Re: [SI-LIST] : Micro Noise

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From: Dennis Tomlinson (det@tellabs.com)
Date: Fri Nov 05 1999 - 11:55:09 PST


Chuck Hill wrote:
>
> Derek,
>
> I remember another fellow having this problem with an Intel 80186
> processor. He placed a piece of copper tape on the package--I don't
> remember whether he grounded it or not.

This is the second or third reference on this thread to a floating shield.
I have some concern over whether or not this would be at all effective.

Wouldn't an E-field be unaffected by such a shield? I can believe that an
H-field could be shielded in this manner, but to what avail? A piece of
copper tape stuck to the top of a plastic IC package is in the "very" near
field - dominated by the E and not the H. I suspect a biconical antenna placed
three meters away would show little or no measurable difference between
shielded and unshielded.

Just my $0.02

Dennis

>
> Charles Hill, consultant
>
> At 10:31 AM 11/3/99 -0500, Lfresearch@aol.com wrote:
> >Hi all,
> >
> >I have a problem with a microprocessor which appears to be radiating very
> >strongly from the package. I've deactivated all other circuits ( pulled
> >crystals, pins etc ) on the board. Additionally, the micro is held in reset,
> >PROM's are pulled, but it's a noisy as heck. Close field probes ( both E and
> >H field ) show the package to be the dominent source of radiation.
> >
> >The device has a maximum clock rate of 50 MHz, this is where we're using it.
> >Clock it at 32 MHz and the emissions fall about 10 dB up to about 300 MHz,
> >more above 300 MHz. Yes it's a CMOS device.......
> >
> >Am I stuck with putting a can over the chip? The product has a plastic
> >package, so there is no shielding available at all.....
> >
> >Thanks,
> >
> >Derek
> >

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