[SI-LIST] Re: Question regarding the differential impedance

Ignore until you fail E1 testing... then go redesign it and make it work.

Return loss testing can be a source of headache.  DON'T IGNORE the 120 ohms.


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Sandor Daranyi
Sent: Thursday, December 19, 2002 9:33 PM
To: kaps@xxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Question regarding the differential impedance



Kaps,

Perhaps others may not agree, but personally, I wouldn't worry too much abo=
ut the 120 ohms for E1/T1.  Considering the wavelengths (and any practica=
l trace lengths you are likely to have) at those low frequencies, my main=
 consideration about the trace width would be mostly to do with the desig=
n of the protection circuit.  Of course, it still makes sense to keep the=
 traces belonging to the same pair close to each other.

Regards,

Sandor

PS: ...and here comes the storm of out-of-office messages!

----------------------------------------------
Sandor Daranyi
Senior Design Engineer
Aristocrat Technologies

> I have a general question regarding the differential=20
> impedance of traces which dont have any plane above or=20
> beneath them at all.
>=20
> Lets say it is 20 layer board and I am routing 100ohm=20
> differential pair on any of the layer but there is absolutely=20
> no plane above or beneath the traces. What will be the trace=20
> width and spacing I will be using for these traces.
> These are the traces for T1/E1 from the connector to the line 
> side of the transformer.
> 
> Do I have to calculate that by defining all of the layers as 
> signal layers? 
> Any suggestions
> 
> Thanx
> Kaps
> 


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