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Under what conditions is it OK to use the on-board PLL multiplier?

I'd like to use the REFCLK multiplier, but I want to know if there are any tradeoffs.

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  • Hi mantow,

    I think there is no general rule saying that an external PLL is always better than the internal. But since an external PLL can have the advantage of being isolated from the IC package and have a dedicated resource on its own. Then potentially it can have better performance than the internal PLLs. From what I've known, the motivation of having an external PLL is due to the limited performance of the integrated VCO in terms of phase noise. Thus achieving the specs that have demanding phase noise requirements makes the solution of external VCO attractive.

    Best Regards

    LouijieC

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  • Hi mantow,

    I think there is no general rule saying that an external PLL is always better than the internal. But since an external PLL can have the advantage of being isolated from the IC package and have a dedicated resource on its own. Then potentially it can have better performance than the internal PLLs. From what I've known, the motivation of having an external PLL is due to the limited performance of the integrated VCO in terms of phase noise. Thus achieving the specs that have demanding phase noise requirements makes the solution of external VCO attractive.

    Best Regards

    LouijieC

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