gmane.technology.electronics.signal-integrity

Re: Causality Condition -why real and imaginary part of a Frequency response of causal system need to be even and odd respectively

Yuriy Shlepnev — 2013-05-18T15:54:54

Piyush,

Time-domain response must be a real function of time. If it is computed with
the inversed Fourier transform of the complex frequency domain response, the
TD response is be always real if the imaginary part of FD response is odd
and real part is even. It is the TD response realness condition. We do not
use negative frequency in analysis of interconnects, but the condition at DC
is useful to control quality of S-parameters: imaginary part  and derivative
of real part of FD response must be zero at DC. 

Best regards,
Yuriy

Yuriy Shlepnev, Ph.D.
President, Simberian Inc.
3030 S Torrey Pines Dr. Las Vegas, NV 89146, USA
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Cell +1-206-409-2368
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-----Original Message-----
From: si-list-bounce-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org [mailto:si-list-bounce-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org] On
Behalf Of piyush bhatt
Sent: Saturday, May 18, 2013 3:47 AM
To: si-list-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org
Subject: [SI-LIST] Causality Condition -why real and imaginary part of a
Frequency response of causal system need to be even and odd respectively

Hi All
An LTI system is causal if and only if h(t)=0 for t<0.

As derivation goes h(t)=h(t)sgn(t).Taking Freq transform both side and doing
some manipulations.We get to point that H(jw) = Hilbert transform of itself.

Then they say we can divide H(jw) into real and imaginary part.And real part
will be even function and imaginary part will be odd function.

Can you tell me why real part will be even function and imaginary part will
be odd function?

regards
Piyush


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Re: Causality Condition -why real and imaginary part of a Frequency response of causal system need to be even and odd respectively

Orin Laney — 2013-05-18T15:32:34

This is not an SI question.  The electrical engineering, mathematics, or
mathematical physics forums at http://www.researchgate.net/ are better tuned
for this sort of question.

Regards,
Orin Laney 

-----Original Message-----
From: si-list-bounce-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org [mailto:si-list-bounce-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org] On
Behalf Of piyush bhatt
Sent: Saturday, May 18, 2013 3:47 AM
To: si-list-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org
Subject: [SI-LIST] Causality Condition -why real and imaginary part of a
Frequency response of causal system need to be even and odd respectively

Hi All
An LTI system is causal if and only if h(t)=0 for t<0.

As derivation goes h(t)=h(t)sgn(t).Taking Freq transform both side and doing
some manipulations.We get to point that H(jw) = Hilbert transform of itself.

Then they say we can divide H(jw) into real and imaginary part.And real part
will be even function and imaginary part will be odd function.

Can you tell me why real part will be even function and imaginary part will
be odd function?

regards
Piyush


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Re: POE Circuitry

Stefan Milnor — 2013-05-18T15:08:32

Is simulation appropriate or feasible here? I think what you want is an
evaluation board, to do physical tests on. All the major vendors of POE
silicon have evaluation boards available.

-----Original Message-----
From: si-list-bounce-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org [mailto:si-list-bounce-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org]
On Behalf Of steve weir
Sent: Saturday, May 18, 2013 2:58 AM
To: si-list-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org
Subject: [SI-LIST] Re: POE Circuitry

Sunil your question is very broad.  If you are interested in using
particular ICs then the obvious next step is to obtain models from those
manufacturers.  Many of the magnetics have models available from their
respective manufacturers as well.

Steve.
On 5/18/2013 2:45 AM, sunil bharadwaz wrote:
available .


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Causality Condition -why real and imaginary part of a Frequency response of causal system need to be even and odd respectively

piyush bhatt — 2013-05-18T10:46:48

Hi All
An LTI system is causal if and only if h(t)=0 for t<0.

As derivation goes h(t)=h(t)sgn(t).Taking Freq transform both side and
doing some manipulations.We get to point that H(jw) = Hilbert transform of
itself.

Then they say we can divide H(jw) into real and imaginary part.And real
part will be even function and imaginary part will be odd function.

Can you tell me why real part will be even function and imaginary part will
be odd function?

regards
Piyush


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Re: POE Circuitry

steve weir — 2013-05-18T09:58:08

Sunil your question is very broad.  If you are interested in using 
particular ICs then the obvious next step is to obtain models from those 
manufacturers.  Many of the magnetics have models available from their 
respective manufacturers as well.

Steve.
On 5/18/2013 2:45 AM, sunil bharadwaz wrote:

POE Circuitry

sunil bharadwaz — 2013-05-18T09:45:38

Hi Friends ,
I was going through some of the POE ( Power over Ethernet ) circuits available .
Design spec is 48V to 5V or 48V to 3.3V < at > 2.5 to 3 Amps .

I will be helpful if some one can share the info or point me to the 

right links .Are there any simulation models available ?


Thanks in Advance !!


Regards
Sunil


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Berkeley spice vs HSPICe for W-model vs U-model

Elias Lozano — 2013-05-17T22:28:04

Hello experts:

I am used to simulating SI/PI with W-model in HSPICe. Recently I have found a customer who uses berkely spice. Has anyone of you tried u-model in Berkely spice and what is the accuracy with respect to W-element in HSPICE? Also, how have you handled (simulated) mutual inductance/capacitance in Bspice?

any comments, ideas, suggestions will be appreciated..

thanks a lot

EL

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Employment Opportunity with Oracle (Burlington, MA)

Jason Miller — 2013-05-17T16:49:07

We have an opening within the Oracle SPARC Processor Group for a signal 
integrity engineer with 3-7 years of relevant industry experience in 
packaging and board design/analysis. The job location is Burlington, MA. 
Please find the job description and requirements below. To apply for 
this position, please use the link below.

Please email me directly at jason.miller-QHcLZuEGTsvQT0dZR+AlfA< at >public.gmane.org with any questions.

------------------------------------------------------------------------------------------------------------------------------------
Description
Our organization is looking for a highly motivated, dedicated team 
member to perform signal integrity modeling, design and characterization 
of server hardware including packages and PCBs.

Signal Integrity engineers participate in all phases of the system 
life-cycle including:
-         Initial concept/architecture
-         Simulation/correlation of high speed passive channels
-         Creation of design rules, driving physical layout and review
-         Bring-up and validation of systems

Job Requirements
- Duties and tasks are varied and complex needing independent judgment
- May have project lead role and or supervise junior engineers
- Ideal candidate will have M.S. or Ph.D in Electrical Engineering or 
Computer Science
- 3-7 years relevant experience in signal integrity
- Experience with printed circuit board design and/or packages
- Background in high-frequency design techniques
- Experience analyzing and optimizing  passive channels in both time and 
frequency domain
- Experience with high-speed simulation tools and field solvers (ADS, 
CST, HFSS, MATLAB)
- Ability to perform multi-GB/s VNA measurements
- Familiar with N-port network analysis (S-parameters, ABCD-parameters)
- Familiar with Cadence Allegro layout tools

To apply:
http://tinyurl.com/IRC2135772
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Re: enforcing passivity on s-parameter

Alfred P. Neves — 2013-05-16T20:07:09

Another solution, which addresses the error with a systematic approach, and is based on good metrology practice is as follows:   
 
Most of the passivity violations occur (in my experience) when the device transmission is low loss such as short interconnects, such that the transmission is similar to the Etf correction, or forward transmission correction in the error box.   It is important to relate the device characteristics to what is being fixed or calibrated for in the VNA calibration.  For non-reflective devices we
 
-        Check THRU with a non-Insertable calibration with the appropriate connector, such as a KF-KF with male-ended SOLT calibrated VNA cable ends. 

-        Validate the VNA calibration with a NIST traceable airline. Check the calibration first with simple adapter, assume approximately 0.1dB of loss for the connector loss to 40GHz, typically 50psec of group delay.   We check group delay noise at this point to make sure IF bandwidth, number of points, etc,   Check passivity with this simple adapter, then use the airline.  The airline has length, no mode issues, and a bit of loss, and represents my perfect short interconnect.   For moderately reflective devices, like VIA fields/connectors we add a stepped impedance line to the mix.

-        You can adjust loss in the VNA using port extension just slightly to clean up minor calibration errors that yield passivity violations.   We then typically store the very minor port extension loss in the state file configuring the VNA, along with the calibration set.   

 
Our experience is that this methodology works for short interconnect measurements.   For moderate to highly reflective devices we add a Stepped Impedance version of the airline to the mix.


Most of this is documented in our Tutorial delivered with Tektronix and Anritsu:  "Methods of Improving 3D EM Model Development and Associated Time/Frequency Domain Measurements"  â¨Jim Bell and Al Neves, Wild River Technologyâ¨, Bob Buxton and Jon Martens, Anritsu Company, Josiah Bartlett, Tektronix





       




Products for the Signal Integrity Practitioner



Alfred P. Neves
Chief Technologist

 

Office: 503-679-2429

www.wildrivertech.com

 








On May 16, 2013, at 12:04 PM, Faraydon Pakbaz <pakbazf-r/Jw6+rmf7HQT0dZR+AlfA< at >public.gmane.org> wrote:



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Re: enforcing passivity on s-parameters

Dmitriev-Zdorov, Vladimir — 2013-05-16T19:52:05

Amit,

Many responses on you original question are valuable. Still, it is difficult to give yes or no answer for all cases. You need to consider several things:

1. Large or small passivity violations?
This can be found as having negative eigenvalues in the matrix (E-SS*), with identity 'E' and Hermitian conjugate S*. If they are small, e.g. 1e-3 or less, non-passivity correction won't not change the data much, but also with high probability you will not experience instability with this model.
If passivity violations are large, you have no choice as to fix that.

2. Can we us the model with large passivity violations?
Assuming we fix non-passivity, what's then? Look where exactly non-passivity is located. Is this e.g. near to base frequency of the channel you need to simulate, or somewhere at very low or high frequency, compared to what's important to you. If the first, you would better not use your model because you should rely right on the data which cannot be trusted. In the second case, you may still use your model with some care.

3. Methods used to fix passivity
There are many ways of fixing non-passivity, good and bad. Scott mentioned adding absorbing models, which at least guarantee that the corrected model does not get causality issues (if it did not before the fix). Beware of methods making local corrections to sampled S-parameter data, like trimming out the portion that shows violations without modifying the neighbor points. Such correction is equivalent to multiplication of your dependence on highly non-causal function. The problem with acquired non-causality is inability to accurately perform time domain simulation, since IFFT of non-causal function contains portions of the impulse response at negative times, which cannot be used. Non-causality by itself (even for passive model) may cause considerable inaccuracies in time domain analysis, including both deficiency or excess in the response's energy (the latter may cause instability as well).

4. Passivity enforcement methods must target the algorithms of your time domain simulation
For convolution-based approached, you need to make sure that the model is passive and causal. After IFFT is taken for the responses, you need to make sure the time domain responses create a passive matrix, too. For methods based of recursive convolution (these involve fit with rational polynomials or fraction expansion), it is more important to make sure that the resulted approximation fit is passive (it is causal by design). Here, passivity should be global, from DC to infinite frequency, otherwise you risk getting instability in your timed domain solution.

Vladimir
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Re: enforcing passivity on s-parameter

Antonis Orphanou — 2013-05-16T19:47:13

Hello Amit,

Enforcing passivity is an interesting problem. Firstly because in enforcing passivity you are trying to guess the low frequency system response of the measured system. Even if you know exactly the dc loss of your channel filling in the missing frequency points is a real challenge. Even the slightest error in the extrapolation can cause your time domain analysis to drift. In reality the low frequency domain error is nothing but a slow modulation of your input bit sequence. The more bits you pass through the erroneous channel, the more energy you accumulate at the other end and the more drift you will notice.

For short channels it might take a lot of bits to notice the drift so you might be able to get away with it. For long channels though (talking about loss here) the task is even more challenging. To test if a tool is good at fixing your passivity issue,  just use a long channel as a bench mark.

I would use a tool that fixes stability using state space  rather than extrapolations by curve fitting.



-----Original Message-----
From: si-list-bounce-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org [mailto:si-list-bounce-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org] On Behalf Of Amit Kumar
Sent: Wednesday, May 15, 2013 10:41 PM
To: si-list-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org
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 the times.
The question I have is : Can we trust the results we get after enforcing passivity on s-parameter or enforcing passivity spoils the s-parameter?

Regards
Amit

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Re: enforcing passivity on s-parameter

Faraydon Pakbaz — 2013-05-16T19:04:03

Content-type: text/plain; charset=ISO-8859-1
Content-transfer-encoding: quoted-printable

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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  |Re: [SI-LIST] Re: enforcing passivity on s-parameter                =
                                                                       =
       |
  >--------------------------------------------------------------------=
-----------------------------------------------------------------------=
-------|





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-r/Jw6+rmf7HQT0dZR+AlfA< at >public.gmane.org>
wrote:
  Content-type: text/plain; charset=3DISO-8859-1
  Content-transfer-encoding: quoted-printable

  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-r/Jw6+rmf7HQT0dZR+AlfA< at >public.gmane.org
  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=
y
  review, use, distribution or
  disclosure by others is strictly prohibited. If you are not the inten=
de=3D
  d
  recipient (or authorized to receive for the recipient), please contac=
t =3D
  the
  sender by reply e-mail
  and delete all copies of this message from your system without copyin=
g =3D
  it
  and notify sender of the misdirection by reply e-mail. "


  |------------>
  | From: =A0 =A0 =A0|
  |------------>
  =A0 >----------------------------------------------------------------=
----=3D
  ---------------------------------------------------------------------=
--=3D
  -------|
  =A0 |Scott McMorrow <scott-3mpTjvN7S/72eFz/2MeuCQ< at >public.gmane.org> =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 >----------------------------------------------------------------=
----=3D
  ---------------------------------------------------------------------=
--=3D
  -------|
  |------------>
  | To: =A0 =A0 =A0 =A0|
  |------------>
  =A0 >----------------------------------------------------------------=
----=3D
  ---------------------------------------------------------------------=
--=3D
  -------|
  =A0 |nitin.chhabra-qxv4g6HH51o< at >public.gmane.org, =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 >----------------------------------------------------------------=
----=3D
  ---------------------------------------------------------------------=
--=3D
  -------|
  |------------>
  | Cc: =A0 =A0 =A0 =A0|
  |------------>
  =A0 >----------------------------------------------------------------=
----=3D
  ---------------------------------------------------------------------=
--=3D
  -------|
  =A0 |"si-list-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org" <si-list-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org>, "Amit.Kumar< at >san=
disk=3D
  .com" <Amit.Kumar-XdAiOPVOjttBDgjK7y7TUQ< at >public.gmane.org> =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 >----------------------------------------------------------------=
----=3D
  ---------------------------------------------------------------------=
--=3D
  -------|
  |------------>
  | Date: =A0 =A0 =A0|
  |------------>
  =A0 >----------------------------------------------------------------=
----=3D
  ---------------------------------------------------------------------=
--=3D
  -------|
  =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=
=3D
  =A0 =A0 =A0 =A0|
  =A0 >----------------------------------------------------------------=
----=3D
  ---------------------------------------------------------------------=
--=3D
  -------|
  |------------>
  | Subject: =A0 |
  |------------>
  =A0 >----------------------------------------------------------------=
----=3D
  ---------------------------------------------------------------------=
--=3D
  -------|
  =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=
=3D
  =A0 =A0 =A0 =A0|
  =A0 >----------------------------------------------------------------=
----=3D
  ---------------------------------------------------------------------=
--=3D
  -------|
  |------------>
  | Sent by: =A0 |
  |------------>
  =A0 >----------------------------------------------------------------=
----=3D
  ---------------------------------------------------------------------=
--=3D
  -------|
  =A0 |si-list-bounce-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org =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 >----------------------------------------------------------------=
----=3D
  ---------------------------------------------------------------------=
--=3D
  -------|





  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-qxv4g6HH51o< at >public.gmane.org>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-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org [mailto:si-list-bounce< at >freelists=
.o=3D
  rg]
  > On Behalf Of Amit Kumar
  > Sent: Thursday, May 16, 2013 7:41 AM
  > To: si-list-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org
  > 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
  >
  > ________________________________
  >
  > PLEASE NOTE: The information contained in this electronic mail mess=
ag=3D
  e is
  > intended only for the use of the designated recipient(s) named abov=
e.=3D
  =A0If
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  > notified that you have received this message in error and that any
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  --

  Scott McMorrow
  Teraspeed Consulting Group LLC
  16 Stormy Brook Road
  Falmouth, ME 04105

  (401) 284-1827=A0Business

  http://www.teraspeed.com

  Teraspeed=3DAE is the registered service mark of
  Teraspeed Consulting Group LLC

  ------------------------------------------------------------------
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  =3D



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 http://www.qsl.net/wb6tpu

Re: enforcing passivity on s-parameter

Ihsan Erdin — 2013-05-16T17:29:06

Curve-fitting to a rational transfer function is not going to help by
itself unless the fitting process is constrained for passivity. But that
takes us back to the original question of whether the constrained
mathematical function is a true representation of the physical system or
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 impractical
results especially for a coupled interconnect system. Except the algorithms
for transmission lines which have matured over the last decade, circuit
simulation of distributed systems is usually more like an art than science,
especially for measured data.

Regards.

Ihsan Erdin


On Thu, May 16, 2013 at 9:02 AM, Faraydon Pakbaz <pakbazf-r/Jw6+rmf7HQT0dZR+AlfA< at >public.gmane.org> wrote:



------------------------------------------------------------------
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Old (prior to June 6, 2001) list archives are viewable at:
 http://www.qsl.net/wb6tpu

Re: enforcing passivity on s-parameter

Faraydon Pakbaz — 2013-05-16T13:02:49

Content-type: text/plain; charset=ISO-8859-1
Content-transfer-encoding: quoted-printable

Amit;

Or another option is to generate the transfer function of S-parameter. =
This
is fitting
for example S21 "Mag vs Freq" and "Phase vs Freq" with rational transfe=
r
function
by fitting appropriate poles and zeros. One can then use this transfer
function in any
simulator that recognizes the transfer function. As always every method=
 has
its trade offs.
This method of transfer function may get complicated due to many abrupt=

changes in phase
but then one may question the causality of existing S-parameters and me=
thod
it was
created.

Regards;

Don Pakbaz

Silicon Solutions Engineering
IBM Systems & Technology Group
Email: pakbazf-r/Jw6+rmf7HQT0dZR+AlfA< at >public.gmane.org
Voice: (802) 769-5638  Tieline: 446-5638   Fax: (802) 769-5722

"This e-mail and its attachments, if any, may contain confidential and
privileged material for the sole use of the intended  recipient. Any
review, use, distribution or
disclosure by others is strictly prohibited. If you are not the intende=
d
recipient (or authorized to receive for the recipient), please contact =
the
sender by reply e-mail
and delete all copies of this message from your system without copying =
it
and notify sender of the misdirection by reply e-mail. "

|------------>
| From:      |
|------------>
  >--------------------------------------------------------------------=
-----------------------------------------------------------------------=
-------|
  |Scott McMorrow <scott-3mpTjvN7S/72eFz/2MeuCQ< at >public.gmane.org>                                =
                                                                       =
       |
  >--------------------------------------------------------------------=
-----------------------------------------------------------------------=
-------|
|------------>
| To:        |
|------------>
  >--------------------------------------------------------------------=
-----------------------------------------------------------------------=
-------|
  |nitin.chhabra-qxv4g6HH51o< at >public.gmane.org,                                               =
                                                                       =
       |
  >--------------------------------------------------------------------=
-----------------------------------------------------------------------=
-------|
|------------>
| Cc:        |
|------------>
  >--------------------------------------------------------------------=
-----------------------------------------------------------------------=
-------|
  |"si-list-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org" <si-list-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org>, "Amit.Kumar< at >sandisk=
.com" <Amit.Kumar-XdAiOPVOjttBDgjK7y7TUQ< at >public.gmane.org>                                         =
       |
  >--------------------------------------------------------------------=
-----------------------------------------------------------------------=
-------|
|------------>
| Date:      |
|------------>
  >--------------------------------------------------------------------=
-----------------------------------------------------------------------=
-------|
  |05/16/2013 08:08 AM                                                 =
                                                                       =
       |
  >--------------------------------------------------------------------=
-----------------------------------------------------------------------=
-------|
|------------>
| Subject:   |
|------------>
  >--------------------------------------------------------------------=
-----------------------------------------------------------------------=
-------|
  |[SI-LIST] Re: enforcing passivity on s-parameter                    =
                                                                       =
       |
  >--------------------------------------------------------------------=
-----------------------------------------------------------------------=
-------|
|------------>
| Sent by:   |
|------------>
  >--------------------------------------------------------------------=
-----------------------------------------------------------------------=
-------|
  |si-list-bounce-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org                                        =
                                                                       =
       |
  >--------------------------------------------------------------------=
-----------------------------------------------------------------------=
-------|

I suggest a different approach.  Passivity violations are due to the er=
rors
in either an EM field solver method or measurement.  In transient
simulation in Hspice, if you cascade multiple elements, each element's
passivity violation can result in convergence problems, since the error=

indicates gain in a passive element.  "Fixing" the passivity violation
involves an algorithmic process to try and "guess" what the value shoul=
d
be, or to at least choose new values for those points that are
well-behaved.  This itself can introduce errors.  Remember, it's just a=

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 pas=
sing
through the model.  The simplest fix is to turn down the gain, that is,=
 add
enough loss so that the total gain is less than 1.  But that's what
interconnect channels do. They have attenuation that is much larger tha=
n
the passivity violations in all but the worst constructed S-parameter
models or measurements. In that case, the best approach to "fixing" the=
 bad
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 all=
 of
the interconnect parameters that I want to sweep and test.  The full
frequency domain response can then be evaluated, and the models can be =
used
in fast transient analysis much more efficiently.  I trade off disk sto=
rage
space for time and efficiency in simulation.  With Terabyte drives this=

seems like a good trade to me.

It's a simple method, adds no additional sources of error, and is what
nature does.  Oh, 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-qxv4g6HH51o< at >public.gmane.org>wrote:

ed
to
re
d do
rg]
times.
ing
r?
e is
 If
eby
review,
notify
destroy
copies

--

Scott McMorrow
Teraspeed Consulting Group LLC
16 Stormy Brook Road
Falmouth, ME 04105

(401) 284-1827 Business

http://www.teraspeed.com

Teraspeed=AE is the registered service mark of
Teraspeed Consulting Group LLC

------------------------------------------------------------------
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Re: enforcing passivity on s-parameter

Scott McMorrow — 2013-05-16T12:06:47

I suggest a different approach.  Passivity violations are due to the errors
in either an EM field solver method or measurement.  In transient
simulation in Hspice, if you cascade multiple elements, each element's
passivity violation can result in convergence problems, since the error
indicates gain in a passive element.  "Fixing" the passivity violation
involves an algorithmic process to try and "guess" what the value should
be, or to at least choose new values for those points that are
well-behaved.  This itself can introduce errors.  Remember, it's just a
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 passing
through the model.  The simplest fix is to turn down the gain, that is, add
enough loss so that the total gain is less than 1.  But that's what
interconnect channels do. They have attenuation that is much larger than
the passivity violations in all but the worst constructed S-parameter
models or measurements. In that case, the best approach to "fixing" the bad
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 all of
the interconnect parameters that I want to sweep and test.  The full
frequency domain response can then be evaluated, and the models can be used
in fast transient analysis much more efficiently.  I trade off disk storage
space for time and efficiency in simulation.  With Terabyte drives this
seems like a good trade to me.

It's a simple method, adds no additional sources of error, and is what
nature does.  Oh, 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-qxv4g6HH51o< at >public.gmane.org>wrote:

Re: enforcing passivity on s-parameter

Nitin Kumar CHHABRA — 2013-05-16T07:29:24

Hi Amit,

Enforcing the passivity do changes the S-parameters.
You can enforce passivity , but before enforcing the passivity you need 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 sure that is not lying in the zone of interest.

After checking the above two things, you can enforce the passivity and do the transient simulation.

With regards,
Nitin


-----Original Message-----
From: si-list-bounce-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org [mailto:si-list-bounce-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org] On Behalf Of Amit Kumar
Sent: Thursday, May 16, 2013 7:41 AM
To: si-list-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org
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 the times.
The question I have is : Can we trust the results we get after enforcing passivity on s-parameter or enforcing passivity spoils the s-parameter?

Regards
Amit

________________________________

PLEASE NOTE: The information contained in this electronic mail message is intended only for the use of the designated recipient(s) named above. If the reader of this message is not the intended recipient, you are hereby notified that you have received this message in error and that any review, dissemination, distribution, or copying of this message is strictly prohibited. If you have received this communication in error, please notify the sender by telephone or e-mail (as shown above) immediately and destroy any and all copies of this message in your possession (whether hard copies or electronically stored copies).


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Re: enforcing passivity on s-parameter

steve weir — 2013-05-16T05:55:20

Amit, this has been the subject of much discussion and the answer is:  
"It depends".  At DC 2013 Al Neves presented different issues that he 
ran into with S-parameters after various packages "fixed them".  See his 
comments yesterday.

Steve.
On 5/15/2013 10:41 PM, Amit Kumar wrote:

enforcing passivity on s-parameter

Amit Kumar — 2013-05-16T05:41:13

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 the times.
The question I have is : Can we trust the results we get after enforcing passivity on s-parameter or enforcing passivity spoils the s-parameter?

Regards
Amit

________________________________

PLEASE NOTE: The information contained in this electronic mail message is intended only for the use of the designated recipient(s) named above. If the reader of this message is not the intended recipient, you are hereby notified that you have received this message in error and that any review, dissemination, distribution, or copying of this message is strictly prohibited. If you have received this communication in error, please notify the sender by telephone or e-mail (as shown above) immediately and destroy any and all copies of this message in your possession (whether hard copies or electronically stored copies).


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Re: Self and Mutual Inductance from S-Parameter

Alfred P. Neves — 2013-05-15T16:04:44

Ron,
Agilent ADS is a very good tool. However...

We routinely use Simbeor to obtain stellar correlation between measurement and simulation using causal/passive, well taken S-parameters. This includes eye diagrams to 15G, step and TDR responses down to 10.7psec measured using Tek TDR. We are in the process of a complete correspondence package to 32G eye using Anritsu BERT products and our Channel Modeling Platform CMP-32.

We have numerous papers from 2009 on our website supporting this. Jim Bell just finished an entire group of correspondence on the more pathologic networks (stepped impedance, VIA fields, ground voids, resonators) and nailed them for both TDR and time domain gated to 40GHz using Simbeor. The data is available in a presentation we are presenting to SI folks interested in this topic.

Although we use Simbeor to design our platforms, our customers have had positive correspondence with Hyperlynx, Ansoft tool correlation has worked well for us, Matlab tools have worked well for us as well using RF toolbox, and yes we did quite a bit of early work with Agilent ADS with our Channel Modeling platforms and obtained good correspondence as well.

Some of the things we learned:

1. Take good S-parameters that includes 5X Nyquist and good DC point. DO NOT correct for causality with any of the tools. They destroy the S-parameters (from our DesignCon2013 tutorial with Anritsu). Dont fix junk measurements, get it right with good metrology practice.
2. Our experience is the low frequency extrapolation to DC can be a problem crux. Simbeor RCM works well and gets you to DC.
3. The stimulus for simulation needs to exactly replicate the source measurement. This is not easy.
4. Windowing can create problems for IFFT. The mag errors hurt eye correspondence.
5. If the launches and general signal integrity yield mediocre return loss all bets are off in establishing good correspondence. Return loss needs to be good for launches out to 40-50GHz at least for 28G.
6. VNA calibration validation using stepped impedance standards works very well.

ping me, Ill send you a copy: "Methods of Improving 3D EM Model Development and Associated Time/Frequency Domain Measurements"â¨ Jim Bell and Al Neves, Wild River Technologyâ¨Bob Buxton and Jon Martens, Anritsu Companyâ¨Josiah Bartlett, Tektronix, DesignCon2013

Products for the Signal Integrity Practitioner

Alfred P. Neves
Chief Technologist

Office: 503-679-2429

www.wildrivertech.com

On May 15, 2013, at 8:31 AM, Ronald Miller <ron-Zo3/zdQu5IxBDgjK7y7TUQ< at >public.gmane.org> wrote:

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Re: Self and Mutual Inductance from S-Parameter

Ronald Miller — 2013-05-15T15:31:30

Hi Vivek
You are barking up the wrong tree.

Forget lumped parameter like inductance.  The basic parameter is the T-Line
impedance and coupling approached from an RF point of view(frequency 
domain).

To get back to the time domain where you are trying to work(eye pattern 
& BER) only
a signal convolution of the S-Parameters will do the job accurately from 
1 Ghz on up.

Lastly, only Agilent ADS is designed to accomplish this and anything 
less is a waste of time
because you will never get convergence between measurement and simulation.

Ron Miller


On 4/29/2013 11:48 PM, Vivek wrote:

Re: PCB Simulations

Weston Beal (wbeal — 2013-05-15T14:17:57

Brendan,

You might start with gEDA at 
http://www.geda-project.org/

I don't think that the layout to simulation package is created. If you are going to create that tool, it would be great to include it in the gEDA project.

Good luck,
Weston


-----Original Message-----
From: si-list-bounce-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org [mailto:si-list-bounce-uGLqWuYN4qMgsBAKwltoeQ< at >public.gmane.org] On Behalf Of Brendan Simpson
Sent: Monday, May 13, 2013 2:25 PM
To: SI LIST
Subject: [SI-LIST] PCB Simulations

Hello Experts,

Does anybody know of a cheap (read: Free) PCB simulation software for doing somewhat basic SI evaluations? I had a thought that maybe I could make a program to import a netlist and gerber files to generate the models necessary for analysis, but if someone else has already done this, it would be better. It doesn't have to be super powerful or super accurate. I do a lot of board layout work, but I do not have a lot of experience modeling complete PCBs. 

Thanks in advance,
Brendan------------------------------------------------------------------
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