[SI-LIST] : RE: [SI-LIST]: Long bus or star?

Grebenkemper, John (john.grebenkemper@compaq.com)
Tue, 6 Apr 1999 10:44:18 -0700

Josip;
The HP Application Note references a broadband power divider using an
impedance transformation. This technique takes a transmission line of
impedance Zo and divides the power into two transmission lines at 2Zo. Both
transmission lines are then parallel terminated with 2Zo. The method will
work for digital systems if the driver is always the same device and one can
parallel terminate at both receivers. However, if you series terminate it,
you will generate a significant reflected wave.
The star termination that I have used is designed to work with any port
being driven. The resistors at the center of the star are adjusted to damp
out the reflected waves to an acceptable level. This is different than what
is presented in the HP note.
-John Grebenkemper
-----Original Message-----
From: Josip Popovic [mailto:jpopovic@cmetele.com]
<mailto:[mailto:jpopovic@cmetele.com]>
Sent: Monday, April 05, 1999 8:31 AM
To: 'si-list@silab.eng.sun.com'
Subject: [SI-LIST] : RE: [SI-LIST]: Long bus or star?

John Grebenkemper,
Here is an interesting HP application note:
http://literature.hp.com:8220/litweb/pdf/5968-0007E.pdf
<http://literature.hp.com:8220/litweb/pdf/5968-0007E.pdf> AN1304-1
AN 1304-1 page 8, TDR example 5 and 6 give star configurations terminated
with (no 10 pF caps - or similar values) 100 resistors (it is assumed that
there is no reflections from the load).
It would be interesting to know if you had to change Zo of separate traces
to minimize reflections at the place where separate star traces are
"branching out" or the main trace (trace from the source to the place of
branching) was short enough so the above didn't have any importance?

PS: Also, I would like to ask you for a copy of your Design Con paper
please.

Josip Popovic email: jpopovic@cmetele.com <mailto:jpopovic@cmetele.com>
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