Abstract:
An impedance matching circuit is provided. The present impedance matching circuit is able to match impedance using a transformer which is arranged inside a dielectric substrate and arranged to overlap with a bonding pad area and an end of a transmission line, thereby enabling transmitting signals at a desired frequency with a minimum insertion loss without using a very thin transmission line which is several to dozens of μm wide or specially designed antennas in order to compensate for inductance. Thus, the present impedance matching circuit may be applied to various millimeter bands.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Methods and apparatuses consistent with the exemplary embodiments relate to an impedance matching circuit, and more particularly, to a bonding wire impedance matching circuit which matches impedance in a case where bonding wire is connected with another circuit. 
         [0003]    2. Background Art 
         [0004]    In millimeter bands, since wavelengths are very short, severe transmission loss may occur even by a small mismatched condition. Especially, bonding wire used between various chips such as transceivers etc. cause severe transmission loss. This is transmission loss due to an impedance mismatch caused by an inductance component of bonding wire which is relatively big in proportion to the wavelength of millimeter frequency broadband, which must be compensated by an impedance matching method to prevent performance degradation. 
         [0005]    In a case of an existing millimeter band matching method, most of the designing were made using LC transmission lines. However, embodying such methods require very thin transmission lines of several to dozens of μm, which is difficult to embody in an actual passive environment. 
         [0006]    The conventional matching methods using general LC transmission lines is the most widely used method in impedance compensation circuits regarding bonding wire. However, if the bonding wire becomes longer to hundreds of μm, the impedance (Lp) required in the actual impedance compensation circuit becomes greater, which means that very thin transmission lines of several to dozens of μm must be used. This means makes embodying transmission lines very difficult, considering the line width limitations (50 μm) in an actual LTCC process. 
         [0007]    In order to compensate this problem, researches have been conducted to design impedance of antennas to match the impedance of bonding wire. However, a problem with this method is that it is difficult to apply to cases where the circuits behind chips are transmission lines and not antennas. 
         [0008]    More specifically, researches have been made for methods of compensating chip compensation circuits with input impedance of passive devices such as antennas. This is a method of compensating the inductance of bonding-wire through the input impedance of antennas when designing the antennas, and since it can minimize the matching circuit and thereby minimize the RF system, this method is widely applied to integrations between antennas and chips. However, a problem with this method is that it is difficult to apply to cases where, on circuits behind chips, chips or other transmission lines are arranged instead of antennas. 
         [0009]    As such, conventional impedance matching methods have problems. Accordingly, there is a need to seek a bonding wire impedance matching method applicable to various millimeter bands. 
       SUMMARY OF THE INVENTION 
       [0010]    The present disclosure has been presented to resolve the aforementioned problems, and the purpose of the present disclosure is to provide an impedance matching circuit which matches impedance using a transformer which is arranged inside a dielectric substrate, and is arranged to overlap with a bonding pad area and an end area of a transmission line. 
         [0011]    According to an exemplary embodiment of the present disclosure, there is provided an impedance matching circuit which includes a dielectric substrate; a ground arranged on a lower surface of the dielectric substrate; a first pad which is arranged on an upper surface of the dielectric substrate, and to which bonding wires is connected; a transmission line which is arranged on an upper surface of the dielectric substrate, and of which an end is arranged by a certain distance from the first pad; and a second pad which is arranged inside the dielectric substrate, and is arranged to overlap with the first pad area and one end area of the transmission line. 
         [0012]    In addition, the second pad may be λ g /4 transformer λ g  being a wavelength of a transmission signal). 
         [0013]    Furthermore, a distance between the first pad area and the one end area of the transmission line may be λ g /4, and the area of the second pad overlapping with the first pad area and the one end of the transmission line may be λ g /4 long. 
         [0014]    In addition, the second pad may have a square pad shape of a length of λ g /4. 
         [0015]    Furthermore, the transmission line may be a micro-strip line, and may have a line width of 50 μm or more. 
         [0016]    In addition, the second pad may generate a series capacitance component with the first pad, generate a parallel capacitance component with the ground, and generate a series capacitance component with an end of the transmission line. 
         [0017]    Furthermore, the first pad, second pad, and one end of the transmission line may form an LC resonation circuit. 
         [0018]    In addition, the impedance matching circuit may be produced on a substrate using an LTCC (Low-Temperature Confired Ceramic) method. 
         [0019]    According to various exemplary embodiments of the present disclosure, it becomes possible to provide an impedance matching circuit which matches impedance using a transformer which is arranged inside a dielectric substrate, and is arranged to overlap with a bonding pad area and an end area of a transmission line, thereby enabling transmitting signals at a desired frequency with a minimum insertion loss without using a very thin transmission line which is several to dozens of μm wide or specially designed antennas in order to compensate for inductance. Thus, the present impedance matching circuit may be applied to various millimeter bands. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The above and/or other aspects of the present disclosure will be more apparent by describing certain present disclosure with reference to the accompanying drawings, in which: 
           [0021]      FIG. 1  is a plane view and side view illustrating a structure of an impedance matching circuit, according to an exemplary embodiment of the present disclosure; 
           [0022]      FIGS. 2A and 2B  are views illustrating an equivalent circuit of the impedance matching circuit of  FIG. 1 , according to an exemplary embodiment of the present disclosure; and 
           [0023]      FIG. 3  is a simulation graph of a transmission loss in a case of applying an impedance matching circuit  100  and in a case of not applying the impedance matching circuit  100 . 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Certain exemplary embodiments are described in higher detail below with reference to the accompanying drawings. 
         [0025]    In the following description, like drawing reference numerals are used for the like elements, even in different drawings. The matters defined in the description, such as detailed construction and elements, are provided to assist in a comprehensive understanding of exemplary embodiments. However, exemplary embodiments can be practiced without those specifically defined matters. Also, well-known functions or constructions are not described in detail since they would obscure the application with unnecessary detail. 
         [0026]      FIG. 1  is a plane view and side view illustrating a structure of an impedance matching circuit  100 , according to an exemplary embodiment of the present disclosure. As illustrated in  FIG. 1 , the impedance matching circuit  100  includes a first pad  110 , transmission line  120 , second pad  130 , dielectric substrate  140 , and its ground  150 . 
         [0027]    The first pad  110  is arranged on an upper surface of the dielectric substrate  140 , and a bonding wire  110  is connected to the first pad  110 . The bonding wire  115  connects a chip such as an antennae or transceiver etc. with another chip or a transmission line. In addition, the first pad  110  is a bonding pad which is an area connected to the bonding wire  115 . 
         [0028]    The transmission line  120  is arranged on an upper surface of the dielectric substrate  140 , and an end is arranged by a certain distance from the first pad  110 . The transmission line  120  is connected to another circuit or a chip and transmits a signal. One end of the transmission line  120  is distanced by a certain distance from the first pad  110 , and the certain distance is λ g /4. 
         [0029]    Herein, λ g  is a wavelength (wavelength where dielectric ratio of the dielectric is reflected) of a signal transmitted in the dielectric substrate  140 . For example, in a case where a transmission signal is 60 GHz, λ g  is 1-2 mm. More specifically, the impedance matching circuit  100  is produced on a substrate using an LTCC (Low-Temperature Confired Ceramic) method, and the transmission line  120  is a micro-strip line, and the line width may be 50 μm or more. 
         [0030]    The second pad  130  is arranged inside the dielectric substrate  130 , and is arranged to overlap with the first pad  110  and an end area of the transmission line  120 . The second pad  130  is a conductor, and performs a function of a λ g /4 transformer (λ g  being a wavelength of the transmission line). 
         [0031]    Herein, as illustrated in  FIG. 1 , the second pad  130  is arranged to be distanced by a certain distance up and low between the first pad  110  and one end area of the transmission line  120  and the dielectric substrate  140 . In addition, the second pad  130  is arranged to be distanced by a certain distance from a ground  150  between the dielectric substrate  140 . By such an arrangement, the second pad  130  performs a λ g /4 transformer function. 
         [0032]    More specifically, the area of the one end of the second pad  130  which overlaps with the first pad  110  area and transmission line  120  may be λ g /4 long, and may have a square pad shape of λ g /4 long. However, the shape of the second pad  130  is not limited thereto, and thus any pad may be used if only it is arranged in such a manner that it overlaps with the first pad  110  area and one end area of the transmission line  120 . 
         [0033]    As such, the second pad  130  generates a series capacitance with the first pad  100  area, generates a series capacitance with the area where it overlaps with the one end of the transmission line, and generates a parallel capacitance with the ground  150 . In such a series capacitance component, the second pad  130  λ g /4 long operates in λ g /4 transformer, and in the first pad  110 , the second pad  130  appears to be a parallel inductance. Through the aforementioned, the first pad  110 , second pad  130 , and one end of the transmission line  120  form an LC resonation circuit. 
         [0034]    The dielectric substrate  140  becomes a basis for a circuit substrate where the impedance circuit  100  is arranged. As illustrated in  FIG. 1 , on the upper surface of the dielectric substrate  140 , circuits are arranged, and especially the first pad  110  and transmission line  120  are arranged. In addition, inside (or in a mid layer) the dielectric substrate  140 , the second pad  130  is arranged. Furthermore, on a lower surface of the dielectric substrate  140 , the ground  150  is arranged. 
         [0035]    The impedance matching circuit  100  of such a structure matches the impedance between the bonding wire  1150  connected to the first pad  110  and the transmission line  120 , enabling transceiving signals of desired frequency with a minimum insertion loss, being applicable to various millimeter bands. 
         [0036]      FIGS. 2A and 2B  are views illustrating an equivalent circuit of the impedance matching circuit  100  of  FIG. 1 . 
         [0037]    As illustrated in  FIG. 2A , the impedance matching circuit  100  may be expressed as an equivalent circuit  200 . The equivalent circuit  200  is formed by Cpad  210  which is a series capacitance by the first pad  110 , L bw    215  which is an inductance by the bonding wire  115 , a series capacitance C MS    220  by the transmission line  120 , C square    230  which is a parallel capacitance by the second pad  130 , and λ g /4 transformer  235  by the second pad  130 . In addition, as illustrated in  FIG. 2B , C MS    220  and λ g /4 transformer  235  are operated by the parallel inductance of L MS    320 . 
         [0038]    As such, according to the equivalent circuit  200 , the first pad  110 , second pad  130 , and one end of the transmission line  120  form an LC resonation circuit. 
         [0039]      FIG. 3  is a simulation graph of a transmission loss in a case of applying an impedance matching circuit  100  and in a case of not applying the impedance matching circuit  100 .  FIG. 3  shows the transmission characteristics in a case of actually embodying the impedance matching circuit  100  according to an exemplary embodiment of the present disclosure. The frequency band has been designed to be 60 GHz, and the bonding wire  115  used is about 500 μm long. 
         [0040]    As illustrated in  FIG. 3 , compared to when the impedance matching circuit  100  is not applied, when the impedance matching circuit  100  is applied, the transmission loss by the bonding wire  115  is perfectly corrected in the central frequency 60 GHz. 
         [0041]    Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.