Reconfigurable RF Front-end Research Articles

An Adaptive RF Front-End Architecture for Multi-Band SDR in Avionics.

This study introduces a reconfigurable and agile RF front-end (RFFE) architecture that significantly enhances the performance of software-defined radios (SDRs) by seamlessly adjusting to varying signal requirements, frequencies, and protocols. This flexibility greatly enhances spectrum utilization, signal integrity, and overall system efficiency-critical factors in aviation, where reliable communication, navigation, and surveillance systems are vital for safety. A versatile RF front-end is thus indispensable, enhancing connectivity and safety standards. We explore the integration of this flexible RF front-end in SDRs, focusing on the detailed design of essential components, such as receivers, transmitters, RF switches, combiners, and splitters, and their corresponding RF pathways. Comprehensive performance evaluations confirm the architecture's reliability and functionality, including an extensive analysis of receiver gain, linearity, and two-tone test results. These assessments validate the architecture's suitability for aviation radios and address considerations of size, weight, and power-cost (SWaP-C), demonstrating significant gains in operational efficiency and cost-effectiveness. The introduction of the new RF front-end on a single SDR board not only substantially reduces size and weight but also adds up to 18 dB gain to the received signal. It also allows for a high level of design flexibility, enabling seamless software transitions between different radios and the capacity to manage three times more radios with the same hardware, thereby significantly boosting the system's ability to handle multiple radio channels efficiently.

Phase-Change RF Devices for Future Communications: Phase-Change Materials and Devices for Reconfigurable RF Front-Ends: State-of-the-Art and Future Perspectives

Phase-Change RF Devices for Future Communications: Phase-Change Materials and Devices for Reconfigurable RF Front-Ends: State-of-the-Art and Future Perspectives

A reconfigurable RF front-end for 5G direct sampling receivers with an optimized calibration scheme

This paper presents a reconfigurable radio frequency front-end (RFFE) tailored for direct RF sampling receivers operating within Frequency Range 1 (FR-1) of the 5G spectrum. It consists of a balun-LNA, a noise-cancelling, current-reuse, Q-enhanced filter, and a programmable gain amplifier (PGA). Fabricated in 22-nm FD-SOI technology, the RFFE covers the entire frequency range from 1.7 to 6.4 GHz with a tunable bandwidth ranging from 50 MHz to 1.2 GHz. The experimental results confirm that the RFFE achieves 3.9 dB NF, 55 dB ultimate OOB rejection, −4 dBm IB-IIP3, and 23 dBm OOB-IIP3. Furthermore, a digital calibration scheme is proposed to compensate for process, voltage, and temperature (PVT) variations, achieving lower than 2 % error in 6.61 µs on average. Subsequently, a proximal policy optimization (PPO) agent is employed to choose the optimal policy for the successive adjustments of quality factors and resonance frequencies of the filter’s resonators. As a result, the proposed reinforcement learning algorithm reduces the calibration’s convergence time by 59 %.

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 Reconfigurable Passive Switched-Capacitor TX RF Front End With −57 dB ACLR2

This letter presents a wireless transmitter (TX) front end in which the functionalities of digital-to-analog conversion, baseband filtering, and signal upconversion are implemented by a passive switched-capacitor (PSC) network. The result is a versatile architecture that fully benefits from CMOS scaling. The front end was integrated in a 65-nm CMOS technology and can support various channel bandwidths simply by adjusting the switching frequency for the PSC network. Thanks to its third-order reconfigurable filter, it maintains a thermal noise floor better than −156 dBc/Hz at a power dissipation of 45 mW. The measured prototype achieves an ACLR2 of −57 dB and an EVM of −31 dB for a 20-MHz 64-QAM OFDM and a 20-MHz 16-QAM signal, respectively.

A 0.7–7 GHz wideband reconfigurable receiver RF front-end in CMOS

A 0.7–7 GHz wideband RF receiver front-end SoC is designed using the CMOS process. The front-end is composed of two main blocks: a single-ended wideband low noise amplifier (LNA) and an in-phase/quadrature (I/Q) voltage-driven passive mixer with IF amplifiers. Based on a self-biased resistive negative feedback topology, the LNA adopts shunt-peaking inductors and a gate inductor to boost the bandwidth. The passive down-conversion mixer includes two parts: passive switches and IF amplifiers. The measurement results show that the front-end works well at different LO frequencies, and this chip is reconfigurable among 0.7 to 7 GHz by tuning the LO frequency. The measured results under 2.5-GHz LO frequency show that the front-end SoC achieves a maximum conversion gain of 26 dB, a minimum noise figure (NF) of 3.2 dB, with an IF bandwidth of greater than 500 MHz. The chip area is 1.67 × 1.08 mm2.

Forward Behavioral Modeling of a Three-Way Amplitude Modulator-Based Transmitter Using an Augmented Memory Polynomial

Reconfigurable and multi-standard RF front-ends for wireless communication and sensor networks have gained importance as building blocks for the Internet of Things. Simpler and highly-efficient transmitter architectures, which can transmit better quality signals with reduced impairments, are an important step in this direction. In this regard, mixer-less transmitter architecture, namely, the three-way amplitude modulator-based transmitter, avoids the use of imperfect mixers and frequency up-converters, and their resulting distortions, leading to an improved signal quality. In this work, an augmented memory polynomial-based model for the behavioral modeling of such mixer-less transmitter architecture is proposed. Extensive simulations and measurements have been carried out in order to validate the accuracy of the proposed modeling strategy. The performance of the proposed model is evaluated using normalized mean square error (NMSE) for long-term evolution (LTE) signals. NMSE for a LTE signal of 1.4 MHz bandwidth with 100,000 samples for digital combining and analog combining are recorded as −36.41 dB and −36.9 dB, respectively. Similarly, for a 5 MHz signal the proposed models achieves −31.93 dB and −32.08 dB NMSE using digital and analog combining, respectively. For further validation of the proposed model, amplitude-to-amplitude (AM-AM), amplitude-to-phase (AM-PM), and the spectral response of the modeled and measured data are plotted, reasonably meeting the desired modeling criteria.

An Interference Tolerant RF Frontend With Capacitive Feedback for Channel Filtering

In this letter, a reconfigurable RF frontend with 4-path passive mixer is presented. Compared with the conventional method of using passive mixer at LNA output only, this design has further transferred the tunable impedance characteristic of passive mixer to the LNA input with capacitive feedback to achieve reconfigurable impedance matching at target frequency. Furthermore, the negative feedback is also able to free the conventional common base amplifier from 50 Ω impedance matching requirement to achieve better noise figure. The design was implemented with 0.18 μm SiGe BiCMOS technology. Measurement results showed a lowest noise figure of 4.6 dB from 0.6 to 1.1 GHz and an in-band IIP3 of −11 dBm, an out-band IIP3 of +3 dBm respectively.

QoE-driven spectrum assignment for 5G wireless networks using SDR

The emerging 5G wireless networks are envisioned to provide dramatically increased network capacity by using significantly expanded frequency band. With already crowded radio spectrum, utilization efficiency of frequency resources needs to be substantially improved in 5G to accommodate more users. On the other hand, the extremely wide and dynamic spectrum resources required by 5G create a significant opportunity to develop advanced resource management techniques. In this article, we propose a novel architecture to support 5G spectrum management, which uses various requirements for QoE as the design objective. With the proposed architecture, an intelligent and dynamic QoE-driven spectrum assignment scheme for 5G is introduced. The proposed scheme accomplishes dynamic spectrum assignment for each macrocell by utilizing global information that reflects the dynamic QoE requirement. In addition, we effectively allocate the spectrum bands for various devices relying on the reconfigurable RF front-end of SDR-based devices. The presented architecture is expected to support dynamic and efficient spectrum management for 5G wireless networks. Meanwhile, the intelligent and dynamic QoE-driven spectrum assignment scheme is expected to achieve an improved spectrum utilization rate, which could directly accelerate the development of 5G wireless networks.

Performance improvement of a reconfigurable series-shunt switch via asymmetric structure based RF-MEMS capacitive switch

This paper presents a series combination of metal to metal contact and capacitive RF-MEMS switches for multi-band wireless applications. For performance improvement a novel capacitive shunt switch is used and the response has been compared with a conventional shunt device. The proposed design shows the insertion loss better than 0.35 dB and return loss below 13.96 dB up to 30 GHz as compared to 1.64 dB insertion loss and 6.14 dB of return loss with conventional device. Isolation peaks of 75.33, 71.58 and 72.98 dB has been observed at 8.2, 7.3 and 15.5 GHz when left, right or both cantilevers are electro-statically actuated in the down-state respectively, whereas conventional device has peak only at 7.3 GHz. Further, a reduction of about 60 % in the pull-in voltage of capacitive switch and 17.5 % in device area has also been observed. The proposed design can be used as a building block for multiple throw switches and switch matrices for the future reconfigurable RF front end applications.

Learning-Aided Sub-Band Selection Algorithms for Spectrum Sensing in Wide-Band Cognitive Radios

We propose wide-band spectrum sensing scheduling solutions for cognitive radios that are equipped with reconfigurable RF front-ends. The wide frequency spectrum of interest is segmented into frequency sub-bands due to software and hardware limitations. These sub-bands can be non-contiguous, and each may contain an arbitrary number of channels from an arbitrary number of systems. It is assumed that the CR can only sense one sub-band at a time. Three sub-band selection policies are proposed to find spectrum opportunities taking into account realistic hardware reconfiguration energy consumptions and time delays. Two of the proposed policies rely on the individual channel Markov properties and the sub-band Markov properties, respectively. Although these two policies may achieve good performance, they rely on complete knowledge of RF environment dynamics and thus may become computationally demanding. The third sub-band selection policy based on Q-learning is proposed to circumvent this. Performance of the three policies are compared and discussed against a performance upper-bound of the optimal solution to the corresponding partially observable Markov decision process formulation. The suitability of the Q-learning technique is validated by showing that it achieves good performance through numerical results in both simulated and real measured RF environments.

RF MEMS for Reconfigurable RF Front-End: Research in Australia

This paper reviews some ground breaking development of RF MEMS technology in Australia at the UNSW, over the past decade. It presents some unique and novel designs using RF MEMS switches to achieve reconfigurable RF front-end circuits. These designs include multiport RF MEMS switches, switch matrices, reconfigurable filters and antennas. The resulting devices achieved RF performance that is unmatched by any existing RF andmicrowave technologies.

RF CMOS Integrated On-Chip Tunable Absorptive Bandstop Filter Using Q-Tunable Resonators

A new approach for protecting sensitive receivers through large attenuation and its realization on-chip is presented for the first time. This paper demonstrates the use of absorptive bandstop filters that gives anomalously deep notches for a given quality factor. This approach is used in a fabricated design example to isolate a sensitive wideband LNA from interference in 45-nm SOI complementary metaloxide-semiconductor (CMOS). For reconfigurable RF front-ends, a frequency-agile design is newly developed with Q tunable resonators because an absorptive bandstop filter must balance both intrinsic Q of the resonators and the resonant frequency of the filter. Therefore, the design requires variable resistors, variable capacitors, and intimate coupling of inductors of disparate values. The layout of overlapping inductors on closely spaced metal layers is required for proper absorptive properties. The size of one filter presented in this paper is 310 by 340 μm, making it the smallest absorptive bandstop filter demonstrated so far. Despite using small-size, on-chip low-Q resonators in the bandstop filter design, an attenuation level from 31 to 63 dB and a frequency tuning range from 2.9 to 4.3 GHz are achieved with potential to suppress potential interference or an image frequency signal.

Design and Analysis of Lithium–Niobate-Based High Electromechanical Coupling RF-MEMS Resonators for Wideband Filtering

This paper reports on a new type of microresonators enabled by micromachining of ion sliced <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> -cut LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> thin films. In operation, the device is excited into lateral vibrations, thus allowing the center frequency to be determined by the lithographically defined dimensions of the excitation electrodes. The demonstrated device has a high electromechanical coupling ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) of 11.5%-the highest attained for laterally vibrating microelectromechanical systems resonators. Device orientation was also varied to investigate its impact on <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and experimental data have shown good agreement with theoretical predictions. Several key performance parameters, including the quality factor ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> ), the static capacitance, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , the temperature coefficient of frequency (TCF), and the power handling, are also characterized and the related experimental data are presented. The devices demonstrate <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> 's up to 1800. The measured TCFs range from -55 to -69 ppm/K and can be considered sufficiently low for wideband RF filtering. The high electromechanical coupling and the high <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> of this new class of devices show promise for the implementation of multifrequency wideband multiplexers and filter banks for reconfigurable RF front-ends.

A dual-band reconfigurable direct-conversion receiver RF front-end

A dual-band reconfigurable wireless receiver RF front-end is presented, which is based on the direct-conversion principle and consists of a low noise amplifier (LNA) and a down-converter. By utilizing a compact switchable on-chip symmetrical inductor, the RF front-end could be switched between two operation frequency bands without extra die area cost. This RF front-end has been implemented in the 180 nm CMOS process and the measured results show that the front-end could provide a gain of 25 dB and IIP3 of 6 dBm at 2.2 GHz, and a gain of 18.8 dB and IIP3 of 7.3 dBm at 4.5 GHz. The whole front-end consumes 12 mA current at 1.2 V voltage supply for the LNA and 2.1 mA current at 1.8 V for the mixer, with a die area of 1.2 × 1 mm2.

System considerations and RF front-end design for integration of satellite navigation and mobile standards

Abstract. The paper presents the challenges involved in a system design of a robust reconfigurable RF front-end for navigation and mobile standards. Receiver architecture is chosen from the point of view of inter-system interference and 130nm CMOS process characteristics. System concept covers the implementation of GPS, Galileo, UMTS, GSM and CDMA2000 using a Zero-IF architecture with reconfigurable analog and digital path. Feasibility studies of the system cover analysis of the wireless regulations and performance criteria, such as overall gain, noise figure (NF), and 1dB compression point (P1dB) of the RF chain, phase noise requirements and VCO tuning range [1]. The presented chip was fabricated in 130 nm CMOS technology. System considerations are confirmed with the chip measurements of gain, noise figure, and linearity. Prospects for the future work are presented including technology shrink.

Design of reconfigurable RF front-end for multi-standard receiver using switchable passive networks

For successful implementation of a multi-standard receiver, a reconfigurable receiver architecture and a reconfigurable component design technique are essential. In this paper, an adaptable receiver architecture and a reconfigurable RF design technique using a switchable passive network are proposed. To verify the proposed design technique, the reconfigurable mixer and QVCO are designed using a flexible matching network and flexible LC tank, respectively. The measurement results of each component well prove the usefulness of the switchable passive network.