It depends on many things, but I don't think you need to use an extra internal RJ45, 
unless there is a manufacturing reason for it.

I use internal Ethernet in all our products.

You need to take into account:
Ethernet speed - 10baseT and you'll probably be OK, 100Base or faster and you need to 
be very careful.

Location of components, keep the internal Ethernet lengths as short as possible.

Trace impedance - keep the trace impedance as close to 100 Ohms as possible.

Discontinuity - there will be an impedance discontinuity at the connector.
If its 10Base, and the components are close to the connector, and the traces are 
short, there should be little trouble.
If its 100Base, the components are well separated, and the lines are long, then you'll 
probably be in trouble.

Lets call the external connector board 'LEFT', and the internal electronics board 
Obviously, I don't know your design, but you could mount the PHY and the magnetics on 
the LEFT, then use the much slower and synchronous MII to interface to the MAC on the 

In any case, always put the magnetics as close to the RJ connector as possible, use 
magjacks if possible.

You could remove the problem by choosing an impedance matched connector, but these are 
much more expensive.

Download Polar si8000 from their website, they do a "pay-as-you-go" version that will 
help you make sure your trace design is correct.

Don't trust Protel's 'Impedance matching' in all but a few cases, its way off the 
mark, just compare polars 'real world models' with protels textbook generic formula 
and you'll see what I mean.

Depending on your board construction, make use of broadside stripline or edge coupled 
differential traces, this will help you get the impedance you want.

If you have use of a network analyser and don't think twice about sending PCBs to fab 
then your job is easy, just make prototypes until its right.

If you have totally internal Ethernet connections, have a search for application notes 
on using 'transformerless' or 'capacitive' coupling between PHYs, this will save loads.

Hope this all helps,


-----Original Message-----
From: Back, Norb [mailto:[EMAIL PROTECTED]
Sent: 21 September 2004 19:26
To: Protel EDA Forum
Subject: [PEDA] Ethernet Connection
Importance: High

Hi all

 First time for a Ethernet connection

The layout calls for all out side connections (RJ-45 jack) to be on one
board and mate with a mother board
threw a 125 pin mating connector, down the mother bd to were a TINI bd
will be mounted

Or would putting another RJ-45 jack on the mother bd right next to the
125 pin connector 
And use a Ethernet patch cord to the TINI bd be better?

The connection bd and mother bd need to be able to separate

Any help or tricks 

Still using 99SE

Norbert J Back C.I.D.
Engineering Technician
Gilson Inc.
3000 W. Beltline Hwy.
Middleton, WI. 53562
PH 1- 800-445-7661 ex-4438
Fax 608-821-4498


* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* To post a message: mailto:[EMAIL PROTECTED]
* To leave this list visit:
* Contact the list manager:
* Forum Guidelines Rules:
* Browse or Search previous postings:
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

Reply via email to