Abstract:
The disclosed is a downsized and power saving antenna duplexer. The antenna duplexer includes: diplexer; first surface acoustic wave filter to transmit/receive low channel frequency band signals; first phase shift circuit to match the transmission phase with the reception phase of first surface acoustic wave filter; second surface acoustic wave filter to transmit/receive high channel frequency band signals; second phase shift circuit to match the transmission phase with the reception phase of second surface acoustic wave filter. Diplexer, first phase shift circuit and second phase shift circuit are formed in a monolithic structure in package that includes surface acoustic wave filters. The configuration can provide the antenna duplexer with a compact size, a lower current consumption and a highly efficient performance.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to an antenna duplexer, particularly used in cell-phones or the like, for transmitting and receiving a plurality of frequency band signals.  
       BACKGROUND ART  
       [0002]      FIG. 10  shows an example of conventional antenna duplexer schematically. The example employs a system having a plurality of antenna duplexers  1  and  2  housed in one package  5 , selecting respective antenna duplexers by switch  3 . In  FIG. 10 , switch  3  connects to antenna  4 . Antenna duplexer  1  includes transmission terminal Tx 1  and reception terminal Rx 1  respectively. Antenna duplexer  2  includes similar terminals Tx 2  and Rx 2  respectively. Another known system (not shown) is to select one of antenna duplexers provided separately using a switching circuit.  
         [0003]     A conventional art related to the present invention is disclosed for instance in Japanese Patent Laid-Open Application No. 2000-349586.  
         [0004]     In a conventional art, generally, a large overall size of the antenna duplexer must be accepted since a switching circuit and respective antenna duplexers are provided separately. A large current consumption must also be accepted due to the switching circuit provided additionally. Even if the current consumption is restrained to a low level, the problem is that signal distortions such as harmonic components generated in signal transmission or intermodulation generated in signal reception are likely to occur due to a non-linearity of the switching circuit. Additionally, switching circuits or surface acoustic wave (SAW) filters used in the antenna duplexer must accept problems of deterioration in electrical characteristics of the antenna duplexer itself or peripheral circuits due to undesired surge pulses intruding through the antenna terminal. Particularly, switching circuits near the antenna or adjacent circuits are likely to be influenced by the surge pulses, causing in some case the circuits to deteriorate in electrical or physical characteristics.  
         [0005]     The present invention can provide an antenna duplexer with a high performance and a high reliability while having a compact size.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention aims at providing an antenna duplexer capable of transmitting/receiving a plurality of frequency band signals simultaneously. The antenna duplexer is provided with a diplexer to combine a plurality of different frequency band signals by transmitting/receiving through a terminal connected to an antenna. The antenna duplexer is additionally provided with a first surface acoustic wave (SAW) filter to transmit/receive low frequency band signals through the diplexer and a first phase shift circuit to match the transmission phase with reception phase of the first SAW filter. A duplexer is composed of the first SAW filter and the first phase shift circuit to match the transmission phase with the reception phase of the first SAW filter.  
         [0007]     Additionally, the antenna duplexer of the present invention is provided with a second SAW filter to transmit/receive high frequency band signals to the diplexer and a second phase shift circuit to match the transmission phase with the reception phase of the second SAW filter. The second SAW filter and the second phase shift circuit to match the transmission phase with the reception phase of the second SAW filter all together make up another duplexer.  
         [0008]     Furthermore, the diplexers, the first and second phase shift circuits, and the first and second SAW filters are housed in one package, forming the antenna duplexer.  
         [0009]     The configuration enables to form the antenna duplexer with a downsized monolithic structure and to consume lesser electric power. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  illustrates a circuit block diagram of an antenna duplexer used in exemplary embodiment  1  of the present invention.  
         [0011]      FIG. 2  illustrates a cross-sectional view of the antenna duplexer.  
         [0012]      FIG. 3  illustrates a circuit diagram of a diplexer used in the antenna duplexer.  
         [0013]      FIG. 4  illustrates a circuit diagram of a surge protector used in the antenna duplexer.  
         [0014]      FIG. 5  illustrates a circuit diagram of a diplexer used in the antenna duplexer.  
         [0015]      FIG. 6  illustrates a cross-sectional view of another antenna duplexer used in exemplary embodiment  1  of the present invention.  
         [0016]      FIG. 7  illustrates a circuit block diagram of an antenna duplexer used in exemplary embodiment  2  of the present invention.  
         [0017]      FIG. 8  illustrates a cross-sectional view of the antenna duplexer used in exemplary embodiment  2  of the present invention.  
         [0018]      FIG. 9  illustrates a circuit block diagram of an antenna duplexer used in exemplary embodiment  3  of the present invention.  
         [0019]      FIG. 10  illustrates a circuit block diagram of a conventional antenna duplexer. 
     
    
     DETAILED DESCRIPTION  
     Exemplary Embodiment 1  
       [0020]     Exemplary embodiment 1 is described with reference to drawings.  
         [0021]      FIG. 1  illustrates a circuit block diagram of an antenna duplexer used in exemplary embodiment  1  of the present invention. Antenna duplexer  50  is provided with first SAW filter  10 . First SAW filter  10  includes a transmission filter (not shown) to pass frequencies ranging 824 to 849 MHz and a reception filter (not shown) to pass frequencies ranging 869 to 894 MHz. First phase shift circuit  11  is provided for impedance matching by phase shifting. Additionally, first SAW filter  10  and first phase shift circuit  11  form a duplexer for low channel frequency band to be used for instance in CDMA (Code Division Multiple Access) system of 800 MHz band.  
         [0022]     Here, the diplexer differs from the duplexer in that: the diplexer locating at the head from an antenna is a filter device to select a double-frequency band or so called a dual band, but the duplexer locating at the way to the antenna plays a role of transmission/reception filter to separate signals into transmission signals and reception signals.  
         [0023]     Moreover, antenna duplexer  50  of the present invention is provided with a second surface acoustic wave (SAW) filter  12 . Second SAW filter  12  includes a transmission filter (not shown) to pass so called a high channel 1850 to 1910 MHz band and a reception filter (not shown) to pass 1930 to 1990 MHz band.  
         [0024]     Second phase shift circuit  13  is provided for impedance matching by phase shifting the reception filter. Second SAW filter  12  and second phase shift circuit  13  form a duplexer for high channel frequency used for instance in PCS (Personal Communication System) CDMA system of 1.9 GHz band in North America. Additionally, diplexer  14  is provided with a low-pass filter (LPF) to pass 800 MHz band and a high-pass filter to pass 1.9 GHz band. Connecting these two filters provides an antenna duplexer capable of transmitting and receiving in both 800 MHz band and 1.9 GHz band, which is capable for a so-called dual mode operation.  
         [0025]      FIG. 2  illustrates a cross-sectional view of the antenna duplexer used in exemplary embodiment  1  of the present invention. Layers of low temperature co-fired ceramic (LTCC)  15  are laminated with first phase shift circuit  11 , second phase shift circuit  13  and diplexer  14  printed using silver or copper and sandwiched between the layers. Cavity  16   a  is further formed on the laminate, forming package  16 . First surface acoustic wave (SAW) filter  10 , second SAW filter  12  are secured in cavity  16   a  of package  16  by die bonding. Terminal pads (not shown) provided on first SAW filter  10  and second SAW filter  12  respectively are connected with terminals (not shown) provided on internal periphery of package  16  by wires  17 . Furthermore package  16  is hermetically sealed by lid  18 .  
         [0026]     Since package is formed from LTCC  15 , terminal patterns can be printed easily on LTCC  15  as well as its upper and bottom side LTCCs  15  by using materials with a high electric conductivity such as silver or copper. This can provide first phase shift circuit  11 , second phase shift circuit  13  and diplexer  14  with low electric losses. Number of LTCC  15  can select 7 to 8 layers.  
         [0027]     Next,  FIG. 3  illustrates a partial circuit diagram of diplexer  14  used for antenna duplexer  50 . Diplexer  14  includes low-pass filter  20  to pass a comparatively low channel of 800 MHz band and high-pass filter  21  to pass a comparatively high channel of 1.9 GHz band connected each other. Antenna terminal  26  connects to these two filters. Compared with dielectric filter, generally, SAW filter used in antenna duplexer  50  makes it difficult to improve a resistance level to static electricity.  
         [0028]      FIG. 4  illustrates a circuit diagram when a surge protector  19  is provided between antenna terminal  26  and ground (GND) to improve the resistance level to the static electricity. The configuration can improve the resistance level to the static electricity. Surge protector  19  shown in  FIG. 14  is basically a circuit to add inductor  22  between signal line  6  transmitting high frequency signals and GND. By introducing surge protector  19 , anti-surge characteristics against undesired static electricity or noises (hereafter referred to surge pulses) intruding through antenna terminal  26  can be improved.  
         [0029]     The present invention depends upon a finding that energy spectra of so-called surge pulses intruding from antenna terminal  26  or antenna duplexer shows a concentration near to DC signals. That is, an impedance value of inductor  22  decreases near DC causing most surge energies to flow to GND, thereby resulting in little influence on circuitry such as the antenna duplexer or the like.  
         [0030]     Additionally, mounting surge protector  19  along with first phase shift circuit  11 , second phase shift circuit  13  and diplexer  14  all together in package  16  can achieve a cost reduction and downsizing of entire antenna duplexer  50 , and can improve anti-surge pulse characteristics.  
         [0031]     Next,  FIG. 5  illustrates the main part of another diplexer  14  of the present invention that can improve the anti-surge pulse characteristics. Inductor  24  is provided in parallel with capacitor  23  that forms low-pass filter  20  of diplexer  14 . Capacitor  25  is added on the side of high-pass filter  21 . The configuration can attenuate comparatively low frequency surge pulses intruding from antenna terminal  26 .  
         [0032]     However, low frequency surge pulses intruding from antenna terminal  26  does not attenuate in low-pass filter  20  but passes directly to SAW filter, causing diplexer  14  at risk of deterioration in electrical or physical characteristics.  
         [0033]     Therefore, the present invention allows improving the anti-surge pulse characteristics by introducing inductor  24  on the side of low-pass filter  20  to bypass undesired surge pulses intruding from antenna terminal  26 .  
         [0034]     Low-pass filter  20  including inductor  24  and high-pass filter  21  can be formed incorporated together with first SAW filter  10 , first phase shift circuit  11  and diplexer  14  shown in  FIG. 2  in one package  16 . The structure can realize the antenna duplexer with a compact size and a reduced production cost.  
         [0035]      FIG. 6  shows a cross-sectional view of another antenna duplexer used in exemplary embodiment  1 . Similar to shown in  FIG. 2 , antenna duplexer  50  shown in  FIG. 6  is provided with first phase shift circuit  11 , second phase shift circuit  13  and diplexer  14 . Similarly, the antenna duplexer is also provided with LTCC  15 , cavity  16   a  and package  16 . Both antenna duplexers have largely the similar structure.  
         [0036]     Antenna duplexer  50  shown in  FIG. 6  differs from that shown in  FIG. 2  in following points: antenna duplexer  50  shown in  FIG. 6  is provided with one SAW filter  40  only, while antenna duplexer  50  shown in  FIG. 2  with two SAW filters of first SAW filter  10  and second SAW filter  12 . That is, SAW filter  40  is thought to include parts corresponding to first SAW filter  10  and second SAW filter  12  built-in one chip.  
         [0037]     Additionally, the antenna duplexer is featured that SAW filter  40  adopts bumps  27  instead of wires  17 . The structure can reduce the height of antenna duplexer since a curve of wire  17  and a space to lid from wire  17  do not present anymore, enabling to realize a low profiling for entire antenna duplexer. There is no relation between a number of SAW filter mounted in package  16  and arrangements of bumps. Therefore, if SAW filter  40  is formed in one integration, wires  17  may be adopted instead of using bumps  27  as shown in  FIG. 2 .  
         [0038]     Comparing antenna duplexer  50  shown in  FIG. 2  with antenna duplexer  50  shown in  FIG. 6 , antenna duplexer  50  shown in  FIG. 6  can increase design freedom because SAW filter  40  can be enlarged, and that number of elements made into first phase shift circuit  11  or second phase shift circuit  13  can be increased, if both packages  16  are the same in size.  
         [0039]     Also for package  16  shown in  FIG. 6 , first phase shift circuit  11 , second phase shift circuit  13  and diplexer  14  should preferably be formed printed using silver or copper and sandwiched between layers of laminated LTCC  15 . This can provide the electric elements with low electric losses.  
       Exemplary Embodiment 2  
       [0040]     Next, exemplary embodiment 2 is described with reference to  FIG. 7 .  
         [0041]     Exemplary embodiment  2  differs from exemplary embodiment 1 in following points: diplexer  14  selects double-frequency band signals or so called dual band signals that includes low channel or low frequency 800 MHz band signals and high channel or high frequency 1.9 GHz band signals in exemplary embodiment 1, on the contrary, a phase shift circuit performs a phase matching of duplexers for different frequency bands in exemplary embodiment 2.  
         [0042]      FIG. 7  shows antenna duplexer  50 . Antenna duplexer  50  includes a low channel of 800 MHz band duplexer including first SAW filter  10  and first phase shift circuit  11 . Second SAW filter  12  together with second phase shift circuit  13  forms a 1.9 GHz high frequency band duplexer. Here, if enough out-of-pass band attenuation amount in respective 800 MHz band and 1.9 GHz band are obtained, diplexer  14  needs not to select signals as attenuation characteristics like in exemplary embodiment 1 but have to perform a phase matching.  
         [0043]     Therefore, antenna duplexer  50  capable of transmitting and receiving both in 800 MHz band and 1.9 GHz band is accomplished by connecting these elements via third phase shift circuit  28 . Phase shift circuit  28  can be composed of for instance a triplate transmission line whose upper and lower portions are sandwiched by grounded terminals. In this case, the configuration of phase shift circuit sandwiched by GND can provide the antenna duplexer with a more stable and higher performance, since electromagnetic interference from surrounding circuits or parts are protected. Antenna terminal  26  connects to phase shift circuit  28 . Such circuit configuration can provide phase shift circuit  28  with reduced electric losses.  
         [0044]     In  FIG. 7 , first SAW filter  10  has transmission terminal Tx 1  and reception terminal Rx 1  respectively. Second SAW filter  12  has similar terminals Tx 2  and Rx 2  respectively.  
         [0045]      FIG. 8  shows a cross-sectional view of the antenna duplexer used in exemplary embodiment  2 . Layers of LTCC  15  are laminated, and first phase shift circuit  11 , second phase shift circuit  13  and third phase shift circuit  28  are formed printed using silver, copper or the like and sandwiched between the layers.  
         [0046]     Cavity  16   a  is further formed on the laminate to form package  16 . Thus antenna multiplexer is produced by a method similar to exemplary embodiment  1 .  
         [0047]     Antenna duplexer  50  of exemplary embodiment 1 needs 6 to 7 layers of LTCC  15 . On the contrary, antenna duplexer  50  of exemplary embodiment 2 can reduce the layer number to  3  to  4 , since whole elements are composed of phase shift circuit  28 . The configuration can realize a low-profile form (1.0 to 1.5 mm) of package  16  as well as a reduced price.  
       Exemplary Embodiment 3  
       [0048]     Next, exemplary embodiment 3 is described with reference to  FIG. 9 .  
         [0049]     Exemplary embodiment 3 differs from exemplary embodiment 1 in following points: first SAW filter  10 , first phase shift circuit  11 , second SAW filter  12 , second phase shift circuit  13  and diplexer  14  are described formed in a monolithic structure in exemplary embodiment 1; on the contrary, only first SAW filter  10 , first phase shift circuit  11  and diplexer  14  are formed in a monolithic structure in exemplary embodiment 3.  
         [0050]      FIG. 9  shows a duplexer comprising first SAW filter  10  and first phase shift circuit  11  for a low channel of 800 MHz band signals. Phase shift circuit  11  connects to diplexer  14 . 1.9 GHz terminal of diplexer  14  connects to external terminal  29 . External terminal  29  of antenna duplexer  50  connects to duplexer  30  to be used for 1.9 GHz band. This can form antenna duplexer for both 800 MHz band and 1.9 GHz band. Duplexer  30  includes second SAW filter  12  and second phase shift circuit  13 .  
         [0051]     In  FIG. 9 , first SAW filter  10  has transmission terminal Tx 1  and reception terminal Rx 1  respectively. Second SAW filter  12  has Tx 2  and Rx 2  respectively. Diplexer  14  connects to antenna terminal  26 .  
         [0052]     Such circuit configuration is not a kind of monolithic structure antenna duplexer but combining duplexers for 800 MHz band and 1.9 GHz band that have been prepared previously separately to form one antenna duplexer. Therefore, even in a case of for instance the supply of accepted high channel duplexers for 1.9 GHz band is short due to an unsatisfactory yield ratio while accepted low channel duplexers for 800 MHz band are supplied sufficiently, combining accepted respective duplexers can produce a complete antenna duplexer  50 .  
         [0053]     The reverse can be a possible case. That is a case when the supply of accepted low channel duplexer  30  for 800 MHz band is short due to an unsatisfactory yield ratio while accepted high channel duplexers for 1.9 GHz band are supplied sufficiently. In this case, second SAW filter  12  and second phase shift circuit  13  can form the high channel duplexer for 1.9 GHz band. A configuration may be that the duplexer connects to diplexer  14  and subsequently a 800 MHz band terminal of diplexer  14  connects to external terminal  29 . Namely, either of for 800 MHz band and for 1.9 GHz band can be mounted on duplexer  30 .  
         [0054]     Antenna duplexer  50  described in exemplary embodiment 1 includes a low channel duplexer for 800 MHz band and a high channel duplexer for 1.9 GHz band in a monolithic structure. Therefore, the entire antenna duplexer must be rejected if either of the duplexers cannot satisfy required values. From this point of view, however, antenna duplexer  50  described in exemplary embodiment 3 can use individual duplexers efficiently.  
         [0055]     In  FIG. 9 , package  13  can include second phase shift circuit  13  internally. That is, these can be formed to a monolithic structure. Second SAW filter  12 , that has been left alone in this case, can be formed in a package made from HTCC, contributing to a cost reduction.  
       INDUSTRIAL APPLICABILITY  
       [0056]     The antenna duplexer disclosed is a system used for a plurality of frequency band signals with a compact size, and can perform well with a high reliability. The system is useful for mobile communication equipment such as cell-phone or the like, having a high industrial applicability.