ted by the growing speeds and decreasing prices of these programmable devices. However, in each system, there are building blocks that are hard to make highly programmable. Analog circuits are typical exam- ples of such blocks. They are small but important parts that are present in almost any system. Systems or subsystems are said to be analog if it is not possible to make abstraction of the continuous nature of the system's input, output and internal signals. Within the overall application, the analog part typically constitutes the interface with the physi- cal world, e.g. the frontend of a telecommunication system. Due to their continuous nature, analog systems are highly complex in their design. As such, they require a dis- proportional fraction of the overall design time as compared to the complexity of the signal processing operations they implement. Moreover, they tend to be highly sen- sitive to all kinds of process parasitics, like substrate couplings and mismatch. Still, these analog subsystems must be made first time right. If not, they become bottlenecks in getting the overall system to market in time. Productivity and reliability demands like this press for structured analog design methods. 1.1.3 Structured analog design As is the case for any design process, analog design will always require creative inputs, e.g. some ground-breaking idea for a new system or circuit topology. However, this does not imply that the design process can not be structured. A structured design flow 1.1 STRUCTURED ANALYSIS, A KEY TO SUCCESSFUL DESIGN Interface specification Create system implementation (synthesis) Adapt and/or complete interface specifications System implementation System Building block Adapt Toplogy interface specifications implementation Analysis results Perform analysis Figure 1.3: A structured design flow implements system realization in a hi- erarchical manner. At each stage, the initial specifications are converted to a candidate implementation. An implementation consists an interconnection of building