Method to Determine Quantization-Related Parameters of the Digital-to-Time Converter in a Fractional-N Frequency Synthesizer

Abstract

Digital-to-time converters (DTC’s) used in fractional-N frequency synthesizers attempt to cancel the accumulated quantization error (QE) introduced by the divider controller with a view to recovering the integer-N phase noise (PN) performance. The resolution of the DTC needs to be sufficiently fine to suppress its own QE below the intrinsic integer-N jitter and, at the same time, sufficiently coarse to limit the DTC’s hardware needs. In this manuscript, we propose optimal strategies to determine the effective dynamic range, number of bits, quantization resolution, and unity delay of the DTC to achieve these goals; the additional jitter power introduced by input-dithered quantization methods to eliminate DTC-quantization-induced spurs is also considered. DTCs parameterized following these strategies can come close to realizing the spur-free integer-N PN with minimum hardware. Behavioral simulations confirm our analysis.