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When it comes to digital circuits, it is often important to get certain internal design signals to an I/O pin and then view it on scope. This is in-spite of all the other techniques that exist to debug such designs. We could get the signal onto an oscilloscope or logic analyser.

If one wants to include a special connector dedicated to this purpose, what options exist? This would be a connector with a small form factor that can be easily connected to logic analyser or oscilloscope probe.

Edit: Please assume that I need 16-20 pins to be dedicated to this purpose and since it is for an FPGA, it is going to be for digital circuits

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  • \$\begingroup\$ I see a lot of evaluation boards with these pegs or loops that stick out off of specific parts of the circuit specifically for connecting clip-on connectors found on oscilloscopes. \$\endgroup\$ – Ron Beyer Feb 4 at 19:58
  • \$\begingroup\$ Please assume that I need 16-20 pins to be dedicated to this purpose and since it is for an FPGA, it is going to be for digital circuits. \$\endgroup\$ – Quantum0xE7 Feb 4 at 22:08
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    \$\begingroup\$ Would probably be good information to put in your question... \$\endgroup\$ – Ron Beyer Feb 4 at 23:19
  • \$\begingroup\$ What kind of speeds are involved? \$\endgroup\$ – SteveSh Feb 5 at 1:43
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The above is "old school". That type of connector falls apart at very high frequencies. There's nothing wrong with it so long as your signals are, say, sub 100Mhz-ish.

Here are two more modern options that are workable and cheap. You have to design these into your PCB before you lay it out.

https://www.newark.com/keysight-technologies/n2766a/test-probe/dp/80K6000?gclid=Cj0KCQiA0-6ABhDMARIsAFVdQv_pIOirjSWQhVAeK3w997OPmyd0fYsO4Ot5-9vxCLqKiUjQUAT5Cd8aAhQiEALw_wcB&mckv=sbyLHITAo_dc|pcrid|434136793584|plid||kword||match||slid||product|80K6000|pgrid|100464452106|ptaid|pla-901419073096|&CMP=KNC-GUSA-GEN-Shopping-NewStructure-Test-Measurement

https://www.newark.com/tektronix/131503100/compact-probe-tip-circuit-board/dp/11B2822

It's not the signal end (the "tip") that's an issue with the old school test points. It's the pigtail ground clip. That 2-3" of wire can cause all kinds of noise in your O-scope traces and will act as a low-pass filter.

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    \$\begingroup\$ "The above..." you probably shouldn't reference other answers by position, currently yours shows up first... \$\endgroup\$ – Ron Beyer Feb 4 at 23:18
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    \$\begingroup\$ What are you referring to by "the above"? \$\endgroup\$ – Hearth Feb 5 at 1:56
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There are several ways to go on this.

  1. You can use a through hole pad, and then solder wires where you need them.

  2. You can also use a SMD type pad, that is just exposed copper that can be probed

  3. You can use something like a 5003 from keystone
    enter image description here

  4. You can use something like the 5015 from keystone
    enter image description here

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  • \$\begingroup\$ Another idea is to find a connector that can mate with the logic analyzer’s probe cable end. \$\endgroup\$ – user69795 Feb 4 at 22:21
  • \$\begingroup\$ You might want to actually tell the OP what those are called. They are called "test points". \$\endgroup\$ – DKNguyen Feb 5 at 4:50
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The cheapest and smallest probe connector is a via hole that fits the tip of the 10x scope probe, with a ground via next to it that fits the tiny ground spring attached to the probe.

It sure beats a fancy probe connector that isn't there because there wasn't enough space to put it in...

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  • \$\begingroup\$ Have you thought of laying out a mail edge card connector at the edge of the board then make a connector to mate with a cable to the analyzer. 1 cable, no connector expense per board. Another way is with pogo pins and pads. \$\endgroup\$ – Gil Feb 5 at 5:38
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OK, the official old school connector for insane speed digital signals is the mictor, and AFAIK is still used for the trace port of some high end DSPs. That said, it's for differential signals and needs a special analyzer.

For general purpose you didn't say which frequencies are you going to use… for low frequencies (about 150MHz) the rectangular strip suggested should work fine: on one side the signal, on the other one reference ground. Maybe even 1 signal followed by 3 grounds, depending on the drive strength/repetition rate.

If you need to go faster you will need something like LVDS, impedance controlled connectors and dedicated probe heads.

With FPGAs you could consider an internal trace buffer accessible via JTAG, depending on the size of your data streams and the use.

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  • \$\begingroup\$ That Mictor looks very similar to the Samtec QMSS and QFSS. \$\endgroup\$ – DKNguyen Feb 5 at 14:59
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We use small 0.1" header pins/assemblies like these all the time to provide test point/probe capability. Something like these, from Samtec.

enter image description here

They work well up to hundreds of MHz, if you're careful about how you connect the probe and gnd lead to the pins. Going along with that, for high speed signals you want to provide a generous amount of signal returns, 1 per signal or 1 per diff pair.

Another advantage is that the probe head of many logic analyzers can plug directly onto the header assembly, without needing flying leads.

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