Scope PCB probe

We often use SMB connectors with series resistors to the circuit nodes to be probed.

The cluster of 9 SMB footprints is for probing PCI Express.

This assumes a 50 ohm cable and scope input. Bandwidth is many GHz.

Those were made by Tektronix. You might try Qservice in Rhodes, Gr. These are HP's version:

Also, here are some:

tm

Thank you but i'll manage with John Larkin suggestion. We may need many of these PCB tests connectors (several hundred) and long term support.

Best Regards, H.

No problem. John knows what he is doing.

Although SMB are less convenient because of more insertion effort i will nevertheless proceed to PCB launch.

Best Regards.

SMBs are relatively cheap. Unlke SMAs, or those scope probe things, you can put them close together.

MCXs would be good, too. They are cheap and have low insertion force. Same footprint, generally.

We only load the SMBs on engineering boards. We can always add them to a production board if needed, which is rare in this case. Sometimes we do leave them on production boards, like to pull out a clock for a scope trigger or something.

What I usually do to snoop a signal is something like

| | | | | 50r trace +--450R-----------------------(o) SMB | | | gnd | | |

With an 0805 or 0603 resistor, that's good to several GHz.

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similar to this:

and you probably don't need to solder the connectors in, I think with a bit of tweaking you could sorta press-fit when you need to measure

-Lasse

No stub effects in that case with GHz's ?

Never used MCX connectors ... i will give it a try tomorrow.

Best Regards, H

No, as long as you use a 50 ohm coax into a 50 ohm scope. It forms a

Without the scope connected, there will be a small reflection at the SMB, but it's attanuated twice by the 450r, so in most situations you won't notice it. 950 ohms makes a 20:1 attenuator, even less loading.

What I want to do next time is use an ADA4960 as a differential signal snoop pickoff, into an SMB or MCX.

MCXs are used in Cisco servers or something, so there's tons of cheap cables on ebay.

Nope. Its basically a passive divider HF probe.

That works, but can keep one hand occupied, which is a nuisance if you need to probe multiple points.

Agilent sells a 6 GHz resistive probe for $3134. You can make your own for well under 1% of that.

That's exactly what i meant with GHz's (in fact very short rise and fall times) a small portion of a inch could ruins a PCB design.

Ok thanks a lot John,

Habib.