SNAU273 December   2022 LMX2820

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2SYNC Category
  5. 3SYNC Examples
    1. 3.1 Category 1 SYNC Example
    2. 3.2 Category 2 SYNC Example
    3. 3.3 Category 3 SYNC Example
  6. 4Other Considerations When Using SYNC
  7. 5References

4 Other Considerations When Using SYNC

  1. Without VCO Calibration:

    The LMX2820 supports faster VCO frequency switching without a VCO calibration. This can be implemented manually (like in full-assist mode) or automatically (Instant Calibration). When the LMX2820 operates in these modes, phase synchronization is still supported with a slightly different behavior or with some additional requirements.

    Category 1 SYNC:

    • Input-output phase may shift after a POWERDOWN cycle. This problem can only be fixed by doing a RESET and then programming all the registers once.
    • Input-output phase remains deterministic after VCO frequency is changed.

    Category 2 and 3 SYNC:

    • Synchronization requires register FCAL_EN = 1. Before feeding the SYNC signal to LMX2820, program register R0 with FCAL_EN = 1.

  2. MASH_RST_COUNT:
    • Can be equal to 0 when PLL_NUM = 0.
    • Must be sufficiently large when PLL_NUM is not equal to 0.
  3. Use both RF Outputs:

    When both outputs are used and the frequencies are not identical, the category of SYNC on each output can be different. Provide the appropriate SYNC pulse according to the highest SYNC category output.