[SI-LIST] Re: 180 degree turns in high speed lines
- From: Duane Mattheisen <duane.mattheisen@xxxxxxx>
- To: Eugenio Simões <eugenio_simoes@xxxxxxxxx>, "otter30@xxxxxxxxxxxxx" <otter30@xxxxxxxxxxxxx>
- Date: Tue, 3 Mar 2009 22:52:24 +0100
Hi Jim,
I've done this a lot and if your edge is >= 1ns for a 5 volt swing you should
be fine. A common problem is if your DUTs pitch is small and the traces have
to tapper in at the DUT you can get an impedance miss match.
Regards, Duane
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Eugenio Simões
Sent: 2009 Mar 03 2:25 PM
To: otter30@xxxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: 180 degree turns in high speed lines
Hi Jim,
As far as I know, the recomendation to avoid high angle turns (more than 45
degres) is to keep the trace with the same cross section area through all
the path. For instance, if you have a 90 degree turn, the cross section area
of the trace is increased in the turn (thats geometry), and this leads to a
capacitance increase in this point (that could lead to signal integrity
issues).
In your case, this is not the problem. However, when the signal moves from
one plane to another, the distance to the ground plane changes, and this
affects the impedance of the line. My feeling is that, in your case (a small
length on the top layer), this effect will have less impact then the via
inductance and etc...
Regards,
Eugenio
2009/2/27 <otter30@xxxxxxxxxxxxx>
> Hello,
> Has anyone had experience with high speed traces that travel in one
> direction on an inner layer of a pcb,
> and then transition to the top layer termination thru a via and then change
> direction 180 degrees?
>
> The distance traveled on the top layer is short - just a short connection
> between a termination resistor and the ic pins, but it's the turn that
> concerns me.
>
> After all the debate through the years on 90 degree turns, I'm interested
> in your opinions.
>
> Thanks,
> Jim
>
>
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