[SI-LIST] Re: lumped model vs distributed model

I would add one more important advantage that a distributed model has
over
a lumped one and that is dynamic range. A lumped model is only as good
as
the calculation for the number of lumps needed in a given situation. One
may decide that 100 lumps is accurate for the application at hand. The
same
100 lump model will at some tr fast enough break down. Not so for the
distributed
model. The distributed model once computed is good for a far greater
range or
application. Therefore it's a better fit for general transmission line
simulation.

There is a caveat to the distributed model. For very short electrical
systems
the lumped model will be faster because a one lump model may be good
enough while
for the distributed model the internal time step taken by the simulator
can become
quite small and lead to long simulation times. 

And as Steve points out this is all without the frequency effects as
different
simulators treat those differently in the time domain. 

Best Regards,

Steve Corey wrote:
> 
> Hi Jason -- the primary difference between lumped and distributed models is
> not accuracy, but simulation speed.  We create both lumped and distributed
> models that accurately characterize transmission lines (dielectric loss and
> skin effect included) all the way to the 35ps risetime of a TDR.  If a
> transmission line is very long compared to the risetime with which you are
> driving it, a distributed model will be noticeably faster than a lumped
> model, and this is its main advantage.
> 
> If you are using a lumped model with frequency-independent RLC parameters,
> which many lumped models have, then you won't effectively model skin effect
> or dielectric loss.  These can become important as low as the 100 MHz range,
> but how important they are really depends on your application.  However, it
> should be noted that not every distributed model handles frequency-dependent
> effects, either.
> 
> If you really want to know what you might be missing in your simulations,
> your best bet is to measure with a TDR and compare the measurements against
> your simulation.
> 
>   -- Steve
> 
> -------------------------------------------
>      Steven D. Corey, Ph.D.
>      Time Domain Analysis Systems, Inc.
>      "The Interconnect Modeling Company."
>      http://www.tdasystems.com
> 
>      email: steve@xxxxxxxxxxxxxx
>      phone: (503) 246-2272
>      fax:   (503) 246-2282
> -------------------------------------------
> 
> Jason D Leung wrote:
> 
> > Hi everyone:
> > For transmission line we can always use a lumped R,L,C model to
> > represent a simple transmission line, or we can use a distributed model
> > .(I know that the distributed model is more accurate and for high freq
> > application we should use this model)
> > But my question is : what is the main difference between the lumped
> > model and distributed model?
> > If we are just using the lumped model for our SI simulation, what are we
> > going to miss ?
> > looking forward for your insight
> > thanks
> > Regards
> > Jason Leung
> >
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-- 
Fred Balistreri
fred@xxxxxxxxxxxxx

http://www.apsimtech.com
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