Patent Publication Number: US-2022231733-A1

Title: Apparatus and methods for multi-antenna communications

Description:
RELATED APPLICATIONS 
     Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet, or any correction thereto, are hereby incorporated by reference into this application under 37 CFR 1.57. 
     BACKGROUND 
     Technical Field 
     Embodiments of the invention relate to electronic systems, and in particular, to radio frequency (RF) electronics. 
     Description of Related Technology 
     A communication system can include a transceiver, a front end, and one or more antennas for wirelessly transmitting and/or receiving signals. The front end can include low noise amplifier(s) for amplifying relatively weak signals received via the antenna(s), and power amplifier(s) for boosting signals for transmission via the antenna(s). 
     Examples of communication systems include, but are not limited to, mobile phones, tablets, base stations, network access points, customer-premises equipment (CPE), laptops, and wearable electronics. 
     SUMMARY 
     In certain embodiments, the present disclosure relates to a radio frequency system. The radio frequency system includes two or more frequency downconverters configured to output two or more analog baseband signals in response to receiving a plurality of radio frequency signals from an antenna array. The radio frequency system further includes a controllable amplification and combining circuit configured to generate two or more amplified analog baseband signals based on amplifying each of the two or more analog baseband signals with a separately controllable gain, and to combine the two or more amplified analog baseband signals to generate a combined analog baseband signal. The radio frequency system further includes a data conversion and signal processing circuit configured to receive the combined signal. 
     In some embodiments, the controllable amplification and combining circuit is configured to generate the combined analog baseband signal in a first mode, and to output the two or more amplified analog baseband signals in a second mode. According to a number of embodiments, the radio frequency system operates with beamforming in the first mode and with diversity communications in the second mode. 
     In several embodiments, the controllable amplification and combining circuit includes two or more controllable gain input amplifiers configured to amplify the two or more analog baseband signals to generate the two or more amplified analog baseband signals. In accordance with various embodiments, the controllable amplification and combining circuit further includes two or more DC offset compensation circuits each configured to provide a separately controllable DC offset correction to a corresponding one of the two or more controllable gain input amplifiers. 
     In some embodiments, the data conversion and signal processing circuit includes two or more analog-to-digital converters each configured to receive a corresponding one of the two or more amplified analog baseband signals. 
     In various embodiments, the radio frequency system further includes two or more local oscillators configured to control downconversion of the two or more frequency downconverters. According to a number of embodiments, the two or more local oscillators each include a phase-locked-loop configured to receive a common timing reference signal. 
     In certain embodiments, the present disclosure relates to a method of radio frequency communication. The method includes receiving a radio wave using a plurality of antenna elements of an antenna array, generating two or more analog baseband signals using a plurality of radio frequency circuit channels each coupled to a corresponding one of the plurality of antenna elements, amplifying each of the two or more analog baseband signals with a separately controllable gain using a controllable amplification and combining circuit, and combining the two or more amplified analog baseband signals to generate a combined analog baseband signal using the controllable amplification and combining circuit. 
     In various embodiments, the method further includes generating the combined analog baseband signal in a first mode of the controllable amplification and combining circuit, and outputting the two or more amplified analog baseband signals in a second mode of the controllable amplification and combining circuit. According to a number of embodiments, the method further includes forming a receive beam in the first mode and operating with diversity communications in the second mode. 
     In a number of embodiments, the method further includes compensating for a DC offset of each of the two or more amplified analog baseband signals. 
     In some embodiments, the method further includes converting the combined analog baseband signal to a digital signal. 
     In various embodiments, the method further includes performing phase shifting in each of the radio frequency circuit channels at an intermediate frequency that is less than a frequency of the radio wave. 
     In several embodiments, the method further includes generating a plurality of clock signals using a plurality of local oscillators operating with a common timing reference signal, and providing each of the plurality of clock signals to a corresponding one of the plurality of radio frequency circuit channels. 
     In some embodiments, the method further includes generating a first intermediate frequency signal using a first radio frequency circuit channel of the plurality of radio frequency circuit channels, generating a second intermediate frequency signal using a second radio frequency circuit channel of the plurality of radio frequency circuit channels, and combining the first intermediate frequency signal and the second intermediate frequency signal. 
     In certain embodiments, the present disclosure relates to a communication system. The communication system includes an antenna array including a plurality of antenna elements, a plurality of radio frequency circuit channels each coupled to a corresponding one of the plurality of antenna elements, and a controllable amplification and combining circuit. The plurality of radio frequency circuit channels are operable to generate two or more analog baseband signals in response to the antenna array receiving a radio wave. Additionally, the controllable amplification and combining circuit is configured to generate two or more amplified analog baseband signals based on amplifying each of the two or more analog baseband signals with a separately controllable gain, and to combine the two or more amplified analog baseband signals to generate a combined analog baseband signal. 
     In various embodiments, the controllable amplification and combining circuit is configured to generate the combined analog baseband signal in a first mode, and to output the two or more amplified analog baseband signals in a second mode. According to a number of embodiments, the communication system operates with beamforming in the first mode and with diversity communications in the second mode. 
     In some embodiments, the controllable amplification and combining circuit includes two or more controllable gain input amplifiers configured to amplify the two or more analog baseband signals to generate the two or more amplified analog baseband signals. According to a number of embodiments, the controllable amplification and combining circuit further includes two or more DC offset compensation circuits each configured to provide a separately controllable DC offset correction to a corresponding one of the two or more controllable gain input amplifiers. 
     In several embodiments, the communication system further includes a data conversion and signal processing circuit including two or more analog-to-digital converters each configured to receive a corresponding one of the two or more amplified analog baseband signals. 
     In a number of embodiments, the plurality of radio frequency circuit channels each include a controllable phase shifter configured to provide phase shifting at an intermediate frequency that is less than a frequency of the radio wave. 
     In some embodiments, the communication system further includes a plurality of local oscillators each configured to provide at least one clock signal to a corresponding one of the plurality of radio frequency circuit channels. According to various embodiments, the plurality of local oscillators each include a phase-locked-loop configured to receive a common timing reference signal. 
     In several embodiments, the plurality of radio frequency circuit channels includes a first radio frequency circuit channel including a first mixer configured to generate a first intermediate frequency signal, and a second radio frequency circuit channel including a second mixer configured to generate a second intermediate frequency signal. According to a number of embodiments, the communication system further includes a combiner configured to generate a first analog baseband signal of the two or more analog baseband signals based on combining the first intermediate frequency signal and the second intermediate frequency signal. 
     In certain embodiments, the present disclosure relates to a semiconductor die. The semiconductor die includes a plurality of controllable gain input amplifiers configured to amplify a plurality of analog baseband signals to generate a plurality of amplified analog baseband signals, each of the plurality of controllable gain input amplifiers configured to amplify a corresponding one of the plurality of analog baseband signals with a separately controllable amount of gain. The semiconductor die further includes a plurality of selection circuits each configured to receive a respective one of the plurality of amplified baseband signals, the plurality of selection signals configured to combine the plurality of amplified analog baseband signals to generate a combined analog baseband signal in a first mode, and to output the plurality of amplified analog baseband signals in a second mode. 
     In a number of embodiments, the semiconductor die further includes a plurality of DC offset compensation circuits each configured to provide a separately controllable DC offset correction to a corresponding one of the plurality of controllable gain input amplifiers. 
     In several embodiments, the plurality of selection circuits are implemented as a plurality of cascode transistors. 
     In some embodiments, the plurality of controllable gain input amplifiers are implemented as a plurality of gain stages, the separately controllable amount of gain based on a number of the plurality of gain stages that are selected. According to a number of embodiments, the plurality of gain stages are weighted. 
     In various embodiments, the semiconductor die further includes a plurality of output buffers each configured to buffer a corresponding one of the plurality of amplified analog baseband signals. 
     In several embodiments, the semiconductor die further includes a plurality of analog-to-digital converters each configured to provide analog-to-digital conversion to a corresponding one of the plurality of amplified analog baseband signals in the second mode. According to a number of embodiments, a first analog-to-digital converter of the plurality of analog-to-digital converters is configured to provide analog-to-digital conversion to the combined analog baseband signal in the first mode. In accordance with various embodiments, one or more of the plurality of analog-to-digital converters are disabled in the first mode to reduce power consumption. 
     In certain embodiments, the present disclosure relates to a method of processing signals in a communication system. The method includes amplifying a plurality of analog baseband signals to generate a plurality of amplified analog baseband signals using a plurality of controllable gain input amplifiers, including amplifying each of the plurality of analog baseband signals using a corresponding one of the plurality of controllable gain input amplifiers. The method further includes separately controlling a gain of each of the plurality of controllable gain input amplifiers. The method further includes processing the plurality of amplified analog baseband signals using a signal selector that includes a plurality of selection circuits each receiving a corresponding one of the plurality of amplified analog baseband signals, including outputting a combined analog baseband signal in a first mode of the signal selector and outputting the plurality of amplified analog baseband signals in a second mode of the signal selector. 
     In some embodiments, the method further includes providing DC offset correction to the plurality of controllable gain input amplifiers using a plurality of DC offset compensation circuits, including correcting a DC offset of each of the plurality of controllable gain input amplifiers using a corresponding one of the plurality of DC offset compensation circuits. 
     In various embodiments, separately controlling a gain of each of the plurality of controllable gain input amplifiers includes controlling a number of active gain stages of each of the plurality of controllable gain input amplifiers. 
     In a number of embodiments, the method further includes buffering the plurality of amplified analog baseband signals. 
     In some embodiments, the method further includes providing analog-to-digital conversion of the plurality of amplified analog baseband signals using a plurality of analog-to-digital converters in the second mode. In accordance with several embodiments, the method further includes providing analog-to-digital conversion of the combined analog baseband signal using a first analog-to-digital converter of the plurality of analog-to-digital converters in the first mode. According to a number of embodiments, the method further includes deactivating one or more of the plurality of analog-to-digital converters in the first mode. 
     In certain embodiments, the present disclosure relates to a communication system. The communication system includes a plurality of radio frequency circuit channels configured to output a plurality of analog baseband signals, and a controllable amplification and combining circuit including a plurality of controllable gain input amplifiers configured to amplify the plurality of analog baseband signals to generate a plurality of amplified analog baseband signals, each of the plurality of controllable gain input amplifiers configured to amplify a corresponding one of the plurality of analog baseband signals with a separately controllable amount of gain. The controllable amplification and combining circuit further includes a plurality of selection circuits each configured to receive a respective one of the plurality of amplified baseband signals, the plurality of selection signals configured to combine the plurality of amplified analog baseband signals to generate a combined analog baseband signal in a first mode, and to output the plurality of amplified analog baseband signals in a second mode. 
     In various embodiments, the controllable amplification and combining circuit further includes a plurality of DC offset compensation circuits each configured to provide a separately controllable DC offset correction to a corresponding one of the plurality of controllable gain input amplifiers. 
     In a number of embodiments, the plurality of selection circuits are implemented as a plurality of cascode transistors. 
     In several embodiments, the plurality of controllable gain input amplifiers are implemented as a plurality of gain stages, and the separately controllable amount of gain based on a number of the plurality of gain stages that are selected. In accordance with some embodiments, the plurality of gain stages are weighted. 
     In various embodiments, the controllable amplification and combining circuit further includes a plurality of output buffers each configured to buffer a corresponding one of the plurality of amplified analog baseband signals. 
     In some embodiments, the communication system further includes a data conversion and signal processing circuit configured to receive the combined analog baseband signal in the first mode, and the plurality of amplified analog baseband signals in the second mode. 
     In several embodiments, the data conversion and signal processing circuit includes a plurality of analog-to-digital converters each configured to provide analog-to-digital conversion to a corresponding one of the plurality of amplified analog baseband signals in the second mode. In accordance with a number of embodiments, a first analog-to-digital converter of the plurality of analog-to-digital converters is configured to provide analog-to-digital conversion to the combined analog baseband signal in the first mode. According to various embodiments, the one or more of the plurality of analog-to-digital converters are disabled in the first mode to reduce power consumption. 
     In some embodiments, the communication system further includes an antenna array including a plurality of antenna elements coupled to the plurality of radio frequency circuit channels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of this disclosure will now be described, by way of non-limiting example, with reference to the accompanying drawings. 
         FIG. 1  is a schematic diagram of one example of a communication network. 
         FIG. 2A  is a schematic diagram of one example of a downlink channel using multi-input and multi-output (MIMO) communications. 
         FIG. 2B  is schematic diagram of one example of an uplink channel using MIMO communications. 
         FIG. 2C  is schematic diagram of another example of an uplink channel using MIMO communications. 
         FIG. 3A  is a schematic diagram of one example of a communication system that operates with beamforming. 
         FIG. 3B  is a schematic diagram of one example of beamforming to provide a transmit beam. 
         FIG. 3C  is a schematic diagram of one example of beamforming to provide a receive beam. 
         FIG. 4A  is a schematic diagram of one embodiment of a communication system operating in a first mode. 
         FIG. 4B  is a schematic diagram of the communication system of  FIG. 4B  operating in a second mode. 
         FIG. 5A  is a schematic diagram of a communication system according to another embodiment. 
         FIG. 5B  is a schematic diagram of a communication system according to another embodiment. 
         FIG. 6A  is a schematic diagram of one embodiment of a controllable amplification and combining circuit in a first mode of operation. 
         FIG. 6B  is a schematic diagram of the controllable amplification and combining circuit of  FIG. 6A  in a second mode of operation. 
         FIG. 7  is a schematic diagram of one embodiment of a portion of the controllable amplification and combining circuit of  FIGS. 6A and 6B . 
         FIG. 8  is a schematic diagram of one embodiment of a DC offset compensation circuit. 
         FIG. 9A  is a schematic diagram of a communication system according to another embodiment. 
         FIG. 9B  is a schematic diagram of one embodiment of a portion of the communication system of  FIG. 9A . 
         FIG. 10  is a schematic diagram of one embodiment of a mobile device. 
         FIG. 11A  is a perspective view of one embodiment of a module that operates with beamforming. 
         FIG. 11B  is a cross-section of the module of  FIG. 11A  taken along the lines  11 B- 11 B. 
     
    
    
     DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS 
     The following detailed description of certain embodiments presents various descriptions of specific embodiments. However, the innovations described herein can be embodied in a multitude of different ways, for example, as defined and covered by the claims. In this description, reference is made to the drawings where like reference numerals can indicate identical or functionally similar elements. It will be understood that elements illustrated in the figures are not necessarily drawn to scale. Moreover, it will be understood that certain embodiments can include more elements than illustrated in a drawing and/or a subset of the elements illustrated in a drawing. Further, some embodiments can incorporate any suitable combination of features from two or more drawings. 
     The International Telecommunication Union (ITU) is a specialized agency of the United Nations (UN) responsible for global issues concerning information and communication technologies, including the shared global use of radio spectrum. 
     The 3rd Generation Partnership Project (3GPP) is a collaboration between groups of telecommunications standard bodies across the world, such as the Association of Radio Industries and Businesses (ARIB), the Telecommunications Technology Committee (TTC), the China Communications Standards Association (CCSA), the Alliance for Telecommunications Industry Solutions (ATIS), the Telecommunications Technology Association (TTA), the European Telecommunications Standards Institute (ETSI), and the Telecommunications Standards Development Society, India (TSDSI). 
     Working within the scope of the ITU, 3GPP develops and maintains technical specifications for a variety of mobile communication technologies, including, for example, second generation (2G) technology (for instance, Global System for Mobile Communications (GSM) and Enhanced Data Rates for GSM Evolution (EDGE)), third generation (3G) technology (for instance, Universal Mobile Telecommunications System (UMTS) and High Speed Packet Access (HSPA)), and fourth generation (4G) technology (for instance, Long Term Evolution (LTE) and LTE-Advanced). 
     The technical specifications controlled by 3GPP can be expanded and revised by specification releases, which can span multiple years and specify a breadth of new features and evolutions. 
     In one example, 3GPP introduced carrier aggregation (CA) for LTE in Release 10. Although initially introduced with two downlink carriers, 3GPP expanded carrier aggregation in Release 14 to include up to five downlink carriers and up to three uplink carriers. Other examples of new features and evolutions provided by 3GPP releases include, but are not limited to, License Assisted Access (LAA), enhanced LAA (eLAA), Narrowband Internet of things (NB-IOT), Vehicle-to-Everything (V2X), and High Power User Equipment (HPUE). 
     3GPP introduced Phase 1 of fifth generation (5G) technology in Release 15, and plans to introduce Phase 2 of 5G technology in Release 16 (targeted for 2019). Subsequent 3GPP releases will further evolve and expand 5G technology. 5G technology is also referred to herein as 5G New Radio (NR). 
     5G NR supports or plans to support a variety of features, such as communications over millimeter wave spectrum, beamforming capability, high spectral efficiency waveforms, low latency communications, multiple radio numerology, and/or non-orthogonal multiple access (NOMA). Although such RF functionalities offer flexibility to networks and enhance user data rates, supporting such features can pose a number of technical challenges. 
     The teachings herein are applicable to a wide variety of communication systems, including, but not limited to, communication systems using advanced cellular technologies, such as LTE-Advanced, LTE-Advanced Pro, and/or 5G NR. 
       FIG. 1  is a schematic diagram of one example of a communication network  10 . The communication network  10  includes a macro cell base station  1 , a small cell base station  3 , and various examples of user equipment (UE), including a first mobile device  2   a , a wireless-connected car  2   b , a laptop  2   c , a stationary wireless device  2   d , a wireless-connected train  2   e , a second mobile device  2   f , and a third mobile device  2   g.    
     Although specific examples of base stations and user equipment are illustrated in  FIG. 1 , a communication network can include base stations and user equipment of a wide variety of types and/or numbers. 
     For instance, in the example shown, the communication network  10  includes the macro cell base station  1  and the small cell base station  3 . The small cell base station  3  can operate with relatively lower power, shorter range, and/or with fewer concurrent users relative to the macro cell base station  1 . The small cell base station  3  can also be referred to as a femtocell, a picocell, or a microcell. Although the communication network  10  is illustrated as including two base stations, the communication network  10  can be implemented to include more or fewer base stations and/or base stations of other types. 
     Although various examples of user equipment are shown, the teachings herein are applicable to a wide variety of user equipment, including, but not limited to, mobile phones, tablets, laptops, IoT devices, wearable electronics, customer premises equipment (CPE), wireless-connected vehicles, wireless relays, and/or a wide variety of other communication devices. Furthermore, user equipment includes not only currently available communication devices that operate in a cellular network, but also subsequently developed communication devices that will be readily implementable with the inventive systems, processes, methods, and devices as described and claimed herein. 
     The illustrated communication network  10  of  FIG. 1  supports communications using a variety of cellular technologies, including, for example, 4G LTE and 5G NR. In certain implementations, the communication network  10  is further adapted to provide a wireless local area network (WLAN), such as WiFi. Although various examples of communication technologies have been provided, the communication network  10  can be adapted to support a wide variety of communication technologies. 
     Various communication links of the communication network  10  have been depicted in  FIG. 1 . The communication links can be duplexed in a wide variety of ways, including, for example, using frequency-division duplexing (FDD) and/or time-division duplexing (TDD). FDD is a type of radio frequency communications that uses different frequencies for transmitting and receiving signals. FDD can provide a number of advantages, such as high data rates and low latency. In contrast, TDD is a type of radio frequency communications that uses about the same frequency for transmitting and receiving signals, and in which transmit and receive communications are switched in time. TDD can provide a number of advantages, such as efficient use of spectrum and variable allocation of throughput between transmit and receive directions. 
     In certain implementations, user equipment can communicate with a base station using one or more of 4G LTE, 5G NR, and WiFi technologies. In certain implementations, enhanced license assisted access (eLAA) is used to aggregate one or more licensed frequency carriers (for instance, licensed 4G LTE and/or 5G NR frequencies), with one or more unlicensed carriers (for instance, unlicensed WiFi frequencies). 
     As shown in  FIG. 1 , the communication links include not only communication links between UE and base stations, but also UE to UE communications and base station to base station communications. For example, the communication network  10  can be implemented to support self-fronthaul and/or self-backhaul. 
     The communication links can operate over a wide variety of frequencies. In certain implementations, communications are supported using 5G NR technology over one or more frequency bands that are less than 6 Gigahertz (GHz) and/or over one or more frequency bands that are greater than 6 GHz. For example, the communication links can serve Frequency Range 1 (FR1), Frequency Range 2 (FR2), or a combination thereof. In one embodiment, one or more of the mobile devices support a HPUE power class specification. 
     In certain implementations, a base station and/or user equipment communicates using beamforming. For example, beamforming can be used to focus signal strength to overcome path losses, such as high loss associated with communicating over high signal frequencies. In certain embodiments, user equipment, such as one or more mobile phones, communicate using beamforming on millimeter wave frequency bands in the range of 30 GHz to 300 GHz and/or upper centimeter wave frequencies in the range of 6 GHz to 30 GHz, or more particularly, 24 GHz to 30 GHz. 
     Different users of the communication network  10  can share available network resources, such as available frequency spectrum, in a wide variety of ways. 
     In one example, frequency division multiple access (FDMA) is used to divide a frequency band into multiple frequency carriers. Additionally, one or more carriers are allocated to a particular user. Examples of FDMA include, but are not limited to, single carrier FDMA (SC-FDMA) and orthogonal FDMA (OFDMA). OFDMA is a multicarrier technology that subdivides the available bandwidth into multiple mutually orthogonal narrowband subcarriers, which can be separately assigned to different users. 
     Other examples of shared access include, but are not limited to, time division multiple access (TDMA) in which a user is allocated particular time slots for using a frequency resource, code division multiple access (CDMA) in which a frequency resource is shared amongst different users by assigning each user a unique code, space-divisional multiple access (SDMA) in which beamforming is used to provide shared access by spatial division, and non-orthogonal multiple access (NOMA) in which the power domain is used for multiple access. For example, NOMA can be used to serve multiple users at the same frequency, time, and/or code, but with different power levels. 
     Enhanced mobile broadband (eMBB) refers to technology for growing system capacity of LTE networks. For example, eMBB can refer to communications with a peak data rate of at least 10 Gbps and a minimum of 100 Mbps for each user. Ultra-reliable low latency communications (uRLLC) refers to technology for communication with very low latency, for instance, less than 2 milliseconds. uRLLC can be used for mission-critical communications such as for autonomous driving and/or remote surgery applications. Massive machine-type communications (mMTC) refers to low cost and low data rate communications associated with wireless connections to everyday objects, such as those associated with Internet of Things (IoT) applications. 
     The communication network  10  of  FIG. 1  can be used to support a wide variety of advanced communication features, including, but not limited to, eMBB, uRLLC, and/or mMTC. 
       FIG. 2A  is a schematic diagram of one example of a downlink channel using multi-input and multi-output (MIMO) communications.  FIG. 2B  is schematic diagram of one example of an uplink channel using MIMO communications. 
     MIMO communications use multiple antennas for simultaneously communicating multiple data streams over common frequency spectrum. In certain implementations, the data streams operate with different reference signals to enhance data reception at the receiver. MIMO communications benefit from higher SNR, improved coding, and/or reduced signal interference due to spatial multiplexing differences of the radio environment. 
     MIMO order refers to a number of separate data streams sent or received. For instance, MIMO order for downlink communications can be described by a number of transmit antennas of a base station and a number of receive antennas for UE, such as a mobile device. For example, two-by-two (2×2) DL MIMO refers to MIMO downlink communications using two base station antennas and two UE antennas. Additionally, four-by-four (4×4) DL MIMO refers to MIMO downlink communications using four base station antennas and four UE antennas. 
     In the example shown in  FIG. 2A , downlink MIMO communications are provided by transmitting using M antennas  43   a ,  43   b ,  43   c , . . .  43   m  of the base station  41  and receiving using N antennas  44   a ,  44   b ,  44   c , . . .  44   n  of the mobile device  42 . Accordingly,  FIG. 2A  illustrates an example of m×n DL MIMO. 
     Likewise, MIMO order for uplink communications can be described by a number of transmit antennas of UE, such as a mobile device, and a number of receive antennas of a base station. For example, 2×2 UL MIMO refers to MIMO uplink communications using two UE antennas and two base station antennas. Additionally, 4×4 UL MIMO refers to MIMO uplink communications using four UE antennas and four base station antennas. 
     In the example shown in  FIG. 2B , uplink MIMO communications are provided by transmitting using N antennas  44   a ,  44   b ,  44   c , . . .  44   n  of the mobile device  42  and receiving using M antennas  43   a ,  43   b ,  43   c , . . .  43   m  of the base station  41 . Accordingly,  FIG. 2B  illustrates an example of n×m UL MIMO. 
     By increasing the level or order of MIMO, bandwidth of an uplink channel and/or a downlink channel can be increased. 
     MIMO communications are applicable to communication links of a variety of types, such as FDD communication links and TDD communication links. 
       FIG. 2C  is schematic diagram of another example of an uplink channel using MIMO communications. In the example shown in  FIG. 2C , uplink MIMO communications are provided by transmitting using N antennas  44   a ,  44   b ,  44   c , . . .  44   n  of the mobile device  42 . Additional a first portion of the uplink transmissions are received using M antennas  43   a   1 ,  43   b   1 ,  43   c   1 , . . .  43   m   1  of a first base station  41   a , while a second portion of the uplink transmissions are received using M antennas  43   a   2 ,  43   b   2 ,  43   c   2 , . . .  43   m   2  of a second base station  41   b . Additionally, the first base station  41   a  and the second base station  41   b  communication with one another over wired, optical, and/or wireless links. 
     The MIMO scenario of  FIG. 2C  illustrates an example in which multiple base stations cooperate to facilitate MIMO communications. 
       FIG. 3A  is a schematic diagram of one example of a communication system  110  that operates with beamforming. The communication system  110  includes a transceiver  105 , signal conditioning circuits  104   a   1 ,  104   a   2  . . .  104   an ,  104   b   1 ,  104   b   2  . . .  104   bn ,  104   m   1 ,  104   m   2  . . .  104   mn , and an antenna array  102  that includes antenna elements  103   a   1 ,  103   a   2  . . .  103   an ,  103   b   1 ,  103   b   2  . . .  103   bn,    103   m   1 ,  103   m   2  . . .  103   mn.    
     Communications systems that communicate using millimeter wave carriers (for instance, 30 GHz to 300 GHz), centimeter wave carriers (for instance, 3 GHz to 30 GHz), and/or other frequency carriers can employ an antenna array to provide beam formation and directivity for transmission and/or reception of signals. 
     For example, in the illustrated embodiment, the communication system  110  includes an array  102  of m×n antenna elements, which are each controlled by a separate signal conditioning circuit, in this embodiment. As indicated by the ellipses, the communication system  110  can be implemented with any suitable number of antenna elements and signal conditioning circuits. 
     With respect to signal transmission, the signal conditioning circuits can provide transmit signals to the antenna array  102  such that signals radiated from the antenna elements combine using constructive and destructive interference to generate an aggregate transmit signal exhibiting beam-like qualities with more signal strength propagating in a given direction away from the antenna array  102 . 
     In the context of signal reception, the signal conditioning circuits process the received signals (for instance, by separately controlling received signal phases) such that more signal energy is received when the signal is arriving at the antenna array  102  from a particular direction. Accordingly, the communication system  110  also provides directivity for reception of signals. 
     The relative concentration of signal energy into a transmit beam or a receive beam can be enhanced by increasing the size of the array. For example, with more signal energy focused into a transmit beam, the signal is able to propagate for a longer range while providing sufficient signal level for RF communications. For instance, a signal with a large proportion of signal energy focused into the transmit beam can exhibit high effective isotropic radiated power (EIRP). 
     In the illustrated embodiment, the transceiver  105  provides transmit signals to the signal conditioning circuits and processes signals received from the signal conditioning circuits. As shown in  FIG. 3A , the transceiver  105  generates control signals for the signal conditioning circuits. The control signals can be used for a variety of functions, such as controlling the gain and phase of transmitted and/or received signals to control beamforming. 
       FIG. 3B  is a schematic diagram of one example of beamforming to provide a transmit beam.  FIG. 3B  illustrates a portion of a communication system including a first signal conditioning circuit  114   a , a second signal conditioning circuit  114   b , a first antenna element  113   a , and a second antenna element  113   b.    
     Although illustrated as included two antenna elements and two signal conditioning circuits, a communication system can include additional antenna elements and/or signal conditioning circuits. For example,  FIG. 3B  illustrates one embodiment of a portion of the communication system  110  of  FIG. 3A . 
     The first signal conditioning circuit  114   a  includes a first phase shifter  130   a , a first power amplifier  131   a , a first low noise amplifier (LNA)  132   a , and switches for controlling selection of the power amplifier  131   a  or LNA  132   a . Additionally, the second signal conditioning circuit  114   b  includes a second phase shifter  130   b , a second power amplifier  131   b , a second LNA  132   b , and switches for controlling selection of the power amplifier  131   b  or LNA  132   b.    
     Although one embodiment of signal conditioning circuits is shown, other implementations of signal conditioning circuits are possible. For instance, in one example, a signal conditioning circuit includes one or more band filters, duplexers, and/or other components. 
     In the illustrated embodiment, the first antenna element  113   a  and the second antenna element  113   b  are separated by a distance d. Additionally,  FIG. 3B  has been annotated with an angle θ, which in this example has a value of about 90° when the transmit beam direction is substantially perpendicular to a plane of the antenna array and a value of about 0° when the transmit beam direction is substantially parallel to the plane of the antenna array. 
     By controlling the relative phase of the transmit signals provided to the antenna elements  113   a ,  113   b , a desired transmit beam angle θ can be achieved. For example, when the first phase shifter  130   a  has a reference value of 0°, the second phase shifter  130   b  can be controlled to provide a phase shift of about −2πf(d/v)cos θ radians, where f is the fundamental frequency of the transmit signal, d is the distance between the antenna elements, v is the velocity of the radiated wave, and π is the mathematic constant pi. 
     In certain implementations, the distance d is implemented to be about ½λ, where λ is the wavelength of the fundamental component of the transmit signal. In such implementations, the second phase shifter  130   b  can be controlled to provide a phase shift of about −π cos θ radians to achieve a transmit beam angle θ. 
     Accordingly, the relative phase of the phase shifters  130   a ,  130   b  can be controlled to provide transmit beamforming. In certain implementations, a baseband processor and/or a transceiver (for example, the transceiver  105  of  FIG. 3A ) controls phase values of one or more phase shifters and gain values of one or more controllable amplifiers to control beamforming. 
       FIG. 3C  is a schematic diagram of one example of beamforming to provide a receive beam.  FIG. 3C  is similar to  FIG. 3B , except that  FIG. 3C  illustrates beamforming in the context of a receive beam rather than a transmit beam. 
     As shown in  FIG. 3C , a relative phase difference between the first phase shifter  130   a  and the second phase shifter  130   b  can be selected to about equal to −2πf(d/v)cos θ radians to achieve a desired receive beam angle θ. In implementations in which the distance d corresponds to about ½λ, the phase difference can be selected to about equal to −π cos θ radians to achieve a receive beam angle θ. 
     Although various equations for phase values to provide beamforming have been provided, other phase selection values are possible, such as phase values selected based on implementation of an antenna array, implementation of signal conditioning circuits, and/or a radio environment. 
     Examples of Multi-Antenna Systems with Analog Signal Combining at Baseband 
     Antenna arrays can be used in a wide variety of applications. For example, antenna arrays can be used to transmit and/or receive radio frequency (RF) signals in base stations, network access points, mobile phones, tablets, laptops, computers, and/or other communications devices. Moreover, in certain implementations, separate antenna arrays are deployed for transmission and reception. 
     Communications devices that utilize millimeter wave carriers (for instance, 30 GHz to 300 GHz), centimeter wave carriers (for instance, 3 GHz to 30 GHz), and/or other carrier frequencies can employ an antenna array to provide beam forming, MIMO communications, and/or diversity communications. 
     Apparatus and methods for multi-antenna communications are provided. In certain embodiments, a communication system includes an antenna array including a plurality of antenna elements, and a plurality of RF circuit channels each coupled to a corresponding one of the antenna elements. The plurality of RF circuit channels generate two or more analog baseband signals in response to the antenna array receiving a radio wave. The communication system further includes a controllable amplification and combining circuit that generates two or more amplified analog baseband signals based on amplifying each of the two or more analog baseband signals with a separately controllable gain, and that combines the two or more amplified analog baseband signals to generate a combined analog baseband signal. 
     The controllable amplification and combining circuit can provide different amounts of amplification to each of the analog baseband signals. In such implementations, the combined analog baseband signal corresponds to a weighted sum of the two or more analog baseband signals. 
     In certain implementations, the controllable amplification and combining circuit is configurable in multiple modes including a first mode in which the two or more amplified analog baseband signals are combined to generate the combined analog baseband signal, and a second mode in which the two or more amplified analog baseband signals are outputted without combining. The amount of amplification provided can vary from signal to signal in the second mode. 
     Implementing the controllable amplification and combining circuit with multiple operating modes can provide a number of advantages, including allowing both beamforming in the first mode and diversity communications in the second mode. This in turn can lead to higher signal-to-noise ratio (SNR), communication at greater distances, higher data rates, and/or communication in harsher radio environments. Furthermore, DC offset correction can be provided for each amplified analog baseband signal, thereby providing DC offset correction for each channel with reduced complexity and/or with higher accuracy. 
     In certain implementations, each RF circuit channel receives one or more clock signals for downconversion from a corresponding local oscillator. Additionally, the local oscillators each receive a common timing reference signal for phase and/or frequency detection. By implementing the communication system in this manner, a number of advantages can be realized, including, but not limited to, lower current consumption in the local oscillators and/or uncorrelated noise between channels after RF. 
     In certain implementations, phase shifting is performed at least in part at intermediate frequency (IF). For example, each RF circuit channel can include an RF-to-IF mixer for downconverting a received RF signal to generate an IF signal (which can be an RF signal of lower frequency than the received RF signal), and an IF phase shifter for providing a desired amount of phase shift to the IF signal. Performing phase shifting at least in part at IF can provide a number of advantages, including, for example, lower loss and/or relaxed design constraints arising from performing phase shifting at decreased frequency relative to that of the received radio wave. 
       FIG. 4A  is a schematic diagram of one embodiment of a communication system  180  operating in a first mode. The communication system  180  includes an antenna array  181 , RF circuit channels  182 , and a controllable amplification and combining circuit  183 . 
     The RF circuit channels  182  each receive an RF signal from a corresponding antenna element of the antenna array  181  in response to a radio wave. Additionally, the RF circuit channels  182  process the RF signals to generate multiple analog baseband signals. Thus, the RF circuit channels  182  operate in part to provide downconversion. In certain implementations, the RF circuit channels  182  process k RF signals and to generate l analog baseband signals, where k and l are each an integer greater than or equal to 2. The integers k and l can be the same or different. 
     As shown in  FIG. 4A , the controllable amplification and combining circuit  183  receives the analog baseband signals, gain control signals for controlling an amount of gain provided to each of the analog baseband signals, and a mode control signal. The mode control signal operates to control the communication system  180  in one of multiple modes including at least a first mode and a second mode. 
     In  FIG. 4A , the communication system  180  is depicted operating in the first mode, in which the controllable amplification and combining circuit  183  combines the analog baseband signals to generate a combined analog baseband signal. When combining the analog baseband signals, the controllable amplification and combining circuit  183  provides gain to each analog baseband signal based on the indicated amount of gain by the gain control signals. The settings for gain can be the same or different for each analog baseband signal, and thus the combined analog baseband signal corresponds to a weighted sum of the analog baseband signals. 
       FIG. 4B  is a schematic diagram of the communication system  180  of  FIG. 4B  operating in a second mode. 
     When operating in the second mode, the communication system  180  outputs multiple analog baseband output signals without combining. The analog baseband output signals are also referred to as amplified analog baseband signals. 
     With reference to  FIGS. 4A and 4B , the communication system  180  is operable in a first mode in which the analog baseband signals are amplified and combined to generate the combined analog baseband signal, and a second mode in which the analog baseband signals are amplified and outputted without analog combining at baseband. The amount of amplification provided the analog baseband signals can also vary from signal to signal in the second mode. 
     Implementing the controllable amplification and combining circuit  183  with multiple operating modes can provide a number of advantages, including allowing both beamforming in the first mode and diversity communications in the second mode. This in turn can lead to higher SNR, communication at greater distances, higher data rates, and/or communication in harsher radio environments. Furthermore, DC offset correction can be provided for each amplified analog baseband signal, thereby providing DC offset correction for each channel with reduced complexity and/or with higher accuracy. 
       FIG. 5A  is a schematic diagram of a communication system  200  according to one embodiment. The communication system  200  includes an antenna array  201 , RF circuit channels  202   a ,  202   b , . . .  202   n , a controllable amplification and combining circuit  203 , a data conversion and signal processing circuit  204 , local oscillators (LOs)  207   a ,  207   b , . . .  207   n , and I/Q dividers  208   a ,  208   b , . . .  208   n . Although circuitry for three signal channels is depicted, more or fewer components can be included as indicated by the ellipses. 
     The antenna array  201  includes antenna elements  212   a ,  212   b ,  212   n . Although three antenna elements are illustrated, the communication system  200  can include more or fewer antenna elements as indicated by the ellipses. The antenna elements  212   a ,  212   b , . . .  212   n  can be implemented in a wide variety of ways, including, but not limited to, using patch antenna elements, dipole antenna elements, ceramic resonators, stamped metal antennas, and/or laser direct structuring antennas. Moreover, antenna elements can be arrayed in other patterns or configurations, including, for instance, rectangular arrays, linear arrays, and/or arrays using non-uniform arrangements of antenna elements. 
     In the illustrated embodiment, the RF circuit channel  202   a  includes an RF controllable gain and phase circuit  214   a , an RF-to-IF mixer  216   a , an IF controllable gain and phase circuit  218   a , an I-path mixer  221   a , and a Q-path mixer  222   a . Similarly, the RF circuit channel  202   b  includes an RF controllable gain and phase circuit  214   b , an RF-to-IF mixer  216   b , an IF controllable gain and phase circuit  218   b , an I-path mixer  221   b , and a Q-path mixer  222   b . Likewise, the RF circuit channel  202   n  includes an RF controllable gain and phase circuit  214   n , an RF-to-IF mixer  216   n , an IF controllable gain and phase circuit  218   n , an I-path mixer  221   n , and a Q-path mixer  222   n.    
     Although one example implementation of the RF circuit channels  202   a ,  202   b , . . .  202   n  is shown, the teachings herein are applicable to RF circuit channels implemented in a wide variety of ways. 
     In the illustrated embodiment, the LOs  207   a ,  207   b , . . .  207   n  generate clock signals for the RF-to-IF mixers  216   a ,  216   b , . . .  216   n , respectively. Additionally, the LOs  207   a ,  207   b , . . .  207   n  each receive a common timing reference (REF), which is used by each LO for phase and/or frequency detection. By providing a common timing reference to distributed LOs, reduced current consumption is realized relative to an implementation using a single LO that distributes a common clock signal to the mixers. Moreover, the communication system  200  can have uncorrelated phase noise after RF, and thus operates with superior SNR relative to a communication system operating with fully synchronized timing. 
     As shown in  FIG. 5A , the LOs  207   a ,  207   b , . . .  207   n  also provide clock signals to the I/Q dividers  208   a ,  208   b , . . .  208   n , respectively. The clock signals provided to the I/Q dividers  208   a ,  208   b , . . .  208   n  can be the same or different as the clock signals provided to the RF-to-IF mixers  216   a ,  216   b , . . .  216   n . The I/Q dividers  208   a ,  208   b , . . .  208   n  operate to provide frequency division to generate clock signals suitable for controlling the I-path mixers  221   a ,  221   b , . . .  221   n  and Q-path mixers  222   a ,  222   b ,  222   n.    
     As shown in  FIG. 5A , each of the RF circuit channels  202   a ,  202   b , . . .  202   n  outputs an analog baseband signal including an I-component and a Q-component. For example, the RF circuit channel  202   a  outputs an analog baseband signal I a , Q a , the RF circuit channel  202   b  outputs an analog baseband signal I b , Q b , and the RF circuit channel  202   n  outputs an analog baseband signal I n , Q n . 
     The controllable amplification and combining circuit  203  processes the analog baseband signals from the RF circuit channels  202   a ,  202   b , . . .  202   n  to generate one or more analog signals for the data conversion and signal processing circuit  204 . 
     In certain implementations, the controllable amplification and combining circuit  203  is configurable in multiple modes. The multiple modes include a first mode in which the analog baseband signals are each amplified by a separately controllable gain to generate amplified analog baseband signals, which are combined to generate a combined analog baseband signal for the data conversion and signal processing circuit  203 . In this example, the combined analog baseband signal includes I and Q components, and thus is implemented using quadrature signaling. The multiple modes further include a second mode in which the analog baseband signals are outputted to the data conversion and signal processing circuit  203  without combining. When operating in the first mode and/or the second mode, the controllable amplification and combining circuit  203  can provide a controllable amount of gain to each analog baseband signal. Thus, the amount of amplification provided can vary from signal to signal. 
     Implementing the controllable amplification and combining circuit  203  with multiple modes allows the communication system  200  to provide beamforming in the first mode and diversity communications in the second mode. Furthermore, DC offset correction can be provided for each input to the controllable amplification and combining circuit  203 , thereby providing DC offset correction with reduced complexity and/or with higher accuracy. 
     In the illustrated embodiment, the IF controllable gain and phase circuits  218   a ,  218   b , . . .  218   n  are included to provide phase shifting at least in part at IF. Performing phase shifting at least in part at IF can provide a number of advantages, including, for example, lower loss and/or relaxed design constraints arising from performing phase shifting at lower frequency relative to the frequency of the radio wave received by the antenna array  201 . 
       FIG. 5B  is a schematic diagram of a communication system  230  according to another embodiment. The communication system  230  includes an antenna array  201 , RF circuit channels  232   a ,  232   b ,  232   n , a variable gain amplifier (VGA) and combiner circuit  233 , a MIMO processing circuit  234 , a timing reference generator  235 , LOs  237   a ,  237   b ,  237   n , and I/Q dividers  238   a ,  238   b ,  238   n . Although circuitry for three signal channels is depicted, more or fewer components can be included as indicated by the ellipses. 
     The communication system  230  of  FIG. 5B  is similar to the communication system  200  of  FIG. 5A , except that the communication system  230  illustrates specific implementations of certain circuitry. 
     For example, as shown in  FIG. 5B , the RF circuit channel  232   a  includes an LNA  241   a , an RF VGA phase shifter  242   a , an RF-to-IF mixer  246   a , an IF automatic gain control (AGC) phase shifter  248   a , an I-path mixer  251   a , and a Q-path mixer  252   a . Likewise, the RF circuit channel  232   b  includes an LNA  241   b , an RF VGA phase shifter  242   b , an RF-to-IF mixer  246   b , an IF AGC phase shifter  248   b , an I-path mixer  251   b , and a Q-path mixer  252   b . Similarly, the RF circuit channel  232   n  includes an LNA  241   n , an RF VGA phase shifter  242   n , an RF-to-IF mixer  246   n , an IF AGC phase shifter  248   n , an I-path mixer  251   n , and a Q-path mixer  252   n.    
     Furthermore, the LO  237   a  includes a phase and/or frequency detector (PFD) and charge pump (CP)  261   a , a loop filter  263   a , a voltage controlled oscillator (VCO)  264   a , an output divider  265   a  ( 1  over integer M, in this example), a feedback divider  266   a  (N/N+1, in this example), and a sigma delta (ΣΔ) modulator  267   a . Similarly, the LO  237   b  includes a PFD/CP  261   b , a loop filter  263   b , a VCO  264   b , an output divider  265   b , a feedback divider  266   b , and a ΣΔ modulator  267   b . Likewise, the LO  237   n  includes a PFD/CP  261   n , a loop filter  263   n , a VCO  264   n , an output divider  265   n , a feedback divider  266   n , and a ΣΔ modulator  267   n.    
     The I/Q divider  238   a  includes a first divider  271   a  (divide by 2, in this example) and a second divider  272   a  (divide by 2, in this example). Likewise, the I/Q divider  238   b  includes a first divider  271   b  and a second divider  272   b . Similarly, the I/Q divider  238   n  includes a first divider  271   n  and a second divider  272   n.    
     With continuing reference to  FIG. 5B , the VGA and combiner circuit  233  includes VGA combining circuits  281   a ,  281   b , . . .  281   n . Additionally, the MIMO processing circuit  234  includes ADCs  284   a ,  284   b , . . .  284   n . In certain implementations, the ADCs  284   a ,  284   b , . . .  284   n  include an I-path ADC and a Q-path ADC for each RF circuit channel. 
       FIG. 6A  is a schematic diagram of one embodiment of a controllable amplification and combining circuit  300  in a first mode of operation.  FIG. 6B  is a schematic diagram of the controllable amplification and combining circuit  300  of  FIG. 6A  in a second mode of operation. The controllable amplification and combining circuit  300  is coupled to the ADCs  308   a ,  308   b , . . .  308   n  of a data conversion and signal processing circuit, such as a MIMO processing circuit. The analog signals outputted from the controllable amplification and combining circuit  300  are associated with channels Ch a , Ch b , . . . Ch n . 
     Although one embodiment of a controllable amplification and combining circuit is shown, the teachings herein are applicable to controllable amplification and combining circuits implemented in a wide variety of ways. 
     With reference to  FIGS. 6A and 6B , the controllable amplification and combining circuit  300  includes controllable gain input amplifiers  301   a ,  301   b ,  301   n , DC offset compensation circuits  302   a ,  302   b , . . .  302   n , selection circuits  303   a ,  303   b , . . .  303   n , first output buffers  305   a ,  305   b , . . .  305   n , and second output buffers  306   a ,  306   b , . . .  306   n . The output buffers can have fixed or controllable gain. The selection circuits  303   a ,  303   b , . . .  303   n  are also collectively referred to herein as a signal selector. 
     The controllable amplification and combining circuit  300  is implemented differentially, in this embodiment. However, other types of signaling can be used, such as single-ended signaling or a combination of differential and signal-ended signaling. 
     The controllable gain input amplifiers  301   a ,  301   b , . . .  301   n  provide controllable amplification to input signals In a , In b , . . . In n . The gain provided by the amplifiers  301   a ,  301   b , . . .  301   n  can be controlled in a wide variety of ways, including, but not limited to, by a transceiver or radio frequency integrated circuit (RFIC) over an interface, such as a MIPI RFFE interface. In certain implementations, the input signals In a , In b , . . . In n  correspond to I-path signals (for instance, I a , I b , . . . I n  of  FIG. 5A or 5B ), and another group of controllable gain input amplifiers and associated circuits process Q-path signals (for instance, Q a , Q b , . . . Q n  of  FIG. 5A or 5B ). Accordingly, in certain implementations multiple instantiations of the controllable amplification and combining circuit  300  are included. 
     A state of the selection circuits  303   a ,  303   b , . . .  303   n  changes based on a mode of the controllable amplification and combining circuit  300 . The selected mode can be controlled in a wide variety of ways, including, but not limited to, by a transceiver or RFIC over a MIPI RFFE interface or other suitable interface. 
     As shown in  FIG. 6A , the controllable amplification and combining circuit  300  generates a combined analog baseband signal  309  in the first mode. Since the gain of the controllable gain input amplifiers  301   a ,  301   b , . . .  301   n  can be separately controlled, the combined analog baseband signal  309  is generated by a weighted sum of the input signals In a , In b , . . . In n , in this embodiment. In certain implementations, unused ADCs are turned off in the first mode to conserve power. For example, as shown in  FIG. 6A , the ADC that is used can have an enable signal (EN) set to an enabled state (EN=1, in this example), while the ADCs that are unused can have the enable signal set to a disabled state (EN=0, in this example). In certain implementations, the ADCs are enabled or disabled using data receiver over a chip interface. 
     As shown in  FIG. 6B , the controllable amplification and combining circuit  300  generates analog baseband signals  321   a ,  321   b , . . .  321   n  in the second mode. In certain implementations, the controllable amplification and combining circuit  300  separately controls the gain of the analog baseband signals  321   a ,  321   b , . . .  321   n.    
     Implementing a controllable amplification and combining circuit with multiple modes provides a number of advantages, including allowing both beamforming in the first mode and diversity communications in the second mode. This in turn can lead to higher SNR, communication at greater distances, communication at greater data rates, and/or communication in harsher radio environments. 
     Furthermore, DC offset correction can be provided for each input to the controllable amplification and combining circuit, thereby providing DC offset correction with reduced complexity and/or with higher accuracy. For example, as shown in  FIG. 6B , the DC offset compensation circuits  302   a ,  302   b , . . .  302   n  provide a differential output signal to compensate for a DC offset of Ch a , Ch b , . . . Ch n , respectively. The amount of DC offset compensation provided by each of the DC offset compensation circuits  302   a ,  302   b , . . .  302   n  can be controlled in a wide variety of ways, including, but not limited to, by a transceiver or RFIC over a MIPI RFFE interface or other suitable interface. 
     In certain embodiments, the controllable amplification and combining circuit  300  is implemented on a semiconductor die, which can be incorporated into a radio frequency module. In certain implementations, the ADCs  308   a ,  308   b , . . .  308   n  are also included on the semiconductor die. In other implementations, the ADCs  308   a ,  308   b , . . .  308   n  are included a second semiconductor die, which can be incorporated with the first semiconductor die in a multi-chip module. 
       FIG. 7  is a schematic diagram of one embodiment of a portion of the controllable amplification and combining circuit  300  of  FIGS. 6A and 6B . The illustrated circuitry  350  includes a first pair of load resistors  351   a - 351   b , a second pair of load resistors  352   a - 352   b , a first pair of selection transistors  353   a - 353   b , a second pair of selection transistors  354   a - 354   b , a first pair of signal amplification transistors  361   a - 361   b , a second pair of signal amplification transistors  362   a - 362   b , a third pair of signal amplification transistors  363   a - 363   b , a fourth pair of signal amplification transistors  364   a - 364   b , a first weighted resistor  371 , a second weighted resistor  372 , a third weighted resistor  373 , a fourth weighted resistor  374 , a first pair of bias current sources  381   a - 381   b , a second pair of bias current sources  382   a - 382   b , a third pair of bias current sources  383   a - 383   b , a fourth pair of bias current sources  384   a - 384   b , a first pair of gain control switches  391   a - 391   b , a second pair of gain control switches  392   a - 392   b , a third pair of gain control switches  393   a - 393   b , a fourth pair of gain control switches  394   a - 394   b , and a DC offset compensation circuit  302 . The circuitry  350  is powered by a supply voltage VDD and ground. 
     The circuitry  350  illustrates one implementation of a controllable gain input amplifier, a selection circuit, and a DC offset compensation circuit. For example, the circuitry  350  can be used to implement the controllable gain input amplifier  301   a , the selection circuit  303   a , and the DC offset compensation circuit  302   a  of  FIGS. 6A and 6B . Additionally, multiple instantiations of the circuitry  350  can be used to implement the controllable amplification and combining circuit  300  of  FIGS. 6A and 6B . Although one embodiment of suitable circuitry for implementing a portion of a controllable amplification and combining circuit is shown, the teachings herein are applicable to controllable amplification and combining circuits implemented in a wide variety of ways. 
     The selection signals Sel_ 0  and Sel_ 1  operate to select the first pair of selection transistors  353   a - 353   b  or the second pair of selection transistors  354   a - 354   b , thereby providing connection to a first differential output Vout_ 0 _ p , Vout_ 0 _ n  or to a second differential output Vout_ 1 _ p , Vout_ 1 _ n . The selection signals Sel_ 0  and Sel_ 1  operate to control the mode of a controllable amplification and combining circuit between the first mode and the second mode, as discussed above. 
     The weighted resistors  371 - 374  are binary weighted, in this embodiment. Additionally, one or more of the gain control signals Gain_ 1 , Gain_ 2 , Gain_ 3 , Gain_ 4  can be activated to provide a desired amount of gain to the differential input signal Vin_p, Vin_n. Although an example with four gain stages is shown, more or fewer gain stages can be included. 
     The DC offset compensation circuit  302  outputs a differential output signal Vout_dc_p, Vout_dc_n to provide a DC offset for compensation. The amount of DC offset is controlled by a control signal CTL, in this example. 
       FIG. 8  is a schematic diagram of one embodiment of a DC offset compensation circuit  400 . The DC offset compensation circuit  400  includes a pair of load resistors  401   a - 401   b , a pair of cascode transistors  402   a - 402   b , a first pair of compensation control transistors  411   a - 411   b , a second pair of compensation control transistors  412   a - 412   b , a third pair of compensation control transistors  413   a - 413   b , a fourth pair of compensation control transistors  414   a - 414   b , a first pair of weighted bias current sources  421   a - 421   b , a second pair of weighted bias current sources  422   a - 422   b , a third pair of weighted bias current sources  423   a - 423   b , a fourth pair of weighted bias current sources  424   a - 424   b , a first pair of selection switches  431   a - 431   b , a second pair of selection switches  432   a - 432   b , a third pair of selection switches  433   a - 433   b , and a fourth pair of selection switches  434   a - 434   b . The circuitry  350  is powered by a supply voltage VDD and ground. As shown in  FIG. 8 , each pair of compensation control transistors receives a bias voltage Vbias, and the pair of cascode transistors  402   a - 402   b  receives a cascode bias voltage Vbias_csc. 
     The first pair of selection switches  431   a - 431   b  is controlled by a first pair of complementary control signals Off_ 1 , Off_ 1   b . Likewise, the second pair of selection switches  432   a - 432   b  is controlled by a second pair of complementary control signals Off_ 2 , Off_ 2   b . Similarly, the third pair of selection switches  433   a - 433   b  is controlled by a third pair of complementary control signals Off_ 3 , Off_ 3   b . Furthermore, the fourth pair of selection switches  434   a - 434   b  is controlled by a fourth pair of complementary control signals Off_ 4 , Off_ 4   b.    
     When a particular current source is activated by a particular selection switch, current from the bias current source flows through the corresponding cascode transistor  402   a  or  402   b  and load resistor  401   a  or  401   b  to control the differential output voltage Vout_dc_p, Vout_dc_n. Although an example with four pairs of weighted bias current sources is shown, other implementations are possible, such as configurations using more or fewer current sources. In this embodiment, the pairs of weighted bias current sources are binary weighted. 
       FIG. 9A  is a schematic diagram of a communication system  500  according to another embodiment. The communication system  500  includes an antenna array  501 , RF circuit channels  522   a ,  522   b ,  522   c ,  522   d , . . .  522   n −1,  522   n , a timing reference generator  235 , LOs  237   a ,  237   b ,  237   c ,  237   d , . . .  237   n −1,  237   n , I/Q dividers  238   a ,  238   b , . . .  238   n/ 2, IF combiners  531   a ,  531   b , . . .  531   n/ 2, I/Q downconverters  532   a ,  532   b , . . .  532   n/ 2, a VGA and combiner circuit  533 , and a MIMO processing circuit  534 . The antenna array  501  includes antenna elements  512   a ,  512   b ,  512   c ,  512   d , . . .  512   n −1,  512   n . Additionally, the VGA and combiner circuit  233  includes VGAs  282   a ,  282   b , . . .  282   n/ 2. Furthermore, the MIMO processing circuit includes ADCs  284   a ,  284   b , . . .  284   n/ 2. In this embodiment, n is an even integer, for instance, an integer of at least 2, or more particularly, 4 or greater. 
     The communication system  500  of  FIG. 9A  is similar to the communication system  230  of  FIG. 5B , except that the communication system  500  includes the RF combiners  531   a ,  531   b , . . .  531   n , which provide combining at IF for signals received from groups of antenna elements (groups of two, in this example). In certain implementations, two or more signals received from the antenna array  201  are combined at IF. 
     After combining at IF and subsequent downconversion, the analog baseband signals are provided to the VGA and combiner circuit  533 , which can provide controllable amplification and combining as described above. 
       FIG. 9B  is a schematic diagram of one embodiment of a portion  9 B of the communication system  500  of  FIG. 9A . The illustrated circuitry includes the timing reference generator  235 , the first antenna element  512   a , the second antenna element  512   b , the first RF circuit channel  522   a , the second RF circuit channel  522   b , the first LO  237   a , the second LO  237   b , the I/F combiner  531   a , the I/Q downconverter  532   a , the I/Q divider  238   a , the VGA  281   a , and the ADC  284   a.    
     As shown in  FIG. 9B , the first RF circuit channel  522   a  includes the LNA  241   a , the RF VGA phase shifter  242   a , the RF-to-IF mixer  246   a , and the IF AGC phase shifter  248   a . Additionally, the second RF circuit channel  522   b  includes the LNA  241   b , the RF VGA phase shifter  242   b , the RF-to-IF mixer  246   b , and the IF AGC phase shifter  248   b . The I/Q downconverter  532   a  includes the I-path mixer  251   a  and the Q-path mixer  252   a . The I/Q divider  238   a  includes the first divider  271   a  and the second divider  272   a . The LO  237   a  includes the PFD/CP  261   a , the loop filter  263   a , the VCO  264   a , the output divider  265   a , the feedback divider  266   a , and the ΣΔ modulator  267   a . Similarly, the LO  237   b  includes the PFD/CP  261   b , the loop filter  263   b , the VCO  264   b , the output divider  265   b , the feedback divider  266   b , and the ΣΔ modulator  267   b.    
       FIG. 10  is a schematic diagram of one embodiment of a mobile device  800 . The mobile device  800  includes a baseband system  801 , a transceiver  802 , a front end system  803 , antennas  804 , a power management system  805 , a memory  806 , a user interface  807 , and a battery  808 . 
     The mobile device  800  can be used 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, WiFi), WPAN (for instance, Bluetooth and ZigBee), WMAN (for instance, WiMax), and/or GPS technologies. 
     The transceiver  802  generates RF signals for transmission and processes incoming RF signals received from the antennas  804 . 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. 10  as the transceiver  802 . In one example, separate components (for instance, separate circuits or dies) can be provided for handling certain types of RF signals. 
     The front end system  803  aids is conditioning signals transmitted to and/or received from the antennas  804 . In the illustrated embodiment, the front end system  803  includes antenna tuning circuitry  810 , power amplifiers (PAs)  811 , low noise amplifiers (LNAs)  812 , filters  813 , switches  814 , and signal splitting/combining circuitry  815 . However, other implementations are possible. 
     For example, the front end system  803  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), or some combination thereof. 
     In certain implementations, the mobile device  800  supports carrier aggregation, thereby providing flexibility to increase peak data rates. Carrier aggregation can be used for both Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD), and may be used to aggregate a plurality of carriers or channels. Carrier aggregation includes contiguous aggregation, in which contiguous carriers within the same operating frequency band are aggregated. Carrier aggregation can also be non-contiguous, and can include carriers separated in frequency within a common band or in different bands. 
     The antennas  804  can include antennas used for a wide variety of types of communications. For example, the antennas  804  can include antennas for transmitting and/or receiving signals associated with a wide variety of frequencies and communications standards. 
     In certain implementations, the antennas  804  support 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 mobile device  800  can operate with beamforming in certain implementations. For example, the front end system  803  can include amplifiers having controllable gain and phase shifters having controllable phase to provide beam formation and directivity for transmission and/or reception of signals using the antennas  804 . For example, in the context of signal transmission, the amplitude and phases of the transmit signals provided to the antennas  804  are controlled such that radiated signals from the antennas  804  combine using constructive and destructive interference to generate an aggregate transmit signal exhibiting beam-like qualities with more signal strength propagating in a given direction. In the context of signal reception, the amplitude and phases are controlled such that more signal energy is received when the signal is arriving to the antennas  804  from a particular direction. In certain implementations, the antennas  804  include one or more arrays of antenna elements to enhance beamforming. 
     The baseband system  801  is coupled to the user interface  807  to facilitate processing of various user input and output (I/O), such as voice and data. The baseband system  801  provides the transceiver  802  with digital representations of transmit signals, which the transceiver  802  processes to generate RF signals for transmission. The baseband system  801  also processes digital representations of received signals provided by the transceiver  802 . As shown in  FIG. 10 , the baseband system  801  is coupled to the memory  806  of facilitate operation of the mobile device  800 . 
     The memory  806  can be used for a wide variety of purposes, such as storing data and/or instructions to facilitate the operation of the mobile device  800  and/or to provide storage of user information. 
     The power management system  805  provides a number of power management functions of the mobile device  800 . In certain implementations, the power management system  805  includes a PA supply control circuit that controls the supply voltages of the power amplifiers  811 . For example, the power management system  805  can be configured to change the supply voltage(s) provided to one or more of the power amplifiers  811  to improve efficiency, such as power added efficiency (PAE). 
     As shown in  FIG. 10 , the power management system  805  receives a battery voltage from the battery  808 . The battery  808  can be any suitable battery for use in the mobile device  800 , including, for example, a lithium-ion battery. 
       FIG. 11A  is a perspective view of one embodiment of a module  940  that operates with beamforming.  FIG. 11B  is a cross-section of the module  940  of  FIG. 11A  taken along the lines  11 B- 11 B. 
     The module  940  includes a laminated substrate or laminate  941 , a semiconductor die or IC  942  (not visible in  FIG. 11A ), surface mount devices (SMDs)  943  (not visible in  FIG. 11A ), and an antenna array including antenna elements  951   a   1 ,  951   a   2 ,  951   a   3  . . .  951   an ,  951   b   1 ,  951   b   2 ,  951   b   3  . . .  951   bn ,  951   c   1 ,  951   c   2 ,  951   c   3  . . .  951   cn ,  951   m   1 ,  951   m   2 ,  951   m   3  . . .  951   mn.    
     Although one embodiment of a module is shown in  FIGS. 11A and 11B , the teachings herein are applicable to modules implemented in a wide variety of ways. For example, a module can include a different arrangement of and/or number of antenna elements, dies, and/or surface mount devices. Additionally, the module  940  can include additional structures and components including, but not limited to, encapsulation structures, shielding structures, and/or wirebonds. 
     The antenna elements antenna elements  951   a   1 ,  951   a   2 ,  951   a   3  . . .  951   an ,  951   b   1 ,  951   b   2 ,  951   b   3  . . .  951   bn ,  951   c   1 ,  951   c   2 ,  951   c   3  . . .  951   cn ,  951   m   1 ,  951   m   2 ,  951   m   3  . . .  951   mn  are formed on a first surface of the laminate  941 , and can be used to receive and/or transmit signals, based on implementation. Although a 4×4 array of antenna elements is shown, more or fewer antenna elements are possible as indicated by ellipses. Moreover, antenna elements can be arrayed in other patterns or configurations, including, for instance, arrays using non-uniform arrangements of antenna elements. Furthermore, in another embodiment, multiple antenna arrays are provided, such as separate antenna arrays for transmit and receive and/or for different communication bands. 
     In the illustrated embodiment, the IC  942  is on a second surface of the laminate  941  opposite the first surface. However, other implementations are possible. In one example, the IC  942  is integrated internally to the laminate  941 . 
     In certain implementations, the IC  942  includes signal conditioning circuits associated with the antenna elements  951   a   1 ,  951   a   2 ,  951   a   3  . . .  951   an ,  951   b   1 ,  951   b   2 ,  951   b   3  . . .  951   bn ,  951   c   1 ,  951   c   2 ,  951   c   3  . . .  951   cn ,  951   m   1 ,  951   m   2 ,  951   m   3  . . .  951   mn . In one embodiment, the IC  942  includes a serial interface, such as a mobile industry processor interface radio frequency front-end (MIPI RFFE) bus and/or inter-integrated circuit (I 2 C) bus that receives data for controlling the signal conditioning circuits, such as the amount of phase shifting provided by phase shifters. In another embodiment, the IC  942  includes signal conditioning circuits associated with the antenna elements  951   a   1 ,  951   a   2 ,  951   a   3  . . .  951   an ,  951   b   1 ,  951   b   2 ,  951   b   3  . . .  951   bn ,  951   c   1 ,  951   c   2 ,  951   c   3  . . .  951   cn ,  951   m   1 ,  951   m   2 ,  951   m   3  . . .  951   mn  and an integrated transceiver. 
     The laminate  941  can include various structures including, for example, conductive layers, dielectric layers, and/or solder masks. The number of layers, layer thicknesses, and materials used to form the layers can be selected based on a wide variety of factors, and can vary with application and/or implementation. The laminate  941  can include vias for providing electrical connections to signal feeds and/or ground feeds of the antenna elements. For example, in certain implementations, vias can aid in providing electrical connections between signal conditioning circuits of the IC  942  and corresponding antenna elements. 
     The antenna elements  951   a   1 ,  951   a   2 ,  951   a   3  . . .  951   an ,  951   b   1 ,  951   b   2 ,  951   b   3  . . .  951   bn ,  951   c   1 ,  951   c   2 ,  951   c   3  . . .  951   cn ,  951   m   1 ,  951   m   2 ,  951   m   3  . . .  951   mn  can correspond to antenna elements implemented in a wide variety of ways. In one example, the array of antenna elements includes patch antenna element formed from a patterned conductive layer on the first side of the laminate  941 , with a ground plane formed using a conductive layer on opposing side of the laminate  941  or internal to the laminate  941 . Other examples of antenna elements include, but are not limited to, dipole antenna elements, ceramic resonators, stamped metal antennas, and/or laser direct structuring antennas. 
     The module  940  can be included a communication system, such as a mobile phone or base station. In one example, the module  940  is attached to a phone board of a mobile phone. 
     Applications 
     Some of the embodiments described above have provided examples of dynamic antenna array management in connection with wireless communications devices. However, the principles and advantages of the embodiments can be used for any other systems or apparatus that benefit from any of the circuits and systems described herein. 
     For example, antenna arrays can be included in various electronic devices, including, but not limited to consumer electronic products, parts of the consumer electronic products, electronic test equipment, etc. Example electronic devices include, but are not limited to, a base station, a wireless network access point, a mobile phone (for instance, a smartphone), a tablet, a television, a computer monitor, a computer, a hand-held computer, a personal digital assistant (PDA), a microwave, a refrigerator, an automobile, a stereo system, a disc player, a digital camera, a portable memory chip, a washer, a dryer, a copier, a facsimile machine, a scanner, a multi-functional peripheral device, a wrist watch, a clock, etc. Further, the electronic devices can include unfinished products. 
     CONCLUSION 
     Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise,” “comprising,” and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to.” The word “coupled”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Likewise, the word “connected”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Additionally, the words “herein,” “above,” “below,” and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the above Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word “or” in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. 
     Moreover, conditional language used herein, such as, among others, “may,” “could,” “might,” “can,” “e.g.,” “for example,” “such as” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment. 
     The above detailed description of embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise form disclosed above. While specific embodiments of, and examples for, the invention are described above for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. For example, while processes or blocks are presented in a given order, alternative embodiments may perform routines having steps, or employ systems having blocks, in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and/or modified. Each of these processes or blocks may be implemented in a variety of different ways. Also, while processes or blocks are at times shown as being performed in series, these processes or blocks may instead be performed in parallel, or may be performed at different times. 
     The teachings of the invention provided herein can be applied to other systems, not necessarily the system described above. The elements and acts of the various embodiments described above can be combined to provide further embodiments. 
     While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosure. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure.