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LMX2571: Minimum Frequency step possible

AMAL K A
Prodigy 10 points
Part Number: LMX2571

Please help to calculate the minimum frequency change possible(frequency step or resolution) with LMX2571 when connected to 10 MHz reference and giving an output frequency of 600 MHz using internal VCO?

  • 0
    TI__Mastermind 28011 points
    Amal,

    Understand that the fractional denominator is fully programmable, supporting 1,2,3,... 16777215. It is not fixed like some of our competitors parts; there is no round-off issue.

    For your calculation, lets just say we choose a fractional denominator of 16000000 and have a phase detector of 10 MHz. The VCO frequency is 4800 MHz with divide by 8.
    If I change the fractional numerator by one, the step is therefore:

    10 MHz * (1/16000000)*(1/8) = 0.078125 Hz

    If that doesn't do it for you, you could further reduce the phase detector frequency to 625 kHz (this does sacrifice phase noise performance) to get a resolution per step of:

    625 * (1/16000000)*(1/8) = 0.004883 Hz

    Regards,
    Dean