[SI-LIST] Re: Cross talk and Trace length
- From: <J_Dong@xxxxxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 17 Aug 2011 09:16:32 -0400
Rajesh,
I am not a SI expert, but I think this is too general a matter to be
answered explicitly. The coupling or isolation between two adjacent pcb
traces could largely depend on the
1. freq. Assuming microstrip pcb, different freq will give different
fringing field distributions around the trace as well as see different
effective trace spacing, which would result in different couplings.
2. the load of each trace. Depending on whether you have matched or
discontinuities along either trace, resonant modes might be created. In some
filter design, you can even achieve 99% coupling between two tracings even
you have pretty wide trace spacing.
3. other physical identifies like dielectric constant of the substrate,
height of the board etc. Those factors affect aforementioned issues too.
The best solution to that is to turn to the "virtual reality"! The ever
growing solvers based on numerous types of numerical techniques (FEM, Finite
Difference, MoM, etc) could accurately solve the Maxwell equations for
arbitrary geometries. You give it a 2D/2D geometry and right boundary
conditions, it gives you a right answer. Products range from 0 dollars (e.g.
GMSH, GetDP http://www.geuz.org/getdp/) to a few tens of thousands of
dollars (e.g. HFSS, CST, etc) are options for people to choose. For this
particular question, I would just suggest getting a free trial version of
some commercial software is sufficient, for example free trail FEKO at
http://www.feko.info/.
Hope it helps.
Junwei Dong
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of steve weir
Sent: Wednesday, August 17, 2011 4:20 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Cross talk and Trace length
Your question fills a good chapter in many of the texts out there such
as "Signal Integrity Simplified" Bogatin, "High Speed Digital Design"
Johnson, etc. There are also excellent web tutorials.
Steve.
On 8/17/2011 12:19 AM, rajesh kumar wrote:
> Hello SI Gurus,
> Please share your thoughts on the relationship between
cross
> talk and trace length. In general i consider that the spacing between
trace
> is the main factor that influences cross talk. Still now i assume that 4X
> spacing between traces (X is a trace width) is a good way to avoid cross
> talk irrespective of the length of trace. Please share your views on this.
>
> Thanks,
> Rajesh
>
>
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--
Steve Weir
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