Best multi-way cable for minimising crosstalk/coupling? - Page 1
Forum section: electronics / general

author: alanambrose
author_rank: Frequent Contributor
timestamp: December 05, 2018, 12:00:06 pm
content: Hi,I have an application with 64 0-3V analogue signals connecting board-to-board, bandwith ~10kHz, distance ~10-15cm / 4-6 inches, into a 50 ohm load. I need to minimise crosstalk/coupling as this is causing a problem right now. (The existing cables are unshielded ffcs with signals side-by-side.) This is for rapid prototype / small quantity so preferably needs off-the-shelf parts. I need to measure signals with max 10,000x / 80dB voltage ratios i.e. the smallest signal is about 0.3mV.I know I could experiment and measure each possible solution, but:+ Does anyone have a go-to solution for this kind of application?+ Does anyone have any experience / opinions on which one of these options (or others) might work best:(1) Shielded FFC / shielded ribbon with each alternate connector GND? (I can see shielded FPC connectors from SMK & Hirose but not shielded FFC. Also, I can see shielded ribbon from Amphenol & 3M but not shielded IDCs.)(2) Multi-way shielded twisted pair?TIA, Alan

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 05, 2018, 12:25:45 pm
content: Yes, every other ground, at least. You can always add more inbetween and get wider ribbon / more of them.Shielded cable as such, isn't very common, but you can always wrap it with copper foil tape, say.Incidentally, a signal surrounded by grounds in ribbon cable isn't much over 50 ohms IIRC, and shield on both sides probably brings it down nicely to around 50. Not that that matters much at this frequency.Tim

author: langwadt
author_rank: Super Contributor
timestamp: December 05, 2018, 12:37:23 pm
content: Quote from: T3sl4co1l on December 05, 2018, 12:25:45 pmafair the ground and signal configuration is ~100R

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 05, 2018, 01:57:21 pm
content: Quote from: langwadt on December 05, 2018, 12:37:23 pmYes, typical example here:http://www.te.com/content/dam/te-com/documents/industrial-automation-and-control/global/Madison-IDC%20Ribbon%20Cable%201108.pdfSo with shield(s) maybe in the 70 ohm range.Tim

author: Andreas
author_rank: Super Contributor
timestamp: December 05, 2018, 07:41:31 pm
content: Quote from: alanambrose on December 05, 2018, 12:00:06 pmHello,Single ended signals or differential pairs?For me it sounds more like GND-shift and not cross talk at 10kHz bandwidth.A lambda/4 coupler at 10kHz would need 7500 m coupling length for a -3dB coupler.At 15 cm you should get in excess of 80 db dampening.with best regardsAndreas

author: alanambrose
author_rank: Frequent Contributor
timestamp: December 06, 2018, 04:30:42 pm
content: Thanks guys for the opinions, very interesting.Andreas - yes, good point, will check.For anyone coming across this thread at a later date:+ Hirose FH41 & FH48 have shielded FPC connectors available off-the-shelf+ Also there's the SMK EF-5D Series available from Allied Electronics+Nicomatic & Esskabel make shielded FFC, but, I think, only to order+3M & AMPHENOL SPECTRA-STRIP are available off-the-shelf as shielded ribbon cables, but there doesn't seem to a be connector to fit, so connecting to the shield seems to be DIYA.