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Fractional-N phase-locked loops using Harmonic-Mixer (HM) based feedback offer good phase noise and spur performance without relying on complex calibration schemes. The HMs in prior art are often realized using… Click to show full abstract
Fractional-N phase-locked loops using Harmonic-Mixer (HM) based feedback offer good phase noise and spur performance without relying on complex calibration schemes. The HMs in prior art are often realized using the Sample-and-Hold (S/H) operation. This, however, can result in unwanted tones due to intermodulation, which must be suppressed using properly-designed filters. This paper proposes a simple and accurate analysis of the location and magnitude of these tones. We also provide a design guideline for the HM based on this analysis to properly suppress these tones. The results are supported through behavioral and transistor-level simulations.
Journal Title: IEEE Transactions on Circuits and Systems I: Regular Papers
Year Published: 2022
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