Re: [SI-LIST] : Micro Noise

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From: Jim Freeman (freeman@broadcom.com)
Date: Wed Nov 03 1999 - 15:14:31 PST


Hi Derek,

Is the microprocessor cavity down or cavity up? If it is cavity up and there is a heat sink, you may have to pull noise off of the heat sink to some appropriate point. The heat sink may be radiating.

Jim Freeman

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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