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HMC980LP4E to bias HMC863ALC4

Category: Hardware

Hello Community,

as mentioned in the subject I am trying to bias the HMC863ALC4 with the HMC980LP4E. I tested the functions of the HMC980 and they seem to work as expected without any amplifier connected.
I could measure:
V_drain ~= 6V
V_gate = +2.8V (if EN high)
V_neg = -2.44V
V_gate = V_neg (if EN low)
V_dd = 6.04V

Now even though the HMC863 is connected there are no changes to the voltages.

Below you can see the schematics of both HMC980 and HMC863.

The diode D1 is a Schottky-diode as on the eval board (BAT54SLT1G). So that's not a problem.
I also checked if the current limiter of the power supply kicks in, but that's neither the case.

Would really appreciate your help.


  • Hi Jan,

                 Have you visited the HMC980 wiki site and downloaded the configuration calculator?

    The calculator will determine the correct resistors and VDD voltage to apply to the HMC980.


    Jim B

  • Hi Jim,

    thanks for your reply.

    I indeed downloaded the calculator to confirm the settings I chosed. And the values I got are almost identical to those shown in the calculator with slight tolerances.

    Side note:
    Talking about the calculator I believe there is a bug as R_ds,on is shown in kOhms, which shouldn't be correct. Should be Ohm instead.
    Also the diode D1 Pin 1 is shown in the wrong direction.
    Suggestion: Would it be ok to be able to freely change the input type of the numbers? Because I am from Germany and the values will be changed automatically to date format.

    Well again, everything is set up according to the calculator as you can see in my schematic. I even used the same schottky diode BAT54SLT1G.

  • Well, what I didn't use is the resistors R5 and R7 as I didn't thought those would be necessary according to the HMC863 specifications.

    Why did you use those in the calculator sheet?

    Also why did you set the I_drain current to 540 mA?



  • Hi Jan,

                  If the current isn't set to 540 mA, you won't make PSAT. The value of current chosen depends on how much Power you need. If you set the current for 350 mA, you will only be able to get ~ 12 dBm Pout. See graph below.

    The HMC980 holds the drain current at the programmed value so, you need to determine the output power needed and set the resistor values according to that current value.

    Which means the device will always be consuming the programmed current event at very low signal levels.

    R5 &R7 are feedback resistors which close the loop allowing the HMC980 to operate. The HMC980 is a closed loop system. 

    Also, you mentioned you tested the functions of the HMC980 without the amp. It doesn't go into operation unless the amp is connected.


    Jim B