[SI-LIST] Re: Combining DC and TRANS analysis
- From: "Scott McMorrow" <scott@xxxxxxxxxxxxx>
- To: Andrew.Ingraham@xxxxxx
- Date: Mon, 20 Jan 2003 10:23:14 -0800
SK,
I believe you are having problems with a device that dynamically changes
it's DC operating point during startup. In that case, what you want to
do is to perform a transient simulation with stable DC inputs, until the
system voltage levels stabilize. In your case, it seems you have
determined that this takes 500 ns. (use the samer DC inputs as you
would use at the start of a mormal transient simulation. At the 500 ns
point you should capture the operating point using a .SAVE:
.SAVE FILE=save_file TIME=500n
You can then use the saved operating point by using a .LOAD for all
subsequent simulations.
.LOAD FILE=save_file
This procedure will allow you to find the correct dc operating point for
a complex device once, and then use is further simulations with real
patterns. DC convergence will happen much more quickly in subsequent
simulations.
best regards,
scott
--
Scott McMorrow
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 239-5536
http://www.teraspeed.com
Ingraham, Andrew wrote:
>>Is there a way to combine DC (.dc) and transient (.trans) analysis in
>>HSPICE?
>>
>>For example, is it possible to perform DC analysis only after 500ns?
>>If it
>>is, how do we go about it?
>>
>>
>
>Exactly what are you trying to find?
>
>In SPICE, DC analysis assumes everything is quiescent forever. Why
>would you need to wait 500ns? Do you have input signals that are
>changing in the first 500ns? Or did you find that a transient analysis
>with no inputs changing, results in the operating point shifting over
>time?
>
>I think the short answer to your inquiry is "no," but it begs further
>questions about what you want to do. Of course you can combine a .DC
>and a .TRAN analysis in the same simulation, but SPICE does the .DC
>first, then goes on to the .TRAN portion.
>
>Regards,
>Andy
>
>
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