Abstract:
Integrated balun and coupler is described. In one example, a radio frequency (RF) device includes a balun and coupler. The balun includes a first winding and a second winding arranged on a magnetic core. Respective inputs of the first winding and the second winding are configured to receive a balanced RF input and respective outputs of the first winding and the second winding are configured to provide a first unbalanced RF output. The coupler includes a third winding arranged on the magnetic core. The third winding is configured to provide a second unbalanced RF output, where the second unbalanced RF output is a fraction of the first unbalanced RF output.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to radio frequency (RF) devices and, more particularly, to an integrated balun and coupler transformer. 
     2. Description of the Background Art 
     A balun is a device designed to convert between balanced radio frequency (RF) signals and unbalanced RF signals, such as between twin-lead (balanced line) and coaxial cables (unbalanced line). A balun is typically implemented through the use of a small isolation transformer, with the earth ground or chassis ground left floating on the balanced side. In such a configuration, the balun can also perform impedance matching. For example, baluns are used in amplifiers having a push-pull configuration in order to convert the balanced output signal to an unbalanced signal. 
     A coupler is a transmission device for sampling (through a known coupling loss) the signal in a transmission line. For example, couplers are used in electronic devices, such as amplifiers, to monitor output signal level and feed a sample to the control logic (e.g., automatic gain control (AGC) logic or other type of monitor circuit for further processing). 
     Some electronic devices, such as the exemplary amplifiers described above, require both a balun and a coupler at their outputs. Conventionally, the balun and the coupler are two separate devices. As such, they take up significant space, contribute added insertion loss, and compromise the output impedance match. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention relates to a radio frequency (RF) device having a balun and coupler. The balun includes a first winding and a second winding arranged on a magnetic core. Respective inputs of the first winding and the second winding are configured to receive a balanced RF input and respective outputs of the first winding and the second winding are configured to provide a first unbalanced RF output. The coupler includes a third winding arranged on the magnetic core. The third winding is configured to provide a second unbalanced RF output, where the second unbalanced RF output is a fraction of the first unbalanced RF output. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  is a schematic diagram depicting an exemplary embodiment of a radio frequency (RF) device constructed in accordance with one or more aspects of the invention; 
         FIG. 2  is a block diagram depicting an exemplary embodiment of an RF system having the RF device of  FIG. 1  constructed in accordance with one or more aspects of the invention; 
         FIG. 3  is a perspective view depicting an exemplary embodiment of a structure for the RF device of  FIG. 1  in accordance with one or more aspects of the invention; and 
         FIG. 4  is a top view of the structure of  FIG. 3  with the top removed. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic diagram depicting an exemplary embodiment of a radio frequency (RF) device  100  constructed in accordance with one or more aspects of the invention. The device  100  includes a balanced RF port  102 , an unbalanced RF port  104 , an unbalanced RF port  106 , a magnetic core  108 , and windings  110 ,  112 , and  114 . The balanced RF port  102  includes a positive terminal  116  and a negative terminal  118 . The unbalanced RF port  104  includes a positive terminal  120  and a ground terminal  122 . The unbalanced RF port  106  includes a positive terminal  124  and a ground terminal  126 . 
     The winding  110  is arranged on the magnetic core  108  and coupled between the positive terminal  116  and the positive terminal  120 . The winding  112  is arranged on the magnetic core  108  coupled between the negative terminal  118  and the ground terminal  122 . The winding  114  is arranged on the magnetic core  108  coupled between the positive terminal  124  and the ground terminal  126 . The winding  110  includes N 1  turns, the winding  112  includes N 2  turns, and the winding  114  includes N 3  turns. In one embodiment, N 1  is equal to N 2  (i.e., the winding  110  has the same number of turns as the winding  112 ). N 3  is less than N 1  and N 2 . In one embodiment, the winding  114  includes a single turn (i.e., N 3 =1). For example, N 1  and N 2  may be between 5 and 10 turns, depending on the bandwidth required and the amount of coupling desired. 
     The balanced RF port  102  is configured to receive a balanced RF input signal. The RF device  100  converts the balanced RF input signal into an unbalanced RF output signal. The unbalanced RF port  104  provides the unbalanced RF output signal via magnetic coupling between the windings  110  and  112  through the magnetic core  108 . The unbalanced RF port  106  is configured to provide a sample of the unbalanced RF output signal provided by the unbalanced RF port  104  (i.e., a fraction of the unbalanced RF output signal) via magnetic coupling between the windings  112  and  114  through the magnetic core  108 . As is well known in the art, the particular fraction of the unbalanced RF output signal provided at the unbalanced RF port  106  is determined by the ratio of turns between the winding  112  and the winding  114  (e.g., ratio between N 2  and N 3 ). The arrangement of the winding  110  and the winding  112  on the magnetic core  108  provides a balun. The arrangement of the winding  114  on the magnetic core  108  provides a coupler. The balun and coupler share the same magnetic core. 
     The terminals  120  and  122  may comprise a connector (e.g., a coaxial cable connector) or may comprise the ends of the windings  110  and  112 , respectively. The terminals  124  and  126  may comprise a connector (e.g., a coaxial cable connector) or may comprise the ends of the winding  114 . The terminals  116  and  118  may comprise a connector or may comprise the ends of the windings  110  and  112 , respectively. 
     In this manner, the RF device  100  provides an integrated balun and coupler. The integrated balun and coupler may be used with various types of electronic devices that require conversion from balanced to unbalanced signals and sampling of RF output, e.g., for control purposes. When used with such electronic devices, the integrated balun and coupler of the invention saves space, reduces insertion loss, and reduces cost compared to the use of two separate components. 
       FIG. 2  is a block diagram depicting an exemplary embodiment of an RF system  200  constructed in accordance with one or more aspects of the invention. The RF system  200  includes a balanced source  202 , a balanced transmission line  203 , an unbalanced transmission line  205 , an unbalanced load  204 , an unbalanced transmission line  209 , a control circuit  206 , an integrated balun and coupler (the RF device  100 ). The balanced source  202  is coupled to the balanced transmission line  203 , which is coupled to the balanced RF port  102 . The balanced transmission line  203  may comprise a twin-lead transmission line or the like known in the art. The unbalanced load  204  is coupled to unbalanced transmission line  205 , which is coupled to the unbalanced RF port  104 . The control circuit  206  is coupled to the unbalanced transmission line  209 , which is coupled to the unbalanced RF port  106 . The unbalanced transmission lines  205  and  209  may comprise coaxial cable or the like known in the art. 
     The balanced source  202  is configured to provide a balanced RF signal. The balanced RF signal is coupled to the balanced RF port  102  via positive and negative lines of the balanced transmission line  203 . The RF device  100  converts the balanced RF signal to an unbalanced RF signal through magnetic coupling between the winding  110  and the winding  112  through the magnetic core  108 . The unbalanced RF signal is output from the unbalanced RF port  104 . The unbalanced RF signal is coupled to the unbalanced load  204  via positive and ground conductors of the unbalanced transmission line  205 . The RF device  100  also samples the unbalanced RF signal through magnetic coupling between the winding  112  and the winding  114  through the magnetic core  108 . The sample of the unbalanced RF signal is output from the unbalanced RF port  106 . The sample of the unbalanced RF signal is coupled to the control circuit  206  positive and ground conductors of the unbalanced transmission line  209 . For example, the RF system  200  may comprise an amplifier driving an unbalanced RF load. The control circuit  206  may comprise automatic gain control (AGC) circuitry for the amplifier. 
       FIG. 3  is a perspective view depicting an exemplary embodiment of a structure  300  for the RF device  100  in accordance with one or more aspects of the invention. In the structure  300 , the magnetic core  108  includes a generally body  350  having a top  301 , a bottom  305 , sides  310  and  312 , ends  302  and  304 , and bores  306  and  308 . The body  350  is generally shaped like a rectangular prism. The body  350  (and hence the magnetic core  108 ) may comprise ferrite. Each of the bores  306  and  308  traverses the length of the body  350  generally parallel to the sides  310  and  312  between the ends  302  and  304 . The bores  306  and  308  are positioned within the body  350  to define a central vane  314 . Each of the windings  110 ,  112 , and  114  comprises a transmission line wrapped around the central vane  314  through the bore  306  and the bore  308 .  FIG. 4  is a top view of the structure  300  with the top  301  removed to reveal the windings  110 ,  112 , and  114  wrapped around the central vane  314 . The ends of each of the windings  110 ,  112 , and  114  extend out from either the bore  306  or the bore  308 . 
     While the foregoing is directed to illustrative embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.