[SI-LIST] Re: Trace Spacing Rule

Erin,

A much better explanation that my tongue in cheek reply.


> [Original Message]
> From: <Erin.McPhalen@xxxxxxxxxxxxxxxxxxxxxxxxx>
> To: <khai77069@xxxxxxxxx>
> Cc: <si-list@xxxxxxxxxxxxx>; <si-list-bounce@xxxxxxxxxxxxx>
> Date: 6/29/2006 9:02:20 AM
> Subject: [SI-LIST] Re: Trace Spacing Rule
>
> Hi Kevin
> Both Howard Johnson's book "High Speed Digital Design" and Lee Ritchey's 
> book "Right the First Time" discuss cross talk in some detail and how to 
> determine the % coupling between traces.  In the end it has to do with 
> your noise budget on the signals and how much cross talk you are willing 
> to tolerate.   Tools such as Hyperlynx can simulate the cross talk based 
> on various factors such as driver IBIS model, parallel length, trace 
> separation, PCB stack up, etc.   Based on your ground bounce budget (PDN 
> impedance, signal reflections, logic levels, etc) you can determine  how 
> much cross talk your system can tolerate before you risk violating the 
> logic lows/highs, min/max voltages of your ICs. 
>
> The main determining factor in crosstalk as far as your question goes 
> would be to use 3h, or three time the height over the reference plane. 
> Using Lee Ritchey's book for instance for a center stripline, at h=10 
> mils, the % coupling at 5 mils separation is about 19%, using 3h the 
> coupling would be 1%.   In reducing the maximum coupling for cross talk, 
> decreasing the separation of your signal layer relative to their
reference 
> planes is a good starting point. 
>
> My main area of expertise is designing for EMC, and we are not involved
in 
> anything other than CMOS logic levels here on boards, so take what I say 
> with a grain of salt.  But either of the previously mentioned books will 
> help you calculate and determine what is the ideal spacing/height for
your 
> application.
>
> Erin McPhalen
>
> Hardware Designer
> R&D Hardware
> SCHNEIDER ELECTRIC
> Victoria,BC, Canada
>
>
>
>
> Kevin K <khai77069@xxxxxxxxx> 
> Sent by: si-list-bounce@xxxxxxxxxxxxx
> 06/28/2006 07:51 PM
> Please respond to
> khai77069@xxxxxxxxx
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> To
> si-list@xxxxxxxxxxxxx
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> Subject
> [SI-LIST] Trace Spacing Rule
>
>
>
>
>
>
> Hi All,
> What's the real rule of thumb for trace spacing? 
> I have seen 3w (w = trace width) and also 3h (h =
> height of trace above reference plane).  I'm
> interested in 100 Ohm diff pairs. 
>
> Thank you,
> Kevin
>
>
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