Noise is a fundamental problem that degrades the performance of every communications device. Noise starts at a very basic level - in the circuits within communications devices and systems. This book is a comprehensive treatment of how noise affects circuit performance. It covers practical methods for optimizing communications performance in a noisy environment. Special coverage is given to phase noise in oscillator circuits, which is a critical problem in cellular and mobile telecommunications. Software has become an indispensable tool for analyzing noise. This book gives circuit designers and software developers a solid understanding of this specialized software, so they can more effectively create noise-resistant circuitry. Noise is the basic stumbling block in creating reliable communications circuits, and this book shows engineers how to overcome this problem.