Cadence Sprobe stabindex

[john.zhang]

Hi all,
I am designing a two stage LNA, and so I am using the Sprobe to check for the stability.
there is a "stab index" function in the sprobe for the sp analysis, however I am unsure how to use it. For stability FACTOR, I know it has to be greater than 1, and my circuit indeed does have stability factor (k) greater than 1. However, for stabfactor in sprobe, the results I get are less than 1, it even goes to the negative value .

Cadence says this

So I am confused, is it |stab factor| < 1 for stability?
is a stab factor of negative alright? this just means that one of my gamma is less than 50 real value, right?

 

[dick_freebird]

I don't have an answer to the specific question, but I have gotten
garbage results from stab / sprobe too many times to trust. Worst
is when you get a sparse FU in big MC char loops, ruining the whole
thing.

I've gone back to basic methods and recommend you "check work"
by "less bundled up" techniques as you go, to decide your own
trust level and basis.

 

[john.zhang]

I don't have an answer to the specific question, but I have gotten
garbage results from stab / sprobe too many times to trust. Worst
is when you get a sparse FU in big MC char loops, ruining the whole
thing.

I've gone back to basic methods and recommend you "check work"
by "less bundled up" techniques as you go, to decide your own
trust level and basis.

do you have any tips for stability checks for multi stage amplifiers?