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Original question:

LMX2820EVM: Phase Noise

LMX2592EVM: LMX2592EVM at Cold temperatures

Amin Amiri
Prodigy 40 points

Part Number: LMX2592EVM
Other Parts Discussed in Thread: LMX2592

Hi there, 

I'm looking to do some phase noise analysis on the LMX2592 at cold temperatures. Is the Eval board OK to be taken cold (-20C or -40C) without compromising its performance, if yes how long is it safe to keep it in particular cold temp?

Any ideas as to why phase noise of a TX board based on the LMX2592 Synth degrades in cold temperatures? Could the loop filter bandwidth or phase margin detune when going cold?

Cheers,

AA

  • 0
    TI__Guru** 122400 points

    Hi Amin,

    The EVM is able to support -40C to 85C operation temperature.

    VCO and PLL performance will definitely change over temperature.

    At cold temperature, Kvco becomes smaller, as a result, loop bandwidth will be smaller at cold.

  • 0 in reply to Noel Fung
    Prodigy 40 points

    Hi Noel, 

    Thanks. I managed to take the Eval board to -40C and take a look at the phase noise. It certainly degrades beyond -20C. However while it was degraded at -40C, I reloaded the registers on the GUI and remeasured the phase noise. It went back to good again to what it was in room temperature. Is there a way to calibrate the VCO with temperature? What are the steps to test this?

    Cheers,

    AA

  • 0 in reply to Amin Amiri
    TI__Mastermind 32152 points

    Hi AA, 
    Noel is currently out of office and will not return till next week. I will support you to the best of my ability.
    Do you know if the device lost locked? You can confirm this via LD... it's possible that with a VCO calibration you acquired lock again and hence the desired performance.

    Regards, 

    Vicente