SNAA366 October   2022 LMX1204

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
    1. 1.1 Basic Clock Distribution System
    2. 1.2 Pre-multiplier Stage
  4. 2Low-Frequency Reference
    1. 2.1 Pre-multiplier Stage
    2. 2.2 LMX1204 Multiplier Stage
    3. 2.3 LMX1204 Multiplier vs RF Synthesizer
  5. 3Real-World Application With AFE7950 RF Sampling Transceiver
    1. 3.1 AFE7950 Clocking Measurement Setup
    2. 3.2 AFE7950 Clocking Measurement Results
  6. 4Conclusion

2 Low-Frequency Reference

The multiplier approach assumes that there is a high-quality, low phase-noise reference signal available. This analysis uses a Wenzel oscillator operating at 491.52 MHz as a good quality, but practical reference source. The performance of the Wenzel is compared against the Rohde & Schwarz SMA100B signal generator. This signal generator is the gold standard of signal synthesis and serves as a gauge of the absolute best performance possible, albeit not practical for use in a production system. The Agilent PSG is another high-quality signal generator used as a reference. The PSG phase noise is not as good as the SMA100B, but is still one of the better test equipment generators available.

Figure 2-1 shows the phase-noise comparison of the SMA100B, the Wenzel oscillator, and the Agilent PSG operating at 491.52 MHz. Table 2-1 reports the RMS jitter performance integrated from 1-kHz offset to 40-MHz offset using the Holzworth phase-noise analyzer.

GUID-20220906-SS0I-7V7W-VLFC-NKWPCZFXWGBS-low.png Figure 2-1 Phase-Noise Comparison at 491.52 MHz
Table 2-1 Integrated Jitter Performance at 491.52 MHz
Frequency Source RMS Jitter
491.52 MHz R&S SMA100B 15.6 fs
Wenzel Oscillator 25.5 fs
Agilent PSG 85.3 fs

As the results show, the SMA100B performs the best. The Wenzel oscillator keeps pace with the SMA100B out to about 300-kHz offset. The SMA100B definitely out-performs the Agilent PSG.