Environmental Engineering Reference
In-Depth Information
The output resistance
is the same as in the previous configuration and is
given by (2.11).
As for the CX configuration with degeneration, we develop an alternative
model useful for simplifying gain calculation in more complex circuits.
Again, due to the current-out nature of the configuration, it is convenient to
represent the circuit at its output node with its Norton equivalent circuit.
Figure 2.8b illustrates this model. The output resistance is given in (2.11),
and the input resistance evaluated with the output shorted to ground) can
be derived directly by setting
in (2.20a) and can be rewritten as
The
inner
current gain,
between the current flowing into the grounded
terminal Z and the current
is
As expected, its value is very close to one. If we assume that a load
resistance, is connected to the output node, the current gain of the
complete amplifier is given by
and the voltage gain is simply
Assuming an ideally unitary inner current gain and a load resistance,
which is much lower than the equivalent out resistance,
(2.23a) can be
approximated as
