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LMX2820EVM: RFOUTA Outputting ~5.5GHz at -2dBm Regardless of VCO value

Luca Ciancanelli
Prodigy 20 points
Part Number: LMX2820EVM
Other Parts Discussed in Thread: USB2ANY

I have been having issues with getting the LMX2820EVM board to output set frequency.

I followed the setup instructions in the user guide for the board (100MHz reference clock, 3.3V power supply, RFOUTAP connected to a microwave analyzer and RFOUTAN terminated with a 50ohm resistor). I then used TICS Pro to connect to the board through a USB2ANY adapter and wrote the EVM Default Mode to the board. When I did this, I could see that RFOUTAP output 5.48GHz at -2.08dBm, even though it should have been outputting 6GHz at 3dBm.

I have tried changing the VCO to 9GHz and calibrating the VCO and this didn't change the value that I saw on the microwave analyzer. I did note that the VCO doubler did work and it output ~11GHz at -22dBm. I have multiple LMX2820EVM boards that I have setup in the same manor and have gotten around the same results.

I'm not sure if I am missing something in the TICS Pro software or something is wrong with my setup. Any help would be appreciated. 

* I have included some images of my setup and results

TICS Pro SetupLMX2820EVM ConnectionsMicrowave Analyzer Measurement 

  • 0
    TI__Guru** 108400 points

    Hi Luca,

    The lock detect LED is ON, that means the PLL is locked.

    Your spectrum analyzer span is 9GHz, could you set the Center frequency to 6GHz and span = 1MHz and then check the frequency again? In addition, did you synchronize the signal generator and the spectrum analyzer? (connect one of the test equipment's 10MHz Ref Out to the other equipment's 10MHz Ref In)

    The lower output power could be due to cable loss, you could try connect the output of the EVM to the spectrum analyzer directly with a sma connector. 

  • 0 in reply to Noel Fung
    Prodigy 20 points

    Noel,

    We were able to solve the issue. It turned out that the power connection to our board was bad and was only supplying 2V, despite our power supply indicating that 3.3V at 0.2A was being supplied. 

    Thank you for your help.