6/13/2005
Filter Approximation Theory
7
Butterworth Continued
•
Pole locations in the s-plane at:
w
2n
= -1 or
w
= (-1)
(1/2n)
•
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•
•
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•
•
–
Poles are equally spaced on the unit circle at
q
=k
p
/2n.
–
H(s) only uses the n poles in the left half plane for stability.
–
There are no zeros
n = 3