Date of Award

1-1-2012

Document Type

Campus Access Dissertation

Department

Electrical Engineering

First Advisor

Paul G Huray

Abstract

Printed Circuit Boards (PCBs) provide the primary signal interconnect medium in current computer systems. Silicon transistor technology is advancing at a pace predicted by Moore's law. Moving data faster on PCBs will thus need increased signal rates in the near future; signaling rates on PCB materials will need to reach the Multi-Gigabits regime (over 25GT/s). Increasing data-rates requires faster signal rise times and pushing the interconnect bandwidth demand to the millimeter wave regime. As the Frequency content of the signals increase, micro scale structures of an interconnect medium, such as the woven glass fabric reinforcements of PCB's, can negatively influence the performance of PCB signal transmission.

The nature of micro-scale periodic structures of PCB materials is not well understood, especially at millimeter wavelength frequencies required to transmit high-speed digital signals. Researchers have observed unexplained resonances in high frequency measurements taken on PCB traces. Designers often ignore these resonances and do not take them in to account in present high-speed system designs. Empirically derived techniques such as rotated artwork to mitigate fiber weave skew effects fail to account for transmission power losses due to periodic variation in transmission media.

This work will explain the Electromagnetic wave propagation in a micro-scale periodic dielectric medium and its impact on multi-gigabit digital signal transmission. Special attention will be given to periodic loading effects due to glass fiber weaves in a PCB. We have treated fiber weave fabrics as a periodic dielectric medium and derived analytical equations based on Floquet's periodic wave propagation theory to predict additional transmission losses in certain frequency bands known as Brillouin zones. Complex fiberweave geometries including sinusoidal cross-sections were addressed in the form of Mathieu's differential equations and solutions using small-perturbation method under appropriate assumptions. Theoretical models were matched to numerical EM simulation results derived from accurate 3D fiber weave models. High Frequency power loss measurements were taken using a state-of-the-art Vector Network Analyzer on test boards and matched to simulations and theoretical model. System eye-margin degradation due to periodic effects was also analyzed and mitigation techniques are recommended.

One of the primary outcomes of this work is analytical formulae to predict the periodic loss profile of a given periodic structure geometry. This work will complement high-speed Signal Integrity simulation model creation by enabling faster analytical algorithms to account and correct for an additional periodic loss mechanism.

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