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

Dima Smolyansky ([email protected])
Fri, 05 Feb 1999 09:07:41 -0800

Although, it could be noted that the propagation delay of a transmission line Pd is related to L and C as
Pd = (LC)^1/2. In addition, the factor of 2*pi is just a conversion between linear and angular frequency, and therefore for even-handed comparison must be dropped. Then, the factor of 4 is apparently due to assumption of quarter
wavelength oscillation. But then, there will be a similar high-order oscillation for an LC circuit. I think this implies good correlation between the two models. The choice between the two comes down to a standard
lumped-distributed type analysis.

Hope this helps.

```--
Thanks,

-Dima

=========================
Dima Smolyansky
TDA Systems, Inc.
7465 SW Elmwood St.
Portland OR 97223
503-977-3629
503-245-5684 (FAX)
[email protected]
http://www.tdasystems.com

Peterson, James F (FL51) wrote:

> 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:[email protected]]
> Sent: Friday, February 05, 1999 3:02 AM
> To: [email protected]
> Cc: [email protected]
> 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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```