Why transformers are required for implementation of ethernet

[zape]

why transformers on ethernet

This is the first time I need to implement ethernet 10/100 links on a hw design. Why transformers are required?
How does the ethernet PHY devices detects the collision in half duplex configuration?
Does anyone know something about capacitive coupling?

Any info or recommendation shall be helpful.

 

[ramesh]

ethernet transformers

Transformers are required for electrical isolation and for differential driving (there is no common ground from one pc to the other). Differential driving gets rid of the common mode noise effect.

 

[zape]

Ethernet transformers

So they are only needed for avoiding large common modes, so if my system is an embeded one (sharing the same ground between all ethernet transceivers) I could work without the transformers. What do you think about this?
Do you know sthg about half douplex collision detection?

 

[Frosty]

Re: Ethernet transformers

You should be able to get this information from the supplier of your MAC/PHY IC.

You did not say if you will use integrated MAC/PHY or seperate parts.

Each will need magnateics which you can have either integrated with the RJ45 connector or seperately. You will save some issue on layout if you use a RJ45 connector with integrated magnetics and the price cost is not that high.

Which part are you looking at? Will it be used as embedded or a PCI design?

 

[dainis]

Re: Ethernet transformers

Look this AN:
https://www.cirrus.com/en/pubs/appNote/an203-1.pdf

 

[zape]

Ethernet transformers

The design shall be based on a PPC including the MACs, so that only the PHY shall implemented on the external device. The problem /desire of avoiding transformers is the requirement of industrial range transformers with low profile. The minimum height I found was 5mm (too much for me). While transformers for PCMCIA are 2.5mm (but only in commercial temperature) range.

I have been looking Micrel PHY devices but they do not provide too much info and I do not know if I could implement multipoint half duplex with capacitive coupling.

 

[yangvic]

Ethernet transformers

If you want use two back to back PHY.
1 these two parts might be on the same board use the same supplies and ground.Therefore,they don't necessarily have to be AC coupled.
2 you may be no need common mode chokes to eliminate common mode noise and EMI.
3 you may be no need to Auto-Negotiate.

 

[EEHardware]

Ethernet transformers

you can find many articles from internet about ethernet 10/100 links , and you can ref ethernet vender and ic spec (or datasheet) for design guide.

 

[neoflash]

Re: Ethernet transformers

So you also believe transformer somehow serve as a CM choke?

If you want use two back to back PHY.
1 these two parts might be on the same board use the same supplies and ground.Therefore,they don't necessarily have to be AC coupled.
2 you may be no need common mode chokes to eliminate common mode noise and EMI.
3 you may be no need to Auto-Negotiate.