Environmental Engineering Reference
In-Depth Information
where is the perimeter of the source junction, excluding the side adjacent
to the channel. Both and are capacitances per unit length.
Consequently, the source-bulk capacitance is given by the sum of (1.53),
(1.54) and (1.55), that is
The fourth capacitor in the model in Fig. 1.9 is the drain-bulk capacitor,
This is similar to the source-bulk capacitance except for the fact that the
channel does not make any contribution. Therefore equations similar to
(1.53) and (1.55) can be written as follows
and the drain-bulk capacitance results as
1.3.7
Triode Region Small Signal Model
The low frequency small signal model for a MOS in triode region is a
resistor whose value can be determined by deriving (1.39) with respect to
that is
If
is small (1.59) is often approximated by
