Environmental Engineering Reference
In-Depth Information
where the DC voltage gain is given by (2.5). The coefficients and
can be found by applying the procedure described in the Appendix or
through a direct analysis of the circuit. They are given by
We see that the contribution of to coefficient (which approximately
determines the first pole) can become dominant for high values of the
voltage gain,
The magnification of
is predicted by the well-
known Miller theorem.
It is worth noting that coefficient related to the (positive) zero can be
evaluated by inspection of Fig. 2.11b [MG91]. Indeed, at the complex
frequency of the zero (i.e.
the output voltage must be zero and all
the current of the controlled source,
flows through the capacitor
Thus, after equating the two currents we get
which gives the frequency of the zero.
2.7.2 Common X with a Degenerative Resistance
Consider now the common X configuration with a degenerative resistance at
node X, and its small-signal model shown in Fig. 2.12a and 2.12b,
respectively.
