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Register configuration issues on the HMC764

Find a typical register configuration for integer division.
Now no matter how many of the registers of the N divider ,the vco are oscillating at around 7.5GHz.

Phase frequency is 10MHz and  reference input is 50MHz.

The following is my register configuration:

02h <= 5d(R divider is 5)

03h <=  770d(N divider is 770,expected RF out is 7.7GHz)

04h <= 0

05h <= 50894C

06h <= 703387

07h <= 4FA

08h <= 31DF

09h <= 900000

0Ah <= 0

0Bh <= 72

0Ch <= 0

0Dh <= A


  • Hi there,

    REG 0 & 1 should also be programmed and I'm assuming that although you mention decimal values you do realize these must be hex values for the program to work. 

    I'll also assume your using the evaluation board.

    Does it lock with other PFD frequencies? 50MHz? 100MHz?

    If so I suspect the loop is unstable and needs to be re-designed for operation with a 10MHz PFD. Typically PM changes enough that this is what happens. PM should be 40 - 70 degrees, 55 degrees is a good starting point.

    You'll also need to adjust the LD window as outlined below.

    Also refer to the attached HMC700 FAQ.

    Best Regards,


  • Dear Mr.Richardson


    First, thank you very much for your reply.


    Actually, I did not use the evaluation board. The PCB board is my own design, according to hmc764 datasheet.


    As the hittite pll design software can not be installed and ADIsim does not support this chip, I can only design the loop filter without any software support.


    At present my loop filter bandwidth of 800kHz, PFD 10MHz, CP is 2mA and the PM is 45 degree.


    I also tried to change the PFD to 50MHz, 20MHz(absolutely I change the loop filter), all the same results, the vco are oscillating at around 7.59GHz.


    In addition, since my loop filter is a passive filter, can Vtune's voltage be tuned at 2 ~ 13V? Is there something that needs for special attention when configuring charge pump?I have tried to change the N divider to 7.2GHz(Vtune = around 2V),the vco are also oscillating at around 7.59GHz.


    Finally, if possible, I want to ask for a register configuration with integer division&single frenquency output.


    Best wishes,




  • Hi Pasqal,

    May I ask what the application is?

    Best Regards,


  • I would like to use hmc764 to achieve a 7.7GHz frequency source.

  • Hi there,

    Please provide as much detail about your application as you can. This information is required in order to be able to support your request.

    What is the source for?

    Who will use it?

    What type if equipment will it be used in?

    What frequency range is needed?

    What setting time is required?  

    Part can be simulated in ADISimPLL - search EZ for the table that outlines how to do this for the integrated HMC VCO/PLL products.

    Best Regards,