FreeLists / si-list / [SI-LIST] Re: Fw: si-list Digest V7 #410

["David Banas" <david.banas@xxxxxxxxxx>]

I believe the 2 requirements that must be met are:

1) For passivity - the total energy in the S-parameter model's impulse
response must be less than 1:

     Int.{h(t) * CC[h(t)]} <=3D 1

where "Int." means integral over infinite limits, and "CC" means complex
conjugate. For a discrete S-parameter model, the integration becomes a
sum, and using Parseval's theorem:

     Sum.{H(n) * CC[H(n)]} <=3D 1

where "Sum." means the summation over all discrete entries in the model,
and "H(n)" is the nth, possibly complex, entry.

2) For causality - the group delay through the S-parameter model must be
greater than zero:

     -d{Arg.[H(w)]}/dw > 0

where "Arg." means "the phase of", and "H(w)" is the transfer function
of the model as a function of angular frequency, "w". Again converting
to discrete algebra:

     -{[Arg.(H(n+1)) - Arg.(H(n))]/W} > 0

Where "W" is the angular frequency step between adjacent entries in the
model.

-db


> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Gregory R Edlund
> Sent: Friday, December 07, 2007 6:12 AM
> To: ria_rr_84@xxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Fw: si-list Digest V7 #410
>=20
> Ria,
> I'll take a stab it this.
>=20
> Passivity - a passive network that has no external power cannot add
energy
> to a signal.  If you look at amplitude vs. frequency for a passive
network
> (e.g. s21 parameter), it should never go above one.  I believe the
math is
> more complicated than that, but this is the general idea.  Anybody
care to
> elaborate?
>=20
> Causality - a signal cannot traverse any transmission medium faster
than
> the speed of light in that medium.  This term comes from relativity
where
> event A cannot cause event B unless it happens before event B.
>=20
> Besides nonphysical simulation results, models that have these
problems
> can also give simulators numerical trouble.
>=20
> Has anyone on the list seen a set of publicly available canned
routines
> for evaluating causality and passivity of s-parameters?
>=20
> Greg
>=20
> Greg Edlund
> Senior Engineer
> Signal Integrity
> IBM Global Engineering Solutions
> 3605 Hwy. 52 N, Dept. HDC
> Rochester, MN 55901
> gedlund@xxxxxxxxxx
>=20
> ----- Forwarded by Gregory R Edlund/Rochester/IBM on 12/07/2007 08:00
AM
> -----
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> FreeLists Mailing List Manager <ecartis@xxxxxxxxxxxxx>
> 12/07/2007 01:19 AM
> Please respond to
> si-list@xxxxxxxxxxxxx
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> To
> si-list digest users <ecartis@xxxxxxxxxxxxx>
> cc
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> Subject
> si-list Digest V7 #410
>=20
>=20
>=20
>=20
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> si-list Digest           Fri, 07 Dec 2007                Volume: 07
Issue:
> 410
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> In This Issue:
>                  #1:             From: Ria R <ria_rr_84@xxxxxxxxx>
>                                  Subject: [SI-LIST]
Passivity/Causality
>=20
> ----------------------------------------------------------------------
>=20
> Msg: #1 in digest
> Date: Thu, 6 Dec 2007 21:58:24 -0800 (PST)
> From: Ria R <ria_rr_84@xxxxxxxxx>
> Subject: [SI-LIST] Passivity/Causality
>=20
> Gurus,
>   I have heard these 2 terms alot in the world of SI: Passivity and
> Causality.
>   I tried googling it and I dont seem to get what I am lookimg for.
>  Can someone please throw some light on the definitions of these 2
terms
> and what significance they have in Signal Integrity?
> Thanks in advance,
> Best Regards,
>=20
> Ria.
>=20
>=20
>=20
>
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> End of si-list Digest V7 #410
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