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Simulators >> Circuit Simulators >> problem about .pz analysis
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Message started by lxie on Sep 18^th, 2006, 1:31am

Title: problem about .pz analysis
Post by lxie on Sep 18^th, 2006, 1:31am

Hello guys,

When I simulating an opamp I encountered a problem. I used .pz to analyze the pole/zero of my circuit, but the list file gives no results, and there is a warning saying,
‘warning: pole analysis stopped --unable to construct the quadratic equation for Muller algorithm. You may have to adjust the value of three initial points’.
Then I checked the hspice manual for .pz analysis, but I found that there is not very clearly clarify this problem in the manual.
(The manual says, ‘In Muller’s method, the selection of the three initial points affects the convergence of the process and accuracy of the roots obtained. If the poles or zeros are spread over a wide frequency range, choose (X0R, X0I) close to the origin to find poles or zeros at zero frequency first. Then find the remaining poles or zeros in increasing order. The values (X1R, X1I) and (X2R, X2I) may be orders of magnitude larger than (X0R, X0I). If there are poles or zeros at high frequencies, X1I and X2I should be adjusted accordingly.’)
I don’t know how to adjust these three initial points? When I trying to change them to some other values (for example .OPTIONS X0R=-1.23456E+1 X1R=-1.23456E+3 X2R=1.23456E+3 ), then the list file don’t give me a correct pole/zero result—some times there were more than 100 poles and zeros in the list file. Is anybody who can help me to solve this problem? And anybody who can give me some reference about Muller algorithm; I can’t find anything in the Internet and library. Thanks very much.

Title: Re: problem about .pz analysis
Post by Geoffrey_Coram on Sep 29^th, 2006, 3:04am

Try http://mathworld.wolfram.com/MullersMethod.html

It's a general root-finding algorithm; Spice uses it to find zeros of the transfer function polynomials.