
Principles of Analog Electronics
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12.1.2 Small-Signal Model
Similarly to what we have seen for the BJT, the AC response of the MOSFET also
can be expressed in terms of two-port small-signal equivalent circuit. The choice
can be among the six different topologies already discussed (Section 5.4.1 in
Chapter5), all of which are possible and useful. But, it is better to select the topol-
ogy that better ties with the theory of the device. In particular, for the input loop,
the presence of the oxide prevents any current owing through the gate, which can
be considered an open circuit. For the output loop transconductance g
m
imposes
the presence ...