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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?
 

frankon_o2

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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?
 

nathan

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

nathan
 

ysz

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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
 

ysz

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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 .
 

always@smart

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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,
 

ysz

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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.
 

ysz

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this is my ugly wave, who can help me?
 

leo_o2

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

ysz

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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
 

leo_o2

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What is TStep that you used for .tran analysis?
 

ysz

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

leo_o2

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

ysz

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

leo_o2

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

joskin

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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.
 

ysz

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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?
 

Hughes

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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
 

fashion

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

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