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Poles and zeros for a frequency response graph

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sajinvm

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Hi all
For a frequency response graph
A pole is defined as the frequency at which the gain becomes infinity
A zero is defined as the frequency at which the gain becomes zero

Are the above defenitions correct.
If correct then why the gain rolls over by -20db/decade instead going to infinity for a pole.

Thanking all in advance
sajinvm
 

Re: poles and zeros

Pole->singularity

Laplace Domain=Complex Domain->s=a+j*b

1/s+u --> s=-u There is infinity

But in Bode Plots you reduce de complex domain to the imaginary axis s=j*b -->j*w

1/s+u-->1/j*w+u--> Bode plot -> 1/ ( (j*w+u)*(u-j*w))=1/distance s=-u to any point in imaginary axis/frequency axis


You can see that above s=j*u the rational function, 1/distance s=-u to any point in imaginary axis/frequency axis, decreases with more slope.
 

poles and zeros

it is just refer to only one pole and one zero
 

Re: poles and zeros

it is only for one pole and one zero
 

poles and zeros

you can go to www.mathworks.com
search for poles and zeros , you will find very good help about hte subject

Added after 2 minutes:

In www.mathworks.com you can find a lot of examples and documents related to poles and zeros for control applications and other math applications
 

Re: poles and zeros

Hi

It is difference between ideal and non ideal. So in practical case for a pole -20db/dec

thanks
 

Re: poles and zeros

Hi all

Thanks for the replies.My specific doubt is why the gain is not going to infinity when a pole comes, in a frequency response. May be my understanding of pole is not correct. Please comment..
 

poles and zeros

the gain goes to infinity at s=wp (i.e. at jw=wp>> w=-j*wp) while at w=wp the gain goes to -3dB , u r mixing between s-domain and freq. domain
 

poles and zeros

yes, ur combining s-domain and frquency domain
 

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