Continuous-time analog circuits for statistical signal processing

Thesis (Ph. D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2003.Vita.Includes bibliographical references (p. 205-209).This thesis proposes an alternate paradigm for designing computers using continuous-time analog circuits. Digital computation sacrifices continuous degrees of freedom. A principled approach to recovering them is to view analog circuits as propagating probabilities in a message passing algorithm. Within this framework, analog continuous-time circuits can perform robust, programmable, high-speed, low-power, cost-effective, statistical signal processing. This methodology will have broad application to systems which can benefit from low-power, high-speed signal processing and offers the possibility of adaptable/programmable high-speed circuitry at frequencies where digital circuitry would be cost and power prohibitive. Many problems must be solved before the new design methodology can be shown to be useful in practice: Continuous-time signal processing is not well understood. Analog computational circuits known as "soft-gates" have been previously proposed, but a complementary set of analog memory circuits is still lacking. Analog circuits are usually tunable, rarely reconfigurable, but never programmable. The thesis develops an understanding of the convergence and synchronization of statistical signal processing algorithms in continuous time, and explores the use of linear and nonlinear circuits for analog memory. An exemplary embodiment called the Noise Lock Loop (NLL) using these design primitives is demonstrated to perform direct-sequence spread-spectrum acquisition and tracking functionality and promises order-of-magnitude wins over digital implementations. A building block for the construction of programmable analog gate arrays, the "soft-multiplexer" is also proposed.by Benjamin Vigoda.Ph.D

A nonlinear dynamic system for spread spectrum code acquisition

Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 1999.Includes bibliographical references (leaves 88-89).Nonlinear differential equations and iterated maps can perform any computation. Sometimes, the most difficult part of performing a useful computation, however, is writing the program. Furthermore, in practice, we often need to build special purpose computing hardware suited to run a particular program. Nonlinear dynamics provides a novel and useful language for constructing "algorithms" and "computer architectures." We apply the language of nonlinear dynamics to solve a fast coding problem which has previously been implemented by a Digital Signal Processor chip in digital wireless receivers. We eventually hope to produce a novel physical system which exhibits the nonlinear dynamics we require, thereby creating one of the first nonlinear dynamic systems engineered to perform a practical computation. This system, called an Analog Feedback Shift Register (AFSR), should be a faster, more reliable, less expensive, and lower power Spread Spectrum (SS) code acquisition system for wireless receivers. A prohibitive factor in creating ubiquitous short range, digital radio transceivers is the difficulty and expense of creating a mechanism for locking onto the incoming Spread Spectrum code sequence. AFSR is also potentially useful in other applications where low cost, low power channel sharing or addressing is required, for example in wireless auto-identification tags.by Benjamin William Vigoda.S.M