Switches and muliplexers are integral building blocks in the telecommunications industry, which is growing at an exponential rate. In this industry, it is important for designers to understand the functional difference between analog and digital devices. This document provides an overview of how analog and digital devices differ in functionality based on whether a standard NMOS or a pass gate configuration is used. A designer can choose one or both of these configurations depending on design requirements. If a simple HIGH (VOH) or LOW (VOL) signal is required, a designer can use either of these configurations. If a sine wave is required, then the designer should choose the analog configuration. The following subjects will be discussed in this document: the difference between analog and digital switches, how NMOS switches will not provide analog rail-to-rail outputs, and how an analog pass gate device will work with any voltage between VSS and VCC.