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Author: Moreira de Passos , Fabio
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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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