This chapter describes how to apply estimation analysis to various systems. We start by discussing phase locked loops (PLL) and show how one can model them simply. One of the key properties of PLLs are their jitter performance. A definition of jitter is followed by a way to model the concept using simple noise sources. Next voltage controlled oscillators are described in some detail and various ways to model them using estimation analysis. This is followed by a design example of a VCO where the lessons from the previous chapters are incorporated including design examples. We then proceed to a discussion of analog-to-digital converters, which are described through some simple models. By incorporating design examples from the previous chapters a full straight flash ADC is implemented, where the ADC performance criteria are applied. This is another example of howthrough estimation analysis one can arrive at a good starting point for fine-tuning of a circuit using a simulator. Sampling methods, such as voltage sampling and charge sampling, are discussed following the estimation analysis method. The chapter concludes with exercises.