A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Chaotic Oscillations in CMOS Integrated Circuits(2013) Park, Myunghwan; Lathrop, Daniel P; Rodgers, John C; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Chaos is a purely mathematical term, describing a signal that is aperiodic and sensitive to initial conditions, but deterministic. Yet, engineers usually see it as an undesirable effect to be avoided in electronics. The first part of the dissertation deals with chaotic oscillation in complementary metal-oxide-semiconductor integrated circuits (CMOS ICs) as an effect behavior due to high power microwave or directed electromagnetic energy source. When the circuit is exposed to external electromagnetic sources, it has long been conjectured that spurious oscillation is generated in the circuits. In the first part of this work, we experimentally and numerically demonstrate that these spurious oscillations, or out-of-band oscillations are in fact chaotic oscillations. In the second part of the thesis, we exploit a CMOS chaotic oscillator in building a cryptographic source, a random number generator. We first demonstrate the presence of chaotic oscillation in standard CMOS circuits. At radio frequencies, ordinary digital circuits can show unexpected nonlinear responses. We evaluate a CMOS inverter coupled with electrostatic discharging (ESD) protection circuits, designed with 0.5 μm CMOS technology, for their chaotic oscillations. As the circuit is driven by a direct radio frequency injection, it exhibits a chaotic dynamics, when the input frequency is higher than the typical maximum operating frequency of the CMOS inverter. We observe an aperiodic signal, a broadband spectrum, and various bifurcations in the experimental results. We analytically discuss the nonlinear physical effects in the given circuit : ESD diode rectification, DC bias shift due to a non-quasi static regime operation of the ESD PN-junction diode, and a nonlinear resonant feedback current path. In order to predict these chaotic dynamics, we use a transistor-based model, and compare the model's performance with the experimental results. In order to verify the presence of chaotic oscillations mathematically, we build on an ordinary differential equation model with the circuit-related nonlinearities. We then calculate the largest Lyapunov exponents to verify the chaotic dynamics. The importance of this work lies in investigating chaotic dynamics of standard CMOS ICs that has long been conjectured. In doing so, we experimentally and numerically give evidences for the presence of chaotic oscillations. We then report on a random number generator design, in which randomness derives from a Boolean chaotic oscillator, designed and fabricated as an integrated circuit. The underlying physics of the chaotic dynamics in the Boolean chaotic oscillator is given by the Boolean delay equation. According to numerical analysis of the Boolean delay equation, a single node network generates chaotic oscillations when two delay inputs are incommensurate numbers and the transition time is fast. To test this hypothesis physically, a discrete Boolean chaotic oscillator is implemented. Using a CMOS 0.5 μm process, we design and fabricate a CMOS Boolean chaotic oscillator which consists of a core chaotic oscillator and a source follower buffer. Chaotic dynamics are verified using time and frequency domain analysis, and the largest Lyapunov exponents are calculated. The measured bit sequences do make a suitable randomness source, as determined via National Institute of Standards and Technology (NIST) standard statistical tests version 2.1.Item Application of Chaotic Synchronization and Controlling Chaos to Communications(2005-04-19) Dronov, Vasily; Ott, Edward; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis addresses two important issues that are applicable to chaotic communication systems: synchronization of chaos and controlling chaos. Synchronization of chaos is a naturally occurring phenomenon where one chaotic dynamical system mimics dynamical behavior of another chaotic system. The phenomenon of chaotic synchronization is a popular topic of research, in general, and has attracted much attention within the scientific community. Controlling chaos is another potential engineering application. A unique property of controlling chaos is the ability to cause large long-term impact on the dynamics using arbitrarily small perturbations. This thesis is broken up into three chapters. The first chapter contains a brief introduction to the areas of research of the thesis work, as well as the summaries the work itself. The second chapter is dedicated to the study of a particular situation of chaotic synchronization which leads to a novel structure of the basin of attraction. This chapter also develops theoretical scalings applicable to these systems and compares results of our numerical simulations on three different chaotic systems. The third chapter consists or two logically connected parts (both of them study chaotic systems that can be modeled with delayed differential equations). The first and the main part presents a study of a chaotically behaving traveling wave tube, or TWT, with the objective of improving efficiency of satellite communication systems. In this work we go through an almost complete design cycle, where, given an objective, we begin with developing a nonlinear model for a generic TWT; we then study numerically the dynamics of the proposed model; we find conditions where chaotic behavior occurs (we argue that TWT in chaotic mode could be more power efficient); then we use the idea of controlling chaos for information encoding; we support the concept with numerical simulations; and finally analyze the performance of the proposed chaotic communication system. The second part of this chapter describes an experiment with a pair of electronic circuits modeling the well-known Mackey-Glass equation. An experiment where human voice was encoded into chaotic signal had been conducted which showed a possibility of engineering application of chaos to secure communications.