[SI-LIST] Re: enforcing passivity on s-parameter
- From: Faraydon Pakbaz <pakbazf@xxxxxxxxxx>
- To: Ihsan Erdin <erdinih@xxxxxxxxx>
- Date: Thu, 16 May 2013 15:04:03 -0400
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It is not curve fitting! Curve fitting is you take data of two or thre=
e
dimensional data and you come up with polynomial fit.
This is matching Mag and Phase with poles and zeros. I agree that this =
sort
of work is an art and as I mentioned it is a tool
in a tool box that may work on many situations. Never claimed it is an
ultimate solution. But for sure it is not just a curve fitting.
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|Faraydon Pakbaz/Burlington/IBM@IBMUS, =
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|"Amit.Kumar@xxxxxxxxxxx" <Amit.Kumar@xxxxxxxxxxx>, nitin.chhabra@st.=
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|05/16/2013 01:29 PM =
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|Re: [SI-LIST] Re: enforcing passivity on s-parameter =
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Curve-fitting to a rational transfer function is not going to help by
itself unless the fitting process is constrained for passivity. But tha=
t
takes us back to the original question of whether the constrained
mathematical function is a true representation of the physical system o=
r
not.
It is possible to guarantee passivity by simply fitting the data to a
circuit of lumped components instead of a transfer function. But anyone=
who
tried that knows that this theoretical remedy usually leads to impracti=
cal
results especially for a coupled interconnect system. Except the algori=
thms
for transmission lines which have matured over the last decade, circuit=
simulation of distributed systems is usually more like an art than scie=
nce,
especially for measured data.
Regards.
Ihsan Erdin
On Thu, May 16, 2013 at 9:02 AM, Faraydon Pakbaz <pakbazf@xxxxxxxxxx>
wrote:
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Amit;
Or another option is to generate the transfer function of S-parameter=
. =3D
This
is fitting
for example S21 "Mag vs Freq" and "Phase vs Freq" with rational trans=
fe=3D
r
function
by fitting appropriate poles and zeros. One can then use this transfe=
r
function in any
simulator that recognizes the transfer function. As always every meth=
od=3D
=A0has
its trade offs.
This method of transfer function may get complicated due to many abru=
pt=3D
changes in phase
but then one may question the causality of existing S-parameters and =
me=3D
thod
it was
created.
Regards;
Don Pakbaz
Silicon Solutions Engineering
IBM Systems & Technology Group
Email: pakbazf@xxxxxxxxxx
Voice: (802) 769-5638 =A0Tieline: 446-5638 =A0 Fax: (802) 769-5722
"This e-mail and its attachments, if any, may contain confidential an=
d
privileged material for the sole use of the intended =A0recipient. An=
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|------------>
| From: =A0 =A0 =A0|
|------------>
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=A0 |Scott McMorrow <scott@xxxxxxxxxxxxx> =A0 =A0 =A0 =A0 =A0 =A0 =A0=
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=3D
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
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=A0 |nitin.chhabra@xxxxxx, =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =3D
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
=3D
=A0 =A0 =A0 =A0|
=A0 >----------------------------------------------------------------=
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=A0 |"si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>, "Amit.Kumar@san=
disk=3D
.com" <Amit.Kumar@xxxxxxxxxxx> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =3D
=A0 =A0 =A0 =A0|
=A0 >----------------------------------------------------------------=
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=A0 |05/16/2013 08:08 AM =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =3D
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
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=A0 |[SI-LIST] Re: enforcing passivity on s-parameter =A0 =A0 =A0 =A0=
=A0 =A0 =A0 =A0 =A0 =A0=3D
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
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=A0 |si-list-bounce@xxxxxxxxxxxxx =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=3D
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
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I suggest a different approach. =A0Passivity violations are due to th=
e er=3D
rors
in either an EM field solver method or measurement. =A0In transient
simulation in Hspice, if you cascade multiple elements, each element'=
s
passivity violation can result in convergence problems, since the err=
or=3D
indicates gain in a passive element. =A0"Fixing" the passivity violat=
ion
involves an algorithmic process to try and "guess" what the value sho=
ul=3D
d
be, or to at least choose new values for those points that are
well-behaved. =A0This itself can introduce errors. =A0Remember, it's =
just a=3D
guess, no matter how educated the tool vendor says it is.
An alternative approach is to realize that the passivity violation is=
usually extremely small with respect to the actual signal amplitude p=
as=3D
sing
through the model. =A0The simplest fix is to turn down the gain, that=
is,=3D
=A0add
enough loss so that the total gain is less than 1. =A0But that's what=
interconnect channels do. They have attenuation that is much larger t=
ha=3D
n
the passivity violations in all but the worst constructed S-parameter=
models or measurements. In that case, the best approach to "fixing" t=
he=3D
=A0bad
s-parameter is to concatenate it with other lossy s-parameters in the=
frequency domain, and then use the resulting composite model section
transient analysis.
In my process, I create full channel s-parameter cascade models for a=
ll=3D
=A0of
the interconnect parameters that I want to sweep and test. =A0The ful=
l
frequency domain response can then be evaluated, and the models can b=
e =3D
used
in fast transient analysis much more efficiently. =A0I trade off disk=
sto=3D
rage
space for time and efficiency in simulation. =A0With Terabyte drives =
this=3D
seems like a good trade to me.
It's a simple method, adds no additional sources of error, and is wha=
t
nature does. =A0Oh, and it's faster in transient simulation, too.
best regards,
Scott
On Thu, May 16, 2013 at 3:29 AM, Nitin Kumar CHHABRA
<nitin.chhabra@xxxxxx>wrote:
> Hi Amit,
>
> Enforcing the passivity do changes the S-parameters.
> You can enforce passivity , but before enforcing the passivity you =
ne=3D
ed
to
> check 2 things :
> 1. What is the algorithm tool is using to enforce the passivity.
> 2. Check the frequencies where the violation is occurring and make =
su=3D
re
> that is not lying in the zone of interest.
>
> After checking the above two things, you can enforce the passivity =
an=3D
d do
> the transient simulation.
>
> With regards,
> Nitin
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@freelists=
.o=3D
rg]
> On Behalf Of Amit Kumar
> Sent: Thursday, May 16, 2013 7:41 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] enforcing passivity on s-parameter
>
> Hello Experts,
> Many a times I face convergence issues in simulation because of
> s-parameter.
> I then enforce passivity on s-parameter and it does work most of th=
e
times.
> The question I have is : Can we trust the results we get after enfo=
rc=3D
ing
> passivity on s-parameter or enforcing passivity spoils the s-parame=
te=3D
r?
>
> Regards
> Amit
>
> ________________________________
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Teraspeed Consulting Group LLC
16 Stormy Brook Road
Falmouth, ME 04105
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