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I am working on LAN Bypass circuit for 1000 Mb/s Ethernet ports. I need to use relays to turn the bypass mode or no link mode on during power failure.

My doubt is whether the relays should be used between RJ45 & Magnetics i.e Line side or between Magnetics & Ethernet PHY i.e. PHY side.

Also, if someone can help with some information on HW implementation of LAN Bypass will be helpful!!

Oshi
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  • relays will be un-controlled impedance, in a stored/reflected-energy critical application. – analogsystemsrf Mar 30 '19 at 17:19
  • You're going to have to find an 8-pole, double-throw relay that has carefully controlled impedance in both positions. You can get [solid-state versions](http://www.ti.com/lit/ds/symlink/ts3l500.pdf), but I doubt that any mechanical versions exist. – Dave Tweed Mar 30 '19 at 18:11
  • Is there a reason you need to use relays instead of solid-state analog switches or similar? They are made with very high pass-bandwidths and (often) matching impedances... – Araho Apr 02 '19 at 22:51
  • Crosspoint switches need to be powered to work. A bypass function goal is to avoid ethernet link "cut" when the equipment is off. – zeqL Apr 02 '19 at 23:41

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You'll need to implement your relays before magnetics else your signal will be go through two transformers and that can trigger issues. Unfortunately I haven't found the document I read few years back on this topic.

We used IM26GR relays from TE. They support up to 2500V/3000V surge and have a 0.03dB insertion loss at 100MHz. It was few years back, so you should check other suppliers for equivalent products also (Panasonic GN series, Omron G6K series or newer).

I only draw the schematic and redacted some hardware documentation but I left when the layout began. I didn't get any feedback regarding the bypass function, so I assumed it worked. Also it was not the first time the company has done an Ethernet bypass function.

zeqL
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