Patent Publication Number: US-10763568-B2

Title: Electromagnetic coupler arrangements for multi-frequency power detection, and devices including same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. § 120 of co-pending U.S. patent application Ser. No. 15/628,749 filed on Jun. 21, 2017 and titled “ELECTROMAGNETIC COUPLER ARRANGEMENTS FOR MULTI-FREQUENCY POWER DETECTION, AND DEVICES INCLUDING SAME,” which claims the benefit under 35 U.S.C. § 119(e) and PCT Article 8 of U.S. Provisional Application No. 62/353,349 filed on Jun. 22, 2016 and titled “ELECTROMAGNETIC COUPLER ARRANGEMENTS FOR MULTI-FREQUENCY POWER DETECTION, AND DEVICES INCLUDING SAME,” each of which is herein incorporated by reference in its entirety for all purposes. 
    
    
     BACKGROUND 
     Electromagnetic couplers, such as radio frequency (RF) couplers are used in a variety of applications to extract a signal for measurement, monitoring, or other uses. For example, an RF coupler can be included in a signal path between an RF source and a load (such as an antenna) to provide an indication of forward RF power of the RF signal traveling from the RF source to the load and/or an indication of reverse RF power reflected back from the load. RF couplers include, for example, directional couplers, bi-directional couplers, multi-band couplers (e.g., dual band couplers), and the like. An RF coupler typically has a coupled port, an isolation port, a power input port, and a power output port. When a termination impedance is presented to the isolation port, an indication of forward RF power traveling from the power input port to the power output port is provided at the coupled port. When a termination impedance is presented to the coupled port, an indication of reverse (e.g., reflected) RF power traveling from the power output port to the power input port is provided at the isolation port. The termination impedance is typically implemented by a 50 Ohm shunt resistor in a variety of conventional RF couplers. 
     SUMMARY OF INVENTION 
     Aspects and embodiments relate to electronic systems and, in particular, to electronic systems and devices incorporating electromagnetic couplers, such as radio frequency (RF) couplers, for example. In particular, aspects and embodiments are directed to a coupling schema to accommodate simultaneous power measurement at multiple frequencies or in multiple frequency bands. 
     According to one embodiment, a multi-frequency electromagnetic coupler module includes a plurality of bi-directional electromagnetic couplers, each configured to individually receive and couple a respective single one of a corresponding plurality of input signals of different frequencies to provide a coupled signal representative of a power level of the respective input signal, a termination network including a plurality of termination loads, and a coupler switch network configured to selectively connect ones of the plurality of termination loads to forward or reverse coupled ports of the plurality of bi-directional electromagnetic couplers and to selectively and alternately connect the forward or reverse coupled ports of the plurality of bi-directional electromagnetic couplers to a coupler output interface to provide the coupled signals at the coupler output interface. The coupler module can be connected to antenna swap switches to multiplex the plurality of input signals among two or more antennas for transmission. As discussed in more detail below, examples of the coupler module provide for power detection at multiple frequencies simultaneously without requiring filters or other frequency selective components in the coupled path, and may relax the linearity requirement for the antenna swap switches by ensuring that multiple signals at different frequencies are not provided to the same input port of the antenna swap switches at the same time. 
     Another embodiment is directed to a wireless device front-end apparatus configured for multi-frequency operation using a plurality of antennas and having an antenna swap architecture. The apparatus may comprise an antenna switch module having first and second antenna contacts for connecting to first and second antennas, respectively, and including a plurality of antenna swap switches each connected to the first and second antenna contacts, and a coupler assembly including a plurality of electromagnetic couplers each having an input port configured to receive a input signal of a unique frequency, a coupled port, an output port connected to one of the plurality of antenna swap switches, and an isolation port, each electromagnetic coupler being configured to provide a coupled signal at the coupled port responsive to receiving the input signal at the input port. The apparatus may further comprise a termination network including a plurality of termination loads, and an output switch network configured to selectively connect the coupled ports of each of the plurality of electromagnetic couplers to a coupler output bank to provide the coupled signals at the coupler output bank, and to selectively connect the isolation ports of each of the plurality of electromagnetic couplers to one of the plurality of termination loads. 
     In one example the coupler output bank includes a number of coupler output contacts corresponding to half the plurality of electromagnetic couplers. 
     In one example each of the plurality of antenna swap switches is a double-pole double throw switch and is connected to two of the plurality of electromagnetic couplers. 
     In another example the plurality of electromagnetic couplers includes at least four electromagnetic couplers, two of the at least four electromagnetic couplers being configured to receive input signals in a first frequency band, and another two of the at least four electromagnetic couplers being configured to receive input signals in a second frequency band higher than the first frequency band, the first and second frequency bands being non-overlapping in frequency. The antenna switch module may further include a first diplexer connected between the plurality of antenna swap switches and the first antenna contact, and a second diplexer connected between the plurality of antenna swap switches and the second antenna contact. 
     In another example the plurality of electromagnetic couplers further includes an additional pair of electromagnetic couplers configured to receive input signals in a third frequency band different from the first and second frequency bands. The antenna switch module further includes a first triplexer connected between the plurality of antenna swap switches and the first antenna contact, and a second triplexer connected between the plurality of antenna swap switches and the second antenna contact. 
     In one example each termination load of the plurality of termination loads has an adjustable impedance. 
     In another example each of the plurality of electromagnetic couplers is bi-directional, and the output switch network is further configured to switch operation of the plurality of electromagnetic couplers between a forward power detection mode and a reverse power detection mode. 
     According to another embodiment wireless device front-end apparatus is configured for multi-frequency operation using a plurality of antennas and having an antenna swap architecture. The apparatus may comprise an antenna switch module having first and second antenna contacts for connecting to first and second antennas, respectively, and including a first antenna swap switch connected to the first and second antenna contacts and a second antenna swap switch connected to the first and second antenna contacts, the first and second antenna swap switches being double-pole double-throw switches. The apparatus may further comprise a first electromagnetic coupler having a first input port configured to receive a first input signal, a first coupled port configured to provide a first coupled signal responsive to receiving the first input signal at the first input port, a first output port connected to the first antenna swap switch, and a first isolation port, a second electromagnetic coupler having a second input port configured to receive a second input signal, a second coupled port configured to provide a second coupled signal responsive to receiving the second input signal at the second input port, a second output port connected to the second antenna swap switch, and a second isolation port, a third electromagnetic coupler having a third input port configured to receive a third input signal, a third coupled port configured to provide a third coupled signal responsive to receiving the third input signal at the third input port, a third output port connected to the first antenna swap switch, and a third isolation port, and a fourth electromagnetic coupler having a fourth input port configured to receive a fourth input signal, a fourth coupled port configured to provide a fourth coupled signal responsive to receiving the fourth input signal at the fourth input port, a fourth output port connected to the second antenna swap switch, and a fourth isolation port, the first, second, third, and fourth input signals having different frequencies. The apparatus may further comprise a termination network including a first termination load, a second termination load, a third termination load, and a fourth termination load, and an output switch network configured to selectively connect the first and second coupled ports to a first coupler output contact to provide the first and second coupled signals at the first coupler output contact, to selectively connect the third and fourth coupled ports to a second coupler output contact to provide the third and fourth coupled signals at the second coupler output contact, and to selectively connect the first termination load to the first isolation port, the second termination load to the second isolation port, the third termination load to the third isolation port, and the fourth termination load to the fourth isolation port. 
     In one example the first, second, third, and fourth termination loads are adjustable. In another example each of the first, second, third, and fourth termination loads includes a plurality of switchable passive impedance elements, the plurality of switchable passive impedance elements including at least one resistive element and one or more capacitive or inductive elements. 
     In one example each of the first, second, third, and fourth electromagnetic couplers is bi-directional, and wherein the output switch network is further configured to switch operation of the first, second, third, and fourth electromagnetic couplers between a forward power detection mode and a reverse power detection mode. 
     In another example the antenna switch module further includes a first diplexer connected between the first and second antenna swap switches and the first antenna contact, and a second diplexer connected between the first and second antenna switches and the second antenna contact. 
     In another example the first and second input signals are within a first frequency band, the third and fourth input signals are within a second frequency band higher than the first frequency band, and the first and second frequency bands do not overlap in frequency. In another example the antenna switch module further includes a third antenna swap switch connected to the first and second antenna contacts. The apparatus may further comprise a fifth electromagnetic coupler having a fifth input port configured to receive a fifth input signal, a fifth coupled port configured to provide a fifth coupled signal responsive to receiving the fifth input signal at the fifth input port, a fifth output port connected to the third antenna swap switch, and a fifth isolation port, and a sixth electromagnetic coupler having a sixth input port configured to receive a sixth input signal, a sixth coupled configured to provide a sixth coupled signal responsive to receiving the sixth input signal at the sixth input port, a sixth output port connected to the third antenna swap switch, and a sixth isolation port, the fifth and sixth input signals being in a third frequency band different from the first and second frequency bands. In one example the termination network further includes a fifth termination load and a sixth termination load, and the output switch network is further configured to selectively connect the fifth coupled port to a third coupler output contact, to selectively connect the fifth termination load to the fifth isolation port, to selectively connect the sixth coupled port to the third coupler output contact, and to selectively connect the sixth termination load to the sixth isolation port. The antenna switch module may further include a first triplexer connected between the first, second, and third antenna swap switches and the first antenna contact, and a second triplexer connected between the first, second, and third antenna switches and the second antenna contact. 
     According to another embodiment a wireless device comprises first and second antennas, an antenna switch module having first and second antenna contacts connected to the first and second antennas, respectively, and including a plurality of antenna swap switches each connected to the first and second antenna contacts, and a plurality of electromagnetic couplers each having an input port configured to receive an input signal of a unique frequency, a coupled port, an output port connected to one of the plurality of antenna swap switches, and an isolation port, each electromagnetic coupler being configured to provide a coupled signal at the coupled port responsive to receiving the input signal at the input port. The wireless device further comprises a termination network including a plurality of termination loads, an output switch network configured to selectively connect the coupled ports of each of the plurality of electromagnetic couplers to a coupler output bank to provide the coupled signals at the coupler output bank, and to selectively connect the isolation ports of each of the plurality of electromagnetic couplers to one of the plurality of termination loads, a transceiver configured to produce the input signals, and a power amplifier module connected between the transceiver and the plurality of electromagnetic couplers and configured to receive and amplify the input signals. 
     In one example the wireless device further comprises a sensor module coupled to the coupler output bank and configured to receive and process the coupled signals. 
     Still other aspects, embodiments, and advantages of these exemplary aspects and embodiments are discussed in detail below. Embodiments disclosed herein may be combined with other embodiments in any manner consistent with at least one of the principles disclosed herein, and references to “an embodiment,” “some embodiments,” “an alternate embodiment,” “various embodiments,” “one embodiment” or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described may be included in at least one embodiment. The appearances of such terms herein are not necessarily all referring to the same embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of at least one embodiment are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide illustration and a further understanding of the various aspects and embodiments, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of the invention. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every figure. In the figures: 
         FIG. 1  is a block diagram of one example of a portion of an electronic system including a multi-output electromagnetic coupler; 
         FIG. 2  is a block diagram of one example of an antenna swap switch illustrating generation of intermodulation distortion products; 
         FIG. 3  is a diagram illustrating one example of a partial front-end sub-system of a wireless device configured for dual-band operation; 
         FIG. 4  is a diagram illustrating another example of a partial front-end sub-system of a wireless device configured for dual-band operation; 
         FIG. 5  is a circuit diagram illustrating another example of a partial front-end sub-system of a wireless device configured for dual-band operation; 
         FIG. 6  is a diagram illustrating another example of a partial front-end sub-system of a wireless device configured for three-band operation; 
         FIG. 7  is a diagram illustrating another example of a partial front-end sub-system of a wireless device configured for four-band operation; 
         FIG. 8A  is a block diagram of one example of a bi-directional electromagnetic coupler; 
         FIG. 8B  is a block diagram of another example of a bi-directional electromagnetic coupler; 
         FIG. 8C  is a block diagram of another example of a bi-directional electromagnetic coupler; 
         FIG. 9A  is a diagram of one example of an adjustable termination load for an electromagnetic coupler; 
         FIG. 9B  is a diagram of another example of an adjustable termination load for an electromagnetic coupler; 
         FIG. 9C  is a diagram of another example of an adjustable termination load for an electromagnetic coupler; 
         FIG. 9D  is a diagram of another example of an adjustable termination load for an electromagnetic coupler; and 
         FIG. 10  is a block diagram of one example of a wireless device including a multi-output electromagnetic coupler. 
     
    
    
     DETAILED DESCRIPTION 
     Many modern communications devices, including mobile phones for example, are multi-band devices that transmit or receive signals in different bands simultaneously or where there are multiple simultaneous carrier frequencies within the same band. New mobile phone standards are emerging for receiving and/or transmitting data on multiple carrier frequencies simultaneously. In mobile phone applications, the ability to accurately monitor and control signal power can be critical. Accordingly, it may be desirable to use electromagnetic couplers to measure the signal power at the various different carrier frequencies. However, the simultaneous presence of two (or more) signals can cause interference problems when the coupler is used to attempt to measure the power of only one signal. In particular, the measurements of the forward or reverse power of one transmit signal can be contaminated by other signals, which may be present due to additional transmit signals in operation, e.g., from the same power amplifier or to the same antenna in a forward direction, or by a combination of received signals and/or reflected signals from an antenna in the reverse direction. One specific application where a solution to this problem is directly applicable is that of LTE-Advanced Uplink Carrier Aggregation Radio Access Technology used in cellular handsets, for example. 
     There are several approaches to measuring multiple frequencies in a system using one or more electromagnetic couplers. For example, referring to  FIG. 1  there is illustrated an example of a portion of a wireless communications device in which a four-port electromagnetic coupler  110  is included in the signal path  120  and can be used to measure signal power. In the example shown in  FIG. 1 , the system includes a first signal path  120  in which the electromagnetic coupler  110  is connected, and a second signal path  122 , also referred to as a “diversity” path, along with first and second antennas  124 ,  126  and an “antenna swap” switch  128  that selectively connects either signal path to either antenna. The use of two antennas  124  and  126  with the antenna swap switch  128  allows for dynamic selection of the best antenna for transmission or diversity in the receiver. 
     The electromagnetic coupler  110  has main transmission line  111  extending between an input port  112  and an output port  114 , and a coupled line  113  extending between a coupled port  116  and an isolation port  118 . In the illustrated example, the electromagnetic coupler  110  is a bi-directional coupler and a pair of mode-select switches  132 ,  134  is used to configure the electromagnetic coupler between a forward power detection mode and a reverse power detection mode. In the forward power detection mode, when the mode-select switches are actuated to connect the isolation port  118  to a termination load  136   a  and to connect the coupled port  116  to a coupler output contact  138  (as shown in  FIG. 1 ), the electromagnetic coupler is configured to provide at the coupled output contact  138  a coupled signal that is representative of the signal power of an input signal received at the input port  112 . Similarly, when configured for reverse power detection, the mode-select switches  132  and  134  are reversed so as to connect the coupled port  116  to a termination load  136   b  (the coupled port  116  acts a reverse isolation port) and to connect the isolation port  118  (acting as a reverse coupled port) to the coupler output contact  138 . In this mode, the electromagnetic coupler  110  provides at the coupler output contact  138  an indication of the signal power either reflected or received at the output port  114 . 
     As shown in  FIG. 1 , in certain instances the signals on the signal path  120  include multiple input frequencies or frequency bands. In the illustrated example, there are two input frequencies, namely F 1  and F 2 ; however, those skilled in the art will readily appreciate that there may be more than two input frequencies and that the structures and methods disclosed herein may be readily modified to accommodate more or fewer input frequencies. As used herein, the term “input frequency” is intended to refer to an RF signal comprised of a single carrier frequency or “tone” or to an RF signal having a certain, typically relatively narrow, bandwidth covering a range of frequencies. 
     In examples such as that shown in  FIG. 1  where multiple input frequencies are present on the signal path  120  simultaneously, multiple coupled signals will also be present simultaneously at the coupler output contact  138 . Thus, there is a need for frequency selective components in the coupled path so as to be able to differentiate between the coupled signals of different frequencies and provide accurate power measurements of each individual input frequency. Accordingly, as shown in  FIG. 1 , the system may include a filter bank  140  connected to the coupler output contact  138  that allows the electromagnetic coupler  110  to provide multiple outputs, in this case “Output  1 ” corresponding to a measurement of the signal power of the first input frequency F 1  and “Output  2 ” corresponding to a measurement of the signal power of the second input frequency F 2 . Thus, the filter bank in this example includes two filters, one having a passband f 1  that passes the first input frequency F 1  and blocks the second input frequency F 2 , and another having a passband f 2  that passes the second input frequency F 2  and blocks the first input frequency F 1 . Typically, there is a need for such a filter bank  140  to have approximately 30 dB of isolation between f 1  and f 2 . This requirement for high isolation between the different frequencies can present significant challenges in the filter design. 
     Directivity of an electromagnetic coupler is dependent on the termination impedance at the isolation port. In a bi-directional electromagnetic coupler, when the forward coupled port is configured for the coupled mode, the reverse coupled port is terminated with an impedance that is selected to provide highest directivity for the forward coupled port, and vice versa. Similarly, the coupling factor of an electromagnetic coupler is frequency-dependent. The coupling factor for a given electromagnetic coupler is a logarithmic function of frequency (proportional to frequency) and is dependent on the physical structure of the coupler. For example, the coupling factor is dependent on the line widths and lengths of the coupler and on the manner in which the main line and coupled line are designed to be capacitively and inductively coupled to one another. Accordingly, to detect power at multiple different frequencies simultaneously, certain embodiments provide for adjustability in the termination impedance(s) or coupler structure, or use multiple couplers, each optimized for a particular input frequency, as discussed further below. 
     Various arrangements can be implemented to tune and adjust electromagnetic couplers to optimize power detection at multiple different input frequencies simultaneously. For example, certain configurable electromagnetic couplers use multiple coupled lines in conjunction with RF switches to form switched coupled line networks to allow for optimization of a multi-output coupler having a desired coupling factor and directivity in the frequency bands of interest. In such systems, the length or width of each coupled line, or the spacing of each coupled line relative to the main coupled line, can be varied from one coupled line section to another to optimize each section for a particular input frequency. In addition, adjustable termination loads can be used to optimize the directivity of the different couplers formed by the multiple coupled lines for a particular input frequency. These types of coupler arrangements can provide a highly flexible coupling schema that can be tuned and optimized for coupling and detection of multiple input frequencies simultaneously. However, because multiple input frequencies can still be present simultaneously on the common main transmission line, frequency selective components are used on the coupled paths to separate the various frequencies from one another in order to be able to accurately measure the power level associated with each individual input frequency. As a result, these systems can be subject to performance limitations resulting from switch non-linearity and the need for frequency selective components in the coupled path. As discussed above, in order to achieve desired accuracy in the power detection measurements, relatively high isolation between the frequency selective components is needed. It can be challenging to design and implement filters having such high levels of isolation, e.g., ˜30 dB, particularly where one input frequency may be relatively close to another. 
     In addition, referring again to  FIG. 1 , the presence of multiple input frequencies on the signal path  120  at the same time may lead to a requirement that the antenna swap switch  128  have very good linearity in order to avoid significant degradation in performance due to signal distortion and interference. This problem is illustrated with reference to  FIG. 2 . 
     Referring to  FIG. 2  there is illustrated an example of an antenna swap switch  128   a  configured to switch transmission (Tx) and receiving (Rx) paths between two antennas  124 ,  126 . When multiple input frequencies (e.g., Freq 1  and Freq 2 ) are present simultaneously on one (or more) transmission paths (e.g., Tx 1  as shown in  FIG. 2 ) and sent through the switch  128   a  together, the inherent non-linear nature of the switch  128   a  generates intermodulation distortion (IMD) products, as shown in  FIG. 2 . These intermodulation distortion products, which may be second order, third order, or higher order intermodulation products, can fall into one or more intended receiver frequency band(s), resulting in desensitizing of the receiver. This can present a very challenging issue for multiple uplink frequencies being transmitted to the same antenna  124  or  126 . Achieving an antenna swap switch  128  with sufficiently good linearity such that generated intermodulation products are minimal can be very difficult, if not impossible, particularly for modern wireless communications standards that have very strict performance and interference specifications. 
     Accordingly, although the use of a single multi-output electromagnetic coupler, as discussed above and variations thereof, may be desirable and useful in certain applications, there are other circumstances in which multi-frequency transmission through the same path (same coupler and same antenna swap or other switch) may not be desired. Certain aspects and embodiments therefore are directed to arrangements of electromagnetic coupler(s) and switches, as well as frequency multiplexing filter(s) (such as diplexers, triplexers, or quad-plexers, for example) that avoid problematic scenarios. Examples of coupling arrangements disclosed herein avoid the need for filters (or other frequency selective components) at the output port of the electromagnetic coupler and reduce the switch linearity requirement on IMD product generation by separating signals into multiple paths so that one input frequency will route through a coupler and switch port and then be combined into a common antenna through a multiplexed filter or transmitted through different antenna. 
     The need for filters in the coupled path can increase the cost of implementation and significantly increase the size of the design. In addition, filters limit the frequency of usage to the passband of the filter. In the case of surface acoustic wave (SAW) filters, the bandwidth of the passband may be very narrow and severely limit the usage of a given design. Aspects and embodiments provide a coupling schema that avoids these drawbacks and limitations by eliminating the use of filters in the coupled path, making the coupler(s) operable at any frequency. Furthermore, by avoiding having multiple input frequencies travelling simultaneously into the same switch port after the coupler, generation of IMD products in the switch is also avoided. As a result, the design may not need an antenna swap switch (or other switch) having extremely high linearity, which may not available. For example, for LTE applications, the linearity requirement can be as high as +94 dBm IP3, whereas current state-of-the-art double-pole-double-throw (DPDT) antenna swap switches can only achieve approximately 75 to 80 dBm IP3. With the methods and arrangements disclosed herein, existing DPDT switches can be used and achieve the performance necessary to meet IMD requirements of wireless communications standards, such as LTE, for example. 
     Certain embodiments include the use of multiple couplers, multiple antenna swap switches, and multiple diplexers (or other higher order multiplexing filters) to separate each input frequency into a separate path. Embodiments leverage the isolation between switches, between different antennas, and between the switch network at the coupled port to maintain the desired level of isolation to separate coupled signals at each input frequency. The separation of input frequencies into each port of the antenna swap switches reduces the requirement of linearity in the antenna swap switches, making it easier to meet system-level requirements for received sensitivity. In addition, various implementations include bi-directional couplers to allow both forward and reverse power detection, optionally in conjunction with adjustable termination loads that allow for individual optimization of the termination impedances for forward and reverse detection modes. 
     Referring to  FIG. 3  there is illustrated an example of a partial front-end sub-system of a wireless device including a pair of antennas  124 ,  126 , and configured for dual-band (e.g., high-band and low-band) operation. In the illustrated example, the sub-system includes a main transmission path  302  and a diversity path  304  for each of a low-band input frequency (f 1  or f 2 ) and a high-band input frequency (f 3  or f 4 ). A pair of antenna swap switches  128  multiplex the high-band and low-band signals to the two antennas  124 ,  126  via a pair of diplexers  306 . In certain examples the diplexers  306  can be implemented using integrated passive devices, rather than surface acoustic wave devices, for example. A dedicated electromagnetic coupler  308   a ,  308   b  is connected in the main transmission path  302  of each of the low-band input frequency and the high-band input frequency, respectively, as shown. In the illustrated example, the electromagnetic couplers  308   a ,  308   b  are bi-directional and therefore each is connected to an output switch circuit  310  that allows either the forward or reverse coupled port to be connected to the coupler output contact  312   a  (of coupler  308   a ) or  312   b  (of coupler  308   b ) and the forward or reverse isolation port to be connected to a termination load  314 , similar to the operation discussed above with reference to  FIG. 1 . In the example shown in  FIG. 3 , the output switch circuits  310  are shown as single-pole-double-throw (SPDT) switches; however, a variety of other switch configurations can be implemented, as will be appreciated by those skilled in the art, given the benefit of this disclosure. Thus, the coupler output  316  in this sub-system includes a low-band coupled output signal (Output 1 ) and a high-band coupled output signal (Output 2 ) without the need for filters in the coupled path because individual couplers  308   a  and  308   b  and transmission paths  302  are used for the low-band input frequency and the high-band input frequency. 
     The configuration shown in  FIG. 3 , and variations thereof, may provide simultaneous dual-band operation; however, some issues may arise in circumstances where more than one low-band or high-band input frequency is present at a given time. For example, referring to  FIG. 4 , in some circumstances there may be multiple low-band input frequencies (e.g., f 1  and f 2 ) or multiple high-band input frequencies (f 3  and f 4 ) transmitted simultaneously. In this circumstance, filters  318   a  and  318   b  are connected to the coupler output contacts  312   a  and  312   b , respectively, to separate the multiple input frequencies within each band from one another. In addition, the presence of multiple input frequencies within a single band results in simultaneous presence of these multiple input frequencies at the same port of the antenna swap switches  128 , which can result in unacceptable degradation of receiver performance due to intermodulation distortion products or a non-achievable linearity requirement for the antenna swap switch, as discussed above. 
     Accordingly, certain embodiments provide a solution in which each input frequency is directed along its own transmission path and through an individual electromagnetic coupler for power detection. An example of this configuration is shown in  FIG. 5 . This arrangement provides multiple transmission paths and multiple couplers to accommodate a corresponding number of multiple input frequencies in one or more bands, and avoids both the need for filters in the coupled path and the presence of two or more input frequencies on the same port of any antenna swap switch at the same time. 
     Referring to  FIG. 5 , there is illustrated an implementation to accommodate four input frequencies, namely two low-band input frequencies (f 1  and f 2 ) and two high-band input frequencies (f 3  and f 4 ). In this examples, four couplers  308   a - d  are provided, one for each input frequency. Each of these four coupler  3081 - d  is a relatively narrowband coupler, designed for its respective input frequency. The main transmission line  320  of each coupler  308   a - d  is connected to a corresponding input port  322  of one of the antenna swap switches  128 , as shown. Thus, each input frequency f 1 , f 2 , f 3 , and f 4  is provided to an individual coupler and to a corresponding port  322  of one of the antenna swap switches  128 . As a result, multiple input frequencies are not provided to the same port of any antenna swap switch  128  at the same time and are not coupled onto the same coupled port of any electromagnetic coupler  308   a - d  at the same time. The coupled path includes a switch network  324  that allows the coupled signals corresponding to each of input frequencies to be provided at the coupler output  316 . In the illustrated example, the switch network includes a coupler switch  326  for each frequency band (i.e., the electromagnetic couplers  308   a  and  308   b  in the signal paths of the low-band input frequencies are connected to one coupler switch  326  and the electromagnetic couplers  308   c  and  308   d  in the signal paths of the high-band input frequencies are connected to another coupler switch  326 ) and an output switch  328 . In this example the coupler switches  326  are double-pole-four-throw switches because each is connected to the forward and reverse coupled ports of two bi-directional electromagnetic couplers; however, a variety of other configurations may be implemented, as will be appreciated by those skilled in the art, given the benefit of this disclosure. Also in the illustrated example the output switch  328  is a double-pole-four-throw switch configured to provide one coupled output signal (Output 1  and Output 2 ) for each of the two frequency bands (low-band and high-band); however, a variety of other configurations may be implemented, as will be appreciated by those skilled in the art, given the benefit of this disclosure. 
     The sub-system implementation illustrated in  FIG. 5  is configured for dual-band operation (e.g., low-band and high-band as illustrated) and two input frequencies in each band. However, the concepts disclosed herein may be readily extended to more than two frequency bands or more than two input frequencies in any of one or more frequency bands. 
     For example,  FIG. 6  illustrates an implementation configured for three-band operation, including low-band, mid-band, and high-band, with two input frequencies in each band. In this case, the diplexers  306  shown in  FIGS. 3-5  are replaced with tri-plexers  330  to accommodate the three frequency bands of operation. In the example illustrated in  FIG. 6  the output switch  328   a  is a three-pole-six-throw switch to allow the coupler output  316  to include one coupled signal for each frequency band at a time; however, a variety of other configurations may be implemented, as will be appreciated by those skilled in the art, given the benefit of this disclosure. 
       FIG. 7  illustrates another example of an implementation configured for four-band operation, including low-band, mid-band, high-band, and ultra-high-band, with two input frequencies in each band. In this example the tri-plexers  330  shown in  FIG. 6  are replaced with quad-plexers  332  to accommodate the four frequency bands of operation. Additionally, in this example the output switch  328   b  is a four-pole-eight-throw switch to allow the coupler output  316  to include one coupled signal for each frequency band at a time; however, a variety of other configurations may be implemented, as will be appreciated by those skilled in the art, given the benefit of this disclosure. 
     In each of the examples shown in  FIGS. 5-7 , and variations thereof, the desired isolation between the coupled signals corresponding different input frequencies is achieved by leveraging the natural isolation between the different antennas  124  and  126  (e.g., approximately 10 dB), the isolation between switches  326  or  328  in the switch network  324  (e.g., approximately 20 dB), and the isolation between ports of the antenna swap switch  128  and the natural isolation achieved by using different and physically separate transmission paths for each input frequency (approximately 30 dB). As a result, a high level of isolation or discrimination between different coupled signals corresponding to different input frequencies can be achieved without the use of filters in the coupled path. As discussed above this arrangement provides the additional benefit of relaxing the linearity requirements for the antenna swap switches because multiple input frequencies are not provided at the same switch port at the same time. 
     As discussed above, in certain embodiments the electromagnetic couplers  308  are bi-directional couplers. Bi-directional electromagnetic couplers can be implemented in a variety of different ways. For example,  FIG. 8A  illustrates an implementation in which a bi-directional electromagnetic coupler  400   a  includes a main transmission line  402 , a coupled transmission line  404 , and a termination circuit  406  connected to the coupled transmission line. In this example the termination circuit  406  includes a pair of single-pole-double-throw switches  408  that respectively connect first and second coupled ports  410   a ,  410   b  of the bi-directional electromagnetic coupler  400   a  to either a termination load  314  or to the coupler output  316 . For transmit signal flow along the main transmission line  402  from left to right in the diagram, the bi-directional electromagnetic coupler  400   a  is shown configured for forward power detection, with the first coupled port  410   a  providing a signal OUT 1  at the coupler output  316  and the second coupled port  410   b , acting as the isolation port in this configuration, connected to a termination load having a termination impedance value Z 2 . Actuating the pair of switches  408  into the opposite configuration, with the first coupled port  410   a  connected to a termination load having an impedance value Z 1  and the second coupled port  410   b  providing a signal OUT 2  at the coupler output  316 , configures the bi-directional electromagnetic coupler for reverse power detection. As will be appreciated by those skilled in the art, the pair of single-pole-double-throw switches  408  may be replaced by a double-pole-double-throw switch, for example. The bi-directional electromagnetic coupler  400   a  is shown in  FIG. 8A  as having two termination loads  314 ; however, the two termination loads may be replaced by a single termination load  314  that is shared between the forward and reverse power detection modes. In certain examples the bi-directional electromagnetic coupler  400   a  can include a single termination load  314  that is adjustable such that it can present two different impedance values Z 1  or Z 2  depending on the mode of power detection or the frequency of operation. 
       FIG. 8B  illustrates another example of a bi-directional electromagnetic coupler  400   b  that includes a pair of coupled transmission lines  404   a ,  404   b  to allow for simultaneous forward and reverse coupling and power detection. As shown, the first coupled transmission line  404   a  is connected to the coupler output  316  (providing signal OUT 1 ) and to a termination load  314  having an impedance value Z 2 , and the second coupled transmission line  404   b  is similarly connected to the coupler output  316  (providing signal OUT 2 ) and to a termination load  314  having an impedance value Z 1 . This configuration eliminates the need for switches  408  and allows simultaneous forward and reverse power detection. 
       FIG. 8C  illustrates a variation on the example shown in  FIG. 8B . In  FIG. 8B , the coupled transmission lines  404   a  and  404   b  are positioned on either side the main transmission line  402 . In the example shown in  FIG. 8C , the coupled transmission lines  404   a  and  404   b  are positioned on the same side of the main transmission line  402 , and each connected to a termination load  314  and to the coupler output  316 . This arrangement similarly allows for simultaneous forward and reverse power detection. 
     Any of the termination loads  314  can be made adjustable to optimize performance for a particular input frequency or frequency band of operation. In some examples an adjustable termination load  314  can be implemented by providing one or more tunable impedance elements, such as a tunable or variable capacitor, inductor, or resistor. In other examples an adjustable termination load  314  can be implemented by providing a switched network of passive impedance elements, any of which can have fixed or variable values.  FIGS. 9A-D  illustrate various examples of switchable impedance networks that can be used to implement any of the termination loads  314  in any examples of the electromagnetic couplers disclosed herein. 
     Referring to  FIG. 9A , in one example an adjustable termination load  314   a  includes a plurality of switchable arms  420 . In this example, each arm includes a series combination of a capacitor  422 , an inductor  424 , and a resistor  426 . However, as will be appreciated by those skilled in the art, many variations can be implemented. For example, any one or more of the arms  420  can include one or more passive or active capacitive, resistive, or inductive components, or any combination thereof, and the configuration of the arms  420  is not limited to the particular example shown in  FIG. 9A . Any of the capacitor  422 , inductor  424 , or resistor  426  may have different values between different arms  420 . A plurality of switches  428  can be actuated to connect any combination of one or more arms  420  to provide the adjustable termination load  314   a  with a desired impedance value. 
       FIG. 9B  illustrates another example in which an adjustable termination load  314   b  includes an impedance network  430  including a plurality of impedance elements  432  and a switch network  434  including a plurality of switches  428  that can selectively connect together any one or more of the impedance elements  432  to achieve a desired impedance value for the adjustable termination load  314   b . The impedance elements  432  can include any one or more active or passive resistive, capacitive, or inductive components, or any combination thereof. The plurality of switches  428  in the switch network  434  can be actuated individually or together. 
     As illustrated in  FIG. 9C  in another example an adjustable termination load  314   c  can include a termination impedance circuit  436  that includes switches  428  and passive impedance elements R 1   a  to R 1   n , L 1   a  to L 1   n , and C 1   a  to C 21   n . Each of the switches  428  can selectively switch in a respective passive impedance element to the termination impedance provided to the isolation port of an electromagnetic coupler. In the example illustrated in  FIG. 9C  the switches  428  of the termination impedance circuit  436  include three banks of parallel switches in series with each other. Having banks of switches in parallel with other banks of parallel switches can increase the number of possible termination impedance values provided by the termination impedance circuit  436 . For example, when the termination impedance circuit  436  includes three banks of three parallel switches in series with each other, the termination impedance circuit can provide  343  different termination impedance values by having one or more of the switches in each bank of switches on while the other switches are off. In the example illustrated in  FIG. 9C , the termination impedance circuit  436  includes series circuits that each include a passive impedance element and a switch in parallel with other series circuits that include other passive impedance elements and other switches. For instance, a first series circuit that includes a switch  428  and the resistor R 1   a  is in parallel with a second series circuit that includes another switch  428  and the resistor R 1   b . The termination impedance circuit  436  further includes switches  428  to switch inductors L 1   a  to L 1   n  in series with one or more resistors R 1   a  to R 1   n , or in parallel with one another. The switches  428  can also switch capacitors C 1   a  to C 1   n  in series with one or more RL circuits or in parallel with each other, for example. 
     The termination impedance circuit  436  can include passive impedance elements having arbitrary values, binary weighted values, values to compensate for variations, values for a particular application, the like, or any combination thereof. While the termination impedance circuit  436  can provide RLC circuits, any suitable combination of circuit elements such as one or more resistors, one or more inductors, one or more capacitors, one or more RL circuits, one or more RC circuits, one or more LC circuits, or one or more RLC circuits can be configured to provide a desired termination impedance. Such combinations of circuit elements can be arranged in any suitable series and/or parallel combination. 
       FIG. 9D  illustrates an adjustable termination load  314   d  implemented as a variation on the example shown in  FIG. 9C . In  FIG. 9C , each of the passive impedance elements in the termination impedance circuit  436  is individually switchable with an associated switch  428 .  FIG. 9D  illustrates another example of a termination impedance circuit  436  in which some passive impedance elements can be individually switched, while others are switched together as a group by a single switch. For example, switch  438  switches a series RLC combination.  FIG. 9D  also illustrates that different passive impedance elements can be ratioed to each other (e.g., capacitors  0 . 1 C and  0 . 2 C; resistors  0 . 1 R,  0 . 2 R, and  0 . 4 R) and can be selectively switched in individually or in parallel with each other. Such impedance elements can be used to compensate for process variations or to configure an electronic system for certain applications, for example. 
     The switches  428  and  438  can be implemented by field effect transistors, for example. Alternatively, or additionally, one or more switches  428 ,  438  can be implemented by MEMS switches, fuse elements (e.g., fuses or antifuses), or any other suitable switch element. 
     While the various adjustable termination loads illustrated in  FIGS. 9A-D  include switches, a tunable termination load can alternatively or additionally be provided by other variable impedance circuits. For instance, an adjustable termination load can use an impedance element having an impedance that varies as a function of a signal provided to impedance element. As one example, a field effect transistor operating in the linear mode of operation can provide an impedance dependent on a voltage provided to its gate. As another example, a varactor diode can provide a variable capacitance as a function of voltage provided to the varactor diode. 
     Thus aspects and embodiments provide a coupling methodology and circuit arrangements that can allow for simultaneous power detection and operation at multiple input frequencies and in multiple frequency bands without requiring the use of filters in the coupled path and without imposing unreasonable linearity requirements on the antenna swap switches. As discussed above, each of the couplers  308  can be a narrowband, frequency-selective coupler that is specifically designed for its corresponding input frequency. For example, each coupler  308  can be optimized to have a desired coupling factor, and the termination impedances can be tuned such that the directivity of each coupler can be optimized for its respective input frequency. This allows high performance and accurate power detection to be achieved at each frequency band of interest. In addition, because each input frequency is provided through a dedicated signal path, both simultaneous detection/measurement and simultaneous transmission of multiple frequencies can be accomplished without introducing intermodulation distortion products at the antenna swap switches  128 . As a result, the linearity requirements for the antenna swap switches can be relaxed. Thus, aspects and embodiments advantageously provide simultaneous multi-frequency precision power detection in an antenna swap architecture. 
     Embodiments of the coupling arrangements disclosed herein can be implemented in a variety of different electronic devices or modules including, for example, a stand-alone RF coupler, an antenna switch module, a module combining an RF coupler and an antenna switch module, an impedance matching module, an antenna tuning module, or a wireless device (e.g., cell phones, tablets, etc.). Examples of electronic devices can include, but are not limited to, consumer electronic products, parts of the consumer electronic products, electronic test equipment, cellular communications infrastructure such as a base station, etc. Further, the electronic devices can include unfinished products. 
       FIG. 10  is a block diagram of a wireless device  500  including a coupler module  502  according to certain embodiments. The wireless device  500  can be a cellular phone, smart phone, tablet, modem, communication network or any other portable or non-portable device configured for voice and/or data communication. The wireless device  500  includes the antennas  124  and  126  that receive and transmit power signals, as discussed above. 
     A transceiver  504  is configured to generate signals for transmission and/or to process received signals. In some embodiments, transmission and reception functionalities can be implemented in separate components (e.g. a transmit module and a receiving module), or be implemented in the same module. 
     Signals generated for transmission are received by a power amplifier (PA) module  506 , which can include one or more PA&#39;s to amplify one or more of the generated signals from the transceiver  504 . The power amplifier module  506  can be used to amplify a wide variety of RF or other frequency-band transmission signals. For example, the power amplifier module  506  can receive an enable signal that can be used to pulse the output of the power amplifier to aid in transmitting a wireless local area network (WLAN) signal or any other suitable pulsed signal. The power amplifier module  506  can be configured to amplify any of a variety of types of signal, including, for example, a Global System for Mobile (GSM) signal, a code division multiple access (CDMA) signal, a W-CDMA signal, a Long Term Evolution (LTE) signal, or an EDGE signal. In certain embodiments, the power amplifier model  506  and associated components including switches and the like can be fabricated on GaAs substrates using, for example, pHEMT or BiFET transistors, or on a Silicon substrate using CMOS transistors. The power amplifier module  506  can be configured to provide the one or more input frequencies to the coupler module  502 , which includes an appropriate number of electromagnetic couplers  308  depending on the number of input frequencies expected, as discussed above. 
     An antenna switch module  508  can include one or more antenna swap switches  128  and be configured to selectively couple the input frequencies to one of the antennas  124 ,  126  and/or to switch between transmit and receive modes, for example, as discussed above. As shown in  FIG. 10  and as discussed above, in certain examples the antennas  124 ,  126  both receive signals that are provided to the transceiver  504  via the antenna switch module  508  and also transmit signals from the wireless device  500  via the transceiver  504 , the power amplifier module  506 , the coupler module  502 , and the antenna switch module  508 . 
     The coupler module  502  can be used to measure transmitted power signals from the power amplifier module  506  and provides one or more coupled signals (coupler output  316 ) to a sensor module  510 . The sensor module  510  can in turn send information to the transceiver  504  and/or directly to the power amplifier module  506  as feedback for making adjustments to regulate the power level of the power amplifier module  506 . In this way the coupler module  502  can be used to boost/decrease the power of a transmission signal having a relatively low/high power. It will be appreciated, however, that the coupler module  502  can be used in a variety of other implementations. 
     In certain embodiments in which the wireless device  500  is a mobile phone having a time division multiple access (TDMA) architecture, the coupler module  502  can advantageously manage the amplification of an RF transmitted power signal from the power amplifier module  806 . In a mobile phone having a time division multiple access (TDMA) architecture, such as those found in Global System for Mobile Communications (GSM), code division multiple access (CDMA), and wideband code division multiple access (W-CDMA) systems, the power amplifier module  506  can be used to shift power envelopes up and down within prescribed limits of power versus time. For instance, a particular mobile phone can be assigned a transmission time slot for a particular frequency channel. In this case the power amplifier module  506  can be employed to aid in regulating the power level one or more RF power signals over time, so as to prevent signal interference from transmission during an assigned receive time slot and to reduce power consumption. In such systems, the coupler module  502  can be used to measure the power of a power amplifier output signal to aid in controlling the power amplifier module  506 , as discussed above. 
     Signals received by the antennas  124 ,  126  can be provided via the antenna switch module  508  to a low noise amplifier (LNA) module  512 , which may include one or more amplifiers. The received signals are amplified by the low noise amplifier module  512  and then provided to the transceiver  504 . 
     Still referring to  FIG. 10 , the wireless device  500  further includes a power management system  514  that is connected to the transceiver  504  that manages the power for the operation of the wireless device. The power management system  514  can also control the operation of a baseband sub-system  516  and other components of the wireless device  500 . In certain examples the power management system  514  includes, or is connected to, a power source, such as a battery (not shown) that provides power to the wireless device  500 . The power management system  514  may further include one or more processors or controllers that can control the transmission of signals. 
     In one embodiment, the baseband sub-system  516  is connected to a user interface  518  to facilitate various input and output of voice and/or data provided to and received from the user. The baseband sub-system  516  can also be connected to memory  520  that is configured to store data and/or instructions to facilitate the operation of the wireless device, and/or to provide storage of information for the user. 
     Having described above several aspects of at least one embodiment, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the invention. Accordingly, the foregoing description and drawings are by way of example only, and it is to be appreciated that embodiments of the methods and apparatuses discussed herein are not limited in application to the details of construction and the arrangement of components set forth in the description or illustrated in the accompanying drawings. The methods and apparatuses are capable of implementation in other embodiments and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use herein of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to “or” may be construed as inclusive so that any terms described using “or” may indicate any of a single, more than one, and all of the described terms. The scope of the invention should be determined from proper construction of the appended claims, and their equivalents.