[SI-LIST] Re: Book - (Chassis - signal ground)

John,

I have a question about one line you wrote:



John Howard wrote:

>   Alternatively if the high speed signal return path
> is provided more intimately (read "smaller loop") in the PCB structure
> then connecting the two grounds together increases your EMI liability.  In the
> limit
> case, where all signal routes are perfectly coupled to their respective return
> paths, it actually doesn't
> matter whether you tie the two grounds together or not.

Isn't the first case just an example of the second?  If the
high-speed signal return is in the PCB (ground plane I
presume) then connecting the signal and chassis grounds
outside this loop should not affect it, because
mutual inductance will keep the return path in the same
place and hence there will be the same radiating loop.
Or am I misinterpreting what you are saying (or the
topology I have outlined here)?

- Gary Rosen




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