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

  • From: "Christian D'Souza" <christian.dsouza@xxxxxxxxx>
  • To: matusov@xxxxxxxxxxxx
  • Date: Fri, 6 Jul 2007 12:28:28 -0500

Hi Mikhail,
A couple of questions:

1. What is the average magnitude of the current through the PWMs?
    What different voltages?
2. What kind of inductor does the switching circuits use?
3. Proximity to the RF circuitry?

Christian

On 7/6/07, Mikhail Matusov <matusov@xxxxxxxxxxxx> wrote:
>
> 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
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> http://www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
> List technical documents are available at:
>                 http://www.si-list.net
>
> List archives are viewable at:
>                 http://www.freelists.org/archives/si-list
> or at our remote archives:
>                 http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
>                 http://www.qsl.net/wb6tpu
>
>
>


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field


List technical documents are available at:
                http://www.si-list.net

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu
  

Other related posts: