ned by the requirement that the principle of superposition holds. This is a general and abstract requirement that is approximately satisfied by systems ranging from a single-stage am- plifier to a complete receiver frontend. However, it can be exploited to construct some dedicated methods useful for the analysis linear system behavior. All these methods have in common that they only rely on superposition for their results to be valid. They can be further refined by taking even more system-specific information into account, e.g time-invariance, as in filters, or periodic time-variance, as in mixers. The extra information can be exploited to speed up analysis. Moreover, by exploiting system- specific information, results can often be presented in a way that is simpler to interpret. THIS WORK Linear Systems Time-Invariant Systems Linear Periodically Time-Vaying Systems Filters Amplifiers Phase-Locked Loops Mixers Leapfrog Biquad Gilbert Cell Linear Mixer simulation Figure 1.4: Structured analysis requires a hierarchical classification of sys- tems according to their behavioral properties and/or implementation. However, results obtained in this manner are only valid for a (more) limited class of systems. The starting point for a structured approach towards analysis requires gathering all a priori information that one has on the application at hand2. This information is used to locate the application's position within our classification of systems and circuits, e.g. the tree in Fig. 1.4. This way, suitable theory and methods for analyzing the application are identified as they are tied to the class or classes of systems to which the application belongs. Often, methods can be further refined by taking more application-specific information into account. This approach promotes the analysis of a particular system by using techniques that, initially, were developed to deal with a completely different application. Furthermore, it supports a transfer of knowledge between different areas of science by making people recognize 