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[FAQ] RF synthesizers: What is PFD delay and how to determine the value?

Can you tell me what is PFD delay and how to determine the value?

  • The non-linearity of charge pump becomes obviously in fractional mode. These nonlinearities degrade phase noise as well as spurs performance.
    These nonlinearities can be improved by adding some delay between the R-divider and N-divider outputs. Unfortunately, the required amount of added delay depends on the MASH order and VCO frequency.
    In integer mode, the delay is not matter, it could be zero or any other values.
    In fractional mode, follow datasheet suggestions.