Nonlinearity-Induced Spur Analysis in Fractional-<italic>N</italic> Synthesizers With ΔΣ Quantization Cancellation
A fractional-N frequency synthesizer with low total jitter [e.g., <50fsrms, accounting for both phase noise (PN) and spurs] is essential for enabling the emerging 5G/6G and other high-speed wireless communication standards (e.g., WiFi-6/7). While fractional-N phase-locked loops (PLLs) and...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
IEEE
2024-01-01
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| Series: | IEEE Open Journal of the Solid-State Circuits Society |
| Subjects: | |
| Online Access: | https://ieeexplore.ieee.org/document/10707313/ |
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| Summary: | A fractional-N frequency synthesizer with low total jitter [e.g., <50fsrms, accounting for both phase noise (PN) and spurs] is essential for enabling the emerging 5G/6G and other high-speed wireless communication standards (e.g., WiFi-6/7). While fractional-N phase-locked loops (PLLs) and injection-locking techniques with delta–sigma <inline-formula> <tex-math notation="LaTeX">$(\Delta \Sigma )$ </tex-math></inline-formula> quantization cancellation using a digital-to-time converter (DTC) (and more recently, DACs) have demonstrated low-jitter performance and are well understood in terms of PN, their spur mechanisms still lack a comprehensive quantitative analysis. In this article, we present a unified theoretical framework for spur analysis, based on the time-domain characteristics of spurs, addressing both instantaneous phase modulation and frequency modulation mechanisms. This approach serves as a thorough guide for choosing a low-jitter fractional-N architecture, considering the integral nonlinearity (INL) shaping of DTCs (or DACs) under the control of either a first- or second-order <inline-formula> <tex-math notation="LaTeX">$\Delta \Sigma $ </tex-math></inline-formula> modulator (DSM). The framework also extends to reference spurs in both charge-pump PLLs (CP-PLLs) and injection-locked synthesizers. The analytical results of spurs are numerically verified through time-domain behavioral simulations and further validated by experimental results from the literature, thereby demonstrating their effectiveness. |
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| ISSN: | 2644-1349 |