Re: [Xylo-SDR] LVDS buss topologies

[KD5NWA <kd5nwa@cox.net>]

You have to treat is as a transmission line, proper impedance on wires,
proper termination, very short stubs.

If you are going a fair distance then twisted wiring is the best because
it meets all the requirements for the wiring. 

If using a PC board, you not only have the burden of making sure the
lines have the correct impedance (determined by line thickness, width,
proximity to it's partner, and the insulators around the lines), but that
you don't make major changes to the composition of the board otherwise
you will start getting reflections. Different glues and material
thickness will throw the impedance off.

If using a bus, you need proper termination on both ends of the bus, if
you put the drivers on one end then you only need termination on the
other end, but you need to have the drivers close to the back-plane or
control the impedance of the lines to avoid reflections, both is the
best.

At 07:04 PM 2/21/2006, you wrote:

Ray
I?m showing my ignorance, but I was under the impression that LVDS used twisted pair and was not a ?buss friendly? design.
Multi-drop would seem logical, since folks already have other designs in mind for buss mounted cards.
Thanks
Eric
 
 

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From: xylo-sdr-bounces@lists.ae5k.us [ mailto:xylo-sdr-bounces@lists.ae5k.us] On Behalf Of Ray Anderson
Sent: Tuesday, February 21, 2006 5:26 PM
To: xylo-sdr@lists.ae5k.us
Cc: Ray Anderson
Subject: [Xylo-SDR] LVDS buss topologies
 
At the following URLs there are  Visio and JPEG drawings of  3 common LVDS buss topologies (Point to Point, Multi-Drop, and Multi-point) that might be found on a backplane. Each comes with it?s own challenges and problems.
 
 
http://www.hamsdr.com/dnld.aspx?id=144      (Visio format)

http://www.hamsdr.com/dnld.aspx?id=145      (.jpg format)
 
 
In the case of the Point to Point topology there is a single driver on the buss and multiple receivers. In the Multi-Point topologies there can be multiple drivers as well as multiple receivers. If I am interpreting the Janus and Lionheart block diagrams correctly it seems that the currently envisioned topology is point-to-point (Janus and Lionheart only). With the desire for extra backplane slots it looks like Multi-Drop. Are there applications envisioned in the future that might place multiple drivers on the buss in the Multi-point topology?
 
 
-Ray    WB6TPU
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Cecil Bayona
KD5NWA
www.qrpradio.com

I fail to see why doing the same thing over and over and getting the same results every time is insanity: I've almost proved it isn't; only a few more tests now and I'm sure results will differ this time ...