LVDS over non-twisted flat ribbon cable
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Posted by Rene Tschaggelar on July 16, 2008, 4:47 am
Please log in for more thread options 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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Posted by John Larkin on July 16, 2008, 10:19 am
Please log in for more thread options 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 | |||||||||||||||||||
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Posted by Rene Tschaggelar on July 16, 2008, 4:49 pm
Please log in for more thread options John Larkin wrote:
> wrote:
> > >>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 >
> > 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 -- Ing.Buero R.Tschaggelar - http://www.ibrtses.com & commercial newsgroups - http://www.talkto.net | |||||||||||||||||||
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Posted by John Larkin on July 16, 2008, 6:46 pm
Please log in for more thread options wrote:
>John Larkin wrote:
>> wrote:
>> >> >>>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 >>
>> >> 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 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. John | |||||||||||||||||||
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Posted by Dirk Bruere at NeoPax on July 16, 2008, 7:01 pm
Please log in for more thread options John Larkin wrote:
> wrote:
> >> John Larkin wrote:
>>> wrote:
>>> >>> >>>> 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 >>> >>> 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 >
> > 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. -- Dirk http://www.transcendence.me.uk/ - Transcendence UK Remote Viewing classes in London | |||||||||||||||||||
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>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