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.)
2270 Sth 88th Street
Louisville CO 80027
> From: Spencer, David H[SMTP:David.Spencer@usa.xerox.com]
> Sent: Monday, July 26, 1999 10:03 AM
> To: 'email@example.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
> 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),
> 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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