[SI-LIST] FW: Re: Sanmina patent on dielectric thicknesses under 4 mi ls
- From: Chris Cheng <chris.cheng@xxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 27 Nov 2001 15:57:11 -0800
Chris,
I suggest you do the following experiment (I've done it so
many times to toy with EMC engineers).
Take a system board with your favorite sub nf caps, do an
EMI scan, replace every single sub nf caps with .1uf or
.01uf on the same PCB and redo your scan. Let's see if they
make any difference.
I never lost my bets but you can be the first one.
-----Original Message-----
From: Chris Padilla [mailto:cpad@xxxxxxxxx]
Sent: Tuesday, November 27, 2001 3:41 PM
To: chris.cheng@xxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: Sanmina patent on dielectric thicknesses
under 4 mi ls
I use plenty of sub nf caps to help curb emission problems in a lot of my
systems and they do work just fine and are necessary.
However, you point specifically to core noise (presumabley on some large
ASIC or processor or something) and while that is not an area I
specifically deal with, it certainly comes into play. EMI is a system
level phenomenon and the size of your PCB most certainly can resonate at
frequencies well above 100 MHz.
I fear I am missing your point here....
----->Chris
EMC Engineer
Cisco Systems
>Ron,
>May I ask what is the intend use for the sub nf caps ?
>
>By no means I claim there is absolutely no need for sub-nf caps,
>however, I always question the need for sub-nf caps for EMI or
>noise decoupling in a digital system. I believe the place for
>such decoupling is either on die or package not on the PCB.
>In fear of sounding like a broken record again, I claimed :
>a) High frequency core noise cannot propagation through the
>package back to the PCB. Same reason you have sso limitation
>on a package, its just as bad to go out of than go into a
>package. Core noise above 100MHz can not be decoupled
>outside the package.
>b) I/O switching noise is related to the image current
>return path which exist between the power plane sandwiching
>the signal layers and dictated by the impedance control
>of the stackup.
>
>I've used Zycon before thinking they can lower EMI or
>power noise but the reality is they don't and the reasons
>are stated above.
>
>If you have other reasons to use distributed sub nf
>decoupling caps, I will keep by mouth shut. And I practice
>what I preach. I never use decoupling below 1nf in any of
>my systems and they pass class B just fine.
>
>
>
------------------------------------------------------------------
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 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:
