PFD frequency selection in TRF372017

Vijaya Suresh Namburi

Prodigy 25 points

Other Parts Discussed in Thread: TRF372017

HI,

I'am using TRF372017 with fLO=1128MHz and fREF=26MHz in integer N mode.

1. what would be the best PFD frequency for better phase noise and spurious response?

2. What will be the effect if I set PFD frequency as 2MHz and design the loop filter for 1.6MHz fPFD?

over 8 years ago

0 RJ Hopper over 8 years ago

TI__Mastermind 18065 points

In integer mode, many times the PFD frequency is determined by required frequency step size. If this is not a concern, then there is additional flexibility. The approach to use Ref = 26 MHz with a PFD off 2 MHz is legitimate. This would provide 2 MHz frequency steps and integer spur at 2 MHz offset. The standard loop filter used with PFD = 1.6 MHz will still be suitable for this situation.

--RJH

0 Vijaya Suresh Namburi over 8 years ago in reply to RJ Hopper

Prodigy 25 points

Thank you for prompt reply. My required fLO is fixed at 1128MHz. In this case, do I need to follow the frequency step size condition?

0 RJ Hopper over 8 years ago in reply to Vijaya Suresh Namburi

TI__Mastermind 18065 points

No. If the frequency is fixed then you have more flexibility to increase the PFD frequency which will push PFD spur farther out and thus more attenuated by the loop filter. --RJH

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PFD frequency selection in TRF372017