highly-parallel highspeed connection between two FPGA boards
Maurice Branson
designing a motherboard featuring a Virtex-4 FX140 FPGA with 24 integrated
RocketIOs (Gigabit SerDes IOs) I am now facing the problem of how to get the
signals off the board in a most space-saving and elegant way?
All 24 differential signals will be connected to some DACs outside the
motherboard to convert the signals into the analog signal domain.
In the definition of the interface I have nearly all effective degrees of
freedom. I once learned that coaxial connections are the most appropriate
way to do so in terms of signal integrity, but with 24 differential signals
and bidirectional connections that would mean at least 96 SMA connectors
(that takes very large board space and implies some skew problems due to the
differences in the line lengths).
I once used the Tyco ZDOK system (plug + receptacle) for board-to-board
connections with up to 80 parallel signals but unfortunately the
performance was not satisfactory, so I won't be using them again. Are there
any other interface systems for the above described purpose or ways to build
a highly-parallel highspeed connection between two boards?
I appreciate every kind of suggestion and help. Thanks a lot in advance.
Regards, Maurice
John_H
you're encountering to help bound the problems in peoples' minds.
Consider the lowly HDMI interface. These are ~1.8 Gbit/s signals that go
over flimsy, mass-produced cables with flawless digital performance to get
1080p signals.
Twisted pairs will get you to where you need to be. The speed will dictate
the eye closure over distance and you *probably* are well within the
appropriate operating range. For the truely demanding applications, twinax
may be necessary but is probably overkill.
If the eye closure is a problem for your chosen transmission media and
distance, preemphasis or receiver compensation can allow your twisted pair
cables to provide an open eye to the A/Ds. There are several products on
the market that provide the transmit and/or recieve functions to allow
multi-gigabit transmission over very cheap lines.
"Maurice Branson" <traub...@arcor.de> wrote in message
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MM
news:469653f8$0$3834$9b4e...@newsspool4.arcor-online.net...
>
> RocketIOs (Gigabit SerDes IOs) I am now facing the problem of how to get
> the
> signals off the board in a most space-saving and elegant way?
>
Do you really need all 24 pairs? What is the DACs' sampling rate?
> All 24 differential signals will be connected to some DACs outside the
> motherboard
What does "outside" mean precisely?
/Mikhail
dave
What's the required signaling rate to the DAQs?
>
>
--
Be Happy. Don't Worry about the difference between lose and loose..
whit3rd
> designing a motherboard featuring a Virtex-4 FX140 FPGA with 24 integrated
> RocketIOs (Gigabit SerDes IOs) I am now facing the problem of how to get the
> signals off the board in a most space-saving and elegant way?
>
> All 24 differential signals will be connected to some DACs
Mass-produced SCSI internal and external cables and terminators
are easy to find. The 68-pin cables go to 320 MHz nowadays,
and connect 27 differential pairs plus some status wires and
power wires for active terminators (which are commonly crimped
onto the internal cable end- no need to populate your board with
the terminators).
If you can drive 110 ohm wiring, and if the low-voltage differential
signal levels are the same as SCSI, your choice may be easy.
Maurice Branson
Oay, to make it more precise: I'm looking for an interconnect system
(multi-channel plug + receptacle) for 24 differential pairs at signaling
rates of 3 - 6 Gbps per channel.
Marc Battyani
"Maurice Branson" <traub...@arcor.de> wrote
>
> Oay, to make it more precise: I'm looking for an interconnect system
> (multi-channel plug + receptacle) for 24 differential pairs at signaling
> rates of 3 - 6 Gbps per channel.
I don't know if you have already looked at them, but for things like that, I
use Samtec connectors and cables.
http://samtec.com/high_speed_connectors/2006/si_b2b.asp
http://samtec.com/high_speed_connectors/2006/SI_C2B.asp?m=hs
Marc
MM
So, I assume it is a motheboard-daughtercard kind of connection, right? I am
running Xilinx Rocket IOs at 3.36 Gb/s over the standard cPCI connectors
(front card to/from rear card through the backplane, but not across the
backplane) with no problems. Since these connectors aren't
designed/specified for such speeds I had to develop my own grounding
solution. Basically, I have enclosed each of the differential pairs in
between GND pins and it worked really well both in simulation and in real
life.
Also, I am not sure what exactly you are up to, but consider doing some
upconversion on your DAC board (maybe even in the DAC itself). By doing this
you might be able to reduce your communication bandwidth requirements
substantially.
/Mikhail
Tom Lucas
news:nPGdnWZQAqSCEArb...@giganews.com...
I can recommend Samtec as well - very fast service and samples turn up
in under two days. Knowledgable reps too.
David L. Jones
> You're seriously overthinking your problem. Please indicate the data speeds
> you're encountering to help bound the problems in peoples' minds.
>
> Consider the lowly HDMI interface. These are ~1.8 Gbit/s signals that go
> over flimsy, mass-produced cables with flawless digital performance to get
> 1080p signals.
I'd second HDMI, certainly worth looking at. I just added HDMI to a
Virtex-4 myself.
The Virtex-4 doesn't have the TMDS signaling used on the real HDMI
interface, but you can use LVDS or whatever over the standard
connector.
The Type A connector has 4 pairs, and the Type B has 7 pairs per
connector.
If you are short on space, the HDMI Mini connector has just been
released.
Dave.
Anton Erasmus
I alos like Samtec, but their prices has been kreeping up over the
last number of years. Every time we buy the price is up from the
previous time.
There are quite a few pretty standard connector families that can take
coax pins. D-Type and Din 41612 to name 2. You can also try Nicomatic.
They make small connectors which can take coax pins. They can do a
custom connector for quite cheap. Less than US$500 if I recall
correctly for NRE charges.
Regards
Anton Erasmus