Criterion (Using Bode' Plots) Study Guide
to material about the Nyquist Criterion for determining stability applying
the criterion on Bode' plots)
The Nyquist criterion is a method for determining stability of closed loop
systems using frequency response information. Nyquist stability analysis
(i.e. applying the Nyquist Stability Criterion) is most often done using
Bode' plots rather than a Nyquist plot even though the criterion is developed
using reasoning about the Nyquist plot.
Why learn to use Bode'
plots for Nyquist analysis?
Bode plots have a number
of advantages over Nyquist plots that make Bode' plots the vehicle of choice
for Nyquist analysis.
In Nyquist plots frequency
is a parameter, and it is difficult to determine the frequency of a point
on a Nyquist plot, where in Bode' plots, magnitude (in db) and phase are
plotted against frequency and that problem does not arise.
In Nyquist plots you can
only see a limited range of gain values on a typical plot. On a Bode'
plot you can see large ranges of gain because the db scale presents information
differently. For example, the open
loop frequency response plot for an operational amplifier has a DC
gain of over 100,000 (i.e. 100 db), but you can still clearly see the point
where the gain drops to 1 (i.e., the zero-db crossing) on that plot.
What should you know to
learn about using Bode' plots with the NSC?
What do you need to know
about using Bode' plots with the NSC?
How do you use the information
you get from applying NSC analysis on Bode' plots?
When you are setting phase
and gain margins, you are doing part of the design for a closed loop system.
The whole concept of using Bode' plots for NSC analysis is really a valuable
design tool for closed loop systems.