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PhD in Computing Thesis Defense by Lucas Machado
February 21, 2019 @ 10:30 am - 11:30 am
Date: February 21, 2019, time: 10:30 h
Sala d’actes Sala de Juntes. Building B6. Campus Nord. UPC
Title: Logic Decomposition and Adaptive Clocking for the Optimization of Digital Circuits
Doctoral student: Lucas Machado
Advisor: Dr. Jordi Cortadella
Over the course of 60 years, since the invention of the integrated circuit (IC), exponential improvements in cost, performance and power consumption were observed. Such advances have been strongly linked with the continuous reduction of the dimensions in manufactured ICs, but this trend has shown decreasing benefits as fundamental limits are reached.
Notice that such tiny devices have increased variability, which generates unpredictable variations in the behavior of the manufactured devices. These uncertainties are typically addressed by defining margins on the clock period, estimated during the design phase. However, the overly conservative margins produce significant degradations in performance.
Additionally, the evolution that enabled circuits with increasingly higher density of components, also resulted in an extremely complex IC design. At every step, electronic design automation (EDA) tools are challenged to handle this increasing complexity, requiring more powerful techniques to comply with the specification constraints within an affordable runtime.
This thesis investigates alternatives in order to improve power, performance, area, and cost, using established IC manufacturing technologies. Advances in EDA are proposed in three distinct topics: area minimization using Boolean methods, area and delay reduction for designs based on field-programmable gate array (FPGA), and an alternative clocking scheme to reduce timing margins.
The first contribution consists of a technology-independent method for area minimization of combinational logic. Local optimization is applied on and-inverter graphs (AIGs), performing multi-output Boolean decomposition using two-literal divisors, targeting node count reduction.
The second contribution regards two methods targeting technology mapping of FPGAs. On one hand, a functional decomposition approach, which uses the support size as cost function, exploring the inherent characteristics of FPGAs. On the other hand, an approach for recursive remapping, which reduces the structural bias of the subject graph, uses the mapping results as cost function, and obtains significant reductions in area and delay.
The third contribution evaluates the dynamic variability mitigation and simplification of power delivery networks (PDNs) using an adaptive clocking scheme based on ring oscillator clocks (ROCs). The impact of the PDN parameters and ROC location is investigated, showing potential improvements in performance, leakage power and cost.