RF Front-end Research Articles

Research in Nonlinearity of Surface Acoustic Wave Devices.

Surface acoustic wave (SAW) devices are one of the indispensable components in the radio frequency (RF) front-end of mobile phones. With the development of mobile communication technology, the requirements for linear specification of devices are more and more strict. Nonlinear distortions of SAW devices have a serious influence on the application of mobile RF modules. To satisfy the strict requirement of linearity of communication system, it is necessary to understand the generation mechanism of nonlinearity and study the accurate modeling, appropriate measurement methods, and nonlinear response elimination technology. In this paper, we summarize the research progress on the nonlinearity of SAW devices in recent years from four aspects: the generation mechanism, simulation methods, measurement system, and suppression technology. The nonlinear harmonics with the nonlinear Mason equivalent circuit model are simulated. Furthermore, harmonics and intermodulation signals of SAW filters are tested by the authors. Thanks to these research studies, it is of great significance to the development of future RF front-end modules with high linear SAW devices.

Design of Active Inductor-Based VCO with Wide Tuning Range for RF Front End

Design of Active Inductor-Based VCO with Wide Tuning Range for RF Front End

Study on high power microwave nonlinear effects and degradation characteristics of C-band low noise amplifier

High power microwaves (HPM) coupled through the front door pose a potential threat to RF front ends, especially for low noise amplifiers (LNA). Therefore, A C-band LNA circuit model is constructed to investigate the non-linear effects and degradation characteristics of the LNA under HPM, and validate it against damaged samples analysis acquired in HPM injection experiment of LNA. The circuit model consists of a pseudocrystalline high electron mobility transistors (pHEMT) device equivalent physical model and other passive device SPICE models. The nonlinear relationship of input and output signals and the distribution of physical parameters of pHEMT device are analyzed by simulation. When the LNA injection power is less than a certain threshold, the nonlinear degradation of LNA is recoverable. However, when the LNA injection power is greater than a certain threshold, the pHEMT device in the circuit will be damaged by combustion. Under the influence of HPM, it forms a high current channel between gate and channel due to the avalanche breakdown of the Schottky junction and generates a hot spot on the side below the gate near the source, which will eventually cause burnout damage. Moreover, an empirical formula is presented to describe the relationship between the damage time of HPM and the injection power and energy. By scanning electron microscope (SEM) observation and energy dispersive spectrometer (EDS) analysis of the damaged samples, the results show that the pHEMT gate is vulnerable to HPM damage. The hot spot inside the pHEMT device in the simulation is consistent with the damage location of the LNA in HPM injection experiment.

Recent advancement in the design of mixers for software‐defined radios

The implementation of software-defined radio necessitates a versatile radio frequency (RF) front-end that can support multiple standards in different frequency bands. This article presents the state-of-the-art multiband and wideband mixers in the context of different receiver architectures suitable for software-defined radio (SDR). Wideband and multiband mixer designs reported in the literature are categorized on the basis of their circuit architecture. This study tabulates the results of mixer designs with an emphasis on noise figure (NF), conversion gain (CG), linearity, and image rejection ratio. The best parameters reported in the comparison are 68–84 dB of CG, 3.2 dB of NF, 2.5 mW of power consumption, 12.5 dBm of third-order input intercept point, and 0.015 mm2 of area at different frequencies. The study also discusses the design challenges and techniques to overcome those issues. The article concludes with the summary and prospective developments for SDR architectures.

Filtering Antennas: Design Methods and Recent Developments

With wireless communication technologies continually and rapidly developing, RF front-end systems are experiencing a profound evolution toward the goal of highly integrated and miniaturized RF front ends with improved performance. Traditionally, passive components in the RF front end, such as filters, antennas, and duplexers, have been designed individually and cascaded through a 50-Ω interface. This inevitably leads to bulky physical dimensions and complex circuits, high insertion loss, and signal distortion, especially at the band edges. In multiband or multistandard communication systems, multiple operating bands of the base station antenna are normally achieved using several separate subarrays operating at different frequencies, which can cause serious interference among different bands for various services due to the limited space on the antenna platform. Highly integrated multifunctional RF front ends would provide a high-efficiency solution to those advanced and miniaturized wireless systems. As the key components in any RF front-end system, the integration of filters and antennas can significantly improve the frequency selectivity and bandwidth; stability of the in-band gain, out-of-band rejection, and system efficiency. They have therefore received much research interest and opened up a broad avenue for antenna R&D in recent years.

Periodic Structures for Reconfigurable Filter Design: A Comprehensive Review

With the advent of 5G, software-defined radios (SDRs), and ultra-wideband systems, there is a rapid rise in the demand for reconfigurable RF front ends. Conventional methods of using filter banks or cascading multiple devices to achieve wideband performance would result in bulky hardware. Devices that can change their characteristics and respond in a controlled manner to a desired input are suitable for such designs. In filtering applications, the most desirable adaptive features include band-switching capabilities, the use of a cutoff frequency and/or bandwidth tuning, and a change in filter response from passband to stopband. Periodic structures have demonstrated great potential in achieving these characteristics.

A Comprehensive Study of Massive MIMO Antenna Arrays in the Next Generation of Communication Networks

The need of a capacity expansion becomes an inevitable factor concerning the increasing of mobile data applications and the unlimited expectation of the fifth generation of communication. Currently, massive Multiple Input Multiple Output (MIMO) technique is the main part of the continuous researches and it has become the major key for the technologies of modern cellular communications not only because it offers very high system throughput but also it improves the energy efficiency in multi-user scenarios. One of the first Base Stations (BSs) was implemented in 2018 for the chain of sixty four digital transceivers. Other BS deployed in many countries, designed by many companies, theoretically verified by many researches and published in many papers, and designed smartphones for working on 3G, 4G, and 5G technologies. Within a few years, designing a massive MIMO antenna array with digital transmitters and receivers will have a master streaming characteristic at both centimeter wave (sub of 6GHz) and millimeter wave (mm wave) frequencies. Recently, diverse design challenges of these arrays have appeared and characterized by using huge number of antennas in the vicinity, integrating them with Radio Frequency (RF) frontends, surpassing the hardware restrictions, and resolving the beamforming techniques. To highlight on these developments, the present paper concentrates on the evolution and growth of the existing massive MIMO array antenna which are designed, implanted, and measured indoors or outdoors for wireless communication systems in both BSs and smartphones. The paper is also expanded to explain the antenna configuration and its integration with beamforming techniques which has a great impact on reducing the cost and the energy consumption matched with the energy-saving design vision of 5G. Some of the challenges that have faced the design and the proposed solutions are also discussed in this paper. In addition, massive MIMO antenna array implemented in some countries around the world are discussed and future ideas to support the improvements in the antenna array communication networks are highlighted.

Micro telecom computing architecture.4-based beam position monitor electronics design for storage ring of Hefei advanced light facility.

The Hefei Advanced Light Facility (HALF) is a fourth-generation vacuum ultraviolet and x-ray diffraction limit synchrotron radiation (DLSR) light source now under preliminary research. To achieve ultralow beam emittance and small beam size, the orbit of the beam in the DLSR storage ring should meet the stability requirement at submicrometer scale. The beam position monitor (BPM) electronics measures the orbit and is hence an essential part of the beam orbit control system. In this article, we designa BPM electronics based on the MicroTCA.4 (Micro Telecom Computing Architecture) standards platform, which consists of a MicroTCA.4 module (including a chassis, a power supply, and a digital board), a customized RF front end module, and a frequency synthesizer. In-phase and quadrature sampling and digital signal processing algorithms are implemented to obtain turn-by-turn data, fast acquisition data at a 10 kHz rate, and slow acquisition data at a 10Hz rate. To evaluate the performance and function of BPM electronics, we conducted offline tests in the laboratory and beam tests based on the storage ring of Hefei Light Source II (HLS II), a light source similar to the HALF as an alternative. Test results indicate that the performance of MicroTCA.4-based BPM electronics can meet the requirements of the HALF storage ring.

Bandpass Filter With Tunable/Switchable In-Band Interference Rejection

This letter presents a wideband bandpass filter (BPF) with a tunable and switchable in-band notch. This allows the RF front end to pass the signal of interest uninterrupted in the absence of an in-band interferer and reject part of the passband in case a narrowband interferer exists. The BPF is based on a two-path architecture, loaded with resonators on one of the paths to deliver an absorptive notch. The resonators are tuned with varactor diodes and are deactivated when the diodes are in forward bias. The implemented proof-of-concept hardware operates in the 4.8–7.8-GHz frequency range, with an in-band notch tunable between 5 and 6.25 GHz, when activated. The transmission lines were implemented as striplines, resulting in a measured insertion loss of 0.6 dB.

Design of a Digital Baseband Processor for UHF Tags

In this paper, we present a new digital baseband processor for UHF tags. It is a low-power and low-voltage digital circuit and adopts the Chinese military standard protocol GJB7377.1. The processor receives data or commands from the RF front-end and carries out various functions, such as receiving and writing data to memory, reading and sending memory data to the RF front-end and killing tags. The processor consists of thirteen main sub-modules: TPP decoding, clock management, random number generator, power management, memory controller, cyclic redundancy check, FM0 encoding, input data processing, output data processing, command detection module, initialization module, state machine module and controller. We use ModelSim for the TPP decoding simulation and communication simulation between tag and reader, and the simulation results meet the design requirements. The processor can be applied to UHF tags and has been taped out using a TSMC 0.18 um CMOS process.

Feasibility of using a software‐defined baseband for multiple space per aperture (MSPA) ground operations

SummaryThis paper presents the feasibility of performing multiple spacecraft per aperture (MSPA) ground operations by using a low‐cost software‐defined baseband (SDB). The SDB is a Consultative Committee for Space Data Systems (CCSDS)‐compliant baseband that employs a personal computer for signal processing and a low‐cost commercial‐off‐the‐shelf RF front end for RF signal sampling. The SDB is customized to offer traditional telemetry, tracking, and command (TT&C) services for near‐Earth missions operating in S band. The study starts by reviewing MSPA methods already studied by space agencies such as NASA and ESA before going to MSPA methods proposed in the latest CCSDS blue book on RF and modulation systems. The feasibility of operating the CCSDS‐proposed multiple uplink carrier MSPA method using the SDB is assessed after evaluating in‐band interference and out‐of‐band emissions from the uplink signals radiated by the low‐cost RF front end employed by the SDB. Furthermore, we present a case study where the SDB is used in MSPA operations on a typical solid‐state amplifier (SSPA) amplifier typically used in near‐Earth missions.

Design and Implementation of RF Front-End Module Based on 3D Heterogenous-Integrated Wafer-Level Packaging

In this paper, a three-dimensional heterogenous-integrated (3DHI) wafer-level packaging (WLP) process is proposed, and a radio frequency (RF) front-end module with two independent ultra-high frequency (UHF) receiving channels are designed and implemented, which covers 400 MHz–600 MHz and 2050 MHz–2200 MHz respectively for unmanned aerial vehicle (UAV) applications. The module is formed by wafer-to-wafer (W2W) bonding of two high-resistivity silicon (HR-Si) interposers with embedded bare dies and through silicon via (TSV) interconnections. Double-sided deep reactive ion etching (DRIE) and conformal electroplating process are introduced to realize the high-aspect-ratio TSV connection within 290 µm-thick cap interposer. Co-plane waveguide (CPW) transmission lines are fabricated as the process control monitor (PCM), the measured insertion loss of which is less than 0.18 dB/mm at 35 GHz. The designed RF front-end module is fabricated and measured. The measured return loss and gain of each RF channel is better than 13 dB and 21 dB, and the noise figure is less than 1.5 dB. In order to evaluate the capability of the 3DHI process for multi-layer interposers, the module is re-designed and fabricated with four stacked high-resistivity silicon interposers. After W2W bonding of two pairs of interposers and wafer slicing, chip-to chip (C2C) bonding is applied to form a four-layer module with operable temperature gradient.

Wideband Bandpass Filter for 5G Millimeter- Wave Application in 45-nm CMOS Silicon-on-Insulator

In this letter, a wideband bandpass filter for 5G application is proposed. The filter is implemented in GF 45-nm CMOS SOI (silicon-on-insulator) and is a 4-pole/ 4-zero design which greatly enhance the filter selectivity and out-of-band rejection. Measurements show a filter 3-dB bandwidth of 22-44 GHz, and covers the millimeter-wave 5G 26/28/39 GHz bands. The minimum insertion loss is 1.5 dB with a return loss better than 10 dB and a filter size of 0.07 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The work shows that wideband high-performance filter can be integrated as part of the wideband/multiband RF front-end on CMOS SOI.

On the Physical Layer Security of Mixed FSO-RF SWIPT System With Non-Ideal Power Amplifier

Free-space optical (FSO) links are contemplated as a potential paradigm to yield efficient point-to-point communication in wireless systems. Notably, these links are used to provide the proficient wireless connectivity between the radio frequency (RF) wireless network and the fiber optic-based network. To this end, more attention has been paid to mixed FSO-RF systems where single-hop FSO transmission and single-hop RF transmission configuration is used. In this paper, we propose a mixed FSO-RF dual-hop simultaneous wireless information and power transfer (SWIPT) relaying system in the presence of power amplifier (PA). It is assumed that FSO links suffer from Málaga (M)-turbulence with pointing errors and RF links experience the double shadowed Rician fading. Particularly, the physical layer security is analyzed by deriving the closed-form expressions for secrecy metrics such as secure outage probability, strictly positive secrecy capacity, and secrecy throughput. We consider the three scenarios: 1) FSO-side eavesdropping attack 2) RF-side eavesdropping attack 3) Simultaneous FSO- and RF-side eavesdropping attacks. The asymptotic approximations for the final results are also derived to obtain secrecy diversity order. The effect of SWIPT parameters and PA efficiency on the secrecy performance are then further investigated in detail. In summary, the results show that the reliability and security of the proposed system can be enhanced by utilizing efficient PAs at the RF front end depending on the eavesdropper's location and can also be controlled by the SWIPT parameters.

Parameter detection for surface acoustic wave filter based on image processing

As core devices for the smartphone RF front end, surface acoustic wave (SAW) filters are in short supply. The detection of SAW filter parameters refers to the connection between layout design and process production, which is an important part of capacity improvement. This paper devises a method based on image processing to detect SAW filter parameters. We improve the morphological operator to recover an image and identify the number of interdigital transducer (IDT) finger bars under noise conditions. The feature points in the color image are selected to extract the scale. The Canny edge detection effect is enhanced through using an adaptive filter, increasing the gradient operator, bilinear interpolation, and other algorithms. We use a minimum shape to enclose the edges to determine the IDT width and period and apply Fourier transform to verify the detection results. The experimental results show that the number of IDT finger bars is accurately identified. The width and period are exactly the same as the real values at the 10th percentile, and the detection requirements are met.

Dual-Band CMOS RF Front-End Employing an Electrical-Balance Duplexer and N-Path LNA for IBFD and FDD Radios

This article proposes a dual-band complementary metal-oxide-semiconductor (CMOS) radio frequency (RF) front end employing a hybrid transformer-based electrical-balance duplexer (EBD) and N-path filter embedded low-noise amplifier (LNA) for both in-band full duplexing (IBFD) and frequency-division duplexing (FDD) radios. To securely obtain sufficient self-interference cancellation (SIC) or transmitter (TX) leakage rejection in IBFD and FDD modes of the EBD at both low-band (LB) (0.7-1 GHz) and mid-band (MB) (1.8-2.2 GHz) frequency ranges, a band-switchable hybrid transformer is designed with a finely adjustable balance network to control the antenna impedance variations. In addition, the four-phase N-path LNA is utilized to further offer TX leakage rejection in the FDD operation. This RF front-end is fabricated using a 65-nm CMOS technology and is mainly characterized by long-term evolution frequency bands. The demonstrated design achieves SIC and TX leakage rejection greater than 55 dB for IBFD and FDD modes of all measured frequency bands, which has a maximum power handling capability of +25 dBm. Furthermore, the design attains voltage gains greater than 8.7 dB for LB and 3.7 dB for MB, noise figures of 10.4 dB for LB and 12.1 dB for MB, out-of-band (OB) P1dBs greater than +21.4 dBm for LB and +21.5 dBm for MB, and OB IIP3s greater than +39.7 dBm for LB and +43.1 dBm for MB. It draws a bias current of 23.8 mA from the LNA and output buffer with a nominal supply of 1.2 V and has an active area of approximately 2 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Design of Ka-band broadband low-noise amplifier using 100nm gate-length GaN on silicon technology

Due to the high breakdown voltage and better linearity of gallium nitride (GaN) high electron mobility transistor (HEMT), GaN based RF front-end is widely researched and studied. In this paper, a Ka-band cascode low-noise amplifier (LNA) designed with 100nm gate-length GaN-on-silicon technology is presented. With novel methods such as the introduction of high-pass filters and standing wave filtering capacitors, the LNA achieves a stable gain of 21-22.8dB and a noise figure (NF) of 0.9-1.3dB from 22GHz to 38GHz. The input and output return loss are better than-10dB in band of concern. This LNA occupies an area of 2.3mm × 0.9mm and consumes 265-mW DC power. Compared with silicon-on-insulator (SOI), indium phosphide (InP) and gallium arsenide (GaAs) LNAs, the proposed GaN LNA exhibits better performance of linearity, as well as competitive gain and NF.

Optimum power transfer in RF front end systems using adaptive impedance matching technique

Matching the antenna’s impedance to the RF-front-end of a wireless communications system is challenging as the impedance varies with its surround environment. Autonomously matching the antenna to the RF-front-end is therefore essential to optimize power transfer and thereby maintain the antenna’s radiation efficiency. This paper presents a theoretical technique for automatically tuning an LC impedance matching network that compensates antenna mismatch presented to the RF-front-end. The proposed technique converges to a matching point without the need of complex mathematical modelling of the system comprising of non-linear control elements. Digital circuitry is used to implement the required matching circuit. Reliable convergence is achieved within the tuning range of the LC-network using control-loops that can independently control the LC impedance. An algorithm based on the proposed technique was used to verify its effectiveness with various antenna loads. Mismatch error of the technique is less than 0.2%. The technique enables speedy convergence (< 5 µs) and is highly accurate for autonomous adaptive antenna matching networks.

A Fast Self-Jamming Cancellation Architecture and Algorithm for Passive RFID Sensor System

In this letter, we propose a fast self-jamming cancellation (SJC) architecture for Ultra High Frequency (UHF) radio-frequency identification (RFID) interrogators. The core SJC architecture includes a Field Programmable Gate Array (FPGA) as the RFID baseband processor, a radio frequency (RF) agile transceiver which has two transmitting ports as the RF front-end, and a combiner. By detecting the amplitude and phase of the interference carrier, the SJC algorithm transmits a suppression carrier through the second transmitting port of the agile RF transceiver. The suppression carrier could effectively suppress the self-jamming carrier without designing complex circuits. Our test results showed the isolation between the transmitting and receiving port achieves 100dB at UHF band, and the cancellation processes can be finished within 0.4ms.

Miniaturized Dual-Band Power Splitter in LTCC for GNSS Applications

Global navigational satellite systems (GNSS) have received considerable attention in recent years, given their dual-band superiority over traditional single-band constellations. As such, there is new interest in compacting the RF front-ends of these systems and their corresponding devices. In this letter, the design and characterization of a low profile two-way equal power splitter operational over the lower- and upper-GNSS bands—1165–1295 MHz and 1560–1606 MHz—is proposed. Miniaturization was achieved by utilizing low temperature cofired ceramics (LTCC) as a 3-D integration method and substrate medium; yielding splitter dimensions of only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.9\times 6.23\times1.28$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . Across both bands, measurements indicate return loss < 27 dB, insertion loss (IL) < 0.6 dB, output isolation < 16.9 dB, amplitude unbalance < 0.4 dB, and phase unbalance < 3.3°.