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How to force rise/fall time? (Read 3122 times)
Tommy
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How to force rise/fall time?
Jun 27th, 2005, 2:48am
 
Hi,
  How to prevent spectre from resetting rise and fall time of transition filter?

**********************:
Warning from spectre at time = 3.35988 us during transient analysis `tran'.
   I11: Value specified for rise or fall time (30 ps) for transition filter is
       too small.  Value set to 80 ps.
       This message will not be repeated for this filter.
**********************

How to prevent spectre resetting to 80ps?

Thanks
Tommy
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Ken Kundert
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Re: How to force rise/fall time?
Reply #1 - Jun 27th, 2005, 7:59am
 
Spectre only has a finite resolution for time. What this message tells you is that Spectre is unable to resolve such a small difference in time (30ps) relative to the total length of the simulation time interval. The only way to avoid it is to
1. specify a longer transition, such as the 80ps it suggests
2. reduce the simulation inteval (the stop time specified to the transient analysis).

-Ken
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Andrew Beckett
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Re: How to force rise/fall time?
Reply #2 - Jun 27th, 2005, 11:22pm
 
In addition, in MMSIM60 USR1 and later, there is now an option for transient "transres" which allows you to control this. From spectre -h tran:

Quote:
26      transres=1e-9*(stop-start) s
                         Transision resolution. The transient analysis
                         attempts to stop at beginning and end of large
                         transitions (ex. corners of rizing/falling edge of a
                         pulse). If such events occur within a time less than
                         transres, the analysis will combine the events into
                         one and stop only once. This may lead to loss of
                         detail.



Regards,

Andrew.

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