Re: [SI-LIST] : Problems with 3rd harmonics on Intel 820 Camino chipset?

Adrian Shiner (adrian.shiner@virgin.net)
Thu, 10 Jun 1999 20:04:01 +0100

You could well be right in your suspicions. I know of a plasma display wh=
ich had exessive RF emmision & failed EMC tests when information interfac=
e was designed in accordance with the device data sheet. Two clocks were
harmonically related. The cure was to lower the higher clock frequency to=
a non integer related frequency.

My good old Eddystone Model 940 communications receiver (vacuum tubes bas=
ed electronics!) using a 100kHz to 80MHz bandwidth active antenna, picks =
up the radiation from an EPSON Stylus 300 printer located 3m away from th=
e antenna.
Low power, low supply voltage semiconductor circuits can easily self inte=
rfere. Are the circuit simulators being used accurately describing the PC=
Bs?? Perhaps the RF and analog circuit designers can contribute to the de=
sign of
these circuits. Knowing about boolean algebra, race conditions, timing s=
kew & a bit of code writing does not solve all digital circuit design pro=
blems.

For those that follow astronomical events, a recent space probe was lost =
due to an 25ms transient overload current demand from an integrated circu=
it when it switched on. Incredible or what?

Best wishes

Adrian

Adrian

Per Torstein R=F8ine wrote:

> As a hobby, I like to follow news and rumors about the PC platform.
>
> The other day, "The Register" had a story called "Rambus Meltdown a
> sorry tale of fudge, mudge and kludge" that may be interesting to
> si-list readers (http://www.theregister.co.uk/990608-000022.html).
>
> The rumors say that Intel can't get their new chipset running stable
> with a 133MHz front side bus frequency and 800Mhz (400Mhz, on both
> clock edges) Direct Rambus frequency. I can imagine that producing
> inexpensive motherboards with such high frequencies is a challenge,
> but it seems like Intel's problems are worse than expected.
>
> I was wondering: Could Intel's problems be related to the fact that
> the Rambus frequency is exactly the third harmonics of the FSB
> frequency? Isn't this especially unfortunate noise-wise? Does any of
> you have any experience to share regarding specific unfortunate
> combinations of on-board frequencies?
>
> The reason I was wondering about this is that, according to the
> article, Intel is considering lowering the Direct Rambus speed to 712
> MHz, which is 16 Rambus data words for each three FSB data words, down
> from 18.
>
> --
> Per Torstein Roeine email: perr@ifi.uio.no
> University of Oslo phone: +47 22 85 24 52
> Dept. of Informatics, Microelectronics Group fax: +47 22 85 24 01
> Box 1080 Blindern, N-0316 OSLO, NORWAY
>
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