Progress and Trends of Low-Jitter Fractional-N Phase-Locked Loops

• Fractional-N PLLs face jitter degradation from quantization error (Q-error), which induces quantization noise and fractional spurs, especially with wide loop bandwidths. • PFD-CP PLLs with offset PFD-CP and MASH DSM achieve low jitter but require large CP currents and loop filter capacitors, limiting power efficiency. • Multipath feedback technology compensates Q-error in the charge domain, reducing quantization noise and enabling high FoM with a dual-core class-F-1 VCO. • High-gain sampling PDs (e.g., sub-sampling PD) allow small CP currents and compact loop filters, but require DTC/DAC linearization to suppress spurs and noise folding.