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

Larry Smith (ldsmith@lisboa.eng.sun.com)
Tue, 27 Jul 1999 10:13:13 -0700 (PDT)

When an EMI engineer talks about ground bounce, many times he is
discussing the voltage on a ground node with respect to the center of
the earth. Measurements and models for this voltage are important for
EMI purposes, but are beyond the scope of what an SI engineer usually
does. When we discuss EMI and SI topics, it is very important to
define our terms.

I hope this helps the discussion. This is a very important topic for
those of us who are trying to make circuits that both work and comply
to EMI standards at the same time.

regards,
Larry Smith
Sun Microsystems

> From: "Grasso, Charles (Chaz)" <GrassC@LOUISVILLE.STORTEK.COM>
> To: "'si-list@silab.eng.sun.com'" <si-list@silab.eng.sun.com>
> Subject: RE: [SI-LIST] : Noise Voltage levels vs. EMI levels
> Date: Tue, 27 Jul 1999 07:24:35 -0600
> MIME-Version: 1.0
>
> 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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