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Enhancing Variation-aware Analog Circuits Sizing

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Enhancing Variation-aware Analog Circuits Sizing

Lahiouel, Ons (2017) Enhancing Variation-aware Analog Circuits Sizing. PhD thesis, Concordia University.

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Abstract

Today's analog design and verification face significant challenges due to circuit complexity and short time-to-market windows. Moreover, variations in design parameters have an adversely impact on the correctness and performance of analog circuits. Circuit sizing consists in determining the device sizes
and biasing voltages and currents such that the circuit satisfies its specifications. Traditionally, analog circuit sizing has been carried out by optimization-based methods, which of course will still be
important in the future. Unfortunately, these techniques cannot guarantee an exhaustive coverage of the design search space and hence, are not able to ensure the non-existence of higher quality design solutions. The sizing problem becomes more complicated and computationally expensive under
design parameters fluctuation. Indeed, existing yield analysis methods are computationally expensive and still encounter issues in problems with a high-dimensional process parameter space.
In this thesis, we present new approaches for enhancing variation-aware analog circuit sizing. The circuit sizing problem is encoded using nonlinear constraints. A new algorithm using Satisfiability
Modulo Theory (SMT) solving techniques exhaustively explores the analog design space and computes a continuous set of feasible sizing solutions. Next, a yield optimization stage aims to select the candidate design solution with the highest yield rate in the presence of process parameters variation.
For this purpose, a novel method for the computation of parametric yield is proposed. The method combines the advantages of sparse regression and SMT solving techniques. The key idea is to characterize the failure regions as a collection of hyperrectangles in the parameters space. The yield
estimation is based on a geometric calculation of probabilistic volumes subtended by the located hyperrectangles. The method can provide very large speed-up over Monte Carlo methods, when a high prediction accuracy is required. A new approach for improving analog yield optimization is also proposed. The optimization is performed in two steps. First, a global optimization phase samples the most potential optimal sub-regions of the feasible design space. The global search locates a design
point near the optimal solution. Second, a local optimization phase uses the near optimal solution as a starting point. Also, it constructs linear interpolating models of the yield to explore the basin of convergence and to reach the global optimum. We illustrate the efficiency of the proposed methods on various analog circuits. The application of the yield analysis method on an integrated ring oscillator and a 6T static RAM proves that it is suitable for handling problems with tens of process parameters
and can provide speedup of 5X-2000X over Monte Carlo methods. Furthermore, the application of our yield optimization methodology on the examples of a two-stage amplifier and a cascode amplifier shows that our approach can achieve higher quality in analog synthesis and unrivaled coverage of the analog design space when compared to traditional optimization techniques.

Divisions:Concordia University > Gina Cody School of Engineering and Computer Science > Electrical and Computer Engineering
Item Type:Thesis (PhD)
Authors:Lahiouel, Ons
Institution:Concordia University
Degree Name:Ph. D.
Program:Electrical and Computer Engineering
Date:April 2017
Thesis Supervisor(s):Tahar, Sofiene
ID Code:982499
Deposited By: ONS LAHIOUEL
Deposited On:31 May 2017 18:34
Last Modified:18 Jan 2018 17:55
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