Problem when using RFDE momentum blocks in Cadence (Drop across Resistance w/o any current)

Dipal,

Given that Momentum is a tool from Keysight (not Cadence) and I don't know which version of Virtuoso, Momentum, or Spectre (assuming that it's spectre you're using as the simulator - you didn't say that either), it's quite hard to give a definitive answer.

So, assuming that the simulator is spectre, can you post what the lines in the input.scs look like for I741 (the highlighted component above)? Also can you mention the versions of the tools you're using?

Thanks,

Andrew.

Hi Andrew,

This is a fresh simulation where I removed everything else. I am using ADS 2016.01, MMSIM15.10.627 and IC6.17.704

Here is the spectre simulator data from the input.scs file for the below schematic

PORT0 (net70 0) port r=50 num=1 type=sine freq=100G dbm=0

R3 (net70 net03) resistor r=1u

R2 (net06 net42) resistor r=1u

R1 (net42 net010) resistor r=3K

R0 (Amp_Vdd Drain_device) resistor r=100

V4 (net010 0) vsource dc=550.00m type=dc

V0 (Amp_Vdd 0) vsource dc=Vdd type=dc

I405 ( net03 0 0 0 net06 0 0 0) nport interp=linear \

       file="workdir/mommdl/text.txt" \

       datafmt=citi

and the mommdl/text.text file is an S parameter file generated for the momentum block I405 (schematic below)

Please let me know if you need any other data.

Thank you.

Regards

Dipal

Dipal,

Some questions:

1. Does the MoM component give you a choice of interpolation method? It would be good if you could pick "bbspice" as this is generally a better choice for passive components. Otherwise you could try using the nport component from analogLib and picking bbspice as the interpolation method, and pointing at the s-parameter file
2. How low in frequency does your s-parameter file go down to? Does it have a DC point in the file?
3. What frequency grid did you pick when you ran your Momentum simulation? We would generally suggest a linear sweep and ensure that there are sufficient points.
4. If you add "-cc" (to clear the cache) on the spectre command line (which you can access via the userCmdLineOptions field on Setup->Environment in ADE), and re-run, does spectre complain about passivity or causality when processing the s-parameter file? Usually this is only done the first time  you use a particular s-parameter file, so the clear cache option forces the checks to be run on subsequent simulations (usually you'd not have this set for best performance though).

Regards,

Andrew.

Hi Andrew,

1. The MoM component does not have an option for interpolation method. I just get a warning when running the DC analysis. It says "Risky extrapolation to DC of data given in S-parameter file". I tried the nport from the analogLib with the "bbspice" as the interpolation method and also selecting the option "Extrapolate to DC". The problem still persist and I still see a drop across the resistance connected to the gate.

2. As it takes a long time to simulate, the lowest point is at 80 GHz. Like you suggested, there is no DC point in the file. Is there anything that I could add into the S Parameter file?

3. I did the simulation with linear sweep and a step size of 1GHz.

4. It does not throw any complaint about passivity or causality.

Please let me know if you need any other data.

Regards

Dipal

Dipal,

Well, I think it's a little optimistic for any model to be built which will simulate at DC and in the time domain if the lowest simulation point you ran in Momentum was at 80GHz! How the spectre is supposed to know that the capacitor is open circuit at DC (after all, it doesn't know it's a capacitor - all it has is the s-parameters). I nearly fell off my chair when you said the minimum frequency is 80GHz!

A 1GHz step is pretty big too.

I'm not sure we can help much more without seeing the data, but to be honest I think the main problem is that the s-parameter data is missing too much low frequency and even high frequency data, plus is too sparse.

Andrew.

Hi Dipal,

You might want to take a look  at the IMS MicroApp “7 Habits of Highly Successful S-Parameters” is on our Cadence website.

On Cadence Online Support,  the in-depth AppNote is here:  20466646 .

Best regards,

Tawna

Hi Tawna,

Thank you for the document. It is really informative.

Regards

Dipal