RE: [SI-LIST] : SSC

About this list Date view Thread view Subject view Author view

From: Zhang, Michael T (michael.t.zhang@intel.com)
Date: Tue Mar 14 2000 - 13:35:28 PST


The reason SSC is not used on USB is because the 48MHz is used for frame
synchronization. It is specifically required not to modulate the 48MHz clock
and the reference clock in Intel's clock generator specs.

I am not sure about the specific Cypress part you are referring to. It may
very well have fixed USB output when other output clocks are modulated, just
like most other SSC generators do.

-Michael T. Zhang
Processor Product Development
Performance Microprocessor Division, Intel Corp.
(503) 264-2301

-----Original Message-----
From: Yu Wang [mailto:wangy_km@yahoo.com]
Sent: Tuesday, March 14, 2000 1:16 PM
To: si-list@silab.eng.sun.com
Subject: RE: [SI-LIST] : SSC

Michael,
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.

Regards,
Yu Wang

--- "Zhang, Michael T" <michael.t.zhang@intel.com>
wrote:
> 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
Tel:713-745-1671
__________________________________________________
Do You Yahoo!?
Talk to your friends online with Yahoo! Messenger.
http://im.yahoo.com

**** To unsubscribe from si-list or si-list-digest: send e-mail to
majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list
or UNSUBSCRIBE si-list-digest, for more help, put HELP.
si-list archives are accessible at http://www.qsl.net/wb6tpu
****

**** To unsubscribe from si-list or si-list-digest: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
si-list archives are accessible at http://www.qsl.net/wb6tpu
****


About this list Date view Thread view Subject view Author view

This archive was generated by hypermail 2b29 : Thu Apr 20 2000 - 11:35:35 PDT