about ADRF6820

Hi,

1. What is the function of  "PWRDWN" switch on evaluation board?? No matter "PWRDWN" is pull high or pull low, ADRF6820 still working.

2. When using internal LO,

    RFIN : 1900MHz, 0dBm, CW tone

    REFIN : 153.6MHz, 0dBm, CW tone

    LO set to 1890MHz (using customer evaluation software)

    => I+ port (we remove transformer T6 and resistors R38 & R42) see a ~38MHz ~358mVpp sinewave (oscilloscope is set to 1Mohm)..

    When using external LO,

    RFIN : same as above setting

    LOIP : 1890MHz, 0dBm, CW tone

    => I+ port see a ~10MHz ~273mVpp sinewave (oscilloscope is set to 1Mohm).

    Our question are:

    a. When using internal LO, why the IQ sinewave frequency is not ~10MHz??

    b. Why the amplitude level of I+ signal has large difference between using internal LO and external LO??

    c. For external LO case, do you have a formula to calculate the I+ Vpp value with RF input power level??

BR,

Henry

Parents
  • +1
    •  Analog Employees 
    on Feb 21, 2019 9:32 PM

    Question 1:

    Not sure why you're not seeing the chip power down.  What indication are you looking for, loss of output signal ?

    Question 2:

    It appears the internal LO is not locked in your first case.

    From the EVAL ADRF6820 User Guide, pg  4:  "For optimum performance using an external LO source, the LO input pins(LOIN− and LOIN+)should be driven differentially. The wide input range of the external LO inputs span from 350 MHz to 6000 MHz. Unless an ac-coupled balun/transformer is used to generate the differential LO, the inputs must be ac-coupled. The input impedance of the differential LO signals is 50 Ω."

    Also make sure the LO drive level to the board is at least -6 dBm after any external baluns, cables, etc.  

    In addition, it's probably best to match the I/Q ports as well:

    Again, from pg 4 of User Guide:

    "On the evaluation board, the quadrature I/Q outputs are terminated with 200 Ω differential. This is achieved by using a 1:1 transformer and an L-impedance matching network. The 1:1 transformer, TC1-1-13M+ from Mini-Circuits, is a very wide bandwidth (4.5 MHz to 3000 MHz) transformer that allows a flat pass-band response of up to 1 GHz."

    We do not advise removing one leg of the I output.

    Thanks,

    Darrell

  • ADRF6820 Issue_20190223.pdf

    Hi Mr./Mrs.

    Could you please help to check the attached file about our setting? 

    Thanks

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