 frontends and their building blocks". Past designs of telecommunication frontends show that their behavior and that of their building blocks all have some important properties in common: Their behavior is almost linear (weakly nonlinear). Here, linearity must be inter- preted in its most general, time-varying setting. They produce signals containing widely spaced time constants. This especially holds for the RF sections of, for example, wireless applications. They all produce noise, i.e. they produce signals containing random elements. Subsequent chapters in this book exploit these and other properties to construct com- pact models that allow accurate and efficient evaluation of telecom frontends and their 2.3 CONCLUSIONS building blocks. This assists us in their design and in the identification of performance bottlenecks. Finally, models should only capture relevant behavior. Irrelevant details only burden analysis and simulation without deepening a designer's understanding of the system's behavior. In communications the relevance of building-block behavioral characteris- tics -and therefore the need to incorporate them into (good) models- is measured by their impact on the system's ability to transmit information without great loss. Unfor- tunately, it turns out that few building block behavior can be neglected. This especially holds when pushing the limits of performance. Hence, one of the great challenges for CAD is to capture complex building block behavior in a manner that is as compact as possible. Chapter 3 A framework for frequency-domain analysis of linear periodically time-varying systems You may always depend on it that algebra, which cannot be translated into good English and sound common sense, is bad algebra. -William Clifford elecom frontend building blocks like mixers and PLLs are known to involve up- and downconversion of signal content. This means that signal content is trans- ferred from one periodic carrier wave (frequency band) to another. Often, these trans- fers are linear in nature: the 