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LVDS over non-twisted flat ribbon cable

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Rene Tschaggelar

Jan 1, 1970
0
I'm lacking the experience of LVDS over flat ribbon
cable that should be twisted, but is not. Different
pairs will couple with the next and with the outside
depending on frequency and length, but by how much ?
The motivation for the question comes from the rather
limited number of possible crimping locations a
twisted ribbon cable provides. Whereas a flat ribbon
cable can be crimped at any arbitrary millimeter.

I'd be using it for short runs, below 0.5m alltogether

Rene
 
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Rene Tschaggelar

Jan 1, 1970
0
John said:
What's your data rate, and what parts will you be using?

That length will be fine for most things short of the ultra-speed
stuff. It's recommend 3 or 4 wires per LVDS pair, with a ground
between a pair and anything else

gnd a+ a- gnd b+ b- gnd ...


The really fast stuff might get nasty over a half meter of standard
ribbon cable.

John

Thanks John,
It'll be 20MHz to 60MHz or so. The parts will be
65LVDS1 @ 65LVDS2. They'll synchronize different
subsystems in a distributed setup.

Rene
 
D

Dirk Bruere at NeoPax

Jan 1, 1970
0
John said:
Not super fast, so you should be OK. Be careful to keep the pair skew
down by routing equal length traces in/out of the ribbon cable
connectors. But it's not really hairy... 100 ps or so shouldn't break
anything.

Anybody know the differential impedance for a regular Scotchflex type
cable in this config, diff pairs with outside grounds? I'm too lazy to
TDR it.

Could also use that fancy ribbon cable that is wrapped in a flat shield.
 
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