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LMX2820: Instant Calibration Initialization in other frequency from 5.56GHz

porat yifrah
Prodigy 150 points
Part Number: LMX2820

Tool/software:

Dear forum members,

We have a question regarding the Instant Calibration feature on LMX2820. (We use external PFD input without the device internal dividers,  the input PFD is by pin PFDIN)

written in data sheet (page 27) that we must to do Instant Calibration once in initialization on 5.65GHZ frequency. after this procedure we can do VCO calibration by f_CAL and the lock time will be 2.5us.

If my application works only over 7GHz.  Can I do the first Instant Calibration initialization on 7GHz? or I must to do this procedure on 5.65GHz. 

Thanks,

Porat.

 

  • 0
    TI__Guru** 108170 points

    Hi Porat,

    Instant Calibration requires a one-time calibration before we can use it. This calibration must start at 5.65GHz.

    After that, when we change the VCO frequency, there will be no more calibration. 

  • 0 in reply to Noel Fung
    Prodigy 150 points

    Thanks! ,

    How I know if Instant Calibration succeeded? (there is a bit that I can read?)

    Porat

  • 0 in reply to porat yifrah
    Prodigy 150 points

    one more question,

    If I understanded right, after first Instant Calibration and start work in normal operation mode I don't need to change any parameters except dividers and INSTCAL_PLL_NUM and run FCAL_EN='1'

    How LMX2820 knows that this is no first Instant Calibration? maybe I need disable any Bit after Instant Calibration?

  • 0 in reply to porat yifrah
    Prodigy 150 points

    one more question Slight smile

    In normal operation mode I use external PFD input without the device internal dividers, but for a first Instant Calibration on 5.65GHz. I forced to work in internal dividers (hardware restriction in my environment ).  after first Instant calibration  I change the frequency and the PFD_SEL to works with external PFDIN. 

    1. First Instant Calibration  - Internal dividers

    2.  Normal operation mode - External divider by mixer 

    Is this a correct scenario? 

    Thanks .

  • 0 in reply to porat yifrah
    TI__Guru** 108170 points

    Hi Porat,

    After one-time calibration is complete, LD pin will turn High, VCO will lock to 5.65GHz. All calibration data will be stored in the chip as long as there is no power cycle. If we use Instant Calibration without a one-time calibration, the chip will use invalid data and it is not going to lock.

    Right, after the calibration, we only need to change those frequency related registers when we are going to change the VCO frequency.

    The one-time calibration is used to find out the VCO parameters (VCO_SEL, VCO_DACISET and VCO_CAPCTRL), they are independent to any dividers.