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Design >> Analog Design >> Filter curve fitting tool??
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Message started by ditka on Sep 28^th, 2007, 5:59am

Title: Filter curve fitting tool??
Post by ditka on Sep 28^th, 2007, 5:59am

Hi,

Does anyone know of a tool that can take a Bode plot input and determine the poles and zeros based on
a curve fit? I'd think that you'd also have to tell the tool the filter order? The Bode plot would be coming
from a Spectre simulation, so it'd be nice if Matlab could do this. If only I knew Matlab better, though :)
I'm more proficient with MathCad...

Thanks!

Title: Re: Filter curve fitting tool??
Post by pancho_hideboo on Sep 28^th, 2007, 6:22am

Hi.

Why don't you use pole-zero analysis of Spectre directly ?
Is there any problem in applying pz-analysis ?

There is Frequency Domain Identification Toolbox for such purpose.
http://www.mathworks.com/products/connections/product_main.shtml?prod_id=309
http://elecwww.vub.ac.be/fdident/

There also exist the following.
http://www.item.uni-bremen.de/research/mimosys/dynamic/

Title: Re: Filter curve fitting tool??
Post by ditka on Sep 29^th, 2007, 6:14am

Thanks for those links!

The circuit I'm simulating has 17,000 eqns and Spectre's pole-zero
analysis works well for <1,000 eqns. I tried running the pole-zero
analysis on a sub-section of the filter circuit (one of the biquad sections)
which has 4,000 eqns and it was taking forever so I killed the session.

Title: Re: Filter curve fitting tool??
Post by loose-electron on Oct 5^th, 2007, 4:23pm

different order filters with different pole placements can produce roughly the same Bode response.

Trash out all the residual poles and find out what your dominant poles are and analyze it from there.