nan appears in stb analysis

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SA,
when I perform an stb analysis in cadence for PLL model I have made using verilog-a i get (nan ) in all the fields of stability
I am putting the Iprobe between the VCO block & the divider block & I am selecting it as a probe of instance
I am sure there is some thing wrong but I do not know which is wrong
 

Not A Number means some calculation failed. Veriloga
models may, or may not, have any useful frequency-
domain output. Try plotting vm(), vp() of some relevant
node and see if there's anything. No mag, no phase,
no chance for stb to work.
 

You get this NAN error I recall when your magnitude never gets above 0dB, hence it can't find the PM and GM. It always looks for the unit-gain bandwidth point.

JGK
 

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