[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: A new design based on the flipped-structure for RF active inductors is presented. The conventional flipped-active inductor (FAI) composed of only two transistors is considered as a starting structure. However, it suffers from low-voltage swing, which increases the nonlinearity. Additionally, it requires high power consumption to achieve adequate inductance and quality factor values. A circuit topology named cascoded FAI (CASFAI) based on the basic FAI is proposed. A common-gate transistor added in the feedback path of the proposed CASFAI results in an increase of the voltage swing and linearity as well as the feedback gain. The performance metrics of such active inductors are benchmarked by analytical models and validated in the ADS using a 0.18 μm CMOS process. The results indicate that the CASFAI can achieve a notably higher quality factor and higher inductance values while consuming less power in comparison to the basic FAI.
[Show abstract][Hide abstract] ABSTRACT: Energy-harvesting-enabled wireless sensor networks (EHE-WSN), despite their disruptive potential impact, still present several challenges precluding practical deployability. In particular, the low power density and random character of the ambient energy sources produce slow deep fadings in the energy that nodes harvest. Unfortunately, the capacity of the energy buffers is very limited, causing that, at some times, the node might interrupt its operation due to lack of stored energy. In this context, a general purpose framework for dimensioning the energy buffer is provided in this work. To achieve this, a dynamics-decoupled, multi-source capable energy model is presented, which can handle fast random patterns of the communications and the energy harvesting, while it can capture slow variations of the ambient energy in both time and space. By merging both dynamics, the model can more accurately evaluate the performance of the sensor node in terms of the energy storage capacity and to estimate the expected energy of the neighboring nodes. In order to evaluate the performance of the sensor node, a statistical unit for energy harvesting resources, referred as the Energy-Erlang (E2), has been defined. This unit provides a link between the energy model, the environmental harvested power and the energy buffer. The results motivate the study of the specific properties of the ambient energy sources before the design and deployment. By combining them in this general-purpose framework, electronics and network designers will have a powerful tool for optimizing resources in EHE-WSNs.
Emerging and Selected Topics in Circuits and Systems, IEEE Journal on. 01/2014; 4(3):301-312.
[Show abstract][Hide abstract] ABSTRACT: Typical radar transmitter signals are frequency-modulated with pulsed constant-amplitude envelopes in order to optimize radio-frequency power amplifier (RFPA) efficiency, which results in spectral broadening and power radiated outside of the radar frequency band. This problem can be alleviated by using an appropriately shaped pulse envelope, provided that high-efficiency operation of the radar transmitter is maintained. This paper introduces a pulse-shaping power supply for RFPAs in radar transmitters which enables high efficiency while reducing the spectral emissions. The pulse-shaping power supply is a simple switched resonant circuit capable of approximating a Gaussian pulse envelope waveform. Operating principles are presented and a state-plane-based design approach is described for the resonant pulse-shaping power supply, which enables improved waveform quality and efficiency. An experimental prototype with efficiency greater than 90% is used to supply a 2.14-GHz GaN RFPA. The RFPA efficiency of up to 76%, overall transmitter efficiency of up to 67%, and output signal having high spectral purity demonstrate feasibility of a high-efficiency, high-performance radar system.
IEEE Transactions on Power Electronics 01/2014; 29(2):707-718. · 4.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Directly interfacing sensors that link sensors to micro-controllers without a signal conditioning circuit or an analogue-to-digital converter on the one side and energy harvesting systems on the other side are two key enabling technologies to create self-powered autonomous low-cost and low-maintenance sensor networks. In this reported work, both technologies are concurrently combined in such a way that the duty cycle of the pulsed power supply provided by the harvesting system itself yields in turn a temperature gradient sensor functionality. Originally conceived to power a low-power satellite beacon in a CubeSat project, it has found application, among other applications, in automatic air conditioning and heating systems aiming smart buildings.
[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: Current trends in microprocessor architecture design are leading towards a dramatic increase of core-level parallelization, wherein a given number of independent processors or cores are interconnected. Since the main bottleneck is foreseen to migrate from computation to communication, efficient and scalable means of inter-core communication are crucial for guaranteeing steady performance improvements in many-core processors. As the number of cores grows, it remains unclear whether initial proposals, such as the Network-on-Chip (NoC) paradigm, will meet the stringent requirements of this scenario. This position paper presents a new research area where massive multicore architectures have wireless communication capabilities at the core level. This goal is feasible by using graphene-based planar antennas, which can radiate signals at the Terahertz band while utilizing lower chip area than its metallic counterparts. To the best of our knowledge, this is the first work that discusses the utilization of graphene-enabled wireless communication for massive multicore processors. Such wireless systems enable broadcasting, multicasting, all-to-all communication, as well as significantly reduce many of the issues present in massively multicore environments, such as data coherency, consistency, synchronization and communication problems. Several open research challenges are pointed out related to implementation, communications and multicore architectures, which pave the way for future research in this multidisciplinary area.
[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: This paper proposes an inductive coupled wireless power transfer (WPT) system with class-E2 dc-dc converter along with its design procedure. The proposed WPT system can achieve high power-conversion efficiency at high frequencies because it satisfies the class-E zero-voltage switching and zero-derivative-voltage switching conditions on both the inverter and the rectifier. By using the class-E inverter as a transmitter and the class-E rectifier as a receiver, high power-delivery efficiency can be achieved in the designed WPT system. By using a numerical design procedure proposed in the previous work, it is possible to design the WPT system without considering the impedance matching for satisfying the class-E ZVS/ZDS conditions. The experimental results of the design example showed the overall efficiency of 85.1 % at 100 W output power and 200 kHz operating frequency.
Circuit Theory and Design (ECCTD), 2013 European Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: Nanonetworks, the interconnection of nanosystems, are envisaged to greatly expand the applications of nanotechnology in the biomedical, environmental and industrial fields. However, it is still not clear how these nanosystems will communicate among them. This work considers a scenario of Diffusion-based Molecular Communication (DMC), a promising paradigm that has been recently proposed to implement nanonetworks. In a DMC network, transmitters encode information by the emission of molecules which diffuse throughout the medium, eventually reaching the receiver locations. In this scenario, a pulse-based modulation scheme is proposed and two techniques for the detection of the molecular pulses, namely, amplitude detection and energy detection, are compared. In order to evaluate the performance of DMC using both detection schemes, the most important communication metrics in each case are identified. Their analytical expressions are obtained and validated by simulation. Finally, the scalability of the obtained performance evaluation metrics in both detection techniques is compared in order to determine their suitability to particular DMC scenarios. Energy detection is found to be more suitable when the transmission distance constitutes a bottleneck in the performance of the network, whereas amplitude detection will allow achieving a higher transmission rate in the cases where the transmission distance is not a limitation. These results provide interesting insights which may serve designers as a guide to implement future DMC networks.
IEEE Journal on Selected Areas in Communications 01/2013; 31(12):726-734. · 3.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Resonant Inductive Coupling Wireless Power Transfer is a key technology to provide an efficient and harmless wireless energy channel to consumer electronics, biomedical implants and wireless sensor networks. However, there are two factors that are limiting the applicability of this technology: the effects of distance variation between transmitter and receiver and the effects of interfering objects. While distance variation in WPT has been thoroughly studied, the effects of interfering objects in resonant inductive coupling links are still unclear. In this article we propose a new circuit-based analytical model that predicts the behavior of a resonant inductive coupled link in the presence of interfering objects and verify the obtained results with a Finite Element Field Solver.
Circuits and Systems (ISCAS), 2013 IEEE International Symposium on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: This paper presents a SiC JFET model comprising static, dynamic and thermal features built from SPICE Analog Behavioral Modeling (ABM) controlled sources. The model is parameterized in such a way that data sheet information is enough to set it to work. The model complexity is not very high and allows for reasonably long simulation times to cope with the rather slow self heating process and still maintain enough accuracy for practical purposes.
Mixed Design of Integrated Circuits and Systems (MIXDES), 2013 Proceedings of the 20th International Conference; 01/2013
[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: 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: A low quiescent current output-capacitorless CMOS LDO regulator based on a high slew-rate current-mode transconductance amplifier (CTA) as an error amplifier is presented. Load transient characteristic of the proposed LDO is improved even at low quiescent currents, by using a local common-mode feedback (LCMFB) in the proposed CTA. This provides an increase in the order of transfer characteristic of the circuit, thereby enhancing the slew-rate at the gate of pass transistor. The proposed CTA-based LDO topology has been designed and post-layout simulated in HSPICE, in a 0.18 μm CMOS process to supply a load current between 0-100 mA. Postlayout 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 10-100 pF.
Circuits and Systems (ISCAS), 2013 IEEE International Symposium on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: In the last decade, the field of microprocessor architecture has seen the rise of multicore processors, which consist of the interconnection of a set of independent processing units or cores in the same chip. As the number of cores per multiprocessor increases, the bandwidth and energy requirements for their interconnection networks grow exponentially and it is expected that conventional on-chip wires will not be able to meet such demands. Alternatively, nanophotonics has been regarded as a strong candidate for chip communication since it could provide high bandwidth with low area and energy footprints. However, issues such as the unavailability of efficient on-chip light sources or the difficulty of implementing all-optical buffering or header processing hinder the development of scalable photonic on-chip networks. In this paper, the area and laser power of several photonic on-chip network proposals is analytically modeled and its scalability is evaluated. Also, a graphene-based hybrid wireless/optical-wired approach is presented, aiming at enabling end-to-end photonic on-chip networks to scale beyond thousands of cores.
Optical Network Design and Modeling (ONDM), 2013 17th International Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: In this paper we present an asynchronous finite-state machine digital controller co-integrated with an on-chip non-inverting buck-boost power converter with dynamic signal-tracking capabilities. The mostly-digital controller functionally implements a non-PWM zone-wise control law through asynchronous circuitry, thus exhibiting self-timed minimum latency and ultra low power operation due to gate switching activity. Experimental results on a 0.35 μm CMOS technology demonstrate an efficiency up to 80 % with a switching frequency of 2.86 MHz.
Analog Integrated Circuits and Signal Processing 01/2013; 74(1). · 0.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This work deals with multi-level switching amplifiers, in the context of high-efficiency power amplification for signal tracking applications. In particular, this paper evaluates the reduction in the error signal's power due to multi-level power amplification (compared to conventional two-level amplifiers) and compares the performance of two multi-level pulse modulations: PWM and Asynchronous ΣΔ Modulation. First the intrinsic bandwidth limits of multi-level switching amplifiers are inferred, to clearly state the advantages and limitations of multi-level power amplification. From the existing analyses of Pulse Width Modulation already reported in the literature, PWM is herein extended to multiple levels based on an equivalent representation, which allows to derive a closed expression for the power spectrum of multi-level PWM in bandlimited signal tracking. The Asynchronous ΣΔ Modulation is extended to multiple levels and the resulting multi-level encoding algorithm is analyzed in both time and frequency domains. The performance of both modulations is characterized and compared at different operating frequencies and using different number of levels. The main outcomes of this in-depth characterization show that, if the switching frequency is high enough, the tracking error is independent of the modulation and the switching frequency, i.e., it only depends upon the number of levels, which points out the suitability of asynchronous modulations for relatively low switching frequencies (compared to the number of levels).
Circuits and Systems I: Regular Papers, IEEE Transactions on 01/2013; 60(6):1621-1634. · 2.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recent research in wireless power transfer (WPT) using resonant inductive coupling has demonstrated very high efficiencies (above 40%) at large distances compared to the transmitting element dimensions, thereby exponentially increasing the number of potential applications of WPT. Since resonant inductive coupling is a very multidisciplinary field, different approaches have been proposed to predict the behaviour of these systems from the physical theory of resonators (coupled-mode theory), reflected load theory and circuit theory. Also, there is in this field a heterogeneous definition of metrics without a clear optimization process. In this article we unify the different metrics and demonstrate how to maximize the power transfer efficiency in a non-radiative resonant wireless power transfer link from a circuit-centric point of view providing design guidelines in terms of optimal load impedance, optimal source impedance and optimal distance between coils.
Circuits and Systems (ISCAS), 2013 IEEE International Symposium on; 01/2013