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LMX2571 PFD_DELAY_F2 in R22

KLi
Prodigy 10 points
Other Parts Discussed in Thread: LMX2571

Hi,

When configuring the LMX2571 the PFD_DELAY_F2 (table15) has a significant effect on the phase noise and spurs.

Q1. Can anybody describe what these bits are doing? PFD_DELAY_F2 in table 15.

Q2. Setting these these bits I can potentially get a lower phase noise. Does this have an impact on anything else?

Q3. Can I use them out of the recommended range if I get a lower noise?  If not why not?


I ask Q1-Q3 since the operation/function of the PFD_DELAY_F2 is not well described.

Thanks all.

  • 0
    TI__Expert 4085 points
    Hi Kim,

    We received your questions, thank you for your interest in our products.
    I forwarded your questions to the applications engineer most familiar with this device.
    Thanks for your patience.

    Regards,
    Julian
  • 0 in reply to Julian Di Matteo
    TI__Guru** 108330 points
    Hi Kim,

    PFD_Delay is part of the PFD circuitry and is used to set the width of the so-called antibacklash pulse. This pulse ensures that there is no dead zone in the PFD transfer function. The setting of this delay will affect phase noise as well as spurs. Datasheet has some recommended settings. However, I encourage you to try different delay setting in order to get the best performance.