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I'm working on a Frequency Response Analyzer based around an Altera/Intel FPGA. I'm using an older Cyclone V educational eval board I got for cheap from my university. The only real GPIO I can use are 2 banks of 2x20 connectors, so basically pin headers. I was able to use those cheap 6" arduino/breadboard type jumpers for the NCO -> DAC upto a few MHz clock rate, but at 25 MHz, I seem to be getting a lot of high speed related problems (crosstalk, reflections/amplitude).

Is there a different connector I can use while prototyping (or even for the finished prototype)? Upto say 100 MHz sample rate? Or is my only solution at that speed an integrated circuit board with the FPGA on it?

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    \$\begingroup\$ The intent for those headers is usually a matching connector soldered directly to a PCB less than an inch above the eval board (aka shield, wing, hat, etc) That's fine at 100MHz with due care (enough ground pins in that connector, etc). Why do you need longer connections than that? \$\endgroup\$
    – user16324
    Commented Feb 24, 2022 at 13:23
  • \$\begingroup\$ @user_1818839 So I wasn't sure on that. I guess it could work for where I'm at now but as I'm doing a sort of deadbug prototype (so tight connections, but sparse layout) I don't know that it will be able to hold up the final prototype. Any ideas on how large a board it could support? I guess it would make for a quicker connection than the cables I have there now. \$\endgroup\$ Commented Feb 25, 2022 at 1:15
  • \$\begingroup\$ @user_1818839 So I realized, I literally have a matching header I ordered a long time ago. But I realize now I can't simply solder in these pins to a copper clad board for support without first isolating each copper "through hole" (yeah, I know a pcb would be preferred, but need to cover my bases first). I might could make some quick work if I cut in a grid fashion.. \$\endgroup\$ Commented Feb 25, 2022 at 1:38
  • \$\begingroup\$ There are copper clad boards with every pad isolated already. \$\endgroup\$
    – user16324
    Commented Feb 25, 2022 at 22:08

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Gbps connectors are certainly possible. Just think of PCIe and DRAM interconnects on computer mainboards. Or serial cable links. But even pin headers can go quite a bit higher than 25 MHz, but two things are needed: a proper pin assignment, where each signal pin has a return current pin next to it (usually ground) and the board traces must be routed with the same impedance of the pin pair in the connector. That said, if you don't follow these two rules, even the "best" connector will fail to give you good signal integrity.

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  • \$\begingroup\$ I thought about this after posting, there's a VGA port right on the board, which after searching can be used upto a few 100 MHz it seems. And I noticed the middle row is solid ground pins. I guess I thought the effects of pairing a ground with each pin would be negligible. I'll have to try this out. Annoyingly, the "datasheet" for this board is extremely vague, they simply show an unnamed resistor attached to each GPIO, and that's it. I guess I could iterate resistors to see which gives me the right output voltage. Thanks. \$\endgroup\$ Commented Feb 25, 2022 at 1:05
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The connector is not your issue. You can use a pin header up to about 100 MHz if you're careful.

The problem is that you don't realize what "careful" means. You need to do some deep reading into the issue of "impedance matching". I've never worked with Cyclone FPGAs, so I don't know if they have programmable input impedances, or what the choices are if they do. Generally, you'll need to feed your signal into the FPGA via a controlled impedance medium such as coax or stripline. You may need to create an intermedate termination board which you plug into the header. Or you might be able to get away with soldering termination resistors directly to the header (probably not an option if the header is surface mount, alas).

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