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How to get a fixed timesetp in hspice?

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ysz

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hello all!
I need a fixed or approximate fixed timestep for .tran sim, who can tell me how to do?
 

for example:
.tran 1u 20m
then 1uSec is the time step of transient simulation
the length of simulation is 20mSec
Is that what u want to know?
 

use delmax (maxdel ???)= ...

nathan
 

frankon_o2 said:
for example:
.tran 1u 20m
then 1uSec is the time step of transient simulation
the length of simulation is 20mSec
Is that what u want to know?
hspice will change the timestep, not always 1u
 

nathan said:
use delmax (maxdel ???)= ...

nathan
I use this opt:
.option post=2 accurate DELMAX=0.0u RMAX=1 DVDT=2 LVLTIM=2 FS=0.1 FT=0.1
it has a little benifit .
 

hi ysz,

how do u know that Hspice will change the timestep? sorry i;m new in using hspice.

can you please also explained the command u have shown us?

.option post=2 accurate DELMAX=0.0u RMAX=1 DVDT=2 LVLTIM=2 FS=0.1 FT=0.1

thanks in advance

regards,
 

Star-Hspice allows the selection of three dynamic timestep control algorithms:
n Iteration count
n Truncation
n DVDT
Each of these algorithms uses a dynamically changing timestep.

you can look it up in the manual.
 

this is my ugly wave, who can help me?
 

Set DELMAX to a value smaller than the minimum pulse width. It might help. Avoid signals with steep edge.
 

leo_o2 said:
Set DELMAX to a value smaller than the minimum pulse width. It might help. Avoid signals with steep edge.
I already set DelMax=0u
 

What is TStep that you used for .tran analysis?
 

.option post=2 accurate DELMAX=0.0u RMAX=1 DVDT=2 LVLTIM=2 FS=0.1 FT=0.1
.tran 10u 120m
 

Obviously, 10us for Tstep is too big. You must decrease it first in my opinion.
 

I have changed it to 1us, the wave is same, I'm so doubt.
 

Try 10ns. However, it will be very slow.
 

The main problem is your simultion time is too long(bigger than 100ms).
Because in (*.tr#)transient sim result file,the valid digital number that describe simulation time is fixed,the wave can't show detailed information when the time exceeds 100ms.
 

joskin said:
The main problem is your simultion time is too long(bigger than 100ms).
Because in (*.tr#)transient sim result file,the valid digital number that describe simulation time is fixed,the wave can't show detailed information when the time exceeds 100ms.
really?
but if I can set a fixed timestep, I will set the timestep longer, so the number of steps are reduced, maybe I can have longer sim time. do you think so?
 

ysz said:
.option post=2 accurate DELMAX=0.0u RMAX=1 DVDT=2 LVLTIM=2 FS=0.1 FT=0.1
.tran 10u 120m

Don't set DELMAX=0, set to a small value other than 0. For example:
.option delmax=0.1n
 

If you set more accurate, the speed of simulation will be very long, sometime set 1/10 of total time.
 

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