A 0.55mW Fractional-N PLL with a DC-DC Powered Class-D VCO Achieving Better than -66dBc Fractional and Reference Spurs for NB-IoT

This paper presents a sub-mW single supply fractional-NPLL for Narrowband IoT (NB-IoT) applications. The analog PLL meets the relatively strict spur requirement of NB-IoT while using a low power class-D oscillator with a resistive header, which improves phase noise by 3dB and reduces power consumption by 25% with negligible area overhead. The VCO, working at 729-960MHz, is powered by an on-chip DC-DC converter with 90% efficiency designed in a manner to not degrade the spur performance of the PLL, which is measured to be -67.5dBc for reference and -66.3dBc for fractional spurs.