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 Putting it Together in the Real World

The performance of the LMX2820 with an external PFD using the Rohde SMA100B as the LO source yields excellent phase noise performance. The performance is very attractive, but not practical in a real application. A realistic option is to use an additional LMX2820 as the mixer LO. Using the standard LMX2820 configuration with internal VCO as the LO yields worse performance than just using the device directly. That is expected given the LO source is not improved compared to the source. Alternatively, use a second LMX2820 configured with the external VCO as the LO source. Figure 6-1 shows the block diagram approach for using two LMX2820 devices. The external VCO is followed by cascaded amplifiers to increase the LO drive signal to 16 dBm (or higher). The mixer needs a high LO drive level to ensure best dynamic range and linearity required for best phase noise performance.

GUID-20220321-SS0I-LKPX-Q6G7-PHKW6HNF6VGC-low.png Figure 6-1 Dual LMX2820 Approach for a Real-World Solution