Spanish National Research Council · University of Seville
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Author: Roca Moreno , Elisenda
Year: Since 2002
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A comparison of automated RF circuit design methodologies: online vs. offline passive component design
F. Passos, E. Roca, R. Castro-López and F.V. Fernández
Journal Paper - IEEE Transactions on Very Large Scale Integration Systems, vol. 26, no. 11, pp 2386-2394, 2018
IEEE    DOI: 10.1109/TVLSI.2018.2859827    ISSN: 1063-8210    » doi
[abstract]
In this paper, surrogate modeling techniques are applied for passive component modeling. These techniques are exploited to develop and compare two alternative strategies for automated radio-frequency circuit design. The first one is a traditional approach where passive components are designed during the optimization stage. The second one, inspired on bottom-up circuit design methodologies, builds passive component Pareto-optimal fronts (POFs) prior to any circuit optimization. Afterward, these POFs are used as an optimized library from where the passive components are selected. This paper exploits the advantages of evolutionary computation algorithms in order to efficiently explore the circuit design space, and the accuracy and efficiency of surrogate models to model passive components.

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]
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]
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
[abstract]
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
[abstract]
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
[abstract]
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
[abstract]
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
[abstract]
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.

Two-Step RF IC Block Synthesis with Pre-Optimized Inductors and Full Layout Generation In-the-loop
R. Martins, N. Lourenço, F. Passos, R. Povoa, A. Canelas, E. Roca, R. Castro-López, J. Sieiro, F.V. Fernández and N. Horta
Journal Paper - IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, first online, 2018
IEEE    DOI: 10.1109/TCAD.2018.2834394    ISSN: 0278-0070    » doi
[abstract]
In this paper, an analysis of the methodologies proposed in the past years to automate the synthesis of radio-frequency (RF) integrated circuit blocks is presented. In the light of this analysis, and to avoid non-systematic iterations between sizing and layout design steps, a multi-objective optimization-based layout-aware sizing approach with pre-optimized integrated inductor(s) design space is proposed. An automatic layout generation from netlist to ready-to-fabricate prototype is carried in-the-loop for each tentative sizing solution using an RF-specific module generator, template-based placer and evolutionary multi-net router with pre-optimized interconnect widths. The proposed approach exploits the full capabilities of the most established computer-aided design tools for RF design available nowadays, i.e., RF circuit simulator as performance evaluator, electromagnetic simulator for inductor characterization, and layout extractor to determine the complete circuit layout parasitics. Experiments are conducted over a widely-used circuit in the RF context, showing the advantages of performing complete layout-aware sizing optimization from the very initial stages of the design process.

Weighted Time Lag Plot Defect Parameter Extraction and GPU-based BTI Modeling for BTI Variability
V.M. van Santen, J. Diaz-Fortuny, H. Amrouch, J. Martin-Martinez, R. Rodriguez, R. Castro-Lopez, E. Roca, F.V. Fernandez, J. Henkel and M. Nafria
Conference - IEEE International Reliability Physics Symposium IRPS 2018
[abstract]
Abstract not avaliable

A noise and RTN-removal smart method for the parameter extraction of CMOS aging compact models
J. Diaz-Fortuny, J. Martin-Martinez, R. Rodriguez, R. Castro-Lopez, E. Roca, F.V. Fernandez and M. Nafria
Conference - Joint Int. EUROSOI Workshop and Int. Conf. on Ultimate Integration on Silicon EUROSOI-ULIS 2018
[abstract]
Abstract not avaliable

A two-step surrogate modeling strategy for single-objective and multi-objective optimization of radiofrequency circuits
F. Passos, R. González-Echevarría, E. Roca, R. Castro-López and F.V. Fernández
Journal Paper - Soft Computing, first online, 2018
SPRINGER    DOI: 10.1007/s00500-018-3150-9    ISSN: 1432-7643    » doi
[abstract]
The knowledge-intensive radiofrequency circuit design and the scarce design automation support play against the increasingly stringent time-to-market demands. Optimization algorithms are starting to play a crucial role; however, their effectiveness is dramatically limited by the accuracy of the evaluation functions of objectives and constraints. Accurate performance evaluation of radiofrequency passive elements, e.g., inductors, is provided by electromagnetic simulators, but their computational cost makes their use within iterative optimization loops unaffordable. Surrogate modeling strategies, e.g., Kriging, support vector machines, artificial neural networks, etc., arise as a promising modeling alternative. However, their limited accuracy in this kind of applications has prevented a widespread use. In this paper, inductor performance properties are exploited to develop a two-step surrogate modeling strategy in order to evaluate the behavior of inductors with high efficiency and accuracy. An automated design flow for radiofrequency circuits using this surrogate modeling of passive components is presented. The methodology couples a circuit simulator with evolutionary computation algorithms such as particle swarm optimization, genetic algorithm or non-dominated sorting genetic algorithm (NSGA-II). This methodology ensures optimal performances within short computation times by avoiding electromagnetic simulations of inductors during the entire optimization process and using a surrogate model that has less than 1% error in inductance and quality factor when compared against electromagnetic simulations. Numerous real-life experiments of single-objective and multi-objective low-noise amplifier design demonstrate the accuracy and efficiency of the proposed strategies.

Quasi-static PEEC planar solver using a weighted combination of 2D and 3D analytical Green's functions and a predictive meshing generator
S. Ahyoune, J. Sieiro, T. Carrasco, N. Vidal, J.M. López-Villegas, E. Roca and F.V. Fernández
Journal Paper - Integration, vol. 63, pp 332-341, 2018
ELSEVIER    DOI: 10.1016/j.vlsi.2018.02.006    ISSN: 0167-9260    » doi
[abstract]
In this work, a quasi-static implementation of the partial element equivalent circuit (PEEC) method for the analysis of planar radiofrequency (RF) and microwave (uW) components is proposed. The procedure is divided in three parts. First, an alternative PEEC formulation based on energy concepts is described. Second, a smart mesh generator is developed in order to provide an accurate solution at minimum computational costs, taking into account both geometry and device physics as metrics for the correct sizing of mesh elements. And third, a weighted combination of the 2D and 3D quasi-static Green's functions (GF) is proposed for extending the valid frequency range of the quasi-static approximation. It is shown that the 3D-GF is very accurate at low frequency, whereas the 2D-GF is more suitable at higher frequencies. Numerical examples are compared to experimental data for different passive components and technologies in a wide frequency range.

Enhanced systematic design of a voltage controlled oscillator using a two-step optimization methodology
F. Passos, R. Martins, N. Lourenço, E. Roca, R. Póvoa, A. Canelas, R. Castro-López, N. Horta and F.V. Fernández
Journal Paper - Integration, vol. 63, pp 351-361, 2018
ELSEVIER    DOI: 10.1016/j.vlsi.2018.02.005    ISSN: 0167-9260    » doi
[abstract]
In this paper a design strategy based on bottom-up design methodologies is used in order to systematically design a voltage controlled oscillator. The methodology uses two computer-aided design tools: AIDA, a multi-objective multi-constraint circuit optimization tool, and SIDe-O, a tool that characterizes and optimizes integrated inductors with high accuracy (around 1% when compared to electromagnetic simulations). By using such tools, the difficult trade-offs inherent to radio-frequency circuits can be explored efficiently and accurately. Furthermore, with the capability that AIDA has at considering process parameter variations during the optimization, the resulting methodology is able to obtain truly robust circuit designs.

Reliability in the circuit design flow: from characterization and modelling to design automation
R. Castro-López, J. Díaz, J. Martín-Martínez, R. Rodríguez, M. Nafría, A. Toro, P. Martín, E. Roca, F.V. Fernández, E. Barajas, X. Aragonés and D. Mateo
Conference - How to survive in an unreliable world, IEEE CEDA Spain Chapter / NANOVAR Workshop 2017
[abstract]
Designing reliable analog circuits in advanced process technologies requires an accurate understanding of both device performance and variability. The unavoidable and increasingly important process-induced variations is, today, not alone in perturbing the ideal, intended performance of analog circuits: the so-called aging phenomena, like Bias Temperature Instability and Hot Carriers Injection, are altogether making the analog design business a much more tortuous endeavour. The work presented here will paint a complete picture of how to deal with variability in analog circuits for advanced process technologies. This picture starts with the characterisation and modelling of the aging phenomena at the device level. It then will show how these models can be used in the simulation of analog circuits, explaining the issues to overcome and the solutions that can be adopted. With these accurate models and capable circuit simulation techniques, the picture ends with a proposal for an analog design methodology that, using advanced optimization techniques, can successfully take into accounts all sources of variations (process and aging related) so that reliable analog circuits can be attained.

Efficient Computation of Yield and Lifetime for Analog ICs under Process Variabiliy and Aging
A. Toro-Frías, P. Martin-Lloret, R. Castro-López, E. Roca, F.V. Fernández, J. Martin-Martinez, R. Rodriguez and M. Nafria
Conference - Conference on Design of Circuits and Integrated Systems DCIS 2017
[abstract]
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 (i.e., spatial or process variability) but also the degradation due to time-dependent variability (i.e., aging). While process variability has been extensively treated, solutions to cope with aging-related problems are, nowadays, not yet mature enough, especially in the field of analog circuit simulation. Nevertheless, considerable efforts are currently being made to develop new simulation tools and simulation methodologies to evaluate the impact of reliability effects. 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.

Statistical characterization of reliability effects in nanometer CMOS using a versatile transistor array IC
J. Díaz-Fortuny, J. Martin-Martinez, R. Rodriguez, M. Nafria, R. Castro-Lopez, E. Roca, F.V. Fernández, E. Barajas-Ojeda, X. Aragones and D. Mateo-Peña
Conference - Conference on Design of Circuits and Integrated Systems DCIS 2017
[abstract]
In this work, an experimental framework for the characterization of various reliability effects in modern CMOS technologies is described. The main element in this framework is a versatile transistor array chip, designed to accurately characterize process variability, Random Telegraph Noise and BTI/HCI related time dependent variability effects. The measurement setup, the other element in the framework, has been designed to take full advantage of the array architecture, which allows parallel testing of its 3136 MOS transistors, thereby reducing considerably the total measurement time. Thanks to a control toolbox and a user-friendly GUI, the setup also facilitates the programming of any of the required characterization tests.

A transistor array chip for the statistical characterization of process variability, RTN and BTI/CHC aging
J. Diaz-Fortuny, J. Martin-Martinez, R. Rodriguez, M. Nafria, R. Castro-Lopez, E. Roca, F.V. Fernandez, E. Barajas, X. Aragones and D. Mateo
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2017
[abstract]
In this work, a CMOS transistor array is presented, which allows performing process variability, Random Telegraph Noise and BTI/CHC aging characterization in a single chip. The array, called ENDURANCE, integrates 3136 MOS transistors, for single and massive electrical testing. This chip, together with a dedicated measurement set-up, allows programming any of these electrical tests, considerably reducing the total time needed for aging measurements by using a parallelization technique.

Statistical characterization of unreliability effects in a 65-nm CMOS transistor array
J. Diaz-Fortuny, J. Martin-Martinez, R. Rodriguez, M. Nafria, R. Castro-Lopez, E. Roca and F.V. Fernandez
Conference - International Mixed-Signals Testing Workshop IMSTW 2017
[abstract]
In this work, a CMOS transistor array is presented which enables characterization of variability, Random Telegraph Noise and BTI/CHC aging. The array integrates 3,136 MOS transistors for massive electrical testing. This array, together with a dedicated test setup with graphical interface feature easy programming of the required characterization tests, visualization of results and post-processing algorithms for the defect characterization required in aging modeling and simulation.

A Size-Adaptive Time-Step Algorithm for Accurate Simulation of Aging in Analog ICs
P. Martín-Lloret, A. Toro-Frías, J. Martin, R. Castro-Lopez, E. Roca, R. Rodriguez, M. Nafria and F.V. Fernandez
Conference - IEEE International Symposium on Circuits and Systems ISCAS 2017
[abstract]
Variability is one of the main and critical challenges introduced by the continuous scaling in integrated technologies and the need for reliable ICs. In this regard, it is necessary to take into account time-zero (i.e., spatial or process variability) and time-dependent variability (i.e., aging). While process variability has been extensively treated, considerable efforts are currently being made to develop new simulation tools to evaluate the impact of aging, but very few works have been focused on reliability simulation for analog ICs. Most of the up to day models focused on the aging phenomena make use of the stress conditions of the analog circuit during its normal operation. However, many of the available solutions often miss the bi-directional link between stress and biasing and their changes over time and, therefore, accuracy losses occurs while evaluating the impact of aging in the circuit performance. This paper proposes a new size-adaptive time-step algorithm to efficiently update the stress conditions in the reliability simulation of analog ICs. Compared to similar solutions, the work presented here is able to attain similar accuracy levels with lower computational budgets.

Including a stochastic model of aging in a reliability simulation flow
A. Toro-Frías, P. Martin-Lloret, R. Castro-López, E. Roca, F.V. Fernández, J. Martin-Martinez, R. Rodriguez and M. Nafria
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2017
[abstract]
The availability and efficiency of reliability simulators for analog ICs is becoming critical with the scaling of devices down to the nanometer nodes. Two of the main challenges here are how to simultaneously include different sources of unreliability (such as the time-zero or spatial variability and the aging or time-dependent variability), and how to account for the self-induced changes in device biasing (i.e., stress conditions) caused by the device wear-out. In addition to the already existing stochastic models for time-zero variability, new models for the stochastically-distributed aging mechanisms have been developed in recent years. The combination of these challenges with the need for dealing with a stochastic model for aging, causes a serious computational load issue. This paper presents different methods to accurately include reliability in the simulation of analog ICs while preventing the simulation to become unaffordable in terms of CPU time and load.

A strategy to efficiently include electromagnetic simulations in optimization-based RF circuit design methodologies
F. Passos, E. Roca, R. Castro-López, F.V. Fernández, J. Sieiro, and J.M. López-Villegas
Conference - IEEE MTT-S Int. Conf. on Numerical Electromagnetic and Multiphysics Modeling and Optimization for RF, Microwave, and Terahertz Applications NEMO 2017
[abstract]
The use of electromagnetic simulations is crucial in radiofrequency and microwave circuits since accurate estimations of parasitics and performances are essential. In addition, design methodologies based on optimization algorithms have been used in order to design such circuits, while efficiently exploring its design trade-offs. However, due to the high computational cost, optimization-based methodologies seldom use electromagnetic simulation. In order to overcome this issue, this paper demonstrates an optimization-based design methodology for radiofrequency circuits which can incorporate electromagnetic simulations without efficiency loss.

Systematic design of a voltage controlled oscillator using a layout-aware approach
F. Passos, E. Roca, R. Castro-López, F.V. Fernández, R. Martins, N. Lourenço, R. Póvoa, A. Canelas and N. Horta
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2017
[abstract]
This paper focuses on the systematic design of voltage controlled oscillators (VCO), a commonly used radiofrequency (RF) electronic circuit. RF circuits are among the most difficult analog circuits to design due to its trade-offs and high operation frequencies. At such operation frequencies, layout parasitics and accurate passive component characterization become of upmost importance, causing re-design iterations if they are not considered by the designer. To avoid this problem, and reduce the design time, this paper presents a systematic design of a VCO, entailing layout parasitics and accurate characterization of passive components from early design stages. Results clearly illustrate the benefit of this strategy.

An algorithm for a class of real-life multi-objective optimization problems with a sweeping objective
F. Passos, E. Roca, R. Castro-López and F.V. Fernández
Conference - IEEE Congress on Evolutionary Computation CEC 2017
[abstract]
This paper describes a class of real-life optimization problems that has not been addressed before: a multi-objective optimization in which one objective is neither minimized nor maximized but uniformly swept over a wide range. The limitations of conventional multi-objective optimization algorithms to deal with this kind of problems are illustrated via the optimization of radiofrequency inductors. For the first time, an algorithm is proposed that provides sets of solutions for this kind of problems.

Layout-aware challenges and a solution for the automatic synthesis of radio-frequency IC blocks
R. Martins, N. Lourenço, R. Póvoa, A. Canelas, N. Horta, F. Passos, R. Castro-López, E. Roca and F.V. Fernández
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2017
[abstract]
In this paper, the major methodologies proposed in the last years to speed-up the synthesis of radio-frequency integrated circuits blocks are overviewed. The challenges to automate this task are discussed, and, to avoid non-systematic iterations between circuit and layout design steps, the architecture of an innovative solution is proposed. The proposed tool exploits the full capabilities of most established computer-aided design tools available nowadays, i.e., off-the-shelf circuit simulator, electromagnetic simulator and layout extractor. The approach intends to bypass the two major bottlenecks of RF-design: the design of reliable integrated inductors and accurate layout parasitic estimates since the early stages of design process.

CASE: A reliability simulation tool for analog ICs
P. Martín-Lloret, A. Toro-Frías, R. Castro-López, E. Roca, F.V. Fernández, J. Martin-Martinez, R. Rodriguez and M. Nafria
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2017
[abstract]
With the evolution in the scale of integration in ICs, aging-related problems are becoming more important and, nowadays, solutions to cope with these issues are not yet mature enough, especially in the field of analog circuit simulation. CASE, the novel simulator presented in this paper, can evaluate the impact of reliability effects in analog circuits through a stochastic physic-based model. The implemented simulation flow is accurate and efficient in terms of CPU. The two main improvements over currently reported and commercial tools, is that the simulator can simultaneously take into account both time-zero and time-dependent variability, and that an adaptive method, to account for the strong link between biasing and stress, can improve the accuracy while keeping acceptable CPU times.

New mapping strategies for pre-optimized inductor sets in bottom-up RF IC sizing optimization
N. Lourenço, R. Martins, R. Póvoa, A. Canelas, N. Horta, F. Passos, R. Castro-López, E. Roca and F. V. Fernández
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2017
[abstract]
This paper presents new indexing and mutation operators, in the context of bottom-up hierarchical multi-objective optimization of radio frequency integrated circuits, for pre-optimized sets of solutions from the hierarchical sub-levels when moving up in hierarchy. Two ideas, one based on a Voronoi decomposition and another based on the nearest neighborhood, are explored, where, and unlike previous approaches that are based on sorting, the distance between elements determines the probability of decisions taken during optimization. Three implementations of those ideas were tried in AIDA's NSGAII evolutionary kernel, and successfully used in the optimization of a Voltage Controlled Oscillator and a Low Noise Amplifier with pre-optimized inductor sets obtained using the SIDeO toolbox, showing their strengths when compared to previous state-of-the-art mapping strategies.

TARS: A toolbox for statistical reliability modeling of CMOS devices
J. Diaz-Fortuny, J. Martin-Martinez, R. Rodriguez, M. Nafria, R. Castro-Lopez, E. Roca and F.V. Fernandez
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2017
[abstract]
This paper presents a toolbox for the automation of the electrical characterization of CMOS transistors. The developed software provides a user-friendly interface to carry out different tests to evaluate time-zero (i.e., process) and time-dependent variability in CMOS devices. Also, the software incorporates a post-processing capability that allows users to visualize the data. Moreover, without loss of generality, the toolbox allows the user, from the measured data, to feed a particular physics-based model that accounts for various aging phenomena.

Dependence of MOSFETs threshold voltage variability on channel dimensions
C. Couso, J. Diaz-Fortuny, J. Martin-Martinez, M. Porti, R. Rodriguez, M. Nafria, F.V. Fernandez, E. Roca, R. Castro-Lopez, E. Barajas, D. Mateo and X. Aragones
Conference - Joint Int. EUROSOI Workshop and Int. Conf. on Ultimate Integration on Silicon EUROSOI-ULIS 2017
[abstract]
The dependence of the MOSFET threshold voltage variability on device geometry (width (W) and length (L)) has been studied from experimental data. Our results evidence, in agreement with other works, deviations from the Pelgrom's rule, especially in smaller technologies. TCAD simulations were also performed which further support the experimental data and provide physical information regarding the origin of such deviation. Finally, a new empirical model that assumes different impact of W and L in the device variability has been proposed, which reproduces the experimental results.

Extending the frequency range of quasi-static electromagnetic solvers
S. Ahyoune, J. Sieiro, T. Carrasco, N. Vidal, J. M. López-Villegas, E. Roca and F.V. Fernández
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2017
[abstract]
In this work, a combination of 2D and 3D quasi-static Green's functions (GF) is proposed for extending the frequency range validity of the quasi-static approximation. It is shown that 3D-GF is very accurate at low frequency, whereas 2D-GF is more suitable at higher frequencies because it is the actual solution of the transverse electromagnetic (TEM) propagation mode. The mixing of both GFs is controlled through the ratio of the main size of the device versus the wavelength at the given simulation frequency. Numerical examples are compared with experimental data for different passives in a broadband frequency range.

Radio-frequency inductor synthesis using evolutionary computation and Gaussian-process surrogate modeling
F. Passos, E. Roca, R.Castro-López and F.V. Fernández
Journal Paper - Applied Soft Computing, vol. 60, pp 495-507, 2017
ELSEVIER    DOI: 10.1016/j.asoc.2017.07.036    ISSN: 1568-4946    » doi
[abstract]
In recent years, the application of evolutionary computation techniques to electronic circuit design problems, ranging from digital to analog and radiofrequency circuits, has received increasing attention. The level of maturity runs inversely to the complexity of the design task, less complex in digital circuits, higher in analog ones and still higher in radiofrequency circuits. Radiofrequency inductors are key culprits of such complexity. Their key performance parameters are inductance and quality factors, both a function of the frequency. The inductor optimization requires knowledge of such parameters at a few representative frequencies. Most common approaches for optimization-based radiofrequency circuit design use analytical models for the inductors. Although a lot of effort has been devoted to improve the accuracy of such analytical models, errors in inductance and quality factor in the range of 5%-25% are usual and it may go as high as 200% for some device sizes. When the analytical models are used in optimization-based circuit design approaches, these errors lead to suboptimal results, or, worse, to a disastrous non-fulfilment of specifications. Expert inductor designers rely on iterative evaluations with electromagnetic simulators, which, properly configured, are able to yield a highly accurate performance evaluation. Unfortunately, electromagnetic simulations typically take from some tens of seconds to a few hours, hampering their coupling to evolutionary computation algorithms. Therefore, analytical models and electromagnetic simulation represent extreme cases of the accuracy-efficiency trade-off in performance evaluation of radiofrequency inductors. Surrogate modeling strategies arise as promising candidates to improve such trade-off. However, obtaining the necessary accuracy is not that easy as inductance and quality factor at some representative frequencies must be obtained and both performances change abruptly around the self-resonance frequency, which is particular to each device and may be located above or below the frequencies of interest. Both, offline and online training methods will be considered in this work and a new two-step strategy for inductor modeling is proposed that significantly improves the accuracy of offline methods The new strategy is demonstrated and compared for both, single-objective and multi-objective optimization scenarios. Numerous experimental results show that the proposed two-step approach outperforms simpler application strategies of surrogate modelling techniques, getting comparable performances to approaches based on electromagnetic simulation but with orders of magnitude less computational effort.

Design and characterization of a miniaturized implantable UHF RFID tag based on LTCC technology
A. Garcia-Miquel, B. Medina-Rodriguez, N. Vidal, F.M. Ramos, E. Roca and J.M. Lopez-Villegas
Conference - European Conference on Antennas and Propagation EuCAP 2017
[abstract]
This paper presents the design and characterization of a novel, compact, multilayer, passive UHF-RFID tag solution for implantable biotelemetry based on low-temperature co-fired ceramic (LTCC) technology. A spiral planar inverted-F antenna (PIFA) was matched to the UHF integrated circuit (IC) impedance by an inductor line. The LTCC process allowed the IC to be embedded in a sealed cavity. Simulations and measurements of the reflection coefficient and the tag range were carried out when the RFID tag was implanted in the center of a 10 cm cubic skin phantom. The dimensions of the prototype were 8x7x2 mm(3), leading to a total volume of 112 mm(3). Results indicated a 6 dB bandwidth of 39 MHz and 84 MHz for simulations and measurements, respectively, and a tag range of approximately 10 cm.

Parametric macromodeling of integrated inductors for RF circuit design
F. Passos, Y. Ye, D. Spina, E. Roca, R. Castro-López, T. Dhaene and F.V. Fernández
Journal Paper - Microwave and Optical Technology Letters, vol. 59, no. 5, pp 1207-1212, 2017
JOHN WILEY & SONS    DOI: 10.1002/mop.30498    ISSN: 1098-2760    » doi
[abstract]
Nowadays, parametric macromodeling techniques are widely used to describe electromagnetic structures. In this contribution, the application of such parametric macromodeling techniques to the design of integrated inductors and radio-frequency circuit design is investigated. In order to allow such different operations, a new modeling methodology is proposed, which improves the modeling accuracy when compared to former techniques. The new methodology is tailored to the unique characteristics of the devices under study. The obtained parametric macromodel is then used in a synthesis methodology and in the design of a voltage controlled oscillator in a 0.35-μm CMOS technology.

An inductor modeling and optimization toolbox for RF circuit design
F. Passos, E. Roca, R. Castro-López and F.V. Fernández
Journal Paper - Integration, the VLSI Journal, vol. 58, pp 463-472, 2017
ELSEVIER    DOI: 10.1016/j.vlsi.2017.01.009    ISSN: 0167-9260    » doi
[abstract]
This paper describes the SIDe-O toolbox and the support it can provide to the radio-frequency designer. SIDe-O is a computer-aided design toolbox developed for the design of integrated inductors based on surrogate modeling techniques and the usage of evolutionary optimization algorithms. The models used feature less than 1% error when compared to electromagnetic simulations while reducing the simulation time by several orders of magnitude. Furthermore, the tool allows the creation of S-parameter files that accurately describe the behavior of inductors for a given range of frequencies, which can later be used in SPICE-like simulations for circuit design in commercial environments. This toolbox provides a solution to the problem of accurately and efficiently optimizing inductors, which alleviates the bottleneck that these devices represent in the radio-frequency circuit design process.

An automated design methodology of RF circuits by using Pareto-optimal fronts of EM-simulated inductors
R. González-Echevarría, E. Roca, R. Castro-López, F.V. Fernández, J. Sieiro, J.M. López-Villegas and N. Vidal
Journal Paper - IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, vol. 36, no. 1, pp 15-26, 2017
IEEE    DOI: 10.1109/TCAD.2016.2564362    ISSN: 0278-0070    » doi
[abstract]
A new design methodology for radiofrequency circuits is presented that includes electromagnetic (EM) simulation of the inductors into the optimization flow. This is achieved by previously generating the Pareto-optimal front (POF) of the inductors using EM simulation. Inductors are selected from the Pareto front and their S-parameter matrix is included in the circuit netlist that is simulated using an RF simulator. Generating the EM-simulated POF of inductors is computationally expensive, but once generated, it can be used for any circuit design. The methodology is illustrated both for a single-objective and a multi-objective optimization of a Low Noise Amplifier.

A Size-Adaptive Time-Step Algorithm for Accurate Simulation of Aging in Analog ICs
P. Martín, A. Toro, R. Castro, E. Roca, F.V. Fernández, J. Martín-Martínez and M. Nafría
Conference - Conference on Design of Circuits and Integrated Systems DCIS 2016
[abstract]
Variability is one of the main and critical challenges introduced by the continuous scaling in integrated technologies and the need for reliable ICs. In this regard, it is necessary to take into account time-zero (i.e., spatial or process variability) and time-dependent variability (i.e., aging). While process variability has been extensively treated, considerable efforts are currently being made to develop new simulation tools to evaluate the impact of aging, but very few works have been focused on reliability simulation for analog ICs. Most of the up to day models focused on the aging phenomena make use of the stress conditions of the analog circuit during its normal operation. However, many of the available solutions often miss the bi-directional link between stress and biasing and their changes over time and, therefore, accuracy losses occurs while evaluating the impact of aging in the circuit performance. This paper proposes a new size-adaptive time-step algorithm to efficiently update the stress conditions in the reliability simulation of analog ICs. Compared to similar solutions, the work presented here is able to attain similar accuracy levels with lower computational budgets.

SIDe-O: A Toolbox for Surrogate Inductor Design and Optimization
F. Passos, E. Roca, R. Castro-López, F. V. Fernández
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2016
[abstract]
This paper presents SIDe-O, a CAD tool developed for the design and optimization of integrated inductors based on surrogate modeling techniques. This tool provides a solution to the problem of accurately and efficiently optimizing the design of inductors. The models used present less than 1% error when compared to EM simulations while reducing the simulation time by several orders of magnitude. Additionally, the tool provides the ability to create new surrogate models for different technologies and inductor topologies. The tool also allows the creation of an S-Parameter file that accurately describes the behavior of the inductor for a given range of frequencies, which can later be used in SPICE-like simulations.

Frequency-Dependent Parameterized Macromodeling of Integrated Inductors
F. Passos, E. Roca, R. Castro-López, F.V. Fernández, Y. Ye, D. Spina and T. Dhaene
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2016
[abstract]
Integrated inductors are one of the most important passive elements in radio frequency design, due to their wide usage in wireless communication circuits. Typically, electromagnetic simulators are used in order to estimate the inductors performance with high accuracy as a function of the inductor geometrical and electrical parameters. Such simulations offer high-accuracy, but are computationally expensive and extremely time consuming. In this paper, a frequency-dependent parameterized macromodeling technique is adopted in order to overcome this problem. The proposed approach offers a high degree of automation, since it is based on sequential sampling algorithms, high efficiency and flexibility: a continuous frequency-domain model is given for each value of the chosen inductors parameters in the design space.

Personal exposure to radiofrequency electromagnetic fields: University of Barcelona study
N. Vidal, A. Garcia-Miquel, A. Rios, J.M. Lopez-Villegas and E. Roca
Conference - European Conference on Antennas and Propagation EuCAP 2016
[abstract]
A study was conducted at the University of Barcelona (Physics Faculty) to assess the electromagnetic field strengths to which students are exposed in their day-to-day lives. We analyzed different radiofrequency sources (GSM900, GSM 1800, UMTS and Wi-Fi). Our aim was to analyze not only electric field strengths but also absorption, so we considered different scenarios and situations: both empty and full classrooms with personal devices switched on and off. Areas with Wi-Fi hotspots nearby were also analyzed. We observed a huge variation in the results, but the strengths were always below the limits set by the relevant regulations.

Reliability simulation for analog ICs: Goals, solutions, and challenges
A. Toro-Frías, P. Martín-Lloret, J. Martin-Martinez, R. Castro-López, E. Roca, R. Rodriguez, M. Nafria and F.V. Fernández
Journal Paper - Integration, the VLSI Journal, vol. 55, pp 341-348, 2016
ELSEVIER    DOI: 10.1016/j.vlsi.2016.05.002    ISSN: 0167-9260    » doi
[abstract]
The need for new tools and simulation methodologies to evaluate the impact of all reliability effects in ICs is a critical challenge for the electronic industry. Issues due to process-related variations (also known as spatial variability) are well-known and off-the-shelf simulation methods are available. On the other hand, models and simulation methods for the aging-related problems, which are becoming more important with each technology node, are far less mature, specially for analog ICs. In this sense, transistor wear-out phenomena such as Bias Temperature Instability (BTI) and Hot Carriers Injection (HCI) cause a time-dependent variability that occurs together with the spatial variability. A fundamental missing piece in the design flow is an efficient and accurate simulation methodology for IC reliability. To this goal, several challenges should be addressed properly: the essential nature of the stochastic behavior of aging (and thus resorting to stochastic models rather than deterministic ones), the correlation between spatial and aging-related variability, and relationship between biasing, stress and aging in analog ICs, among others. This paper discusses some of these challenges in detail.

Accurate Synthesis of Integrated RF Passive Components using Surrogate Models
F. Passos, R. González-Echevarría, E. Roca, R. Castro-López and F.V. Fernández
Conference - Design, Automation and Test in Europe DATE 2016
[abstract]
Passive components play a key role on the design of RF CMOS integrated circuits. Their synthesis, however, is still an unsolved problem due to the lack of accurate analytical models that can replace the computationally expensive electromagnetic simulations (EM). Both, physical-based and surrogate models have been reported that fail to accurately model the complete design space of inductors. Surrogate-assisted optimization techniques, where coarse models are locally enhanced during the inductor synthesis process by using new EM-simulated points to update the model, have been proposed, but either the efficiency is dramatically decreased due to the online EM simulations or the optimization may converge to suboptimal regions. In this paper, we present a new surrogate model, valid in the entire design space with less than 1% error when compared with EM simulations. This model can be generated offline, and, when embedded within an optimization algorithm, allows the synthesis of integrated inductors with high accuracy and high efficiency, reducing the synthesis time in three orders of magnitude.

Introduction to the special issue on Radio Frequency Integrated Circuits (RFIC) design techniques
E. Roca and J. Sieiro
Journal Paper - Integration, the VLSI Journal, vol. 52, pp. 183-184, 2016
ELSEVIER    DOI: 10.1016/j.vlsi.2015.11.001    ISSN: 0167-9260    » doi
[abstract]
The growing demand for new and more complex wireless communication devices is pushing continuous innovation in the design of Radio Frequency Integrated Circuits. New and stronger performance requirements are to be met in shorter times-to-market, using technologies which are not always RF-friendly, making the design of these circuits a challenging job.
Miniaturization and cost have driven CMOS technologies as attractive candidates for the design of RF integrated circuits. Furthermore, the scaling of these technologies down to the nanometric regime has pushed their frequencies of operation well into the millimeter-wave region. Currently, CMOS coexists with other high-performance technologies, like SiGe, providing the RF designer with a wide catalog of alternatives for the optimal system design considering a variety of aspects like size, cost, power consumption, performance, etc. .
One the most important challenges of RF design is the lack of good simulation and modeling tools that can combine the electrical characteristics of the different devices (active and passive) with their electromagnetic properties when operating at GHz frequencies. The development of new simulation methodologies and mathematical modeling for RFIC are crucial aspects for designing RF circuits that fulfill the requirements of the communication standards and effectively reduce the design time.

Aplicación de algoritmos evolutivos multiobjectivo al diseño de circuitos integrados: criterios de detención
E. Roca, R. Castro-Lopez and F.V. Fernández
Conference - Congreso Español de Metaheurísticas, Algoritmos Evolutivos y Bioinspirados MAEB 2015
[abstract]
Abstract not avaliable

Computational Intelligence Techniques for Determining Optimal Performance Trade-Offs for RF Inductors
E. Roca, R. Castro-López, F.V. Fernández, R. González-Echevarría, J. Sieiro, N. Vidal and J.M. López-Villegas
Book Chapter - Computational Intelligence in Analog and Mixed-Signal (AMS) and Radio-Frequency (RF) Circuit Design, pp 277-296, 2015
SPRINGER    DOI: 10.1007/978-3-319-19872-9_10    ISBN: 978-3-319-19871-2    » doi
[abstract]
The automatic synthesis of integrated inductors for radio frequency (RF) integrated circuits is one of the most challenging problems that RF designers have to face. In this chapter, computational intelligence techniques are applied to automatically obtain the optimal performance trade-offs of integrated inductors. A methodology is presented that combines a multi-objective evolutionary algorithm with electromagnetic simulation to get highly accurate results. A set of sized inductors is obtained showing the best performance trade-offs for a given technology. The methodology is illustrated with a complete set of examples where different inductor trade-offs are obtained.

A Fast and Accurate Reliability Simulation Method for Analog Circuits
A. Toro-Frias, R. Castro-Lopez, E. Roca, F.V. Fernández, J. Martin-Martinez, R. Rodriguez and M. Nafria
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2015
[abstract]
Reliability has become a critical challenge in integrated circuit design in today's CMOS technologies. Aging problems have been added to the well-known issues due to spatial variations that are caused by imperfections in the fabrication process. In this sense, transistor wear-out phenomena such as Bias Temperature Instability (BTI) and Hot Carriers (HC) cause a time-dependent variability that is added to the spatial variability. In addition, the BTI presents a stochastic behaviour, which may cause, for instance, time-varying mismatch. In this work, a model based on the physics of this phenomenon is implemented to accurately know its impact on the circuit performances. This method is focused on the analysis of analog circuits, taking into account the impact of both temporal and spatial variability. An effient simulation flow is implemented to evaluate the circuit performance at any instant of the circuit lifetime.

Transformation conditions of performance fronts of operational amplifiers
E. Roca, R. Castro-Lopez, M. Velasco-Jiménez and F.V. Fernandez
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2015
[abstract]
Pareto fronts of circuits whose performance depend on other circuits that they are connected to must be updated for each interconnection conditions. This paper reports, for the first time, the conditions for which a transformation without loss of information is guaranteed.

Surrogate Modeling and Optimization of Inductor Performances using Kriging functions
F. Passos, R. González-Echevarría, E. Roca, R. Castro-López and F.V. Fernandez
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2015
[abstract]
Integrated inductors are one of the most important passive elements in RF circuits. However, time-consuming simulations, such as electromagnetic simulations, have to be used to evaluate their performances with high accuracy. In order to overcome this problem, analytical models can be used. In this paper, a surrogate model based on Kriging functions is presented that accurately predicts the performance parameters of integrated inductors. The different approaches followed to obtain the model are presented. Finally, the model is linked to an evolutionary algorithm to optimize inductor performances.

A simulation methodology for the reliability-aware design of analog circuits
A. Toro, R. Castro-López, E. Roca, F.V. Fernández, J. Martín-Martinez, R. Rodriguez and M. Nafria
Conference - International Mixed-Signals Testing Workshop IMSTW 2015
[abstract]
With the scale of integration of modern transistors entering the atomic size and an increase of the gate-oxide field, reliability of electronic circuits is today more demanding than ever. Both spatial (i.e., process) variations and time-dependent (i.e., aging) variations dramatically reduce the yield and shortens the circuit lifetime, which prompt for reliability aspects to be considered in the design flow in order to attain resilient circuits featuring longer lifetimes. Aging effects such as as Bias Temperature Instability (BTI) and Hot Carriers Injection (HCI) should be included just as well as process variations are.

Design Space Exploration using Hierarchical Composition of Performance Models
M. Velasco-Jiménez, R. Castro-López, E. Roca and F.V. Fernández
Conference - IEEE International Symposium on Circuits and Systems ISCAS 2015
[abstract]
Bottom-up synthesis approaches based on the hierarchical composition of performance models have been proposed as a promising alternative to conventional top-down hierarchical synthesis approaches. This paper discusses problems related to the context-dependence of performance models and proposes possible solutions. Techniques for the composition of multi-dimensional performance models so that the efficiency of the design space exploration is maximized are also discussed. An active filter is used to demonstrate the accuracy and efficiency of the techniques discussed here.

Physical vs. Surrogate Models of Passive RF Devices
F. Passos, M. Kotti, R. González-Echevarría, M.H. Fino, M. Fakhfakh, E. Roca, R.Castro-López and F.V. Fernández
Conference - IEEE International Symposium on Circuits and Systems ISCAS 2015
[abstract]
The accuracy of high-frequency models of passive RF devices, e.g., inductors or transformers, presents one of the most challenging problems for RF integrated circuits. Accuracy limitations lead RF designers to time-consuming iterations with electromagnetic simulators. This paper will explore and compare two advanced modeling techniques. The first one is based on the segmented model approach, in which each device segment is characterized with a lumped element model. The second technique is based on the generation of surrogate models from the electromagnetic simulation of a set of device samples. Different modeling strategies (frequency separation, filtering according to self-resonance frequency, etc.) will be considered. Efficiency and accuracy of both, physical and surrogate, modeling techniques will be compared using a Si process technology.

Single-Objective Optimization Methodology for the Design of RF Integrated Inductors
F. Passos, M.H. Fino AND E. Roca
Conference - IFIP WG 5.5/SOCOLNET Doctoral Conference on Computing, Electrical and Industrial Systems DoCEIS 2014
[abstract]
Designing integrated inductors for RF applications is quite a challenging task due to the necessity of minimizing the parasitic effects arising from using today´s technologies. The multiplicity of non-ideal effects to be minimized makes imperious the use of optimization-based design methodologies. In this paper a model-based optimization methodology is considered as a way of offering the designer the possibility to obtain inductors with maximum quality factor. The inductor model accounts for square, hexagonal or octagonal topologies. Furthermore tapered inductors are also accounted for in the proposed model. The use of the inductor model reduces the optimization time significantly. The validity of the results obtained is checked against electromagnetic (EM) simulations. As an application example, the particular case for the design of inductors for 2.4 GHz is illustrated.

Hierarchical Composition of Pareto-Optimal Fronts of Analog Circuits: Implementation Issues
M. Velasco-Jiménez, R. Castro-López, E. Roca and F.V. Fernández
Conference - Conference on Design of Circuits and Integrated Systems DCIS 2014
[abstract]
The use of Pareto-optimal fronts (PoFs) is becoming key in the development of new hierarchical design methodologies that aim to reduce the bottleneck in the design of analog and mixed-signal systems caused by the design of the analog components. An important aspect of these new methodologies, the hierarchical composition of lower-level PoFs, has received little attention in the literature. This composition presents two key issues. The first issue is the context-dependent performances of analog circuits, which obligate to re-evaluate the PoFs of these circuits when their surrounding circuitry changes. The second issue is related to how multi-dimensional low-level PoFs are used when generating the PoFs of high-level blocks so that the efficiency of the design space exploration is not affected. This work presents new mechanisms that can be used to solve both issues. The generation of the performance model of an active filter by hierarchical composition of previously generated PoFs of operational amplifiers is used to demonstrate the validity of the approaches presented here.

Characterization of Random Telegraph Noise and its impact on reliability of SRAM sense amplifiers
J. Martin-Martinez, J. Diaz, R. Rodriguez, M. Nafria, X. Aymerich, E. Roca, F.V. Fernandez and A. Rubio
Conference - European Workshop on CMOS Variability VARI 2014
[abstract]
A new method for the analysis of multilevel Random Telegraph Noise (RTN) signals has been recently presented, which can also be applied in the case of large background noise. In this work, the method is extended to evaluate the RTN-related variation of the device drain current. The RTN parameters obtained from experimental traces are used to simulate the impact of RTN in the drain current of pMOS transistors in SRAM voltage sense amplifiers. The results show that RTN can lead to read errors of the stored data.

Fully analytical characterization of the series inductance of tapered integrated inductors
F. Passos, M.H. Fino and E. Roca
Journal Paper - International Journal of Electronics and Telecommunications, vol 60, no. 1, pp 65-69, 2014
DE GRUYTER    DOI: 10.2478/eletel-2014-0007    ISSN: 2081-8491    » doi
[abstract]
In this paper a general method for the determination of the series inductance of polygonal tapered inductors is presented. The value obtained can be integrated into any integrated inductor lumped element model, thus granting the overall characterization of the device and the evaluation of performance parameters such as the quality factor or the resonance frequency. In this work, the inductor is divided into several segments and the corresponding self and mutual inductances are calculated. In the end, results obtained for several working examples are compared against electromagnetic (EM) simulations are performed in order to check the validity of the model for square, hexagonal, octagonal and tapered inductors. The proposed method depends exclusively on the geometric characteristics of the inductor as well as the technological parameters. This allows its straight forward application to any inductor shape or technology.

Automated generation of the optimal performance trade-offs of integrated inductors
R. González-Echevarría, R. Castro-López, E. Roca, F.V. Fernández, J. Sieiro, N.Vidal and J.M. López-Villegas
Journal Paper - IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, vol. 33, no. 8, pp. 1269-1273, 2014
IEEE    DOI: 10.1109/TCAD.2014.2316092    ISSN: 0278-0070    » doi
[abstract]
In this paper, a new methodology for the automated generation of the optimal performance trade-offs of integrated inductors is presented. The methodology combines a multiobjective optimization algorithm with electromagnetic simulation to get highly accurate results. A set of sized inductors is obtained showing the best performance trade-offs for a given technology. Unlike reported approaches for inductor synthesis, performance trade-offs are generated offline, i.e., before any specific inductance or quality factor are required. The tight efficiency versus accuracy trade-off of existing approaches is, in this way, avoided and performance evaluation via electromagnetic simulation becomes affordable.

Generation of surrogate models of Pareto-optimal performance trade-offs of planar inductors
M. Kotti, R. González-Echevarría, F.V. Fernández, E. Roca, J. Sieiro, R. Castro-López, M. Fakhfakh and J.M. López-Villegas
Journal Paper - Analog Integrated Circuits and Signal Processing, vol. 78, no. 1, pp 87-97, 2014
SPRINGER    DOI: 10.1007/s10470-013-0230-8    ISSN: 0925-1030    » doi
[abstract]
Systematic design methodologies for wireless transceivers require an efficient design of integrated inductors. Early availability of feasible trade-offs between inductance, quality factor, self-resonance frequency and area, is a key enabler towards the improvement of such design methodologies. This paper introduces such an approach in two steps. First, a Pareto-optimal performance front of integrated inductors is generated by embedding a performance evaluator into a multi-objective optimization tool. Then, starting from the optimal front samples, a surrogate model of the performance front is obtained. Experimental results in a 0.35-μm CMOS technology are provided.

Introduction to the special issue on SMACD 2012
F.V. Fernández, E. Roca and R. Castro-López
Journal Paper - Analog Integrated Circuits and Signal Processing, vol. 78, no. 1, pp 61-63, 2014
SPRINGER    DOI: 10.1007/s10470-013-0227-3    ISSN: 0925-1030    » doi
[abstract]
Abstract not avaliable

Implementation Issues in the Hierarchical Composition of Performance Models of Analog Circuits
M. Velasco-Jiménez, R. Castro-López, E. Roca and F.V. Fernández
Conference - Design Automation and Test in Europe DATE 2014
[abstract]
Emerging hierarchical design methodologies based on the use of Pareto-optimal fronts (PoFs) are promising candidates to reduce the bottleneck in the design of analog circuits. However, little work has been reported about how to transmit the information provided by the PoFs of low hierarchical level blocks through the hierarchy to compose the performance models of higher-level blocks. This composition actually poses several problems such as the dependence of the PoF performances on the surrounding circuitry and the complexity of dealing with multi-dimensional PoFs in order to explore more efficiently the design space. To deal with these problems, this paper proposes new mechanisms to represent and select candidate solutions from multi-dimensional PoFs that are transformed to the changing operating conditions enforced by the surrounding circuitry. These mechanisms are demonstrated with the generation of the performance model of an active filter by composing previously generated PoFs of operational amplifiers.

A Wideband Lumped-Element Model for Integrated Spiral Inductors
F. Passos, M.H. Fino, E. Roca, R. González-Echevarría and F.V. Fernández
Conference - Conference on Design of Circuits and Integrated Systems DCIS 2013
[abstract]
Abstract not available

Lumped Element Model for Arbitrarily Shaped Integrated Inductors - A Statistical Analysis
F. Passos, M.H. Fino, E. Roca, R. González-Echevarría and F.V. Fernández
Conference - IEEE Int. Conf. on Microwaves, Communications, Antennas and Electronic Systems COMCAS 2013
[abstract]
In this paper a model based in lumped elements is presented for the haracterization of integrated inductors. The model allows the modelling of integrated inductors for a wide range of frequencies and different inductor topologies, thus granting the evaluation of important design parameters such as inductance, quality factor and self-resonance frequency. The model will be explained in detail and compared against electromagnetic simulations for a 0.35μm and 0.13μm CMOS technologies. Results for square and octagonal geometries are presented. A statistic analysis is also presented for the octagonal topology in order to validate the model over a wide range of geometric variables in 0.35μm CMOS technology.

A Wideband Lumped-Element Model for Arbitrarily Shaped Integrated Inductors
F. Passos, M.H. Fino and E. Roca
Conference - European Conference on Circuit Theory and Design ECCTD 2013
[abstract]
In this paper a model based on lumped elements is used to characterize integrated inductors. The method proposed allows the modelling of integrated inductors for a wide range of frequencies, thus granting the overall characterization of the device and the evaluation of important design parameters such as inductance, quality factor and resonance frequency. The model can easily be applied to any polygonal shape inductor due to its inductance calculation through self and mutual inductances. Electromagnetic simulations results are presented to demonstrate the validation of the model.

Analythical Characterization of Variable Width Integrated Spiral Inductors
F. Passos, M.H. Fino and E. Roca
Conference - International Conference Mixed Design of Integrated Circuits and Systems MIXDES 2013
[abstract]
In this paper a general method for characterizing tapered inductors with square, hexagonal or octagonal shape is presented. The method proposed allows the evaluation of the series inductance to integrate in any integrated inductor lumped element model, thus granting the overall characterization of the device and the evaluation of design parameters such as the quality factor or the resonance frequency. In this work, the inductor is divided into several segments and the corresponding self and mutual inductances are calculated. In the end, results obtained for several working examples are compared against a field solver. Relative errors below 3% are obtained for square, hexagonal or octagonal inductors, thus proving the validity of the method proposed. Furthermore, the methodology adopted may be easily applied to any polygonal shape.

Systematic Generation of Performance Models of Reconfigurable Analog Circuits
M. Velasco-Jiménez, R. Castro-López, E. Roca and F.V. Fernández
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2012
[abstract]
In this work, a systematic technique to generate performance models of reconfigurable analog circuits is presented. The performance models are obtained in the form of multi-mode Pareto-optimal fronts (mm-PoFs), a new type of Pareto-optimal front (PoF) that characterizes the set of different performances that reconfigurable circuits can attain. The technique is based on the use of an evolutionary algorithm (EA) that acts as an optimizer, and the simulator HSPICE to measure the circuit performances. The use of this technique will be illustrated for a wireless multistandard problem, where a reconfigurable op-amp will be considered.

Symbolic Pole/Zero Analysis
F.V. Fernández, C. Sánchez-López, R. Castro-López and E. Roca
Book Chapter - Design of Analog Circuits through Symbolic Analysis, pp 287-304, 2012
BENTHAM    DOI: 10.2174/978160805095611201010287    ISBN: 978-1-60805-425-1    » doi
[abstract]
Extraction of pole/zero expressions as a function of circuit parameters has traditionally been an essential tool for designers. In this Chapter, the main specific techniques for symbolic pole/zero extraction are described and their pros and cons are discussed. The application of the different techniques is illustrated with experimental results on practical circuits.

Surrogate models of Pareto-optimal planar inductors
M. Kotti, R. González-Echevarría, E. Roca, R. Castro-López, F.V. Fernández, M. Fakhfakh, J. Sieiro and J.M. López-Villegas
Conference - Int. Conf. on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2012
[abstract]
Systematic design methodologies for wireless transceivers require an efficient design of integrated inductors. Early availability of feasible trade-offs between inductance, quality factor and area, is a key enabler towards the improvement of such design methodologies. This paper introduces such an approach in two steps. First, a Pareto-optimal performance front of integrated inductors is obtained by embedding an electromagnetic simulator into a multi-objective optimization tool. Then, starting from the obtained optimal samples, a surrogate model of the performance front is obtained. Experimental results in a 0.35 μm CMOS technology are provided.

New approaches to bridge the design gap of analog and RF circuits
F.V. Fernández, E. Roca and R. Castro-López
Conference - International Conference on Analog VLSI Circuits AVIC 2012
[abstract]
The increasing gap between IC complexity and the capacity to deal with it in the design process is worrisome. Design productivity has and must be improved in this sense. The picture is even worse for analog, mixed-signal and radiofrequency circuits due to the lesser development of commercial CAD tools and methodologies with respect to their digital counterparts. From the several directions proposed to bridge this gap, this talk will focus on two of them: improving existing hierarchical synthesis methods and reducing the iterations between separate design stages.

Approximation Techniques in Symbolic Circuit Analysis
F.V. Fernández, C. Sánchez-López, R. Castro-López and E. Roca
Book Chapter - Design of Analog Circuits through Symbolic Analysis, pp 173-201, 2012
BENTHAM    DOI: 10.2174/978160805095611201010173    ISBN: 978-1-60805-425-1    » doi
[abstract]
Symbolic circuit analysis suffers from the exponential growth of expression complexity with circuit size. Therefore, either if the symbolic expressions are used for gaining insight into circuit operation or for repetitive computer-based evaluations, simplification becomes mandatory. This chapter reviews the different existing techniques for symbolic expression simplification, classifying them into three categories according to the step at which the simplification is performed: on the circuit equations, during the solution of the circuit equations or after the circuit equations have been solved. Pros and cons of each approach are discussed.

An Automated Layout-Aware Design Flow
A. Toro-Frías, R. Castro-López, E. Roca and F.V. Fernández
Conference - Int. Conference on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2012
[abstract]
In analog integrated circuit design, it has always been necessary to improve the designer's productivity. The iterations between the electrical and physical synthesis, required to correct deviations due to parasitics, do degrade that productivity. The inclusion of the physical implementation directly within the electrical synthesis process, would in principle remove many or all of these iterations. This paper presents a fully-automated layout-aware design flow, whose key aspects are: (1) it uses commercially available tools and platforms to attain a highly integrated solution, (2) it provides solutions in the form of Pareto-optimal fronts, which represent the circuit's valuable trade-offs (and can be used in modern design flows), and (3) it allows including the impact of parasitics right into the fronts. This paper details the necessary tools and their integration for automation of the design flow and provides several examples of its use.

A fully automated design flow for planar inductors
R. González-Echevarría, R. Castro-López, E. Roca, F.V. Fernández, J.M. López-Villegas and J. Sieiro
Conference - Int. Conference on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design SMACD 2012
[abstract]
Integrated inductors performances are difficult to model due to the parasitic effects present at high frequencies. Typically, RF designers use electromagnetic simulation during the design flow to tune their circuits until all designs requirements are fulfilled or use the set of, not always conveniently tuned, inductors provided by the foundries. In this paper, a multi-objective optimization algorithm is combined with a full-wave electromagnetic evaluator to obtain a tool for synthesis of inductors with optimum performance trade-offs. The automation of layout generation and simulation tasks are described in details.

Context-dependent transformation of Pareto-optimal performance fronts of operational amplifiers
E. Roca-Moreno, M. Velasco-Jiménez, R. Castro-López and F.V. Fernández-Fernández
Journal Paper - Analog Integrated Circuits and Signal Processing, vol. 73, no. 1, pp 65-76, 2012
SPRINGER    DOI: 10.1007/s10470-011-9785-4    ISSN: 1573-1979    » doi
[abstract]
The use of Pareto-optimal performance fronts in emerging design methodologies for analog integrated circuits is a keystone to overcome the limitations of traditional design methodologies. However, most techniques to generate the fronts reported so far neglect the effect that the surrounding circuitry (such as the load impedance) has on the Pareto-front, thereby making it only realistic for the context where the front was generated. This strongly limits the use of the Pareto front because of the strong dependence between the key performances of an analog circuit and its surrounding circuitry, but, more importantly, because this circuitry remains unknown until the Pareto-optimal front is being used. Since performance front generation is a costly process, this paper proposes that performance fronts for a new context of use of a given circuit can be obtained from fronts that were previously generated under some different conditions. Towards this goal, a transformation methodology for performance objectives of operational amplifiers has been developed. Experimental results for a folded-cascode and a Miller-compensated operational amplifiers show that this is a promising approach to reuse the fronts in multiple contexts.

Mixed-mode impedance and reflection coefficient of two-port devices
T. Carrasco, J. Sieiro, J.M. López-Villegas, N. Vidal, R. Gonzalez-Echevarria and E. Roca
Journal Paper - Progress in Electromagnetics Research-Pier, vol. 130, pp 411-428, 2012
E M W PUBLISHING    DOI: 10.2528/PIER12052906    ISSN: 1559-8985    » doi
[abstract]
From the point of view of mixed-mode scattering parameters, S, a two-port device can be excited using different driving conditions. Each condition leads to a particular set of input reflection and input impedance coefficient definitions that should be carefully applied depending on the type of excitation and symmetry of the two-port device. Therefore, the aim of this paper is to explain the general analytic procedure for the evaluation of such reflection and impedance coefficients in terms of mixed-mode scattering parameters. Moreover, the driving of a two-port device as a one-port device is explained as a particular case of a two-port mixed-mode excitation using a given set of mixed-mode loads. The theory is applied to the evaluation of the quality factor, Q, of symmetrical and non-symmetrical inductors.

Closing the gap between electrical and physical design: the layout-aware solution
R. Castro-López, E. Roca and F.V. Fernández
Book Chapter - Analog layout synthesis. A Survey of Topological Approaches, pp 243-268, 2011
SPRINGER    DOI: 10.1007/978-1-4419-6932-3_6    ISBN: 978-1-4419-6931-6    » doi
[abstract]
Iterations between separate phases in any procedural design process, usually a by-product of unexpected (or, simply, very complex to consider) adverse effects, clearly play against any time-to-market requirements. In analog integrated circuit (IC) design, going back and forth between electrical and physical synthe- sis to counterbalance layout-induced performance degradations needs to be thus avoided as much as possible. One possible solution involves the integration of the 1 traditionally separated electrical and physical synthesis phases, by including layout- induced effects, in the form of layout parasitics, right into the electrical synthesis phase, in what has been called parasitic-aware synthesis. This solution, as such, is not yet complete since there are geometric requirements (minimization of the occu- pied area or fulfillment of certain layout aspect ratio, among others), whose effects on the resulting parasitics are not usually considered during electrical synthesis. In this chapter, a layout-aware solution that tackles both geometric and parasitic-aware electrical synthesis is proposed. This technique uses a combination of simulation- based optimization, procedural layout generation, exhaustive geometric evaluation algorithms, and several mechanisms for parasitic estimation. Thanks to the nature of this combination, the solution benefits from, and also fosters, reuse of analog intellectual property (IP) blocks. Several detailed design examples are provided.

Layout-aware Pareto fronts of electronic circuits
A. Toro-Frías, R. Castro-López, E. Roca and F.V. Fernández
Conference - European Conference on Circuit Theory and Design ECCTD 2011
[abstract]
Pareto-optimal performance fronts have gained popularity as a representation of performance trade-offs of electronic circuits. They are also essential to support efficient bottom-up hierarchical design methodologies. Being such a key element in these methodologies, there have been many reported efforts to enhance the fronts with valuable information that goes beyond the nominal circuit behavior, such as the yield or the reconfiguration capabilities. However, the effect of layout parasitics is the factor that has been missing in the literature: the accuracy may be seriously degraded by layout parasitics not considered during the front generation. In this paper, we present a technique to generate layout-aware Pareto fronts that accurately accounts for the impact of both geometry and parasitics. © 2011 IEEE.

High-dynamic range tone-mapping algorithm for focal plane processors
S. Vargas-Sierra, G. Liñan-Cembrano, E. Roca and A. Rodríguez-Vázquez
Conference - SPIE Microtechnologies for the New Millennium 2011
[abstract]
This paper presents a Dynamic Range improvement technique which is specially well-suited to be implemented in Focal Plane Processors (FPP) due to its very limited computing requirements since only local memories, little digital control and a comparator are required at the pixel level. The presented algorithm employs measurements during exposure time to create a 4-bit non-linear image whose histogram determines the shape of the tone-mapping curve which is applied to create the final image. Simulations results over a highly bimodal 120dB image are presented showing that both the highly and poorly illuminated parts of the image keep a sufficient level of details.

Load-Independent Characterization of Trade-Off Fronts for Operational Amplifiers
E. Roca, M. Velasco-Jiménez, R.l Castro-López and F.V. Fernández
Conference - Conference on Design of Circuits and Integrated Systems DCIS 2010
[abstract]
In emerging design methodologies for analog integrated circuits, the use of performance trade-off fronts, also known as Pareto fronts, is a keystone to overcome the limitations of the traditional top-down methodologies. However, most techniques reported so far to generate the front neglect the effect of the surrounding circuitry (such as the output load impedance) on the Pareto-front, thereby making it only valid for the context where the front was generated. This strongly limits its use in hierarchical analog synthesis because of the heavy dependence of key performances on the surrounding circuitry, but, more importantly, because this circuitry remains unknown until the synthesis process. We will address this problem by proposing a new technique to generate the trade-off fronts that is independent of the load that the circuit has to drive. This idea is exploited for a commonly used circuit, the operational amplifier, and experimental results show that this is a promising approach to solve the issue.

A Pareto-based systematic design technique for reconfigurable analog circuits using an evolutionary optimization algorithm
M. Velasco-Jiménez, R. Castro-López, E. Roca and F.V. Fernández
Conference - Conference on Design of Circuits and Integrated Systems DCIS 2010
[abstract]
Abstract not avaliable

A bottom-up approach to the systematic design of LNAs using evolutionary optimization
C. Sánchez-López, R. Castro-López, E. Roca, F.V. Fernández, R. González-Echevarría, J. Esteban-Muller, J.M. López-Villegas, J. Sieiro and N. Vidal
Conference - International Workshop on Symbolic and Numerical Methods, Modeling and Applications to Circuit Design SM2ACD 2010
[abstract]
A systematic design methodology for low-noise amplifiers (LNAs) is introduced. This methodology follows a bottom-up approach that employs a multi-objective evolutionary optimization algorithm, which is used at two levels. First, it is used to generate Pareto-based performance models for integrated planar inductors. To do so, an electromagnetic simulator that takes into account the inductor's layout, thus providing highly accurate performance evaluations, is coupled to the optimizer. Unlike foundry-provided inductor libraries, these Pareto-based models offer a detailed insight of the trade-offs between inductance, quality factor and area. Afterwards the Pareto-based models for the inductors are used as design variables to generate the LNA Pareto surface, thus providing highly accurate performance trade-offs of the LNA.

A FPP-Oriented Tone Mapping Technique for High Dynamic Range Imagers Using Temporal and Final Exposure Measurements
S. Vargas-Sierra, G. Liñán-Cembrano, E. Roca-Moreno and A. Rodríguez-Vázquez
Conference - European Solid State Circuits Conference ESSCIRC 2010
[abstract]
This paper presents a Dynamic Range improvement technique which is specially well-suited to be implemented in Focal Plane Processors due to its very limited computing requirements since only local memories and a comparator are required at the pixel level. The presented algorithm employs measurements during exposure time to create a 4-bit artificial image whose histogram determines the shape of the tone-mapping curve which is applied to create the final image. Simulations results over a highiy bimodal120dB image are presented showing that both the highiy and poorly iiiuminated parts of the image keep a sufficient level of details.

Multi-objective performance optimization of planar inductors
J. Esteban-Muller, R. González-Echevarría, C. Sánchez-López, E. Roca, R. Castro-López, F.V. Fernández, J.M. López-Villegas, J. Sieiro and N. Vidal
Conference - Int. Workshop on Symbolic and Numerical Methods, Modeling and Applications to Circuit Design SM2ACD 2010
[abstract]
Inductors play an essential role in the design of RF circuits. The parasitic effects plaguing integrated planar inductors require an accurate modeling and the careful exploration of their performance trade-offs. In this paper, a multi-objective performance modeling technique of planar inductors is presented, that supports both top-down and bottom-up design of RF circuits. ©2010 IEEE.

Context-independent performance modeling of operational amplifiers using Pareto fronts
E. Roca, M. Velasco-Jiménez, R. Castro-López and F.V. Fernández
Conference - Int. Workshop on Symbolic and Numerical Methods, Modeling and Applications to Circuit Design SM2ACD 2010
[abstract]
The use of performance trade-off fronts, also known as Pareto fronts, in emerging design methodologies for analog integrated circuits is a keystone to overcome the limitations of the traditional top-down methodologies. However, most techniques reported so far to generate the fronts neglect the effect of the surrounding circuitry (such as the output load impedance) on the Pareto-front, thereby making it only valid for the context where the front was generated. This strongly limits its use in hierarchical analog synthesis because of the heavy dependence of key performances on the surrounding circuitry, but, more importantly, because this circuitry remains unknown until the synthesis process. We propose a new technique to generate the trade-off fronts that is independent of the load that the circuit has to drive. This idea is exploited for a Miller operational amplifier, and experimental results show that this is a promising approach to solve the issue. ©2010 IEEE.

Stopping criteria in evolutionary algorithms for multi-objective performance optimization of integrated inductors
F.V. Fernández, J. Esteban-Muller, E. Roca and R. Castro-López
Conference - International Conference on Evolutionary Computation CEC 2010
[abstract]
In this paper, the application of multi-objective evolutionary algorithms to the evaluation of performance trade-offs of planar inductors, an almost ubiquitous device in radio-frequency microelectronics, is studied. The absence of appropriate stopping criteria in most evolutionary algorithms reveals to be critical in this application. A new stopping criterion based on monitoring a set of performance metrics that account for convergence and diversity is proposed and demonstrated with practical radio-frequency circuit design problems.

Pixel Design and Evaluation In CMOS Image Sensor Technology
S. Vargas-Sierra, E. Roca-Moreno and G. Liñán-Cembrano
Conference - Conference on Design of Circuits and Integrated Systems DCIS 2009
[abstract]
A chip designed in a 0.18 μm CMOS Image Sensor Technology (CIS) is presented which incorporates different pixel design alternatives for Active Pixel Sensor (APS). CIS technology improves characteristics such as sensitivity, dark current and noise, that are strongly layout dependent. This chip includes a set of pixel architectures where different parameters have been modified: layout of active diffusion, threshold voltage of the source follower transistor and the use of microlenses. Besides, structures to study the influence of crosstalk between pixels have been incorporated.

Applications of evolutionary computation techniques to analog, Mixed-signal and RF circuit design - an overview
E. Roca, M. Fakhfakh, R. Castro-López and F.V. Fernández
Conference - IEEE International Conference on Electronics, Circuits and Systems ICECS 2009
[abstract]
This paper review. The application of evolutionary computation techniques to analog, mixed-signal and radio-frequency design problems. Design needs, limitations of existing approaches and open challenges are pointed out. © 2009 IEEE.

APS design alternatives in 0.18 μm CMOS image sensor technology
S. Vargas-Sierra, E. Roca, G. Liñán-Cembrano
Conference - European Conference on Circuit Theory and Design ECCTD 2009
[abstract]
This paper presents a chip designed for the purpose of evaluating different design alternatives in a 0.18 mu m CMOS Image Sensor Technology (CIS) for Active Pixel Sensor (APS) based vision applications. CIS technology improves characteristics such as sensitivity, dark current and noise, that are strongly layout dependent. It also allows the use of special structures, such as color light filters and microlenses. This chip includes a set of pixel architectures where different parameters have been modified: layout of active diffusion, threshold voltage of the source follower transistor and the use of microlenses. Besides, structures to study the influence of crosstalk between pixels have been incorporated.

A focal plane processor for continuous-time 1-D optical correlation applications
G. Liñán-Cembrano, L. Carranza, B. Alexandre, E. Roca and A. Rodríguez-Vázquez
Conference - European Conference on Circuit Theory and Design ECCTD 2009
[abstract]
This paper describes a 1-D Focal Plane Processor incorporating 200 pixels for Continuous-Time Optical Correlation Applications. Each pixel incorporates a 2mmx10.9mm photodiode whose current is scaled, at the pixel level, by 5 independent 3-bit programmable-gain current amplifiers. Correlation patterns, defined as 5 sets of 200 3-bits numbers, are communicated to the chip via . a standard (IC)-C-2 interface. Correlation outputs are provided in current form through independent 8-bit-programmable amplifiers whose gains are also defined via I2C. The chip contains an alignment help by incorporating 3 rows of 100 conventional Active Pixel Sensors (AI'S) inserted at the top, middle, and lower part of the main photodiode array. The chip has been fabricated in a standard 0.35mm CMOS technology and maximum power consumption is below 30mW.

Hierarchical synthesis based on Pareto-optimal fronts
E. Roca, R. Castro-López and F.V. Fernández
Conference - European Conference on Circuit Theory and Design ECCTD 2009
[abstract]
Pareto-optimal fronts have recently arisen as a promising alternative for design space exploration, potentially enabling better and more efficient hierarchical synthesis. This paper reviews the Pareto front generation problem, extends this concept to reconfigurable circuits, and discusses alternative applications to hierarchical synthesis approaches.

Using Pareto-optimal fronts in the design of reconfigurable data converters
R. Castro-López, E. Roca and F.V. Fernández
Conference - International Conference on Advances in Circuits, Electronics and Microelectronics CENICS 2009
[abstract]
Analog design is a bottleneck in the design of integrated circuits. A recently proposed method to cope with the complexity of analog design is the use of a multi-objective bottom-up flow, which makes use of the concept of Pareto-optimal front (POF) to capture performance trade-offs of analog components, and through which these can be exploited during top-down design of a complex (hierarchically-wise) analog circuit. In this paper, we describe a step forward and transform this technique, through a new type of front we call Multi-Mode Pareto-optimal Front, to design reconfigurable Analog-to-Digital Converters (ADCs). We demonstrate that not only design time is shortened but also that design complexity of reconfigurable circuits can be more systematically and efficiently managed.

A memetic approach to the automatic design of high-performance analog integrated circuits
B. Liu, F.V. Fernández, G. Gielen, R. Castro-López and E. Roca
Journal Paper - Transactions on Design Automation of Electronic Systems, vol. 14, no. 3, pp 42, 2009
ASSOC COMPUTING MACHINERY    DOI: 10.1145/1529255.1529264    ISSN: 1084-4309    » doi
[abstract]
This article introduces an evolution-based methodology, named memetic single-objective evolutionary algorithm (MSOEA), for automated sizing of high-performance analog integrated circuits. Memetic algorithms may achieve higher global and local search ability by properly combining operators from different standard evolutionary algorithms. By integrating operators from the differential evolution algorithm, from the real-coded genetic algorithm, operators inspired by the simulated annealing algorithm, and a set of constraint handling techniques, MSOEA specializes in handling analog circuit design problems with numerous and tight design constraints. The method has been tested through the sizing of several analog circuits. The results show that design specifications are met and objective functions are highly optimized. Comparisons with available methods like genetic algorithm and differential evolution in conjunction with static penalty functions, as well as with intelligent selection-based differential evolution, are also carried out, showing that the proposed algorithm has important advantages in terms of constraint handling ability and optimization quality.

Multimode Pareto fronts for design of reconfigurable analogue circuits
R. Castro-López, E. Roca and F.V. Fernández
Journal Paper - Electronics Letters, vol. 45, no. 2, pp 95-96, 2009
INSTITUTION OF ENGINEERING AND TECHNOLOGY-IET    DOI: 10.1049/el:20091795    ISSN: 0013-5194    » doi
[abstract]
Multimode Pareto-optimal fronts are presented. This is a novel concept that can be key in the design of reconfigurable analogue circuits, because it contains information not only on the trade-offs among the circuit performances, but also on its reconfiguration capabilities. A method to generate the front, relying on evolutionary optimisation, and a general dominance sorting algorithm that guides the optimisation, are both described.

Quality Metrics of Pareto-Optimal Fronts for Multi-Objective Synthesis of Analog ICs
F.V. Fernández, B. Liu, R. Castro-López and E. Roca
Conference - International Workshop on Symbolic and Numerical Methods, Modeling and Applications to Circuit Design SM2ACD 2008
[abstract]
Evolutionary computation (EC) techniques can be applied to synthesize analog integrated circuits via the Pareto dominance concept and multi-objective optimization. In order to find out which of the EC techniques available yields better results for analog circuit design, a set of metrics are required that compares and characterizes the Pareto-optimal fronts in terms of their analog design quality. In this paper, we select and classify existing, widely used quality metrics and propose new ones for analog multi-objective synthesis. Several experiments are used that back up the proposed metrics.

MSOEA: A New Methodology for Synthesis of High Performance Analog Integrated Circuits
B. Liu, F.V. Fernández, G. Gielen, R. Castro-López, E. Roca and J. Luo
Conference - Xth International Workshop on Symbolic and Numerical Methods, Modeling and Applications to Circuit Design SM2ACD 2008
[abstract]
This paper introduces an evolution-based methodology, named memetic single objective evolutionary algorithm (MSOEA), for automated sizing of high performance analog integrated circuits. By combining operators from the differential evolution algorithm, the real-coded genetic algorithm, operators inspired by the simulated annealing algorithm, and a set of constraint handling techniques, MSOEA specializes on handling analog circuit synthesis problems with numerous and tight design constraints. The method has been tested on several analog circuits. Comparisons with available methods show that the proposed algorithm presents important advantages in constraint handling ability and optimization quality.

Hierarchical Design of Reconfigurable Analog Circuits using Multi-Mode Pareto Fronts
R. Castro-López, F.V. Fernández and E. Roca
Conference - Int. Workshop on Symbolic and Numerical Methods, Modeling and Applications to Circuit Design SM2ACD 2008
[abstract]
Most reconfigurable analog integrated circuits reported follow an ad-hoc design approach, which do not guarantee neither efficient area occupation nor minimized power consumption for all operation modes. A clear example is the Analog-to-Digital Converter (ADC), used in multi-standard transceivers. This paper tries to formulate a hierarchical design approach based on the following elements: (1) An improved top-down synthesis with bottom-up generated low-level design information; (2) An original definition of the reconfiguration capabilities of the building blocks; (3) A optimization-based technique for the exploration of candidate architectures; (4) Last but not least, a clear definition of metrics for reconfigurability to measure how good is a design in terms its reconfiguration capabilities. This methodology is illustrated through the design of a multi-standard ΣΔ modulator.

An integrated layout-synthesis approach for analog ICs
R. Castro-López, O. Guerra, E. Roca and F.V. Fernández
Journal Paper - IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, vol. 27, no. 7, pp 1179-1189, 2008
IEEE    DOI: 10.1109/TCAD.2008.923417    ISSN: 0278-0070    » doi
[abstract]
In analog integrated circuit design, iterations between electrical and physical syntheses to counterbalance layout-induced performance degradations should be avoided as much as possible. One possible solution involves the integration of traditionally separated electrical and physical synthesis phases by including layout-induced effects right into the electrical synthesis phase in what has been called parasitic-aware synthesis. This solution, as such, is not yet complete since there are geometric requirements (minimization of area or fulfillment of certain layout aspect ratio, among others) whose effects on the resulting parasitics are not usually considered during the electrical synthesis. In this paper, a layout-aware solution for analog cells that tackles both geometric and parasitic-aware electrical synthesis is proposed. Several design examples are provided.

Systematic design of high-resolution high-frequency cascade continuous-time sigma-delta modulators
R. Tortosa, R. Castro-López, J.M. de la Rosa, E. Roca, A. Rodríguez Vázquez and F.V. Fernández
Journal Paper - ETRI Journal, vol. 30, no. 4, pp 535-545, 2008
ETRI    DOI: 10.4218/etrij.08.0107.0225    ISSN: 1225-6463    » doi
[abstract]
This paper introduces a systematic top-down and bottom-up design methodology to assist the designer in the implementation of continuous-time (CT) cascade sigma-delta (SIGMA DELTA) modulators. The salient features of this methodology are (a) flexible behavioral modeling for optimum accuracy-efficiency trade-offs at different stages of the top-down synthesis process, (b) direct synthesis in the continuous-time domain for minimum circuit complexity and sensitivity, (c) mixed knowledge-based and optimization-based architectural exploration and specification transmission for enhanced circuit performance, and (d) use of Pareto-optimal fronts of building blocks to reduce re-design iterations. The applicability of this methodology will be illustrated via the design of a 12-bit 20 MHz CT SIGMA DELTA modulator in a 1.2 V 130 nm CMOS technology.

Towards systematic design of multi-standard converters
V.J. Rivas, R. Castro-López, A. Morgado, O. Guerra, E. Roca, R. del Río, J.M. de la Rosa and F.V. Fernández
Conference - Conference on VLSI Circuits and Systems III, 2007
[abstract]
In the last few years, we are witnessing the convergence of more and more communication capabilities into a single terminal. A basic component of these communication transceivers is the multi-standard Analog-to-Digital Converter (ADC). Many systematic, partially automated approaches for the design of ADCs dealing with a single communication standard have been reported. However, most multi-standard converters reported in the literature follow an ad-hoc approach, which do not guarantee either an efficient occupation of silicon area or its power efficiency in the different standards. This paper aims at the core of this problem by formulating a systematic design approach based on the following key elements: (1) Definition of a set of metrics for reconfigurability: impact in area and power consumption, design complexity and performances; (2) Definition of the reconfiguration capabilities of the component blocks at different hierarchical levels, with assessment of the associated metrics; (3) Exploration of candidate architectures by using a combination of simulated annealing and evolutionary algorithms; (4) Improved top-down synthesis with bottom-up generated low-level design information. The systematic design methodology is illustrated via the design of a multi-standard YEA modulator meeting the specifications of three wireless communication standards.

Early slip detection with a tactile sensor based on retina
R. Maldonado-López, F. Vidal-Verdú, G. Liñán, E. Roca and A. Rodríguez-Vázquez
Journal Paper - Analog Integrated Circuits and Signal Processing, vol. 53, no. 2-3, pp 97-108, 2007
SPRINGER    DOI: 10.1007/s10470-007-9059-3    ISSN: 0925-1030    » doi
[abstract]
The interest in tactile sensors is increasing as their use in complex unstructured environments is demanded, like in telepresence, minimal invasive surgery, robotics etc. The array of pressure data provided by these devices can be treated with different image processing algorithms to extract miscellaneous information. However, as in the case of vision chips or artificial retinas, problems arise when the size of the array and the computational complexity increase. Having a look at the skin, the information collected by every mechanoreceptor is not sent to the brain for its processing, but some complex pre-processing is performed to fit the limited throughput of the nervous system. This is specially important for high bandwidth demanding tasks, as the case of slip detection with tactile sensors, which is demanding in computing requirements. Here we show some results from a tactile processor based on circuitry proposed for an artificial retina that has been modified to mimic the way the biological skin works.

Locust-Inspired Vision System On Chip Architecture for Collision Detection in Automotive Applications
L. Carranza-González, R. Laviana-Gonzalez, S. Vargas-Sierra, J. Cuadri-Carvajo, G. Liñan-Cembrano and E. Roca-Moreno
Conference - IEEE International Symposium on Circuits and Systems ISCAS 2006
[abstract]
Abstract not available

Tactile retina for slip detection
R. Maldonado López, F. Vidal-Verdú, G. Liñán, E. Roca and A. Rodríguez-Vázquez
Conference - IEEE International Conference on Virtual Environments, Human-Computer Interfaces and Measurement Systems VECIMS 2006
[abstract]
The interest in tactile sensors is increasing as their use in complex unstructured environments is demanded, like in telepresence, minimal invasive surgery, robotics etc. The array of pressure data provided by these devices can be treated with different image processing algorithms to extract the required information. However, as in the case of vision chips or artificial retinas, problems arise when the array size and the computation complexity increase. Having a look at the skin, the information collected by every mechanoreceptor is not sent to the brain for its processing, but some complex pre-processing is performed to fit the limited throughput of the nervous system. This is specially important for high bandwidth demanding tasks. Experimental works report that neural response of skin mechanoreceptors encodes the change in local shape from an offset level rather than the absolute force or pressure distributions. Something similar happens in the retina, which implements a spatio-temporal averaging. We propose the same strategy in tactile preprocessing, and we show preliminary results illustrated for the case of slip detection, which is certainly demanding in computing requirements. © 2006 IEEE.

Experiments on global and local adaptation to illumination conditions based on focal-plane average computation
C.M. Domínguez-Matas, F.J. Sánchez-Fernández, R. Carmona-Galán and E. Roca-Moreno
Conference - International Workshop on Cellular Nanoscale Networks and their Applications CNNA 2006
[abstract]
This paper presents some experiments with an integrating pixel with adjustable gain for adaptive image capture. The adaptation mechanism consists in regulating the exposure time according to both global and local illumination conditions. Local adaptation is based in the concurrent processing of local information in the present and previous frames. Global adaptation corrects the average integration time towards the optimum starting on the average pixel value in the previous frame. Experimental results from a prototype chip, which contains a 16x16 array of adaptive pixels, are presented. Tests results have shown that global adaptation enlarges the interframe dynamic range up to 4 decades (80dB). This image DR is limited by test setup, as part of the control scheme is implemented off-chip. Meanwhile, local adaptation produces some histogram equalization and reaches the theoretical intraframe DR enhancement of 6dB. Both adaptive mechanisms have been incorporated into an analog parallel array processor based on a multilayer CNN for image capture based on focal-plane processing.

Locust-inspired vision system on chip architecture for collision detection in automotive applications
L. Carranza, R. Laviana, S. Vargas, J. Cuadri, G. Liñán, E. Roca and A. Rodríguez-Vázquez
Conference - International Symposium on Circuits and Systems ISCAS 2006
[abstract]
This paper describes a programmable digital computing architecture dedicated to process information in accordance to the organization and operating principles of the four-layer neuron structure encountered at the visual system of Locusts. This architecture takes advantage of the natural collision detection skills of locusts and is capable of processing images and ascertaining collision threats in real-time automotive scenaRíos. In addition to the Locust features, the architecture embeds a Topological Feature Estimator module to identify and classify objects in collision course.

Vehículo-Robot para aplicaciones de Control y Visión Artificial
L. Carranza-González, E. Roca-Moreno and A. Rodríguez-Vázquez
Conference - V Jornadas de Computación Reconfigurable y Aplicaciones CEDI 2005
[abstract]
Este trabajo presenta el diseño del vehículo-robot LRC-1, ideado para aplicaciones de control y visión en tiempo real. El LRC-1 está compuesto por sistemas electrónicos y mecánicos. Los sistemas electrónicos se han basado en un microcontrolador, circuitería de control, adquisición de datos y cómputo sintetizada en lógica reconfigurable, un subsistema de comunicaciones bidireccional de radiofrecuencia, una cámara de vídeo y un transmisor de microondas. Las aplicaciones del robot son generales y actualmente se está usando como plataforma para el desarrollo de un SoC sensor-procesador para automoción. Con esa finalidad, en fase de descripción HDL se encuentran una unidad de detección temprana de colisiones inspirada en el sistema de visión del insecto langosta (Locusta migratoria) y un clasificador topológico-estadístico de objetos que en breve estarán sintetizados en lógica reconfigurable formando parte del LRC-1, junto con un sensor de imágenes CMOS de gran rango dinámico diseñado en el IMSE-CNM. Por otra parte, el sistema mecánico está compuesto por un motor eléctrico, un sistema de tracción diferencial y servomecanismos. El robot puede operar básicamente en tres modos: control manual, control automático gobernado por un ordenador y modo autónomo.

A bioinspired collision detection algorithm for VLSI implementation
J. Cuadri, G. Liñán, R. Stafford, M.S. Keil and E. Roca
Conference - Conference on Bioengineered and Bioinspired Systems II, 2005
[abstract]
In this paper a bioinspired algorithm for collision detection is proposed, based on previous models of the locust (Locusta migratoria) visual system reported by F.C. Rind and her group, in the University of Newcastle-upon-Tyne(1,2). The algorithm is suitable for VLSI implementation in standard CMOS technologies as a system-on-chip for automotive applications. The working principle of the algorithm is to process a video stream that represents the current scenaRío, and to fire an alarm whenever an object approaches on a collision course. Moreover, it establishes a scale of warning states, from no danger to collision alarm, depending on the activity detected in the current scenaRío. In the worst case, the minimum time before collision at which the model fires the collision alarm is 40 msec (1 frame before, at 25 frames per second). Since the average time to successfully fire an airbag system is 2 msec, even in the worst case, this algorithm would be very helpful to more efficiently arm the airbag system, or even take some kind of collision avoidance countermeasures. Furthermore, two additional modules have been included: a "Topological Feature Estimator" and an "Attention Focusing Algorithm". The former takes into account the shape of the approaching object to decide whether it is a person, a road line or a car. This helps to take more adequate countermeasures and to filter false alarms. The latter centres the processing power into the most active zones of the input frame, thus saving memory and processing time resources.

ACE16k based stand-alone system for real-time pre-processing tasks
L. Carranza, F. Jiménez Garrido, G. Liñán-Cembrano, E. Roca, S. Espejo-Meana and A. Rodríguez-Vázquez
Conference - Conference on VLSI Circuits and Systems II, 2005
[abstract]
This paper describes the design of a programmable stand-alone system for real time vision pre-processing tasks. The system's architecture has been implemented and tested using an ACE16k chip and a Xilinx xc4028xl FPGA. The ACE16k chip consists basically of an array of 128x128 identical mixed-signal processing units, locally interacting, which operate in accordance with single instruction multiple data (SIMD) computing architectures and has been designed for high speed image pre-processing tasks requiring moderate accuracy levels (7 bits). The input images are acquired using the optical input capabilities of the ACE16k chip, and after being processed according to a programmed algorithm, the images are represented at real time on a TFT screen. The system is designed to store and run different algorithms and to allow changes and improvements. Its main board includes a digital core, implemented on a Xilinx 4028 Series FPGA, which comprises a custom programmable Control Unit, a digital monochrome PAL video generator and an image memory selector. Video SRAM chips are included to store and access images processed by the ACE16k. Two daughter boards hold the program SRAM and a video DAC-mixer card is used to generate composite analog video signal.

A bioinspired vision chip architecture for collision detection in automotive applications
R. Laviana, L. Carranza, S. Vargas, G. Liñán and E. Roca
Conference - Conference on Bioengineered and Bioinspired Systems II, 2005
[abstract]
This paper describes the architecture and retino-topic unit of a bio-inspired vision chip intended for automotive applications. The chip contains an array of 100 x 150 sensors which are able to capture high dynamic range (HDR) images, with a programmable compressive characteristic. The chip also incorporates a mechanism for adaptation of the global exposition time to the average illumination conditions. Average values are evaluated over image areas which are programmable by the user. In addition to the HDR pixel, every retino-topic unit in the array incorporates digital memory for three 6-bit pixel values (18-bits), as required for the implementation of a bionspired computing model for collisions detection which has been developed in the framework of a multidisciplinary European research project. All processing steps are executed off-chip, though we are currently working in the design of tiny digital processors (one per column) which will allow for running the whole model on-chip in a future version of this prototype. The chip has been designed in a 0.3 5 mu m 2P-4M technology and maintains its correct operation in extreme temperature conditions (from -40 degrees C to 110 degrees C).

Tactile on-chip pre-processing with techniques from artificial retinas
R. Maldonado-López, F. Vidal-Verdú, G. Liñán, E. Roca and A. Rodríguez-Vázquez
Conference - Conference on Bioengineered and Bioinspired Systems II, 2005
[abstract]
The interest in tactile sensors is increasing as their use in complex unstructured environments is demanded, like in tele-presence, minimal invasive surgery, robotics etc. The matrix of pressure data these devices provide can be managed with many image processing algorithms to extract the required information. However, as in the case of vision chips or artificial retinas, problems arise when the array size and the computation complexity increase. Having a look to the skin, the information collected by every mechanoreceptor is not carried to the brain for its processing, but some complex pre-processing is performed to fit the limited throughput of the nervous system. This is specially important for high bandwidth demanding tasks. Experimental works report that neural response of skin mechanoreceptors encodes the change in local shape from an offset level rather than the absolute force or pressure distributions. This is also the behavior of the retina, which implements a spatio-temporal averaging. We propose the same strategy in tactile preprocessing, and we show preliminary results when it faces the detection of the slip, which involves fast real-time processing.

ACE16k-Ds: un Sistema autónomo programable para el preprocesamiento de imágenes en tiempo real
L. Carranza-González, F.J. Jimenez-Garrido, G. Liñán-Cembrano, E. Roca-Moreno, S. Espejo-Meana and A. Rodríguez-Vázquez
Conference - Jornadas de Computación Reconfigurable y Aplicaciones JCRA 2004
[abstract]
Este artículo describe un sistema electrónico autónomo y programable, denominado ACE16k-DS, que permite sensar y procesar imágenes en tiempo real. La arquitectura del sistema está basada en el chip ACE16k y en la FPGA Xc4028xl de Xilinx en la que se han sintetizado una Unidad de Control Programable de propósito específico y un generador de vídeo digital. Las imágenes son sensadas y procesadas, en modo analógico, en el chip ACE16k, siguiendo instrucciones secuenciadas por la Unidad de Control Programable. El generador de vídeo digital permite visualizar, en una pantalla TFT, las imágenes procesadas en tiempo real.

A neural model of the locust visual system for detection of object approaches with real-world scenes
M.S. Keil, E. Roca-Moreno and A. Rodríguez-Vázquez
Conference - International Conference on Visualization, Imaging, and Image Processing VIIP 2004
[abstract]
In the central nervous systems of animals like pigeons and locusts, neurons were identified which signal objects approaching the animal on a direct collision course. Unraveling the neural circuitry for collision avoidance, and identifying the underlying computational principles, is promising for building vision-based neuromorphic architectures, which in the near future could find applications in cars or planes. At the present there is no published model available for robust detection of approaching objects under real-world conditions. Here we present a computational architecture for signalling impending collisions, based on known anatomical data of the locust lobula giant movement detector (LGMD) neuron. Our model shows robust performance even in adverse situations, such as with approaching low-contrast objects, or with highly textured and moving backgrounds. We furthermore discuss which components need to be added to our model to convert it into a full-fledged real-world-environment collision detector.

ACE16k: The third generation of mixed-signal SIMD-CNN ACE chips toward VSoCs
A. Rodríguez-Vázquez, G. Liñán-Cembrano, L. Carranza, E. Roca-Moreno, R. Carmona-Galán, F. Jiménez-Garrido, R. Domínguez-Castro and S. Espejo-Meana
Journal Paper - IEEE Transactions on Circuits and Systems I-Regular Papers, vol. 51, no. 5, pp 851-863, 2004
IEEE    DOI: 10.1109/TCSI.2004.827621    ISSN: 1057-7122    » doi
[abstract]
Today, with 0.18-μm technologies mature and stable enough for mixed-signal design with a large variety of CMOS compatible optical sensors available and with 0.09-μm technologies knocking at the door of designers, we can face the design of integrated systems, instead of just integrated circuits. In fact, significant progress has been made in the last few years toward the realization of vision systems on chips (VSoCs). Such VSoCs are eventually targeted to integrate within a semiconductor substrate the functions of optical sensing, image processing in space and time, high-level processing, and the control of actuators. The consecutive generations of ACE chips define a roadmap toward flexible VSoCs. These chips consist of arrays of mixed-signal processing elements (PEs) which operate in accordance with single instruction multiple data (SIMD) computing architectures and exhibit the functional features of CNN Universal Machines. They have been conceived to cover the early stages of the visual processing path in a fully parallel manner, and hence more efficiently than DSP-based systems. Across the different generations, different improvements and modifications have been made looking to converge with the newest discoveries of neurobiologists regarding the behavior of natural retinas. This paper presents considerations pertaining to the design of a member of the third generation of ACE chips, namely to the so-called ACE16k chip. This chip, designed in a 0.35-μm standard CMOS technology, contains about 3.75 million transistors and exhibits peak computing figures of 330 GOPS, 3.6 GOPS/mm(2) and 82.5 GOPS/W. Each PE in the array contains a reconfigurable computing kernel capable of calculating linear convolutions on 3 x 3 neighborhoods in less than 1.5 μs, imagewise Boolean combinations in less than 200 ns, imagewise arithmetic operations in about 5 μs, and CNN-like temporal evolutions with a time constant of about 0.5 μs. Unfortunately, the many ideas underlying the design of this chip cannot be covered in a single paper; hence, this paper is focused on, first, placing the ACE16k in the ACE chip roadmap and, then, discussing the most significant modifications of ACE16K versus its predecessors in the family.

A versatile sensor interface for programmable vision systems-on-chip
A. Rodríguez-Vázquez, G. Liñán, E. Roca, S. Espejo and R. Dominguez-Castro
Conference - Conf. on Sensors and Camera Systems for Scientific, Industrial, and Digital Photography 2003
[abstract]
This paper describes an optical sensor interface designed for a programmable mixed-signal vision chip. This chip has been designed and manufactured in a standard 0.35mum n-well CMOS technology with one poly layer and five metal layers. It contains a digital shell for control and data interchange, and a central array of 128 x 128 identical cells, each cell corresponding to a pixel. Die size is 11.885 x 12.230mm(2) and cell size is 75.7mum x 73.3mum. Each cell contains 198 transistors dedicated to functions like processing, storage, and sensing. The system is oriented to real-time, single-chip image acquisition and processing. Since each pixel performs the basic functions of sensing, processing and storage, data transferences are fully parallel (image-wide). The programmability of the processing functions enables the realization of complex image processing functions based on the sequential application of simpler operations. This paper provides a general overview of the system architecture and functionality, with special emphasis on the optical interface.

A multimode gray-scale CMOS optical sensor for Visual computers
G. Liñán, A. Rodríguez-Vázquez, S. Espejo, R. Domínguez-Castro and E. Roca
Conference - IEEE International Workshop on Cellular Neural Networks and Their Applications CNNA 2002
[abstract]
This paper presents a new multimode optical sensor architecture for the optical interface of Visual CNN chips. The sensor offers to the user the possibility of choosing the photo-sensitive device as well as the mechanism for transducing the photogenerated charges into the correspondent pixel voltage. Both linear or logarithmic compression acquisition modes are available. This makes the sensor very suitable to be used in very different illumination conditions.

Approximate symbolic analysis of hierarchically decomposed analog circuits
O. Guerra, E. Roca, F.V. Fernandez and A. Rodríguez-Vázquez
Journal Paper - Analog Integrated Circuits and Signal Processing, vol. 31, no. 2, pp 131-145, 2002
KLUWER ACADEMIC    DOI: 10.1023/A:1015094011107    ISSN: 0925-1030    » doi
[abstract]
This paper presents a methodology for the symbolic analysis of large analog integrated circuits using a hierarchical approach. The drawbacks of previous approaches are solved by the introduction of error-controlled approximation strategies. A proper modeling methodology through the different hierarchical levels allows to combine the optimum techniques for generation of the symbolic expressions and the most efficient numerical techniques for error control. These approximation strategies together with mechanisms for partitioning and union of blocks through the hierarchy yield optimum results in terms of speed, accuracy and complexity of the symbolic results.

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