Re: [SI-LIST] : Micro Noise

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From: Roland F. Portman (portman@bitmicro.com)
Date: Wed Nov 03 1999 - 14:22:31 PST


I am assuming this processor has an internal multiplying PLL since your emissions
are in the 300MHz range. If you have an external PLL loop filter, be sure it is
properly designed and VERY close to the PLL pins.

It is a thought.

Roland

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.
>
> 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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--
Roland F. Portman
BiT Microsystems, Inc.
48499 Milmont Drive
Fremont, CA  94538

(510) 623-2341 Ext 129 (510) 623-2342 Fax (925) 323-2393 Pager/VM/Cellphone

portman@bitmicro.com http://www.bitmicro.com

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