Patent Publication Number: US-2022239430-A1

Title: Unified sounding reference signal input/output functionality

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application Ser. No. 63/142,264, titled “UNIFIED SOUNDING REFERENCE SIGNAL INPUT/OUTPUT FUNCTIONALITY,” filed on Jan. 27, 2021, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates generally to front-end modules (FEM). Some examples relate to systems and methods for improving sounding reference signal functionality in FEM architectures. 
     SUMMARY 
     According to at least one aspect of the present disclosure, a front-end module for a wireless device is provided comprising at least one transmit path configured to provide a first sounding reference signal, at least one transmit/receive path coupled to at least one antenna port, a sounding-reference-signal port configured to provide the first sounding reference signal and to receive a second sounding reference signal, an antenna switching module coupled between the at least one transmit path, the at least one transmit/receive path, and the sounding-reference-signal port, the antenna switching module being configured to provide the first sounding reference signal from the transmit path to the at least one transmit/receive path and the sounding-reference-signal port and to provide the second sounding reference signal received at the sounding-reference-signal port to the at least one transmit/receive path. 
     In some examples, the first sounding reference signal and the second sounding reference signal are provided to the at least one transmit/receive path to be transmitted by one or more antennas coupled to the at least one antenna port. In at least one example, the first sounding reference signal and the second sounding reference signal are transmitted to at least one base station to characterize an uplink channel between the wireless device and the base station. In various examples, the first sounding reference signal is provided from the sounding-reference-signal port to a second front-end module included in the wireless device. In some examples, the second sounding reference signal is received from the second front-end module. 
     In at least one example, the at least one transmit path includes at least one power amplifier. In various examples, the at least one receive path includes at least one low-noise amplifier. In some examples, the front-end module is configured to support 5G wireless communication. In at least one example, the antenna switch module includes a single pin connection configured to be coupled to the sounding-reference-signal port. 
     According to at least one aspect of the disclosure, a mobile-communications-device system is provided comprising a first front-end module including a first sounding-reference-signal port configured to provide a first sounding reference signal and to receive a second sounding reference signal, and a first antenna switching module coupled to the first sounding-reference-signal port, the first antenna switching module being configured to route the first sounding reference signal to the first sounding-reference-signal port and to route the second sounding reference signal from the first sounding-reference-signal port, and a second front-end module including a second sounding-reference-signal port configured to provide the second sounding reference signal to the first front-end module and to receive the first sounding reference signal from the first front-end module, and a second antenna switching module coupled to the second sounding-reference-signal port, the second antenna switching module being configured to route the second sounding reference signal to the second sounding-reference-signal port and to route the first sounding reference signal from the second sounding-reference-signal port. 
     In some examples, the first front-end module includes at least one first transmit path coupled to the first antenna switch module, the first antenna switch module being configured to route the first sounding reference signal from the at least one first transmit path to the first sounding-reference-signal port, and the second front-end module includes at least one second transmit path coupled to the second antenna switch module, the second antenna switch module being configured to route the second sounding reference signal from the at least one second transmit path to the second sounding-reference-signal port. In at least one example, the first front-end module includes at least one first transmit/receive path coupled to at least one first antenna port and coupled to the first antenna switch module, the first antenna switch module being configured to route the second sounding reference signal from the first sounding-reference-signal port to the at least one first transmit/receive path, and the second front-end module includes at least one second transmit/receive path coupled to at least one second antenna port and coupled to the second antenna switch module, the second antenna switch module being configured to route the first sounding reference signal from the second sounding-reference-signal port to the at least one second transmit/receive path. 
     In various examples, the first sounding reference signal is provided to the at least one first antenna port to be transmitted by one or more first antennas coupled to the at least one first antenna port, and the second sounding reference signal is provided to the at least one second antenna port to be transmitted by one or more second antennas coupled to the at least one second antenna port. In some examples, the first sounding reference signal and the second sounding reference signal are transmitted to at least one base station to characterize an uplink channel between the mobile-communications-device system and the at least one base station. In at least one example, the first antenna switch module includes a single pin connection configured to be coupled to the first sounding-reference-signal port and the second antenna switch module includes a single pin connection configured to be coupled to the second sounding-reference-signal port. 
     According to at least one example of the disclosure, a non-transitory computer-readable medium storing thereon sequences of computer-executable instructions for controlling a front-end module for a wireless device comprising a sounding-reference-signal port, at least one transmit path, at least one transmit/receive path coupled to at least one antenna port, and an antenna switching module coupled between the sounding-reference-signal port, the at least one transmit path, and the at least one transmit/receive path is provided, the sequences of computer-executable instructions including instructions that instruct at least one processor to control the antenna switching module to route a first sounding reference signal from the at least one transmit path to the sounding-reference-signal port, and control the antenna switching module to route a second sounding reference signal from the sounding-reference-signal port to the at least one transmit/receive port. 
     In some examples, the instructions instruct the at least one processor to route the first sounding reference signal and the second sounding reference signal to the at least one transmit/receive path to be transmitted by one or more antennas coupled to the at least one antenna port. In at least one example, the wireless device includes a transceiver, and the instructions instruct the at least one processor to route the first sounding reference signal from the transceiver and to route the second sounding reference signal to the transceiver. In various examples, the instructions instruct the at least one processor to provide the first sounding reference signal from, and receive the second sounding reference signal at, a single pin coupled to the sounding-reference-signal port. In some examples, the instructions further instruct the at least one processor to operate the front-end module pursuant to a 5G wireless-communication standard. 
    
    
     
       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  illustrates a block diagram of a front-end module according to an example; 
         FIG. 2  illustrates a block diagram of a front-end module system according to an example; 
         FIG. 3  illustrates a block diagram of a front-end module system according to an example; 
       and 
         FIG. 4  illustrates a block diagram of a front-end module system according to an example. 
     
    
    
     DETAILED DESCRIPTION 
     Examples of the methods and systems discussed herein are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The methods and systems 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. In particular, acts, components, elements and features discussed in connection with any one or more examples are not intended to be excluded from a similar role in any other examples. 
     Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Any references to examples, embodiments, components, elements or acts of the systems and methods herein referred to in the singular may also embrace embodiments including a plurality, and any references in plural to any embodiment, component, element or act herein may also embrace embodiments including only a singularity. References in the singular or plural form are not intended to limit the presently disclosed systems or methods, their components, acts, or elements. 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. In addition, in the event of inconsistent usages of terms between this document and documents incorporated herein by reference, the term usage in the incorporated features is supplementary to that of this document; for irreconcilable differences, the term usage in this document controls. 
     Examples of the disclosure may relate to front-end modules (FEMs) implemented in connection with one or more communication devices, such as mobile communication devices.  FIG. 1  illustrates a schematic diagram of a mobile device  100  according to an example. The mobile device  100  includes a baseband system  101 , a transceiver  102 , a front-end module  103  (“FEM  103 ”), antennas  104 , a power-management system  105 , a memory  106 , a user interface  107 , and a battery  108 . 
     The mobile device  100  can be used to communicate using a wide variety of communications technologies, including, but not limited to, 2G, 3G, 4G (including LTE, LTE-Advanced, and LTE-Advanced Pro), 5G NR, WLAN (for instance, Wi-Fi), WPAN (for instance, Bluetooth and ZigBee), WMAN (for instance, WiMax), GPS technologies, and/or other communications technologies. 
     The transceiver  102  may generate RF signals for transmission via the antennas  104  and process incoming RF signals received from the antennas  104 . It will be understood that various functionalities associated with the transmission and receiving of RF signals can be achieved by one or more components that are collectively represented in  FIG. 1  as the transceiver  102 . In one example, separate components (for instance, separate circuits or dies) can be provided for handling certain types of RF signals. 
     The FEM  103  aids in conditioning signals transmitted to and/or received from the antennas  104 . In the illustrated embodiment, the FEM  103  includes antenna-tuning circuitry  110 , power amplifiers (PAs)  111 , low-noise amplifiers (LNAs)  112 , filters  113 , switches  114 , and signal splitting/combining circuitry  115 . However, other implementations are possible. The filters  113  can include one or more filter circuits with harmonic rejection that include one or more features of the examples disclosed herein. In some examples, the FEM  103  may be a FEM system having multiple FEMs. 
     For example, the FEM  103  can provide a number of functionalities, including, but not limited to, amplifying signals for transmission, amplifying received signals, filtering signals, switching between different bands, switching between different power modes, switching between transmission and receiving modes, duplexing of signals, multiplexing of signals (for instance, diplexing or triplexing), transmitting and/or receiving SRS signals, or some combination thereof. The antennas  104  can include antennas used for a wide variety of types of communications. For example, the antennas  104  can include antennas for transmitting and/or receiving signals associated with a wide variety of frequencies, including RF signals, and communications standards. 
     The antennas  104  may include one or more antennas. In certain implementations, the antennas  104  support Multiple Input Multiple Output (MIMO) communications and/or switched diversity communications. For example, MIMO communications use multiple antennas for communicating multiple data streams over a single radio-frequency channel. MIMO communications benefit from higher signal-to-noise ratio, improved coding, and/or reduced signal interference due to spatial multiplexing differences of the radio environment. Switched diversity refers to communications in which a particular antenna is selected for operation at a particular time. For example, a switch can be used to select a particular antenna from a group of antennas based on a variety of factors, such as an observed bit error rate and/or a signal-strength indicator. 
     The baseband system  101  is coupled to the user interface  107  to facilitate processing of various user input and output (I/O), such as voice and data. The baseband system  101  provides the transceiver  102  with digital representations of transmit signals which the transceiver  102  processes to generate RF signals for transmission. The baseband system  101  also processes digital representations of received signals provided by the transceiver  102 . As shown in  FIG. 1 , the baseband system  101  is coupled to the memory  106  to facilitate operation of the mobile device  100 . 
     The memory  106  can be used for a wide variety of purposes, such as storing data and/or instructions to facilitate the operate of the mobile device  100  and/or to provide storage of information, such as user information. In some examples, the memory  106  may be coupled to at least one controller configured to control operate of the mobile device  100 . For example, the mobile device  100  may include the at least one controller. The at least one controller may be coupled to one or more components of the mobile device  100  and, in some examples, the mobile device  100  includes the at least one controller. The memory  106  may include one or more non-transitory computer-readable media configured to store instructions, which the at least one controller may be configured to read to operate the mobile device  100 . 
     The power-management system  105  provides a number of power-management functions of the mobile device  100 . In certain implementations, the power-management system  105  includes a PA-supply control circuit which controls the supply voltages of the power amplifiers  111 . For example, the power-management system  105  can be configured to change the supply voltage(s) provided to one or more of the power amplifiers  111  to improve efficiency, such as power-added efficiency (PAE). 
     As shown in  FIG. 1 , the power-management system  105  receives a battery voltage from the battery  108 . The battery  108  can be any suitable battery for use in the mobile device  100 , including, for example, a lithium-ion battery. 
     In one example, the FEM  103  may support sounding reference signal (SRS) functionality to provide an estimate or characterization of the uplink (that is, transmit) channel quality over a wide bandwidth. In some examples, the SRS is an RF signal. The FEM  103  may transmit an SRS to a base station and the base station may utilize or analyze the received SRS to estimate channel quality and determine resource (for example, channel) allocations. In some examples, the SRS may provide information corresponding to multipath fading, scattering, Doppler effects, power loss, and other radio frequency transmission characteristics. In certain cases, the FEM  103  may be configured as a 5G system and may utilize SRS functionality to support 5G communication. In some cases, SRS support on each TX/RX antenna of the FEM  103  (for example, antenna  104 ) may be a requirement and/or may be desirable for 5G systems (or devices). 
     In many cases, wireless-communication devices include multiple FEMs. The multiple FEMs may be included in a FEM system having an integrated SRS implementation. To support full SRS functionality, the transmit path(s) of each FEM may be connected to the transmit/receive path(s) of each other FEM of the FEM system via respective ports (or pins). As such, each FEM of the FEM system (including, for example, FEM  103 ) may include a multi-port (or pin) SRS interface. For example, the FEM  103  may include an input SRS port to receive an SRS from another FEM included in the FEM system. Likewise, the FEM  103  may include an output SRS port to provide an SRS to another FEM included in the FEM system. 
     In some cases, each additional SRS port of the multi-port SRS interfaces of each FEM can reduce the input/output (IO) availability of the FEM and increase the overall package size of the FEM. In addition, routing between the multi-port SRS interfaces of each FEM can occupy valuable area within the wireless-communication device (for example, on a circuit board). In certain cases, to support these multi-port SRS interfaces, the FEMs may include larger antenna switching modules which incur additional losses and occupy additional area within the FEMs (and the wireless-communication device that includes the FEMs). 
     In light of the foregoing, an improved FEM and FEM system is provided herein. In at least one embodiment, each FEM in a multi-FEM system includes a single-port SRS interface configured to receive an SRS and to provide an SRS. In some examples, the FEM includes a simplified antenna switching module that incurs reduced losses. In addition, the FEM can be included in the FEM system with reduced routing between the SRS interfaces of each FEM. 
       FIG. 2  illustrates a block diagram of a FEM system  200  according to an example. In some examples, the FEM system  200  may be included in a wireless-communication device, such as the mobile device  100 . For example, the FEM system  200  may be an implementation of the FEM  103 . The FEM system  200  includes a first FEM  202   a  and a second FEM  202   b  (collectively, FEMs  202 ). The FEMs  202  may each be an example of, or included in, the FEM  103 . In at least one example, each of the FEMs  202   a ,  202   b  is substantially identical to one another. For purposes of example, each of the FEMs  202   a ,  202   b  is illustrated in a one-transmit (including, for example, one PA), two-receive (including, for example, two LNAs) arrangement such that the FEM system  200  as a whole depicts a two-transmit, four-receive arrangement (2T4R). It is appreciated that this arrangement is illustrated for purposes of example only, and that different arrangements are within the scope of the disclosure. 
     The first FEM  202   a  includes a first antenna switch module (ASM)  204   a , a first SRS input port  206   a  (or pin), a first SRS output port  208   a  (or pin), a first transmit port  210   a  (or pin), a first receive port  212   a  (or pin), a second receive port  214   a  (or pin), a first antenna port  216   a  (or pin), and a second antenna port  218   a  (or pin). The second FEM  202   b  includes a second ASM  204   b , a second SRS input port  206   b  (or pin), a second SRS output port  208   b  (or pin), a second transmit port  210   b  (or pin), a third receive port  212   b  (or pin), a fourth receive port  214   b  (or pin), a third antenna port  216   b  (or pin), and a fourth antenna port  218   b  (or pin). Like-named components of the FEMs  202   a ,  202   b  may be referred to collectively herein, such as by referring to the ASMs  204   a ,  204   b  collectively as the “ASMs  204 .” Similar principles apply to the FEMs  202  themselves. 
     Each of the ASMs  204  is configured to be coupled to respective ports  208 - 218 , that is, the ASM  204   a  is configured to be coupled to the SRS input port  206   a , the SRS output port  208   a , and so forth, and the ASM  204   b  is configured to be coupled to the SRS input port  206   b , the SRS output port  208   b , and so forth. The first SRS input port  206   a  is coupled to the first ASM  204   a  via an SRS-input path (labeled “SRS In”), and is configured to be coupled to the second SRS output port  208   b  via a first trace  220 . The first SRS output port  208   a  is coupled to the first ASM  204   a  via an SRS-output path (“SRS Out”), and is configured to be coupled to the second SRS input port  206   b  via a second trace  222 . 
     The first transmit port  210   a  is coupled to the first ASM  204   a  via a transmit path (“TX Path”), and is configured to be coupled to a transceiver (not illustrated in  FIG. 2 ), such as the transceiver  102 . The first receive port  212   a  and the second receive port  214   a  are each coupled to the first ASM  204   a  via respective receive paths (“RX Path 1” and “RX Path 2,” respectively), and are each configured to be coupled to a transceiver, such as the transceiver  102 . The first antenna port  216   a  and the second antenna port  218   a  are each coupled to the first ASM  204   a  via respective transmit/receive paths (“T/R Path 1” and “T/R Path 2,” respectively), and are each configured to be coupled to a respective antenna (not illustrated in  FIG. 2 ), such as in connection with the antennas  104 . 
     The second SRS input port  206   b  is coupled to the second ASM  204   b  via an SRS-input path (“SRS In”), and is configured to be coupled to the first SRS output port  208   a  via the second trace  222 . The second SRS output port  208   b  is coupled to the second ASM  204   b  via an SRS-output path (“SRS Out”), and is configured to be coupled to the first SRS input port  206   a  via the first trace  220 . 
     The second transmit port  210   b  is coupled to the second ASM  204   b  via a transmit path (“TX Path”), and is configured to be coupled to a transceiver, such as the transceiver  102 . The third receive port  212   b  and the fourth receive port  214   b  are each coupled to the second ASM  204   b  via respective receive paths (“RX Path 1” and “RX Path 2,” respectively), and are each configured to be coupled to a transceiver, such as the transceiver  102 . The third antenna port  216   b  and the fourth antenna port  218   b  are each coupled to the second ASM  204   b  via respective transmit/receive paths (“T/R Path 1” and “T/R Path 2,” respectively), and are each configured to be coupled to a respective antenna, such as in connection with the antennas  104 . 
     At least because each of the identified paths may be coupled to a respective port, it is to be appreciated that providing a signal to, from, via, and so forth, a port may be understood to be providing the signal to, from, via, and so forth, a corresponding path. For example, a signal provided at the first antenna port  216   a  may be understood to be provided via the T/R Path 1 of the first FEM  202   a , an SRS output at the first SRS output  208   a  may be understood to be provided via the SRS Out path, and so forth. 
     In various examples, the ASMs  204  are controlled or operated to connect the transmit ports  210  and the receive ports  212 ,  214  of each respective FEM  202  to respective antenna ports  216 ,  218 .  FIG. 2  illustrates several example switchable connections that the ASMs  204  may facilitate or establish based on one or more control signals, and it is to be appreciated that in other examples, the ASMs  204  may facilitate or establish additional, fewer, or different switchable connections. In some examples, the FEM system  200  and/or the mobile device  100  includes at least one controller configured to control the ASMs  204 , such as by opening and/or closing one or more switchable connections. The at least one controller may be coupled to the memory  106  as discussed above. 
     Transmit/receive paths (“T/R paths”) corresponding to each of the antenna ports  216 ,  218  are coupled between the ASMs  204  and the respective antenna ports. In some examples, each T/R path includes a band-pass filter corresponding to the wireless application of the FEM system  200  (for example, 5G). 
     In a transmit mode of operation, the ASMs  204  may be operated to connect the transmit port  210  (and, by extension, the TX Path) of each respective FEM  202  to one of the respective antenna ports  216 ,  218  (and, by extension, the T/R Path 1 or the T/R Path 2). As understood by one of ordinary skill in the art, an ASM may include a plurality of switchable connections such that one connection to the ASM may be coupled to another connection to the ASM.  FIG. 2  illustrates switchable connections within the ASMs  204  that may be established in some examples, and in alternate examples, different connections may be established. 
     Likewise, in a receive mode of operation, the ASMs  204  may be operated to connect at least one of the receive ports  212 ,  214  (and, by extension, at least one of the RX Path 1 or the RX Path 2) to the antenna ports  216 ,  218  (and, by extension, the T/R Path 1 and the T/R Path 2). For example, the ASMs  204  can be operated to connect each of the receive ports  212 ,  214  to a respective one of the antenna ports  216 ,  218 , thereby connecting each of the receive paths (RX Path 1, RX Path 2) to a respective one of the T/R paths (T/R Path 1, T/R Path 2). In some cases, in a transmit/receive mode of operation, the ASMs  204  may be operated to connect the transmit ports  210  (via the TX Path) to one of the antenna ports  216 ,  218  (via T/R Path 1 or T/R Path 2) and to connect one of the receive ports  212 ,  214  (via RX Path 1 or RX Path 2) to the other antenna port  216 ,  218  (via T/R Path 2 or T/R Path 1). In certain examples, the FEMs  202  can be controlled in unison (for example, in the same mode of operation). In other examples, the FEMs  202  may be controlled independently. 
     In one example, the FEM system  200  is configured with full SRS functionality. To support full SRS functionality, each transmit path in the FEM system  200  may be connected to each respective T/R path. For example, in the first FEM  202   a , the TX path coupled to the transmit port  210   a  may be coupled to the T/R Path 1 coupled to the first antenna port  216   a  and to the T/R Path 2 coupled to the second antenna port  218   a.    
     The ASMs  204  can be controlled to connect each transmit path to each respective T/R path within the FEMs  202 . However, in order to connect the transmit path of the first FEM  202   a  to the T/R paths of the second FEM  202   b  (or vice versa), an SRS interface is included in each of the FEMs  202 . For example, the first FEM  202   a  includes the first SRS input port  206   a  and the first SRS output port  208   a , and the second FEM  202   b  includes the second SRS input port  206   b  and the second SRS output port  208   b.    
     As discussed above, the first SRS input port  206   a  is coupled to the second SRS output port  208   b  via the first trace  220 , and the first SRS output port  206   b  is coupled to the second SRS input port  206   b  via the second trace  222 . As such, when a first SRS is provided from the first transmit port  210   a , the ASM  204   a  may be controlled to provide the first SRS to the first antenna port  216   a , the second antenna port  218   a , and the first SRS output port  208   a  via the T/R Path 1, T/R Path 2, and SRS Out path, respectively, of the first FEM  202   a . For example, the first ASM  204   a  can be operated to switchably connect the TX Path of the first FEM  204   a  to the T/R Path 1, the T/R Path 2, and the SRS Out path of the first FEM  202   a.    
     The first SRS is provided from the first SRS output port  208   a  to the second SRS input port  206   b  of the second FEM  202   b  via the first signal trace  222 , and the second ASM  204   b  is controlled to provide the first SRS to the third antenna port  216   b  and the fourth antenna port  218   b  of the second FEM  202   b . For example, the second ASM  204   b  can be operated to connect the second SRS input port  206   b  of the second FEM  202   b  to each of the antenna ports  216   b ,  218   b  of the second FEM  202   b . In some examples, the second ASM  204   b  may be operated to connect the second SRS input port  206   b  to the second SRS output port  208   b  of the second FEM  202   b.    
     Similarly, when a second SRS is provided from the second transmit port  210   b  of the second FEM  202   b , the second ASM  204   b  is controlled to provide the second SRS to the third antenna port  216   b , the fourth antenna port  218   b , and the second SRS output port  208   b  via the T/R Path 1, the T/R Path 2, and the SRS Out path, respectively, of the second FEM  202   b . For example, the second ASM  204   b  can be operated to switchably connect the TX Path of the second FEM  204   b  to the T/R Path 1, the T/R Path 2, and the SRS Out path of the second FEM  202   b . The second SRS is provided from the second SRS output port  208   b  to the first SRS input port  206   a  of the first FEM  202   a  via the first signal trace  220  and the first ASM  204   a  is controlled to provide the second SRS to the T/R Path 1 and the T/R Path 2 of the first FEM  202   a . For example, the first ASM  204   a  can be operated to connect the first SRS input port  206   a  of the first FEM  202   a  to each of the antenna ports  216   a ,  218   a  of the first FEM  202   a . In some examples, the first ASM  204   a  may be operated to connect the first SRS input port  206   a  to the first SRS output port  208   a  of the first FEM  202   a . In some examples, the first SRS and the second SRS may be the same signal. In other examples, the first SRS and the second SRS may be different signals. 
     As described above, the traces  220 ,  222  between the SRS ports  206 ,  208  may occupy valuable area within a wireless-communication device (for example, on a circuit board). In some examples, given that the SRS may be an RF signal, the traces  220 ,  222  may be RF transmission lines having specific characteristics (for example, length, width, and so forth) and routing limitations (for example, cross-talk spacing). As such, the inclusion of traces  220 ,  222  can increase the complexity of signal routing within the wireless-communication device. In addition, the SRS ports  206 ,  208  of each of the FEMs  202  may reduce the input/output (IO) availability of each of the FEMs  202  and increase the overall package size of the FEMs  202 . For example, in one example of a 24-pin device package, the input and output SRS-interface pins may occupy about 8% of the total IO availability. As such, a larger device package (and thus more pins) may be needed to include the multi-port SRS interface while maintaining full FEM functionality. In some examples, the pin selections for the SRS interface may dictate or otherwise affect the orientation of the FEMs  202 , thus increasing the design/layout complexity of the FEM system  200  (or the wireless device). 
     In addition, being that in some examples the ASMs  204  are configured to direct an SRS between the transmit and T/R paths of the FEMs  202  and provide regular transmit/receive functionality, the ASMs  204  may be large and complex. For example, the ASMs  204  may include input/output ports corresponding to the multi-port SRS interface of each of the FEMs  202 . In some examples, the ASMs  204  can incur additional losses and occupy additional area within the FEMs  202  due to the inclusion of additional ports for the multi-port SRS interfaces. As such, an improved FEM and FEM system may be desired to simplify the SRS interface, the associated signal routing, and a respective ASM included in each FEM. 
       FIG. 3  illustrates a block diagram of a FEM system  300  according to an example. As shown, the FEM system  300  includes a first FEM  302   a  and a second FEM  302   b . In one example, the FEM system  300  is substantially similar to the FEM system  200  of  FIG. 2 , except the FEMs  302   a ,  302   b  each include a single-port SRS interface. For example, the first FEM  302   a  includes a first SRS input/output port  306   a , and the second FEM  302   b  includes a second SRS input/output port  306   b . In one example, the first SRS input/output port  306   a  is coupled to the second SRS input/output port  306   b  via a trace  318 . 
     The first FEM  302   a  includes a first ASM  304   a , the first SRS input/output port  306   a , a first transmit port  308   a , a first receive port  310   a , a second receive port  312   a , a first antenna port  314   a , and a second antenna port  316   a . The second FEM  302   b  includes a second ASM  304   b , the second SRS input/output port  306   b , a second transmit port  308   b , a third receive port  310   b , a fourth receive port  312   b , a third antenna port  314   b , and a fourth antenna port  316   b . The connections of the ports  308 - 316  are substantially similar or identical to the like-named ports  210 - 218 , respectively, and are not repeated for purposes of brevity. 
     In one example, the first ASM  304   a  can be operated to connect the first transmit port  308   a  to any of the first SRS input/output port  306   a , the first antenna port  314   a , and the second antenna port  316   a . The first ASM  304   a  may also be operated to connect each of the receive ports  310   a ,  312   a  to any of the antenna ports  314   a ,  316   a , and to connect the first SRS input/output port  306   a  to any of the antenna ports  314   a ,  316   a.    
     Similarly, the second ASM  304   b  can be operated to connect the second transmit port  308   b  to any of the second SRS input/output port  306   b , the third antenna port  314   b , and the fourth antenna port  316   b . The second ASM  304   b  may also be operated to connect each of the receive ports  310   b ,  312   b  to any of the antenna ports  314   b ,  316   b , and to connect the second SRS input/output port  306   b  to any of the antenna ports  314   b ,  316   b . In other examples, the ASMs  304  may be configured differently (for example, enabling additional, fewer, or different interconnections). 
     In some examples, when a first SRS is provided from the transmit port  308   a  of the first FEM  302   a , the first ASM  304   a  is controlled to provide the first SRS to the antenna ports  314   a ,  316   a  and to the first SRS input/output port  306   a . For example, the first ASM  304   a  can be operated to connect the transmit port  308   a  of the first FEM  302   a  to each of the antenna ports  314   a ,  316   a , and to the first SRS input/output port  306   a . The first SRS may be provided from the first SRS input/output port  306   a  to the second SRS input/output port  306   b  of the second FEM  302   b  via the trace  318 . The second ASM  304   b  may be controlled to provide the first SRS to the antenna ports  314   b ,  316   b . For example, the second ASM  304   b  can be operated to connect the second SRS input/output port  306   b  to either of the antenna ports  314   b ,  316   b.    
     Similarly, when a second SRS is provided from the transmit port  308   b  of the second FEM  302   b , the second ASM  304   b  is controlled to provide the second SRS to the second SRS input/output port  306   b , the third antenna port  314   b , and the fourth antenna port  316   b . For example, the second ASM  304   b  can be operated to connect the transmit port  308   b  to each of the antenna ports  314   b ,  316   b  and the second SRS input/output port  306   b . The second SRS is provided from the second SRS input/output port  306   b  to the first SRS input/output port  306   a  via the signal trace  318 . The first ASM  304   a  may be controlled to provide the second SRS to the antenna ports  314   a ,  316   a . For example, the first ASM  304   a  can be operated to connect the first SRS input/output port  306   a  to either of the antenna ports  314   a ,  316   a.    
     In one example, the area occupied by the FEM system  300  is less than an area occupied by the FEM system  200 . For example, an area occupied by the SRS input/output ports  306 , and the trace  318  therebetween, may be less than the area occupied by the SRS input ports  206 , the SRS output ports  208 , and the traces  220 ,  222 . In some examples, the implementation of the SRS ports  306  may reduce the overall routing complexity of the FEM system  300  relative to other systems, such as the FEM system  200 . In addition, the implementation of the SRS input/output ports  306  may increase the IO availability of the FEM system  300  and/or reduce the overall package size of the FEM system  300  relative to other arrangements, such as the FEM system  200 . 
     For example, in a 24-pin device package, the SRS input/output ports  306  and associated routing may occupy only about 4% of the total IO availability. As such, the SRS input/output ports  306  can be included in a standard (or smaller) package size (as compared to the FEM system  200 , for example) while maintaining full FEM functionality. In some examples, the SRS input/output ports  306  may provide additional flexibility in the orientation of the FEMs  302 , reducing the design and/or layout complexity of the FEM system  300  (or a device in which the FEM system  300  is implemented). 
     In addition, being that an SRS may be directed between the transmit ports  308  and antenna ports  314 ,  316  via the SRS input/output ports  306 , the size and complexity of the ASMs  304  can be reduced (for example, relative to multi-port SRS interfaces, such as those implemented in connection with the FEM system  200 ). For example, rather than including discrete input and output ports for the SNS interface, the ASMs  304  may each include a single input/output port corresponding to the SRS input/output ports  306 . In some examples, losses incurred by the ASMs  304  and the area occupied within the FEMs  302  by the ASMs  304  can be reduced due to the reduction of ports for the SRS interface relative to other arrangements, such as the FEM system  200 . 
     It should be appreciated that the FEM system  300  is configured with a two-transmit, four-receive arrangement (2T4R) for purposes of example only. Similar SRS interfaces can be included in different FEM configurations. For example,  FIG. 4  illustrates a block diagram of a FEM system  400  according to an example. As shown, the FEM system  400  includes a first FEM  402   a  and a second FEM  402   b . In one example, the FEM system  400  is substantially similar to the FEM system  300  of  FIG. 3 , except the FEMs  402  are each configured with additional transmit and receive ports. 
     For example, the first FEM  402   a  includes a first ASM  404   a , a first SRS input/output port  406   a , a first plurality of transmit ports  408   a , a first plurality of receive ports  410   a , and a first plurality of antenna ports  412   a . The second FEM  402   b  includes a second ASM  404   b , a second SRS input/output port  406   b , a second plurality of transmit ports  408   b , a second plurality of receive ports  410   b , and a second plurality of antenna ports  412   b . The first SRS input/output port  406   a  is coupled to the second input/output port  406   b  via a trace  414 . 
     In one example, the pluralities of transmit ports  408  each include two transmit ports, the pluralities of receive ports  410  each include four receive ports, and the pluralities of antenna ports  412  each include four antenna ports such that the FEM system  400  may be configured in a four-transmit, eight-receive (4T8R) configuration. However, it is to be appreciated that in other examples, each of the pluralities may include additional or fewer ports. In various examples, each of the FEMs  402  includes only a single respective SRS input/output port for any arbitrary number of transmit, receive, and/or antenna ports. 
     In one example, the first ASM  404   a  can be operated to connect any transmit port of the first plurality of transmit ports  408   a  to any antenna port of the first plurality of antenna ports  412   a , and to the first SRS input/output port  406   a . The first ASM  404   a  may also be operated to connect any receive port of the first plurality of receive ports  410   a  to any antenna port of the first plurality of antenna ports  412   a , and to connect the first SRS input/output port  406   a  to any antenna port of the first plurality of antenna ports  412   a.    
     Similarly, the second ASM  404   b  can be operated to connect any transmit port of the second plurality of transmit ports  408   b  to any antenna port of the second plurality of antenna ports  412   b , and to the second SRS input/output port  406   b . The second ASM  404   b  may also be operated to connect any receive port of the second plurality of receive ports  410   b  to any antenna port of the second plurality of antenna ports  412   b , and to connect the second SRS input/output port  406   b  to any antenna port of the second plurality of antenna ports  412   b . In other examples, the ASMs  404  may be configured differently (for example, enabling additional, fewer, or different interconnections). 
     In some examples, when the SRS is provided from one of the transmit ports of the first plurality of transmit ports  408   a , the first ASM  404   a  is controlled to provide a first SRS to at least one antenna port of the first plurality of antenna ports  412   a  and/or to the first SRS input/output port  406   a . For example, the first ASM  404   a  may be operated to connect any of the transmit ports of the first plurality of transmit ports  408   a  to any antenna port of the first plurality of antenna ports  412   a  and to the first SRS input/output port  406   a . The first SRS is provided from the first SRS input/output port  406   a  to the second SRS input/output port  406   b  via the trace  414 . The second ASM  404   b  may be controlled to provide the first SRS to any antenna port of the second plurality of antenna ports  412   b . For example, the second ASM  404   b  can be operated to connect the second SRS input/output port  406   b  to any antenna port of the second plurality of antenna ports  412   b.    
     Similarly, when a second SRS is provided from a transmit port of the second plurality of transmit ports  408   b , the second ASM  404   b  may be controlled to provide the second SRS to any antenna port of the second plurality of antenna ports  412   b  and/or to the second SRS input/output port  406   b . For example, the second ASM  404   b  can be operated to connect any of the transmit ports of the second plurality of antenna ports  408   b  to any of the antenna ports of the second plurality of antenna ports  412   b  and to the second SRS input/output port  406   b . The second SRS is provided from the second SRS input/output port  406   b  to the first SRS input/output port  406   b  via the trace  404 . The first ASM  404   a  may be controlled to provide the second SRS to any antenna port of the first plurality of antenna ports  412   a . For example, the first ASM  404   a  can be operated to connect the first SRS input/output port  406   a  to any antenna port of the first plurality of antenna ports  412   a.    
     In some examples, the first SRS and the second SRS may be the same signal. In other examples, the first SRS and the second SRS may be different signals. 
     In one example, an area occupied by the SRS ports and/or routing in the FEM system  400  may be reduced relative to a 4T8R system in which multiple SRS input ports and multiple SRS output ports are implemented. In some examples, the SRS input/output ports  406  of the FEMs  402  can reduce the overall routing complexity of the FEM system  400  relative to other arrangements, such as the FEM system  200 . In addition, the SRS input/output ports  406  may increase the IO availability of each FEM  402  and/or reduce the overall package size of each FEM  402  relative to other arrangements, such as the FEM system  200 . For example, in a 24-pin device package, the SRS-interface pin may occupy only about 4% of the total IO availability. As such, the SRS input/output ports  406  may be included in a standard (or smaller) package size while maintaining full FEM functionality. In some examples, the SRS input/output ports  406  may provide additional flexibility in the orientation of the FEMs  402 , reducing the design/layout complexity of the FEM system  400  (or the wireless device). 
     In addition, the size and/or complexity of the ASMs  404  may be reduced by implementing the SRS input/output ports  406 . For example, rather than including discrete input and output ports to couple to an SRS interface, each of the ASMs  404  may include a single input/output port to be coupled to a respective one of the SRS input/output ports  406 . In some examples, losses incurred by the ASMs  404  and the area occupied within the FEMs  402  by the ASMs  404  can be reduced due to the reduction of ports for the SRS interface relative to other arrangements, such as the FEM system  200 . 
     It should be appreciated that while the FEM systems  300 ,  400  have been described above with reference to various 5G cellular applications, similar FEM architectures may be used in different wireless applications. For example, the FEM systems  300 ,  400  may be configured for use in wireless local area network (WLAN), ultra-wideband (UWB), wireless personal area network (WPAN), 4G cellular, LTE cellular applications, and so forth. In addition, the single-port interfaces of each FEM may be configured for different calibration or characterization purposes corresponding to the specific application of use. 
     In some examples, one or more components of the FEMs  302 ,  402  included in the FEM systems  300 ,  400  may include gallium arsenide (GaAs) heterojunction bipolar transistors (HBT) and/or silicon germanium (SiGe) HBTs. In certain examples, the FEMs or one or more components of the FEMs may be fabricated using silicon-on-insulator (SOI) techniques. 
     Embodiments of the FEMs  302 ,  402  and/or the FEM systems  300 ,  400  described herein may be advantageously used in a variety of electronic devices. Examples of the electronic devices can include, but are not limited to, consumer electronic products, parts of consumer electronic products, electronic test equipment, cellular communications infrastructure such as a base station, etc. Examples of the electronic devices can include, but are not limited to, a router, a gateway, a mobile phone such as a smart phone, a telephone, a television, a computer monitor, a computer, a modem, a hand-held computer, a laptop computer, a tablet computer, an electronic book reader, a wearable computer such as a smart watch, a personal digital assistant (PDA), an appliance, such as a microwave, refrigerator, or other appliance, an automobile, a stereo system, a DVD player, a CD player, a digital music player such as an MP3 player, a radio, a camcorder, a camera, a digital camera, a portable memory chip, a health-care-monitoring device, a vehicular electronics system such as an automotive electronics system or an avionics electronic system, a peripheral device, a wrist watch, a clock, etc. Further, the electronic devices can include unfinished products. 
     In light of the foregoing, an improved FEM and FEM system are provided herein. In at least one embodiment, the FEM includes a single-pin SRS interface configured to receive an SRS and to provide an SRS. In some examples, the FEM includes a simplified antenna switching module that incurs reduced losses. In addition, the FEM can be included in the FEM system with reduced routing between the SRS interfaces of each FEM. 
     It is to be appreciated that example FEMs and FEM systems provided herein are provided for purposes of explanation. In some examples, certain FEMs and/or FEM systems may include additional, fewer, or different components than those illustrated. Certain FEMs and/or FEM systems may include additional components that have not been illustrated for purposes of clarity. For example, one or more of the FEMs  302   a ,  302   b ,  410 ,  420  may include an interface configured according to the Mobile Industry Processor Interface (MIPI) standard and having one or more ports or pins, one or more voltage input or output ports or pins, one or more filters, one or more amplifiers (including, for example, PAs, LNAs, and so forth), one or more coupling elements, one or more coupler ports or pins, one or more resistors, inductors, and/or capacitors, one or more switches, and so forth. 
     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 the scope of the invention should be determined from proper construction of the appended claims, and their equivalents.