HMC460LC5 biasing using the HMC981LP3


I found the attached file on EngineerZone.

Q1: Is this the latest and greatest biasing circuit for the HMC460LC5?

Q2: How is VGate calculated and what is its value?


Kind regards,



  • Hi Paul,

    - There is no the latest and greatest circuit, just depends on DUT that you use. In your case, you can use any of these HMC920, HMC980 and HMC981

    -Since Absolute maximum ratings for HMC460LC5 for Gate bias =-2 to 0V. Therefore you need to use this for Vgate=-2V. You can use for Vneg=-2.2V

    but both of these voltages are set by adjusting Resistors R5,6,7,8 so for your case R6=R8=open; R5=3038kOhm and R7=1603.3kOhm

    I have attached pics so you can see which resistors. Although I sent pic for HMC980, these adjustments are applicable HMC981 as well.

    -Now you need to calculate Vdd and Idrain:

    Vdd=Vdarin+IdrainxRds  page13-12

    Idrain =32(A)/Rsense      page13-13

    I hope this helps. Let me know if you need something else.


    Ivan S

  • 0
    •  Analog Employees 
    on Jan 16, 2019 1:01 PM over 1 year ago in reply to ADIApproved

    Hi Ivan

    I have a few question please:

    The datasheet for the HMC981 has a Power Up Waveform where Vdd has to power up before VDIG.

    Page 13:

    How critical is this datasheet spec?

    However I have an issue. I am using 2 LDO's and the power up time for the VDD is slower than the VDIG.

    i.e. VDD = ~200ms   VDIG ~ 10ms

    I am considering the attached circuit to help with the startup. i.e. it will ensure the VDD is 80-90% up before VDIG;  What do you think?

    What is the PSSR like on the HMC981? I am using low noise LDO's for the power management. Is this overkill?


    Kind regards



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