[SI-LIST] Re: lumped model vs distributed model
- From: "Muranyi, Arpad" <arpad.muranyi@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 3 Dec 2001 12:22:26 -0800
Jason,
I am sorry, but I can't answer your XFX questions because
I am not an XFX user. However, I think I heard it somewhere
(someone correct me if I am wrong) that XFX really does not
have an inductor element, they approximate it using T-lines.
So watch out when you do experiments with that tool. I would
suggest to use some flavor of SPICE for these experiments.
Arpad
==============================================================
-----Original Message-----
From: Jason D Leung [mailto:jleung@xxxxxxxxxxxxxxx]
Sent: Monday, December 03, 2001 11:28 AM
To: arpad.muranyi@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: lumped model vs distributed model
Hi Arpad:
I am trying your approach and I am using xfx in XTK to capture the L,C and
R lumped values.
Assumption : I am using a Trise of 100 ps and Er=3.5 and 1 meter long
transmission line to exaggerate the effect
*******the configuration for the stackup
CONFIG SINGLE e: 1.00 tan:0.035 rho:0.667
DIELECTRIC e: 3.50 HORIZ_PLANE y: 1.2 13.8000
CONDUCTOR 1 RECTANGLE x: 0 5.00000 y: 7.2 7.8000
GROUND HORIZ_PLANE y: 13.8 15
GROUND HORIZ_PLANE y: 0.00000 1.2000
;
and the .tlp file is
************
Configuration Name: SINGLE Conductors: 1
Conductor index: 0 name: $$GND$$
Conductor index: 1 name: 1
i j Lij Cij Ze Zo Se So Fwdx Rvsx
from to (nh/in) (pf/in) (ohms) (ohms) (ns/ft)(ns/ft) (s/s) (v/v)
--------------------------------------------------------------------------
1 1 8.748 2.872 55.19 - 1.90 - - -
: LOSS MATRICES
i j Rsij Gij Rdcij Gdcij
from to (ohm-nsec^.5) (mS-ns) (ohms) (mS) PER INCH
--------------------------------------------------------------------------
1 1 0.45405 0.100524 0.22233 0.00000
;
********
In the spice deck , I have the following for the lumped transmission line
model:
c1 in 0 56.55p ****c1=2.872*39.37inch /2
rp in rmid 8.753 ***rp=0.22233*39.37 inch
l1 rmid out 344.4n ****l1=8.748*39.37 inch
c2 out 0 56.55p
and for the distributed model I have the following for the spice deck:
***********
.subckt DSPKG in out ref
c1 in ref 5.655p *whatever the values I have divided by 10 sections
rp in rmid 0.8753m
l1 rmid out 34.4n
c2 out ref 5.655p
.ends DSPKG
**********************
xdspkg1 in_dist pkgsec1 gnd dspkg
xdspkg2 pkgsec1 pkgsec2 gnd dspkg
xdspkg3 pkgsec2 pkgsec3 gnd dspkg
xdspkg4 pkgsec3 pkgsec4 gnd dspkg
xdspkg5 pkgsec4 pkgsec5 gnd dspkg
xdspkg6 pkgsec5 pkgsec6 gnd dspkg
xdspkg7 pkgsec6 pkgsec7 gnd dspkg
xdspkg8 pkgsec7 pkgsec8 gnd dspkg
xdspkg9 pkgsec8 pkgsec9 gnd dspkg
xdspkg10 pkgsec9 out_dist gnd dspkg
*
However, when I compare the lumped and distributed model together , I
didn't see any difference, do I miss something here or ...
thanks
Jason Leung
"Muranyi, Arpad" wrote:
> Jason,
>
> I am sure you will get many good theoretical answers
> to this question. However, I would suggest that in
> order to get a better understanding, try it out yourself!
>
> If you have a spice simulator, build a network with a single
> RLC lump, and compare it with say 10 of them in series, or
> 100 of them in series (don't forget to divide the individual
> element values by the number of lumps, though). This is not
> too hard if you know how to make a subcircuit... For the
> "driver" you can just use a Thevenin circuit, with a Pulse
> (or PWL) source where you can vary the edge rate from very
> steep (1.0 ps) to less steep (10 ns). Then run the
> simulations and put the waveforms on top of each other.
> You should see pretty good differences...
>
> Arpad Muranyi
> Intel Corporation
> ===========================================================
>
> -----Original Message-----
> From: Jason D Leung [mailto:jleung@xxxxxxxxxxxxxxx]
> Sent: Friday, November 30, 2001 12:19 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: lumped model vs distributed model
>
> 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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