[SI-LIST] Re: Mixed digital/RF board with switching power supplies

Dear Mikhail
Are the circuits that are interfered  implemented as differential 
circuits? 

Kind regards
Boris Traa
System design engineer EMC

It's the currents that make circuits work or fail.

Philips Applied Technologies/EM&C Competence Center
Room 1.024
High Tech Campus 26 
5656AE Eindhoven, The Netherlands
Tel: ++ 31 40 27 43766
Fax: ++ 31 40 27 42224
E-mail:  boris.traa@xxxxxxxxxxxx Seri: nlv09273@nlwayhp








"Mikhail Matusov" <matusov@xxxxxxxxxxxx> 
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[SI-LIST] Mixed digital/RF board with switching power supplies
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Dear experts,

I have designed a mixed digital/RF board, which performs rather well, but 
we 
want it to perform even better in the next revision. The problem we are 
having is spurious components in the RF chain caused by the high harmonics 

of the DC/DC switching regulators. The regulators run at about 1.2 MHz and 

the band of our interest is roughly 50 to 90 MHz, although obviously, 
since 
it is a sampling system, much higher harmonics can be aliased into the 
band 
of interest... The absolute level of the offending components is -94 dBm 
and 
below, so it is in microvolts, which probably makes it more of an EMI sort 

of problem than a SI one. I believe, based on some experiments we did, 
that 
the problem is caused by the switching currents travelling in the ground 
planes. The board is quite dense and there is no easy way to divide it 
into 
an analog and digital sections... I was wondering if someone here has any 
experience in resolving this sort of problems? Also, what would be the 
best 
book to pick up on the subject? I looked at a few EMI/PCB design books on 
Amazon, but couldn't make my choice as their "look inside" feature is very 

limiting and wouldn't let me see the chapters I wanted... The books I am 
considering are Introduction to Electromagnetic Compatibility by Paul 
Clayton,  Noise Reduction Techniques in Electronic Systems by Henry Ott, 
EMC 
& and the Printed Circuit Board by Mark Montrose...

Thanks,
=======================
Mikhail Matusov
Senior Hardware Design Engineer
Square Peg Communications
Tel.: +1 (613) 271-0044 ext.231
Fax: +1 (613) 271-3007
http://www.squarepeg.ca

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