[SI-LIST] Re: EMI Question Related to Spread Spectrum Clock Generator
- From: khardin@xxxxxxxxxxx
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 5 May 2004 10:08:43 -0400
To all,
The FCC class B radiated emissions limits are stepped above 30MHz.
The 3m limits are:
Frequency Range Limit Detector
30MHz - 88MHz 40dBuV/m Quasi-Peak Detector
88MHz-216MHz 43.5dBuV/m Quasi-Peak Detector
216MHz-960MHz 47dBuV/m Quasi-Peak Detector
>960MHz 54duBuVm Average Detector
>960MHz 74duBuVm Peak Detector
There are different limits for CISPR 22 (the rest of the world) that are a
bit more stringent.
Refering to previous appends on this thread.
1) To determine if your processor is compatible with Spread Spectrum
Clock Generation (SSCG), an analysis must be performed by the designer
of the PLL and system that is tracking the modulated clock. Many processor
manufactures are very aware of SSCG and design for some ranges of SSCG
operation. Some data sheets discuss SSCG specification. If not you must
contact the manufacturer.
For more information see: www.lexmark.com/sscg and see technical papers
link.
2) SSCG reduces the amplitude in any 120kHz given bandwith by distributing
energy uniformily over a much greater bandwidth. There has been much
discusion
over the last 10 years about the EMI implications. A number of studies
have been
performed with several communications methods and SSCG has been found not
to cause additional interference. There may be other communciation schemes
that may have a higher risk of interference but none have been found
significant.
See above link for interference studies.
Hope this helps,
Keith Hardin
|---------+---------------------------->
| | "Steven M. |
| | Waldstein" |
| | <swldstn@xxxxxxxx|
| | .com> |
| | Sent by: |
| | si-list-bounce@fr|
| | eelists.org |
| | |
| | |
| | 05/04/2004 07:41 |
| | PM |
| | Please respond to|
| | swldstn |
| | |
|---------+---------------------------->
>------------------------------------------------------------------------------------------------------------------------------|
|
|
| To: <si-list@xxxxxxxxxxxxx>
|
| cc:
|
| Subject: [SI-LIST] EMI Question Related to Spread Spectrum Clock
Generator |
>------------------------------------------------------------------------------------------------------------------------------|
To all,
Here's another spread spectrum PLL question.
Assume you are taking a 33 MHz clock in generating
800 MHz from it with a spread spectrum PLL. ( 24x multiplier ).
From the 800 MHz you divide by 4 and 6 to get 200 MHz and 133 MHz.
Since the 800 MHz is the signal that has been modulated to spread
the energy, the 200 MHz and 133 MHz or even lower ( say 66 MHz ),
have different power densities. The 200 MHz would have a low power
density than the 133 or 66 MHz because it is divided by a smaller
amount.
So the question is....
Do FCC emission limit change as a function of frequency band to
allow a single high frequency clock to be divided down to several
different bands?
Does anybody know where I can find info on allowed emissions energy
and is it a function of frequency or a hard and fast maximum limit,
independent of frequency?
Thanks in advance for any help
Steve
swldstn@xxxxxxxxxxxx
------------------------------------------------------------------
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:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//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:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//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:
