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Input impedance measurement using sp analysis for 3 port Cfmom

yayla
Hi,

I have a problem when I try to measure a input impedance of Cfmom cap. I have two inputs and one ground port for mom cap. When I try to measure the ideal two port capacitor there is no problem but when I connect Cmom cap, I am measuring almost 6 times less the value when I measure it single ended(I connected port 2 to ground). I am using sp analysis and Zm option under Main form window.

 Could you know what might be the problem?

 Thanks,

 yayla

p.s I have also connected Port element to the ground port but the result is same. I think I am missing something very simple.

[URL=http://imageshack.us/photo/my-images/12/sp3port.png/][IMG]img12.imageshack.us/.../URL]

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Parents
  • yayla

     I think I solved the problems. For small Cmom values, parasitics become comparable to main cap and diff. and single-ended measurement gives different results. They are converging for high Cmom values.

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  • yayla

     I think I solved the problems. For small Cmom values, parasitics become comparable to main cap and diff. and single-ended measurement gives different results. They are converging for high Cmom values.

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