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LMX2820: Behavior during divider value change

Chase W
Mastermind 23780 points
Part Number: LMX2820

Hi team,

What is the behavior of the output during the transition of one divider value to the new divider value? Is the signal continuous or is there a discrete jump from one frequency to the other?

For instance, if I have R and N dividers such that the output is f1 and then change the dividers and do the fast VCO calibration such that the output is f2, will the transition look like the left image (continuous) or the right image (non-continuous)?

Thanks, Chase

  • 0
    TI__Mastermind 23780 points

    The VCO and dividers will change such that the output frequency changes approximately 5MHz (let's say from 2600MHz to 2595MHz). 

  • +1 in reply to Chase W
    TI__Guru** 108630 points

    Hi Chase,

    Neither of these transitions will happen. 

    Both R and N divider are part of the PLL close loop components, any change from them will affect the loop significantly. Interruption from these changes will lead to sudden change in output frequency. For example, output frequency may change significantly for a short period of time before returning to the set frequency.