Re: poles
A.Anand Srinivasan,
In a system defined by the ratio of 2 polynomials, by definition, a pole is a root of the denominator, that is, a value which when substituted for the unkonwn, results in a value of zero for the denominator. For example, let a system be defined by the following expression:
f(s) = 1/[(s+1)(s+2).]
The poles of this expression are -1 and -2. Substituting either value for s results in a denominator of zero, and a value of infinity for f(s).
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As far as the 3 db vaslue you refer to, I believe that you are confusing the cutoff frequency for the pole. They are very different things.
Regards,
Kral