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how cadence do to calculate Z11 in a psp analysis

Reda21

hi,   

i'm simuliting a circuit, where i connect 4 switching caps to the port, than i run a psp annalysis to get the input impedance"Z11", and i want to know how spectre do to give such result, it's for helping me understandind how the input impedance behave.

  • It's not clear what you're asking here. It sounds as if you're asking how the simulator works - if so, I don't see how that helps you understand how the input impedance behaves - so something is not clear. Please clarify.

    Regards,

    Andrew

  • thank you andrew for your response.  

    actually, the results i got, show that the input impedance is a function of the source impedance (the impedance of the port), so there is to possible response:

    the psp is not the good analisys i have to run,

    or the input impedance do really change with the source resistance ( it's the first time i'm seeing someting like that)

    so my question was to know wich is the good response to my problem.

  • Hi Reda21,

    Let's define the question a bit more...it's not entirely clear what you are measuring and why you're using psp analysis for this.  What kind of circuit is this?    If you can use sp analysis, it's much easier to use/understand.    Say you have a 2 port circuit.  If you want to look at input impedance, then S11 is what I would plot.

     You may want to look at Article 11663828 Location of tutorials/information on Spectre sp and SpectreRF psp analyses on Cadence Online Support.

    best regards,

    Tawna

     

    Reda21 said:

    thank you andrew for your response.  

    actually, the results i got, show that the input impedance is a function of the source impedance (the impedance of the port), so there is to possible response:

    the psp is not the good analisys i have to run,

    or the input impedance do really change with the source resistance ( it's the first time i'm seeing someting like that)

    so my question was to know wich is the good response to my problem.

  • If there is a large signal clock that drives those switches then psp is the right choice. And yes sometimes the input impedance does depend on the source impedance, such as the input impedance of a passive mixer driven by large LO signals which is probably similar to your case here. This is because the up/down converted impedance at the output of the mixer is affected by the impedance seen at the source.

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