Project 1: Circuit properties of MOS transistors

Introduction: There are two types of MOS transistors, pMOS and nMOS, which are usually employed as digital switches to implement some Boolean functions. Although the MOS transistors are treated conceptually as digital devices that have logical values either “true” or “false”, they are intrinsically analog devices whose node voltage and branch current are real numbers. Thus, in order to make best use of these transistors, one has to understand the basic circuit properties of these transistors. These basic circuit properties depict the relationship between inputs and outputs in terms of branch current and node voltage and are governed by the materials used and the physical structure created to form the MOS transistors. Generally, the relationship between input and output can be specified by some equations like those found in the majority of text books. Alternatively, their relationship can be obtained by circuit simulation. The most often used tool for circuit simulation is called SPICE (Simulation Program with Integrated Circuit Emphasis). SPICE was designed in the early of 1970s at the University of California at Berkeley. Although it was originally used with emphasis to simulate the behavior of integrated circuits, it is general e nough to simulate analog circuits. In fact, it has become an i ndustry standard for analog simulation. More technical details about SPICE can be found in many books, while a history about SPICE can be found in [1].