High Performance Tunable Active Inductors For Microwave Circuits

Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2016Thesis (PhD) -- İstanbul Technical University, Institute of Science and Technology, 2016RF uygulamalarında enduktif karakteristiğe önemli ölçüde ihtiyaç duyulmaktadır; bunlar, özellikle filtreler, düşük gürültülü yükselteçler (LNA, low noise amplifiers), gerilim kontrollü osilatörler (VCO, voltage controlled oscillators), pek çok farklı türde yükselteç için band genişliği iyileştirilmesi, faz kaydırıcılar, güç bölücüler ve eşleştirme (matching) devreleri vb. uygulamalardır. Pasif sarmal çip-içi CMOS endüktansların eksik yönleri ayrıntılı olarak literatürde tartışılmıştır. Bu tür endüktanslar düşük değer katsayısı (quality factor), düşük öz-rezonans frekansı (SRF, self-resonance frequency), sabit ve düşük değerli endüktans ve geniş bir silikon (silicon) alanı gerektirmeleri gibi istenmeyen özelliklere sahiptirler. Diğer yandan, MOS transistorlar kullanılarak sentezlenen CMOS aktif endüktansların, pasif sarmal eşdeğer yapıları ile karşılaştırıldığında pek çok çekici karakteristik özellik sunabildikleri gösterilmiştir. Bunlar; geniş bir bölgede ayarlanabilir öz-rezonans frekansı başarımı, geniş bir bölgede ayarlanabilir endüktans başarımı, geniş bir bölgede ayarlanabilir değer katsayısı başarımı, CMOS teknolojileri ile tümüyle gerçeklenebilme ve az alan kaplama gibi karakteristik özellikleri olarak ortaya konulmaktadır. Literatürde jiratör-C (GC) prensibi, topolojisi, karakterizasyonu ve uygulamaları ayrıntılı olarak ele alınmaktadır. İşlemsel geçiş-iletkenliği kuvvetlendiricisi (OTA, operational transconductance amplifier) ile gerçeklenen GC devreleri, RF uygulamaları için oldukça uygundur. Bu özellik, GC yapılarının söz konusu yapı kullanılarak en az sayıda aktif eleman ile gerçeklenebilmesinden kaynaklanmaktadır. Gerek topraklı (grounded) gerekse yüzen (floating) aktif endüktansların GC devreleri ile gerçeklenebildiği gösterilmiştir. Aktif endüktansların başarımlarının nicel olarak ölçülmesi amacıyla, çok sayıda ölçüt ortaya konulmuştur. Bu ölçütler frekans çalışma aralığı, endüktans ayarlanabilirliği, değer katsayısı, gürültü ve güç tüketimi gibi temel özellikleri içerirler. CMOS transistorların parazitik bileşenlerinden dolayı tasarlanan aktif endüktanslar belirli bir frekans bölgesinde endüktif davranış gösterirler. Alt frekans sınırı, GC devrelerinin sıfır frekansı ile belirlenirken; üst frekans sınırı ise öz-rezonans frekansı ile belirlenir. Aktif endüktansların pasif sarmal eşdeğer yapılarına göre en önemli üstünlüklerinden biri de; endüktanslarının geniş bir değer aralığıunda ayarlanabilir olmasıdır. GC aktif endüktansların endüktans değeri, transistorların geçiş-iletkenliklerinin ya da MOS varaktörlerle gerçeklenen yük kapasitanslarının değiştirilmesi ile ayarlanabilir. Literatürde, GC topolojisine dayalı pek çok CMOS AI (active inductor) devresi bildirilmiştir. Bunların tümü, farklı teknikler kullanılarak yüksek başarımlı AI yapıları oluşturmayı amaçlamışlardır. Bu tezde, bunlardan güncel olan bazı GAI (grounded AI) ve FAI (floating AI) yapıları gözden geçirilmiştir. Bunlardan bazıları, değer katsayısını (QF) iyileştirmek amacıyla, AI kaybını telafi etmek için negatif direnç kullanmışlardır. GC yapıları RF uygulamaları için tasarlandıklarında en az sayıda transistor kullanımı çok kritiktir. Çünkü bu durum AI öz-rezonans frekansının artmasına yardımcı olur. AI’ler, kazanç artırma amacıyla LNA’lerde geniş kullanım alanı bulabilmektedirler. Diğer taraftan, AI yapılarının en önemli dezvantajlarından biri gürültü başarımının pasif endüktanslara nispeten yüksek olmasıdır. Literatürde bu dezavantajı gidermek amacıyla teklif edilen yaklaşımlardan biri dejenerasyon direncinin bulunduğu bir geribesleme katı kullanılarak girişe gelen gürültü katkısını azaltmayı amaçlamıştır. Literatürde teklif edilen tekniklerin amacı, parazitik bileşenlerin etkisini azaltmak ya da tümüyle ortadan kaldırmaktır. Bu tezde, ileri devre teknikleri kullanılarak, yeni topraklı (grounded) ve yüzen (floting) AI yapıları tasarlanmıştır. AI giriş ve çıkış düğümlerine ait iletkenlikleri azaltmak için çoklu-düzenlenmiş kaskod (multi-regulated cascode, MRC) katları QF değerini iyileştirme amacıyla kullanılmaktadır. MRC katı PMOS transistorlarıyla oluşturulmuştur. PMOS transistor kullanımı, • ikinci kat kutuplamasını ayarlayabilmek amacıyla, giriş transistor boyutunun mümkün olduğunca azaltılmasını, • ana AC işaret yolundaki transistor sayısının azaltılmasını, sağlamaktadır. Tezde sunulan teorik analiz ve serim sonrası benzetim sonuçları, MRC katı kullanımının AI özelliklerine yaptığı etkiyi göstermektedir. Elde edilen sonuçlar bu katların AI tasarımında yüksek QF elde edilmesini imkan tanıdığını ortaya koynaktadır. Literatürde, iki ana AI başarım karakteristiği olan SRF ve QF başarımlarının iyileştirmesi için çok sayıda çalışma bulunmaktadır. Bu tezde, birbirlerini etkilemeksizin SRF ve QF başarımlarının ayarlanabilmesi özelliğine sahip bir AI’ın tasarımı ve benzetgimi yapılmıştır. Kaskod ve RC geribesleme yapıları yeni AI tasarımında kullanılmıştır. Daha önce de tartışıldığı üzere, AI karakterizasyonu açısından giriş transistoru çok önemlidir. Girişi transistorunun kaskodlanması, ilk jiratörün geçiş-iletkenliğinin ve giriş parazitik kapasitansının birbirinden bağımsız olarak ayarlanması gibi önemli ve kullanışlı bir özelliği beraberinde getirir. Bunun yanısıra, endüktansın değeri diğer transistorun iletkenliği ile ayarlanabilir. AI parazitik seri-rezistansını yok etmek amacıyla kullanılan RC geribeslemesi, QF iyileştirmesini sağlayabilmektedir. Kaskod transistorların kutuplama koşulu bir diyot-bağlı transistor ile sağlandığından; önerilen yapı proses, gerilim ve sıcaklık değişimleri açısından kararlı ve yüksek başarımlıdır. AI yapılarında karşılaşılan düşük gürültü başarımı, AI’ların LNA gibi RF uygulamalarda kullanımını sınırlamaktadır. Bir AI’ın ana gürültü kaynağı giriş transistorudur. Düşük gürültülü AI elde etmek için, giriş transistoru yeterince büyük boyutlu olarak tasarlanmalıdır. Ne var ki, büyük boyutlu böyle bir transistor, düşük bir SRF ve dolayısıyla sınırlı bir endüktif bandı beraberinde getirir. Bu tezde, düşük gürültülü ve az kayıplı uygun bir AI, düşük gürültü gerektiren RF uygulamaları için sunulmuştur. Teklif edilen AI devresindeki tüm transistorların ortak-kaynak (common-source, CS) yapısında kullanılması, düşük iletkenliğe sahip düğümlerin dolayısıyla yüksek QF değerine sahip bir AI’ın elde edilmesine olanak sağlamaktadır. AI gürültüsünü azaltmak için, sırasıyla P-tipi MOS transistorlar ve ileri-besleme yolu yapısı (feed-forward path, FFP) kullanılmaktadır. Bilindiği gibi, sensörler çok çeşitli fiziksel büyüklüklerin eletrik mühendisiliği alanına taşınmasını sağlamaktadır. Çok geniş kullanım alanı bulan sensör tiplerinden biri kapasitif mikro algılıyıcılardır. Kapasitif mikro algılayıcılar mekanik hareketleri küçük kapasitans değişimlerine çevirirler. Micro algılayıcıdaki kapasitans değişimi femto-Farad mertebesinde olup algılamayı zorlaştırmaktadır. Diğer yandan, küçük bir kapasitans değişimini yüksek bir empedans değişimine çevirebilmeleri dolayısıyla, GC topolojilerinin kapasitif algılayıcılarda kullanılabileceğini söylemek mümkündür. Bu tezde, bu düşünceden yola çıkılarak, kesit duyarlılığını yok etme yeteneğine sahip yeni bir 3-eksen ivme-ölçer tasarlanmıştır. Yapının, her eksendeki ivmeyi bağımsız olarak algılayabilmesi için, algılayıcı elektrodları uygun olarak yerleştirilmiştir. Daha sonra, bir kapasitif algılayıcıdaki çok küçük kapasitans değişimlerini algılayabilmek için yeni bir GC yapısı teklif edilmiştir. Önerilen yapıda, çalışma frekansı aralığı ve ölçekleme çarpanı, kutuplama akımlarının ayarlanması suretiyle birbirini etkilemeksizin ayarlanabilmektedir. Ayrıca, önerilen yapıda, parazitik bileşenlerin etkisini yok etmek için RC geribesleme ve kaskod yapılar kullanılmaktadır. Son olarak, bu tezde sunulan AI’ların çok amaçlı özellikte olduğunu göstermek amacıyla, 3 ve 6. dereceden geniş bantlı mikrodalga filtrelerde kullanılmaları ele alınmıştır. İlki 3. dereceden bir Chebyshev alçak geçiren filtredir. Basitleştirilmiş gerçel frekans tekniği (SRFT, simplified real frequency technique) ile tasarlanan ikincisi ise, 6. dereceden bir Chebyshev band geçiren filtredir. Filtrelerin benzetimle elde edilmiş frekans yanıtları, bu tezde sunulan AI’ların literatürdeki yapılara güçlü birer alternatif olduklarını ortaya koymaktadır.There is critical need for inductive characteristics in RF applications, especially in filters, LNA, VCO, bandwidth-enhancement in many kinds of amplifiers, phase shifters, power divider and matching networks. The drawbacks of using passive and spiral inductors in CMOS process are discussed in the literature. It is shown that these kind of inductors suffer from a low quality factor, a low self-resonant frequency, a low and fixed inductance value and the need for a large silicon area. Furthermore, it is shown in the literature that CMOS Active Inductors (AIs), which are synthesized using MOS transistors, offer a number of attractive characteristics as compared with their spiral counterparts. These characteristics include a low silicon consumption, a large and tunable self-resonant frequency, a large and tunable inductance, a large and tunable quality factor, and fully realizable in digital CMOS technologies. Then principles, topologies, characterizations and implementation of the Gyrator-C (GC) network is discussed in-depth. The GC networks, which are implemented by operational transconductance amplifier, are suitable for RF application. This property arises from their minimum usage of active elements. It is shown that both grounded and floating active inductors can be implemented by GC networks. To provide a quantitative measure of the performance of AIs, a number of figure-of-merits have been introduced in the thesis. These figure-of-merits include frequency range, inductance tunability, quality factor, noise and power consumption. Due to parasitic components of CMOS transistors, designed AIs have inductive behavior in a specified frequency range. The low frequency bound is set by the frequency of the zero of the gyrator-C networks while the upper frequency bound is set by Self-Resonance Frequency (SRF). One of the key advantages of active inductors over their spiral counterparts is the large tunability of their inductance. The inductance of GC AIs can be tuned by varying either the transconductances of the transconductors or the load capacitance, which is implemented by MOS varactor. Based on GC topology, there are many reported CMOS AI circuits in literature. All of them have tried to invent high performance AI by using different techniques. Some of recent proposed Grounded AI (GAI) and Floating AI (FAI) circuits are reviewed in the thesis. Some of them use negative resistor to compensate the loss of AI for QF enhancement. Some others try to use minimum number of transistors in order to increase the self-resonance frequency of AI for RF applications. In some applications, AIs are used in LNA circuits for gain boosting purpose. In that applications, designers have tried to cancel the noise of AI by using a feedback stage with a degeneration resistor to reduce the noise contribution to the input. The main aim of all the techniques is to cancel or reduce the effects of parasitic components. In the thesis, four new grounded and floating AIs are designed by using advanced circuit techniques. The first one, Multi Regulated Cascode (MRC) stages are employed for lowering conductance in input and output nodes of AI. Thus, Q performance is improved. Since these stages are used only for increasing impedance of input/output nodes, they are made up of PMOS transistors in order to: • minimize the input transistor as small as possible in order to adjust second stage biasing, • decrease the number of transistors in main path of AC signal Theoretical analysis and post-layout simulation results shows the effectiveness of using MRC stages usage in properties of AI. High Q symmetric floating version of low loss inductor is also designed by utilizing MRC stages. Designers do their best to improve SRF and QF, two main characteristics in term of AI performance. An AI with ability to adjust its SRF and QF without affecting each other is designed and simulated as a third. The cascoding and RC feedback structures are used in the new design of AI. As it discussed before, input transistor is very important regarding to AI characterizations. Cascoding input transistor gives the ability to adjust the first gyrator’s transconductance and input parasitic capacitance independently which it results in adjusting the self-resonance frequency and quality factor separately. Due to our best knowledge from literature reviewing, it is first time that the properties of an inductor can be adjusted independently. Furthermore, the inductance value can be adjusted by other transistor’s transconductances. Also, the RC feedback is utilized to cancel the parasitic series-resistance of AI which results in QF enhancement. Since, bias condition of cascoding transistors is provided by a diode-connected transistor, the proposed structure is robust in terms of performance over variation in process, voltage and temperature. The Noise of designed AIs has limited the use of them in RF applications such as LNAs. The main noise source of an AI is its input transistor. In order to have low noise AI, the input transistor should be designed large enough. But it leads to low SRF which limited the inductive frequency band. As a fourth active inductor design, a low-noise and low-loss AI is presented suitable for RF low noise applications. Utilizing all transistors in Common Sourse (CS) configuration on the AI circuit leads to low conductance nodes which causes the AI to have high Q. P-type MOS transistors and Feed-Forward Path (FFP) are employed to decrease noise of the AI, respectively. The GC topologies can convert a low capacitance variation to high impedance changing which makes it a good choice for capacitive sensors. The capacitive based micro sensors convert mechanical signals to small capacitance variation. The capacitance variation in micro sensor is in the range of femto-Farads which makes it difficult to sense. Thus, the GC topologies can be used in capacitive sensors in order to sense small capacitive variations. In the thesis, this technique is used in a new accelerometer sensor. It is first time that a gyrator-C network is employed as an interface circuit for capacitive change detection in micro sensors. The new accelerometer structure is designed by using with ability to cancel cross section sensitivity. The sensor’s electrodes are located in such a way that enables the structure to detect acceleration in 3-axis independently. Embedding all 3-axis detecting electrodes in a single proof mass and ability to detect acceleration orientation are salient features of the proposed sensor. Consequently, a new GC configuration for sensing very small capacitance changes in a capacitive sensor is presented in the thesis. In the proposed configuration, the operating frequency range and scaling factor can be adjusted without affecting each other by tuning the bias currents of utilized gyrators. In addition, the proposed configuration employs RC feedback together with the cascoding technique to cancel the effect of the parasitic components in order to get accurate scaling from gyrator-C network. Finally, in order to show versatility of designed AIs, they are used in designed third and sixth order broadband microwave filters. The first one is a third order Chebyshev low pass filter. The second one, which is designed by using simplified real frequency technique is a sixth order Chebyshev band pass filter. The simulated frequency response of filters prove the workability of the designed AIs.DoktoraPh

Ultra-Wideband CMOS Transceiver Front-End for Bio-Medical Radar Sensing

Since the Federal Communication Commission released the unlicensed 3.1-10.6 GHz frequency band for commercial use in early 2002, the ultra wideband (UWB) has developed from an emerging technology into a mainstream research area. The UWB technology, which utilizes wide spectrum, opens a new era of possibility for practical applications in radar sensing, one of which is the human vital sign monitoring. The aim of this thesis is to study and research the possibility of a new generation humanrespiration monitoring sensor using UWB radar technology and to develop a new prototype of UWB radar sensor for system-on-chip solutions in CMOS technology. In this thesis, a lowpower Gaussian impulse UWB mono-static radar transceiver architecture is presented. The UWB Gaussian pulse transmitter and receiver are implemented and fabricated using 90nm CMOS technology. Since the energy of low order Gaussian pulse is mostly condensed at lower frequency, in order to transmit the pulse in a very efficient way, higher order Gaussian derivative pulses are desired as the baseband signal. This motivates the advancement of the design into UWB high-order pulse transmitter. Both the Gaussian impulse UWB transmitter and Gaussian higher-order impulse UWB transmitter take the low-power and high-speed advantage of digital circuit to generate different waveforms. The measurement results are analyzed and discussed. This thesis also presents a low-power UWB mono-static radar transceiver architecture exploiting the full benefit of UWB bandwidth in radar sensing applications. The transceiver includes a full UWB band transmitter, an UWB receiver front-end, and an on-chip diplexer. The non-coherent UWB transmitter generates pulse modulated baseband signals at different carrier frequencies within the designated 3-10 GHz band using a digitally controlled pulse generator. The test shows the proposed radar transceiver can detect the human respiration pattern within 50 cm distance. The applications of this UWB radar sensing solution in commercialized standard CMOS technology include constant breathing pattern monitoring for gated radiation therapy, realtime monitoring of patients, and any other breathing monitoring. The research paves the way to wireless technology integration with health care and bio-sensor network

Passive and active components development for broadband applications

Recently, GaN HEMTs have been proven to have numerous physical properties, resulting in transistors with greatly increased power densities when compared to the other well-established FET technologies. This advancement spurred research and product development towards power-band applications that require both high power and high efficiency over the wide band. Even though the use of multiple narrow band PAs covering the whole band has invariably led to better performance in terms of efficiency and noise, there is an associated increase in cost and in the insertion loss of the switches used to toggle between the different operating bands. The goal, now, of the new technology is to replace the multiple narrow band PAs with one broadband PA that has a comparable efficiency performance. In our study here, we have investigated a variety of wide band power amplifiers, including class AB PAs and their implementation in distributed and feedback PAs.Additionally, our investigation has included switching-mode PAs as they are well-known for achieving a relatively high efficiency. Besides having a higher efficiency, they are also less susceptible to parameter variations and could impose a lower thermal stress on the transistors than the conventional-mode PAs. With GaN HEMTs, we have demonstrated: a higher than 37 dBm output power and a more than 30% drain efficiency over 0.02 to 3 GHz for the distributed power amplifier; a higher than 30 dBm output power with more than a 22% drain efficiency over 0.1 to 5 GHz for the feedback amplifier; and at least a 43 dBm output power with a higher than 63% drain efficiency over 0.05 to 0.55 GHz for the class D PA. In many communication applications, however, achieving both high efficiency and linearity in the PA design is required. Therefore, in our research, we have evaluated several linearization and efficiency enhancement techniques.We selected the LInear amplification with Nonlinear Components (LINC) approach. Highly efficient combiner and novel efficiency enhancement techniques like the power recycling combiner and adaptive bias LINC schemes have been successfully developed and verified to achieve a combined high efficiency with a relatively high linearity

Multi-frequency microwave energy harvesting receivers: theory and applications

Mención Internacional en el título de doctorEmissions across the electromagnetic spectrum are not only used for communications, but they can also be used for powering electronic devices. This resource has been made more and more abundant in the last years thanks to the recent deployment of 4G and 5G, and the popularization of broadband wireless networks such as WiFi, including traditional services such as TV and radio broadcasting. In order to take advantage of the energy (currently wasted), rectennas (a rectifier integrated with an antenna) are used. This thesis has the objective of studying these rectifying elements, to reduce or eliminate the use of batteries that are employed in millions of low-power devices and sensor networks planned for deployment in the near future. To do this, a self-supply system in situ is required. This could be achieved with photovoltaics or piezoelectrics, but they require the presence of light or vibration. However, the electromagnetic energy produced by mobile communications, TV base stations and radar is noticeable inside a large coverage area, 24 hours a day. This includes difficult access areas where it is nearly impossible to provide appropriate maintenance to replace batteries. As explained through the thesis, energy harvesting applications have a severe limitation on the available levels of power density to scavenge, constraining the RF-DC power conversion effciencies. Therefore, the amount of DC power to feed a sensor is limited and some techniques must be applied to improve the performance. This thesis proposes an alternative for improving the RF-DC power conversion efficiency based on the multiple-tone scenario (the electromagnetic spectrum). Previous studies have been published about an empirical improvement in the power efficiency when working with high Peak to Average Power Ratio (PAPR) multiple-tone signals, compared to a CW signal with the same average power, although the theoretical proof was not accurate enough. A mathematical model that predicts the expected DC current of the diode when excited with multiple tones is proposed along the thesis, having good agreement with simulations and measurements, demonstrating the good performance of the theoretical model. With this mathematical approach, convergence problems in simulation software can be avoided. This document comprises six chapters and it is organized as follows: In the first chapter a brief introduction on the evolution of wireless power transfer is presented, including all the different approaches that compose it, emphasizing the far-filed non-directional powering or harvesting, which is the topic of this thesis. In addition, an analysis of the state of the art is presented with the most signifficant values of conversion effciency, as well as the main characteristics of various designs. In the second chapter, the performance of the diode is explored theoretically. For very low incident power densities (those present in the environment), the diode works in a non-linear region, where a power effciency improvement is obtained when using high PAPR multiple-tone signal instead of a single tone with the same average power. This fact has been empirically tested but an accurate theoretical model has not been accomplished. Therefore, this chapter deals with this issue, showing a novel mathematical analysis of the diode operation in that region for multiple input tones, varying their relative amplitude and frequency. In Chapter 3, the theoretical analysis is compared with simulations and experiments for multiple input tones with a large resulting PAPR using three different rectifier circuits. To properly compare the results, it is necessary to use an accurate Spice diode model (including parasitics) and an appropriate measurement setup. Otherwise, results will differ due to an inadequate characterization of the non-linear device. This chapter addresses those issues. The analysis shows that the relative frequency and amplitude of multiple simultaneous signals impacts the amount of efficiency improvement. Once the recti er element is studied, Chapter 4 deals with the antenna design, which is part of the rectenna deployment. It is seen that different design criteria must be used when working with a WPT directive beaming application or a non-directive harvesting one, as happens in this thesis. The integration between the antenna and the recti er is analyzed, showing possible alternatives. Finally, a rectenna design is built and tested through indoor and outdoor measurements. An analysis of the electromagnetic spectrum is included to demonstrate the feasibility of the rectenna model. In Chapter 5 a wearable rectenna application is shown, with a broadband 2 to 5 GHz rectenna array, implemented on a cotton shirt. This application allows to collect enough energy to power energy-efficient devices. Different rectenna array sizes were tested at different power densities. The single element is a self-complementary tightly-coupled bow-tie. Simulations and measurements were performed over a phantom and over body tissues taking into account the electrical properties of the torso. The thickness of each layer was varied analyzing its influence in the antenna performance, to check what happens under different body compositions (people with more adipose tissue or on the contrary more brous). Finally, Chapter 6 collects the conclusions of the work shown in this thesis and ideas for future work. Some ideas are proposed about Chapter 2 to reduce the error of the mathematical approach when working in the non-linear region. Also, some possible improvements to the printed antenna of Chapter 5 are included such as adding a dual linear polarization.Las emisiones a lo largo de todo el espectro electromagnético no sólo se pueden utilizar para las comunicaciones, sino que también pueden emplearse para la alimentación de dispositivos electr onicos. Este recurso se ha hecho cada vez más abundante en los ultimos años gracias a los recientes despliegues en telefonía móvil de 4G y 5G y a la popularización de las redes inalámbricas de banda ancha (WiFi), sin olvidar las comunicaciones de difusión ya existentes como la radio o televisión. Para poder aprovechar este recurso (actualmente desaprovechado), se utilizan las llamadas rectenas, que son antenas con un elemento rectificador integrado. Esta tesis tiene por objetivo el estudio de estos elementos rectificadores, para desarrollar aplicaciones capaces de reducir o eliminar el uso de baterías en los millones de dispositivos y redes de sensores de bajo consumo existentes hoy día, mediante el autoabastecimiento de energía. Este proceso podría llevarse a cabo con paneles fotovoltaicos o sistemas piezoeléctricos, pero estos requieren de la presencia continua de la fuente que los origina (vibraciones, horas de sol). Sin embargo, la energía electromagnética producida por las estaciones base, de telefonía o televisión, está presente bajo su zona de cobertura las 24 horas del día, lo cual incluye zonas de difícil acceso, en las que es complicado el recambio o mantenimiento de las baterías. Además, estas emisiones tienen como principal limitación la baja densidad de potencia, obteniéndose valores de eficiencia de conversión RF-DC muy bajos. Esto conlleva que los valores de corriente DC para alimentar al sensor sean muy pequeños, de nA o uA, y por tanto, deben emplearse técnicas para la mejora del rendimiento. Esta tesis propone una alternativa para mejorar la eficiencia de conversión, basada en la probada mejora de eficiencia cuando se trabaja con señales con un Peak to Average Power Ratio (PAPR) grande. Esto se da en escenarios multitonales como puede ser el espectro electromagnético. Esta mejora no ha sido abordada teóricamente con resultados precisos en trabajos previos, por lo que en esta tesis se desarrolla un modelo matemático que predice la componente DC de la corriente del diodo, cuando se excita con múltiples tonos. Los resultados obtenidos han sido validados en el laboratorio, demostrándose la mejora en la eficiencia de conversión y el buen comportamiento del modelo teórico. De esta forma, se pueden agilizar los cálculos cuando no se tiene un software de simulación disponible, o cuando este arroja problemas de convergencia. Esta tesis consta de seis capítulos y está organizada de la siguiente manera: En el primer capítulo se expone una breve introducción sobre la evolución de la transferencia inalámbrica de potencia y sobre las diferentes tecnologías que la componen, haciéndose hincapié en la transferencia de potencia no directiva en campo lejano, puesto que se corresponde a la recolección de la energía electromagnética ambiental. Además, se incluye un análisis del estado del arte con los valores más significativos de eficiencia de conversión, así como las principales características de varios diseños (como por ejemplo la potencia o las bandas de trabajo empleadas). En el segundo capítulo se explora el comportamiento del diodo desde el punto de vista matemático. Bajo densidades de potencia pequeñas, como las presentes en este entorno, el diodo opera en su región no lineal, produciendo un incremento de eficiencia cuando se trabaja con señales con gran PAPR, respecto a un tono con la misma potencia media. Este hecho ha sido probado empíricamente pero ningún modelo teórico preciso ha sido realizado. En este capítulo se incluye un novedoso análisis matemático del funcionamiento del diodo en esa región para múltiples tonos de entrada, variando la amplitud y frecuencia de estos. En el capítulo 3 se muestra la comparativa entre el modelo teórico, las simulaciones y las medidas en el laboratorio, usando múltiples tonos entrada en tres rectificadores. Para comparar adecuadamente todos los resultados, es necesario utilizar un modelo Spice del diodo preciso (incluyendo los parásitos del encapsulado) y un correcto setup de medida. De lo contrario, existiría un error en los resultados debido a una caracterización inadecuada del dispositivo no lineal. Este capítulo aborda esos problemas. El análisis muestra que la frecuencia y amplitud relativa de múltiples señales simultáneas afectan a la eficiencia. Una vez estudiado el rectificador, el capítulo 4 de la tesis aborda el diseño de la antena. Para ello, se analizan los diferentes criterios de diseño que deben emplearse cuando se trabaja con una transmisión de potencia inalámbrica directiva o no directiva, como es en caso bajo estudio, así como las técnicas de integración entre rectificador y antena. Para concluir, se diseña y mide una rectena tanto en laboratorio como en espacio abierto, usando la energía ambiental, previamente caracterizada con medidas espectrales. Los resultados demuestran que es posible recolectar y rectificar la energía ambiental. En el capítulo 5 se muestra una posible aplicación al integrarse una rectena impresa en una camiseta para alimentar sensores biológicos o \wearable". Se trata de un diseño de banda ancha que opera en el rango de 2 a 5 GHz, que permite recolectar suficiente energía para alimentar sensores de bajo consumo. Se analiza el funcionamiento de dos tamaños distintos de arrays con diferentes densidades de potencia. Al ser un diseño \wearable", la aplicación ha sido diseñada y probada sobre un maniquí y un cuerpo humano, analizándose el comportamiento de la antena impresa sobre distintas composiciones corporales (personas con más tejido adiposo o por el contrario más fibrosas). Finalmente, el capítulo 6 recopila las conclusiones del trabajo que se muestra en esta tesis e ideas para trabajos futuros, proponiéndose desde enfoques para reducir más el error en la aproximación del comportamiento no lineal del diodo en el capítulo 2, a posibles mejoras en la antena impresa del capítulo 5, incluyendo la doble polarización lineal.Programa de Doctorado en Multimedia y Comunicaciones por la Universidad Carlos III de Madrid y la Universidad Rey Juan CarlosPresidente: Carlos Martín Pascual.- Secretario: Simon Jacques Hemour.- Vocal: Nuno Miguel G. Borges De Carvalh

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

Circuit-Theoretic Physics-Based Antenna Synthesis and Design Techniques for Next-Generation Wireless Devices

Performance levels expected from future-generation wireless networks and sensor systems are beyond the capabilities of current radio technologies. To realize information capacities much higher than those achievable through existing time and/or frequency coding techniques, an antenna system must exploit the spatial characteristics of the medium in an intelligent and adaptive manner. This means that such system needs to incorporate integrated multi-element antennas with controlled and adjustable performances. The antenna configuration should also be highly miniaturized and integrated with circuits around it in order to meet the rigorous requirements of size, weight, and cost. A solid understanding of the underlying physics of the antenna function is, and has always been, the key to a successful design. In a typical antenna design process, the designer starts with a simple conceptual model, based on a given volume/space to be occupied by the antenna. The design cycle is completed by the antenna performing its function over a range of frequencies in some complex scenarios, i.e., packaged into a compact device, handled in different operational environments, and possibly implanted inside a human/animal body. From the conceptual model to the actual working device, a large variety of design approaches and steps exist. These approaches may be viewed as simulation-driven steps, experimental-based ones, or a hybrid of both. In any of these approaches, a typical design involves a large amount of parametric/optimization steps. It is no wonder, then, that due to the many uncertainties and ‘unknowns’ in the antenna problem, a final working design is usually an evolved version of an initial implementation that comes to fruition only after a considerable amount of effort and time spent on “unsuccessful” prototypes. In general, the circuit/filter community has enjoyed a better design experience than that of the antenna community. Designing a filter network to meet specific bandwidth and insertion loss is a fairly well-defined procedure, from the conceptual stages to the actual realization. In view of the aforementioned, this work focuses on attempting to unveil some of the uncertainties associated with the general antenna design problem through adapting key features from the circuit/filter theory. Some of the adapted features include a group delay method for the design of antennas with a pre-defined impedance bandwidth, inverter-based modeling for the synthesis of small-sized wideband antennas, and an Eigen-based technique to realize multi-band/multi-feed antennas, tunable antennas, and high sensitivity sensor antennas. By utilizing the proposed approaches in the context of this research, the design cycle for practical antennas should be significantly simplified along with various physical limitations clarified, all of which translates to reduced time, effort, and cost in product development.4 month

Optimization of 5G Second Phase Heterogeneous Radio Access Networks with Small Cells

Due to the exponential increase in high data-demanding applications and their services per coverage area, it is becoming challenging for the existing cellular network to handle the massive sum of users with their demands. It is conceded to network operators that the current wireless network may not be capable to shelter future traffic demands. To overcome the challenges the operators are taking interest in efficiently deploying the heterogeneous network. Currently, 5G is in the commercialization phase. Network evolution with addition of small cells will develop the existing wireless network with its enriched capabilities and innovative features. Presently, the 5G global standardization has introduced the 5G New Radio (NR) under the 3rd Generation Partnership Project (3GPP). It can support a wide range of frequency bands (<6 GHz to 100 GHz). For different trends and verticals, 5G NR encounters, functional splitting and its cost evaluation are well-thought-out. The aspects of network slicing to the assessment of the business opportunities and allied standardization endeavours are illustrated. The study explores the carrier aggregation (Pico cellular) technique for 4G to bring high spectral efficiency with the support of small cell massification while benefiting from statistical multiplexing gain. One has been able to obtain values for the goodput considering CA in LTE-Sim (4G), of 40 Mbps for a cell radius of 500 m and of 29 Mbps for a cell radius of 50 m, which is 3 times higher than without CA scenario (2.6 GHz plus 3.5 GHz frequency bands). Heterogeneous networks have been under investigation for many years. Heterogeneous network can improve users service quality and resource utilization compared to homogeneous networks. Quality of service can be enhanced by putting the small cells (Femtocells or Picocells) inside the Microcells or Macrocells coverage area. Deploying indoor Femtocells for 5G inside the Macro cellular network can reduce the network cost. Some service providers have started their solutions for indoor users but there are still many challenges to be addressed. The 5G air-simulator is updated to deploy indoor Femto-cell with proposed assumptions with uniform distribution. For all the possible combinations of apartments side length and transmitter power, the maximum number of supported numbers surpassed the number of users by more than two times compared to papers mentioned in the literature. Within outdoor environments, this study also proposed small cells optimization by putting the Pico cells within a Macro cell to obtain low latency and high data rate with the statistical multiplexing gain of the associated users. Results are presented 5G NR functional split six and split seven, for three frequency bands (2.6 GHz, 3.5GHz and 5.62 GHz). Based on the analysis for shorter radius values, the best is to select the 2.6 GHz to achieve lower PLR and to support a higher number of users, with better goodput, and higher profit (for cell radius u to 400 m). In 4G, with CA, from the analysis of the economic trade-off with Picocell, the Enhanced multi-band scheduler EMBS provide higher revenue, compared to those without CA. It is clearly shown that the profit of CA is more than 4 times than in the without CA scenario. This means that the slight increase in the cost of CA gives back more than 4-time profit relatively to the ”without” CA scenario.Devido ao aumento exponencial de aplicações/serviços de elevado débito por unidade de área, torna-se bastante exigente, para a rede celular existente, lidar com a enormes quantidades de utilizadores e seus requisitos. É reconhecido que as redes móveis e sem fios atuais podem não conseguir suportar a procura de tráfego junto dos operadores. Para responder a estes desafios, os operadores estão-se a interessar pelo desenvolvimento de redes heterogéneas eficientes. Atualmente, a 5G está na fase de comercialização. A evolução destas redes concretizar-se-á com a introdução de pequenas células com aptidões melhoradas e características inovadoras. No presente, os organismos de normalização da 5G globais introduziram os Novos Rádios (NR) 5G no contexto do 3rd Generation Partnership Project (3GPP). A 5G pode suportar uma gama alargada de bandas de frequência (<6 a 100 GHz). Abordam-se as divisões funcionais e avaliam-se os seus custos para as diferentes tendências e verticais dos NR 5G. Ilustram-se desde os aspetos de particionamento funcional da rede à avaliação das oportunidades de negócio, aliadas aos esforços de normalização. Exploram-se as técnicas de agregação de espetro (do inglês, CA) para pico células, em 4G, a disponibilização de eficiência espetral, com o suporte da massificação de pequenas células, e o ganho de multiplexagem estatística associado. Obtiveram-se valores do débito binário útil, considerando CA no LTE-Sim (4G), de 40 e 29 Mb/s para células de raios 500 e 50 m, respetivamente, três vezes superiores em relação ao caso sem CA (bandas de 2.6 mais 3.5 GHz). Nas redes heterogéneas, alvo de investigação há vários anos, a qualidade de serviço e a utilização de recursos podem ser melhoradas colocando pequenas células (femto- ou pico-células) dentro da área de cobertura de micro- ou macro-células). O desenvolvimento de pequenas células 5G dentro da rede com macro-células pode reduzir os custos da rede. Alguns prestadores de serviços iniciaram as suas soluções para ambientes de interior, mas ainda existem muitos desafios a ser ultrapassados. Atualizou-se o 5G air simulator para representar a implantação de femto-células de interior com os pressupostos propostos e distribuição espacial uniforme. Para todas as combinações possíveis do comprimento lado do apartamento, o número máximo de utilizadores suportado ultrapassou o número de utilizadores suportado (na literatura) em mais de duas vezes. Em ambientes de exterior, propuseram-se pico-células no interior de macro-células, de forma a obter atraso extremo-a-extremo reduzido e taxa de transmissão dados elevada, resultante do ganho de multiplexagem estatística associado. Apresentam-se resultados para as divisões funcionais seis e sete dos NR 5G, para 2.6 GHz, 3.5GHz e 5.62 GHz. Para raios das células curtos, a melhor solução será selecionar a banda dos 2.6 GHz para alcançar PLR (do inglês, PLR) reduzido e suportar um maior número de utilizadores, com débito binário útil e lucro mais elevados (para raios das células até 400 m). Em 4G, com CA, da análise do equilíbrio custos-proveitos com pico-células, o escalonamento multi-banda EMBS (do inglês, Enhanced Multi-band Scheduler) disponibiliza proveitos superiores em comparação com o caso sem CA. Mostra-se claramente que lucro com CA é mais de quatro vezes superior do que no cenário sem CA, o que significa que um aumento ligeiro no custo com CA resulta num aumento de 4-vezes no lucro relativamente ao cenário sem CA

Miniaturization and evaluation methods of mobile terminal antenna structures

In recent years, the trend in the mobile communications market has been towards thinner and mechanically more complex terminal devices, which are able to operate in several wireless systems. Due to this development, miniaturization and performance enhancement of internal mobile terminal antennas have become major challenges for the industry of the field. Not only should an internal antenna be small in size and broadband, it must also be able to ensure reliable power transmission in a real multipath propagation environment. A well-known way to improve the reliability of a radio connection is to use multi-antenna reception in the mobile terminal. In multiple-input multiple-output (MIMO) systems, multiple antennas are additionally used at the base station. In both cases, fast and reliable methods are needed for the performance evaluation of multi-antenna terminals. In the first part of this thesis, the main benefits, drawbacks and applications of coupling element based mobile terminal antenna structures are studied, with special emphasis on antenna miniaturization. Optimum shaping and placement of capacitive coupling elements are first studied in this work. Next, it is demonstrated by simulations and measurements that the bandwidth-to-volume ratio of a mobile terminal antenna structure can be improved significantly by using optimized coupling elements instead of traditional self-resonant antenna elements. To facilitate the implementation of coupling element based multi-resonant antenna structures, a theoretical study on the dual-resonant impedance matching of non-resonant coupling elements is also presented. The feasibility of coupling elements for multi-band terminals is demonstrated with a novel quad-band GSM antenna, which consumes a total volume of only 0.7 cm3. Finally, a novel frequency tunable matching circuitry designed for non-resonant coupling elements is introduced. In this work, also the bandwidth, efficiency in talk position, and SAR (specific absorption rate) of mobile phone antennas are studied as a function of frequency over wide frequency band (0.6 GHz - 6 GHz) by applying the idea of coupling elements. The results show that below 3 GHz the three parameters are strongly affected by the resonant wavemodes of the chassis, whereas above 3 GHz, the wavemodes of the coupling element dominate. In addition to the above, the resonant wavemodes of the chassis of a clamshell phone are investigated in this work by using coupling elements. The results bring out several challenges, such as a non-radiating resonance, that an antenna designer may face with clamshell phones. The second part of this thesis concentrates on the performance evaluation of mobile terminal multi-antenna configurations. First, the accuracy of a novel measurement based antenna test bed (MEBAT) is thoroughly studied. After this, the performance of several mobile terminal multi-antenna configurations is systematically investigated using the MEBAT. The emphasis is kept on the power reception properties (effective array gain or EAG) of the multi-antenna configurations. An accurate and fast theoretical way of predicting the median EAG of an antenna configuration is proposed in the work. Based on a comprehensive analysis of the theoretical and empirical EAG results, guidelines for optimum radiation pattern characteristics of a multi-antenna configuration are given. Based on the eigenvalue dispersion and capacity results obtained in the studied MIMO environments, it is concluded that it may be difficult to affect the spatial multiplexing properties of a MIMO system by means of handset antenna design. The presented results indicate that a handset antenna designer should mainly focus on maximizing the EAG.Viime vuosina yleinen kehityssuunta matkaviestinmarkkinoilla on ollut kohti ohuempia ja mekaanisesti monimutkaisempia päätelaitteita, jotka kykenevät toimimaan useissa langattomissa järjestelmissä. Tämän kehityksen johdosta matkapuhelinten sisäisten antennien koon pienentäminen ja suorituskyvyn parantaminen ovat muodostuneet merkittäviksi haasteiksi alan teollisuudelle. Sen lisäksi, että sisäisen antennin tulee olla pienikokoinen ja laajakaistainen, tulee sen myös kyetä takaamaan luotettava tehonsiirto todellisessa monitie-etenemisympäristössä. Hyvin tunnettu tapa radioyhteyden luotettavuuden parantamiseksi on hyödyntää moniantennivastaanottoa matkapuhelimessa. Multiple-input multiple-output (MIMO)-järjestelmissä useita antenneja hyödynnetään lisäksi tukiasemassa. Kummassakin tapauksessa tarvitaan nopeita ja luotettavia menetelmiä matkapuhelinten moniantennirakenteiden suorituskyvyn arvioimiseksi. Työn ensimmäisessä osassa tutkitaan kytkentäelementteihin perustuvien antennirakenteiden tärkeimpiä hyötyjä, haittoja ja sovelluksia painottaen antennien koon pienentämistä. Työssä tutkitaan ensin kapasitiivisten kytkentäelementtien optimaalista muotoilua ja sijoittamista. Seuraavaksi osoitetaan simulaatioin ja mittauksin, että matkapuhelimen antennirakenteen kaistanleveys-tilavuus-suhdetta saadaan parannettua huomattavasti käyttämällä optimoituja kytkentäelementtejä perinteisten resonanssityyppisten antennielementtien sijaan. Kytkentäelementteihin perustuvien moniresonanssi antennirakenteiden toteuttamisen helpottamiseksi työssä esitetään myös teoreettinen tutkimus ei-resonoivien kytkentäelementtien sovittamisesta kaksoisresonanssiin. Kytkentäelementtien soveltuvuutta monitaajuuspäätelaitteisiin havainnollistetaan uudentyyppisellä nelitaajuus-GSM-antennilla, jonka kokonaistilavuus on ainoastaan 0.7 cm3. Lopuksi esitellään uudentyyppinen kytkentäelementeille suunniteltu taajuussäädettävä sovituspiiri. Tässä työssä tutkitaan myös matkapuhelinantennien kaistanleveyttä, hyötysuhdetta puheasennossa ja SAR- (specific absorption rate) arvoja taajuuden funktiona laajalla taajuuskaistalla (0.6 GHz - 6 GHz) hyödyntäen kytkentäelementtejä. Tulokset osoittavat, että 3 GHz:n alapuolella näihin kolmeen parametriin vaikuttavat vahvasti rungon resonoivat aaltomuodot, kun taas 3 GHz:n yläpuolella kytkentäelementin aaltomuodot dominoivat. Yllä olevan lisäksi työssä tutkitaan taitettavan puhelimen rungon resonoivia aaltomuotoja kytkentäelementtien avulla. Tulokset tuovat esille useita haasteita, kuten säteilemättömän resonanssin, joita antennisuunnittelija saattaa kohdata taitettavien puhelinten kanssa. Työn toinen osa keskittyy matkapuhelinten moniantennirakenteiden suorituskyvyn arviointiin. Ensin uudentyyppisen mittauksiin perustuvan antennien testialustan (MEBAT) tarkkuutta arvioidaan perusteellisesti. Tämän jälkeen useiden matkapuhelinten moniantennirakenteiden suorituskykyä tutkitaan järjestelmällisesti MEBATin avulla. Painotus on moniantennirakenteiden tehovastaanotto-ominaisuuksissa (effective array gain tai EAG). Työssä ehdotetaan tarkkaa ja nopeaa teoreettista tapaa antennirakenteen EAG:n mediaanin ennustamiseksi. Teoreettisten ja empiiristen EAG-tulosten perusteellisen analyysin pohjalta annetaan suosituksia moniantennijärjestelmän säteilykuvion optimaalisille ominaisuuksille. Tutkituissa MIMO-järjestelmissä saatujen ominaisarvohaje- ja kapasiteettitulosten perusteella tehdään johtopäätös, että matkapuhelimen antennisuunnittelun keinoin voi olla vaikeaa vaikuttaa MIMO-järjestelmän kykyyn muodostaa rinnakkaisia kanavia. Esitetyt tulokset ehdottavat, että matkapuhelimen antennisuunnittelijan tulisi pääasiassa keskittyä EAG:n maksimointiin.reviewe