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!!

  • \$\begingroup\$ relays will be un-controlled impedance, in a stored/reflected-energy critical application. \$\endgroup\$ – analogsystemsrf Mar 30 at 17:19
  • \$\begingroup\$ 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, but I doubt that any mechanical versions exist. \$\endgroup\$ – Dave Tweed Mar 30 at 18:11
  • \$\begingroup\$ 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... \$\endgroup\$ – Araho Apr 2 at 22:51
  • \$\begingroup\$ Crosspoint switches need to be powered to work. A bypass function goal is to avoid ethernet link "cut" when the equipment is off. \$\endgroup\$ – zeqL Apr 2 at 23:41

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.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.