The fundamentals of metal–oxide–semiconductor (MOS) transistors are introduced in this chapter. Basic structure of an MOS transistor is introduced along with the concept of enhancement- and depletion-mode MOS transistors. The behavior of MOS transistors is explained with the help of the fluid model, which helps to visualize the operation of MOS transistors without going into the details of device physics. Then, the three modes of operation of an MOS transistor, namely accumulation, depletion, and inversion, are introduced. The electrical characteristics of MOS transistors are explained in detail by deriving the expression of drain current. The threshold voltage and transconductance of MOS transistors are defined, and their dependence on various parameters is highlighted. The body effect and channel-length modulation effect are explained. Use of MOS transistors to realize transmission gate and to use it as a switch is discussed in detail.
KeywordsFluid model Threshold voltage Transconductance Cutoff region Nonsaturated region Saturated region Figure of merit Channel-length modulation effect Body effect MOS switch Transmission gate
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