RE: [SI-LIST] : Attenuation on a PCB trace

About this list Date view Thread view Subject view Author view

From: Lorang, David D ([email protected])
Date: Mon Apr 23 2001 - 13:01:57 PDT

I interested in whether on not anyone has modeled this degradation of rise
time (see excerpt below) that Mike has mentioned using a simulator. Can it
be done by building two transmission lines in the simulator, one for air
dielectric and one for FR4? If the two parallel transmission line method
works how would one calculated how much impedence to allocate to each
dielectric? Will a field solver tell you this?
Dave Lorang

-----Original Message-----
From: [email protected] [mailto:[email protected]]
Sent: Thursday, April 12, 2001 3:47 PM
To: [email protected]
Subject: Re: [SI-LIST] : Attenuation on a PCB trace


Surface traces will have at least two major elements of signal propagation,
one in the dielectric and the other above the surface. The latter is the
fastest. Summing the two signal elements at the termination causes
considerable risetime degradation for a "digital" signal because of
phases (and probably magnitude attenuation) of the same frequency
The phase relationships of the different harmonics are also changed;
therefore, an analytically predicted signal may be considerably off the mark

from the real signal. In short, I would have no confidence in an
predicted microstrip waveform until proven by correlation with lab
measurements. I have observed about 2:1 risetime degradation in a 9-inch,
50-Ohm microstrip versus the same length of stripline in the same board
during TDR tests; therefore, I would have little confidence in using a
20-inch microstrip interconnection at the bit rate you noted.


Michael L. Conn
Owner/Principal Consultant
Mikon Consulting

*** Serving Your Needs with Technical Excellence ***

**** To unsubscribe from si-list or si-list-digest: send e-mail to
[email protected] In the BODY of message put: UNSUBSCRIBE
si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
si-list archives are accessible at

About this list Date view Thread view Subject view Author view

This archive was generated by hypermail 2b29 : Thu Jun 21 2001 - 10:11:41 PDT