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IIP3 for a mixer: shooting vs. hb

itos

Hello,

Again I need to dig up this old topic on shooting/hb. I want to simulate IIP3 for a passive mixer (ideal current input, simple double-balanced passive current-mode mixer using MOS, ideal current sink (small resistance or TIA using ideal OTA). It's really frustrating because results are unpredictibale and jump around wildly although effectively there are no changes.

For example:

  • There is huge difference between hb and shooting engine in qpss although the IIP3 curves look OK (they just shift)
  • Adding a 1 F AC coupling capacitance (i.e., effectively NO cap!) lets IIP3 drop by up to 24dB. Again, curves look OK

The mixer switches are the only non-ideal thing in the setup so I tried:

  • Replacing the mixer by ideal switches and adding a non-linear resistance (using pvccs). Now the results are complete garbage (either the 3rd order has no slope of 3 but of 1 or the curves just jump around wildly). Clearly the results between hb and shooting are not consistent but I cannot trust them anyway
  • I though maybe it's the models of my 28nm process which can't deal with that. So I tried using a solid 180nm process. Now I do not even get the IIP curves correctly - for hb and shooting. For example, I get curves like:

How to deal with something like that?

Which parameters could I tweak?

And what is the right engine for a passive, current-mode switch (with rectangular LO)? hb or shooting? According to

community.cadence.com/.../tip-of-the-week-when-to-use-harmonic-balance-engine-vs-shooting-newton-engine

it should be hb but I am not sure since the LO is rectangular ...

Parents
  • Andrew Beckett

    There should be a way of you getting support. If you're under the Europractice scheme (mostly in Europe) you can go to Europractice for support, and if they need support in turn they come to us in the UK. For other University programmes it is done typically via the designated owner of the programme at that institution - often a Professor.

    There is some detail on the process here: 

    Without seeing your actual design and simulation setup, I doubt we can do much more...

    Regards,

    Andrew.

Reply
  • Andrew Beckett

    There should be a way of you getting support. If you're under the Europractice scheme (mostly in Europe) you can go to Europractice for support, and if they need support in turn they come to us in the UK. For other University programmes it is done typically via the designated owner of the programme at that institution - often a Professor.

    There is some detail on the process here: 

    Without seeing your actual design and simulation setup, I doubt we can do much more...

    Regards,

    Andrew.

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