From: Gary Steinkogler ([email protected])
Date: Sun Feb 06 2000 - 21:27:19 PST
I went to a Certification/EMI House to find out where/why we were failing
radiated emissions. There are 13 cables attached to my system - some
shielded and some not. All the cables were hot - especially the video and
audio cables.. After testing we determined it was our grounds on the pc
board. We have 2 ground planes, with one of them being split, digital
ground, audio gound, and video ground. The other ground is digital ground.
You can view my system at www.dmida.com. Any type of filtering did
nothing to reduce the emissions. I do not have a simulation package. Any
suggestions?
-----Original Message-----
From: [email protected] [SMTP:[email protected]]
Sent: Thursday, January 20, 2000 4:23 PM
To: [email protected]
Subject: [SI-LIST] : 10 layer board stackup
I presently have an 8 layer board as follows:
sig top
grd
pwr
internal 1
internal 2
pwr
grd
sig bottom
We failed radiated emissions. All clock/fast signals were routed on
surface of board - since system is battery operated, ie keep the power
consumption down. Routing these signals on inner layers will draw more
power? Since we failed radiated emissions miserably, the plan is to now
bury the clock signals on the inner layers. Emissions exceeded - out to
7th harmonic of clocks (19.66MHz - from which the following clocks are
generated, 117.96MHz, 58.9824Mhz, and 29.4912MHz) Three other clocks
are
at 32.514MHz, 12.000MHz, and 24.576MHz. We are adding damping
resistors.
We are also adding 2 more signal layers to the board for the clock/fast
signals - impossible to route clock signals on either internal 1 or 2,
also under a time crunch. I am looking for advise on the board stackup
for this now 10 layer board.
Stackup as planned
Sig top
grd
pwr 3.3V
new layer for clocks/fast edge rates/repetitive
internal 1
internal 2
new layer for clocks/fast edge rates/repetitive
pwr 5V
grd
sig bottom
Also checking into smaller decoupling capacitors - higher self-resonant
frequency - presently my board has all decoupling capacitors with 0.1uF
values.
I have seen 10 layer stackups with pwr and grd layers separated by as
many
as 6 layers. I want to keep the pwr and grd layers close in my
application
for good board decoupling.
Please email me at [email protected] as I will be offsite from my
office for the next couple of weeks.
Regards,
Gary Steinkogler
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