2,984 research outputs found
Amplificador de potĂȘncia para sistemas 5G
In recent years, 5G systems have been in the spotlight and the discussion
of how its requirements will change peopleâs lives is becoming increasingly
more relevant. The fact that one of these requirements is to provide users with
hundreds of MHz of available bandwidth, coupled with a scarce and crowded
spectrum below 3GHz, has led to an increase in the operating frequency. Following
this idea, this dissertation has the objective to design, implement and
test a power amplifier for 5G systems, specifically for frequencies in the X band
(8-12GHz).
In this frequency band, the behaviour of RF components (capacitors) and
other structures (via hole, substrate and connectors) have to be carefully analysed
in order to better understand how these elements can affect the overall
performance of the circuits. For this purpose several test circuits were
designed, implemented and then, the simulated and measured results were
compared. This initial step on the practical work allowed to make some updates
on the simulation process and to draw other useful conclusions. After
that, the design of a power amplifier for the X band was conceived.
In order to reach the final objective, several intermediate prototypes were designed
to make possible the identification and correction of potential error
sources, for example in the matching networks and in the transistor model.
In the end, a power amplifier for the frequency band of 9 to 9.6GHz, which
means, 600MHz of bandwidth, was designed and implemented. The maximum
drain efficiency achieved was 41-55% with a gain between 6-12dB.
These results have proved to be competitive with the actual state-of-the-art.
All design and simulation were performed using the Advanced Design System
2019 and Momentum software from Keysight Technologies.Nos Ășltimos anos, os sitemas 5G tĂȘm estado em destaque e a forma como os
seus requisitos irĂŁo mudar a vida da sociedade estĂĄ a tornar-se ainda mais relevante.
O facto de um desses requisitos ser providenciar os utilizadores com
centenas de MHz de largura de banda, juntamente com um espetro escasso
e lotado abaixo dos 3GHz, levou a um aumento da frequĂȘncia de operação.
Seguindo esta ideia, esta dissertação tem como objetivo projetar, implementar
e testar um amplificador de potĂȘncia para sistemas 5G, em particular para
a banda X (8-12GHz).
Nesta banda de frequĂȘncias, o comportamento dos componentes de RF (condensadores)
e outras estruturas (vias, substrato e conetores) tĂȘm de ser cuidadosamente
analisados de modo a entender como Ă© que estes elementos
podem afetar o desempenho geral dos circuitos. Com esse propĂłsito, vĂĄrios
circuitos de teste foram projetados, implementados, e de seguida, os resultados
simulados e medidos foram comparados. Este passo inicial no trabalho
pråtico permitiu fazer algumas atualizaçÔes no processo de simulação e tirar
outras conclusĂ”es Ășteis. Posteriormente, um amplificador de potĂȘncia para a
banda X foi concebido.
Para atingir o objetivo final, foram projetados vårios protótipos intermédios
de modo a tornar possĂvel a identificação e correção de potenciais fontes de
erro, como por exemplo nas malhas de adaptação e no modelo do transĂstor.
No final foi possĂvel projetar e implementar um amplificador de potĂȘncia
para a banda de frequĂȘncias de 9 a 9.6GHz, ou seja, com 600MHz de largura
de banda. A eficiĂȘncia de dreno mĂĄxima alcançada foi de 41-55% com um
ganho entre 6-12dB. Estes resultados demonstraram-se competitivos com o
estado-da-arte atual.
Todo o projeto e simulação foram realizados usando o software Advanced
Design System 2019 e Momentum da Keysight Technologies.Mestrado em Engenharia Eletrónica e TelecomunicaçÔe
Experimental realization of an ideal Floquet disordered system
The atomic Quantum Kicked Rotor is an outstanding "quantum simulator" for the
exploration of transport in disordered quantum systems. Here we study
experimentally the phase-shifted quantum kicked rotor, which we show to display
properties close to an ideal disordered quantum system, opening new windows
into the study of Anderson physics.Comment: 10 pages, 7 figures, submitted to New Journal of Physics focus issue
on Quantum Transport with Ultracold Atom
Planar waveguide CO2 laser amplifiers
The scaling of diffusion-cooled planar waveguide carbon dioxide laser oscillators to very high
average power levels (> 5 kilowatts) is limited by mechanical constraints, associated with the
physical size of the laser electrodes. Moreover, the operation of such lasers in pulsed mode is limited
to pulse duration larger than - 50flS. However, there are important laser applications, for example in
material processing, where the requirement is for high peak power level and short pulses combined
with high average power.
The principal objective of this project is to investigate a laser architecture based on the master
oscillator power amplifier concept, but involving planar waveguide gain medium structures. Such an
amplifier system may be used either for simple power amplification (long pulse/cw) or for amplifying
short pulses using a 'pulse forming' modulator at the input for the amplifier. The laser excitation
method involves transverse radio frequency discharges designed to match the large area slab-like
structures. This excitation technique would permit multiple "stacked" slab operation with a single
power generator, and in the future, may facilitate an "integrated" MOPA construction.
The gain and power amplification characteristics of RF discharge excited planar waveguide
amplifiers have been investigated over a range of operating parameters (gas pressure, RF power
density, input beam intensity etc.) for both pulsed and cw input beams and also for single and
multiple (folded) passes of the planar amplifier. Short pulses at the input to the amplifier ('p ~ 1 flSec)
were generated using a long pulse oscillator and an acousto-optic modulator as a pulse slicer. In all
cases, beam transformation optics were designed and utilised to ensure the excitation of the
fundamental waveguide mode with minimal mode coupling. Studies of discharge-induced mode
matching effects (phase shifts, amplitude variations) have also been conducted, and techniques for the
elimination of parasitic oscillation have been developed. The future potential for the MOP A concept
utilising this technology is evaluated for high power laser applications
Comb-based WDM transmission at 10 Tbit/s using a DC-driven quantum-dash mode-locked laser diode
Chip-scale frequency comb generators have the potential to become key
building blocks of compact wavelength-division multiplexing (WDM) transceivers
in future metropolitan or campus-area networks. Among the various comb
generator concepts, quantum-dash (QD) mode-locked laser diodes (MLLD) stand out
as a particularly promising option, combining small footprint with simple
operation by a DC current and offering flat broadband comb spectra. However,
the data transmission performance achieved with QD-MLLD was so far limited by
strong phase noise of the individual comb tones, restricting experiments to
rather simple modulation formats such as quadrature phase shift keying (QPSK)
or requiring hard-ware-based compensation schemes. Here we demonstrate that
these limitations can be over-come by digital symbol-wise phase tracking
algorithms, avoiding any hardware-based phase-noise compensation. We
demonstrate 16QAM dual-polarization WDM transmission on 38 channels at an
aggregate net data rate of 10.68 Tbit/s over 75 km of standard single-mode
fiber. To the best of our knowledge, this corresponds to the highest data rate
achieved through a DC-driven chip-scale comb generator without any
hardware-based phase-noise reduction schemes
All-fibre wavelength versatile short pulsed laser sources
Pulsed lasers operating in the picosecond or femtosecond regimes find a wide range of applications in optical sciences, such as spectroscopy, laser surgery, material processing and optical communications. Among the existing sources of short-pulses, mode-locked fibre lasers play an important role mainly due to their robust and compact nature, and also due to their ability to generate outputs over a wide range of repetition-rates, pulse durations, pulse shapes, peak powers and optical wavelengths.
Considering the case of wavelength versatility, Raman amplification can be used to fill the spectral gaps that are not covered by the emission band of traditional rare-earth doped elements such as ytterbium and erbium, allowing the generation of light at unconventional wavelengths. Additionally, another contribution has come from the recent development of new nanomaterials such as graphene and carbon nanotubes that can be used as saturable absorbers over a broadband wavelength range.
The experimental work reported in this thesis is mainly focused in combining the wavelength versatility allowed by Raman gain and carbon nanotubes and graphene to generate short-pulsed fibre lasers at different wavelengths. High power ytterbium and erbium lasers and also a high power Raman laser operating at 1450 nm are used as pump sources to seed the Raman gain and carbon nanotubes and graphene are the saturable absorbers used as mode-lockers. All the fibres utilized in the oscillators are highly non-linear single mode silica fibres doped with GeO2.
The lasers operate in the dissipative soliton regime, generating chirped pulses with durations on the order of hundred of picosecond that are suitable for external compression. We demonstrate for example an erbium-pumped Raman oscillator generating 500 ps pulses that are linearly compressed to 2 ps. The results presented in this document are a contribution towards making fibre based lasers more universal devices in terms of wavelength operation.Open Acces
ELECTRON DEVICE NONLINEAR MODELLING FOR MICROWAVE CIRCUIT DESIGN
The electron device modelling is a research topic of great relevance, since the performances
required to devices are continuously increasing in terms of frequency, power and linearity: new
technologies are affirming themselves, bringing new challenges for the modelling community. In
addition, the use of monolithic microwave integrated circuits (MMIC) is also increasing, making
necessary the availability, in the circuit design phase, of models which are computationally efficient
and at the same more and more accurate. The importance of modelling is even more evident by
thinking at the wide area covered by microwave systems: terrestrial broadband, satellite communications, automotive applications, but also military industry, emergency prevention systems
or medical instrumentations.
This work contains a review of the empirical modelling approach, providing the description of
some well-known equivalent-circuit and black-box models.
In addition, an original modelling approach is described in details, together with the various
possible applications: modelling of nonquasi-static phenomena as well as of low-frequency
dispersive effects. A wide experimental validation is provided, for GaAs- and GaN-based devices.
Other modelling issues are faced up, like the extraction of accurate models for Cold-FET or the
more convenient choice of the data-interpolator in table-based models.
Finally, the device degradation is also treated: a new measurement setup will be presented, aimed
to the characterization of the device breakdown walkout under actual operating conditions for
power amplifiers
Contributing to Second Harmonic Manipulated Continuum Mode Power Amplifiers and On-Chip Flux Concentrators
The current cellular network consumes a staggering 100 TWh of energy every year. In the coming years, millions of devices will be added to the existing network to realize the Internet of Things (IoT), further increasing its power consumption. An RF power amplifier typically consumes a large proportion of the DC power in a wireless transceiver, improving its efficiency has the largest impact on the overall system. Additionally, amplifiers need to demonstrate high linearity and bandwidth to adhere to constraints imposed by wireless standards and to reduce the number of amplifiers required as an amplifier with a broader bandwidth can potentially replace several narrowband amplifiers. A typical approach to improve efficiency is to present an appropriate load at the harmonics generated by the transistor. Recently proposed continuous modes based on harmonic manipulation, such as class B/J continuum, continuous class F (CCF) and continuous class F-1 (CCF-1), have shown the capability of achieving counteracting requirements viz., high efficiency, high linearity, and broad bandwidth (with a fractional bandwidth greater than 30%). In these classes of amplifiers, the second harmonic is manipulated by placing a reactive second harmonic load and the reactive component of the fundamental load is adjusted while keeping a fixed resistive component of the fundamental load.
The first contribution of this work is to investigate the reason for amplifiers designed in classes B/J continuum and CCF to achieve high efficiency at back-off and 1dB compression. In this thesis, we demonstrate that the variation of the phase of the current through the non-linear intrinsic capacitances due to the variation of the phase in the continuum of drain voltage waveforms in Class B/J/J* continuum leads to either a reduction or enhancement of intrinsic drain current. Consequently, a subset of voltage waveforms of the class B/J/J* continuum can be used to design amplifiers with higher P1dB, and efficiency at P1dB than in Class B. A simple choice of this subset is demonstrated with a 2.6GHz Class B/J/J* amplifier, achieving a P1dB of 38.1dBm and PAE at P1dB of 54.7%, the highest output power and efficiency at P1dB amongst narrowband linear amplifiers using the CGH40010 reported to date, at a comparable peak PAE of 72%.
Secondly, we propose a new formulation for high-efficiency modes of power amplifiers in which both the in-phase and out-of-phase components of the second harmonic of the current are varied, in addition to the second harmonic component of the voltage. A reduction of the in-phase component of the second harmonic of current allows reduction of the phase difference between the voltage and current waveforms, thereby increasing the power factor and efficiency. Our proposed waveforms offer a continuous design space between class B/J continuum and continuous F-1 achieving an efficiency of up to 91% in theory, but over a wider set of load impedances than continuous class F-1. These waveforms require a short at third and higher harmonic impedances, which are easier to achieve at a higher frequency. The load impedances at the second harmonic are reactive and can be of any value between -jâ and jâ, easing the amplifier design. A trade-off between linearity and efficiency exists in the newly proposed broadband design space, but we demonstrate inherent broadband capability. The fabricated narrowband amplifier using a GaN HEMT CGH40010F demonstrates 75.9% PAE and 42.2 dBm output power at 2.6 GHz, demonstrating a comparable frequency weighted efficiency for this device to that reported in the literature.
IoT devices may be deployed in critical applications such as radar or 5G transceivers of an autonomous vehicle and hence need to operate free of failure. Monitoring the drain current of the RF GaN MMIC would allow to optimize the device performance and protect it from surges in its supply current. Galvanic current sensors rely on the magnetic field generated by the current as a non-invasive method of current sensing. In this thesis, our third major contribution is a planar on-chip magnetic flux concentrator, is enhance the magnetic field at the current sensor, thereby improving the current detection capability of a current sensor. Our layout utilizes a discontinuity in a magnetic via, resulting in penetration of the magnetic field into the substrate. The proposed concentrator has a magnetic gain x1.8 in comparison to air. The permeability of the magnetic core required is 500, much lower than that reported in off-chip concentrators, resulting in a significant easing of the specifications of the material properties of the core. Additionally, we explore a novel three-dimensional spiral-shaped magnetic flux concentrator. It is predicted via simulations that this geometry becomes a necessity to enhance the magnetic field for increased form factor as the magnetic field from a single planar concentrator deteriorates as its size increases
Communications techniques and equipment: A compilation
This Compilation is devoted to equipment and techniques in the field of communications. It contains three sections. One section is on telemetry, including articles on radar and antennas. The second section describes techniques and equipment for coding and handling data. The third and final section includes descriptions of amplifiers, receivers, and other communications subsystems
Linear Operation of Switch-Mode Outphasing Power Amplifiers
Radio transceivers are playing an increasingly important role in modern society. The
âconnectedâ lifestyle has been enabled by modern wireless communications. The demand
that has been placed on current wireless and cellular infrastructure requires increased spectral
efficiency however this has come at the cost of power efficiency. This work investigates
methods of improving wireless transceiver efficiency by enabling more efficient power
amplifier architectures, specifically examining the role of switch-mode power amplifiers in
macro cell scenarios. Our research focuses on the mechanisms within outphasing power
amplifiers which prevent linear amplification. From the analysis it was clear that high power
non-linear effects are correctable with currently available techniques however non-linear effects
around the zero crossing point are not. As a result signal processing techniques for suppressing
and avoiding non-linear operation in low power regions are explored. A novel method of digital
pre-distortion is presented, and conventional techniques for linearisation are adapted for the
particular needs of the outphasing power amplifier. More unconventional signal processing
techniques are presented to aid linearisation of the outphasing power amplifier, both zero
crossing and bandwidth expansion reduction methods are designed to avoid operation in nonlinear
regions of the amplifiers. In combination with digital pre-distortion the techniques
will improve linearisation efforts on outphasing systems with dynamic range and bandwidth
constraints respectively.
Our collaboration with NXP provided access to a digital outphasing power amplifier,
enabling empirical analysis of non-linear behaviour and comparative analysis of behavioural
modelling and linearisation efforts. The collaboration resulted in a bench mark for linear
wideband operation of a digital outphasing power amplifier. The complimentary linearisation
techniques, bandwidth expansion reduction and zero crossing reduction have been evaluated in
both simulated and practical outphasing test benches. Initial results are promising and indicate
that the benefits they provide are not limited to the outphasing amplifier architecture alone.
Overall this thesis presents innovative analysis of the distortion mechanisms of the
outphasing power amplifier, highlighting the sensitivity of the system to environmental effects.
Practical and novel linearisation techniques are presented, with a focus on enabling wide band
operation for modern communications standards
Photonic based Radar: Characterization of 1x4 Mach-Zehnder Demultiplexer
This work is based on a research activity which aims to implement an optical transceiver for a photonic-assisted fullyâdigital radar system based on optic miniaturized optical devices both for the optical generation of the radiofrequency (RF) signal and for the optical sampling of the received RF signal. The work is more focused on one very critical block of receiver which is used to parallelize optical samples. Parallelization will result in samples which will be lower in repetition rate so that we can use commercial available ADCs for further processing. This block needs a custom design to meet all the system specifications. In order to parallelize the samples a 1x4 switching matrix (demux) based on Mach Zehnder (MZ) interferometer has been proposed. The demux technique is Optical Time Division Demultiplexing. In order to operate this demux according to the requirements the characterization of device is needed. We need to find different stable control points (coupler bias and MZ bias) of demux to get output samples with high extinction ratio. A series of experiments have been performed to evaluate the matrix performance, issues and sensitivity. The evaluated results along with the whole scheme has been discussed in this document
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