[SI-LIST] Re: guard traces (huge)
- From: "Edwin Bennett" <ewbennett@xxxxxxxxxxx>
- To: <lgreen22@xxxxxxxxxxxxxx>, <moshef@xxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Mon, 19 Jul 2004 10:22:56 -0500
One can think of the guard trace as a ground plane that is narrow. As such,
it need to be connected to the main ground plane through low inductance
conductors such as vias. In addition, the combination signal and guard
trace can be thought of as coupled lines, where directional couplers are
special cases. As such, the current flowing in the signal trace induces a
current in the guard trace that flows in the opposite direction provided the
guard trace is grounded. The two currents flowing in opposite directions
cause the magnetic fields cancel at a far distance from the two lines.
However, adjacent lines will not see any significant cancellation since the
adjacent lines are closer to one signal carrying line than to the other. I
hope that this makes sense.
Ed Bennett
----- Original Message -----
From: "Lynne Green" <lgreen22@xxxxxxxxxxxxxx>
To: <moshef@xxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
Sent: Sunday, July 18, 2004 12:07 PM
Subject: [SI-LIST] Re: guard traces (huge)
> Guard traces that are not stitched to a plane can conduct crosstalk noise
to
> other parts of the board. (Designs have been known to "fail" because of
> this!) Also, guard traces do not protect from inductance-coupled
crosstalk.
>
> Simulation of the layout can help determine whether guard traces help or
> hurt.
>
> - Lynne
>
>
>
> "IBIS training when you need it, where you need it."
>
> Dr. Lynne Green
> Green Streak Programs
> http://www.greenstreakprograms.com
> 425-788-0412
> lgreen22@xxxxxxxxxxxxxx
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On
> Behalf Of Moshe Frid
> Sent: Sunday, July 18, 2004 8:27 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] guard traces (huge)
>
> Hi All
> can someone tell me something about rules of guard trace
> what space need to be kept
> do they have to be connected to the ground plane and how do they affect
> the impedance of the trace that is guarded ?
>
>
> Moshe Frid
> Adcom pcb design
>
> Mobile :066-573232
>
> Tel. 972-9-7417411 (108)
>
> Email:moshef@xxxxxxxxxxx
>
>
>
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