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hmc439 loop filter design

I am interested in using the HMC439 Phase-Frequency Detector (PFD) for a PLL application. Our application needs different VCO and narrower loop filter than the one shown in the datasheet (page-7, application circuit). I am not able to find a PLL design tool that will help me plug-in PFD gain/ offset, VCO parameters or loop-bandwidth requirements to calculate RC component values for the loop filter. I downloaded one PLL design tool from Hittite but it does not have a HMC439 PFD model.

I would appreciate any help in designing custom PFD + Loop filter using HMC439 + THS4031 with any off-the-shelf VCO modules.



  • Hello AB,

    Please provide the datasheet for the specific VCO you plan to use as well as the desired loop filter BW and whether or not you intend on using an active or a passive loop and I'll try to help.

    Best regards,


  • Hello AB,

    I see that this was re-posted with the info requested so no need to re-send. I'll respond shortly. Good question by the way.


  • Hi AB,

    I've put together a brief application note illustrating how to setup and use the legacy HMC PLL Design tool to design a loop filter for the legacy Hittite (now Analog Devices) HMC439QS16G, HMC3716LP4E Phase Frequency Detectors or HMC440QS16GE, HMC4069LP4E, HMC698LP4E and HMC699LP4E Integer-N synthesizers with a PFD output (as opposed to a charge pump output). Hope this helps.




  • Hi.

    I'm using the HMC439 as well, and found your app note very informative... thanks!

    I'm using the HMC439 in a circuit that locks the phase of two signals with the same frequency (110MHz). The VCO is replaced with a phase shifter. My question is what value do I enter into the "VCO Gain (Hz/V)" field in the main window? The shifter I'm using has a slope of approximately 50Deg/V at the nominal control voltage and operating frequency.



  • Hi Marc,

    Although phase is the integral of frequency with respect to time and  you may be able to use the phase shifter datasheet or measure the phase shifter sensitivity at your operating frequency and convert this to MHz/V the HMC439LP4E is a Phase Frequency Detector and specifically designed to function with a VCO and loop filter. When used as a 'Phase Detector' it does not provide the same performance as a mixer would which is what I'd recommend you consider using for your application. Please refer to the FAQ in the attached link. The HMC application is based on the premise that the HMC439LPQ4E is being used as a Phase Frequency Detector.


    Best Regards,


  • Thanks for the prompt reply! I wasn't aware that this part wasn't recommended for phase detector applications!Unfortunately this is a legacy design and I'm looking to improve the loop response in the short term. I will investigate your recommendation of using a mixer on the next re-spin. I'm a little confused on how to convert  degrees/V into the required MHz/V for the PLL tool without knowing the rate of phase change. The operating frequency is 110MHz, and the phase detector sensitivity is 50Deg/V. Any suggestions?

  • This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

    Thank you,
    EZ Admin
  • Hi, where can I find the application note? I tried looking but no luck. Thank you

  • Hi Richardson,

    Hi, I want to use HMC439 and Loop Filter to compare difference between two frequencies(One reference frequency and other input frequency which changes). I do not want to use VCO. 

    The idea is to input two different frequencies to HMC439 then use a loop filter and read the output voltage of loop filter to draw the comparison between the input frequencies.

    Can i do it using HMC439 because in doing so, i will not be using VCO and hence loop is not closed?