[SI-LIST] Re: Regarding considering a transmission line as lumped or distributed
- From: "Lynne C. Green" <lgreen22@xxxxxxxxxxxxxx>
- To: malli.1729@xxxxxxxxx, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Wed, 24 Jul 2013 00:40:24 -0700
re: number of segments (delaytime/risetime ratios)
If one downloads SPICE 3f5, one can try the following experiment:
- simulate using the W element (distributed line)
- divide the transmission line into N series-shunt segments (Ltotal/N,
Ctotal/N) = [multi-lump]
- use a ramp source with the desired edge rate
- use a resistive load (Z0, open, and/or short)
- take a look at delay, min and max ringing voltages, and anything else
of interest.
Another experiment:
- vary the delaytime/risetime ratio by varying the length of the Tline.
- use same ramp source and resistive load
Note: In SPICE, one might wish to specify some time step and accuracy
options.
These experiments give a feel for the number of lumps compared to the
delaytime/risetime ratio. What happens is that for very short lines
(delay << rise time), N=1 is sufficient. First experiment helps
understand difference between lumped and distributed models. Second
experiment helps understand the "rule of 6" as a transition between
lumped and distributed modeling.
Hope this helps.
Regards,
Lynne
"IBIS training when you need it, where you need it."
Dr. Lynne Green
Green Streak Programs
http://www.greenstreakprograms.com
425-788-0412
lgreen22@xxxxxxxxxxxxxx
On 7/23/2013 10:13 PM, mallikarjun K wrote:
> I am a from non-profit organisation. I don't access to these 3D/2D solvers.
> i am simulating things with free simulation softwares like MC10. that's why
> i am understaning thumb rules, when they will be applicable and limitations
>
> On Tue, Jul 23, 2013 at 6:26 PM, <Joseph.Schachner@xxxxxxxxxxxxxxxxxx>wrote:
>
>> Transmission lines are always distributed. We can approximate their
>> behavior with lumped parameter models but if there are performance
>> differences large enough to matter between the model and what we observe
>> then the model is too simple, so it's wrong.
>>
>> I don't actually know which rule-of-thumb for approximating true behavior
>> by lumped parameter model is closer to truth. I'm just encouraging you,
>> instead of seeking a rule of thumb, to aim closer to the truth (ie,
>> simulation in at best a 3D solver, or at least a 2D solver).
>>
>> --- Joe S.
>
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