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Pavel

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Posts: 174
Lausanne/Switzerland

impedance measurement problem
Apr 14^th, 2008, 7:02am

Hello,

For my simulation I need to modelize my block as blackbox.
In order to measure interface pin impedances, I used Z-parameter measurement technique provided by Eldo (the same thig exists also in Spectre) and based on AC analysis.
From this measurement I extracted equivalent schema of my blackbox - R(Vin) and C(Vin) in parallel.
Then I did DC analysis of this blackbox. From this analysis I've get also R(Vin).

Once compared the results of 2 analysis - AC and DC, I discovered that R(Vin) is different in each case.

Where is my error?

Thanks in advance.

Pavel.

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didac

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There's a million
ways to see the
things in life

Posts: 247
manresa,spain

Re: impedance measurement problem
Reply #1 - Apr 15^th, 2008, 6:57am

Hi,
Not sure about this one, but how do you know it's an error? I think that you have a frequency dependant impedance, so it's not strange to have a real part different in AC an in DC. Probably the simple R in parallel with C isn't suitable and you need a more complex lumped model to capture the behaviour, or if you are interested only on a limited set of frequency you must calculate the R and C for each frequency and use a different parallel for each sim.
Hope it helps,

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Pavel

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Posts: 174
Lausanne/Switzerland

Re: impedance measurement problem
Reply #2 - Apr 22^nd, 2008, 4:42am

Thank you for response, Didac.

For my simulation I need equivalent schema for only one frequency. So in my AC simulation setup there was one frequency and Vin was a parameter.

If I properly understood you, I can use C(Vin), R(Vin), extracted from AC analysis, for my transistion analysis?
And these values (I mean AC-measured C(Vin), R(Vin)) will properly represent my "blackbox"?

Thanks.

Pavel.

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