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PeterB
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Registered: ‎06-05-2020

Kintex-7 MCMM: Dynamic phase shift for frequency modulation?

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I have existing hardware based on a Kintex-7 that requires a user-driven PLL for clock alignment.  That is, I can measure a phase error via fabric or even via software, and need to correct a ~100Mhz clock based on that error.  The correction range needs to cover +/- 50ppm or so.  I do *not* have an actual related clock to feed to an MCMM block.

It looks like the dynamic phase shift might get the job done: by continuously commanding a phase increment (or decrement) at a fixed interval, it seems one could shift the resulting frequency.  The documentation claims "no maximum phase shift or phase-shift overflow", which suggests a continuous increment like this would work.  But then it says "When the end of the period is reached, the phase shift wraps around round-robin style", which is strange language.  I cannot tell from this if a wrap would create a glitch as the shift jumps from +55/56 to 0, or whether the wrap does what one would hope and smoothly increments the phase again.

My application can tolerate the jitter that would come from this bursty phase noise, but I also consider feeding the resulting uneven clock back through another MCMM or PLL block to smooth out.

Has anyone experimented with frequency offsetting in this manner and had success?

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pthakare
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Registered: ‎08-08-2017

Hi @PeterB 

Phase shift here is linear increment in step of (1/56Fvco).

There will not be glitch. Its like if you phase shift the clock by 370 deg linearly , but considering period its actually 10 Deg with respect to original clock.

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pthakare
Moderator
Moderator
458 Views
Registered: ‎08-08-2017

Hi @PeterB 

Phase shift here is linear increment in step of (1/56Fvco).

There will not be glitch. Its like if you phase shift the clock by 370 deg linearly , but considering period its actually 10 Deg with respect to original clock.

-------------------------------------------------------------------------------------------------------------------------------
Reply if you have any queries, give kudos and accept as solution
-------------------------------------------------------------------------------------------------------------------------------

View solution in original post

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