Metodologia Per la Caratterizzazione di amplificatori a basso rumore per UMTS

In questo lavoro si presenta una metodologia di progettazione elettronica a livello di sistema, affrontando il problema della caratterizzazione dello spazio di progetto dell' amplificatore a basso rumore costituente il primo stadio di un front end a conversione diretta per UMTS realizzato in tecnologia CMOS con lunghezza di canale .18u. La metodologia è sviluppata al fine di valutare in modo quantititativo le specifiche ottime di sistema per il front-end stesso e si basa sul concetto di Piattaforma Analogica, che prevede la costruzione di un modello di prestazioni per il blocco analogico basato su campionamento statistico di indici di prestazioni del blocco stesso, misurati tramite simulazione di dimensionamenti dei componenti attivi e passivi soddisfacenti un set di equazioni specifico della topologia circuitale. Gli indici di prestazioni vengono successivamente ulizzati per parametrizzare modelli comportamentali utilizzati nelle fasi di ottimizzazione a livello di sistema. Modelli comportamentali atti a rappresentare i sistemi RF sono stati pertanto studiati per ottimizzare la scelta delle metriche di prestazioni. L'ottimizzazione dei set di equazioni atti a selezionare le configurazione di interesse per il campionamento ha al tempo stesso richiesto l'approfondimento dei modelli di dispositivi attivi validi in tutte le regioni di funzionamento, e lo studio dettagliato della progettazione degli amplificatori a basso rumore basati su degenerazione induttiva. Inoltre, il problema della modellizzazione a livello di sistema degli effetti della comunicazione tra LNA e Mixer è stato affrontato proponendo e analizzando diverse soluzioni. Il lavoro ha permesso di condurre un'ottimizzazione del front-end UMTS, giungendo a specifiche ottime a livello di sistema per l'amplificatore stesso

A survey on RF and microwave doherty power amplifier for mobile handset applications

This survey addresses the cutting-edge load modulation microwave and radio frequency power amplifiers for next-generation wireless communication standards. The basic operational principle of the Doherty amplifier and its defective behavior that has been originated by transistor characteristics will be presented. Moreover, advance design architectures for enhancing the Doherty power amplifier’s performance in terms of higher efficiency and wider bandwidth characteristics, as well as the compact design techniques of Doherty amplifier that meets the requirements of legacy 5G handset applications, will be discussed.Agencia Estatal de Investigación | Ref. TEC2017-88242-C3-2-RFundação para a Ciência e a Tecnologia | Ref. UIDP/50008/201

An accurate, trimless, high PSRR, low-voltage, CMOS bandgap reference IC

Bandgap reference circuits are used in a host of analog, digital, and mixed-signal systems to establish an accurate voltage standard for the entire IC. The accuracy of the bandgap reference voltage under steady-state (dc) and transient (ac) conditions is critical to obtain high system performance. In this work, the impact of process, power-supply, load, and temperature variations and package stresses on the dc and ac accuracy of bandgap reference circuits has been analyzed. Based on this analysis, the a bandgap reference that 1. has high dc accuracy despite process and temperature variations and package stresses, without resorting to expensive trimming or noisy switching schemes, 2. has high dc and ac accuracy despite power-supply variations, without using large off-chip capacitors that increase bill-of-material costs, 3. has high dc and ac accuracy despite load variations, without resorting to error-inducing buffers, 4. is capable of producing a sub-bandgap reference voltage with a low power-supply, to enable it to operate in modern, battery-operated portable applications, 5. utilizes a standard CMOS process, to lower manufacturing costs, and 6. is integrated, to consume less board space has been proposed. The functionality of critical components of the system has been verified through prototypes after which the performance of the complete system has been evaluated by integrating all the individual components on an IC. The proposed CMOS bandgap reference can withstand 5mA of load variations while generating a reference voltage of 890mV that is accurate with respect to temperature to the first order. It exhibits a trimless, dc 3-sigma accuracy performance of 0.84% over a temperature range of -40°C to 125°C and has a worst case ac power-supply ripple rejection (PSRR) performance of 30dB up to 50MHz using 60pF of on-chip capacitance. All the proposed techniques lead to the development of a CMOS bandgap reference that meets the low-cost, high-accuracy demands of state-of-the-art System-on-Chip environments.Ph.D.Committee Chair: Rincon-Mora, Gabriel; Committee Member: Ayazi, Farrokh; Committee Member: Bhatti, Pamela; Committee Member: Leach, W. Marshall; Committee Member: Morley, Thoma

Experimental demonstration of metamaterials application for mitigating scan blindness in phased array antennas

This paper presents two metamaterial-inspired solutions to mitigate the scan blindness effects in a phased array antenna. In the first solution, portions of a bed of nails are introduced in the radome to prevent the excitation of surface waves. In the second solution, a superstrate metasurface is designed to synthesize a permittivity tensor optimized to achieve a wide angle impedance matching. In both approaches, the numerical simulations are successfully compared with measurements of a phased array antenna prototype with 100 elements. The wire medium-based solution reveals an effective way for reducing the blind-spot in a wide bandwidth, while the metaradome has been found less suitable for the same purpose.This work was supported by the METALESA project A-1089- RT-GC that was coordinated by the European Defence Agency (EDA) and funded by 11 contributing Members (Cyprus, France, Germany, Greece, Hungary, Italy, Norway, Poland, Slovakia, Slovenia and Spain) in the framework of the Joint Investment Programme on Innovative Concepts and Emerging Technologies (JIP-ICET)

Design of Radio-Frequency Arrays for Ultra-High Field MRI

Magnetic Resonance Imaging (MRI) is an indispensable, non-invasive diagnostic tool for the assessment of disease and function. As an investigational device, MRI has found routine use in both basic science research and medicine for both human and non-human subjects. Due to the potential increase in spatial resolution, signal-to-noise ratio (SNR), and the ability to exploit novel tissue contrasts, the main magnetic field strength of human MRI scanners has steadily increased since inception. Beginning in the early 1980’s, 0.15 T human MRI scanners have steadily risen in main magnetic field strength with ultra-high field (UHF) 8 T MRI systems deemed to be insignificant risk by the FDA (as of 2016). However, at UHF the electromagnetic fields describing the collective behaviour of spin dynamics in human tissue assume ‘wave-like’ behaviour due to an increase in the processional frequency of nuclei at UHF. At these frequencies, the electromagnetic interactions transition from purely near-field interactions to a mixture of near- and far-field mechanisms. Due to this, the transmission field at UHF can produce areas of localized power deposition – leading to tissue heating – as well as tissue-independent contrast in the reconstructed images. Correcting for these difficulties is typically achieved via multi-channel radio-frequency (RF) arrays. This technology allows multiple transmitting elements to synthesize a more uniform field that can selectively minimize areas of local power deposition and remove transmission field weighting from the final reconstructed image. This thesis provides several advancements in the design and construction of these arrays. First, in Chapter 2 a general framework for modeling the electromagnetic interactions occurring inside an RF array is adopted from multiply-coupled waveguide filters and applied to a subset of decoupling problems encountered when constructing RF arrays. It is demonstrated that using classic filter synthesis, RF arrays of arbitrary size and geometry can be decoupled via coupling matrix synthesis. Secondly, in Chapters 3 and 4 this framework is extended for designing distributed filters for simple decoupling of RF arrays and removing the iterative tuning portion of utilizing decoupling circuits when constructing RF arrays. Lastly, in Chapter 5 the coupling matrix synthesis framework is applied to the construction of a conformal transmit/receive RF array that is shape optimized to minimize power deposition in the human head during any routine MRI examination

Sub-GHz Wrist-Worn Antennas for Wireless Sensing Applications: A Review

With recent advances in wearable wrist-worn wireless sensing applications, the demand for smartwatches and wristbands is rapidly increasing due to their widespread adoption in applications such as smart health monitoring, security, and fitness tracking. Currently, these devices primarily operate in the 2.45 GHz band, leveraging the availability of Bluetooth and Wi-Fi wireless technologies. However, the use of Sub-GHz frequencies (e.g., 433 MHz, 868 MHz, 915 MHz, 923 MHz) for wearable systems has also gained interest due to the emergence of wireless technologies like long-range wide area network (LoRaWAN), narrowband-IoT (NB-IoT) and Sigfox, which offer the potential for long-range wireless communications and sensing applications. In recent times, there has been a notable surge in the commercial production of a variety of Sub-GHz wrist-worn wireless sensing devices for health monitoring and tracking applications. Nevertheless, communications at Sub-GHz frequencies present significant challenges in antenna design, primarily due to the practical size constraints of wrist-worn devices and the necessity for using electrically small antennas. This paper meticulously reviews wrist-worn Sub-GHz antennas reported in the literature, analyzing key antenna parameters such as antenna topology, size, impedance bandwidth, peak realized gain, radiation efficiency, and specific absorption rate (SAR). Additionally, it underlines antenna design challenges, limitations, current trends, and presents potential future perspectives. To the best of the author’s knowledge, there is currently no existing literature comprehensively reviewing Sub-GHz wrist-worn antennas. Therefore, this paper represents the inaugural effort to provide a comprehensive review in this specific domain