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Passivity violation in S param file

Binhngo1210

Hi everybody, 

I am designing LNA  whose testbench uses some S-parameter files for off-chip components from vendors(L,C, balun...). the warning arises as in the logfile below 

I think that it is due to the frequency range in S-param files does not go down to 0 frequency point or even not close to such the lower point (10 Mhz or  1Mhz..) . It is tough to change it without each component measurement..

Is that affect the accuracy of frequency response and other merits at other frequencies ( in terms of gain, noise, and oip3....).. I am aware that a violated passivity of S-param can possibly impact on stability and causality at a single frequency point (correct me if I'm wrong). 

Thanks, 

Binh Ngo

Parents

  • Dear Binh,

    You are correct that if an S-parameter file is missing a DC term, it can present an issue in a transient simulation. In short, without a DC term, the simulator may attempt to extrapolate its data to solve the initial DC operating point - which may produce an incorrect DC term.

    However, the lack of a DC term does not necessarily lead to passivity issues. What I might suggest is the following. - assuming you have not already considered either of these!

    1. With ViVA, open each S-parameter file you are using and inspect its contents. With ViVA, you can plot its contents in your favorite coordinates and determine if it's behavior is what you expect.

    2. Consider looking through the excellent presentation by Mrs. Tawna Wilsey ( of Cadence) entitled "7 Habits of Highly Successful S-Parameters "at the Cadence On-line Support site URL:

    support.cadence.com/.../ArticleAttachmentPortal

    This provides not only a very good background on their use with spectre, but also numerous troubleshooting and useful conditions to avoid to allow for an accurate simulation with S-parameter files.

    I hope these help you a bit Binh!

    Shawn

Reply

  • Dear Binh,

    You are correct that if an S-parameter file is missing a DC term, it can present an issue in a transient simulation. In short, without a DC term, the simulator may attempt to extrapolate its data to solve the initial DC operating point - which may produce an incorrect DC term.

    However, the lack of a DC term does not necessarily lead to passivity issues. What I might suggest is the following. - assuming you have not already considered either of these!

    1. With ViVA, open each S-parameter file you are using and inspect its contents. With ViVA, you can plot its contents in your favorite coordinates and determine if it's behavior is what you expect.

    2. Consider looking through the excellent presentation by Mrs. Tawna Wilsey ( of Cadence) entitled "7 Habits of Highly Successful S-Parameters "at the Cadence On-line Support site URL:

    support.cadence.com/.../ArticleAttachmentPortal

    This provides not only a very good background on their use with spectre, but also numerous troubleshooting and useful conditions to avoid to allow for an accurate simulation with S-parameter files.

    I hope these help you a bit Binh!

    Shawn

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