Re: [SI-LIST] : RE: 2.5 GHz in FR4

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From: RMELLISON@aol.com
Date: Mon Apr 30 2001 - 03:56:08 PDT


Larry,
 After reading all of the replies to the 2.5GHz questiion, I can see the need
for using stripline to keep phaseshift constant on long runs. In trying to
make the stubs a part of the transmission line, wouldn't it be advisable to
utilise most of the via as part of the line by using the stripline located on
the opposite side of a card from the IC?
Consider the 8 layer stackup shown here for clarification.

------- Sig and IC layer
------------- Plane
------- Sig
------------- Plane
------------- Plane
------- Sig 2.5 GHz stripline
------------- Plane
------ Sig

The stub resulting from the the unused portion of the via is reduced in
length. The trick would be to make the vias look like the transmission line
impedance.

Another thought--It seems like an imbedded microstrip line would possess
almost the same qualities of a stripline in terms of dielectric affecting
phaseshift. Can a card be made so that the vias would go only from the IC
layer to an imbedded microstrip layer directly below? This would get rid of
any stubs. What do you think?

Richard Ellison
972-569-8317

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