chapter  2
76 Pages

- MOS Transistor Properties

To make the material accessible also to readers with little back-ground in electron-

ics, we start reviewing a few concepts of semiconductor physics that are essential to

understand the working principles of the MOSFET. A broader treatment of these no-

tions can be found in standard textbooks on semiconductor devices, such as [1] and [2].

In the central part of the chapter we examine the most important terms contributing

to the transistor threshold voltage and we derive the key relationships between the

device current and the voltages applied to its terminals. We then study the parasitic

capacitance affecting the MOSFET behavior at high frequency and we introduce the

small signal equivalent circuits commonly employed in hand circuit analysis. In this

treatment, we make use of a very simplified description of the MOSFET physics,

allowing to derive analytical equations with a minimum of mathematical complexity.

We are thus forced to neglect fundamental effects that play a major role in devices

fabricated in modern deep submicron CMOS technologies. These aspects are dealt

with in the last part of the chapter.