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

From: "Kai, Francis" <francis.kai@xxxxxxxxx>
To: "'mark.gailus@xxxxxxxxxxxx'" <mark.gailus@xxxxxxxxxxxx>,"Kai, Francis" <francis.kai@xxxxxxxxx>
Date: Tue, 23 Apr 2002 16:42:38 -0700
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

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

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