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Ethernet over non RJ45 connectors?

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sddsfgadasd:
Hi

I'm working on a design where it needs to use only circular DIN connectors (for instance https://www.amazon.co.uk/PIN-Solder-Connector-Audio-Video/dp/B008MI9G34) to connect to a board which has a generic ethernet PHY IC (not yet selected). From a signal integrity perspective, this sounds to be a challenge because there may be an impedance mismatch at the connector end because it is not a standard ethernet connector. I'm thinking it might be ok because the ethernet throughput should be under 10Mbps (only using 10 or maybe 100BASE-T) and I could use twisted pair cable for the other end of the connector cable.

Any issues from an EMI perspective that can be addressed? Additionally, should I still use a discrete ethernet isolation transformer (magnetics) on the board?

jonpaul:
Bonjour

Ethernet has a RS-485 PHY, and 110 Ohm balanced on UTP, TP.

The TX, RX, transceivers are balanced and transformer coupled. 
Thus some CM noise immunity and tolerant of overshoot, etc.

Broadcast and pro audio industry uses a similar protocol, AES/EBU at baud rates 6.144....24.576 Mhz
We use all types of CAT5,6,7 and many connectors besides RJ45, eg XLR, DB25, DIN, with no issues.
The small Zo discontinuity in connectors   different  from 110 ohm is not signifiant if the cable is 110 ohm balanced TP, UTP.
See AES/EBU std, and Ethernet PHY, also Belden Cable for digital audio cables and connectors

RE EMI,
"Any issues from an EMI perspective that can be addressed? Additionally, should I still use a discrete ethernet isolation transformer (magnetics) on the board?"
A transformer at both ends is required for CMRR and isolation between devices.
SMD and TH parts are available from Pulse Engineering, Halo, Coilcraft.
https://www.haloelectronics.com/products/lan/ethernet/discrete-transformers/10-100base-tx/
https://www.mouser.com/datasheet/2/336/-349690.pdf

Bon journée

Jon

jkostb:
No problem. I have done this for an industrial project and it passed without problems all EMI tests. You still need to use an ethernet transformer and can use another type of connector. Wiring should be shielded and if possible twisted pair. For speeds till 100Mbit/s this will work.  The max distance will drop if wiring is not twisted pair

Siwastaja:

--- Quote from: jkostb on November 27, 2022, 01:52:01 pm ---Wiring should be shielded and if possible twisted pair.

--- End quote ---

I think it's the other way around: not "if possible", but must be twisted pair; and when it is twisted pair, shielding is optional and usually not necessary, because twisted pair itself rejects interference by its mechanical construction by cancellation, as you probably are aware of.

In other words, bog-standard Ethernet cable: CAT5, CAT5e or CAT6. Wrong type of connector does not change rest of the advice, normal Ethernet stuff applies.

I'm pretty sure if you tried speaker cable of any non-trivial distance (> 1 meter or so), both communications and EMC would fail.

But the connector represents such short length that the connector causing impedance discontinuity does not matter much. Just keep the transformers very close to the connector, and PHY close to the transformers, and it's fine. Of course I'm assuming the connector is not insanely large. With 100M ethernet and some 1-2cm of wrong type of connector, you'll likely pass EMC; at very least it will work "in practice".

T3sl4co1l:
8P8C is an abomination unto electronics; a DIN connector is perfectly fine. :)

Plain vanilla "multi-conductor cable" is probably fine too, certainly for 10BASE over modest lengths (10s of m, probably less than the full 100m though).  You may want to inspect it before applying connectors, to ensure you're using adjacent wires (they won't really be pairs).  Shielding will probably help in that case.

With twisted-pair cable, as said, unshielded is fine, both connectors and cable of course.

On that note, if you do use shielding, note it's meaningless unless connected at both ends, at least at RF.  It doesn't need to be galvanically tied to ground, but enough bypass caps in parallel are needed to tie it in to keep noise out.  Typically a connector will be assembled with foil tape joining the screen/braid to the shell; a single wire (gathered-up braid or drain wire) is worse, and the longer the unshielded length is, the worse still it gets until it might as well be unshielded.  The length dimension being on par with the frequencies of concern, so, RFI and ESD are a problem for more than a few inches unshielded length.

Tim

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