[SI-LIST] Re: SSO pushout, ground bounce definition

From: "Kai, Francis" <francis.kai@xxxxxxxxx>
To: "'mark.gailus@xxxxxxxxxxxx'" <mark.gailus@xxxxxxxxxxxx>
Date: Thu, 25 Apr 2002 11:14:59 -0700
Mark,

     I agree with you that "ground bounce" is a misleading terminology
because it implies that the "ground" is "bouncing", which is not the case. I
only say that it is tough to find an appropriate term to describe it, even
"simultaneous switching noise" may not be a term that fully describes this
physical phenomenon.
     When I was an Assistant Professor at Northeastern University many years
ago, I happened to know
Prof. Lance Glacer of MIT. He was teaching the VLSI course and I had to
learn from him (using his book) to teach an advance VLSI course at
Northeastern. I told him that "VLSI" was very tough. He replied, "Of course,
it is a multi-billion dollar business." Prof. Glacer measured the level of
difficulty based on the dollar in business. I believe the "signal integrity"
is getting tougher and tougher because it has pulled more money into it.
        For the "electromotive force" term, you can say that you are right
because in engineering applications we can always use a definition in a much
broader sense. Usually engineers are not scientists and they do not care
much about definitions and scientific concepts. What engineers do care is
whether they can design a working product and sell it to make a profit. I
came from a family of Liberal Arts and I was trained to use words correctly
and properly (in the Chinese language) when I was a boy. For example, I
don't like the term "high tech" but it generates a lot of money and it also
supports my family. So I live with it. "High tech" translates into "Gao Ke
Zi" in Chinese and in fact it should have been translated into "Gao ji ke
Zi." Nobody uses the term "Gao ji ke Zi."
      I hope we do not bore the whole si-list subscribers.

Best regards,

Francis
   

-----Original Message-----
From: mark.gailus@xxxxxxxxxxxx [mailto:mark.gailus@xxxxxxxxxxxx]
Sent: Thursday, April 25, 2002 9:50 AM
To: Kai, Francis
Cc: 'mark.gailus@xxxxxxxxxxxx'; Kai, Francis; si-list@xxxxxxxxxxxxx;
tom_pitten@xxxxxxxxxxxxxxxxxx; phil_stokoe@xxxxxxxxxxxxxxxxxx
Subject: RE: [SI-LIST] Re: SSO pushout, ground bounce definition



Hello, Francis.

1) I agree completely with your words:

"The "high-speed ground" has new meaning embedded in it."

That is an excellent statement and I like your background discussion
leading up to it.

2) I see that I cannot convince you that "ground bounce" is misleading
terminology and should not be used, so I will not try any further on that
topic. :-)

3) As far as the use of the term "electromotive force" (EMF) goes, I think
that you are correct in pointing out that the original and most correct
meaning of this term is for the voltage produced accross a chemical cell or
battery.  However, there exists a widespread electrical engineering usage
of the term EMF to include also the voltages induced by changing magnetic
fields, or induced on conductors which are moving through a magnetic field.
Shadowitz is more precise in distinguishing betweeen EMFs and voltages.  He
writes (page 385 of "The Electromagnetic Field", Dover 1988):

"The nonconservative electric field Eind ( "E induced" ) induced in one
part of a circuit by some means is not usually the primary object of
interest; that role is played by (equation: Vba=the line integral of Eind
from point a to point b) a quantity called the induced voltage.  MOST
PEOPLE CALL THIS QUANTITY THE ELECTROMOTIVE FORCE, OR THE EMF, BUT WE WILL
USE THE TERM VOLTAGE EXCLUSIVELY."

(Emphasis mine -- mg)

This whole discussion may seem like nit-picking to some, but "circuit" (as
opposed to "field") engineers would benefit from more precise terminology
that matches if possible the established terminology of physics.

Regards,  Mark Gailus








"Kai, Francis" <francis.kai@xxxxxxxxx> on 04/23/2002 07:42:38 PM

To:   "'mark.gailus@xxxxxxxxxxxx'" <mark.gailus@xxxxxxxxxxxx>, "Kai,
      Francis" <francis.kai@xxxxxxxxx>
cc:   si-list@xxxxxxxxxxxxx, tom_pitten@xxxxxxxxxxxxxxxxxx,
      phil_stokoe@xxxxxxxxxxxxxxxxxx

Subject:  RE: [SI-LIST] Re: SSO pushout, ground bounce definition


Dear Gurus and Mark,

     I read Mark's new message and the only thing I agree with him is that
there are not enough English words to describe the modern technology today.
(English majors: where are you?) Since there are not enough English words,
a term is used for different concepts can cause confusion and misleading
in science and technology.

     When I was a student in National Taiwan University, our teacher in
the Electromagnetic Wave course, Chen Tsun-hsiung, told us that there are
two different concepts in Electromagnetic theory, i.e., the "field concept"
and the "circuit concept." Later I found them out in the book,
"Time-Harmonic
Electromagnetic Fields," by R.F. Harrington. The "circuit folks" care about
the "grounds," and the "field folks" normally don't care about "grounds."
In
the
famous book, "Field Theory of Guided Waves," by Robert E. Collin, the term
"ground" is not even in the subject index! Collin belongs to the "field
folks."
Therefore Mark pointed out that "there is wisdom in the microwave
engineers'

dictum that 'there is no such thing as ground'," which is based on the
"field folks"
concept.

     A ground is originally defined as an equipotential point or plane that
serves
as a reference potential for a circuit or system. The "equipotential"
concept
is originated in electrostatics, where charge is involved. Unfortunately,
in

modern high-speed digital circuit when coupling is involved, such
"electostatic equipotential" no longer exists in this system. Therefore we
use
the term, "ground," is no longer identical to the original term "ground"
developed long time ago in electrostatics. The "high-speed ground" has new
meaning embedded in it.

     The "electromotive force," or emf, concept derives from the line
integral of
an electric field, Ee, generated by the chemical action in the battery.
(I have the book by Albert Shadowitz but it is not in my office now.)
Therefore it has nothing to do with the "ground bounce" concept discussed
here.
I do not think it is appropriate to use the term "electromagnetic force
caused by
changing currents in these same conductors," or "common-mode effects may
produce
roughly the same electromotive force along all power, ground, etc.," since
it was
not originally defined in this way.

    The "ground bounce" effect is a relatively new but important concept in
high-speed
digital circuitry. Before our English majors find a new term for this
concept, I
believe we shall still use it.

Regards,

Francis







-----Original Message-----
From: mark.gailus@xxxxxxxxxxxx [mailto:mark.gailus@xxxxxxxxxxxx]
Sent: Tuesday, April 23, 2002 11:24 AM
To: francis.kai@xxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx; tom_pitten@xxxxxxxxxxxxxxxxxx;
phil_stokoe@xxxxxxxxxxxxxxxxxx
Subject: [SI-LIST] Re: SSO pushout, ground bounce definition



(Sorry: my previous message was missing its last few lines.  --mg)

Dear Francis,

(1) I agree with your criticism of the use of the term "fluctuation" for
this phenomenon.  It does have special meanings in other areas of physics,
and for that reason should not be used in this case.  However, I still
agree with Raymond Chen that "ground bounce" is a misleading and, I think,
even a nonsensical term.  Perhaps "power/ground noise", "power/ground
transients", or even "power/ground bounce" would be an improvement.  "SSO",
etc, are also OK with me.  What do other SI-Listers have to say? The
crucial point here, I feel, is that it is not an effect that is determined
by the configuration of "ground" conductors or ground currents alone, but
by the interaction of ground conductors with signal and power conductors
and currents, etc.

(2) With regard to uniqueness of voltages, you have encouraged me to
clarify my thoughts -- thank you -- that is always a good thing -- and I
agree that my terminology was imprecise.

Let's see if I can be any clearer today:

I agree that in an actual physical circuit, Electric and Magnetic Fields
and Fluxes (as well as charges and currents) are uniquely determined.

Where I think there are pitfalls, is in the "mapping" of a transient
electromagnetic problem such as SSO, into the more restricted types of
descriptions allowed by circuit theory.

In electromagnetics we can separate an arbitrary electric field into
conservative (i.e, curl free) and purely nonconservative components, and
speak of the path integral of one as "potential difference" and the other
as "voltage" or "electromotive force".

(Typically, this electromotive force might involve something like a
chemical battery, or something like a conductor placed in a region with a
changing magnetic field, such as  the secondary of a transformer, or the
various pins of a device package, connector, etc.  There is an nice short
discussion of "voltage" or "electromotive force" versus "potential
difference" at the start of Chapter 11-1 on Faraday's Law, in  the book
"The Electromagnetic Field", by Albert Shadowitz, Dover Publications. )

It is a common practice to model the set of conductive pins in a device
package or a connector as coupled inductors.  Up to some frequency, a set
of coupled inductors includes the effects of electromotive forces caused by
changing currents in these same inductors, and if expanded into a lumped or
distributed multiconductor transmission line model includes the effects of
electromagnetic waves travelling "along" the intended transmission
direction.  However, by itself, neither model includes the effects of
electromotive forces in these same conductors associated with radiating
fields from the whole set of conductors, or with "externally" incident
fields on the outside of the set of conductors, or in other words, "common
mode" effects. This omission can give rise to differences of certain
predictions of these circuit theory models versus the real system.
Accuracy of agreement depends upon whether these differences are important
to the particular results being sought in the simulation. These common mode
effects, by definition, may produce roughly the same electromotive force
along all power, ground, and signal conductors in the "length" of the
interconnection, and therefore substantially "cancel out" in calculation of
"voltage differences" between various conductors at one or the other end of
the interconnections.

The result is that of the various voltages measureable in the simulation
circuit, some accurately match the real world, and some do not.  As you
said, it is a separate problem to determine which "voltages" we can
measure.  Even here, I think, the ones we can most easily measure are
exactly those which are more "automatically" in agreement between the
circuit model and the real world.

(You can tell -- I am still thinking.)

Thanks and best egards,

Mark Gailus




"Kai, Francis" <francis.kai@xxxxxxxxx>@freelists.org on 04/19/2002 06:20:20
PM

Please respond to francis.kai@xxxxxxxxx

Sent by:  si-list-bounce@xxxxxxxxxxxxx


To:   "'mark.gailus@xxxxxxxxxxxx'" <mark.gailus@xxxxxxxxxxxx>,
      chen@xxxxxxxxxxx
cc:   si-list@xxxxxxxxxxxxx, "Kai, Francis" <francis.kai@xxxxxxxxx>

Subject:  [SI-LIST] Re: SSO pushout, ground bounce definition



Dear Gurus,

     I do not agree with Mark on certain concepts listed below, however,
any

comments are welcome.

(1) "Fluctuation" has a quite different meaning if you agree with the
concept
in Statistical Mechanics or Thermodynamics. The "Fluctuation theory"
phenomena
do differ from the "ground bounce" effect occurred in signal integrity.
Therefore, if we want
to be consistent with physics (or physical concepts), the term
"Power/ground
fluctuation" will
not be as nice as "ground bounce" in signal integrity.

(2) I do not see the term "voltages" is not "uniquely defined". All those
theorems,
Ohms Law, Tellegen theorem, Maxwell Equations, do represent that voltages
are well-defined uniquely in an Electrical System. These theorems satisfy
the ODE (ordinary differential equations) and PDE (partial differential
equations)
and are well-posed. Therefore, "uniqueness" is guaranteed. There is no
theorem
to prevent voltages to be measurable, like Heisenberg's Uncertainty
Principle in
quantum mechanics. However, whether Mark or any other engineers/technicians
can
accurately measure those voltages is a different story.

Best regards,

Francis Kai

-----Original Message-----
From: mark.gailus@xxxxxxxxxxxx [mailto:mark.gailus@xxxxxxxxxxxx]
Sent: Friday, April 19, 2002 2:06 PM
To: chen@xxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: SSO pushout, ground bounce definition




Raymond,

Thanks for a very clear presentation.  I agree with you on all points,
especially the following:

(1) "Power/ground fluctuation" is a much clearer term than "ground boun=
ce",
which is always misleading and should not be used.

(2) In the real world and in EM theory, "voltages" (i.e., differences o=
f
electric potential) are frequently not uniquely defined or measurable,
particularly between "distant" points or where radiation can take place=
.

(3) With respect to multiconductor transmission lines: "Voltage drop al=
ong
the ground conductor (except DC) is not well defined based on EM theory=
."

I will add a couple of generic observations:

Much confusion and mischief results when inappropriate oversimplified
circuit-theory models are applied to electromagnetic problems.

There is wisdom in the microwave engineers' dictum that "there is no su=
ch
thing as ground".

Best regards,

Mark Gailus

Teradyne

------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List archives are viewable at:
          //www.freelists.org/archives/si-list
or at our remote archives:
          http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
          http://www.qsl.net/wb6tpu







------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List archives are viewable at:
          //www.freelists.org/archives/si-list
or at our remote archives:
          http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
          http://www.qsl.net/wb6tpu




------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List archives are viewable at:     
                //www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages 
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu
Follow-Ups:
- [SI-LIST] Re: SSO pushout, ground bounce definition
  - From: Alex McPheeters
[SI-LIST] Re: SSO pushout, ground bounce definition

Other related posts:
