Compact, broadband, transformer-based quadrature hybrid coupler

Abstract

A compact, broadband, transformer-based Quadrature Hybrid Coupler (QHC) (34) exhibits improved gain and phase imbalance over a broadband frequency range, compared to conventional QHCs (30) The QHC (34) comprises a combination of a conventional transformer- based QHC (30) and a constant-R bridged-T all pass delay element (32). The QHC (34) operates as a 90° phase shift splitter and combiner. Applications of the QHC (34) include balanced amplifiers and Load Modulated Balanced PAs (LMBA). The constant-R network provides a discrete equivalent of a wideband dispersion free transmission line, increasing the QHC (34) bandwidth. It introduces a constant phase delay for all frequencies. More than a mere combination of these two circuits, however, the inventive QHC (34) merges several of the passive elements (inductors / transformers) to reduce component count, and some capacitors are placed conveniently at the center of the transformer, resulting in a compact, broadband QHC (34).

Description

[0001] COMPACT, BROADBAND, TRANSFORMER-BASED QUADRATURE HYBRID COUPLER

[0002] TECHNICAL FIELD

[0003] The present disclosure relates generally to wireless communications, and in particular to a Quadrature Hybrid Coupler having good performance over a wide frequency band, and a compact physical layout.

[0004] BACKGROUND

[0005] Wireless communication networks are ubiquitous in many parts of the world. These networks continue to grow in capacity and sophistication. To accommodate more users, different types of devices, and different use cases, the technical standards governing the operation of wireless communication networks continue to evolve. The fourth generation (4G) of network standards has been deployed, the fifth generation (5G) is in development and early deployment, and the sixth generation (6G) is in design. With each generation, technological advances improve the capacity and spectral efficiency of the wireless communication system. For example, 5G added new frequency bands, and applied beamforming. This trend is expected to continue in 6G by exploiting additional frequency bands, and applying more advanced beamforming.

[0006] 5G added a second frequency range, FR2. This provided significant new available spectrum in the range 24.25-52.6 GHz. At these high frequencies, wavelengths are small. This is advantageous, as antenna elements are also small, allowing for antenna arrays with hundreds, or even thousands, of antenna elements. However, carriers at these high frequencies suffer higher path loss, and hence have limited range, compared to conventional wireless telecom operating frequencies. Beamforming is one technique featured in 5G and 6G, to improve both coverage and capacity.

[0007] Beamforming refers to the use of antennas having increased and controllable directionality, whereby an RF transmission (or reception sensitivity) is narrow, and is “aimed” in a specific direction. This is enabled by transmitting or receiving signals with controlled relative phase and gain in the antenna elements (or subarrays of antenna elements). The relative phases of, e.g., transmit signals sent to each antenna element are controlled to create constructive or destructive interference, thus amplifying the signal in some directions, and attenuating it in others, and hence controlling the direction in which the beam is transmitted. Similar phase manipulation of signals from antenna elements (or subarrays) in a receive antenna can also result in beamforming the sensitivity of an antenna array in receiving signals. Also, multiple orthogonal beams can be formed and aimed in different directions, thus simultaneously addressing multiple wireless devices, also known as User Equipment (UE).

[0008] To form robust beams, antenna elements are normally placed tightly together. For example, a distance of A / 2 is commonly used (where A is the RF wavelength), to form arbitrary beams without folding. However, the tight antenna spacing causes high electromagnetic coupling between the antennas, and additionally signals leak in between the antennas. The beamsteering, combined with the antenna coupling, makes the impedance seen by each power amplifier (PA) driving the antenna elements (or subarrays) deviate from a designed impedance.

[0009] The PA is designed assuming a nominal load impedance for optimal output power, linearity, and efficiency. The PA amplifies and delivers electrical power to the antenna element / subarray, which converts it to an electromagnetic signal. However, if the load impedance seen by the PA diverges from its designed (optimum) value, there is an impedance mismatch, which degrades PA performance.

[0010] To direct a beam to a desired direction, a phase shift is required between signals sent to different antenna elements (or subarrays). The same signal, except for the phase shift, is present at all antenna elements, and electromagnetic energy of the signal leaks between them. This is seen by the PAs as a mismatch from an optimal (matched) impedance, which is not present when no phase shifts are introduced to steer the beam. The designed impedance seen by the PA is referred to as the impedance in the boresight direction ( / .e., where the RF signal is radiated normal to the plane of the antenna element). When coupling is present between the antenna elements (due to spacing), and the same signal is sent on all antennas, but with different phases, this is experienced by the PA as load impedance variation and mismatch, even though it originates from antenna leakage and to the delay introduced by the phase shifter ( / .e., the mismatch typically grows higher as the beam-angle increases, since the relative phase shift between antennas increases). Because the impedance mismatch causes a partial reflection of the RF signal from the antenna element (or subarray) back toward the PA, a standing wave is generated along the transmission line connecting the two. This is quantified in the art as an antenna impedance Voltage Standing Wave Ratio (VSWR), which is calculated in terms of the reflection coefficient or return loss (also known as the S11 parameter). Assuming the antenna and PA are impedance-matched for signals transmitted in the boresight direction, the active impedance load, or VSWR, typically grows higher as the beam-angle increases, since the relative phase shift in between antenna elements (or subarrays) increases.

[0011] Thus, when PAs are coupled to antennas, the PAs and antenna elements interact with each other through the antenna coupling. Accordingly, the PAs effectively see a time-varying impedance mismatch due to beamforming, which is expressed in terms of VSWR. The VSWR impacts PA output power, efficiency, and linearity, and consequently the phased-array beam and its direction.

[0012] At low frequencies, an isolator can be inserted in between a PA and its antenna element / subarray, to ensure that the VSWR is not transferred to the PA. In a high frequency Advanced Antenna System (AAS), there is no room to fit an isolator at each PA output.

[0013] Reducing the sensitivity of PAs to the varying load impedance would thus improve RF system performance. Various means of reducing PA load sensitivity are known in the art. As shown in FIG. 1 , one known approach to reducing the sensitivity of PAs to impedance mismatches is a balanced PA circuit. A balanced PA comprises two amplifiers, each amplifying the same RF signal, but with a relative 90° phase offset (quadrature). An input splitter, such as a Quadrature Hybrid Coupler (QHC), splits an RF signal to be amplified into two RF signals with a quadrature phase relationship. An output QHC acts as a signal combiner, combining the amplified, quadrature RF signals into a single output RF signal. FIG. 1 shows impedance matching circuits at the PA outputs. As known in the art, input impedance matching may also, or alternatively, be implemented, or the balanced PA may be implemented with no input or output matching. The balanced PA is highly insensitive to load impedance variation, and hence is a good choice for RF PAs for beamforming systems.

[0014] Conventional QHCs, however, have numerous limitations. They are inherently narrowband, and have good amplitude balance and phase cohesion but only over a limited frequency range. QHCs may be implemented with transmission lines or lumped reactive components, both of which require a lot of integrated circuit die space. This makes layout challenging, particularly for driving phased-array antennas with tight spacing between antenna elements.

[0015] The Background section of this document is provided to place aspects of the present disclosure in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Approaches described in the Background section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.

[0016] SUMMARY

[0017] The following presents a simplified summary of the disclosure in order to provide a basic understanding to those of skill in the art. This summary is not an extensive overview of the disclosure and is not intended to identify key / critical elements of aspects of the disclosure or to delineate the scope of the disclosure. The sole purpose of this summary is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later.

[0018] A compact and broadband transformer-based transmission-line Quadrature Hybrid Coupler (QHC) targets the limitations in conventional QHCs. The QHC consists of a combination of a conventional transformer-based QHC and a constant-R bridged-T all pass delay element. The QHC operates conventionally - as a 90° phase shift splitter and combiner. This ISOLATION port provides the possibility of use as a Load Modulated Balanced PA (LMBA). The constant-R network provides a discrete equivalent of a wideband dispersion free transmission line (ideally down to DC) and introduces a nearly constant phase delay for all frequencies, while increasing the QHC bandwidth. The constant-R network provides a discrete equivalent of a wideband dispersion free transmission line (ideally down to DC) and introduces a nearly constant phase delay for all frequencies, while increasing the QHC bandwidth. More than a mere combination of these two circuits, however, the inventive circuit merges several of the passive elements (inductors I transformers) to reduce component count, and some capacitors are placed conveniently at the center of the transformer, resulting in a compact, broadband QHC.

[0019] One aspect relates to a compact, broadband QHC. The QHC includes a transformer, comprising a primary winding connected between first and second ports, the primary winding comprising a first inductive part and a second inductive part connected at a first node. The transformer further comprises a secondary winding connected between third and fourth ports, the secondary winding comprising a third inductive part and a fourth inductive part connected at a second node. All of the first, second, third and fourth inductive parts are configured to be inductively coupled. The QHC further includes a first capacitor connected between the first and third ports; a second capacitor connected between the second and fourth ports; a third capacitor connected between the first node and the second node; a first shunt capacitor connected between the first node and a ground node; and a second shunt capacitor connected between the second node and the ground node.

[0020] Another aspect relates to a balanced RF Power Amplifier (PA). The balanced RF PA includes an input QHC as described above, configured to receive an RF signal at the first port and output quadrature RF signals at the second and third ports; two RF PAs, each configured to amplify one of the quadrature RF signals output by the input QHC; and an output QHC configured to receive the amplified quadrature RF signals output by the RF PAs at the second and third ports, and to output a single, combined amplified RF signal at the first port.

[0021] Yet another aspect relates to a wireless device operative in a wireless communication network. The wireless device includes processing circuitry and communication circuitry operatively connected to the processing circuitry. The communication circuitry contains one or more compact, broadband, transformer-based QHCs. Each QHC includes a transformer, comprising a primary winding connected between first and second ports, the primary winding comprising a first inductive part and a second inductive part connected at a first node. The transformer further comprises a secondary winding connected between third and fourth ports, the secondary winding comprising a third inductive part and a fourth inductive part connected at a second node. All of the first, second, third and fourth inductive parts are configured to be inductively coupled. Each QHC further includes a first capacitor connected between the first and third ports; a second capacitor connected between the second and fourth ports; a third capacitor connected between the first node and the second node; a first shunt capacitor connected between the first node and a ground node; and a second shunt capacitor connected between the second node and the ground node. Still another aspect relates to a base station operative in a wireless communication network. The base station includes processing circuitry and communication circuitry operatively connected to the processing circuitry. The communication circuitry contains one or more compact, broadband, QHCs. Each QHC includes a transformer, comprising a primary winding connected between first and second ports, the primary winding comprising a first inductive part and a second inductive part connected at a first node. The transformer further comprises a secondary winding connected between third and fourth ports, the secondary winding comprising a third inductive part and a fourth inductive part connected at a second node. All of the first, second, third and fourth inductive parts are configured to be inductively coupled. Each QHC further includes a first capacitor connected between the first and third ports; a second capacitor connected between the second and fourth ports; a third capacitor connected between the first node and the second node; a first shunt capacitor connected between the first node and a ground node; and a second shunt capacitor connected between the second node and the ground node.

[0022] BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which aspects of the disclosure are shown. However, this disclosure should not be construed as limited to the aspects set forth herein. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like numbers refer to like elements throughout.

[0024] FIG. 1 depicts a known balanced Power Amplifier (PA) circuit using Quadrature Hybrid Couplers (QHC) as splitter and combiner circuits.

[0025] FIG. 2 depicts a known implementation of a QHC using transmission lines or microstrips. FIG. 3A depicts a known implementation of a QHC using coupled transmission lines. FIG. 3B is an equivalent circuit model of the coupled transmission line QHC of FIG. 3A. FIG. 4 depicts a known Lange QHC.

[0026] FIG. 5A depicts a known inductor-based QHC.

[0027] FIG. 5B depicts a known transformer-based QHC.

[0028] FIG. 6 depicts a general case of a known transformer-based QHC.

[0029] FIG. 7 depicts a known constant-R, bridged-T all pass delay circuit.

[0030] FIG. 8 depicts a compact, broadband, transformer-based QHC formed by replacing each windings in the transformer-based QHC of FIG. 6 with the constant-R, bridged-T all pass delay circuit of FIG. 7.

[0031] FIG. 9 depicts a multi-layer layout option for the compact, broadband, transformer-based QHC of FIG. 8. FIG. 10 is a graph of the simulated phase difference between the COUPLED and THROUGH ports, for the conventional, transformer-based QHC of FIG. 6, over the FR2 operating band of 37-43.5GHz.

[0032] FIG. 11 is a graph of the simulated phase difference between the COUPLED and THROUGH ports, for the compact, broadband, transformer-based QHC FIG. 8, over the FR2 operating band of 37-43.5GHz.

[0033] FIG. 12 is a graph of the simulated gain imbalance between the COUPLED and THROUGH ports, for the conventional, transformer-based QHC of FIG. 6, over the FR2 operating band of 37-43.5GHz.

[0034] FIG. 13 is a graph of the simulated gain imbalance between the COUPLED and THROUGH ports, for the compact, broadband, transformer-based QHC FIG. 8, over the FR2 operating band of 37-43.5GHz.

[0035] FIG. 14 is a graph of the simulated input port voltage reflection coefficient (S11) for the conventional, transformer-based QHC of FIG. 6, over the FR2 operating band of 37-43.5GHz.

[0036] FIG. 15 is a graph of the simulated input port voltage reflection coefficient (S11), for the compact, broadband, transformer-based QHC FIG. 8, over the FR2 operating band of 37- 43.5GHz.

[0037] FIG. 16 is a block diagram of a wireless device operative in a wireless communication network.

[0038] FIG. 17 is a block diagram of a base station operative in a wireless communication network.

[0039] DETAILED DESCRIPTION

[0040] For simplicity and illustrative purposes, the present disclosure is described by referring mainly to an exemplary aspect thereof. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be readily apparent to one of ordinary skill in the art that the present disclosure may be practiced without limitation to these specific details. In this description, well known methods and structures have not been described in detail so as not to unnecessarily obscure the present disclosure.

[0041] As discussed above, a compact, broadband, low-component-count, highly integrable QHC would be beneficial for modern wireless communications systems - particularly those implementing beamforming.

[0042] A QHC is a special case of the general class of directional couplers for which the coupling is 3dB. An ideal QHC is a symmetric, lossless, passive, four-port network. The ports of a QHC are often labeled SIGNAL, COUPLED, THROUGH, and ISOLATED. When configured as a splitter, an RF signal input to the SIGNAL port appears at the COUPLED port with a -3dB attenuation and no phase shift. The same signal appears at the THROUGH port with the same - 3dB attenuation, and a relative phase of -90°. Because it is symmetric, the QHC can combine two quadrature input signals ( / .e., having 90° phase offsets) at the THROUGH and COUPLED ports, into one output signal at the SIGNAL port. When configured as a splitter or combiner, the isolation port is often terminated to ground through a characteristic impedance (e.g., 50Q).

[0043] A QHC may also be a device which can replace conventional quadrature couplers and in some cases polyphase filters (PPF), e.g. in vector modulators or phase shifters designed with Gilbert cells that use a quadrature input as well as in mixers with quadrature LO drive for LO suppression and / or image rejection with quadrature IF / RF input / output (up or down converters).

[0044] FIG. 2 depicts one implementation of a QHC using transmission lines or microstrips, known as a branch line coupler. The transmission lines are of electrical length A / 4, where A is the wavelength of the fundamental frequency. Because the transmission lines are determined by one frequency, this type of QHC is inherently narrowband. The evolution of modern wireless communications is clearly towards larger bandwidths. Additionally, transmission lines require a lot of valuable IC die space, especially for phased-array antennas, where the spacing between the antenna elements on the PCB / substrate is shrinking and must be compatible with the on- chip TX / RX port separation.

[0045] Other implementations for QHCs include coupled line, as shown in FIG. 3A with an equivalent circuit model in FIG. 3B, and a Lange configuration QHC, as shown in FIG. 4.

[0046] For on-chip implementations, either inductor- or transformer-based coupled QHCs are preferable. FIG. 5A shows the inductor-based option, and FIG. 5B the transformer-based QHC. Design equations for tuning and coupling capacitors, and the inductor sizes with the necessary coupling factor, are derived from the required characteristic impedance and operating frequency as described by Robert C. Frye, et al. in the paper A 2GHz Quadrature Hybrid Implemented in CMOS Technology, published at the IEEE 2002 Custom Integrated Circuits Conference p. 287, the disclosure of which is incorporated herein by reference in its entirety. As FIGs. 5A and 5B show, lumped element QHCs require six capacitors, for tuning and correct signal phases. The layout of these circuits is challenging, and the impact of the wiring needs to be accurately modeled to capture the correct frequency characteristics. Also, the Frye paper concludes that the relative bandwidth over which a lumped element QHC has good amplitude balance (within 0.1 dB) and the desired phase difference (within 2 degrees) is about 30% of the resonant frequency. However, that is the performance of an ideal QHC. When implemented on-chip, the performance can be expected to deviate significantly, mainly due to the non-negligible series resistance of the inductor windings, and the substrate losses.

[0047] It is also known to use RC polyphase networks in IC designs to generate quadrature signals. However, these generally suffer from high losses, particularly if they are made wideband by adding several poles.

[0048] FIG. 6 depicts a transformer-based QHC 30, similar to that depicted in FIG. 5B, but in more general terms. The transformer primary and secondary winding are implemented as inductors Li. The inductors Li have the same inductance, so the transformer 30 neither steps its input voltage up nor down. The term k is a coupling factor, for example 0.707, which depends on the inductive coupling. The coupling factor k is engineered by controlling the size and length of the inductors Li traces, and their proximity on the die. As discussed above, the transformerbased QHC 30 has good amplitude balance and maintains a 90° phase shift only over a relatively narrow bandwidth.

[0049] FIG. 7 depicts a constant-R, bridged-T all pass delay circuit 32. An inductive bridged-T circuit (also known as a T-coil) is a form of an inductive peaking circuit. It is often used to extend an amplifier’s bandwidth (e.g., by double) and may improve output signal rise times. The circuit 32 comprises an inductor Li center-tapped by a shunt capacitor, with a bridging capacitor spanning from the input to the output. A coupling factor k inductively couples the left and right sides of the inductor (which may be implemented as two series-connected inductors). The bridging capacitor ensures the input impedance of the bridged-T circuit 32 is constant and resistive - hence the characterization “constant-R, bridged-T.

[0050] According to aspects of the present disclosure, the bandwidth of the transformer-based QHC 30 is improved by substituting, for each of its inductors L1 (i.e., the transformer windings) and CG, with the constant-R, bridged-T circuit 32. The equivalent of Fig 7 Cshunt is in Fig 8 split into C2a, C2b and C3. This can be seen as a "hybrid" between two coupled bridged-T networks and a conventional transformer based cascaded two-stage design. This provides a discrete equivalent of a wideband (ideally down to DC) dispersion-free transmission line. The result is the compact, broadband, transformer-based QHC 34 depicted in FIG. 8.

[0051] Each transformer winding comprises a pair of series-connected inductors, which are inductively coupled, as indicated by the left-right curved arrows. The primary and secondary windings are similarly inductively coupled, as indicated by the up-down curved arrows. Additionally, each inductor is inductively cross-coupled to the inductor in the opposite corner, as indicated by the crossed, curved arrows. Each arrow represents different coupling factors k between any pair of inductors. Hence, the compact, broadband, transformer-based QHC 34 splits the two windings of the transformer-based QHC 30 (FIG. 5) into four inductors L1 , all of which are inductively cross-coupled. Although not required for the compact, broadband, transformer-based QHC 34 operation, the inductive cross-coupling between all four inductors L1 is a design parameter than can be optimized for broadband amplitude and phase balance.

[0052] The compact, broadband, transformer-based QHC 34 functionality is split into broadband sections, which adds more degrees of freedom in terms of more coupling and crosscoupling coefficients, as well as cross-coupled and shunt capacitors, to optimize the frequency characteristics.

[0053] FIG. 9 shows one approach to a physical layout of the compact, broadband, transformerbased QHC 34. In FIG. 9, each transformer winding (comprising two inductors L1) comprises metal traces on adjacent layers of the die, with one overlying the other, and inductively coupling through a dielectric layer between them. That is, e.g., the inductors between the VSIG and VTHRU ports of FIG. 8 overlie the inductors between the VCPL and Viso ports (or vice versa). FIG. 9 shows the compactness of this layout option in terms of area.

[0054] As shown in Fig. 9, several of the tuning capacitors C2, C3 are placed at the center of the transformer, further reducing die area. Additionally, the coupling capacitances C4 between each pair of the terminals of the inductive elements (the bridging capacitors in the bridged-T circuit 32) can be consumed by the layout parasitics. This leaves only one unit-sized tuning capacitor Ci between the SIGNAL and COUPLED ports, and another between the THROUGH and ISOLATED ports. Thus, rather than having six capacitors at the QHC 34 terminals (as in the QHC 30 of FIG. 6), in a physical implementation the number is reduced to two capacitors C1. The remaining tuning capacitors can be placed in the center of the transformer, where they are “free” from an area consideration.

[0055] The compact, broadband, transformer-based QHC 34 of FIG. 8 was simulated, and compared to simulations of a conventional transformer-based QHC 30 (FIG. 6). The results are based on electro-magnetic simulations of the QHC structures 30, 34, and using mm-Wave modeled capacitors.

[0056] FIG. 10 shows the phase difference between the COUPLED and THROUGH ports, for the conventional, transformer-based QHC 30 of FIG. 6, over the FR2 operating band of 37- 43.5GHz, which was 5.60 degrees. FIG. 11 shows the phase difference between the COUPLED and THROUGH ports, for the compact, broadband, transformer-based QHC 34 of FIG. 8, over the same frequency band, which was 0.68 degrees.

[0057] FIG. 12 shows the gain imbalance between the COUPLED and THROUGH ports, for the conventional, transformer-based QHC 30 of FIG. 6, over the FR2 operating band of 37- 43.5GHz, which was 1.71 dB. FIG. 13 shows the gain imbalance between the COUPLED and THROUGH ports, for the compact, broadband, transformer-based QHC 34 of FIG. 8, over the same frequency band, which was 0.61 dB.

[0058] FIG. 14 shows the input port voltage reflection coefficient, also known as the S11 parameter, for the conventional, transformer-based QHC 30 of FIG. 6, over the FR2 operating band of 37-43.5GHz, which was -18.2 dB. FIG. 15 shows the input port voltage reflection coefficient, or S11 parameter, for the compact, broadband, transformer-based QHC 34 of FIG. 8, over the same frequency band, which was -18.5 dB.

[0059] Table 1 lists these simulation values, along with some other parameters of interest.

[0060] Table 1 : Performance Comparison

[0061] Over this frequency range, while the S11 parameters are comparable for both QHCs 30, 34, the compact, broadband, transformer-based QHC 34 exhibits a gain imbalance of only ~0.6 dB (compared to -1.7 dB for the conventional QHC 30), and a phase difference of only -0.7 deg (compared to 5.6 deg for the conventional QHC 30). Furthermore, due to the compact layout options, the compact, broadband, transformer-based QHC 34 achieves this performance while consuming less than half the die area of the conventional QHC 30.

[0062] As described herein (and depicted in FIG. 1), one application of the compact, broadband, transformer-based QHC 34 is in balanced PAs, particularly in beamforming communications systems, where widely varying load impedances deleteriously affect the performance of conventional PAs. The QHC 34, however, is not so limited. For example, the compact, broadband, transformer-based QHC 34 is also an excellent choice for generating l / Q signals for local oscillator, frequency conversion circuits, and the like.

[0063] The compact, broadband, transformer-based QHCs 34 may be utilized in a number of ways. For example, the compact, broadband, transformer-based QHCs 34 may be used to form balanced PAs for driving antenna arrays that implement beamforming.

[0064] PCT Patent Application No. PCT / EP2023 / 051188 filed on 19thJanuary 2023 describes a power amplifier arrangement comprising two balanced amplifiers, each with two PAs and a QHC, and additionally at least one delay line imparting a phase shift, and optionally an output combining network, to achieve line averaging, which reduces the PAs’ susceptibility to dynamic load impedance variations (e.g., caused by beamforming). This application cites to G. Berretta, D. Cristaudo and S. Scaccianoce, "A balanced cdma2000 SiGe HBT load insensitive power amplifier," 2006 IEEE Radio and Wireless Symposium, 2006, pp. 523-526, the disclosure of which is incorporated herein by reference in its entirety. The compact, broadband, transformerbased QHCs 34 may advantageously be utilized as the QHCs in such applications.

[0065] FIG. 16 illustrates a hardware block diagram of a wireless device 40 as implemented in accordance with one or more embodiments. A wireless device 40 is any type of device capable of communicating with a network node and / or access point using radio signals. A wireless device 40 may therefore refer to a machine-to-machine (M2M) device, a machine-type communications (MTC) device, a Narrowband Internet of Things (NB loT) device, etc. The wireless device 40 may also be referred to as a User Equipment (UE), such as a cellular telephone or “smartphone,” however, the term UE should be understood to encompass any wireless device 40. A wireless device 40 may also be referred to as a radio device, a radio communication device, a wireless device, a wireless terminal, or simply a terminal - unless the context indicates otherwise, the use of any of these terms is intended to include device-to- device UEs or devices, machine-type devices, or devices capable of machine-to-machine communication, sensors equipped with a wireless device, wireless-enabled table computers, mobile terminals, smart phones, laptop-embedded equipped (LEE), laptop-mounted equipment (LME), USB dongles, wireless customer-premises equipment (CPE), etc. In the discussion herein, the terms machine-to-machine (M2M) device, machine-type communication (MTC) device, wireless sensor, and sensor may also be used. It should be understood that these devices, although referred to as UEs, but may be configured to transmit and / or receive data without direct human interaction.

[0066] In some embodiments, the wireless device 40 includes a user interface 42 (display, touchscreen, keyboard or keypad, microphone, speaker, and the like); in other embodiments, such as in many M2M, MTC, or NB loT scenarios, the wireless device 40 may include only a minimal, or no, user interface 42 (as indicated by the dashed lines of block 42 in FIG. 16). The wireless device 40 also includes processing circuitry 44; memory 46; and communication circuitry 48 to effect wireless communication across an air interface to one or more radio network nodes, such as a base station, and / or access points. The communication circuitry 48 is connected to an antenna element array 49, such as an AAS, which implements beamforming by phase control. As indicated by the dashed lines, the antenna array 49 may protrude externally from the wireless device 40, or the antenna array 49 may be internal. In some embodiments, a wireless device 40 may include a sophisticated user interface 42, and may additionally include features such as a camera, accelerometer, satellite navigation signal receiver circuitry, vibrating motor, and the like (not depicted in FIG. 16).

[0067] According to aspects of the present disclosure, the communication circuitry 48 includes parallel constructions of balanced PAs built using compact, broadband, transformer-based QHCs 34 as input and / or output combiners, wherein the balanced PAs have an intrinsic 90° phase shift between the PAs. This makes the balanced PAs less susceptible to the deleterious effects of dynamically varying impedance mismatch at the antenna, such as that caused by beamforming. In some embodiments, the balanced PAs may be arranged as described in the above-referenced PCT patent application.

[0068] Figure 17 depicts a hardware block diagram of a base station 50 operative in a wireless communication network. The base station 50 includes processing circuitry 52; memory 54; and communication circuitry 56 to effect wireless communication across an air interface to one or more wireless devices 40. The communication circuitry 56 is connected to an antenna element array 58, such as an AAS, which implements beamforming by phase control. As indicated by the broken connection to the antenna array 58, the antenna array 58 may be physically located separately from the base station 50, such as mounted on a tower, building, or the like. Although the memory 56 is depicted as being internal to the processing circuitry 54, those of skill in the art understand that the memory 56 may also be external. Those of skill in the art additionally understand that virtualization techniques allow some functions nominally executed by the processing circuitry 54 to actually be executed by other hardware, perhaps remotely located (e.g., in the so-called “cloud”). The base station 50 is known in LTE as an eNodeB or eNB, and in New Radio (NR) as gNB. In general, in other wireless communication networks, the base station 50 may be known as a Radio Base Station, Base Transceiver Station, Access Point, or the like.

[0069] According to aspects of the present disclosure, the communication circuitry 56 includes parallel constructions of balanced PAs built using compact, broadband, transformer-based QHCs 34 as input and / or output combiners, wherein the balanced PAs have an intrinsic 90° phase shift between the PAs. This makes the balanced PAs less susceptible to the deleterious effects of dynamically varying impedance mismatch at the antenna, such as that caused by beamforming. In some embodiments, the balanced PAs may be arranged as described in the above-referenced PCT patent application.

[0070] The circuits or circuitry may comprise circuits dedicated to performing certain functional processing and / or one or more microprocessors in conjunction with memory. For instance, the circuitry may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include digital signal processors (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as read-only memory (ROM), randomaccess memory, cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory may include program instructions for executing one or more telecommunications and / or data communications protocols as well as instructions for carrying out one or more of the techniques described herein, in several embodiments. In embodiments that employ memory, the memory stores program code that, when executed by the one or more processors, carries out the techniques described herein.

[0071] Those skilled in the art will also appreciate that aspects herein further include corresponding computer programs.

[0072] A computer program comprises instructions which, when executed on at least one processor of an apparatus, cause the apparatus to carry out any of the respective processing described above. A computer program in this regard may comprise one or more code modules corresponding to the means or units described above.

[0073] Aspects further include a carrier containing such a computer program. This carrier may comprise one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

[0074] In this regard, aspects herein also include a computer program product stored on a non- transitory computer readable (storage or recording) medium and comprising instructions that, when executed by a processor of an apparatus, cause the apparatus to perform as described above.

[0075] Aspects further include a computer program product comprising program code portions for performing the steps of any of the embodiments herein when the computer program product is executed by a computing device. This computer program product may be stored on a computer readable recording medium.

[0076] Aspects of the present disclosure present numerous advantages over the prior art. The compact, broadband, transformer-based QHCs 34 are more broadband, and hence less sensitive to component variations and modeling deficiencies, than conventional transformerbased QHCs 32. In particular, simulations indicate that the amplitude and phase imbalance of compact, broadband, transformer-based QHCs 34 are improved compared to conventional, lumped element implementations. In layout, the compact, broadband, transformer-based QHC 34 eliminates the need for A / 4 transmission lines, both reducing die area and improving broadband performance by not designing to a single, specific frequency. The transformer windings can be formed by placing metal trace loops side by side on the same layer, or stacked on top of each other on different layers, whichever is more convenient with the available metal stack. Both variants work equally well on a theoretical level, as long as desired coupling factors can be achieved. The inevitable inductive coupling between windings on each side of the center taps, as well as inductive cross-coupling, are key parts of the design of the compact, broadband, transformer-based QHCs 34 - as opposed to traditional transformer-based QHCs 30 where these effects are either not used, or must be compensated to reduce or eliminate their negative impact on performance. Several tuning capacitors can be placed at the center of the transformer, thus reducing occupied die area. As compared to conventional implementations, the number of tuning capacitors at the terminals of the compact, broadband, transformer-based QHCs 34 can be reduced to four, further reducing the occupied area and the wiring complexity. In some aspects of the present disclosure, this number could be reduced to as few as two capacitors, by implementing the bridging capacitors (C4 in FIG. 8) with parasitic capacitance arising from the transformer winding layout. The reduced die area required to realize the compact, broadband, transformer-based QHC 34 is particularly beneficial in the mm- Wave frequency range, where the spacing between the antenna elements on the PCB / substrate is shrinking, and must be compatible with the on-chip TX / RX port separation. The compact, broadband, transformer-based QHCs 34 is useful to cover larger bandwidths and to allow for non-idealities and model limitations / inaccuracies, especially at mm-Wave frequencies and when moving towards THz frequencies. Possible (non-limiting) application of the compact, broadband, transformer-based QHCs 34 include 0 90° l / Q phase generation, as well as load-insensitive balanced PA designs.

[0077] Generally, all terms used herein are to be interpreted according to their ordinary meaning in the relevant technical field, unless a different meaning is clearly given and / or is implied from the context in which it is used. All references to a / an / the element, apparatus, component, means, step, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any methods disclosed herein do not have to be performed in the exact order disclosed, unless a step is explicitly described as following or preceding another step and / or where it is implicit that a step must follow or precede another step. Any feature of any of the aspects disclosed herein may be applied to any other aspect, wherever appropriate. Likewise, any advantage of any of the aspects may apply to any other aspects, and vice versa. Other objectives, features and advantages of the enclosed aspects will be apparent from the description.

[0078] The term “unit” may have conventional meaning in the field of electronics, electrical devices and / or electronic devices and may include, for example, electrical and / or electronic circuitry, devices, modules, processors, memories, logic solid state and / or discrete devices, computer programs or instructions for carrying out respective tasks, procedures, computations, outputs, and / or displaying functions, and so on, as such as those that are described herein.

[0079] As used herein, the term “configured to” means set up, organized, adapted, or arranged to operate in a particular way; the term is synonymous with “designed to.”

[0080] Some of the aspects contemplated herein are described more fully with reference to the accompanying drawings. Other aspects, however, are contained within the scope of the subject matter disclosed herein. The disclosed subject matter should not be construed as limited to only the aspects set forth herein; rather, these aspects are provided by way of example to convey the scope of the subject matter to those skilled in the art.

[0081] The present disclosure may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the disclosure. The present aspects are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended aspects are intended to be embraced therein.

Claims

CLAIMS1. A compact, broadband Quadrature Hybrid Coupler, QHC (34), comprising: a transformer comprising a primary winding (L1) connected between first and second ports, the primary winding comprising a first inductive part (L1a) and a second inductive part (L1b) connected at a first node (N1), and a secondary winding (L2) connected between third and fourth ports, the secondary winding comprising a third inductive part (L2a) and a fourth inductive part (L2b) connected at a second node (N2), wherein all of the first, second, third and fourth inductive parts are configured to be inductively coupled; a first capacitor (C1a) connected between the first and third ports; a second capacitor (C1b) connected between the second and fourth ports; a third capacitor (C3) connected between the first node (N1) and the second node (N2); a first shunt capacitor (C2a) connected between the first node (N1) and a ground node (G); and a second shunt capacitor (C2b) connected between the second node (N2) and the ground node (G).

2. The QHC (34) of claim 1 wherein the primary and secondary windings (L1 , L2) are implemented as loops of metal traces on a semiconductor die, and wherein at least one of the first capacitor (C1a), second capacitor (C1b), third capacitor (C3) first shunt capacitor (C2a) and second shunt capacitor (C2b) is disposed inside the loops.

3. The QHC (34) of claim 2 wherein the loops of metal traces implementing the primary and secondary windings (L1 , L2) are routed adjacent on the same layer.

4. The QHC (34) of claim 2 wherein the loops of metal traces implementing one of the primary and secondary windings (L1 , L2) are routed over the other of the primary and secondary windings (L1 , L2), and separated by a dielectric layer.

5. The QHC (34) of any of claims 1-4 further comprising a first bridge capacitor (C4a) connected across the primary winding (L1) between the first and second ports.

6. The QHC (34) of any of claims 1-4 further comprising a second bridge capacitor (C4b) connected across the secondary winding (L2) between the third and fourth ports.

7. The QHC (34) of any of claims 2-4 wherein the first and second ports are connected by parasitic capacitance (C4a) associated with the primary winding (L1).

8. The QHC (34) of any of claims 2-4 wherein the third and fourth ports are connected by parasitic capacitance (C4b) associated with the secondary winding (L2).

9. The QHC (34) of any of claims 7-8 wherein the size and spacing of the metal traces are configured to yield predetermined values of the parasitic capacitances (C4a, C4b).

10. The QHC (34) of any preceding claim wherein an RF signal input to the first port is output with equal power at the second and third ports, but with a 90 degree relative phase shift.

11. The QHC (34) of claim 10 wherein the RF signals output at the second and third ports have a frequency-invariant, constant phase delay.

12. The QHC (34) of any of claims 1-9 wherein a quadrature RF signal input to the second and third ports is output as a combined signal at the first port.

13. A balanced Radio Frequency, RF, Power Amplifier, PA, comprising: an input QHC (34) according to any of claims 10-11 , configured to receive an RF signal at the first port and output quadrature RF signals at the second and third ports; two RF PAs, each configured to amplify one of the quadrature RF signals output by the input QHC (34); and an output QHC (34) according to claim 12, configured to receive the amplified quadrature RF signals output by the RF PAs at the second and third ports, and to output a single, combined amplified RF signal at the first port.

14. The balanced RF PA of claim 13, further comprising: two input impedance matching circuits, each interposed between an output port of the input QHC (34) and an input of the associated RF PA.

15. The balanced RF PA of claim 13, further comprising: two output impedance matching circuits, each interposed between an output port of the an RF PA and an associated input port of the output QHC (34).

16. The balanced RF PA of any of claims 13-15, further comprising termination impedances connected between the fourth ports of the input and output QHCs (34) and ground.

17. A wireless device (40) operative in a wireless communication network, characterized by: processing circuitry (44); and communication circuitry (48) operatively connected to the processing circuitry (24) and containing one or more compact, broadband, transformer-based Quadrature Hybrid Couplers, QHC (34), each of which is characterized by: a transformer comprising a primary winding connected between first and second ports and a secondary winding connected between third and fourth ports, wherein the primary and secondary windings are configured to be inductively coupled; a first capacitor connected between the first and third ports; and a second capacitor connected between the second and fourth ports; wherein each of the primary and secondary windings comprises a bridge-T circuit comprising an inductor, a shunt capacitor connected between a center tap of the inductor and RF signal ground, and a bridge capacitance connected across the inductor.

18. A base station (50) operative in a wireless communication network, characterized by: processing circuitry (52); and communication circuitry (56) operatively connected to the processing circuitry (52) and containing one or more compact, broadband, transformer-based Quadrature Hybrid Couplers, QHC (34), each of which is characterized by: a transformer comprising a primary winding connected between first and second ports and a secondary winding connected between third and fourth ports, wherein the primary and secondary windings are configured to be inductively coupled; a first capacitor connected between the first and third ports; and a second capacitor connected between the second and fourth ports; wherein each of the primary and secondary windings comprises a bridge-T circuit comprising an inductor, a shunt capacitor connected between a center tap of the inductor and RF signal ground, and a bridge capacitance connected across the inductor.

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