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PFD Gain of hmc3716


    In the datasheet of hmc3716, it told me that the PFD Gain is 2/2π V/rad. What confused me a lot is that the unit of PFD Gain is A/rad in a traditional PLL. Using the PFD gain in A/rad multiplied by the loop filter transfer function gives the tuning voltage to adjust the VCO frequency. However, we can not get the tuning voltage when the unit of PFD Gain is V/rad. So how should I deal with this issue? Look forward to hearing from you!


  • The HMC3716 requires an op amp in the loop filter to function correctly since as you pointed out, the outputs on this PFD do not source any current. We call these particular loop filters "PFD filters" or "Phi R / Phi V Detector filters".

    Is there a reason you are trying to calculate the transfer function manually, we have an HMC3716 model in ADIsimPLL you should be able to design a loop filter that way. 



  • Thank you for your reply! I use ADF5610 as the VCO which we bought 20 pcs last year and hmc3716 as the PFD instead of the phase detector inside ADF5610. But in my loop there is additional mixer and low-pass filter. It seems impossible to implement this simulation design in ADIsimPLL. We have implemented the loop and tested its performance which is not satisfactory enough. So we want to simulate to validate feasibility. That is why we want to derive the transfer function of the active loop filter given by ADIsimPLL. But we just started to encounter great difficulties.

    Look forward to your reply!



  • Understood. Since the PFD output in this case is voltage and PFD gain is V/rad I believe the loop filter gain equation to find the transfer function should be Vo(s)/Vi(s) as you suggested in the other post you made on this topic.

    I suggest trying to calculate the transfer function for one of the the filter topologies we have in ADIsimPLL first to confirm your equations match with an ADIsimPLL simulation first.

    Please take a look at this question here. I think the mistake they initially made assuming the CP was a voltage output is what you would need to do in this case.

  • Hi, I forgot to mention while I was researching this I found a paper/book by Dean Banerjee called "PLL Performance, Simulation, and Design 5th Edition." In this book there is a short section on the differential integrator type PFD filters used here. It should help with your calculations

  • Hi aandrews,

    Thanks a lot for your advice! It seems I made the same mistake as the person in the post you mentioned. By using the PFD gain in unit of A/rad mentioned in ADIsimPLL, my derivation results are basically consistent with the software simulation. Then I can continue with the simulation with mixers and filters. Thanks a lot again! By the way, it would be especially nice for ADIsimPLL to become more customizable.