SNAA361A april   2022  – may 2023 LMX2820

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Reference Frequency
  6. 3Standard LMX2820 Phase Noise Performance
  7. 4 Pre-multiplier Stage Performance
    1. 4.1 External VCO Loop Filter Design
    2. 4.2 Active Loop Filter Implementation
    3. 4.3 External VCO Performance Results
  8. 5External PFD Topology
    1. 5.1 External PFD Loop Filter Modification
    2. 5.2 External PFD Measurement Results
  9. 6Putting it Together in the Real World
    1. 6.1 Real-World Performance Results
    2. 6.2 Why use the Dual Approach?
  10. 7Conclusion
  11. 8Revision History

6.1 Real-World Performance Results

Figure 6-2 shows the phase noise performance of the dual LMX2820 approach compared with the stand-alone external PFD (using SMA100B as the LO), the stand-alone external VCO, and the internal VCO. Table 6-1 shows the comparison of integrated jitter between the different configurations.

GUID-20220321-SS0I-XD8W-RZLL-LD4TVXZTHTP5-low.pngFigure 6-2 Dual LMX2820 Real-World Phase Noise Results
Table 6-1 Integrated RMS Jitter Performance Comparison With External PFD
RF Out Freq Source Integrated Phase Noise

9000 MHz

Internal VCO

37.9 fs

9000 MHz

External VCO

13.2 fs

9375 MHz

External PFD (LO = SMA100B)

13.9 fs

9375 MHz

External PFD (LO = LMX2820 with Ext VCO)

18.5 fs

The dual LMX2820 approach yields an integrated phase noise performance under 20 fs. Though not quite as good as the stand-alone external VCO or external PFD with SMA100B as the LO, it is a significant improvement to the internal VCO and provides a response that is comparable to many high-end signal generators. It is a real-world topology that supports the most stringent communication and defense applications.