Synthesis of all-digital delay lines

© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other worksThe synthesis of delay lines (DLs) is a core task during the generation of matched delays, ring oscillator clocks or delay monitors. The main figure of merit of a DL is the fidelity to track variability. Unfortunately, complex systems have a great diversity of timing paths that exhibit different sensitivities to static and dynamic variations. Designing DLs that capture this diversity is an ardous task. This paper proposes an algorithmic approach for the synthesis of DLs that can be integrated in a conventional design flow. The algorithm uses heuristics to perform a combinatorial search in a vast space of solutions that combine different types of gates and wire lengths. The synthesized DLs are (1) all digital, i.e., built of conventional standard cells, (2) accurate in tracking variability and (3) configurable at runtime. Experimental results with a commercial standard cell library confirm the quality of the DLs that only exhibit delay mismatches of about 1% on average over all PVT corners.Peer ReviewedPostprint (author's final draft

State encoding of asynchronous controllers using pseudo-boolean optimization

State encoding of asynchronous controllers is a challenging problem that faces a vast space of solutions. Subtle differences in the insertion of signals may result in significant variations in the complexity of the logic. This paper proposes a novel approach that models the encoding problem as Pseudo-Boolean formula. A cost function that estimates the complexity of the logic is incorporated, where the estimator of essential literals becomes one of the most important terms of the function. The new approach has been tested in 175 benchmarks with encoding conflicts, including 127 four-phase latch controllers. The presence of logic estimators in the formula contributes to an average reduction of 43% in literals when compared to a plain SAT version of the problem, at the expense of a longer runtime. When comparing to the region-based approach in petrify, an average reduction of 14% in literals is obtained.Peer ReviewedPostprint (author's final draft

Waveform Transition Graphs: a designer-friendly formalism for asynchronous behaviours

The paper proposes a new formal model for describing asynchronous behaviours involving the interplay of causality, concurrency and choice. The model is called Waveform Transition Graphs. Its main aim is simplifying the learning process for industrial engineers in accessing powerful synthesis tools provided for Signal Transition Graphs by sacrificing some of the expressive power of the latter. This formalism is developed based on feedback from engineers of Dialog Semiconductor.Peer ReviewedPostprint (author's final draft

Ring oscillator clocks and margins

How much margin do we have to add to the delay lines of a bundled-data circuit? This paper is an attempt to give a methodical answer to this question, taking into account all sources of variability and the existing EDA machinery for timing analysis and sign-off. The paper is based on the study of the margins of a ring oscillator that substitutes a PLL as clock generator. A timing model is proposed that shows that a 12% margin for delay lines can be sufficient to cover variability in a 65nm technology. In a typical scenario, performance and energy improvements between 15% and 35% can be obtained by using a ring oscillator instead of a PLL. The paper concludes that a synchronous circuit with a ring oscillator clock shows similar benefits in performance and energy as those of bundled-data asynchronous circuits.Peer ReviewedPostprint (author's final draft

Synthesis of variability-tolerant circuits with adaptive clocking

Improvements in circuit manufacturing have allowed, along the years, increasingly complex designs. This has been enabled by the miniaturization that circuit components have undergone. But, in recent years, this scaling has shown decreasing benefits as we approach fundamental limits. Furthermore, the decrease in size is nowadays producing an increase in variability: unpredictable differences and changes in the behavior of components. Historically, this has been addressed by establishing guardband margins at the design stage. Nonetheless, as variability grows, the amount of pessimism introduced by these margins is taking an ever-increasing cost on performance and power consumption. In recent years, several approaches have been proposed to lower the impact of variability and reduce margins. One such technique is the substitution of a classical PLL clock by a Ring Oscillator Clock. The design of the Ring Oscillator Clock is done in such a way that its variability is highly correlated to that of the circuit. One of the contributions of this thesis is in the automatic design of such circuits. In particular, we propose a novel method to design digital delay lines with variability-tracking properties. Those designs are also suitable for other purposes, such as bundled-data circuits or performance monitors. The advantage of the proposed technique is based on the exclusive use of cells from a standard cell library, which lowers the design cost and complexity. The other focus of this thesis is on state encoding for asynchronous controllers. One of the main properties of asynchronous circuits is their ability to, implicitly, work under variable conditions. In the near future, this advantage might increase the relevance of this class of circuits. One of the hardest stages for the synthesis of these circuits is the state encoding. This thesis presents a SAT-based algorithm for solving the state encoding at the state level. It is shown, by means of a comprehensive benchmark suite, that results obtained by this technique improve significantly compared to results from similar approaches. Nonetheless, the main limitation of techniques at the state level is the state explosion problem, to which the sequential modeling of concurrency is often subject to. The last contribution of this thesis is a method to process asynchronous circuits in order to allow the use of state-based techniques for large instances. In particular, the process is divided into three stages: projection, signal insertion and re-composition. In the projection step, the behavior of the controller is simplified until the signal insertion can be performed by state-based techniques. Afterwards, the re-composition generalizes the insertion of the signal into the original controller. Experimental results show that this process enables the resolution of large controllers, in the order of 10 6 states, by state-based techniques. At the same time, only a minor impact in solution quality is observed, preserving one of the main advantages for state-based approaches.A lo largo de los años, mejoras en la fabricación de circuitos han permitido diseños cada vez más complejos. Esta tendencia, que ha tenido lugar gracias a la miniaturización de los componentes que forman estos circuitos, recientemente está mostrando beneficios decrecientes a medida que nos acercamos a ciertas limitaciones fundamentales. Además de estos beneficios decrecientes, la reducción en tamaño está produciendo un aumento, cada vez mayor, en la variabilidad: diferencias impredecibles y cambios en el comportamiento de los componentes. Esto se ha compensado históricamente con el uso de márgenes de seguridad en la fase de diseño. No obstante, a medida que la variabilidad crece, la cantidad de pesimismo que estos márgenes introducen está afectando significativamente el coste en rendimiento y consumo energético. En los últimos años se han propuesto diferentes técnicas para limitar el impacto de la variabilidad y reducir márgenes de seguridad. Una de estas técnicas consiste en substituir un reloj PLL clásico por un Ring Oscillator Clock. El diseño de un Ring Oscillator Clock se realiza de manera que su variabilidad este altamente correlacionada con la del circuito. Una de las contribuciones de esta tesis consiste en el diseño automático de estos relojes. Concretamente, se propone un nuevo método para diseñar líneas de retardo digitales (digital delay lines) que tengan como propiedad la capacidad de imitar la variabilidad de un circuito dado. Estos diseños son también apropiados para otros propósitos, tal y como circuitos con ?bundled-data? o monitorizadores de rendimiento. La ventaja del método propuesto con respecto a otras técnicas similares radica en el uso exclusivo de celdas provenientes de una librería de celdas estándar, lo que reduce considerablemente el coste de diseño y su complejidad. Por otro lado, esta tesis también se centra en la codificación de estados de circuitos asíncronos. Una de las principales propiedades de estos circuitos reside en su capacidad implícita para trabajar bajo condiciones de variabilidad. Es previsible que, en un futuro próximo, esta ventaja se vuelva aún más relevante. La síntesis de circuitos asíncronos consta de varias etapas, una de las cuales es la codificación de estados. Este trabajo presenta un algoritmo basado en SAT que permite resolver la codificación de estados a nivel de estado. Mediante el uso de un exhaustivo banco de pruebas, esta tesis muestra como resultados obtenidos por esta técnica mejoran significativamente en comparación con otros métodos similares. A pesar de ello, técnicas que trabajan a nivel de estado tienen como principal limitación el problema conocido como "explosión de estados" que aparece habitualmente cuando se modelan elementos concurrentes de manera secuencial. Así pues, la última contribución de esta tesis es la propuesta de un método para procesar circuitos asíncronos de manera que técnicas a nivel de estado sean usables para instancias grandes. En concreto, el proceso está dividido en tres fases: proyección, inserción de señal y re-composición. En la etapa de proyección, el comportamiento del controlador es simplificado suficientemente como para que la inserción de la señal se pueda realizar con técnicas a nivel de estado. A continuación, la re-composición generaliza esta inserción en el controlador original. Resultados experimentales muestran que este proceso permite la resolución de grandes controladores, del orden de 10^6 estados, mediante el uso de técnicas a nivel de estado. Al mismo tiempo, solo se observa un impacto mínimo en la calidad de las soluciones, preservando una de las mayores ventajas de los métodos a nivel de estado

Synthesis of timing paths with delays adaptable to integrated circuit variability

This project proposes to substitute the Clock of a circuit for a Ring Oscillator. This Ring Oscillator is designed to be susceptible to variability in the same way than the rest of the system, allowing to drastically reduce variability guard band margins at design stage

Assessing the Risk of Spatial Spreading of Diseases in Hospitals

In recent years, the transmission of healthcare-associated infections (HAIs) has led to substantial economic loss, extensive damage, and many preventable deaths. With the increasing availability of data, mathematical models of pathogen spreading in healthcare settings are becoming more detailed and realistic. Here, we make use of spatial and temporal information that has been obtained from healthcare workers (HCWs) in three hospitals in Canada and generate data-driven networks that allow us to realistically simulate the spreading of an airborne respiratory pathogen in such settings. By exploring in depth the dynamics of HAIs on the generated networks, we quantify the infection risk associated with both the spatial units of the hospitals and HCWs categorized by their occupations. Our findings show that the "inpatient care" and "public area" are the riskiest categories of units and "nurse" is the occupation at a greater risk of getting infected. Our results provide valuable insights that can prove important for measuring risks associated with HAIs and for strengthening prevention and control measures with the potential to reduce transmission of infections in hospital settings

Networks, Epidemics and Collective Behavior: from Physics to Data Science

In the final quarter of the XX century the classical reductionist approach that had been driving the development of physics was questioned. Instead, it was proposed that systems were arranged in hierarchies so that the upper level had to convey to the rules of the lower level, but at the same time it could also exhibit its own laws that could not be inferred from the ones of its fundamental constituents. This observation led to the creation of a new field known as complex systems. This novel view was, however, not restricted to purely physical systems. It was soon noticed that very different systems covering a huge array of fields, from ecology to sociology or economics, could also be analyzed as complex systems. Furthermore, it allowed physicists to contribute with their knowledge and methods in the development of research in those areas. In this thesis we tackle problems covering three areas of complex systems: networks, which are one of the main mathematical tools used to study complex systems; epidemic spreading, which is one of the fields in which the application of a complex systems perspective has been more successful; and the study of collective behavior, which has attracted a lot of attention since data from human behavior in huge amounts has been made available thanks to social networks. In fact, data is also the main driver of our discussion of the other two areas. In particular, we use novel sources of data to challenge some of the classical assumptions that have been made in the study of networks as well as in the development of models of epidemic spreading. In the case of networks, the problem of null models is addressed using tools coming from statistical physics. We show that anomalies in networks can be just a consequence of model oversimplification. Then, we extend the framework to generate contact networks for the spreading of diseases in populations in which both the contact structure and the age distribution of the population are important. Next, we follow the historical development of mathematical epidemiology and revisit the assumptions that were made when there was no data about the real behavior of this kind of systems. We show that one of the most important quantities used in this kind of studies, the basic reproduction number, is not properly defined for real systems. Similarly, we extend the theoretical framework of epidemic spreading on directed networks to multilayer systems. Furthermore, we show that the challenge of incorporating data to models is not only restricted to the problem of obtaining it, but that it is also really important to be aware of its characteristics to do it properly.Lastly, we conclude the thesis studying two examples of collective behavior using data extracted from online systems. We do so using techniques that were originally developed for other purposes, such as earthquake prediction. Yet, we demonstrate that they can also be used to study this new type of systems. Furthermore, we show that, despite their unique characteristics, they possess properties similar to the ones that have been observed in the offline world. This not only means that modern societies are intertwined with the online world, but it also signals that if we aim to understand socio-technical systems a holistic approach, as the one proposed by complex systems, is indispensable.<br /

Optimización de un motor de combustible sólido tipo KNSB para cohetería experimental

Este artículo muestra de manera general el proceso de optimización para un motor de combustible sólido basado en una mezcla de Nitrato de Potasio y Sorbitol (KNSB) con una configuración de grano tipo Bates, generalmente usada en cohetería experimental de baja potencia. En este proceso, el máximo empuje es seleccionado para la menor cantidad de masa requerida, indicando el tamaño estimado del motor más eficiente mediante múltiples iteraciones, donde a partir de un rango inicial de valores de empuje se calcula la cantidad de masa de propelente necesaria. Adicionalmente, a través de la estimación gráfica de la segunda derivada de la relación de empuje con respecto a la masa, se establece un límite de eficiencia donde el aumento de la cantidad de propelente debe representar al menos un incremento superior al 0.5% en la pendiente de dicha relación. Finalmente se propone un modelo con el ensamble del motor esquematizado mediante software de diseño asistido por computador

Notes on Dependent Attributes in TOPSIS

AbstractTOPSIS is a multicriteria decision making technique based on the minimization of geometric distances that allows the ordering of compared alternatives in accordance with their distances from the ideal and anti-ideal solutions. The technique, that usually measures distances in the Euclidean norm, implicitly supposes that the contemplated attributes are independent. However, as this rarely occurs in practice, it is necessary to adapt the technique to the new situation. Using the Mahalanobis distance to incorporate the correlations among the attributes, this paper proposes a TOPSIS extension that captures the dependencies among them, but, in contrast to the Euclidean distance, does not require the normalization of the data. Results obtained by the new proposal have been compared by means of the three Minkowski norms most commonly employed for the calculation of distance: (i) the Manhattan distance (p=1); (ii) the Euclidean distance (p=2); and (iii) the Tchebycheff distance (p=∞). Furthermore, simulation techniques are used to analyse the connection between the TOPSIS results traditionally obtained with the Euclidean distance and those obtained with the Mahalanobis distance