how to control the time step in .Tran analysis in spice3?

C

cici

Guest
Hello, everyone,

I am doing some simulation of VCO (4 stage differential) in spice3.
When I do the .tran analysis, the time interval of the output is not
uniformly distributed. It is not the time step I gave in the command:

..tran Tstep Tstop.

In my work, I need the timestep to be uniformly distributed. How can I
control it?

Thanks!
 
In article <22a89a25.0409230804.675e11a0@posting.google.com>,
wangllu@yahoo.com (cici) wrote:
I am doing some simulation of VCO (4 stage differential) in spice3.
When I do the .tran analysis, the time interval of the output is not
uniformly distributed. It is not the time step I gave in the command:

.tran Tstep Tstop.

In my work, I need the timestep to be uniformly distributed. How can I
control it?
use the 'linearize' command:

http://newton.ex.ac.uk/teaching/CDHW/Electronics2/userguide/sec5.html#5.3.23

Also, note the comments about not setting Tmax in

http://newton.ex.ac.uk/teaching/CDHW/Electronics2/userguide/sec4.html#4.3.9


Charles.
 
On Thu, 23 Sep 2004 17:36:48 +0100, Charles DH Williams
<C.D.H.Williams@exeter.ac.uk> wrote:

In article <22a89a25.0409230804.675e11a0@posting.google.com>,
wangllu@yahoo.com (cici) wrote:
I am doing some simulation of VCO (4 stage differential) in spice3.
When I do the .tran analysis, the time interval of the output is not
uniformly distributed. It is not the time step I gave in the command:

.tran Tstep Tstop.

In my work, I need the timestep to be uniformly distributed. How can I
control it?

use the 'linearize' command:
That will certainly work, although if the samples are intended for use
with an FFT, the linear interpolation will introduce enough error that
the noise floor will be rather high -- like -90db from the signal, at
best...

--Steve
 
Steve <shamm@austin-not-me.rr.com> wrote in message news:<ujp6l09objhkke0fh2knpi9ak90os4k6in@4ax.com>...
On Thu, 23 Sep 2004 17:36:48 +0100, Charles DH Williams
C.D.H.Williams@exeter.ac.uk> wrote:

In article <22a89a25.0409230804.675e11a0@posting.google.com>,
wangllu@yahoo.com (cici) wrote:
I am doing some simulation of VCO (4 stage differential) in spice3.
When I do the .tran analysis, the time interval of the output is not
uniformly distributed. It is not the time step I gave in the command:

.tran Tstep Tstop.

In my work, I need the timestep to be uniformly distributed. How can I
control it?

use the 'linearize' command:

That will certainly work, although if the samples are intended for use
with an FFT, the linear interpolation will introduce enough error that
the noise floor will be rather high -- like -90db from the signal, at
best...

--Steve
Thanks for your reply. I tried the command "linearize", it does work
when I
type the command in spice3 invironment. However, when I put the all
the commands into one spice file, it does not work. I was using :

.tran .. ..
.linearize V(1)
.print tran V(1)

The result is still as there is no ".linearize" command.
How can I solve this problem? Thanks!

cici
 

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