A rigorous mathematical treatment of noise is lengthy and complex and in this
chapter we provide only a concise overview of the topic. In the first section, the key
concepts are introduced, while in the second one the expressions of thermal and shot
noise spectral densities are derived. The main noise sources found in MOS devices
are reviewed in section 3 and examples of noise calculations in practical circuits are
discussed in section 4. The concept of optimumnoise filtering is introduced in section
5. A more detailed coverage of the matter can be found in [5-8].