FreeLists / si-list / [SI-LIST] Re: Termination Topology for Bidirectional Bus

[steve weir <weirsi@xxxxxxxxxx>]

Lynne, if by long you mean a trace that is multiple UI's long, then 
yes a damping resistor in the middle of the line isn't of much 
benefit.  However for lines that are sub one UI, there are any number 
of situations where a damping resistor mid-trace improves signal integrity.

The original question does not have a global answer.  As others have 
pointed out a "best" scheme is only best when it meets all the design 
requirements with fewer drawbacks than alternatives.

Regards,


Steve.
At 09:39 AM 3/2/2007, Lynne D. Green wrote:
>Hello, Saril,
>
>Simulation is important for determining an acceptable termination scheme,
>especially with multiple drivers on a bus.  For example, simulation will
>show that placing a series resistor in the middle of a long trace produces
>no improvement in signal integrity.  Since only one driver is driving at a
>time, one would do one simulation suite for each driver.
>
>Remember that each time a trace branches, there is an impedance
>discontinuity.  Once you have a layout, you will probably want to run
>post-layout simulations.
>
>Regards,
>Lynne
>
>
>"IBIS training when you need it, where you need it."
>
>Dr. Lynne Green
>Green Streak Programs
>http://www.greenstreakprograms.com
>425-788-0412
>lgreen22@xxxxxxxxxxxxxx
>
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
>Behalf Of Saril
>Sent: Friday, March 02, 2007 12:30 AM
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Termination Topology for Bidirectional Bus
>
>Hi,
>What would be the best termination topology for a Bidirectional Data bus?
>
>Is it a good thought to place the series termination resistor in the middle
>of the trace?
>
>Also when there are mulitple devices on the bus how can we boil down the SI
>issues.
>
>Its clear that HyperLinx can help on this but, it would be great to know a
>generic rule.
>
>
>Thanks in advance..
>
>Best regads
>Saril Kaiprath
>Design Engineer
>Fkextronics Design, Bangalore
>
>
>
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