Hi, everyone.
I have now a little problem, concerning mixed signal simulation.
I can not set rise and fall time for transition function for modules written in VerilogAMS less than 2ns. I have warning in SimVision console:
"../INV/verilogams/verilog.vams"
      18: instance (INV+verilogams+0x10000001
      behavioral) 3 of INV+verilogams+0x10000001:
      Value specified for rise or fall time (1 ns) for transition filter is
      too small.  Value set to 2 ns.
      This message will not be repeated for this filter.
How can I overcome this problem?

Geoffrey_Coram wrote on Apr 18^th, 2007, 3:52am:


No, I haven't.
Additional: I use UltraSim. This schematic isn't big, just 4 simple units. They are written in VerilogAMS and Verilog.
Could it be that my ncsim is very old and this couses problems? Our IT now are updating UltraSim to the IUS5.8
s004 version, may be it will help.
Fill free to suggest.
Thanks in advance!

BTW, there is a parameter transres which can be used to relax this requirement (don't push it too far though):

Code:

27	transres=1e-9*stop s
				  Transition resolution. The transient analysis attempts to stop at corners of
				  input waveforms. (ex. corners of rising/falling edge of a pulse). If such
				  events occur within a time less than transres, the analysis will combine the
				  events into one and force only one time point. The rest of the steps will be
				  determined by error control. This may lead to loss of detail. 

The above is from the spectre help on tran, but it can also be used with AMS.

You need to be careful if you tighten this that you don't run out of numerical headroom on the timestep resolution - with sufficient accuracy to follow the transition.

Regards,

Andrew.