Patent Application
20210105047
This application relates to transceivers, and more particularly to a transformer-based antenna switching network for selectively coupling transceivers and antennas.
Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources. Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.
These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example telecommunication standard is 5G New Radio (NR). 5G NR is part of a continuous mobile broadband evolution promulgated by Third Generation Partnership Project (3GPP) to meet new requirements associated with latency, reliability, security, scalability (e.g., with Internet of Things (IoT)), and other requirements. 5G NR includes services associated with enhanced mobile broadband (eMBB), massive machine type communications (mMTC), and ultra reliable low latency communications (URLLC). Some aspects of 5G NR may be based on the 4G Long Term Evolution (LTE) standard. There exists a need for further improvements in 5G NR technology. These improvements may also be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.
In accordance with a first aspect of the disclosure, a transformer-based antenna switching network is disclosed that includes: a first transformer having a secondary winding, a first switch coupled between a first terminal for the secondary winding of the first transformer and ground; a first antenna coupled to the first terminal; a second switch coupled between a second terminal of the secondary winding of the first transformer and ground; and a second antenna coupled to the second terminal.
In accordance with a second aspect of the disclosure, an antenna switching method is disclosed that includes: opening a first switch coupled between a first terminal of a secondary winding of a first transformer and ground; and closing a second switch coupled between a second terminal of the secondary winding of the first transformer and ground to select for a first antenna connected to the first terminal and to isolate a second antenna connected to the second terminal.
In accordance with a third aspect of the disclosure, a transformer-based antenna switching network is disclosed that includes: a first transformer having a first secondary winding; a second transformer having a second secondary winding, wherein the second secondary winding includes a first terminal connected to a first terminal of the first secondary winding; a third transformer having a third secondary winding; a fourth transformer having a fourth secondary winding, wherein the fourth secondary winding includes a first terminal connected to a first terminal of the third secondary winding; a first antenna connected to a second terminal of the first secondary winding; a first switch coupled between ground and the second terminal of the first secondary winding; a second switch coupled between ground and a second terminal of the second secondary winding; a third switch coupled between ground and a second terminal of the third secondary winding; a fourth switch coupled between ground and a second terminal of the fourth secondary winding; and a second antenna connected to the second terminal of the fourth secondary winding.
In accordance with a fourth aspect of the disclosure, a transformer-based antenna switching network is provided that includes: a transformer including a secondary winding and a primary winding; a first switch coupled between a first terminal of the secondary winding of the transformer and ground; a second switch coupled between a second terminal of the secondary winding of the transformer and ground; and a differential power amplifier having a first output connected to a first terminal of the primary winding for the transformer and having a second output connected to a second terminal of the primary winding of the transformer.
These and other advantageous features may be better appreciated through the following detailed description.
Embodiments of the present disclosure and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures.
To support the high data rates for modern cellular communication protocols such as the fifth generation (5G) cellular network technology, the transmission wavelength is being expanded to the millimeter wave spectrum. Due to the smaller wavelength size at these higher frequencies, a mobile device may incorporate an array of antennas despite the mobile device having a relatively small form factor. By utilizing different types of antennas within the array, the mobile device may change its beam width and other transmission parameters depending upon the radio frequency (RF) environment.
To drive the different antennas within an array, a mobile device may include separate transmitters that drive specific antennas through dedicated transmitter paths. But the use of separate transmitters increases costs due to the increased semiconductor die space needed to form the various transmitters. To lower costs, a shared transmitter may be used to select between two or more antennas through an antenna switching network having switches in series with the shared transmitter and corresponding ones of the antennas. For example, by closing a first switch transistor in series between the shared transmitter and a first antenna while opening a second switch transistor in series between the shared transmitter and a second antenna, a shared transmitter may drive the first antenna while isolating the second antenna. If the first switch transistor is then opened while the second switch transistor is closed, the shared transmitter may then drive the second antenna while isolating the first antenna.
Although such a shared transmitter architecture is feasible at lower frequencies, note that a switch transistor will have a certain amount of off-capacitance (Coff) when switched off. At the millimeter wave frequencies used such as for 5G, significant amount of leakage power will thus leak through the off-capacitance in the switched-off switch transistor for a shared transmitter. Power is then undesirably lost as radiation from the unselected antenna that should otherwise be isolated.
To provide an improved antenna switching network with reduced leakage power losses, a transformer-based antenna switching network is disclosed for a shared transmitter to select between a plurality of antennas. The transformer-based antenna switching network includes an antenna switching network formed by a transformer that includes a primary winding driven by the shared transmitter. The following discussion will be directed to differential shared transmitter embodiments, but it will be appreciated that a single-ended shared transmitter may be implemented in alternative embodiments. One output port for the shared transmitter drives a first terminal for the primary winding whereas a remaining second output port for the shared transmitter drives a second terminal for the primary winding.
Depending upon the desired transmission characteristics, a controller controls a pair of switch transistors coupled to a secondary winding of the transformer in the antenna switching network to select between the antennas. In particular, a first one of the switch transistors couples between ground and a first terminal for the secondary winding. Similarly, a second one of the switch transistors couples between ground and a second terminal for the secondary winding. The secondary winding extends between the first terminal and the second terminal. The secondary winding's first terminal couples through a first transmission line to a first one of the antennas. Similarly, the secondary winding's second terminal couples through a second transmission line to a second one of the antennas. As used herein, a “transmission line” refers to any suitable form of transmission line such as a microstrip line, a coplanar waveguide, a slotline, or a stripline. In addition, as used herein, the term couples” or “coupled” refers to an electrical connection that may be direct (no intervening elements) or may be indirect such as coupled through an intervening element such a filter.
To select for the first antenna while isolating the second antenna, the controller switches off the first switch transistor and switches on the second switch transistor. In such a configuration, the second terminal for the secondary winding is thus the ground terminal whereas the secondary winding's first terminal is a single-ended drive terminal for the first antenna. It will thus be appreciated that the transformer-based antenna switching network is then functioning as a balun that allows the differential transmitter to single-endedly drive the first antenna. In addition, the transformer-based antenna network matches an output impedance for the shared transmitter to an input impedance for the first transmission line (this input impedance also being matched to an input impedance for the first antenna).
To select for the second antenna while isolating the first antenna, the controller switches on the first switch transistor and switches off the second switch transistor. In this configuration, it is the first terminal for the secondary winding that becomes the ground terminal whereas the second terminal for the secondary winding becomes a single-ended drive terminal for the second antenna. While selecting for the second antenna, the transformer-based antenna switching network again functions as a balun and also matches the output impedance of the shared transmitter to the impedance of the second transmission line (which in turn matches the input impedance of the second antenna). Regardless of which antenna is selected, note that the power leakage to the isolated antenna is inversely proportional to the on-resistance for the switched-on switch transistor. The power leakage for the resulting transformer-based antenna switching network is thus reduced as compared to a serial-switch antenna switching topology.
An example transformer-based antenna switching network 100 is shown in
A secondary winding S for transformer T includes a first terminal 102 connected to a first antenna 135 through a first transmission line 125. In addition, the secondary winding includes a second terminal 103 connected to a second antenna 140 through a second transmission line 130. To better match an output impedance of PA 115 to an input impedance for first antenna 135 and second antenna 140, a capacitor C1 is arranged in parallel with primary winding P. Similarly, a capacitor C2 is arranged in parallel with secondary winding S to further aid in the impedance matching. To select between first antenna 135 and second antenna 140 for transmitting a radio frequency (RF) signal as amplified by power amplifier 115, a controller 120 controls a first switch such as a first switch transistor M1 and controls a second switch such as a second switch transistor M2. Controller 120 is a logic circuit that may be implemented by a processor, a field programmable gate array, a state machine, or other suitable types of logic circuits. First switch transistor M1 is coupled between first terminal 102 of the secondary winding and ground. Similarly, second switch transistor M2 is coupled between second terminal 103 of the secondary winding and ground. Both switch transistors may be n-type metal-oxide semiconductor (NMOS) field-effect transistors but it will be appreciated that other suitable transistors may be used such as p-type metal-oxide semiconductor (PMOS) or bipolar junction transistors other types of electronic switching devices. In some embodiments, antenna 135 and antenna 140 are part of a phased-array of antennas.
To transmit an RF signal through antenna 135, controller 120 switches off switch transistor M1 and switches on switch transistor M2. Conversely, controller 120 switches on switch transistor M1 and switches off switch transistor M2 to transmit an RF signal through antenna 140. Regardless of which antenna is selected, the switched-off transistor presents an off-capacitance (Coff) to the secondary winding terminal that connects to the selected antenna. The switched-on transistor presents an on-resistance (Ron) between ground and the secondary winding terminal that connects to the non-selected antenna. For example, the off-capacitance for switch transistor M1 and the on-resistance for switch transistor M2 are shown in
Note that the off-capacitance for the switch transistor connected to the selected antenna is in parallel with the secondary winding inductance. The off-capacitance of the switch transistor, the C2 capacitance, and the secondary winding inductance thus form a parallel LC resonant circuit, where L is the secondary winding inductance and C is a sum of the off-capacitance and the C2 capacitance. The resonant frequency of such a parallel LC resonant circuit is proportional to an inverse of a square root of the LC product. By an appropriate selection of the off-capacitance, the C2 capacitance. and the secondary winding inductance so that the parallel LC circuit is resonant for the operating bandwidth of PA 115, the off-capacitance can thus be resonated out by the secondary winding inductance (or by the primary winding inductance) of the transformer T. Since the effects of the off-capacitance can thus be eliminated or reduced, the switch transistors M1 and M2 may both be relatively large so as to reduce their on-resistance despite the increase in off-capacitance that results from the larger transistor dimensions. In alternative embodiments, the off-capacitance may be sufficient for resonance such that capacitor C2 may be eliminated.
The selection of either antenna 135 or antenna 140 for receiving an RF signal is analogous as will be explained further herein. Regardless of whether the selected antenna is transmitting or receiving, the switch transistor that is switched off connects to the same secondary winding terminal as the selected antenna whereas the remaining switch transistor is switched on.
Network 100 may be modified to include serial switches to further isolate the antennas in alternative embodiments. For example, a transformer-based antenna switching network 150 shown in
An array of more than two antennas may be selectively driven using the transformer-based antenna switching networks disclosed herein. For example, a transformer-based antenna switching network 200 shown in
Switches S1, S2, S3, and S4 may each be implemented using a switch transistor as discussed for network 100. To select for simultaneous transmission through patch antennas 215 and 225, switches S1 and S4 are opened and switches S2 and S3 are closed. Power amplifier 205 may then drive first patch antenna 215 while power amplifier 210 drives second patch antenna 225. Dipole antenna 220 is isolated by the closing of switches S2 and S3. To select for transmission with dipole antenna 220, switches S2 and S3 are opened and switches S4 and S1 closed. Power amplifiers 205 and 210 would then drive dipole antenna 220 differentially but it will be appreciated that a dipole antenna may be driven in a single-ended fashion in alternative antenna switching network embodiments. A controller analogous to controller 120 for controlling the switching of switches S1, S2, S3, and S4 is not shown in
As compared to patch antennas 215 and 225, dipole antenna 220 has an omnidirectional beam pattern. In contrast, the beam pattern from patch antennas 215 and 225 is much more directional. A controller (not illustrated) for antenna switching network 200 may thus select for patch antennas 215 and 225 when the radiated RF power should be concentrated in a particular direction whereas dipole antenna 220 is selected by controller 120 during omnidirectional modes of transmission.
The antenna array of
The action of switches S1 and S2 with regard to selecting for patch antenna 215 or dipole antenna 220 is as discussed with regard to network 200. The power from each power amplifier 305 and 310 is thus added to drive the selected antenna due to the serial connection of the secondary windings for the transformers T1-1 and T1-2. In contrast, the power would be reduced by one-half in a serial switch architecture because power amplifier 305 would only drive first patch antenna 215 in that case. Similarly, power amplifier 310 would only drive dipole antenna 220 in a serial switch architecture. Network 300 thus provides twice the output power as would be obtained from a serial switch architecture with the same number of power amplifiers.
The bifurcation of transformer T2 of network 200 into a transformer T2-1 and a transformer T2-1 in network 300 is analogous. A third power amplifier 315 is configured to drive a primary winding of transformer T2-1. Similarly, a fourth power amplifier 320 is configured to drive a primary winding of transformer T2-2. A first terminal of the secondary winding of transformer T2-1 connects to a second terminal of dipole antenna 220 and couples to ground through switch S3. A second terminal of the secondary winding of transformer T2-1 connects to a first terminal of the secondary winding for transformer T2-2. A second terminal of the secondary winding for transformer T2-2 connects to second patch antenna 225 and couples to ground through switch S4. The secondary windings for transformers T2-1 and T2-2 are thus arranged in series. A capacitor C4 connects in series from the first terminal of the secondary winding for transformer T2-1 with a capacitor C5 that connects to the second terminal of the secondary winding for transformer T2-2. The action of switches S3 and S4 with regard to selecting for second patch antenna 225 or dipole antenna 220 is as discussed with regard to network 200. The power from power amplifier 315 and power amplifier 320 is thus added to drive the selected antenna due to the serial connection of the secondary windings for the transformers T2-1 and T2-2. A controller analogous to controller 120 for controlling the switching of switches S1, S2, S3, and S4 is not shown in
In network 300, the secondary winding for transformer T1-1 may be denoted as a first secondary winding. Similarly, the secondary winding for transformer T1-2 may be denoted as a second secondary winding whereas the secondary winding for transformer T2-1 may be denoted as a third secondary winding. Finally, the secondary winding for transformer T2-2 may be denoted as a fourth secondary winding. Similarly, transformers T1-1, T1-2, T2-1, and T2-2 may be deemed to be first, second, third, and fourth transformers respectively. Finally, power amplifiers 305, 310, 315, and 320 may be deemed to be first, second, third, and fourth power amplifiers, respectively.
The receive path for a transceiver coupled to a transformer-based antenna switching network as disclosed herein may depend upon whether the low-noise amplifier(s) in the receive path are single-ended or differential. For example, a transformer-based switching network 400 shown in
A receive path including a differential LNA 505 is shown in
A flowchart for a method of operation for a transformer-based antenna switching network is shown in
A transformer-based antenna switching network as disclosed herein may be incorporated into a wide variety of electronic systems. For example, as shown in
A transformer-based antenna switching networks as disclosed herein may also be advantageously combined with beam-forming as noted earlier. An example beam-forming RF architecture 800 is shown in
Broadly,
Each of the antenna elements 820 may include one or more sub-elements (not shown) for radiating or receiving RF signals. For example, a single antenna element 820 may include a first sub-element cross-polarized with a second sub-element that can be used to independently transmit cross-polarized signals. The antenna elements 820 may include patch antennas or other types of antennas arranged in a linear, two dimensional, or other pattern. A spacing between antenna elements 820 may be such that signals with a desired wavelength transmitted separately by the antenna elements 820 may interact or interfere (e.g., to form a desired beam). For example, given an expected range of wavelengths or frequencies, the spacing may provide a quarter wavelength, half wavelength, or other fraction of a wavelength of spacing between neighboring antenna elements 820 to allow for interaction or interference of signals transmitted by the separate antenna elements 820 within that expected range.
The modem 802 processes and generates digital baseband signals and may also control operation of the DAC 804, first and second mixers 806, 808, splitter 810, first amplifiers 812, phase shifters 814, and/or the second amplifiers 816 to transmit signals via one or more or all of the antenna elements 820. The modem 802 may process signals and control operation in accordance with a communication standard such as a wireless standard discussed herein. The DAC 804 may convert digital baseband signals received from the modem 802 (and that are to be transmitted) into analog baseband signals. The first mixer 806 upconverts analog baseband signals to analog IF signals within an IF using the local oscillator A 830. For example, the first mixer 806 may mix the signals with an oscillating signal generated by the local oscillator A 830 to “move” the baseband analog signals to the IF. In some implementations, some processing or filtering (not shown) may take place at the IF. The second mixer 808 upconverts the analog IF signals to analog RF signals using the local oscillator B 832. Analogously to the first mixer, the second mixer 808 may mix the signals with an oscillating signal generated by the local oscillator B 832 to “move” the IF analog signals to the RF, or the frequency at which signals will be transmitted or received. The modem 802 may adjust the frequency of local oscillator A 830 and/or the local oscillator B 832 so that a desired IF and/or RF frequency is produced and used to facilitate processing and transmission of a signal within a desired bandwidth.
In the illustrated architecture 800, signals upconverted by the second mixer 808 are split or duplicated into multiple signals by the splitter 810. The splitter 810 in architecture 800 splits the RF signal into a plurality of identical or nearly identical RF signals, as denoted by its presence in box 828. In other examples, the split may take place with any type of signal including with baseband digital, baseband analog, or IF analog signals. Each of these signals may correspond to an antenna element 820 and the signal travels through and is processed by amplifiers 812, 816, phase shifters 814, and/or other elements to be provided to and transmitted by the corresponding antenna element 820 as selected for by antenna switching network 818. In one example, the splitter 810 may be an active splitter that is connected to a power supply and provides some gain so that RF signals exiting the splitter 810 are at a power level equal to or greater than the signal entering the splitter 810. In another example, the splitter 810 is a passive splitter that is not connected to power supply and the RF signals exiting the splitter 810 may be at a power level lower than the RF signal entering the splitter 810.
After being split by the splitter 810, the resulting RF signals may enter an amplifier, such as a first amplifier 812, or a phase shifter 814 corresponding to an antenna element 820. The first and second amplifiers 812, 816 are illustrated with dashed lines because one or both of them might not be necessary in some implementations. In one implementation, both the first amplifier 812 and second amplifier 816 are present. In another, neither the first amplifier 812 nor the second amplifier 816 is present. In other implementations, one of the two amplifiers 812, 816 is present but not the other. By way of example, if the splitter 810 is an active splitter, the first amplifier 812 may not be used. By way of further example, if the phase shifter 814 is an active phase shifter that can provide a gain, the second amplifier 816 might not be used. Amplifiers 812 and 816 represent an instantiation of power amplifier 115 and are shown separately from antenna switching network 818 for illustration purposes. The amplifiers 812, 816 may provide a desired level of positive or negative gain. A positive gain (positive dB) may be used to increase an amplitude of a signal for radiation by a specific antenna element 820. A negative gain (negative dB) may be used to decrease an amplitude and/or suppress radiation of the signal by a specific antenna element. Each of the amplifiers 812, 816 may be controlled independently (e.g., by the modem 802) to provide independent control of the gain for each antenna element 820. For example, the modem 802 may have at least one control line connected to each of the splitter 810, first amplifiers 812, phase shifters 814, and/or second amplifiers 816 which may be used to configure a gain to provide a desired amount of gain for each component and thus each antenna element 820.
The phase shifter 814 may provide a configurable phase shift or phase offset to a corresponding RF signal to be transmitted. The phase shifter 814 could be a passive phase shifter not directly connected to a power supply. Passive phase shifters might introduce some insertion loss. The second amplifier 816 could boost the signal to compensate for the insertion loss. The phase shifter 814 could be an active phase shifter connected to a power supply such that the active phase shifter provides some amount of gain or prevents insertion loss. The settings of each of the phase shifters 814 are independent meaning that each can be set to provide a desired amount of phase shift or the same amount of phase shift or some other configuration. The modem 802 may have at least one control line connected to each of the phase shifters 814 and which may be used to configure the phase shifters 814 to provide a desired amounts of phase shift or phase offset between antenna elements 820.
In the illustrated architecture 800, RF signals received by the selected antenna elements 820 are provided to one or more of first amplifier 856 to boost the signal strength. The boosted RF signal is input into one or more of phase shifter 854 to provide a configurable phase shift or phase offset for the corresponding received RF signal. The phase shifter 854 may be an active phase shifter or a passive phase shifter. The settings of the phase shifters 854 are independent, meaning that each can be set to provide a desired amount of phase shift or the same amount of phase shift or some other configuration. The modem 802 may have at least one control line connected to each of the phase shifters 854 and which may be used to configure the phase shifters 854 to provide a desired amount of phase shift or phase offset between antenna elements 820.
The outputs of the phase shifters 854 may be input to one or more second amplifiers 852 for signal amplification of the phase shifted received RF signals. The second amplifiers 852 may be individually configured to provide a configured amount of gain. The second amplifiers 852 may be individually configured to provide an amount of gain to ensure that the signal input to combiner 850 have the same magnitude. The amplifiers 852 and/or 856 are illustrated in dashed lines because they might not be necessary in some implementations. In one implementation, both the amplifier 852 and the amplifier 856 are present. In another, neither the amplifier 852 nor the amplifier 856 are present. In other implementations, one of the amplifiers 852, 856 is present but not the other.
In the illustrated architecture 800, signals output by the phase shifters 854 (via the amplifiers 852 when present) are combined in combiner 850. The combiner 850 in architecture 800 combines the RF signals into a signal, as denoted by its presence in box 828. The combiner 850 may be a passive combiner, e.g., not connected to a power source, which may result in some insertion loss. The combiner 850 may be an active combiner, e.g., connected to a power source, which may result in some signal gain. When combiner 850 is an active combiner, it may provide a different (e.g., configurable) amount of gain for each input signal so that the input signals have the same magnitude when they are combined. When combiner 850 is an active combiner, it may not need the second amplifier 852 because the active combiner may provide the signal amplification.
The output of the combiner 850 is input into mixers 848 and 846. Mixers 848 and 846 generally down convert the received RF signal using inputs from local oscillators 872 and 870, respectively, to create intermediate or baseband signals that carry the encoded and modulated information. The output of the mixers 848 and 846 are input into an analog-to-digital converter (ADC) 844 for conversion to analog signals. The analog signals output from ADC 844 is input to modem 802 for baseband processing, e.g., decoding, de-interleaving, etc.
The modem 802 may function as controller 120 to control antenna switching network 818 to select one or more antenna elements 820 and/or to form beams for transmission of one or more signals. For example, the antenna elements 820 may be individually selected or deselected for transmission of a signal (or signals) by controlling an amplitude of one or more corresponding amplifiers, such as the first amplifiers 812 and/or the second amplifiers 816. Beamforming includes generation of a beam using a plurality of signals on different antenna elements where one or more or all of the plurality signals are shifted in phase relative to each other. The formed beam may carry physical or higher layer reference signals or information. As each signal of the plurality of signals is radiated from a respective antenna element 820, the radiated signals interact, interfere (constructive and destructive interference), and amplify each other to form a resulting beam. The shape (such as the amplitude, width, and/or presence of side lobes) and the direction can be dynamically controlled by modifying the phase shifts or phase offsets imparted by the phase shifters 814 and amplitudes imparted by the amplifiers 812, 816 of the plurality of signals relative to each other.
It will be appreciated that many modifications, substitutions and variations can be made in and to the materials, apparatus, configurations and methods of use of the devices of the present disclosure without departing from the scope thereof. In light of this, the scope of the present disclosure should not be limited to that of the particular embodiments illustrated and described herein, as they are merely by way of some examples thereof, but rather, should be fully commensurate with that of the claims appended hereafter and their functional equivalents.
