RE: [SI-LIST] : Oscillation in lumped circuits and transmission l

Peterson, James F (jfpeterson@space.honeywell.com)
Fri, 5 Feb 1999 08:14:24 -0500

Good question Arani,
I have often wondered the same thing (every time someone uses the term
ringing and reflection to describe the same phenomenon). The more I study
the SI area of engineering the more I notice that people can be describing
things differently based on different perspectives but still be correct.
That said, I believe that a lumped LRC circuit's behavior is not related to
a transmission line reflection. One good reason is that the period of the
lumped circuit's oscillation will be 2*pi*(LC)^1/2, whereas the period of a
reflection will always be 4*Pd (where Pd is the 1 way prop. time of the
signal). In fact this is a great way to tell the difference. If the period
of a measured signal is much larger than 4 * Pd, then it's a lumped LRC
problem (add some series r to get rid of it).
Hope this helps,
Jim

-----Original Message-----
From: Arani Sinha [mailto:sinha@poisson.usc.edu]
Sent: Friday, February 05, 1999 3:02 AM
To: si-list@silab.Eng.Sun.COM
Cc: sinha@poisson.usc.edu
Subject: [SI-LIST] : Oscillation in lumped circuits and transmission
lines

Hi,

I have the following question.

We can model an interconnect as either a lumped circuit or a
transmission line. By means of lumped modeling, we can say that
it has an oscillatory response if its damping factor is less
than 1. By means of transmission line modeling, we can say that
it has an oscillatory response if the signal reflection
co-efficients at source and load satisfy certain conditions.

My question is whether oscillation in a lumped circuit and
signal reflection in a transmission line are actually the same
phenomenon. If so, there should be a correlation between
conditions for oscillation in a lumped circuit and those for
oscillation in a transmission line.

After many discussions and much thought, I have not been able
to determine a correlation. I am also ambivalent about whether
they are the same phenomenon.

I understand that the damping factor in a lumped circuit is
equivalent to the attenuation constant in a transmission line
and that condition of no reflection is equivalent to the
maximum power transfer theorem.

I will really appreciate help in this regard.

Thanks,

Arani

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