Environmental Engineering Reference
In-Depth Information
In other words, we have an external feedback loop through and an
inner one through The stability of the inner loop must first be
established so that we can proceed to the external one. Any design attempt
not providing a proper phase margin for the inner loop would inevitably
require an extremely high value of or even not achieve stability at all.
Now we return to the frequency response of the whole open-loop
amplifier, which can be rewritten as in (4.54) and is here reported for clarity
Evaluation of the phase margin yields (see (4.55))
Solving (5.56) for
and combining with (5.48) and (5.53) gives the
expression of capacitance
as a function of the required phase margin
Equations (5.54) and (5.57), are very similar to those in [EH95], where a
third-order Butterworth frequency response in unity-gain configuration is
assumed. However, (5.57) is more general because allows to set
compensation capacitor
for the desired phase margin.
5.4.2 RHP Cancellation with Nulling Resistors
Now we extend the considerations on the nulling resistor network
reported in 5.3.1, to the three-stage nested-Miller compensated amplifier.
Figure 5.9 illustrates the
RC
compensation network which includes two
nulling resistors
and
to be used in the amplifier of Fig. 5.2.
