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LMX2582: Decrease Lock Time (possible negative effects)

Samuel Salvisberg
Prodigy 50 points
Part Number: LMX2582


Dear all

 

I like to speed up the calibration time as fast as possible. I’m not interested in optimal phase noise.
There are two registers (FCAL_FAST and ACAL_FAST) which can be selected easily. What will changes in the LMX2582 ? Can occur negative effects?
If I set the ACAL_CMP_DLY too low, can it be that the LMX2582 cannot lock? Or will it always lock but with a bad phase noise?
When I turn off the amplitude calibration, how I know which amplitude I must set manually?
Finally, if I set the VCO core by my own, how much time I will save normally? Compared to the other options?

Thank you for your help

Best regards

Samuel

Dear all
 
I like to speed up the calibration time as fast as possible. I’m not interested in optimal phase noise.
There are two registers (FCAL_FAST and ACAL_FAST) which can be selected easily. What will changes in the LMX2582 ? Can occur negative effects?
If I set the ACAL_CMP_DLY too low, can it be that the LMX2582 cannot lock? Or will it always lock but with a bad phase noise?
When I turn off the amplitude calibration, how I know which amplitude I must set manually?
Finally, if I set the VCO core by my own, how much time I will save normally? Compared to the other options?
Thank you for your help
Best regards
Samuel
  • 0
    TI__Expert 5370 points
    Dear Samuel, someone will answer your question shortly thank you for your patience, regards, Simon.
  • 0
    TI__Expert 8505 points
    Samuel,

    Good questions. To answer in sequence:
    - FCAL_FAST and ACAL_FAST will make frequency calibration search in step sizes of FJUMP_SIZE and amplitude calibration search in AJUMP_SIZE correspondingly. There is some optimal fastest calibration time depending on jump size and the target frequency. This should have no effect on phase noise.
    - ACAL_CMP_DLY is the comparitor time for each step of the amplitude calibration algorithm. See datasheet for suggested values. If too low, there is not enough time to decide of the right amplitude codes, and could mean non-optimal phase noise.
    - This would be what you want. Amplitude calibration is the longest portion of the calibration time for this part. Turn off with ACAL_EN=0, and set VCO_IDAC which is the manual amplitude codes. See datasheet for suggested range. If you dont care about phase noise just set this to 350.
    - Setting VCO amplitude (ie VCO_IDAC) will save you alot of time and is more predictable as there is no search process for best amplitude value. Should expect 20 - 30us type calibration times.


    Regards,

    Brian Wang
  • 0 in reply to Brian Wang
    Prodigy 50 points
    Dear Mr. Wang

    Thank you for the fast and detailed answer.
    Do you have suggested values for AJUMP_SIZE and FJUMP_SIZE in connection with target frequency?

    Best regards
    Samuel