Question about AD9549 output clk frequency

Hello,

My customer use AD9549 and ask some question about AD9549 output clk frequency in their below test result.

They set AD9549 PLL output with S/R Devider x4, and then test below conditions.

1) If source is 25MHz, output of AD9549 is exact 100MHz. (25x4 = 100)

2) But if source is 49.952Mhz, output of AD9549 is 199.840MHz, not 199.808MHz. (49.953 x 4 = 199.808)

Q1) Is above result correct? ( Source input is a 10 bit digitized signal.)

  

Q2) Would you let me know whty this difference is occurred?

       Is this a PLL characteristic? conversion error? error from PPM? 

      or need to review schematic & configuration? device fault?

Please advise me.

Regards,

Se-woong

 

  • HI,

    in order to determine the AD9549 configuration, they must have used the AD9549 evaluation software. Please send me the stp file they created.

    Then I'll respond to your questions

    Petre

  • Dear Petre,

    Thank you for your kind concern.

    Please refer attached their STP file.

    ABLEE AD9549.zip

    Regards,

    Se-woong

  • Hi,

    I took an AD9549 evaluation board, I provided REFA=10.24MHz (from an AD9545 evaluation board, HSTL, 15 mA driver) and SYSCLK=25MHz (from a Rohde & Schwartz SMA 100A, 2dBm), I launched the evaluation software and I loaded the stp program you sent me. I then measured the OUT frequency with a Agilent E5052B as 24.479998 MHz.

    So the output was exactly the desired frequency.

    You say: "If source is 25MHz, output of AD9549 is exact 100MHz. (25x4 = 100)"

    When you say source, I suppose you refer to REFA, so if I set the feedback divider to 4, I would get a 100MHz. I changed accordingly the setup and save it. I then powered down the board and closed the evaluation software. I then powered back the board (this time I provided 25MHz at REFA from the AD9545 evaluation board, HSTL, 15 mA driver), launched the evaluation software and loaded the setup. I measured 99.999988 MHz, which I believe is very good.

    I then repeated the procedure for REFA=49.952MHz. I obtained 199.807976MHz, which I consider very close to the targeted 199.8080000000010 MHz indicated by the evaluation software.

    I suppose the error you get if from the clock source which you say is digital on 10 bits. I recommend measuring the 49.952MHz clock to see if the frequency is the one desired.

    I attach the stp files I used for REFA=25MHz and REFA=49.952MHz.

    AD9549_setup_REFA_25M_49p952M.zip

    Petre