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pnoise and pac contradiction

radiowaves over 10 years ago

Hi,

First I want to know hoe does spectre compute flicker and thermal noise

1) using a current modelbetween drain and source

2) using a voltage model at the gate

I am using BSIM 4.5 models where doc says both are modled as current source.

Second,

I have simulated noise transfer function of thermal & flicker noise of M1 from RF to IF using pss+pnoise and noise separation. (sideband=+1). Why are they different? I believe both thermal and flicker are modeled as current source and hence transfer function should be same. The transistor model is BSIM 4.5 and noise model is holistic. Is it because contribution from noise source modulation is different for them?

I tried modeling the noise using a current source (red) and use PXF analysis. But the gain is around 150 in contrast with 1.2K from pnoise simulation. Why is pxf resulting in such low value? Is this method of modeling noise not correct?

radiowaves over 10 years ago

Here are the plots using pnoise and pxf analysis
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Andrew Beckett over 10 years ago

I'm sure there's something that you've done wrong here - it's hard to know precisely how you're simulating this too. I'd need to look into the bsim4 documentation (probably from Berkeley in order to see the noise modelling) and this would take some time to do some experiments (I've not even looked at the documentation to check this). Not sure what you're trying to prove here, but if you want to look into this further please contact customer support so that somebody can spend the time needed to work through this. It's certainly beyond what I can do in my spare time...
Regards,
Andrew.
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Frank Wiedmann over 10 years ago

This case has been discussed in more detail at http://www.designers-guide.org/Forum/YaBB.pl?num=1409840321. It seems to me like the noise separation feature should be verified (and better documented) by Cadence, so I also recommend to contact Customer Support.
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