> Is there a digital/power board-to-board connector that is known to be > compatible with SMP? Connectors of different types are often not meant to > be used together and their heights can be significantly different - certainly > by > more than 2.54mm.
One can purchase bullets of varying lengths to give the desired full stackup depth for SMP connectors. Bullet lengths of .243", .254", .286", .395", .517" are standard, for example, and custom bullet lengths are available. The mating board connectors add further length to these bullets, typically .051" or .090" each. Just to give two examples, two .051" connectors plus a .243" bullet is 8.75 mm, and two .091" connectors plus a .243 bullet is 10.75 mm. You typically run the SMP connectors with the bullets not inserted fully flush - this is called "axial misalignment". The measured specification on this at frequencies below ~3.5 GHz (where we are concerned) is such that we should be able to tolerate .025" or even a bit more of axial misalignment and still have this not limit the overall signal performance. Thus for the two examples above, using digital connectors with a 9 mm or 11 mm total stackup height would give 250 um axial misalignment (.010"), which is a typical tolerance one would want to use anyway with SMP. More information is available in this application note: https://www.corning.com/media/worldwide/coc/documents/applications/microwaveApplicationNotes.pdf There are many multipin connector types available suitable for power or digital signal transmission (remember, these digital signals will not be extremely high speed, definitely <100 MHz and probably <20 MHz given typical hardware they would be addressing) with stackups of 9 mm or 11 mm. For comparison with FMC, the spec value on RF leakage for SMP is -80 dB to 3 GHz (this should be measured to verify as well). I will work on a test board that compares FMC with SMP using otherwise identical traces on the two PC boards. _______________________________________________ ARTIQ mailing list https://ssl.serverraum.org/lists/listinfo/artiq
