[SI-LIST] Re: Twisting of differential pair traces

Hi Joaquin,

There is no problem in doing so but only when you are trying to twist, you=
 will introduce an extra length for one of the trace. In other words you=
 will introduce some skew b/w 'p' & 'n' trace. If that skew is under your=
 tolerance level, no issues otherwise you will have to compensate for that=
 skew maintaining your 100ohm differential impedance. If you have loosely=
 coupled traces matching p & n length is not a problem. You can do it=
 anywhere b/w your driver & receiver. But if you have edge coupled traces,=
 the best way is to add extra trace length to p/n (which ever is short) at=
 driver or receiver pins only. Hope it helps.

With regards,
Nitin=0D

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On=
 Behalf Of Fonseca, Joaquin
Sent: Thursday, June 22, 2006 11:39 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Twisting of differential pair traces

I have a question regarding routing differential signals on a board.=0D
For the case that the pair of traces of a given differential pair travels=
 from layer to layer using vias, what is the effect if the traces are=
 allowed to twist?. That is, what is the effect of having the plus trace on=
 one side of the pair on a layer, and then having it on the other side on=
 another layer (after transitioning thru vias)? (I hope I am able to=
 explain the "twist" issue).

Any comments are welcome.

Regards,
Joaqu=EDn

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