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From: Yu Wang (
Date: Tue Mar 14 2000 - 13:16:05 PST

What do you mean SSC can NOT be used on any
 fixed frequency clocks like USB, actually, I read
an SSC's datasheet from cypress. It does have a
dedicated output for USB.

Yu Wang

--- "Zhang, Michael T" <>
> Ravinder,
> As you said, SSC is a percentage frequency
> modulation. So it spreads the
> higher harmonic of clock frequency over a wider MHz
> range, therefore, brings
> a larger amount of EMI reduction of the peak
> amplitude, NOT higher emission.
> This has been seen in actual PC systems. In
> addition, SSC benefit increases
> at frequencies over 1GHz due to the use of average
> detector.
> SSC itself does not introduce more jitter because of
> the small percentage of
> frequency modulation. This is the reason it has been
> successfully used with
> RDRAM, which has 400MHz differential clocks with
> very tight jitter
> requirement. However, SSC can not be used on any
> fixed frequency clocks,
> like USB.
> -Michael T. Zhang
> Processor Product Development
> Performance Microprocessor Division, Intel Corp.
> (503) 264-2301

Yu Wang, Ph.D
U.T. MD Anderson Cancer Center
1100 Holcombe Blvd., Box 217
Houston, TX, 77030
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