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I'm using a development kit which is made a camera board and a FPGA board. So far, in this kit, the camera board is directly plugged onto the FPGA board.

I have tested a new code for my FPGA. However, this new design requires a specific hardware where the camera board should be connected using a flexible "cable" to the FPGA board. The length of this cable should be about 150-200 mm. It must carry the following signals:

  • 6 differential pairs (LVDS 720 Mbps)
  • 9 single wires (1 MHz - 72 MHz).

On the PCB, I used the following specifications for the traces (based on the development kit I'm using):

  • differential pairs: 100 Ohms (+- 5 %)
  • single ended signals: 50 Ohms (+- 10 %)

So far, I was considering using a cable such as this one. That's the first time I read about micro-coax for LVDS differential pairs but this solution seems appealing to me (also because of the tiny connector they use). Are this type of cables used for LVDS signals around 720 Mbps or are they designed for much lower speed? Are there any other proper solutions to make the connection between the two boards (flex-PCB, ribbon cables,... maybe)?

My last question is more about the PCB layout. If I'm using a cable instead of a direct board-to-board connection between my board, are there any specific points I must take care of in my PCB layout?

Thank you

EDIT 1:

I have checked different commercial type cables (comments of MadHatter). The ones I have seen so far do not have enough wires: SATA (2 pairs), HDMI (4 pairs and 7 single wires), USB 3.0 (3 pairs), RJ45 (4 pairs). Even though I could have multiple cables going between the boards, I would like to have the smallest camera board as possible (40x40 mm2). Ideally, I would be happy with one cable for signals, one cable for power (but I did not talk about this one in my initial post since there is no problem with it).

EDIT 2:

I accidentally found this link: Micro-Coax connector product series. They basically say cables such as this one are basically good up to 20 Gbps speed which is really far above my specifications.

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  • \$\begingroup\$ You also could look at consumer style cables such as using multiple SATA, LB or HDMI cables to accomplish this purpose. \$\endgroup\$ – MadHatter Aug 26 '17 at 18:10
  • \$\begingroup\$ @MadHatter That's interesting. The ones that I have checked so far did not have enough wires: SATA (2 pairs), HDMI (4 pairs and 7 single wires), USB 3.0 (3 pairs), RJ45 (4 pairs). I'm not sure what LB is. Even though I could have multiple cables going between the boards, I would like to reduce this number to the minimum: one for power, one for signals. \$\endgroup\$ – Marmoz Aug 26 '17 at 19:53
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    \$\begingroup\$ You are correct they do not have enough pairs, I was thinking if this is a non production model etc. it is an easy and sometimes much cheaper way to do high speed communication, especially if you need longer distances. \$\endgroup\$ – MadHatter Aug 27 '17 at 14:08
  • \$\begingroup\$ Micro coax works well. Watch out for the current rating if you are also hoping to supply power through the same cable. \$\endgroup\$ – pericynthion Aug 27 '17 at 15:31
  • \$\begingroup\$ A flexible PCB would certainly work for high-volume production. Maybe Infiniband or FC cables have enough pairs? You could do dual RJ-45 also potentially. \$\endgroup\$ – Krunal Desai May 26 '18 at 8:14
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I'm gonna offer options

  • Serial Attached SCSI or SAS

Basically glorified SATA. You can get 8 differential pairs, 6Gbps each, for $8. Perhaps not exactly what you want, but there are many options, so maybe...

  • PCI-Express

You can get PCI-Express riser cables to make a PCI-Express card work outside of the PC for debugging. There are many models, depending on how many lanes are needed, so you can actually pick the number of differential pairs according to your needs. Some have fancy twinax diff pairs. Plus it also carries power and various signals. Problem is, it comes with a PCIExpress connector...

Then, there is this, notice the flat flex cables are probably rated for PCI-Express bandwidth, and they are connected to both boards with nice connectors.

You could also get a "mini pci-express riser."

  • DIY

You can get a 25cm x 5cm double sided flat flex manufactured to your specifications for about $130.

Kind of expensive (but we used to pay that a few years ago for double sided which is like $5 these days). Maybe you can find a cheaper source.

This will be the most flexible option, as you will be able to get exactly what you want, choose your connectors, or even solder both ends directly onto your boards if you feel like it.

You can also buy pre-made flat flex jumpers, but then you'll probably be stuck with the extra-filmsy connectors which break if you look at them wrong.

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