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Arria 10 CLKUSR - Can a spread spectrum clock be used?

JCann
Partner
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I can't find any specification for absolute frequency / jitter / etc for the CLKUSR input (other than it shall be 100MHz). Looking at options for removing emissions @ 100MHz that appears to be related to crystal oscillator. Figure that spread spectrum clock would help, but don't know for sure if A10 input can handle it. I believe that this CLKUSR simply runs state machines / PreSICE, so don't believe it needs to be super accurate, but want to confirm.

 

Any help would be appreciated.

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Kenny_Tan
Moderator
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JCann
Partner
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I had checked there, but doesn't appear to give me any insight into the frequency accuracy of the 100MHz clock. If I use spread-spectrum and the center spread is 98-102MHz, will that violate timing or anything else related to CLKUSR functionality? It calls out that it needs a "stable" clock, but it doesn't say how stable it needs to be. That is what I'm looking for (freq accuracy + jitter specs).

Kenny_Tan
Moderator
249 Views
In general CLKUSR has the same requirements as of general single ended PLL input pin. There are no characterization yet but our guidance is that the input jitter should be less than 120 ps. Essentially we have no spec that is specific to CLKUSR, so suggest just using the PLL input clock spec. Thanks
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