SNAA342 September   2020 LMX2820

 

  1.   Trademarks
  2. 1 Overview of Frequency Hopping
  3. 2 Integrated VCO Overview
    1. 2.1 Integrated Silicon VCO Structure
    2. 2.2 Robustness and Consistency of VCO Calibration
  4. 3Components of Synthesizer Lock Time
    1. 3.1 Write Time
    2. 3.2 VCO Calibration Time
    3. 3.3 Analog Settling Time
  5. 4Improving VCO Calibration Time With the LMX2820
    1. 4.1 Improving LMX2820 VCO Calibration With Partial Assist
    2. 4.2 Full Assist Method of Improving VCO Calibration Time
    3. 4.3 Instant Calibration – The Ultimate to Blazing-Fast VCO Calibration
  6. 5Conclusion
  7. 6References

2.2 Robustness and Consistency of VCO Calibration

The VCO calibration should be designed to be robust overtemperature. Even if the VCO is calibrated at one extreme temperature and it drifts to the other extreme temperature, the VCO should retain lock and not require reprogramming. For integrated silicon VCOs from Texas Instruments, one can choose to re-calibrate the VCO for some improvement, but this improvement in doing this is less than 1 dB in phase noise. As VCO is designed to tolerate wide temperature drifts, this implies that there is considerable overlap between the frequency bands. This leads to the next aspect of consistency of VCO calibration. As there is considerable overlap of the frequency bands, there are multiple frequency bands that can hit the same frequency. When the VCO does not choose the same calibration settings (VCO_CORE, VCO_CAPCTRL, VCO_DACISET), then there can be differences in spurs, VCO gain, VCO phase noise, and propagation delay. This is especially true if a different VCO core is chosen.