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Ethernet Design

Elfernro , 09-05-2017, 08:30 AM
Hello everybody,

The truth is that I am pretty new with Altium, so I really appreciate if you could help me in anything.

I am trying to make a PCB design with Ethernet connections. I have been looking the specifications for this type of connections and the main one is the impedance of 100 ohms.
For this I have created in my schematic differential pairs for my signals Tx + / Tx- and Rx + / Rx-.
I have also asked a supplier for the design- specifications, considering only two layers and typical characteristics of 35um copper and 1,6mm subtrate high.

I have recieved the following information:
Dielectric Er = 5.1, Width W1 = 0.228mm W2 = 0.193mm, Space S = 0.15mm (for impedance100.14 ohms).
W1 is the width without the lacquer layer and W2 the upper lacquer surface.
  • Here begins my doubts, What width should I take for my design? W1? or an average between the two measures?

I start my design in Altium.
In Rules, I have created a rule in Clearance for my differential pairs (InDifferentialPair ('DiffPairName')) where I have included a minimum of 0.15mm (if not I get an error every time I route the pairs).

In Routing I have also created another rule with these specifications Differential Pairs Routing (0.228mm Width; 0.15mm Gap) and I have included in Max Uncopled Length a value of 12.7mm,
  • For Ethernet connections is this value correct or should it be considered a lower value ??

Finally in Matched Lengths, I have activated "Within Differential Pair Length" with tolerance of 0.127mm

Then, I have implemented my routing design.
In the routing, the truth is that I have been doing it taking care of the length instead of using the Interactive Length tuning tool.
I have run then, the Design Rule check without any error.
I have an average length in all sections of 42.5 mm (I have read that the maximum for Ethernet is about 75mm).
I attached the connection that I have made.

On the other hand, I have also tried to implemented with the xSignals tool, but I dont really appreciate many differences. I have created the different Xsignals with the wizard and I have been checking the different signals length in the PCB menu.

Do you think it could work? should i change anything??
I would appreciate any feedback and comment since I am totally beginner in this.

Thanks so much in advance
robertferanec , 09-06-2017, 10:38 AM
Here begins my doubts, What width should I take for my design? W1? or an average between the two measures?
- Use the value relevant to your final PCB. I am not exactly sure what you mean by lacquer, but if this is going to be on your final PCB, that is the value you should use.

Important: If you are using impedance controlled track you need to have reference layer under or/and above the tracks.

Have a look how we routed differential pairs in our open source designs. You can download Altium files and check how we setup rules and adjusted the length. Also check how the differential pairs look in our designs. That will give you an idea how you can make it. Download our Altium projects here: http://www.imx6rex.com/

PS: What is very interesting, I would expect the track width and space to be larger for 2 layer PCB.

I hope this helps
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