Push-Pull Based High Efficiency and High Power Broadband Power Amplifiers for Wireless Base Stations

The monthly data throughput by 2021 is forecasted to be ten times that of December 2015. As a result of the on going dramatic increase in demand, service providers are assigned new frequency bands to accommodate more channels to carry more data. However, the usable part of the spectrum is a limited resource so modern communication signals were designed to be more spectrally efficient to send more bits over the same channel bandwidth. However, these spectrally efficient signals have high PAPR. The immediate reaction to these changes was to add additional RF front-end branches to accommodate the new frequency bands. Initially, the PAs used at the time were not optimized for back-off efficiency and where operating at low efficiency which caused significant increase in heat generation for the same average power produced which in turn increased cooling costs and reduced the life time of the PA. After the introduction of back-off efficiency enhancement techniques the PAs became more efficient however they were limited in bandwidth which is typically 10-15%. This work focuses on reducing the redundancy of power amplifiers in communication base stations while maintaining high back-off efficiency. After exploring the literature to understand the limitations of current implementations, it was found that the push-pull topology is often used at low frequency in broadband high power PAs. In the absence of a complimentary transistor pairs the push-pull implantation requires the use of balanced to unbalanced (balun) transformers. Various balun implantations were hence investigated to identify the most suitable option for broadband planar implementation. As a result, a methodology was proposed to co-design the balun and the matching network in order to have better control over the harmonic impedance. An 85 W push-pull PA was then designed based on the proposed methodology with a multi-octave bandwidth as a demonstration of the broadband potential of push-pull PAs at RF frequencies. Next, the two most popular techniques for back-off efficiency enhancement, i.e., ET and load modulation, were studied and the principle of load modulation was found to be more suitable for broadband signal transmission. The Doherty architecture is the most common implementation of load modulation and it comes in two basic variations, the PCL and SCL DPAs. The original architecture concepts are not only band limited but also ill-suited for high frequency designs where the transistors' parasitics introduce significant effect. However, later literature expanded on the original concept of the PCL variation which provided the needed flexibility for wider bandwidth implementations at a higher frequency. Using the broadband implementation and the co-design methodology two push-pull amplifiers were used in a PCL DPA topology and demonstrated that the push-pull utilization doesn't have a significant impact on the bandwidth of the output combiner as an octave bandwidth was achieved with the use of digital Doherty. Lastly, the thesis proposes a new approach for designing high power DPAs with extended bandwidth. It starts with a generic SCL DPA architecture to derive the equations that relate its underlying combiner's ABCD parameters to the transistor's optimum impedance and load impedance. These equations featured the possibility of significantly increasing the load impedance in SCL DPA compared to the one of the popular PCL DPA architecture. This is particularly beneficial when targeting very high power DPAs for macro-cell base stations and broadcast applications where very low load impedance can seriously complicate the design and limit the achievable bandwidth. To further maximize the load impedance increase, the proposed SCL DPA uses a push-pull topology for the main and peaking amplifier stages. A low-loss planar balanced to unbalanced transformer (balun) combiner network is then utilized to realize the SCL DPA combining. The proposed approach was finally applied to design a proof-of-concept 350 W SCL DPA which operates over the band spanning from 720 to 980 MHz. The prototype demonstrated a peak output power of about 55 dBm over a 30% FBW with a 6 dB back-off efficiency, measured using pulsed signal, between 46.6% and 54.6%. Furthermore, the modulated signal based measurement results confirmed the linearizability of the SCL DPA prototype while maintaining a back-off efficiency over 50% for a 7.1 dB peak to average power ratio signal

60 Watts Broadband Push Pull RF Power Amplifier Using LTCC Technology

The continuous increase in wireless usage forces an immense pressure on wireless communication in terms of increased demand and spectrum scarcity. Service providers for communication services had no choice but to allocate new parts of the spectrum and present new communication standards that are more spectrally efficient. Communication is not only limited to mobile phones but recently attention has been given to intelligent transportation systems (ITS) where cars will be given a significant place in the communication network. Vehicular Ad-Hoc Network (VANET) is already assigned a slice of the spectrum at 5.9GHz using the IEEE802.11p standard also known as Dedicated Short-Range Communication (DSRC); however, this assignment will have limited range and functionality at first, and users are expected to depend on existing wireless mobile channels for some services such as video streaming and car entertainment. Therefore, it is essential to integrate existing wireless mobile communication standards into the skeleton of ITS at launch and most probably permanently. An investigation was carried out regarding the existing communication standards including wireless local area networks (WLAN) and it was found that frequency bands from 400MHz up to 6GHz are being used in various regions around the world. It is also noted that current state of the art transceivers are composed of several transmitter front-ends targeting certain bands and standards. However, the more standards to be supported the more components to be added and the higher the cost not to mention the limited space in mobile devices. Multimode Multiband (MMMB) transmitters are therefore proposed as a potential solution to the existing redundancy in the number of front-end paths in modern transmitters. Broadband amplifiers are an essential part of any MMMB transmitter and they are also among the most challenging especially for high power requirements. This work explains why single ended topologies with efficiencies higher than 50% have a fundamental bandwidth limit such that the highest frequency of operation must be lower than twice the lowest frequency of operation. Hence, Push-Pull amplifier topology is being proposed as it was found that it has inherent broadband capabilities exceeding those of other topologies with comparable efficiency. The major advantage of Push-Pull power amplifiers is its capability of isolating the even harmonics present in the even mode operation of a Push-Pull amplifier from the less critical odd mode harmonics and the fundamental frequency. This separation between even and odd signals comes from the inclusion of a Balun at the output of push-pull amplifiers. Such separation makes it possible to operate amplifiers beyond the existing limit of single ended power amplifiers. To prove the concept, several Baluns were designed and tested and a comparison was made between different topologies in terms of balance, bandwidth and odd and even mode performances; moreover, to illustrate the concept a Push-Pull power amplifier design was implemented using the multilayer Low Temperature Co-fired Ceramics (LTCC) technology with a bandwidth ratio of more than 100%

Copolymères doubles hydrophiles dégradables pour applications en santé

Les copolymères amphiphiles dégradables à base de poly (éthylène glycol) PEG et de polyesters aliphatiques (poly(ε-caprolactone) (PCL), poly(lactide) (PLA), poly(glycolide) (PGA)) sont largement utilisés dans les applications médicales en raison de leur innocuité et leur acceptation par les autorités de santé. Cependant leur capacité à répondre aux enjeux auxquels sont confrontés les nanomédicaments (ciblage, réponse programmée etc…) est limitée du fait de l’absence de groupes fonctionnels. Pour pallier cette limitation, ce travail de thèse s’intéresse aux voies de modification post-polymérisation de copolymères amphiphiles PEG-b-PCL donnant un accès simple à des familles de copolymères à blocs double hydrophiles (DHBC) dégradables. Nous nous intéressons en particulier à la synthèse de DHBC en trois étapes incluant une étape de photoaddition thiol-yne qui permet à partir d’un même précurseur macromoléculaire la synthèse de familles de DHBC à bloc PEG et blocs PCL fonctionnalisés en chaîne latérale à caractère neutre, cationique ou anionique. Le potentiel de ces DHBC pour la formulation d’actifs au sein de nanosystèmes de libérations pH-répondants est tout d’abord évalué à l’aide d’un anti-cancéreux à large spectre d’activité antitumorale. Dans un second temps, la formulation de micelles de complexes polyioniques tripartites de siRNA pour application en thérapie génique à partir de DHBC anioniques est étudiée. Enfin, la préparation de nanocomplexes DHBC/gadolinium pour imagerie médicale par résonance magnétique nucléaire (IRM) est abordée.Biodegradable amphiphilic copolymers based on poly(ethylene glycol) PEG and aliphatic polyesters (poly(ε-caprolactone) (PCL), poly(lactide) (PLA), poly(glycolide) (PGA)) are widely used in medical applications due to their safety and their acceptance by health authorities. However, their ability to address the challenges faced by the nanomedicines (targeting, programmed response etc…) is limited due to the absence of functional groups. To overcome this limitation, this work focuses on the post-polymerization modification strategies of amphiphilic PEG-b-PCL giving easy access to families of degradable double hydrophilic block copolymers (DHBC). We are particularly interested in the three-step synthesis of DHBC including a thiol-yne photoaddition step which allows, starting from the same macromolecular precursor, the synthesis of DHBC families composed of PEG blocks and side chain functionalized PCL blocks with a neutral, cationic or anionic character. The potential of these DHBC for the formulation of active pharmaceutical ingredients within pH-responsive drug delivery nanosystems is first evaluated using an anti-cancer agent with a broad spectrum of antitumor activity. In another part, we study the formulation of tripartite polyionic complex micelles with an anionic DHBC and siRNA for applications in gene therapy. Finally, the preparation of DHBC/gadolinium nanocomplexes for medical imaging by nuclear magnetic resonance (MRI) is discussed

Double hydrophilic block copolymers self-assemblies in biomedical applications

International audienceDouble-hydrophilic block copolymers (DHBCs), consisting of at least two different water-soluble blocks, are an alternative to the classical amphiphilic block copolymers and have gained increasing attention in the field of biomedical applications. Although the chemical nature of the two blocks can be diverse, most classical DHBCs consist of a bioeliminable non-ionic block to promote solubilization in water, like poly(ethylene glycol), and a second block that is more generally a pH-responsive block capable of interacting with another ionic polymer or substrate. This second block is generally non-degradable and the presence of side chain functional groups raises the question of its fate and toxicity, which is a limitation in the frame of biomedical applications. In this review, following a first part dedicated to recent examples of non-degradable DHBCs, we focus on the DHBCs that combine a biocompatible and bioeliminable non-ionic block with a degradable functional block including polysaccharides, polypeptides, polyesters and other miscellaneous polymers. Their use to design efficient drug delivery systems for various biomedical applications through stimuli-dependent self-assembly is discussed along with the current challenges and future perspectives for this class of copolymers

Double-Hydrophilic Block Copolymers Based on Functional Poly(ε-caprolactone)s for pH-Dependent Controlled Drug Delivery

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Degradable double hydrophilic block copolymers and tripartite polyionic complex micelles thereof for small interfering ribonucleic acids (siRNA) delivery

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Global impact of the first coronavirus disease 2019 (COVID-19) pandemic wave on vascular services

This online structured survey has demonstrated the global impact of the COVID-19 pandemic on vascular services. The majority of centres have documented marked reductions in operating and services provided to vascular patients. In the months during recovery from the resource restrictions imposed during the pandemic peaks, there will be a significant vascular disease burden awaiting surgeons. One of the most affected specialtie