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SPECIFICATIONS IN THE FREQUENCY DOMAIN:

A transfer function can be represented in the Laplace s domain OR in terms of frequency domain jω.

Basically in a transfer represented in Laplace s domain we substitute jω for each s term in the transfer function.

Some examples:

Transfer Functions

Laplace - s domain Frequency - jω domain
0.1
----------
10 s + 0.1
0.1
----------
10 jω + 0.1
   
s + 0.1
----------
10 s + 0.1
jω + 0.1
----------
10 jω + 0.1
   
ωn2
-----------------------
s2n2 + 2s*ζ*ωn + 1
ωn2
---------------------------
(jω)2n2 + 2jω*ζ*ωn + 1
   

The parameters usually associated with specifications in the frequency domain are the following:

bulletBandwidth of the system

 

bulletGain Margin

 

bulletPhase Margin