Environmental Engineering Reference
In-Depth Information
Underdamped amplifiers are not unstable systems, but nonetheless they
are usually unacceptable, because overshoot arises in the time domain which
is responsible for slow settling behaviour.
Normalising the step response to
u
(t), we can draw the plots in Fig
4.7,
illustrating the step response of a two-pole feedback amplifier for different
.
values of versus
To maintain peaking in both the frequency and step responses below a
desired value, parameter must be properly set. To this end, relationship
(4.8) implicitly provides the required relation between the two (open-loop)
poles for a given value of and In order to avoid excessive
underdamping, open-loop amplifiers must be designed with a dominant pole
and a second pole at a frequency higher than the gain-bandwidth product of
the loop gain Thus, to analyse and design feedback
amplifiers, it is useful to introduce a new parameter called the
separation
factor, K,
which is the ratio between the second pole and the gain-bandwidth
product of the return ratio
T
(
s
)
