some questions about ADF5901 and ADF4159


i use ADF5901 with ADF4159. But i have two questions about ADF5901. 

1. Does the output power of TX out of ADF5901 can be changed from -20dBm to +8dBm  by change the Tx AMP CAL REF CODE? i connect a amplifier after ADF5901. So I should check this.

2. I think the VCO-CAL  in ADF5901 is useless  when  i use ADF4159 to control the Vtune of VCO in ADF5901. So i want to know how do i set the N-Divider and R-Divider in ADF5901?  

 Because in a PLL,the  N-divider and R-divider i really use is  in PLL just the ADF4159 but not in VCO just the ADF5901.

look forward for your reply.

  • 0
    •  Analog Employees 
    on May 8, 2017 8:36 AM

    1. Yes output power is adjustable by using TX_AMP_CAL_REF_CODE

    Power should be check at the output of any additional amplifier after the ADF5901.

    2. VCO-CAL  in ADF5901 is not useless and VCO calibration is needed on the ADF5901 to ensure the VCO is centered in the band of operation.

    The N-Divider and R-Divider on the ADF5901 should be setup for the center frequency of operation. 

    Example from initialization sequence in data sheet.

    REFin = 100MHz, R-Divider = 2 => RCLK = 50MHz

    Center Frequency = 24.125GHz, divide-by-2 version feedback to N-Divider (12.0625GHz) = > N = 241.25

    => INT = 241, FRAC_MSB = 1024 (i.e. 1/4) 

  • So if i use ADF4159 with ADF5901. the R-DIVIDER and N-DIVIDER in ADF4159 and ADF5901 should be set the same.

  • 0
    •  Analog Employees 
    on May 9, 2017 1:12 PM

    The PFD clock on the ADF4159 can run up to 110MHz where as the R-cnounter output on the ADF5901 can run to 50MHz.

    So if using 100MHz reference clock the ADF4159 can run at 100MHz while the ADF5901 would be 50MHz.

    So R-DIVIDER and N-DIVIDER on ADF5901 would be twice the ADF4159 values.

  • Hi,

    I have a question to consult obout Tx output power.

     What is the function of REFin in ADF5901? The datasheet shows that it relates to VCO frequency calibration, does it relate to Tx outout power? I use ADF4159 and ADF5901 to get 24GHz , in my PCB board, the REFin pin of ADF5901 is suspended and has no input signal, and the Tx1 output power is still only -16dBm. I wonder the Tx output power is decided by the power of REFin pin and my design is wrong? The register1 of ADF5901 is the amplitude calibration reference code, so the power of REFin pin is the  reference value for TX output amplitude calibration code?

    What is the registers writing order after initialization sequence?  Does the recalibration sequence decide the Tx output power?

    Thank you very much.