[SI-LIST] Mixed digital/RF board with switching power supplies
- From: "Mikhail Matusov" <matusov@xxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Fri, 6 Jul 2007 10:27:50 -0400
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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