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kelly Community Member Offline Posts: 67	Re: achievable IIP3 for cmos passive mixer Reply #30 - Jan 14^th, 2011, 2:36pm Hi ssahl, Thanks. I verified the same Ids_vds characteristics with the BSIM4 mode I am using too. With the absence of the PSP model, do you know how much off is the IIP3 from BSIM compared to that obtained from PSP? Is the P1dB from BSIM still correct though? Thanks. kelly
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rfidea

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Re: achievable IIP3 for cmos passive mixer
Reply #31 - Jan 14^th, 2011, 2:51pm

Hi kelly!

I think it is very hard to say how much off the IIP3 simulations are. To give an answer one has to understand how qpss is working. What you can do is to apply a real two-tone test with a transient analysis and measure the IM3 levels with a fft. If you sweeping the power you will also see the P1dB. Maybe this take longer simulation time but you vill modulate the nmos mixer with a real signal.

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kelly

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Re: achievable IIP3 for cmos passive mixer
Reply #32 - Jan 14^th, 2011, 11:34pm

hi ssahl,

please see
http://www.designers-guide.org/Forum/YaBB.pl?num=1286953333

If I understand it correctly, the shooting method should give you the same answer as the transient. HB, on the other hand, it's a little different.

I am just wondering since the Ids is ok, shouldn't the P1dB result with BSIM be ok?

Thanks.

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Andrew Beckett

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Re: achievable IIP3 for cmos passive mixer
Reply #33 - Jan 15^th, 2011, 11:08am

I think the P1dB should be OK, because at higher input powers things behave OK (from what I've seen).

I don't think transient would solve the problem with the IIP3 sim - if I've understood the effect properly (and sorry, I've not looked deeply into this for a while). The discontinuity should affect that too, I believe.

Regards,

Andrew.

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rfidea

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Re: achievable IIP3 for cmos passive mixer
Reply #34 - Jan 15^th, 2011, 12:59pm

After some more thinking I agree with Andrew that the discontinuity problem should be there even for the transient case. The problem is that the BSIM3 model is non-physical around Vds=0. But I also believe that simulation methods that tries to linearise around the qusient point are more sensitive to this model problem. So, transient and pss with shooting would be least sensitive, HB and qpss next, and rapidIP3 most sensitive, I would guess.

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