[show abstract][hide abstract] ABSTRACT: Graphene, owing to its ability to support plasmon polariton waves in the
terahertz frequency range, enables the miniaturization of antennas to allow
wireless communications among nanosystems. One of the main challenges in the
demonstration of graphene antennas is finding suitable terahertz sources to
feed the antenna. This paper estimates the performance of a graphene RF
plasmonic micro-antenna fed with a photoconductive source. The terahertz source
is modeled and, by means of a full-wave EM solver, the radiated power of the
device is estimated with respect to material, laser illumination and antenna
geometry parameters. The results show that the proposed device radiates
terahertz pulses with an average power up to 1$\mu$W, proving the feasibility
of feeding miniaturized graphene antennas with photoconductive materials.
[show abstract][hide abstract] ABSTRACT: This paper presents a current-steering approach to implement a fast transient response low-dropout regulator (LDO) based on a current feedback amplifier (CFA) topology. The circuit does not require any internal compensation capacitor, being stable for a wide range of output load currents [0–100 mA] and a 1 μF output capacitor. The CFA consists of an open-loop voltage follower with output local current–current feedback based on a level-shifted flipped voltage follower (LSFVF) which is instrumental to achieve high regulation and fast transient response. The inverting output buffer stage of the CFA together with current-mirror-based driving of the power pass transistor results in high PSRR. Post-layout simulation results for a 0.35 μm CMOS process design reveal that the proposed LDO requires 59 μA quiescent current at no-load condition and at full-load condition has a current efficiency of 99.8%. For a 1 μF output capacitor, the maximum output voltage variation to a 0–100 mA load transient with rise and fall times of 10 and 100 ns is only 3 mV, and the PSRR is smaller than −56 dB over the entire load current range.
Integration the VLSI Journal 03/2013; 46(2):165–171. · 0.41 Impact Factor
[show abstract][hide abstract] ABSTRACT: This paper surveys and discusses the state-of-the-art of integrated switched-capacitor and inductive power converters. After introducing applications that drive the need for integrated switching power converters, implementation issues to be addressed for integrated switched-capacitor and inductive converters are given, as well as design examples. At the end of this paper, a comprehensive set of integrated power converters are compared in terms of the main specifications and performance metrics, thereby allowing a categorization and providing application-oriented design guidelines.
IEEE Transactions on Power Electronics 01/2013; 28(9):4156-4167. · 4.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: A number of techniques have been recently proposed to implement molecular communication, a novel method which aims to implement communication networks at the nanoscale, known as nanonetworks. A common characteristic of these techniques is that their main resource consists of molecules, which are inherently discrete. This paper presents DIRECT, a novel networking model which differs from conventional models by the way of treating resources as discrete entities; therefore, it is particularly aimed to the analysis of molecular communication techniques. Resources can be involved in different tasks in a network, such as message encoding, they do not attenuate in physical terms and they are considered 100% reusable. The essential properties of DIRECT are explored and the key parameters are investigated throughout this paper.
Nano Communication Networks 01/2013; 4(4):181–188.
[show abstract][hide abstract] ABSTRACT: This paper presents a CMOS low quiescent current output-capacitorless low-dropout regulator (LDO) based on a high slew rate current mode transconductance amplifier (CTA) as error amplifier. Using local common-mode feedback (LCMFB) in the proposed CTA, the order of transfer characteristic of the circuit is increased. Therefore, the slew rate at the gate of pass transistor is enhanced. This improves the LDO load transient characteristic even at low quiescent current. The proposed LDO topology has been designed and post simulated in HSPICE in a 0.18 µm CMOS process to supply the load current between 0 and 100 mA. The dropout voltage of the LDO is set to 200 mV for 1.2–2 V input voltage. Post-layout simulation results reveal that the proposed LDO is stable without any internal compensation strategy and with on-chip output capacitor or lumped parasitic capacitances at the output node between 10 and 100 pF. The total quiescent current of the LDO including the current consumed by the reference buffer circuit is only 3.7 µA. A final benchmark comparison considering all relevant performance metrics is presented.
Integration the VLSI Journal 01/2013; · 0.41 Impact Factor
[show abstract][hide abstract] ABSTRACT: Diffusion-based molecular communication is a promising bio-inspired paradigm to implement nanonetworks, i.e., the interconnection of nanomachines. The peculiarities of the physical channel in diffusion-based molecular communication require the development of novel models, architectures and protocols for this new scenario, which need to be validated by simulation. N3Sim is a simulation framework for nanonetworks with transmitter, receiver, and harvester nodes using Diffusion-based Molecular Communication (DMC). In DMC, transmitters encode the information by releasing molecules into the medium, thus varying their local concentration. N3Sim models the movement of these molecules according to Brownian dynamics, and it also takes into account their inertia and the interactions among them. Harvesters collect molecules from the environment to reuse them for later transmissions. Receivers decode the information by sensing the particle concentration in their neighborhood. The benefits of N3Sim are multiple: the validation of channel models for DMC and the evaluation of novel modulation schemes are just a few examples.
Simulation Modelling Practice and Theory 01/2013; · 1.16 Impact Factor
[show abstract][hide abstract] ABSTRACT: The scattering of terahertz radiation on a graphene-based nano-patch antenna is numerically analyzed. The extinction cross section of the nano-antenna supported by silicon and silicon dioxide substrates of different thickness are calculated. Scattering resonances in the terahertz band are identified as Fabry–Perot resonances of surface plasmon polaritons supported by the graphene film. A strong tunability of the antenna resonances via electrostatic bias is numerically demonstrated, opening perspectives to design tunable graphene-based nano-antennas. These antennas are envisaged to enable wireless communications at the nanoscale.
Photonics and Nanostructures - Fundamentals and Applications 10/2012; 10(4):353–358. · 1.79 Impact Factor
[show abstract][hide abstract] ABSTRACT: This paper presents a design-oriented analytical approach for predicting fast-scale instability in power electronics converters under voltage-mode control strategy. This approach is based on the use of the ripple amplitude of the feedback control voltage as an index for predicting subharmonic oscillations in these systems. First, the work revisits the stability analysis technique based on the nonlinear discrete-time model, demonstrating that the ripple amplitude can be included within the expression of the Jacobian matrix of this model, hence giving a mathematical support to extend the ripple index to more complex topologies. A simple but representative buck converter under voltage-mode control is used to illustrate the approach. Using the ripple-based index, closed-form expressions of stability boundaries are derived. Unlike other available results obtained from existing methods, the stability boundary, in this work is expressed analytically in terms of both power stage and controller design parameters. Moreover, one can determine how these parameters are involved in the closed form expressions and, furthermore, how each parameter affects the stability of the system. The approach is validated by numerical simulations from the state equations and also experimentally within a wide range of the design parameter space.
Circuits and Systems I: Regular Papers, IEEE Transactions on 02/2012; · 2.24 Impact Factor
[show abstract][hide abstract] ABSTRACT: This paper explores the modulation bandwidth limits for switching amplifiers, by analyzing the fundamental tracking capabilities of two-level switching signals. With this aim, this work synthesizes two-level switching signals by obtaining the distribution of switching events providing both minimum average switching frequency and inband-error-free encoding, targeting to minimize the amplifier switching losses when tracking a generic bandlimited signal. This analysis also provides a framework reference to characterize the deviation from such limit in modulations used in actual amplifiers.
Circuits and Systems I: Regular Papers, IEEE Transactions on 11/2011; · 2.24 Impact Factor
[show abstract][hide abstract] ABSTRACT: Scattering of the terahertz radiation on a graphene-based nano-antenna
is considered. Different electromagnetic models of graphene are
discussed and applied to calculate extinction, scattering and absorption
cross sections of the nano-antenna. Scattering resonances in the
terahertz band are identified as longitudinal Fabry-Perot resonances of
surface plasmon polaritons supported by the graphene layer. A simple
while powerful model, based on the effective mode index of plasmon
polaritons, is proposed to predict the antenna resonant properties. A
systematic numerical study of the graphene-based nano-antenna is
presented for different antenna dimensions. Finally, the potential of
graphene-based nano-antennas for terahertz applications is discussed.
[show abstract][hide abstract] ABSTRACT: The type of transversal competences and skills to be acquired by EE students is in open debate. It is argued in this paper that beyond core technical skills and soft skills, the competences of Conceiving, Designing, Implementing and Operating Circuits and Systems are key for a comprehensive electrical engineering education. CAS- centric learning activities and methodologies oriented to expose the student to such skills are discussed. This description is carried out both at curriculum architecture level as well as at course level, in the framework of the CDIO approach, an engineering education methodology which considers design-oriented analysis techniques included in an integral project-based learning methodology.
Circuits and Systems (ISCAS), 2011 IEEE International Symposium on; 06/2011
[show abstract][hide abstract] ABSTRACT: Nanotechnology is enabling the development of devices in a scale ranging from one to a few hundred nanometers, known as nanomachines. How these nanomachines will communicate is still an open debate. Molecular communication is a promising paradigm that has been proposed to implement nanonetworks, i.e., the interconnection of nanomachines. Recent studies have attempted to model the physical channel of molecular communication, mainly from a communication or information-theoretical point of view. In this work, we focus on the diffusion-based molecular communication, whose physical channel is governed by Fick's laws of diffusion. We characterize the molecular channel following two complementary approaches: first, we obtain the channel impulse response, transfer function and group delay; second, we propose a pulse-based modulation scheme and we obtain analytical expressions for the most relevant performance evaluation metrics, which we also validate by simulation. Finally, we compare the scalability of these metrics with their equivalents in a wireless electromagnetic channel. We consider that these results provide interesting insights which may serve designers as a guide to implement future molecular nanonetworks.
[show abstract][hide abstract] ABSTRACT: Nanonetworks are the interconnection of nanomachines and as such expand the limited capabilities of a single nanomachine. Several techniques have been proposed so far to interconnect nanomachines. For short distances (nm-mm ranges), researchers are proposing to use molecular motors and calcium signaling. For long distances (mm-m), pheromones are envisioned to transport information. In this work we propose a new mechanism for medium-range communications (nm-μm): flagellated bacteria. This technique is based on the transport of DNA-encoded information between emitters and receivers by means of a bacterium. We present a physical channel characterization and a simulator that, based on the previous characterization, simulates the transmission of a DNA packet between two nanomachines.
[show abstract][hide abstract] ABSTRACT: Resumen— Dentro de los convertidores DC/DC híbridos, formados por un regulador lineal en paralelo con un convertidor conmutado, existen diferentes estrategias de control que permiten fijar la frecuencia de conmutación en función de alguna característica del regulador lineal. El presente artículo compara dos estrategias de control que, aunque pueden aplicarse a la misma estructura circuital de convertidor híbrido, son sensiblemente diferentes. La primera de ella, presentada en , considera como bloque principal al convertidor conmutado y, al regulador lineal, como módulo auxiliar. Por su parte, la propuesta realizada por los autores del presente artículo considera como conjunto principal al lineal y al conmutado como módulo auxiliar. Palabras Clave— Convertidores de potencia continua– continua, reguladores lineales, control de convertidores de potencia. I. INTRODUCCIÓN os convertidores DC/DC híbridos (conocidos también como linear–assisted) son estructuras circuitales que presentan un interés creciente a la hora de implementar sistemas de alimentación que requieran dos importantes especificaciones de diseño: elevado slew–rate de la corriente de salida y elevado consumo de corriente por parte de la carga. Este es el caso de los sistemas basados en los modernos microprocesadores y DSPs, donde convergen ambos requisitos , . Dichos convertidores híbridos intentan converger, en una misma estructura, las ventajas presentes en las dos alternativas típicas existentes para la realización de reguladores de tensión, minimizando a su vez los inconvenientes de éstas. Estas dos alternativas son sobradamente conocidas: la utilización de reguladores lineales serie de tensión, estructuras ampliamente utilizadas desde hace décadas , , y los convertidores conmutados DC/DC, gracias a los cuales pueden conseguirse sistemas de alimentación de elevado rendimiento –. Estas estructuras híbridas pueden ser implementadas sobre circuitos impresos utilizando componentes discretos. Sin embargo, son también una atractiva alternativa susceptibles de ser integradas en sistemas de alimentación on–chip.
[show abstract][hide abstract] ABSTRACT: Diffusion-based molecular communication is a promising bio-inspired paradigm to implement nanonetworks, i.e., the interconnection of nanomachines. The peculiarities of the physical channel in diffusion-based molecular communication require the development of novel models, architectures and protocols for this new scenario, which need to be validated by simulation. With this purpose, we present N3Sim, a simulation framework for diffusion-based molecular communication. N3Sim allows to simulate scenarios where transmitters encode the information by releasing molecules into the medium, thus varying their local concentration. N3Sim models the movement of these molecules according to Brownian dynamics, and it also takes into account their inertia and the interactions among them. Receivers decode the information by sensing the particle concentration in their neighborhood. The benefits of N3Sim are multiple: the validation of channel models for molecular communication and the evaluation of novel modulation schemes are just a few examples.
Proceedings of the Global Communications Conference, GLOBECOM 2011, 5-9 December 2011, Houston, Texas, USA; 01/2011
[show abstract][hide abstract] ABSTRACT: This work presents the first design and modelling of bonding-wire-based triangular spiral inductors (Fig. 1), targeting their application to on-chip switching power converters. It is demonstrated that the equilateral triangular shape compared to other polygonal shapes best balances the inductive density as well as the total Equivalent Series Resistance (ESR). Afterwards, a design procedure is presented in order to optimize the inductor design, in terms of ESR and occupied area reduction. Finally, finite-elements simulation results of an optimized design (27nH, 1) are presented to validate the proposed expressions. Index Terms—On-chip switching power converter, integrated inductor, bonding-wire. I. INTRODUCTION The traditional 3-dimensional conception of inductive structures has become the main handicap for their monolithic integration, since in standard CMOS ICs only planar designs are viable. However, their strong interest and usefulness in circuit design have pushed many researchers to work in their integration on silicon via different approaches. Roughly, these can be classified in two different research lines: those that use MEMS techniques and their implementation capabilities, and those that remain constrained by the possibilities of standard CMOS processes. Since the main inductor of a switching power converter is consid- ered as an energy-storing component, its main required characteristics are: • Low equivalent series resistance (ESR), to reduce the energy losses due to Joule-Effect. • High inductance coefficient, which means that high amounts of energy can be stored in the corresponding magnetic field. Focusing on the implementation of an integrated design, in this work component values are often considered relative to area occupation. Therefore, a high inductive density (ratio between inductance value and occupied area) is desired. • If a ferromagnetic core is used to increase the inductance value (and also in pursuit of field confinement to improve interference effects), it is desired to narrow its corresponding hysteresis cycle, which results in energy losses associated to magnetizing and demagnetizing the core. With the evolution of MEMS processes and techniques, it is feasible to develop fully integrated inductors on silicon using ferro- magnetic materials to increase their inductance, and thick conductors to reduce the resulting ESR. In this area, interesting works from C.H. Ahn can be pointed out (1), and many other authors have developed integrated inductors by means of non-standard CMOS processes (2)- (5). On the other hand, successful research has been carried out in the integration of inductors in standard CMOS process towards RF circuits applications. In this field a clear subdivision appears when developing on-chip inductors: those based on the use of the metal layers available in the standard CMOS process, and research on the inductive effects of the bonding wires. a sext r IL
International Symposium on Circuits and Systems (ISCAS 2011), May 15-19 2011, Rio de Janeiro, Brazil; 01/2011
[show abstract][hide abstract] ABSTRACT: A mixed-signal continuous-time-processing standard CMOS implementation of an asynchronous sigma-delta modulator aimed to drive a switching amplifier operating as an on-chip wideband adaptive power supply is presented in this work. The paper first briefly discusses the fundamental limit tracking capabilities of a two-level switching signal to inband- error-free track a bandlimited signal with minimum average switching frequency. It is argued the adequacy of an adaptive asynchronous sigma-delta modulator (AA∑∆) to approximate such fundamental characteristics. The second part of the paper presents mixed-signal design details of the various subcircuits implementing a CMOS low-power digitally-programmable AA∑∆ modulator, with 7 MHz average switching frequency operation and 1000 µm x 640 µm area occupancy.
International Symposium on Circuits and Systems (ISCAS 2011), May 15-19 2011, Rio de Janeiro, Brazil; 01/2011