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pnoise ignores "no noise" flag on resistors?

itos

Hi,


I am measuring NFdsb for a simple voltage mode passive mixer using pss+pnoise Without any resistance I get NF=5dB. Now I shunt the input with R=50 for matching and NF increases to 10dB. While I am not sure about the numbers it makes sense due to additional noise of the matching resistor.

However, then I set "Generate noise?" to "No" but the result is still the same. I found then the flag "Suppress noise" which I checked too but still same results. In short: pnoise ignores the flag that I do not want to consider the noise from one resistor (this happens a lot, e.g. when the resistor is merely a modeling resistor such as ro).

Is this a bug? How can I turn off noise for a resistor for pnoise?

  • My guess is that the resistor you are using is from a PDK and it's the PDK device that has the bug. If it's analogLib - that doesn't have a "Suppress Noise" flag - so I assume you're talking about something else.

    Fundamentally, all (or nearly all) low level devices support the isnoisy parameter and this will work in pnoise (unless you're using some ancient version). In fact in the Simulator->Options->Analog where there's the ability to specify "noise on" and "noise off", this works inside the simulator by it setting isnoisy appropriately on the specified instances.

    So I would check your PDK device - and see what is actually appearing in the netlist. Of course, if you're using analogLib - it would be useful to know which version of IC and MMSIM you're using - and also to check that the analogLib is really our analogLib not one that's been extended/modified for another simulator.

    Regards,

    Andrew.

  • Thank you. Indeed, I have analogLib from Mentor. It seems to work now though for some strange reasons ... (keeping fingers crossed)

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