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Simulators >> AMS Simulators >> Overcoming Blowup of Quantities in NCSIM
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Message started by badamsssl on Mar 20^th, 2007, 9:57pm

Title: Overcoming Blowup of Quantities in NCSIM
Post by badamsssl on Mar 20^th, 2007, 9:57pm

HI
could you please help me overcoming the following problem while simulating a Behavioral Charge Controlled model developed in VHDL AMS through an inverter:

Error found by spectre during DC solution estimation, during IC analysis,
during transient analysis `amsAnalysis'.
There were 7 attempts to find the DC solution. In 13 of those attempts, a
signal exceeded the blowup limit of it's quantity. The last signal that
failed is U(uInv.A1.qIn) = -1.80144 G, for which the quantity is `U'
and the blowup limit is (1 G). It is possible that the circuit has no
DC solution. If you really want signals this large, set the `blowup'
parameter of this quantity to a larger value.

Thanks in Advance
--Srinivas

Title: Re: Overcoming Blowup of Quantities in NCSIM
Post by Ken Kundert on Mar 20^th, 2007, 10:59pm

The signal on uInv.A1.qIn exceeds 1.8e9, and as a result the simulator thinks something is going wrong. Have you looked to see why the signal on uInv.A1.qIn is greater than 1.8e9?

-Ken

Title: Re: Overcoming Blowup of Quantities in NCSIM
Post by badamsssl on Mar 21^st, 2007, 6:12pm

HI

Thanks for your reply....But I have fixed the problem....
The mistake I did was to initialize the free quantities (as we usually do in VHDL digital modules or a typical C++ code) to either 0.0 or 1.0.
so when I have the Gate Capacitences or Charges which would typically be in the range of E-34 or even less, the rise in those quantites when compared to 0.0 or 1.0(which it was initialized to in the model...) exceed the blowup limit of the quanitity (which according Cadence Spectre is around 10E-8 or some value which is leass than that seen in the quantity).....So , It gave an error message and stopped analysing

So Now I removed the initialization of those quantities and the model working pretty well

Any how thanks for having such a wonderful forum for the designers and your book " The Designer's guide to Spectre and Spice" which gives an outline on a typical simulator.....

---Srinivas