Using behavioral modeling and simulation for learning communication circuits and systems

Comunicación presentada al "Global Engineering Education Conference (EDUCON)" celebrado en Marrakech (Marruecos) del 17 al 20 de Abril del 2012.This paper analyzes the use of behavioral simulation techniques to enhance the teaching-learning process in electrical engineering courses, specifically those dealing with circuits for communication systems. The method - which can be applied to both undergraduate and master courses - allows students to better understand complex circuit- and device-level phenomena, by describing them at a higher abstraction level. As a demonstration vehicle of the presented methodology, two examples are considered in this work: an analog front-end of a direct-conversion digital radio receiver and a ΣΔ modulator. In both cases, behavioral models of the different subcircuits have been implemented in MATLAB/SIMULINK and used by the students enrolled in two different courses: an undergraduate course and a master course. The results presented in this paper reveal that students become highly motivated and satisfied with the course contents and the proposed simulation-based learning methodology.This work has been supported in part by the Spanish Ministry of Science and Innovation (with support from the European Regional Development Fund) under contracts TEC2007-67247-C02-01/MIC, TEC2010-14825/MIC, in part by the Consejería de Innovación, Ciencia y Empresa, under contract TIC-2532 and in part by the I Plan Propio de Docencia de la U. de Sevilla, LabCMA2010 project.Peer Reviewe

Biochar as Soil Amendment: Impact on Soil Properties and Sustainable Resource Management

The role of biochar in improving soil fertility is increasingly being recognized and is leading to recommendations of biochar amendment of degraded soils. In addition, biochars offer a sustainable tool for managing organic wastes and to produce added-value products. The benefits of biochar use in agriculture and forestry can span enhanced plant productivity, an increase in soil C stocks, and a reduction of nutrient losses from soil and non-CO2 greenhouse gas emissions. Nevertheless, biochar composition and properties and, therefore, its performance as a soil amendment are highly dependent on the feedstock and pyrolysis conditions. In addition, due to its characteristics, such as high porosity, water retention, and adsorption capacity, there are other applications for biochar that still need to be properly tested. Thus, the 16 original articles contained in this book, which were selected and evaluated for this Special Issue, provide a comprehensive overview of the biological, chemicophysical, biochemical, and environmental aspects of the application of biochar as soil amendment. Specifically, they address the applicability of biochar for nursery growth, its effects on the productivity of various food crops under contrasting conditions, biochar capacity for pesticide retention, assessment of greenhouse gas emissions, and soil carbon dynamics. I would like to thank the contributors, reviewers, and the support of the Agronomy editorial staff, whose professionalism and dedication have made this issue possible

Reconfigurable switched-current ΣΔ power amplifier

Trabajo presentado al XIV Iberchip celebrado en Puebla (México) del 20 al 22 de febreo de 2008.In this paper a reconfigurable switched-current sigma delta modulator for power amplifier is shown, which is a suitable topology to save energy and integrated area in portable applications. Results have shown the correct operation of a 1.8V , 0.18¿ m CMOS reconfigurable switched-current sigma delta modulator with 11bits dynamic range within 1MHz and 7.8bits within 3.8MHz bandwidth.One of the authors Rosalino Rodríguez Calderon thanks the economic support received from CONACYT (México).Peer Reviewe

A novel low-voltage reconfigurable ΣΔ modulator for 4G wireless receivers

Trabajo presentado al 23rd DCIS celebrado en Grenoble (Francia) del 12 al 14 de noviembre de 2008.This paper presents a new adaptable cascade ΣΔ modulator architecture for low-voltage multi-standard applications. It uses two reconfiguration strategies: a programmable global resonation and a variable loop-filter order. These techniques are properly combined in a novel topology that allows to increase the effective resolution in a given bandwidth, whereas keeping relaxed output swing requirements and high robustness to mismatch and to non-linearities of the amplifiers. Time-domain simulations including the main circuit-level non-idealities are shown to demonstrate the benefits of the presented modulator when it is configured to cope with the requirements of GSM, UMTS, WLAN and Wi-Max.This work has been supported by the Spanish Ministry of Science and Education (with support from the European Regional Development Fund) under contract TEC2007-67247-C02-01/MIC and the Andalusian (Regional) Ministry of Innovation, Science and Enterprise under contract TIC-2532.Peer Reviewe

A SIMULINK Block Set for the High-Level Simulation of Multistandard Radio Receivers

This paper describes a SIMULINK block set for the behavioral simulation of RF receivers. Building blocks are modeled including their main circuit-level non idealities. These models are incorporated into the SIMULINK environment making an extensive use of C-coded S-functions and reducing the number of library block elements. This approach reduces the simulation time while keeping high accuracy, what makes the proposed toolbox very appropriate to be combined with an optimizer for the automated high-level synthesis of radio receivers. As a case study, a direct-conversion receiver intended for 4G telecom systems is modeled and simulated using the proposed toolbox.This work has been supported by the Spanish Ministry of Science and Education (with support from the European Regional Development Fund) under contract TEC2004-01752/MIC.Peer reviewe

Design of an adaptive LNA for hand-held devices in a 1-V 90-nm standard RF CMOS technology: From circuit analysis to layout

[EN]: This paper deals the design of a reconfigurable Low-Noise Amplifier (LNA) for the next generation of wireless hand-held devices by using a lumped circuit approach based on physical laws. The purpose is not only to present simulation results showing the fulfillment of different standard specifications, but also to demonstrate that each design step has a physical meaning such that the mathematical design flow is simple as well as suitable for hand-work in both laboratory and classroom. The circuit under analysis, which is designed according to technological design rules of a 90nm CMOS technology, is a two-stage topology including inductive-source degeneration, MOS-varactor based tuning networks, and programmable bias currents. This proposal, with reduced number of inductors and minimum power dissipation, adapts its performance to different standard specifications; the LNA is designed to cope with the requirements of GSM (PCS1900), WCDMA, Bluetooth and WLAN (IEEE 802.11b-g). In order to evaluate the effect of technology parasitics on the LNA performance, simulation results demonstrate that the LNA features NF16dB, S11-3.3 dBm over the 1.85-2.48 GHz band. For all the standards under study the adaptive power consumption varies from 25.3 mW to 53.3mW at a power supply of 1-V. The layout of the reconfigurable LNA occupies an area of 1.8mm2.[ES]: Este trabajo presenta el diseño de un amplificador de bajo ruido, LNA (del inglés Low‐Noise Amplifier) reconfigurable para la siguiente generación de dispositivos portátiles de comunicación inalámbricos, usando la aproximación de circuitos concentrados sustentada en leyes físicas. El propósito de este trabajo no es sólo presentar resultados de simulación que muestran el cumplimiento de especificaciones para cada estándar, sino también demostrar que cada paso de diseño tiene un significado físico haciendo que el procedimiento matemático de diseño sea simple y adecuado para el trabajo a mano tanto para actividades en laboratorio como en el aula. El circuito bajo análisis, diseñado en una tecnología CMOS 90nm, consta de dos etapas que incluyen degeneración inductiva de fuente, redes de entonado basadas en varactores MOS, y corrientes de polarización programables. Esta propuesta, con reducido número de inductores y mínima disipación de potencia, adapta su desempeño a las diversas especificaciones de cada estándar; el LNA se diseña para cubrir los requerimientos de GSM (PCS1900), WCDMA, Bluetooth y WLAN (IEEE 802.11b‐g). Para evaluar el efecto de las no idealidades de la tecnología en el desempeño del LNA, las simulaciones demuestran que el circuito cumple parámetros como NF16dB, S11< ‐5.5dB, S22‐3.3dBm en la banda 1.85‐ 2.48GHz. Para todos los estándares bajo estudio, el consumo adaptivo de potencia varía de 25.3 mW a 53.3mW usando una fuente de alimentación de 1‐V. El patrón geométrico del LNA reconfigurable consume un área de 1.8mm2.Peer Reviewe

Dual encoding of muscle tension and eye position by abducens motoneurons

Extraocular muscle tension associated with spontaneous eye movements has a pulse-slide-step profile similar to that of motoneuron firing rate. Existing models only relate motoneuron firing to eye position, velocity and acceleration. We measured and quantitatively compared lateral rectus muscle force and eye position with the firing of abducens motoneurons in the cat to determine fundamental encoding correlations. During fixations (step), muscle force increased exponentially with eccentric eye position, consistent with a model of estimate ensemble motor innervation based on neuronal sensitivities and recruitment order. Moreover, firing rate in all motoneurons tested was better related to eye position than to muscle tension during fixations. In contrast, during the postsaccadic slide phase, the time constant of firing rate decay was closely related to that of muscle force decay, suggesting that all motoneurons encode muscle tension as well. Discharge characteristics of abducens motoneurons formed overlapping clusters of phasic and tonic motoneurons, thus, tonic units recruited earlier and had a larger slide signal. We conclude that the slide signal is a discharge characteristic of the motoneuron that controls muscle tension during the postsaccadic phase and that motoneurons are specialized for both tension and position-related properties. The organization of signal content in the pool of abducens motoneurons from the very phasic to the very tonic units is possibly a result of the differential trophic background received from distinct types of muscle fibers

A CMOS fully-differential bandpass ΣΔ modulator using switched-current circuits

Comunicación presentada al "38 th MWSCAS" celebrado en Rio de janeiro del 13 al 16 de Agosto de 1995.This paper presents a fourth-order bandpass sigma-delta modulator that has been designed using fully-differential switched-current circuits in a 0.8μm CMOS technology. The modulator prototype has been obtained by applying a lowpass to bandpass transformation to a second-order lowpass ΣΔ modulator. Specifications are SNR [email protected]±15Khz, for a clock frequency of 1OMhz. Preliminary results from the fabricated prototype obtains the correct noise shaping up to 2.5Mhz clock frequency.Peer reviewe

A 2.5MHz 55dB Switched-Current BandPass ΣΔ Modulator for AM Signal Conversion.

We present a Switched-Current (SI) fourth-order bandpass ΣΔ modulator IC prototype. It uses fully-differential circuits in 0.8μm CMOS technology to obtain a Dynamic Range (DR) larger than 55dB at 2.5MHz center frequency with 30kHz bandwidth - in accordance to the requirements of AM digital receivers. The prototype incorporates a single-ended to fully-differential current-mode buffer for testing purposes. The power consumption of the whole prototype (modulator plus buffer) is 60mW from a 5V supply voltage.This work has been supported by the European Union, under ESPRIT Project 8795-AMFIS.Peer reviewe