From: Krishnan S Rengarajan ([email protected])
Date: Tue Mar 14 2000 - 19:56:52 PST
Please look at the datashseet more carefully.
USB will NOT be spread. SS would be applicable
to CPU/PCI/SDRAM outputs, not USB/REF/IOCLK etc.
Yu Wang wrote:
> 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" <[email protected]>
> > 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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