what's the role of Ethernet transformer?

ethernet transformer

I guess that is for isolation:1, safety reason, 2, different potential of linked two system. Is there any other reason we need transformer?
If that's true, do I need transformer if I connect two PHY on the same board within
10cm.
Should I put transformer close to port or PHY? My guess is close to PHY.

thanks

ethernet transformers

I guess so too.

transformerless ethernet

The transformer may be necessary for some drivers to feed the supply voltage, but it could be replaced by two small chokes in this case.

Generally in 10BASE-T (10 MBit Ethernet), the transformer is also a low pass filter, not absolutely required but necessary to get the specified waveform from square wave at the driver. At the receiver, a low-pass filter increases noise immunity.

In 100 MBit Ethernet, the transformer is really a transformer, and it's 100ohms 1:1 matched impedance usually. For that reason it could be placed anywhere in the differential line between connector and PHY and for isolation purposes one would be enough instead of two. For the said on-board connection it could be omitted and replaced by capacitive coupling at each receiver, to my opinion. Bothside 100 Ohms termination should be used as with a transformer. If you are able to control the transmitter PHY, you could decrease transmitter current and modify the matching to reduce power consumption, however.

You should also consider, that the receiver has considerable gain reserve to compensate for line losses.

ethernet trafo

How does the host know when there is a device is connected to it?

transformer ethernet

Really transformerless application depends from PHY vendor and speed. For example 10/100 differ from 1000; Broacom differ from Vitesse. Exist number of application notes to implement it. For example you can use Broadcom's application notes to implement it.

ethernet transformer circuit

dear david90,

It's just not the physical connection that makes the connection in the ethernet. the real connection is in the tranport layer. it should send a connection request. if there is a physical connection, the request shall be transmitted and received by the other end-point, and if possible the connection shall be established. that's how devices talk to each other and know that they're connected. the physical connection alone is not important.

what is an ethernet transformer

Hi all,
I have been looking for a book that talks about topics related to transformer in ehternet design, or something about ethernet design in hardware perspective. Does anybody know any good books about this?

Thanks in advance.

ethernet transformer

The role of the transformer is isolation. For example if you are using ethernet on a backplane you can replace the transformers by capacitors.

When using transformerless ethernet you may lose some of the Ethernet features as autonegotiation.

I'm attaching two application notes, one from Intel and one from the old CICADA explainig the issue.

Hope it helps.

Re: ethernet transformer

Transformer's differential step response are exactly the same as ac coupling circuits. So, for differential signaling case, it should be the same.

However, for common mode noise, transformer seems to have sort of rejection for CM noise, thus improve EMI performance.

Also, I'm curious why magnetics are important for auto negotiation?

Thanks.

zape said:

The role of the transformer is isolation. For example if you are using ethernet on a backplane you can replace the transformers by capacitors.

When using transformerless ethernet you may lose some of the Ethernet features as autonegotiation.

I'm attaching two application notes, one from Intel and one from the old CICADA explainig the issue.

Hope it helps.

Click to expand...

I have trobule on the " Magnetic-Less" Ethernet. That's good information for me.