RE: [SI-LIST] : Noise Voltage levels vs. EMI levels

Grasso, Charles (GrassC@LOUISVILLE.STORTEK.COM)
Tue, 27 Jul 1999 07:24:35 -0600

The most ubiquitous phrase used for noise - EMI levels translation
is ground bounce. A term the experienced SI folks are very familiar with
I'm sure. Indeed the EMC folk spend a lot of energy minimizing
the noise that is developed across the ground plane inductance.

A general rule of thumb is that "noise" on the ground plane should
not exceed 300mV. (From Henry Ott - Noise Reduction
Techniques in Electronic Circuits.)
Thank you
Charles Grasso
StorageTek
2270 Sth 88th Street
Louisville CO 80027
Tel: (303)673-2908
Fax(303)661-7115

> ----------
> From: Spencer, David H[SMTP:David.Spencer@usa.xerox.com]
> Sent: Monday, July 26, 1999 10:03 AM
> To: 'si-list@silab.eng.sun.com'
> Subject: [SI-LIST] : Noise Voltage levels vs. EMI levels
>
> I'm looking to correlate PCB ground noise voltage to an EMI levels.
>
> My understanding goes as far as: the voltage is measured from the PCB
> ground
> input to a point on the board differentially. That voltage drop is the
> noise voltage. The voltage drop tells us that there is common mode
> current. If we knew the impedance between the two points we could then
> calculate the common mode current.
> Since every PCB and has different geometry's and cables (power and I/O),
> the
> difficult unknown is the impedance.
>
> My questions:
> Is there is an absolute noise voltage level that should never be exceeded?
> Is there a way to "accurately" quantify the impedance's of the PCB ground
> plane and cables?
> Can noise voltage become a PCB design specification?
> Most importantly, when all is said and done, is there an "accurate"
> correlation between noise voltage and EMI levels?
>
> Thanks for the input
>
> David Spencer
> Xerox Corporation
>
>
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