Environmental Engineering Reference
In-Depth Information
Similarly to the DC analysis, it would be useful to develop an equivalent
model of the common X configuration with a degenerative resistance for the
high-frequency analysis. The schematic of the model, which recalls that of a
common X configuration without resistance
is shown in Fig. 2.14.
It is apparent that to account for frequency behavior, we have introduced the
new capacitor
while the other two capacitors,
and
are those
intrinsic to the device model. After replacing the transistor and
in Fig.
2.12a with the above equivalent model, coefficients
and
of the transfer
function become
Equating (2.42) and (2.43) with (2.36) and (2.38), respectively, under the
assumption that
and hence
are much greater than
we obtain the
condition for the equivalence of the two models
Hence, after some algebraic manipulation we get
