Spanish National Research Council · University of Seville
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Recent publications
Latitudinal variation in biophysical characteristics of avian eggshells to cope with differential effects of solar radiation
J. Gómez, C. Ramo, M. Stevens, G. Liñán-Cembarno, M.A. Rendón, J.C. Troscianko and J.A. Amat
Journal Paper - Ecology and Evolution, pp 1-11, 2018
JOHN WILEY & SONS    DOI: 10.1002/ece3.4335    ISSN: 2045-7758    » doi
Solar radiation is an important driver of animal coloration, not only because of the effects of coloration on body temperature but also because coloration may protect from the deleterious effects of UV radiation. Indeed, dark coloration may protect from UV, but may increase the risk of overheating. In addition, the effect of coloration on thermoregulation should change with egg size, as smaller eggs have higher surface-volume ratios and greater convective coefficients than larger eggs, so that small eggs can dissipate heat quickly. We tested whether the reflectance of eggshells, egg spottiness, and egg size of the ground-nesting Kentish plover Charadrius alexandrinus is affected by maximum ambient temperature and solar radiation at breeding sites. We measured reflectance, both in the UV and human visible spectrum, spottiness, and egg size in photographs from a museum collection of plover eggshells. Eggshells of lower reflectance (darker) were found at higher latitudes. However, in southern localities where solar radiation is very high, eggshells are also of dark coloration. Eggshell coloration had no significant relationship with ambient temperature. Spotiness was site-specific. Small eggs tended to be light-colored. Thermal constraints may drive the observed spatial variation in eggshell coloration, which may be lighter in lower latitudes to diminish the risk of overheating as a result of higher levels of solar radiation. However, in southern localities with very high levels of UV radiation, eggshells are of dark coloration likely to protect embryos from more intense UV radiation. Egg size exhibited variation in relation to coloration, likely through the effect of surface area-to-volume ratios on overheating and cooling rates of eggs. Therefore, differential effects of solar radiation on functions of coloration and size of eggshells may shape latitudinal variations in egg appearance in the Kentish plover.

A 0.9-V 100-μW Feedforward Adder-Less Inverter-Based MASH ΔΣ Modulator With 91-dB Dynamic Range and 20-kHz Bandwidth
M. Honarparvar, J.M. de la Rosa and M. Sawan
Journal Paper - IEEE Transactions on Circuits and Systems I: Regular Papers
IEEE    DOI: 10.1109/TCSI.2018.2854220    ISSN: 1549-8328    » doi
A 0.9-V ΔΣ modulator integrated into a 0.18-μm 2 CMOS technology for digitizing signals in low-power devices is presented in this paper. To do so, a cascade (multistage noise shaping) architecture based on an adder-less feedforward structure is proposed. The proposed modulator has a unity signal transfer function in both stages of the modulator in order to reduce the integrator´s output swings. To mitigate the failure of slow process corner in the weak inversion as well as to further diminish the power consumption of the presented modulator, a fully differential self- and bulk-biased inverter based operational transconductance amplifier is proposed. Experimental results are shown to demonstrate the efficiency of the proposed ΔΣ converter, showing state-of-the-art performance, by featuring 88.7-dB signal-to-noise ratio, 86.4-dB signal-to-noise plus distortion ratio, and 91-dB dynamic range within a signal bandwidth of 20 kHz, with a power dissipation of 103.4 μW when the circuit is clocked at 5.12 MHz.

CMOS characterization and compact modelling for circuit reliability simulation
J. Diaz Fortuny, J. Martin-Martinez, R. Rodriguez, M. Nafria, R. Castro-Lopez, E. Roca and F.V. Fernandez
Conference - IEEE Int. Symposium on On-Line Testing and Robust System Design IOLTS 2018
Abstract not avaliable

Analysis of Body Bias and RTN-induced Frequency Shift of Low Voltage Ring Oscillators in FDSOI Technology
E. Barajas, X. Aragones, D. Mateo, F. Moll, J. Martin-Martinez, R. Rodríguez, M. Portí, M. Nafria, R. Castro-López, E. Roca and F.V Fernández-Fernández
Conference - Int. Symposium on Power and Timing Modeling, Optimization and Simulation PATMOS 2018
Abstract not avaliable

Handling the Effects of Variability and Layout Parasitics in the Automatic Synthesis of LNAs
F. Passos, R. Martins, N. Lourenço, E. Roca, R. Castro-López, R. Póvoa, A. Canelas, N. Horta and F.V. Fernández
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2018
This paper exposes the problematic issue of not considering device variability and layout parasitic effects in optimization-based design of radiofrequency integrated circuits. Therefore, in order to handle these issues, a new design methodology that performs an all-inclusive optimization is proposed, by taking into account the process variability, and, performing the complete layout automatically while performing an accurate parasitic extraction during the optimization for each candidate solution. Furthermore, the problematic inductor parasitics are also taken into account with EM-accuracy, by using a state-of-the-art surrogate modelling technique. The methodology was applied in the design and optimization of a low-noise amplifier, obtaining a set of extremely robust designs ready for fabrication.

Design considerations of an SRAM array for the statistical validation of time-dependent variability models
P. Saraza-Canflanca, D. Malagon, F. Passos, A. Toro, J. Nuñez, J. Diaz-Fortuny, R. Castro-Lopez, E. Roca, J. Martin-Martinez, R. Rodriguez, M. Nafria and F.V. Fernandez
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2018
Modeling and characterization of time-dependent variability phenomena as well as the simulation of their impact on circuit operation have attracted considerable efforts. This paper digs into the validation of compact models and simulation tools in the real operation of circuits. One of the most popular blocks, the 6T SRAM, is proposed for this purpose and a test chip containing an SRAM array is designed. The array allows individual access to each SRAM cell, the application of accelerated aging tests as well as the characterization of common performance metrics.

Lifetime Calculation Using a Stochastic Reliability Simulator for Analog ICs
A. Toro-Frías, P. Martín-Lloret, J. Martinez, R. Castro-Lopez, E. Roca, R. Rodriguez, M. Nafria and F.V. Fernandez
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2018
With the downscale of integration well into the nanometer scale, designers have to take into account not only the performance of circuits due to time-zero variability but also the degradation due to time-dependent. To evaluate the impact of variability in the performance of the circuit, a critical metric is the time-dependent yield, the percentage of designs that operate correctly with respect to a set of performance constraints and that, in presence of time-dependent variability, varies over time. With this metric, the lifetime of the circuit, or the time the circuit is working within a pre-defined yield threshold, is another crucial metric, even fundamental in many applications that require a high degree in accuracy for its calculation. This work proposes a new efficient simulation methodology to estimate the lifetime using a stochastic reliability simulator that can provide accurate yield and lifetime metrics for analog circuits while keeping CPU times low.

A Model Parameter Extraction Methodology Including Time-dependent Variability for Circuit Reliability Simulation
J. Diaz-Fortuny, P. Saraza-Canflanca, A. Toro-Frias, R. Castro-Lopez, J. Martin-Martinez, E. Roca, R. Rodriguez, F.V. Fernandez and M. Nafria
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2018
In current CMOS advanced technology nodes, accurate extraction of transistor parameters affected by timedependent variability, like threshold voltage (Vth) and mobility (μ), has become a critical issue for both analog and digital circuit simulation. In this work, a precise VTH0 and U0 BSIM parameters extraction methodology is presented, together with a straightforward IDS to VTH0 shift conversion, to allow the complete study of aging device effects for reliability circuit

Automated massive RTN characterization using a transistor array chip
P. Saraza-Canflanca, J. Diaz-Fortuny, A. Toro-Frias, R. Castro-Lopez, E. Roca, J. Martin-Martinez, R. Rodriguez, M. Nafria and F.V. Fernandez
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2018
In this work, a CMOS transistor array for the massive measurement of random telegraph noise (RTN), together with a dedicated experimental setup, is presented. The array chip, called ENDURANCE, allows the massive characterization of the RTN parameters needed for a complete understanding of the phenomenon. Additionally, some experimental results are presented that demonstrate the convenience of the setup.

On the analysis and detection of flames with an asynchronous spiking image sensor
J.A. Leñero-Bardallo, J.M. Guerrero-Rodríguez, R. Carmona-Galán and A. Rodríguez-Vázquez
Journal Paper - IEEE Sensors Journal, first online, 2018
ELSEVIER    DOI: 10.1109/JSEN.2018.2851063    ISSN: 1530-437X    » doi
We have investigated the capabilities of a custom asynchronous spiking image sensor operating in the Near Infrared (NIR) band to study flame radiation emissions, monitor their transient activity, and detect their presence. Asynchronous sensors have inherent capabilities, i.e. good temporal resolution, high dynamic range, and low data redundancy. This makes them competitive against Infrared (IR) cameras and CMOS frame-based NIR imagers. In the article, we analyze, discuss and compare the experimental data measured with our sensor against results obtained with conventional devices. A set of measurements have been taken to study the flame emission levels and their transient variations. Moreover, a flame detection algorithm, adapted to our sensor asynchronous outputs, has been developed. Results show that asynchronous spiking sensors have an excellent potential for flame analysis and monitoring.

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