Environmental Engineering Reference
In-Depth Information
Again, like the series-shunt amplifier, we have only one inverting gain
stage with high-resistance input and output nodes, which correspond to the Y
and Z nodes, respectively, of transistor T1. Thus Miller compensation can be
usefully applied (although dominant-pole compensation could in principle be
performed at node Z1 or even at Y1).
By using the equivalent circuit in Fig. 6.31, the transconductance of the
second stage
now coincides with the equivalent transconductance of
transistor T1
and the second-stage output resistance is
where is the input resistance (at terminal Y2) of the common Z transistor.
It can be calculated using the expressions in Chapter 2, however, it is large
and can be generally neglected.
The transconductance of the first stage, is evaluated by applying a
test voltage source at node Y2, calculating the short-circuit current at node
Y1, and then taking their ratio. If we approximate the voltage gain between
Y2 and X2 to be exactly unitary, we get
Resistance
is the equivalent one at node Y of transistor T1, and is
equal to
where node X of transistor T2 is assumed to have an output resistance small
enough to be considered as a ground connection.
Finally, we calculate the equivalent capacitor
which is given by the
capacitive contribution at node Z1-Y2
