Geoffrey Coram, Colin McAndrew, Kiran Gullapalli, and Ken Kundert (me) have written a paper that describes a fundamental problem with the implementation of flicker noise in the models, both built-in and Verilog-A, of most commercial simulators.  It has been accepted for publication in TCAD, and is currently available as a preprint. Everything you need to duplicate their results is given in the Semiconductor Models section of Verilog-AMS.

The problem is illustrated in the attached figure. A correct model should have one peak at 131kHz. With an incorrect implementation you will see peaks at frequencies that are multiples of 262kHz.

-Ken

The above results were generated by Spectre 15.1.0. You can see that the built-in resistor model and the BSIM4 fnoimod1 models are correct, but the BSIM4 fnoimod0 is not.  Also, you can get correct results with Verilog-A if you write your model properly. I encourage you to try your own simulator and report the results here.

-Ken

I think it's odd that in BSIM3, the "old" noimod=1 (just using kf and af) gives the correct results. The new unified flicker noise model[1] (using noia, noib, noic) is noimod=2 (or 3) in BSIM3, and has incorrect results.

This is flipped from BSIM4, where the new unified flicker noise model, fnoimod=1, gives the correct spectrum.

[1] K.K. Hung, P.K. Ko, and C. Hu, "A unified model for the flicker noise in metal-oxide-semiconductor field-effect transistors." IEEE Transactions on Electron Devices 37.3 (1990): 654-665.

I'm not sure it's entirely fair to say the error is in the original C code from Berkeley, since Spice doesn't support Pnoise and thus the model has no way of communicating the sign of the modulation.

The R3 code on nanoHub does have this error, as do the R2_CMC and R3_CMC models from the Compact Model Coalition (http://www.si2.org/cmc). I have update those latter two models and the beta code is being tested by other CMC member companies.

Geoffrey_Coram wrote on Jan 16^th, 2020, 6:36am:

Thank you for sending me your BSIM3 testcase. I can exactly reproduce your plot with the most recent Spectre version 19.1.0.237.isr3.

Quote:

Actually this problem was identified and resolved by the initial SpectreRF developers (Ricardo Telichevesky, Jacob White, and myself) before SpectreRF was first released.  We did not think much of it at the time and the idea seemed to have been lost after we all moved on to other things. It was Geoffrey that resurrected the idea while trying to resolve anomalies he was seeing in the flicker noise of various models and simulators.  He then recruited Colin and Kiran to work through all the details, verify the results, and write the paper.

-Ken

Here are the results for BSIM3 from the current Spectre Version 19.1.0.348.isr6: