Abstract:
Disclosed is a balun including a film bulk acoustic resonator (FBAR). The balun may be implemented using the FBAR to fabricate a small sized balun. Also, the balun may be implemented using the FBAR, thereby reducing a difference in two outputs.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2009-0102540, filed on Oct. 28, 2009, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes. 
     BACKGROUND 
     1. Field 
     The following description relates to a balun, and more particularly, to a balun including a film bulk acoustic resonator (FBAR) that may convert a balanced signal into an unbalanced signal, and/or convert an unbalanced signal into a balanced signal. 
     2. Description of Related Art 
     A balun may be used as a circuit/structure that may convert balanced signals into unbalanced signals or unbalanced signals into balanced signals. The balun may include a passive element that may operate even when an input and an output are reversed. 
     A conventional balun is fabricated to include a plurality of transistors, or using a wavelength of a signal on a single plane. The conventional balun is a part of a parallel type circuit such as a mixer, an amplifier, a multiplier, a phase shifter, and the like, and is generally implemented using a Lange coupler or an interdigital coupling. 
     However, the size of the balun using the wavelength of the signal plane may be significantly great. Also, a balun including a plurality of transistors may have a large difference between two outputs, and a supplementary circuit may need to be inserted in the balun to correct the difference between outputs. In addition, the power consumption of the conventional balun is relatively great due to the plurality of transistors, and the yield of the circuit may be reduced by such power consumption. Accordingly, these two types of baluns may cause a reduction in a degree of integration of a semiconductor, and therefore may not be readily implemented in an integrated circuit. 
     SUMMARY OF THE INVENTION 
     In one general aspect, there is provided, a balun including two conversion units to control the phase of an input signal, the two conversion units including at least one film bulk acoustic resonator (FBAR) and at least one passive element that is connected with the at least one FBAR. 
     At least one of the two conversion units may include two FBARs connected to a ground, and the passive element may be located between the two FBARs. 
     At least one of the two conversion units may include two passive elements connected to a ground, and the FBAR may be located between the two passive elements. 
     At least one of the two conversion units may include two FBARs, and the passive element may be located between the two FBARs and connected to a ground. 
     At least one of the two conversion units may include two passive elements, and the FBAR may be located between the two passive elements and may be connected to a ground. 
     The passive element may be at least one of a capacitor and an inductor. 
     The FBAR may be at least one of a bulk acoustic wave resonator (BAWR) and a thin film bulk acoustic resonator (TFBAR). 
     The FBAR may be connected in series with a capacitor to change a frequency response characteristic. 
     The FBAR may be connected in parallel with a capacitor to change a frequency response characteristic. 
     The FBAR may be connected in series with an inductor to change a frequency response characteristic. 
     The FBAR may be connected in parallel with an inductor to change a frequency response characteristic. 
     In another aspect, there is provided a balun including two conversion units to control the phase of an input signal, the two conversion units including a first FBAR connected to a ground, a second FBAR connected to the ground, and a third FBAR located between the first FBAR and the second FBAR. 
     In another aspect, there is provided a balun including two conversion units to control the phase of an input signal, the two conversion units including a first FBAR, a second FBAR, and a third FBAR located between the first FBAR and the second FBAR, the third FBAR also being connected to a ground. 
     Other features and aspects may be apparent from the following description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an example of a balun. 
         FIGS. 2 through 11  are diagrams illustrating examples of a conversion unit. 
         FIGS. 12 through 15  are diagrams illustrating examples of a film bulk acoustic resonator (FBAR). 
         FIG. 16  is a diagram illustrating another example of a conversion unit. 
     
    
    
     Throughout the drawings and the description, unless otherwise described, the same drawing reference numerals should be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein may be suggested to those of ordinary skill in the art. The progression of processing steps and/or operations described is an example; however, the sequence of steps and/or operations is not limited to that set forth herein and may be changed as is known in the art, with the exception of steps and/or operations necessarily occurring in a certain order. Also, description of well-known functions and constructions may be omitted for increased clarity and conciseness. 
       FIG. 1  illustrates an example of a balun. 
     Referring to  FIG. 1 , balun  100  includes two conversion units  110 . Each conversion unit  110  includes a film bulk acoustic resonator (FBAR)  120  and a passive element  130  connected with the FBAR. 
     The balun  100  may receive as an input a signal via a first port  101 . 
     The conversion unit  110  may include at least one FBAR  120  and at least one passive element  130  connected with the at least one FBAR  120 . However, it should be understood that the conversion unit  110  may include more than one FBAR  120  and/or more than one passive element  130 . 
     The conversion unit  110  may control a phase of the inputted signal via the first port  101 . According to various embodiments, the conversion unit  110  may convert the inputted signal into a signal having the same amplitude as that of the inputted signal. For example, the conversion unit  110  may convert the inputted signal into a signal having a phase difference of 90 degrees between the phase of the inputted signal and a phase of the current signal, while at the same time having the same amplitude. 
     The passive element  130  may be, for example, a capacitor and/or an inductor. The FBAR  120  may be, for example, a bulk acoustic wave resonator (BAWR), a thin film bulk acoustic resonator (TFBAR), and the like. 
     The signal converted by the conversion unit  110  may be outputted via a second port  102  and/or a third port  103 . For example, the conversion unit  110  may convert the inputted signal via the first port  101 , such that the difference between the phase of the outputted signal via the second port  102  and the phase of the outputted signal via the third port  103  is 180 degrees. 
       FIGS. 2 through 11  illustrate various examples of a conversion unit. 
     Referring to  FIG. 2 , conversion unit  200  includes a first FBAR  210 , a second FBAR  220 , and a third FBAR  230 . A balun may include two conversion units to control a phase of an input signal, wherein each of the two conversion units are configured the same as the conversion unit  200 . In this example, the third FBAR  230  is located between the first FBAR  210  and the second FBAR  220 , and the third FBAR  230  may also be connected with a ground. 
     In this example, the conversion unit  200  includes the three FBARs  210 ,  220 , and  230  that are configured in a T-shape. 
     Referring to  FIG. 3 , the conversion unit  300  may be used to control the phase of an input signal and includes a first FBAR  310  connected with a ground, a second FBAR  320  connected with the ground, and a third FBAR  330  located between the first FBAR  310  and the second FBAR  320 . A balun may include two conversion units to control a phase of an input signal, wherein each of the two conversion units are the same as the conversion unit  300 . 
     In this example, the conversion unit  300  includes the three FBARs  310 ,  320 , and  330  that are configured in the shape of a π symbol. 
     Accordingly, the balun may include two conversion units to control the phase of the input signal, and any one of the two conversion units may include two FBARs and a passive element. For example, the passive element may be located between the two FBARs, and connected with a ground. 
     Referring to  FIG. 4 , conversion unit  400  includes two FBARs  410  and a capacitor  420 . In this example, the capacitor  420  is located between the two FBARs  410 , and connected with a ground. Also in this example, the conversion unit  400  includes the two FBARs  410  and the capacitor  420  that are configured in a T-shape. 
     Referring to  FIG. 5 , conversion unit  500  includes two FBARs  510  and an inductor  520 . For example, the inductor  520  may be located between the two FBARs  510 , and connected with a ground. In this example, the conversion unit  500  includes the two FBARs  510  and the inductor  520  that are configured in a T-shape. 
     Accordingly, the balun may include two conversion units to control a phase of an input signal, and any one of the two conversion units may include two passive elements and an FBAR. For example, the FBAR may be located between the two passive elements and connected with a ground. 
     Referring to  FIG. 6 , conversion unit  600  includes two capacitors  610  and an FBAR  620  located between the two capacitors  610  and connected with a ground. In this example, the conversion unit  600  includes the two capacitors  610  and the FBAR  620  and that are configured in a T-shape. 
     Referring to  FIG. 7 , conversion unit  700  includes two inductors  710  and an FBAR  720 . For example, the FBAR  720  may be located between the two inductors  710  and connected with a ground. In this example, the conversion unit  700  includes the two inductors  710  and the FBAR  720  that are configured in a T-shape. 
     According to various aspects, the balun may include two conversion units to control the phase of an input signal, and, as is further discussed herein, any one of the two conversion units may include two FBARs and a passive element. For example, the two FBARs may be connected with a ground, and the passive element may be located between the two FBARs as shown in the examples of  FIGS. 8 and 9 . 
     Referring to  FIG. 8 , conversion unit  800  includes two FBARs  810  and a capacitor  820 . For example, the two FBARs  810  may be connected with a ground, and the capacitor  820  may be located between the two FBARs  810 . In this example, the conversion unit  800  includes the two FBARs  810  and the capacitor  820  configured in the shape of a π symbol. 
     Referring to  FIG. 9 , conversion unit  900  includes two FBARs  910  and an inductor  920 . For example, the two FBARs  910  may be connected with a ground, and the inductor  920  may be located between the two FBARs  910 . In this example, the conversion unit  900  includes the two FBARs  910  and the inductor  920  configured in the shape of a π symbol. 
     Accordingly, the balun may include two conversion units to control the phase of an input signal, and any one of the two conversion units may include two passive elements and an FBAR. As another example, the two passive elements may be connected with a ground, and the FBAR may be located between the two passive elements. 
     Referring to  FIG. 10 , conversion unit  1000  includes two capacitors  1010  and an FBAR  1020 . For example, the two capacitors  1010  may be connected with a ground, and the FBAR  1020  may be located between the two capacitors  1010 . In this example, the conversion unit  1000  includes the two capacitors  1010  and the FBAR  1020  that are configured in the shape of a π symbol. 
     Referring to  FIG. 11 , conversion unit  1100  includes two inductors  1110  and an FBAR  1120 . For example, the two inductors  1110  may be connected with a ground, and the FBAR  1120  may be located between the two inductors  1110 . In this example, the conversion unit  1100  includes the two inductors  1110  and the FBAR  1120  that are configured in the shape of a π symbol. 
     Accordingly, the balun may include two conversion units, and each of the two conversion units may be one of the conversion units illustrated in  FIGS. 2 through 11 . For example, as for the balun including a first conversion unit and a second conversion unit, the first conversion unit may include three FBARs configured in a T-shape as illustrated in the example shown in  FIG. 2 , and the second conversion unit may include three FBARs configured in a shape of the symbol π as illustrated in the example shown in  FIG. 3 . 
       FIGS. 12 to 15  illustrate various examples of an FBAR. 
     Referring to  FIG. 12 , FBAR  1200  is connected in series with a capacitor  1210  to obtain a changed frequency response characteristic. 
     Referring to  FIG. 13 , FBAR  1300  is connected in series with an inductor  1310  to obtain a changed frequency response characteristic. 
     Referring to  FIG. 14 , FBAR  1400  may be connected in parallel with a capacitor  1410  to obtain a changed frequency response characteristic. 
     Referring to  FIG. 15 , FBAR  1500  is connected in parallel with an inductor  1510  to obtain a changed frequency response characteristic. 
     Accordingly, the balun may include two conversion units, and each of the two conversion units may include at least one FBAR. For example, the at least one FBAR may be connected in series or in parallel with a capacitor or an inductor to obtain the changed frequency response characteristic, as illustrated in the examples shown in  FIGS. 12 through 15 . A configuration in which the at least one FBAR is connected in series or in parallel with the capacitor or the inductor to obtain the changed frequency response characteristic is described with reference to  FIG. 16 . 
       FIG. 16  illustrates another example of a conversion unit. In this example, an additional inductor  1602  is added to conversion unit  1620  to obtain a changed frequency response characteristic. 
     Referring to  FIG. 16 , a conversion unit  1610  includes two capacitors and an FBAR  1601 . For example, the two capacitors may be connected with a ground, and the FBAR  1601  may be located between the two capacitors. Also, the FBAR  1601  may be connected in series with an inductor  1602  to obtain a changed frequency response characteristic. In this example, the conversion unit  1620  includes the FBAR  1601  connected in series with the inductor  1602  to obtain the changed frequency response characteristic with the conversion unit  1610 . 
     Accordingly, the example baluns described herein, including one or more FBARs, may have a minimal difference between two outputs, without the need for a supplementary circuit to be inserted in the balun to correct the difference between outputs. In addition, the power consumption of the baluns described herein may be reduced in comparison to the conventional balun including the plurality of transistors. Thus, the yield of the circuit may be reduced. 
     A number of examples have been described above. Nevertheless, it should be understood that various modifications may be made. For example, suitable results may be achieved if the described techniques are performed in a different order and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Accordingly, other implementations are within the scope of the following claims.