[SI-LIST] Re: source-termination and daisy chain question
- From: "Abe (Abbas) Riazi" <ariazi@xxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 5 Jul 2007 11:41:34 -0700
=20
Dear Han Li,
There is a powerful relationship between termination, topology and
technology,
which are sometimes called the "the three Ts". Subsequently,
determining
an effective termination strategy (for optimizing signal quality or
timing margins)
requires taking into account various features of topology and technology
(of=20
driver and receiver components). This can necessitate modeling and
simulation.
Certain guidelines exist for use of series (source) and parallel (end)
terminations.
For instance, series termination is well suited for point-to-point
(uni-directional)
connections. It may be also applied for star topologies, or for cases
when multiple
receivers are clustered close to the end of the net. Parallel
termination is=20
normally the superior choice for daisy chain (multi-drop) routing.
Mathematical equations are available for estimating series terminator
values
as a function of driver output impedance and line characteristic
impedance (Zo).
Also, the values of parallel/far-end terminators are directly related to
Zo.
However, as mentioned earlier in this thread, the optimum type, location
and=20
values of terminators (for high-speed nets) are usually ascertained
with aid of simulation.
Of course, in addition to series and parallel terminations there are
other
choices (such as Thevenin, AC parallel and Schottky diode terminations,
etc.)=20
which are useful to know. A good paper on this topic is:
http://www.edn.com/archives/1998/021698/04df_04.pdf
Best Regards,
Abe Riazi
ServerWorks
P.S. My article, "Signal Quality Assessment" PCD&M June 2007, discusses
signal quality, noise management and the tree Ts, plus ten references
for further
studies.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Han Li
Sent: Monday, July 02, 2007 11:26 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] source-termination and daisy chain question
Hi everyone,
It seems a simple question,But I still have something i cannot
completly understand.
A daisy chain is often used in multidrop topology, which need an
end-termination. And, source-termination doesnot work properly in daisy
chain,because the device in the middle of the chain would get a
plateau;using source-termination, all load should be at the end of the
line.
So, in a design , i should figure out minimul distance between, say
two receivers. In other words, I should decide beyond what distance
between two receivers , source-termination should not be used, and this
topology can be named a daisy chain?
Could anyone provide a deeper explanation? Thanks a lot!
---- ------ -------
Driver---------revceiver_1-----------------------receiver_2
---- ------- --------
|-------------distance---------|
-=20
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