Digital Enhancement Techniques for Digital Fractional-N Phase-Locked Loops

Phase-locked loops (PLLs) are critical components in modern electronics communication systems, where they are used to synthesize local oscillator signals for modulation and demodulation in wireless transceivers. They are also used to clock digital-to-analog converters (DACs), analog-to-digital converters (ADCs), and digital processors.Most PLLs incorporate either analog filters and voltage-controlled oscillators (VCOs) or digital filters and digitally-controlled oscillators (DCOs). The former are called analog PLLs and the latter are called digital PLLs. To date, analog PLLs have the best phase error performance, but digital PLLs have the lowest circuit area and are more compatible with highly-scaled CMOS IC technology. Thus, improving the performance of digital PLLs has been the subject of intensive research for many years.The first chapter of this dissertation presents a multi-rate dynamic element matching (MR-DEM) technique and an adaptive mismatch-noise cancellation (MNC) technique that work together to mitigate spectral breathing in digital PLLs, a problem caused by mismatches among the frequency control elements (FCEs) within the DCO. It presents a theoretical analysis of the techniques, as well as behavioral simulation results that support this analysis.The second chapter of this dissertation presents delta-sigma (ΔΣ) frequency-to-digital converter (FDC) all-digital enhancements for FDC-based digital fractional-N PLLs. It describes an enhanced ΔΣ FDC architecture that has relaxed timing constraints and reduced phase-frequency detector (PFD) output pulse-span compared to prior-art ΔΣ FDCs. It also describes and analyses a ΔΣ FDC forward gain calibration technique that reduces the complexity associated with the system’s implementation and improves the phase noise performance of PLLs with high loop bandwidths.The third chapter of this dissertation presents an integrated circuit high-performance PLL which implements the MR-DEM and MNC techniques presented in the first chapter. It demonstrates the detrimental effects of the spectral breathing phenomenon, as well as the effectiveness of the MR-DEM and MNC techniques to mitigate this problem