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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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  • The benefit of using the PLL multiplier is that it allows you to use a low frequency clock source (a crystal oscillator, for example).

    You sould avoid using the PLL multiplier, however, if your application has a very demanding phase noise requirement. The PLL multiplier performs well, but the performance of its integrated VCO cannot compete with a high quality RF frequency source. Furthermore, the PLL amplifies the phase noise at its input (within the loop bandwidth of the PLL), so applications that need very good close-in phase noise performance are not well suited for using the PLL multiplier.

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  • The benefit of using the PLL multiplier is that it allows you to use a low frequency clock source (a crystal oscillator, for example).

    You sould avoid using the PLL multiplier, however, if your application has a very demanding phase noise requirement. The PLL multiplier performs well, but the performance of its integrated VCO cannot compete with a high quality RF frequency source. Furthermore, the PLL amplifies the phase noise at its input (within the loop bandwidth of the PLL), so applications that need very good close-in phase noise performance are not well suited for using the PLL multiplier.

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