ΔΣ Fractional-N PLL With Hybrid IIR Noise Filtering

This brief presents a noise filtering method for wideband $\Delta \Sigma $ fractional-N phase-locked loop (PLL). The proposed hybrid infinite impulse response (IIR) phase noise filtering method reduces the building blocks compared to that of hybrid finite impulse response (FIR) filtering technique. A prototype 2-GHz $\Delta \Sigma $ fractional-N PLL with 1-MHz loop bandwidth is implemented in 130-nm CMOS process. Measurement results show that the proposed IIR filtering technique can suppress 5 dB more phase noise than the same order of FIR filter.