Environmental Engineering Reference
In-Depth Information
which is lastly approximated by
if
Observe, as a special
case, that if
equals
is approximated by
Finally, the voltage gain is
The above discussion is helpful in developing a simple model of the
configuration considered, which is similar to the pure CX configuration,
without explicitly including resistance The model is shown in Fig. 2.7b,
with its parameters already defined in (2.11), (2.13), and (2.15). It can be
used to simplify the analysis of complex circuits including, as building
blocks, CX stages with degeneration. In particular, it provides exact voltage
and current gains and output resistance. Note, however, that the input
resistance
is evaluated with the output short-circuited. It (slightly) differs
from the actual input resistance, which depends instead on
Of course,
is very well approximated by
if the condition
is met.
The current gain is related to the equivalent parameter,
which is nearly equal to
It is further reduced by the output coupling loss,
so that
Except for the lower loss at the output, it is similar to that of CX without the
degenerative resistance.
