Basic MOSFET Circuits

A MOSFET transistor is a four-terminal semiconductor electronic device that can operate as a voltage-controlled current source. The current from the source to drain regions is controlled by the voltage of a gate terminal that resides between these regions over an oxide layer. The source and drain regions lie inside substrate regions, biased so that all p–n junctions are reverse-biased. In a turned-on transistor, a thin channel, which is an inverted substrate region located under the gate oxide, is created under the gate region whenever the gate voltage exceeds a certain threshold voltage. The channel provides electrical connection between the source and drain regions. Systems-on-a-chip consist of a large number of interconnected MOSFET transistors for digital and analog electronic applications. The chapter covers MOSFET DC circuits, simple small-signal voltage amplifiers, and MOSFET current mirror current sources. An important ADS concept, introduced in this chapter, is that of model cards used to create a variety of MOSFET Level 1 models having different levels of complexity, allowing transistor second-order effects to be studied comparatively.