Running 100MHz line over a long cable

Thread Starter

moosefet

Joined Jun 18, 2020
3
Hi,
I am trying to run bi-directional lines through a cable of 5 ft in length. the frequency is gonna be 109MHz or so. These are open-drain lines so i am concerned about reliability. Any thoughts?
 

Thread Starter

moosefet

Joined Jun 18, 2020
3
@nsaspook
Thanks.
yea, the idea is without using signal drivers. We would need pull-ups for the open drain lines but i am guessing the cable itself is a degrading factor. Thought about using coax but then 5 ft will be highly capacitive so the rise time will get affected, and plus pull up values have to be significantly smaller.

How will signal drivers work for a bi-directional signal?
 

nsaspook

Joined Aug 27, 2009
7,356
@nsaspook
Thanks.
yea, the idea is without using signal drivers. We would need pull-ups for the open drain lines but i am guessing the cable itself is a degrading factor. Thought about using coax but then 5 ft will be highly capacitive so the rise time will get affected, and plus pull up values have to be significantly smaller.

How will signal drivers work for a bi-directional signal?
Exactly what type of signal is this?

5 feet is not a just connect two wires task if you want reliability in a digital signal transfer at that speed. There are RS485 half duplex (bi-directional) transceivers that can handle 100Mbps.
https://para.maximintegrated.com/en/search.mvp?fam=rs485&hs=1
 

Thread Starter

moosefet

Joined Jun 18, 2020
3
Exactly what type of signal is this?

5 feet is not a just connect two wires task if you want reliability in a digital signal transfer at that speed. There are RS485 half duplex (bi-directional) transceivers that can handle 100Mbps.
https://para.maximintegrated.com/en/search.mvp?fam=rs485&hs=1
That may not be a bad idea. This is some custom signal but open-drain bidirectional. We would need support for 200 Mbps, if we dont have any other solution, i will try RS485 as backup. Will keep posted.
 

cmartinez

Joined Jan 17, 2007
7,022
With those requirements, I'd seriously consider using optical fiber instead... it might seem like overkill, but it would be far more reliable than any wire.
 

ronsimpson

Joined Oct 7, 2019
726
I have no fear of running 100mhz data over long lines. (double terminated) I have used differential cables. Send the signal and not-signal and use good drivers and receivers.
I do not have a good idea how your bidirectional thing works.
Look at network cabling.
 

nsaspook

Joined Aug 27, 2009
7,356
I have no fear of running 100mhz data over long lines. (double terminated) I have used differential cables. Send the signal and not-signal and use good drivers and receivers.
I do not have a good idea how your bidirectional thing works.
Look at network cabling.
Sure, Ethernet works just fine too. It seems the OP wants a 200Mbps i2c type connection that's 5 feet long. That's a problem.
 

Papabravo

Joined Feb 24, 2006
13,967
.... or squeeze them in... which is what happened to me ... I had to pay hell for all my ignorance when I first went freelancer ... although I prefer the term "noobieness" better :)
You survive by dealing with unexpected events in an honest and forthright manner. You make it up to the customer in whatever way you have to, and all will usually be well. If not, there is always Art History.
 
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