Abstract:
This invention discloses a laminated balun transformer realized by a structure with three λ/4 strip lines for converting an unbalanced signal in an unbalanced transmission line into a balanced signal in a balanced transmission line. Disclosed is a laminated balun transformer comprising a first dielectric sheet on which a first strip line is provided, a second dielectric sheet placed under the first dielectric sheet and on which a second strip line electro-magnetically coupled to the first strip line is provided, a third dielectric sheet placed under the second dielectric sheet and on which a ground pattern is provided, and a fourth dielectric sheet placed under the third dielectric sheet and on which a third strip line is provided. The laminated balun transformer in accordance with the present invention includes the reduced number of strip lines in comparison with the convention laminated balun transformer, so that the production cost thereof is reduced.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a laminated balun transformer, more particularly to a laminated balun transformer realized by a structure including three λ/4 strip lines, thereby reducing a size thereof.  
           [0003]    2. Description of the Related Art  
           [0004]    “Balun” stands for BALanced to UNbalanced. A balun transformer is a balanced-unbalanced signal converter for converting a balanced signal in a balanced transmission line into an unbalanced signal in an unbalanced transmission line and vice versa.  
           [0005]    Such balun transformer is used for connecting a component such as a mixer and a Surface Acoustic Wave (SAW) filter using balanced signals, which are widely used in wireless signal processing units, and a component such as an amplifier using unbalanced signals.  
           [0006]    A balun transformer is usually implemented by combining a plurality of distribution constant transmission lines or concentrated constant transmission lines. Further, the balun transformer can by realized by resonance waveguides when the balun transformer is applied in the antenna field.  
           [0007]    U.S. Pat. No. 6,285,273 issued to Takehiko Morikawa and titled “Laminated Balun Transformer” discloses a conventional laminated balun transformer comprising a plurality of strip lines vertically stacked.  
           [0008]    With reference to FIG. 7 and FIG. 8, a conventional laminated balun transformer  101  comprises four dielectric sheets  102   c ,  102   d ,  102   f ,  102   g  on which four strip lines  104 ,  105 ,  108 ,  109  are provided, respectively, three dielectric sheets  102   a ,  102   e ,  102   h  on which ground electrodes  112 ,  113 ,  114  are provided, respectively, and a dielectric sheet  102   b  on which a lead electrode  103  is provided.  
           [0009]    Of a first, second, third and fourth strip lines  105 ,  106 ,  108 ,  109 , the first and second strip lines  105 ,  106 , and the third and fourth strip lines  107 ,  108  are electro-magnetically coupled together to form two pairs of electro-magnetically coupled strip lines. The second and third strip lines  106 ,  108  are electrically connected to a ground electrode  113  at respective ends  120   b ,  108   b  thereof through a via hole.  
           [0010]    All the ground electrodes  112 ,  113 ,  114  are connected to all the external electrodes  125 ,  129 ,  132  in common. The first strip line  104  is connected to an external electrode  131  through the lead electrode  103  at an end thereof, and further connected to an external electrode  128  at the other end thereof. The strip lines  105 ,  108  are connected to the ground electrode  113  at an end thereof and connected to external electrodes  127 ,  126 , respectively at the other ends thereof. The fourth strip line  109  is connected to the external electrode  128  at an end thereof, and is opened at the other end thereof. That is, the first strip line  104  and the fourth strip line  109  are electrically connected to each other through the external electrode  128 .  
           [0011]    The external electrodes  125 ,  129  and  132  serve as ground electrodes, the external electrodes  126 ,  127  serve as output terminals for balanced signals, and the external electrode  31  serves as an input terminal for an unbalanced signal.  
           [0012]    [0012]FIG. 9 illustrates an electric equivalent circuit diagram of the laminated balun transformer shown in FIGS. 7 and 8.  
           [0013]    The conventional laminated balun transformer with reference to FIGS.  7  to  9  are realized by using four λ/4 strip lines and two couplers, so that a large number of external electrodes are needed, and a configuration and structure of the laminated balun transformer are complicated.  
         SUMMARY OF THE INVENTION  
         [0014]    Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a laminated balun transformer for converting an unbalanced signal line in an unbalanced transmission line into a balanced signal, the laminated balun transformer being realized by a structure including three λ/4 strip lines.  
           [0015]    In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a laminated balun transformer comprising: a first dielectric sheet on a surface of which a first strip line is provided; a second dielectric sheet placed under the first dielectric sheet and on a surface of which a second strip line electro-magnetically coupled to the first strip line is provided; a third dielectric sheet placed under the second dielectric sheet and on a surface of which a ground pattern is provided; and a fourth dielectric sheet placed under the third dielectric sheet and on a surface of which a third strip line is provided.  
           [0016]    Preferably, the laminated balun transformer further comprises an external connection electrode formed on an external surface of a body forming the laminated balun transformer, wherein the second strip line and the third strip line are electrically connected to each other through the external connection electrode.  
           [0017]    Preferably, the laminated balun transformer further comprises an unbalanced signal input electrode, a first and second balanced signal output electrodes and a ground electrode formed on corresponding external surfaces of a body forming the laminated balun transformer, wherein the first strip line is connected to the ground electrode at an end thereof and connected to the unbalanced signal input electrode at the other end thereof, and the first and second strip lines electrically connected to each other have respective ends which are connected to the first and second balanced signal output electrodes, respectively.  
           [0018]    Preferably, the laminated balun transformer further comprises: a fifth dielectric sheet on which a first lead electrode for connecting the first strip line to the unbalanced signal input electrode is provided; a sixth dielectric sheet on which a second lead electrode for connecting the second strip line to the first balanced signal output electrode is provided; and a seventh dielectric sheet on which a third lead electrode for connecting the third strip line to the second balanced signal output electrode is provided.  
           [0019]    Preferably, the laminated balun transformer further comprises an eighth and a ninth dielectric sheets serving as an uppermost layer and a lowermost layer, respectively, and on which respective ground electrodes are provided.  
           [0020]    In accordance with another aspect of the present invention, there is provided with a laminated balun transformer comprising: an unbalanced signal electrode through which an unbalanced signal is input and output; a first and second balanced signal electrodes through which a first and second balanced signals are input and output; a ground electrode connected to ground voltage; a first dielectric sheet on which a first strip line is provided, the first strip line having an end connected to the unbalanced signal electrode and the other end connected to the first strip line; and a second dielectric sheet on which a second and a third strip lines is provided, the second and third strip lines having respective first ends connected to each other and respective second ends connected to the first and second balanced signal electrodes, respectively, wherein one strip line of the second and third strip lines is partially overlapped with the first strip line. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0022]    [0022]FIG. 1 illustrates a perspective view of a laminated balun transformer showing an external form thereof in accordance with a preferred embodiment of the present invention;  
         [0023]    [0023]FIG. 2 illustrates an exploded, perspective view showing an internal structure of a laminated balun transformer in accordance with the preferred embodiment of the present invention;  
         [0024]    [0024]FIG. 3 is an electric equivalent circuit diagram of a laminated balun transformer in accordance with the preferred embodiment of the present invention;  
         [0025]    [0025]FIG. 4 is an exploded, perspective view of a laminated balun transformer in accordance with an alternative embodiment of the present invention;  
         [0026]    [0026]FIG. 5 illustrates a perspective view of a laminated balun transformer showing an external form thereof in accordance with the alternative embodiment of the present invention;  
         [0027]    [0027]FIG. 6 illustrates an electric equivalent circuit diagram of a laminated balun transformer in accordance with the alternative embodiment of the present invention;  
         [0028]    [0028]FIG. 7 illustrates an exploded, perspective view of a laminated balun transformer in accordance with a prior art;  
         [0029]    [0029]FIG. 8 illustrates a perspective view of a laminated balun transformer in accordance with the prior art; and  
         [0030]    [0030]FIG. 9 illustrates an electric equivalent circuit diagram of a laminated balun transformer in accordance with the prior art. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    A detailed description of a laminated balun transformer in accordance with preferred embodiments of the present invention will be given below with reference to the accompanying drawings.  
         [0032]    [0032]FIG. 1 illustrates a perspective view of a laminated balun transformer in accordance with a preferred embodiment of the present invention.  
         [0033]    Referring to FIG. 1, a laminated balun transformer  1  in accordance with the first embodiment of the present invention comprises a dielectric block  2  having a hexahedral shape, or a cube shape, unbalanced signal input electrode  2   a , a first and second balanced signal output electrodes  2   c ,  2   f , and a non-contact (NC) electrode  2   d  which are formed on corresponding external side surfaces of the dielectric block  2 .  
         [0034]    The dielectric block  2  is comprised of a plurality of dielectric sheets sequentially stacked.  
         [0035]    Referring to FIG. 2, the laminated balun transformer  1  comprises a first dielectric sheet  24  on which a first strip line  51  is provided, a second dielectric sheet  26  on which a second strip line  52  is provided and which is arranged in parallel with the first dielectric sheet  24  on or under the first dielectric sheet  24 , a third dielectric sheet  27  on which a ground electrode  32  is provided, and a fourth dielectric sheet  29  on which a third strip line  27  is provided and which is electro-magnetically separated from the first and second dielectric sheet  24 ,  26  by the third dielectric sheet  27 .  
         [0036]    The dielectric sheets  24 ,  26 ,  27 ,  29  may be sequentially stacked in order of the first dielectric sheet  24 , the second dielectric sheet  26 , the third dielectric sheet  27  and the fourth dielectric sheet  29 , and may be stacked in order of the second dielectric sheet  26 , the first dielectric sheet  24 , the third dielectric sheet  27  and the fourth dielectric sheet  29 .  
         [0037]    That is, the third dielectric sheet  27  having the ground electrode  32  thereon is interposed between the first and second dielectric sheets  24 ,  26  and the fourth dielectric sheet  27 , so as for the fourth dielectric sheet  27  to be electro-magnetically separated from the first and the second dielectric sheets  24 ,  26 .  
         [0038]    The laminated balun transformer with reference to FIG. 1 further comprises a fifth, a sixth and a seventh dielectric sheets  23 ,  25 ,  28  on which lead electrodes  41 ,  42 ,  43  are provided, respectively. The lead electrodes  41 ,  42 ,  43  connect the respective first, second and third strip lines  51 ,  52 ,  53  to corresponding external electrodes  2   a ,  2   c ,  2   d ,  2   f.    
         [0039]    The first lead electrode  41  is connected to the NC electrode  2   d  at a first end  41   a  thereof and connected to the first strip line  51  at a second end  41   b  thereof through a via hole  41   c  formed at a second end  51   b  of the first strip line  51 , thereby connecting the first strip line  51  to the NC electrode  2   d.    
         [0040]    The second lead electrode  42  is connected to the unbalanced signal input electrode  2   a  at a first end  42   a  thereof and connected to a second end  52   b  of the second strip line  52  at a second end  42   b  thereof through a via hole  42   c , thereby transferring an unbalanced signal input from the unbalanced signal input electrode  2   a  to the second strip line  52 .  
         [0041]    The third lead electrode  43  is connected to the first balanced signal output electrode  2   c  at a first end  43   a  thereof and connected to a first end  53   a  of the third strip line  53  at a second end  43   b  thereof through a via hole  43   c , thereby transferring a first balanced signal generated at a second end  53   b  of the third strip line  53  to the first balanced signal output electrode  2   c.    
         [0042]    Further, the first strip line  51  is directly connected to the second balanced signal output electrode  2   f  at a first end  51   a  thereof, the second strip line  52  is directly connected to the ground electrode at a first end  52   a  thereof, and the third strip line is directly connected to the NC electrode  2   d  at a second electrode  53   b  thereof.  
         [0043]    The laminated balun transformer  1  in accordance with the preferred embodiment of the present invention further comprises an eighth and a ninth dielectric sheets  22 ,  3 Q, each having respective ground electrodes  31 ,  33  on a surface of an internal part thereof.  
         [0044]    Further, in the case of modifying patterns of the first, second and third strip lines  51 ,  52  and  53 , the first, second and third strip lines  51 ,  52  and  53  can be connected to the corresponding external electrodes  2   a ,  2   b ,  2   c ,  2   d ,  2   e  and  2   f  without using the lead electrodes  41 ,  42  and  43 .  
         [0045]    [0045]FIG. 3 illustrates an electric equivalent circuit diagram corresponding to the laminated balun transformer  1  shown in FIG. 2.  
         [0046]    The operation of the circuit shown in FIG. 3 will be described below.  
         [0047]    When an unbalanced signal having a certain frequency is applied to the unbalanced signal input electrode  2   d  of the laminated balun transformer  1 , the unbalanced signal is induced to the first strip line  51  electro-magnetically coupled to the second strip line  52 , the signal induced to the first strip line  51  is transferred to the third strip line  53  through the NC electrode  2   d , and then the signal transferred to the third strip line  53  is output through the first and second balanced output electrodes  2   c ,  2   f  in a from of a signal having the same frequency as the unbalanced signal but having a different phase from the unbalanced signal.  
         [0048]    In accordance with the present invention, the first and second strip lines  51 ,  52  can be formed on the same dielectric sheet. In such case, the ground electrode  32  for decoupling the first and second strip lines  51 ,  51  from the third strip line  53  is not necessary, so that a structure of the laminated balun transformer may be further simplified.  
         [0049]    [0049]FIG. 4 illustrates an exploded view and a perspective view of a laminated balun transformer in accordance with an alternative embodiment of the present invention, and FIG. 6 illustrates an electric equivalent circuit diagram of the laminated balun transformer in accordance with the alternative embodiment of the present invention.  
         [0050]    Referring to FIG. 4 to FIG. 6, a laminated balun transformer  61  in accordance with the alternative embodiment of the present invention comprises a dielectric block  62  having a hexahedral shape, unbalanced signal input electrode  71   a , a first and second balanced signal output electrodes  71   b ,  71   c , and ground electrodes  71   d ,  71   e ,  71   f  which are formed on corresponding external surfaces of the dielectric block  62 .  
         [0051]    As shown in FIG. 4, the dielectric block  62  is comprised of a dielectric sheet  62   a  which is the uppermost layer of the dielectric block  62  and has a certain thickness, a dielectric sheet  62   b  placed under the dielectric sheet  62   a  and having a ground pattern  63  thereon, which is connected to the ground electrodes  71   d ,  71   e ,  71   f , a dielectric sheet  62   d  placed under the dielectric sheet  62   b  and having a first strip line  65  thereon, which has a first end connected to the ground electrodes  71   d ,  71   e ,  71   f  and a second end connected to the unbalanced signal electrode  71   a . The dielectric block  62  further comprises a dielectric sheet  62   e  placed under the dielectric sheet  62   d  and being provided thereon with a second strip line  66  arranged in parallel with the first strip line  65  and connected to the first balanced signal electrode  71   b  at an end thereof and a third strip line  67  connected to the other end of the second strip line  66  and the second balanced signal electrode  71   c . The dielectric block  62  further comprises a dielectric sheet  62   g  placed under the dielectric  62   e  and on which a ground pattern  70  connected to the ground electrodes  71   d ,  71   e ,  71   f  is provided, and a dielectric sheet  62   b  placed under the dielectric sheet  62   g  and having a certain thickness.  
         [0052]    The dielectric block  62  may further comprise a dielectric sheet  62   c  on which a lead electrode  64  for connecting an end of the first strip line  65  to the unbalanced signal electrode  71   a  is provided, and a dielectric sheet  62   f  on which lead electrodes  68 ,  69  for connecting the second and third strip lines  66 ,  67  to the first and second balanced signal electrodes  71   b ,  71   c , respectively, are provided.  
         [0053]    In the laminated balun transformer shown in FIG. 4, the first strip line  65  and the second strip line  66  correspond to the second strip line  52  and the first strip line  51  in the laminated balun transformer shown in FIG. 2, respectively.  
         [0054]    In the same manner as the laminated balun transformer shown in FIG. 2, the laminated balun transformer with reference to FIG. 4 includes only three λ/4 strip lines  65 ,  66 ,  67  instead of four λ/4 strip lines, so that the laminated balun transformer in accordance with the alternative embodiment of the present invention may be produced by a simpler fabrication process than the conventional laminated balun transformer.  
         [0055]    Further, in accordance with the alternative embodiment of the present invention, since the second and third strip lines  66 ,  67  are formed on the same dielectric sheet  62   c , the total thickness of the laminated balun transformer is reduced, so that the laminated balun transformer in accordance with the alternative embodiment of the present invention is advantageous in terms of thinness.  
         [0056]    As described above, the laminated balun transformer in accordance with the present invention is realized by a structure including three λ/4 strip lines, thereby being advantageous in terms of easy design thereof.  
         [0057]    Further, since the laminated balun transformer in accordance with the present invention is realized by three λ/4 strip lines, it is advantageous in terms of miniaturization and thinness, which are required properties for advanced radio frequency (RF) components.  
         [0058]    Further, since the laminated balun transformer in accordance with the present invention is realized by a coupler and an independent λ/4 strip line, the laminated balun transformer in accordance with the present invention is advantageous in that it is less susceptible to malfunctions caused by a misalignment during a fabrication thereof, in comparison with the conventional laminated balun transformer having two couplers.  
         [0059]    Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.