Hi all,

I am trying to simulate a simple 2 stage comparator in Cadence Spectre.
However in the transient simulation, its taking a long time with warnings like mentioned below, and finally terminates the simulation:

"
  tran: time = 10.05 us       (1 %), step = 15.63 ns    (1.56 m%)
   tran: time = 10.05 us       (1 %), step = 57.5 fs     (5.75 n%)
   tran: time = 10.05 us       (1 %), step = 7.019 as     (702 f%)

Warning from spectre during transient analysis `tran'.
   WARNING (SPECTRE-16266): Error requirements were not satisfied because of convergence difficulties.

Error found by spectre during transient analysis `tran'.
ERROR (SPECTRE-16384): Signal I(M1:d_s_flow) = 1.00277 GA exceeds the blowup limit for the quantity `I' which is (1 GA). It is likely that the circuit is unstable. If you really want signals this large, set the `blowup' parameter of this quantity to a larger value.

Analysis `tran' was terminated prematurely due to an error.
finalTimeOP: writing operating point information to rawfile.
"

I know this blow up is a common problem, still I am not able to bypass this. I introduced cmin=0.1fF still no luck. Also the current values are so low [I am using a verilog a based look up table based model] so that I am wondering how can it exceed GA ? The initial transistor sizing was also not that big to cause so much difference in current.

I relaunched with the attached netlist, but its taking hours to finish 1%. Normally it crashes at 22% of transient.

Can anyone help with this ?

Thanks and regards,

batmanbeginz wrote on Feb 19^th, 2013, 1:43pm:


What does your table look-up say to do when the voltages are outside the table (what extrapolation method)?  If the voltages somehow get outside the modeled range, is your model set up to guide the simulator back to reasonable values?