to be in a conducting state in the case of frequency band f 3 . 
         [0014]    In this way, by providing auxiliary matching blocks connected via switch elements between the delay circuits along with connecting in series in multiple stages delay circuits whose impedances do not vary with frequency, there is implemented a matching circuit capable of matching with respect to a plurality of frequency bands. Further, the delay value required in frequency band f 3  can be considered to be the sum of the values for delay circuit  172  and delay circuit  180 . 
         [0015]    As for delay circuits  172  and  180 , it is realistic to choose them to be transmission lines which are distributed parameter networks. However, particularly in cases where the frequency is low, transmission lines become comparatively large components inside the circuit. E.g., if load  170  is taken to be a FET and in case an amplifier for the 1 GHz band is designed, a 50□ transmission line has a width of 0.63 mm and a length of 9.22 mm, so the result is a component having a length of about 10 mm. 
         [0016]    In the technology shown in the aforementioned Reference 2, the delay circuits are realistically constituted by transmission lines. However, in the case of transmission lines, the length easily becomes comparatively long. In particular, in the case where the used frequency is low, the area of a transmission line serving as a delay circuit becomes large, so there has been the problem that the matching circuit as a whole also was made bigger. Further, this problem increases as the frequency becomes lower, and as the number of frequencies rises. 
       BRIEF SUMMARY OF THE INVENTION 
       [0017]    The matching circuit of the present invention has a first matching block, connected at one end to a load having an impedance with frequency-dependent characteristics and a second matching block formed by a lumped-parameter element connected in series to the first matching block. E.g., the second matching block matches the impedances of the signal source and the load in the lowest frequency band. Moreover, for the purpose of impedance matching in high frequency bands, it has a □-type circuit. A □-type circuit is a circuit in which respective switch elements and auxiliary matching blocks are connected to both ends of the second matching block. 
         [0018]    According to a configuration like this, the matching conditions in the aforementioned low frequency band can be created by a series connection of the first matching block and the second matching block. Further, in the case of a high frequency band, by setting an appropriate value for the □-type circuit, it is possible to choose the impedance of the □-type circuit to be Z 0  and to choose the impedance of the second matching block to be one with no influence for the high frequency band. Moreover, since the second matching block is constituted by lumped elements, it is possible to make the matching circuit smaller-sized than the conventional matching circuit constituted by transmission lines. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a diagram showing the configuration of a conventional 800 MHz/2 GHz band power amplifier 
           [0020]      FIG. 2  is a diagram showing the configuration of each power amplifier in  FIG. 1 . 
           [0021]      FIG. 3  is a diagram showing a conventional matching circuit. 
           [0022]      FIG. 4  is a diagram showing an example where the number of frequency bands which can be handled by the conventional matching circuit has been taken to be three. 
           [0023]      FIG. 5  is a diagram showing the base configuration of a matching circuit of this invention. 
           [0024]      FIG. 6A  is a diagram explaining the operation in a low frequency band f 2 . 
           [0025]      FIG. 6B  is a diagram explaining the operation in a high frequency band f 1 . 
           [0026]      FIG. 7  is a diagram showing the configuration where the □-type circuit of a matching circuit of this invention, shown in  FIG. 5 , has been replaced with a T-type circuit. 
           [0027]      FIG. 8  is a diagram where the matching circuit of the present invention, shown in  FIG. 5 , has been generalized so that it can be adapted to a plurality of frequency bands. 
           [0028]      FIG. 9  is a diagram showing the image of N frequency bands. 
           [0029]      FIG. 10  is a diagram showing an embodiment of a matching circuit using two T-type circuits. 
           [0030]      FIG. 11  is a diagram where a matching circuit of the present invention, using T-type matching circuits, has been generalized so that it can be adapted to a plurality of frequency bands. 
           [0031]      FIG. 12  is a diagram showing another configuration example of a matching circuit of the present invention using T-type matching circuits. 
           [0032]      FIG. 13  is a diagram showing a configuration example of a matching circuit of the present invention, using T-type matching circuits where auxiliary matching blocks have been connected in series. 
           [0033]      FIG. 14  is a diagram showing an example where the second matching block of  FIG. 5  is configured with an L-type circuit. 
           [0034]      FIG. 15  is a diagram showing the configuration of the second matching block using a T-type circuit. 
           [0035]      FIG. 16  is a diagram showing another configuration of the second matching block using a T-type circuit. 
           [0036]      FIG. 17  is a diagram showing an example where the first matching block has been configured with a plurality of elements. 
           [0037]      FIG. 18  is a diagram showing an example where a matching circuit of this invention has been applied to an amplification circuit. 
           [0038]      FIG. 19A  is a diagram showing the simulation results in the case of a setting for the 2 GHz band, with the configuration of  FIG. 18 . 
           [0039]      FIG. 19B  is a diagram showing the simulation results in the case of a setting for the 1 GHz band, with the configuration of  FIG. 18 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiment 1 
       [0040]    In  FIG. 5 , the basic configuration of a matching circuit of the present invention is shown. The matching circuit of the present invention is constituted by a first matching block  2  and a matching circuit part  8  consisting of lumped elements. Matching circuit part  8  is a □-type circuit constituted by a second matching block  3 , switch elements  4  and  5 , and auxiliary matching blocks  6  and  7 . One end of first matching block  2  is connected to a first terminal P 1  to which an element  1  (a load in this example) having an impedance Z L (f) with frequency-dependent characteristics is connected. To the other end of first matching block  2 , one end of second matching block  3  is connected in series. The other end of second matching block  3  is connected, via a second terminal P 2 , to an element  9 , e.g. a signal source, with an impedance Z 0  whose impedance does not depend on the frequency. Also, to the terminal on the first matching block  2  side of second matching block  3 , there is connected a series circuit of switch element  4  and auxiliary matching block  6 . To the other end of second matching block  3 , there is connected a series circuit of switch element  5  and auxiliary matching block  7 . By being connected in this way, matching circuit part  8  becomes a □-type circuit. 
         [0041]    The operation of the matching circuit in  FIG. 5  will be explained using  FIG. 6A  and  FIG. 6B .  FIG. 6A  is a diagram showing the operation in a low frequency band f 2 .  FIG. 6B  is a diagram showing the operation in a high frequency band f 1 . In the case of frequency band f 2 , switch elements  4  and  5  of  FIG. 5  are non-conducting. Consequently, in the case of frequency band f 2 , impedance Z 2  of the second matching block is set so that the sum Z A  of impedance Z L (f 2 ) of element  1  in the frequency band f 2 , impedance Z 1  of first matching block  2 , and impedance Z 2  of second matching block  3  (below, the impedances will be omitted in portions where the same can be considered not to be particularly necessary) becomes Z 0 . As a result, the impedances are matched at second terminal P 2 . 
         [0042]    In the frequency band f 1 , switch elements  4  and  5  in  FIG. 5  are in a conducting state. Consequently, as shown in  FIG. 6B , matching circuit  8  becomes a □-type circuit in which auxiliary matching blocks  6  and  7  are respectively connected to both ends of second matching block  3 . Here, since first matching block  2  is a matching circuit for the frequency band f 1 , impedance matching is obtained with impedance Z 0  of element  9  at point A at frequency f 1 . Accordingly, by making a design so that, in the frequency band f 1 , the combined impedance Z□ seen from point A toward the second terminal P 2  side becomes identical to Z 0  (Z 0 =Z□, it is possible to remove the influence of the impedance of second matching block  3  in the frequency band f 1 . Specifically, if the impedance of auxiliary matching block  6  is taken to be Z 3  and the impedance of auxiliary matching block  7  is taken to be Z 4 , Z 3  and Z 4  may be designed so that the condition shown in Eq. 2 is met. 
         [0000]        Z □=( Z 0 Z 2 Z 3 +Z 4 Z 2 Z 3 +Z 0 Z 4 Z 3)/( Z 0 Z 4 +Z 0 Z 2 +Z 0 Z 3 +Z 4 Z 2 +Z 1 Z 3)  (2) 
         [0043]    As was stated above, in the frequency band f 1 , it is first matching block  2  which operates to match impedance Z L (f 1 ) of element  1  to impedance Z 0  of element  9 . Also, it is second matching block  3  which operates to match the impedance Z L (f 2 ) of element  1 , changed by the modification of the frequency band from f 1  to f 2 , to the impedance Z 0  of element  9 . Further, it is auxiliary matching blocks  6  and  7  which operate to remove the influence of second matching block  3  which is a hindrance in frequency band f 1 . 
         [0044]    Matching circuit part  8  in  FIG. 5  can also be configured with a T-type circuit. An example where the matching circuit part has been configured with a T-type circuit is shown in  FIG. 7 . In  FIG. 7 , second matching block  3  in  FIG. 5  is replaced by a second matching block  31  and a series second matching block  32 . One end of second matching block  31  is connected to point A. The other end of second matching block  31  is connected to one end of series second matching block  32 . The other end of series second matching block  32  is connected to second terminal P 2 . To the connection point of second matching block  31  and series second matching block  32 , there is connected an auxiliary matching block  34  via a switching element  33 . 
         [0045]    The relationship between  FIG. 5  and  FIG. 7  cannot be converted with the well known Y-□ conversion (T-□ conversion) relationship. In order to adopt a matching circuit equivalent to that of  FIG. 5 , first, the value of the impedance of second matching block  3  must be Z 2  as a condition in frequency band f 2 . Consequently, if the impedance of second matching block  31  is taken to be Za and the impedance of series second matching block  32  is taken to be Zb, the relationship Z 2 =Za+Zb must be satisfied. In order to choose a T-type circuit which is equivalent to a □-type circuit, the impedance value of auxiliary matching block  34  may be designed by adding this condition. Of course, it goes without saying that matching block part  8  may be designed with a T-type circuit from the beginning. In this way, it is possible for matching circuit part  8  to have a configuration which is not limited to a □-type circuit but can also be a T-type circuit. 
       Embodiment 2 
       [0046]      FIG. 8  is an example where the basic structure of this invention, shown in  FIG. 5 , has been generalized so that it can be adapted to a plurality of frequency bands. This matching circuit is composed of first matching block  2 , L-type blocks  43   a  to  43   n , and shunt circuit blocks  46   a  to  46   n . Each L-type block  43   i  (i=a to n) is composed of a second matching block  40   i , a first switch element  41   i , and a first auxiliary matching block  42   i . One terminal of second matching block  40   a  is connected to first matching block  2 . Also, the other end of second matching block  40   a  is connected to one terminal of second matching block  40   b . In this way, each second matching block  40   i  is connected in series. First auxiliary matching block  42   i  is connected, via first switch element  41   i , to the terminal of second matching block  40   i  on the side of first terminal P 1 . In other words, an L-type circuit is formed by means of second matching block  40   i , first switch element  41   i , and first auxiliary matching block  42   i.    
         [0047]    To the second terminal P 2  side of L-type block  43   n , there are connected in parallel shunt circuit blocks  46   a  to  46   n . Each shunt circuit block  46   i  (i=a to n) is composed of a second switch element  44   i  connected in series and a second auxiliary matching block  45   i.    
         [0048]    Below, an explanation will be given on the operation and design method of a matching circuit in which three L-type blocks  43   a  to  43   c  and three shunt circuit blocks  46   a  to  46   c  are connected. 
         [0049]    First, an explanation will be given for the case of frequency band f 4 . In the case of frequency band f 4 , first switch elements  41   a  to  41   c  and second switch elements  44   a  to  44   c  are all in a non-conducting state. Element  1  (impedance Z L (f 4 )) is connected, via three second matching blocks  40   a  to  40   c  connected in series, to element  9  (impedance Z 0 ). Here, the impedance Z L (f) of element  1  changes with frequency. Also, element  9  is a signal source or the like, the impedance of which does not depend on the frequency. Here, second matching block  40   c  is designed so that the combined impedance of element  1 , first matching block  2 , and second matching blocks  40   a  and  40   b  is converted to Z 0 . If second matching block  40   c  is designed in this way, the impedance Z 0  is matched at the second terminal P 2  side end of second matching block  40   c.    
         [0050]    In the case of frequency band f 3 , switch element  41   c  of L-type block  43   c  and second switch element  44   a  of shunt circuit block  46   a  are chosen to be in a conducting state. In this case, since first auxiliary matching block  42   c  and second auxiliary matching block  45   a  are connected to both ends of second matching block  40   c , a □-type circuit is configured. Here, second matching block  40   b  is designed so that the combined impedance due to element  1  (impedance Z L (f 3 )), first matching block  2 , and second matching block  40   a  is matched to Z 0 . If second matching block  40   b  is designed in this way, the impedance seen from the second terminal P 2  side of second matching block  40   b  (the first terminal P 1  side of second matching block  40   c ) toward element  1  becomes Z 0 . Also, first auxiliary matching block  42   c  and second auxiliary matching block  45   a  are designed so that Eq. 2 is satisfied at frequency f 3 . By designing in that way, the impedance seen from the first terminal P 1  side of second matching block  40   c  (the second terminal P 2  side of second matching block  40   b ) toward element  9  also becomes Z 0 . In other words, it is possible to remove the influence of the impedance of second matching block  40   c , so the impedances are matched. 
         [0051]    In the case of frequency band f 2 , switch element  41   b  of L-type block  43   b  and second switch element  44   b  of shunt circuit block  46   b  are chosen to be in a conducting state. In this case, since first auxiliary matching block  42   b  and second auxiliary matching block  45   b  are connected to both ends, connected in series, of second matching block  40   c  and second matching block  40   b , a □-type circuit is configured. Second matching block  40   a  is designed so that the combined impedance due to element  1  (impedance Z L (f 2 )) and first matching block  2  is matched to Z 0 . If second matching block  40   a  is designed in this way, the impedance seen from the second terminal P 2  side of second matching block  40   a  (the first terminal P 1  side of second matching block  40   b ) toward element  1  becomes Z 0 . Also, first auxiliary matching block  42   b  and second auxiliary matching block  45   b  are designed so that Eq. 2 is satisfied at frequency f 2 . By designing in that way, the impedance seen from the first terminal P 1  side of second matching block  40   b  (the second terminal P 2  side of second matching block  40   a ) toward element  9  also becomes Z 0 . In other words, it is possible to remove the influence of second matching blocks  40   b  and  40   c , so the impedances are matched. 
         [0052]    In the case of frequency band f 1 , switch element  41   a  of L-type block  43   a  and second switch element  44   c  of shunt circuit block  46   c  are in a conducting state. In this case, since first auxiliary matching block  42   a  and second auxiliary matching block  45   c  are connected to both ends of second matching blocks  40   c  to  40   a , a □-type circuit is configured. First matching block  2  is designed so that impedance Z L (f 1 ) of element  1  is matched to Z 0 . If first matching block  2  is designed in this way, the impedance seen from the second terminal P 2  side of first matching block  2  (the first terminal P 1  side of second matching block  40   a ) toward element  1  becomes Z 0 . Also, first auxiliary matching block  42   a  and second auxiliary matching block  45   c  are designed so that Eq. 2 is satisfied at frequency f 1 . By designing in that way, the impedance seen from the first terminal P 1  side of second matching block  40   a  (the second terminal P 2  side of first matching block  2 ) toward element  9  also becomes Z 0 . In other words, it is possible to remove the influence of the impedances of second matching blocks  40   a  to  40   c , so the impedances are matched. 
         [0053]    As stated above, it is possible to combine three L-type blocks and shunt circuits to match the impedances at four frequencies. If this is generalized, the result is that it is possible, with a combination of N L-type blocks and shunt circuits, to match the impedances in N+1 frequency bands. 
         [0054]      FIG. 9  expresses the image of N frequency bands. The abscissa axis of  FIG. 9  is the frequency and the ordinate axis is the power of transmission. In this diagram, a relation that the frequency becomes lower as N increases is shown as an example. 
         [0055]    Further, in  FIG. 8 , the frequencies are arranged in the order corresponding to shunt circuit blocks  46   a  to  46   n . However, as long as a one-to-one relationship with first auxiliary matching blocks  42   a  to  42   n  is satisfied, the order of arranging shunt circuit blocks  46   a  to  46   n  is indifferent. 
         [0056]    Also, the second matching block is configured with lumped elements connected in series between the conductively connected first switch element and second switch element. Consequently, even if the number of second matching blocks becomes large, it is possible to make the whole circuit remarkably small, compared to the case of a configuration with transmission lines. 
       Embodiment 3 
       [0057]    A matching circuit generalized by using □-type circuits was explained in  FIG. 8 , but it is also possible to configure a generalized matching circuit using T-type circuits. In  FIG. 10 , there is shown an embodiment of a matching circuit using two T-type circuits. This matching circuit is composed of first matching block  2 , an L-type block part  63   a , an L-type block part  63   b , and a second matching block  60   c . One end of first matching block  2  is connected to a first terminal P 1  at which it is connected to element  1 . Also, the other end of first matching block  2  is connected to one end of a second matching block  60   a  inside L-type block part  63   a . To the other end of second matching block  60   a , there is connected an auxiliary matching block  62   a  via a first switch element  61   a . Moreover, the other end of second matching block  60   a  is also connected to one end of a second matching block  60   b  inside L-type block part  63   b . To the other end of second matching block  60   b , an auxiliary matching block  62   b  is connected via a second switch element  61   b . In addition, the other end of second matching block  60   b  is also connected to one end of second matching block  60   c . Here, L-type block part  63   a  is composed of second matching block  60   a , first switch element  61   a , and auxiliary matching block  62   a . Also, L-type block part  63   b  is composed of second matching block  60   b , second switch element  61   b , and auxiliary matching block  62   b . Also, T-type matching circuits  64  and  65  are composed of two L-type block parts  63   a  and  63   b  and one second matching block  60   c . T-type matching circuit  64  is composed of second matching blocks  60   a  and  60   b , first switch element  61   a , and auxiliary block  62   a . Also, T-type matching circuit  65  is composed of second matching blocks  60   c  and  60   b , second switch element  61   b , and auxiliary matching block  62   b . In this way, a matching circuit which matches impedances in three frequency bands is configured in two stages with T-type matching circuits  64  and  65 . 
         [0058]    In the case of frequency band f 3 , switch elements  61   a  and  61   b  are chosen to be in a non-conducting state. The impedance of element  1  changes with the frequency band. Element  1  with an impedance Z L (f 3 ) is connected, via the serially connected first matching block  2  and second matching blocks  60   a ,  60   b , and  60   c , to element  9  which has an impedance of Z 0 . 
         [0059]    Second matching block  60   b  and second matching block  60   c  are designed so that the combined impedance with element  1 , first matching block  2 , and second matching block  60   a  becomes Z 0 . By designing second matching block  60   b  and second matching block  60   c  in this way, it is possible to match the impedances at second terminal P 2  of second matching block  60   c.    
         [0060]    In the case of frequency band f 2 , switch element  61   b  constituting T-type matching circuit  65  is in a conducting state. Second matching block  60   a  is designed so that the combined impedance with element  1 , having an impedance Z L (f 2 ), and first matching block  2  is taken to be Z 0 . By designing second matching block  60   a  in this way, the impedance seen from point D toward element  1  becomes Z 0 . Also, auxiliary matching block  62   b  is designed so that the combined impedance of second matching blocks  60   b  and  60   c , auxiliary matching block  62   b , and element  9  becomes Z 0 . If auxiliary matching block  62   b  is designed in this way, the impedance seen from point D toward the element  9  side becomes Z 0 . Consequently, it is possible to match the impedances at point D. Also, even on the side of second terminal P 2 , the impedance seen toward element  1  is Z 0 . Consequently, the combined impedance of second matching blocks  60   c  and  60   b  and auxiliary matching block  62   b  does not exert any influence on the matching condition. In other words, auxiliary matching block  62   b  removes the influence of second matching blocks  60   c  and  60   b  at frequency f 2 . 
         [0061]    In the case of frequency band f 1 , switch element  61   b  constituting T-type matching circuit  65  is in a non-conducting state, and switch element  61   a  constituting T-type matching circuit  64  is in a conducting state. First matching block  2  is designed so that the combined impedance with impedance Z L (f 1 ) of element  1  becomes Z 0 . By designing first matching block  2  in this way, the impedance seen from point A toward element  1  becomes Z 0 . Next, first auxiliary matching block  62   a  is designed so that the combined impedance of second matching blocks  60   a ,  60   b , and  60   c , auxiliary matching block  62   a , and element  9  becomes Z 0 . By designing first auxiliary matching block  62   a  in this way, the impedance seen from point A toward element  9  becomes Z 0 . Consequently, it is possible to obtain matching of the impedances at point A. Also, on the second terminal P 2  side as well, the impedance seen toward element  1  is Z 0 . Consequently, the combined impedance of second matching blocks  60   a ,  60   b ,  60   c  and auxiliary matching block  62   a  does not exert influence any more on the matching conditions. In other words, auxiliary matching block  62   a  removes the influence of second matching blocks  60   a ,  60   b ,  60   c  at the frequency f 1 . 
         [0062]    With the aforementioned explanation, the case where switch element  61   b  is non-conducting was explained. However, it is not mandatory to take switch element  61   b  to be non-conducting. In case switch element  61   b  is taken to be conducting when the frequency band is f 1 , auxiliary matching block  62   a  may be designed with that assumption. 
         [0063]    In this way, it is possible to configure a matching circuit handling three frequency bands by means of two T-type matching circuits  64  and  65 . 
       Embodiment 4 
       [0064]    An example showing a generalization of the T-type matching circuit explained in Embodiment 3 is shown in  FIG. 11 . The configuration up to the second-stage L-type block  63   b  seen from first matching block  2  is identical to that of  FIG. 10 . On the second terminal P 2  side of second-stage L-type block  63   b , L-type blocks are added. In  FIG. 11 , a total of N L-type blocks  63   a  to  63   n  are connected. To the other end of L-type block  63   n , one end of series second matching block  70  is connected, the other end of series second matching block  70  being connected to second terminal P 2 . N is an integer equal to or greater than 1. The matching circuit shown in  FIG. 11  is a subordinate connection configuration of N T-type matching circuits and is capable of matching in N+1 frequency bands. The operation is the same as in  FIG. 10 . 
       Embodiment 5 
       [0065]    Another T-type matching circuit embodiment is shown in  FIG. 12 . In  FIG. 10 , a T-type circuit was formed using second matching blocks of adjacent L-type blocks.  FIG. 12  is an example in which a plurality of auxiliary matching blocks are connected, via switch elements, between two second matching blocks connected in series. This matching circuit is composed of first matching block  2  and T-type matching circuits  83   a ,  83   b , and  83   c . T-type matching circuit  83   a  is composed of second matching blocks  80   a  and  80   b , a switch element  81   a , and an auxiliary matching block  82   a . One end of second matching block  80   a  is connected to first matching block  2 . The other end of second matching block  80   a  is connected to one end of second matching block  80   b . Also, auxiliary matching block  82   a  is connected, via switch element  81   a , between second matching block  80   a  and second matching block  80   b . By this kind of connection relationship, second matching blocks  80   a  and  80   b , switch element  81   a , and auxiliary matching block  82   a  make up a T-type circuit. T-type matching circuit  83   b  is composed of second matching blocks  80   c  and  80   d , a switching element  81   b , and an auxiliary matching block  82   b . T-type matching circuit  83   c  is composed of second matching blocks  80   c  and  80   d , a second switching element  84 , and an auxiliary matching block  85 . Here, second matching blocks  80   c  and  80   d  are constituent parts of both T-type matching circuit  83   b  and T-type matching circuit  83   c . With this configuration, auxiliary matching block  82   b  is connected, via switch element  81   b , to the connection point of second matching block  80   c  and second matching block  80   d . Moreover, auxiliary matching block  85  is also connected, via second switch element  84 , to the connection point of second matching block  80   c  and second matching block  80   d . One end of second matching block  80   c  is connected to second matching block  80   b . Also, the other end of second matching block  80   d  is connected to the second terminal P 2  to which element  9  is connected. 
         [0066]    As stated above, a T-type matching circuit may be connected in multiple stages between element  1  and element  9 . The present embodiment is capable of matching in three frequency bands by means of three T-type matching circuits. 
         [0067]    In the case of frequency band f 3 , switch elements  81   a  and  81   b  and second switch element  84  are non-conducting. Second matching blocks  80   c  and  80   d  are designed so that the combined impedance with element  1  (impedance Z L (f 3 )), first matching block  2 , and second matching blocks  80   a ,  80   b  is made to match the impedance Z 0  of element  9  in the frequency band f 3 . Consequently, impedance matching can be obtained at second terminal P 2 . 
         [0068]    In the case of frequency band f 2 , it is only switch element  81   b  forming T-type matching circuit  83   b  that is conducting. Second matching blocks  80   a  and  80   b  are designed so that the combined impedance of element  1  (impedance Z L (f 2 )) and first matching block  2  is made to match the impedance Z 0  of element  9  in the frequency band f 2 . Consequently, the impedance seen from the second terminal P 2  side of second matching block  80   b  (the first terminal P 1  side of second matching block  80   c ) toward element  1  becomes Z 0 . Also, auxiliary matching block  82   b  is designed so that the combined impedance of second matching blocks  80   c  and  80   d , auxiliary matching block  82   b , and element  9  becomes Z 0  at the frequency f 2 . By designing auxiliary matching block  82   b  in this way, the impedance seen from the first terminal P 1  side of second matching block  80   c  (the second terminal P 2  side of second matching block  80   b ) toward element  9  becomes Z 0  at the frequency f 2 . Consequently, the impedances are matched. 
         [0069]    In the case of frequency band f 1 , switch element  81   a  and second switch element  84  are conducting. First matching block  2  is designed so that the impedance of element  1  (impedance Z L (f 2 )) is made to match the impedance Z 0  of element  9  in the frequency band f 1 . Consequently, the impedance seen from the second terminal P 2  side of first matching block  2  toward element  1  becomes Z 0 . Auxiliary matching block  82   a  and  85  are designed so that, in the frequency band f 1 , the combined impedance of second matching blocks  80   a ,  80   b ,  80   c  and  80   d , auxiliary matching block  82   a , and element  9  becomes Z 0 . Consequently, the impedance seen from the second terminal P 2  side of first matching block  2  (the first terminal P 1  side of second matching block  80   a ) toward element  9  becomes Z 0 . 
         [0070]    In this way, in the case of connecting T-type matching circuits, the two second matching blocks and the auxiliary matching block only make up a set with respect to one frequency band. In order to make the second matching blocks handle a plurality of frequency bands, a plurality of auxiliary matching blocks becomes necessary. 
       Embodiment 6 
       [0071]    As explained in Embodiment 5, in the case of connecting T-type matching circuits, there are cases in which, for two second matching blocks, a plurality of auxiliary matching blocks becomes necessary. In  FIG. 13 , there is shown a configuration example of a matching circuit using an additional auxiliary matching block.  FIG. 13  shows a configuration example where a second switch element  90  and a second auxiliary matching block  91  have been connected in series with auxiliary matching block  82   b  of  FIG. 12 . Having auxiliary matching blocks connected in series in two stages is done so that second matching blocks  80   c  and  80   d  constituting T-type matching circuit  83   b  can handle two frequency bands. 
         [0072]    In the case of this example, in order for the circuit to function also in the case where only switch  81   b  is conducting, it is necessary to choose auxiliary matching block  82   b  to be a transmission line. In case it is not desired to provide such conditions, switch element  81   b  may be configured with a Single Pole Double Throw (SPDT) switch or a multi-contact switch, and switching may be performed between auxiliary matching blocks with different values. 
         [0073]    If the circuit configuration is such that the impedance of the second matching block inserted between element  1  and element  9  can be made Z 0 , seen from both the aforementioned matching point and the element  9  directions, the invention is not limited to the T type or the □type. 
       Embodiment 7 
       [0074]    In the explanations so far, the second matching blocks were explained as black boxes. In  FIG. 14 , there is shown a configuration example of second matching block  3  of  FIG. 5 . Second matching block  3  is constituted by an L-type circuit consisting of a series matching block  100 , a switch element  101  for matching, and a matching element  102 . One end of series matching block  100  is connected to first matching block  2 . Matching element  102  is connected to the other end of series matching block  100  via switch element  101  for matching. 
         [0075]    In the case of frequency band f 1 , switch elements  4  and  5  are in a non-conducting state, and only switch element  101  for matching is conducting. At this point, the sum of the impedances of element  1  and first matching block  2  are matched to impedance Z 0  of element  9  by means of series matching block  100  and matching element  102 . 
         [0076]    In the case of frequency band f 2 , switch elements  4  and  5  are made to conduct and switch element  101  for matching is chosen to be non-conducting. As for this configuration, it is possible, by the existence of matching element  102 , to broaden the options of second matching block  3  and auxiliary matching block  6  and  7 . In other words, it is possible to increase the freedom in designing second matching block  3  by configuring second matching block  3  with series matching block  100 , first switch element  101  for matching, and matching element  102 . In general, the values of the lumped elements constituting second matching block  3  are discrete, making delicate tuning difficult. However, according to this embodiment, it is possible to broaden the lumped element options. 
       Embodiment 8 
       [0077]    Another configuration of the second matching block is shown in  FIG. 15 . Second matching block  3  in  FIG. 15  is constituted by a T-type circuit consisting of second matching blocks  60   a  and  60   b , a switch element  110  for matching, and a matching element  111 . Second matching block  60   a  and second matching block  60   b  are connected in series. One end of second matching block  60   a  is connected to first matching block  2 . The other end of second matching block  60   b  is connected to second terminal P 2 . Matching element  111  is connected, via switch element  110  for matching, to the connection point of second matching block  60   a  and second matching block  60   b.    
         [0078]    Switch element  110  for matching and matching element  111  are provided in order to increase the freedom in designing the second matching blocks and auxiliary matching block  7  and auxiliary matching block  6 . Regarding the function, it is the same as in Embodiment 7. 
       Embodiment 9 
       [0079]    Another configuration of the second matching blocks is shown in  FIG. 16 .  FIG. 16  differs from  FIG. 7  in the point that, on the second terminal P 2  side of T-type matching circuit part  30 , there are provided a switch element  120  form matching and a matching element  121 . In the case of frequency f 2 , switch element  33  and switch element  120  for matching are e.g. made to conduct exclusively. Matching element  121  and second matching block  31  and  32  are designed so that the combined impedance with element  1  and first matching block  2  is chosen to be Z 0 . By configuring the circuit in this way, it is possible to increase the freedom in designing the second matching blocks. 
       Embodiment 10 
       [0080]    In the same way as configuring second matching block  3  by using a plurality of elements, first matching block  2  may also be configured with a plurality of elements. A configuration example thereof is shown in  FIG. 17 . In this example, first matching block  2  is composed of a first series matching block  130  and an auxiliary matching block  131  connected to one end thereof. Further, auxiliary matching block  131  may be connected to either end of first series matching block  130 . First series matching block  130  is connected to element  9  via matching circuit part  8 . 
         [0081]    As for the configuration of the first matching block, modes other than this are possible. All things considered, in a predetermined frequency band f, if the impedance seen from point A toward element  1  (impedance Z L (f)) can be chosen to be Z 0 , any circuit configuration is acceptable. 
       Application Example 
       [0082]    An exemplification of the matching circuit which has been gradually explained this far is shown in  FIG. 18 .  FIG. 18  is an example applied to an amplifying circuit operating in two frequency bands, the 2 GHz band and the 1 GHz band. On the input side of an FET  140 , which is a power amplifier element, the matching circuit shown in  FIG. 17  is connected, and on the input side, the matching circuit shown in  FIG. 16  is connected. As for the matching circuit on the input side, first matching block  2  has become a first matching block  141 . The output side matching circuit has, based on the matching circuit shown in  FIG. 16 , first matching block  2  configured with a first matching block  142 . 
         [0083]    The operation has been explained this far, so an explanation thereof will be omitted. In  FIG. 19A  and  FIG. 19B , the simulation results for the amplifier in  FIG. 18  are shown.  FIG. 19A  is a diagram showing the frequency characteristics in the case where the circuit has been set for the 2 GHz band. The abscissa axis indicates the frequency and the ordinate axis indicates the S parameter. The reflection S 11  of the signal input into first terminal P 1  gets attenuated abruptly at 2 GHz. The transmission S 21  of the signal input in first terminal P 1  exhibits a value of approximately 14 dB at 2 GHz, so the circuit transmits well.  FIG. 19B  is a diagram showing the frequency characteristics in the case where the circuit has been set for the 1 GHz band. The reflection S 11  of the signal input into first terminal P 1  gets attenuated abruptly at 1 GHz. The transmission S 21  of the signal input in first terminal P 1  exhibits a value of approximately 19 dB at 1 GHz, so the circuit transmits well. It is seen that the matching circuit according to the present invention functions as a multiband matching circuit. 
         [0084]    The matching circuit according to the present invention has an impedance seen from both ends of a second matching block, inserted between element  9  and element  1  and formed with lumped-parameter elements, which is made to match the impedance Z 0  by means of an auxiliary matching block. Also, by raising the number of auxiliary matching blocks, a matching circuit handling a plurality of frequency bands is adopted. Further, since the second matching block is formed with lumped elements, it can be made smaller than prior-art matching circuits configured with transmission lines. 
         [0085]    The effect of the reduction in size is possible to see by comparing  FIG. 3  showing a conventional matching circuit and  FIG. 5  showing the matching circuit of the present invention.  FIG. 3  and  FIG. 5  are diagrams of circuits made capable of matching in two frequency bands together. As against the conventional matching circuit ( FIG. 3 ), the matching circuit of the present invention ( FIG. 5 ) requires in total two additional components, one switch element and one auxiliary matching circuit. However, the delay circuit  172  required in the conventional matching circuit is a large-size component. The size thereof varies with the frequency band and the used power amplification element, but when e.g., the frequency band is taken to be 1 GHz with a certain amplification element, the width is 0.63 mm and the length is 9.22 mm, or the length is 15.32 mm. 
         [0086]    On the other hand, the matching circuit of the present invention can be configured with a chip circuit commonly known by the name 0603 and having a width of 0.3 mm and a length of 0.6 mm and a Monolithic Microwave Integrated Circuit several mm square. In other words, all of the components constituting the matching circuit of the present invention end up amply fitting into the space of delay circuit  172 . In order to handle still more frequency bands, the number of delay circuits  172  must be increased. Consequently, as a matching circuit for multiband use, the matching circuit of the present invention can be further reduced in size, compared to a conventional matching circuit.