Environmental Engineering Reference
In-Depth Information
The resulting high-frequency small signal model is depicted in Fig. 1.12
1.3.8
Cutoff Region Small Signal Model
In the cutoff region the resistance
is assumed to be infinite so the
equivalent model is purely capacitive.
Since the channel is not present, both
and
are due only to the
overlap contribution, that is
Source-bulk and drain-bulk capacitances are similar to those given in
(1.62) with the difference that the channel does not make any contribution,
that is
The fact that no channel exists, generates a new capacitor, which
connects the gate and the bulk. Its value is given by the oxide capacitance
multiplied by the device area, that is
