Patent Publication Number: US-6657511-B2

Title: Nonreciprocal circuit device and communication apparatus including the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to nonreciprocal circuit devices, and in particular, to a nonreciprocal circuit device such as an isolator or a circulator for use in microwave bonds, and a communication apparatus including the nonreciprocal circuit device. 
     2. Description of the Related Art 
     In general, a lumped-constant isolator for use in a mobile communication apparatus such as a mobile phone has a function of allowing signals to pass only in a transmission direction so that a reverse transmission of the signals is prevented. As for conventional mobile communication apparatuses, a reduction in thickness and weight is in great demand, due to their uses. 
     A lumped-constant isolator of the above type includes a permanent magnet, a ferrite member to which a direct current magnetic field is applied by the permanent magnet, a plurality of central electrodes arranged on the ferrite member, a resistor element, a resin case for accommodating the ferrite member, the central electrodes, and the resistor element, and a metal case for accommodating the permanent magnet, the ferrite member, and the central electrodes. 
     In general, an isolator is often formed such that a permanent magnet is provided to cover the entire surfaces of a ferrite member and a resistor element so that the isolator exhibits its performance to the maximum. In the case of a conventional isolator, the upper surface of a resistor element provided in a resin case is above the upper surface of an insulating spacer on a ferrite member and a matching capacitor. Thus, the total of the thicknesses of the permanent magnet and the resistor element determines the overall height of the isolator. 
     In actuality, in accordance with the total of the thicknesses or the resistor element and the permanent magnet, by increasing the thickness of the insulating spacer to be more than a value that is essentially required, the upper surface of the insulating spacer is level with the height of the resistor element. This is because the permanent magnet is stably and horizontally disposed in the isolator. Here, it is possible that the thickness of the permanent magnet be reduced. This causes a problem in that the magnitude of a direct current magnetic field which is applied to the ferrite member is insufficient, so that a reduction in thickness is difficult. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a nonreciprocal circuit device having a height reduced without reducing the thickness or a permanent magnet, and a communication apparatus including the nonreciprocal circuit device. 
     To this end, according to an aspect of the present invention, the foregoing object is achieved through provision of a nonreciprocal circuit device including a permanent magnet; a ferrite member to which a direct current magnetic field is applied by the permanent magnet, said ferrite member including a plurality of central electrodes; a resistor element which has a thickness of not less than 0.1 mm and not greater than 0.5 mm and in which a resistor is provided between lead electrodes formed on two ends of a main surface of a substrate; a resin case for accommodating the ferrite member, the central electrodes, and the resistor element; and a metal case for accommodating the permanent magnet, the ferrite member, and the central electrodes. 
     The above-described construction enables a nonreciprocal circuit device to have a low height without reducing the thickness of the permanent magnet. 
     By allowing the lead electrodes in the resistor element to extend on two sides of the substrate or to extend to the other main surface of the substrate via the two sides, an area of contact between the lead electrodes in the resistor element and terminals provided on the resin case is increased. This increases the strength of bonding by solder or the like, and reliability is enhanced. 
     According to another aspect of the present invention, a communication apparatus includes a nonreciprocal circuit device having the above-described characteristics, whereby the thickness of the communication apparatus is reduced. This provides high reliability. 
     Since the thickness of a resistor element is reduced to not less than 0.1 mm and not greater than 0.5 mm, the height of a nonreciprocal circuit device can be reduced without reducing the thickness of a permanent magnet. In addition, since lead electrodes in the resistor element are provided to extend on two sides of one main surface of a substrate or to extend to the other main surface of the substrate via the two sides, an area of contact between the lead electrodes in the resistor element and terminals provided on the resin case is increased. Accordingly the strength of bonding by solder or the like can be increased enhancing reliability. As a result, a highly reliable thin nonreciprocal circuit device and a communication apparatus having the nonreciprocal circuit device are obtained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective exploded view showing a nonreciprocal circuit device according to a first embodiment of the present invention; 
     FIG. 2 is a perspective exterior view showing the nonreciprocal circuit device shown in FIG. 1 in an assembled state; 
     FIG. 3 is a sectional view taken on the line III—III shown in FIG. 2; 
     FIG. 4 is a sectional view taken on the line IV—IV shown in FIG. 2; 
     FIG. 5 is an electrically equivalent circuit diagram of the nonreciprocal circuit device shown in FIG. 2; 
     FIG. 6 is a sectional view showing a nonreciprocal circuit device according to a second embodiment of the present invention; 
     FIG. 7 is a sectional view showing a nonreciprocal circuit device according to a third embodiment of the present invention; and 
     FIG. 8 is a block diagram showing a communication apparatus according to a fourth embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A nonreciprocal circuit device and a communication apparatus according to embodiments of the present invention are described below with reference to the accompanying drawings. 
     FIG. 1 is a perspective exploded view of a nonreciprocal circuit device  1  according to an embodiment of the present invention. FIG. 2 is a perspective view of the nonreciprocal circuit device  1  in FIG. 1 in an assembled state. FIG. 3 is a sectional view taken along the line III—III in FIG.  2 . FIG. 4 is a sectional view taken along the line IV—IV in FIG.  2 . The nonreciprocal circuit device  1  is a lumped constant isolator. 
     As shown in FIG. 1, the nonreciprocal circuit device  1  as a lumped-constant isolator schematically includes a metal lower case portion  12 , a resin terminal case  13 , a central electrode assembly  14 , a metal upper case portion  15 , a permanent magnet  16 , an insulating spacer  17 , a resistor element R, and matching capacitors C 1  to C 3 . 
     The central electrode assembly  14  is formed such that central electrodes  21  to  23  are arranged on the upper surface (one magnetic pole surface) of a circular microwave ferrite member  20  so as to cross at each angle of approximately 120 degrees with respect to each other, with the central electrodes  21  to  23  electrically insulated from each other. In the center of the upper surface of the ferrite member  20 , the central electrodes  21  to  23  and three insulating sheets are stacked. In the periphery of the ferrite member  20 , the central electrodes  21  to  23  are separately arranged. 
     Ports P 1  to P 3  at one end of the central electrodes  21  to  23  are arranged horizontally to the central electrodes  21  to  23 . The central electrodes  21  to  23  form a common shielding portion at the other end thereof which abuts on the lower surface (the other magnetic poles surface) of the ferrite member  20 . The common shielding portion covers substantially all of the lower surface of the ferrite member  20 , and is connected to a bottom wall  12   b  of the metal lower case portion  12  through an aperture portion  13   a  of the resin terminal case  13  by a technique such as soldering so as to be grounded. In the first embodiment, the ferrite member  20  has a thickness T 4  of 0.45 mm, each of the central electrodes  21  to  23  has a thickness T 5  of 0.05 mm, and the central electrodes  21  to  23  and the three insulating sheets have a total thickness of 0.2 mm. Thus, the central electrode assembly  14  has a thickness of 0.7 mm. 
     The resin terminal case  13  is insert-molder so that input/output terminals  51  and  52 , ground terminals  53 , and a relay terminal  54  (see FIG. 3) are provided. One end of the input/output terminal  51  is exposed from the outer wall of the resin terminal case  13 , and the other end of the input/output terminal  51  is exposed from the inner surface of the resin terminal case  13 , so that an input/output lead electrode portion  51   a  is formed. One end of the input/output terminal  52  is exposed from the outer wall of the resin terminal case  13 , and the other end of the input/output terminal  52  is exposed from the inner surface of the resin terminal case  13 , so that an input/output lead electrode portion (not shown) is formed. Similarly, respective ends of the two ground terminals  53  are exposed from opposing outer walls of the resin terminal case  13 , and the other ends of the ground terminals  53  are exposed from the inner surface of the resin terminal case  13 , so that ground lead electrode portions  53   a  are formed. In the case of the first embodiment, the thickness T 10  of a portion of the resin terminal case  13  in which the matching capacitors C 1  to C 3  are provided is 0.2 mm, including the thickness of each terminal  53 . 
     The hot-side capacitor electrodes of the matching capacitors C 1  to C 3  (capacitors each having a relative dielectric constant ε r  of 9 to 200 are used based on the operating frequency of the lumped-constant isolator  1 ) are respectively connected to the ports P 1  to P 3  by soldering, and the cold-side capacitor electrodes of the matching capacitors C 1  to C 3  are respectively connected by soldering to the ground lead electrode portions  53   a  of the ground terminals  53 , which are exposed from the inner surface of the resin terminal case  13 . In the case of the first embodiment, the thickness T 9  of each of the matching capacitors C 1  to C 3  is 0.2 mm. 
     As shown in FIG. 3, the resistor element R is formed such that lead electrodes  3  are formed on two ends of a main surface of the insulating substrate  4  by thick-layer printing or the like, and a resistor  2  of a metal thin film or of a thick film made of cermet-based, carbon-based, or ruthenium-based material is provided between the lead electrodes  3 . For example, a dielectric ceramic such as alumina is used as material for the insulating substrate  4 . The surface of the resistor  2  may be coated with glass or the like. The thickness T 8  of the resistor element R is set to not less than 1.0 mm and not more than 0.5 mm. In the case of the first embodiment, the thickness T 8  of the resistor element R is substantially 0.5 mm. The resistor element R is disposed with the resistor  2  and the lead electrodes  3  facing downward such that the lead electrodes  3  are electrically connected to the ground lead electrode portions  53  exposed from the inner surface of the resin terminal case  13  and the relay terminal  54 , respectively. 
     One end of the lead electrode  3  of the resistor element R is connected to the hot-side capacitor electrode of the matching capacitor C 3  via the relay terminal  54 , and the other end is connected to one ground terminal  53 . In other words, the matching capacitor C 3  and the resistor element R are electrically connected in parallel to each other between the port P 3  of the central electrode  23  and the ground. 
     As shown in FIG. 1, the insulating spacer  17  is arranged on an upper surface of the central electrode assembly  14 . As shown in FIG. 4, in the insulating spacer  17  is formed a hole  17   a  for accommodating the central electrodes  21  to  23  and the three insulating sheets, which overlap in the center of the upper surface of the ferrite member  20 . The thickness or the insulating spacer  17  differs depending on portions thereof. In the case of the first embodiment, the thickness T 3  of the insulating spacer  17  arranged on the ferrite member  20  is 0.15 mm, and a thickness T 4  thereof arranged on the capacitors C 1  to C 3  is 0.25 mm. 
     The metal lower case portion  12  is made of magnetic metal, and has right and left sidewalls  12   a  and a bottom wall  12   b . The resin terminal case  13  is provided on the metal lower case portion  12 . In the resin terminal case  13 , the central electrode assembly  14 , the matching capacitors C 1  to C 3 , etc., are accommodated, and the metal upper case portion  15 , which is made of magnetic metal, is provided. The permanent magnet  16  is bonded to a lower surface of the metal upper case portion  15 , and is used to apply a direct current magnetic field to the central electrode assembly  14 . The metal lower case portion  12  and the metal upper case portion  15  constitute a magnetic circuit, and function as a yoke. Each of the metal lower case portion  12  and the metal upper case portion  15  is obtained by stamping a predetermined shape from a sheet material exhibiting high permeability such as iron or silicon steel, bending it, and plating its surface with copper or silver. In the first embodiment, the thickness T 11  of the metal lower case portion  12  is 0.2 mm, the thickness T 1  of the metal upper case portion  15  is 0.25 mm, and the thickness T 2  of the permanent magnet  16  is 1.0 mm. 
     In the above manner, the lumped constant isolator  1  is obtained. FIG. 5 is an electrically equivalent circuit diagram of the lumped-constant isolator  1 . 
     The following table shows the thicknesses T 1  to T 11  of the components of the lumped-constant isolator  1  and its overall thickness T 12 . For comparison, values of a conventional isolator are also shown. 
     
       
         
           
               
               
            
               
                   
                   
               
               
                   
                 [unit: mm] 
               
            
           
           
               
               
               
            
               
                   
                 First 
                 Conventional 
               
               
                   
                 embodiment 
                 example 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                 Thickness T1 of upper case portion 15 
                 0.250 
                 0.250 
               
               
                 Thickness T2 of permanent magnet 16 
                 1.000 
                 1.000 
               
               
                 Thickness of insulating spacer 17 
               
               
                 (portions above ferrite member) T3 
                 0.150 
                 0.280 
               
               
                 (portions above capacitor) T4 
                 0.250 
                 0.380 
               
               
                 Thickness T5 of each of central electrodes 
                 0.050 
                 0.050 
               
               
                 21 to 23 
               
               
                 Total thickness T6 of central electrodes 21 
                 0.200 
                 0.200 
               
               
                 to 23 and three insulating sheets 
               
               
                 Thickness T7 of ferrite member 20 
                 0.450 
                 0.450 
               
               
                 Thickness T8 of resistor element R 
                 0.500 
                 0.680 
               
               
                 Thickness T9 of each of capacitors C1 to C3 
                 0.200 
                 0.200 
               
               
                 Thickness T10 of resin terminal case 13 
                 0.200 
                 0.200 
               
               
                 (including terminal 53) 
               
               
                 Thickness T11 of lower case portion 12 
                 0.200 
                 0.200 
               
               
                 Total thickness T12 of the isolator 1 
                 2.150 
                 2.280 
               
               
                   
               
            
           
         
       
     
     In FIG. 4, the thickness T 3  of the insulating spacer  17  (above the ferrite member  20 ) must be 0.15 mm or greater that is obtained by adding each thickness T 5  (=0.05 mm) of the central electrodes  21  and  22 , and a total the thicknesses (=0.05 mm) of the three insulating sheets. In addition, the thickness of the insulating spacer  17  is determined so as to flatten a difference in level which is caused by stacking the central electrodes  21  to  23  and the insulating sheets. Accordingly, the thickness T 3  of the insulating spacer  17  (above the ferrite member  20 ) may be 0.15 mm from the point of view of reduction in the height of the lumped-constant isolator  1 . 
     Therefore, a distance from the lower surface of the permanent magnet  16  which corresponds to the ferrite member  20  to the bottom surface of the lumped-constant isolator  1  is calculated by the following expression: 
     
       
         “Thickness T 11  of the metal lower case portion  12 ”+ 
       
     
     
       
         “Thickness of the common shielding portion of the central electrodes  21  to  23 ”+ 
       
     
     
       
         “Thickness T 7  of the ferrite member  20 ”+ 
       
     
     
       
         “Thickness T 5  of the central electrode  23 ”+ 
       
     
     
       
         “Thickness T 3  of the insulating spacer  17  above the ferrite member  20 ”= 
       
     
     
       
         0.2 mm+0.05 mm+0.45 mm+0.05 mm+0.15 mm=0.9 mm  (1) 
       
     
     In FIG. 3, a distance from the lower surface of the resistor element R to the bottom surface of the lumped-constant isolator  1  is calculated by the following expression: 
     
       
         “Thickness T 11  of Metal Lower Case Portion  12 ”+ 
       
     
     
       
         “Thickness T 10  of Portion of Resin Terminal Case  13  in which Matching Capacitor C 3  is provided”+ 
       
     
     
       
         “Thickness T 10  or a portion of the resin terminal case  13  in which the matching capacitor C 3  is provided”=0.2 mm+0.2 mm=0.4 mm  (2) 
       
     
     Thus, the maximum thickness T 8  of the resistor element R is 0.9 mm−0.4 mm=0.5 mm from expression (1)-expression (2). 
     When the thickness T 8  of the resistor element R exceeds 0.5 mm, a total thickness from the lower surface of the permanent magnet  16  to the bottom surface of the lumped-constant isolator  16  is greater than 0.9 mm, so that the thickness of the lumped-constant isolator  1  is increased. In this case, it is considered that the thickness of the permanent magnet  16  should be reduced. However, this makes it impossible to apply a sufficient direct current magnetic field to the ferrite member  20 . Accordingly, the thickness T 2  of the permanent magnet  16  cannot be reduced. Thus, from the point of view of reduction in the height of the lumped-constant isolator  1 , the upper limit of the thickness T 8  of the resistor element R is 0.5 mm. In addition, stress such as thermal stress acts on the resistor element R when it is soldered to the terminals  53  and  54 . It is required that resistor element R have a thickness not less than a certain value in order that the resistor element R may resist to pressure generated when the resistor element R is formed by printing, thermal stress generated when the resistor element R is fired, and pressure applied when the lumped-constant isolator  1  is assembled. Accordingly, from the standpoints of reliability, processability, and easiness of assembling process, the lower limit of the thickness of the resistor element R is 0.1 mm. 
     As shown in FIG. 3, the resistor element R and the matching capacitors C 1  to C 3  are disposed at the same level in the resin terminal case  13  (i.e., the level of a surface on which the terminals  51  to  54  are exposed). In the lumped-constant isolator  1 , the permanent magnet  16  is stabily and horizontally disposed by setting, with respect to the thickness T 8  (=0.5 mm) of the resistor element R, the thickness of a portion in which the matching capacitor C 3  (C 1 , C 2 ) to “Thickness T 9  of the matching capacitor C 3 ”+“Thickness T 5  of the central electrode  23 ”+“Thickness T 4  of the insulating spacer  17  above the matching capacitor C 3 ”=0.2 mm+0.05 mm+0.25 mm=0.5 mm. 
     As a result, the overall thickness T 12  of the lumped-constant isolator  1  according to the first embodiment is calculated, for example, by the following expression: 
     
       
         “Thickness T 11  of the metal lower case portion  12 ”+ 
       
     
     
       
         “Thickness T 10  of the resin terminal case  13 ”+ 
       
     
     
       
         “Thickness T 8  of the resistor element R”+ 
       
     
     
       
         “Thickness T 2  of the permanent magnet  16 ”+ 
       
     
     
       
         “Thickness T 1  of the metal upper case portion  15 ”=0.2 mm+0.2 mm+0.5 mm+1.0 mm+0.25 mm=2.15 mm  (3) 
       
     
     The overall thickness of the conventional isolator is 2.28 mm as a result of calculation similar to the expression (3). 
     As described above, the height of the lumped-constant isolator  1  according to the first embodiment can be reduced without reducing the thickness of the permanent magnet  16 . 
     Referring to FIG. 6, a lumped-constant isolator  1   a  according to a second embodiment of the present invention is obtained such that in the first embodiment, a resistor element Ra is used instead of the resistor element R. The resistor element Ra is configured such that a resistor  2  is provided between lead electrodes  7  formed so as to extend on two ends of a main surface of the insulating substrate  4  and on sides of the insulating substrate  4 . In the second embodiment, the resistor element Ra is provided with the resistor  2  facing downward, similarly to the resistor element R in the first embodiment. 
     Because the lead electrodes  7  extend on the sides of the insulating substrate  4 , the resistor element Ra has a large area of connection between the lead electrodes  7  and terminals  53  and  54 , and a solder filet is formed. Accordingly, the soldering strength increases and the reliability improves. 
     Referring to FIG. 7, a lumped-constant isolator  1   b  according to a third embodiment of the present invention is obtained such that a resistor element Rb is used instead of the resistor element R in the first embodiment. The resistor element Rb is formed such that a resistor  2  is provided between lead electrodes  8  so as to extend from two ends of one main surface of the insulating substrate  4  to the other main surface opposite to the main surface. In the third embodiment, the resistor element Rb is provided with the resistor  2  facing upward, in reverse to a case where the resistor R is provided in the first embodiment. 
     Because the load electrodes  8  extend to the other main surface via the sides of the insulating substrate  4 , the resistor element Rb has as large area of connection between the lead electrodes  8  and the terminals  53  and  54 , and a solder filet is formed. Accordingly, the soldering strength increases and the reliability improves. 
     A mobile phone  120  as a communication apparatus according to a fourth embodiment of the present invention is described below with reference to FIG.  8 . 
     FIG. 8 is an electric circuit block diagram showing the RF part of the mobile phone  120  in FIG.  8 . The RF part includes an antenna device  122 , a duplexer  123 , a transmitting isolator  131 , a transmitting amplifier  132 , a transmitting interstage band-pass filter  133 , a transmitting mixer  134 , a receiving amplifier  135 , a receiving interstage band-pass filter  136 , a receiving mixer  137 , a voltage-controlled oscillator (VCO)  138 , and a local band-pass filter  139 . 
     Each of the lumped-constant isolators  1  to  1   b  according to the first to third embodiments may be used as the transmitting isolator  131 . By mounting each of the lumped-constant isolators  1  to  1   b , a thin mobile phone having suppressed insertion loss and high reliability is achieved. 
     A lumped-constant isolator and a communication apparatus of the present invention are not limited to the foregoing embodiments, but may be variously modified within the gist of the present invention. 
     By way of example, in the resistor elements Rd and Rb shown in FIGS. 6 and 7, the lead electrodes  7  and  8  do not need to be provided on both ends. On either end, the lead electrode  3  of the resistor element R shown in FIG. 3 may be used. 
     The present invention can be applied not only to isolators to which a three-port isolator is applied, but also to isolators in which a resistor is connected to a gyrator having two central electrodes. In the present invention, the central electrodes can be formed not only by stamping a predetermined shape from a metal sheet and bending it, but also by providing a pattern electrode on a substrate such as a dielectric substrate, a magnetic substrate, or a laminated substrate. The three central electrodes do not always need to be arranged so as to cross at 120 degrees with respect to one another, but may be arranged so as to cross at an angle of 110 to 140 degrees with respect to one another. The metal case does not need to be divided as in the foregoing embodiments. The metal case may be divided into three or more portions.