The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design Languages >> Verilog-AMS >> How to force rise/fall time?
https://designers-guide.org/forum/YaBB.pl?num=1119865727

Message started by Tommy on Jun 27^th, 2005, 2:48am

Title: How to force rise/fall time?
Post by Tommy on Jun 27^th, 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

Title: Re: How to force rise/fall time?
Post by Ken Kundert on Jun 27^th, 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

Title: Re: How to force rise/fall time?
Post by Andrew Beckett on Jun 27^th, 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.