A Sub-mW 2.4-GHz Active-Mixer-Adopted Sub-Sampling PLL Achieving an FoM of −256 dB

An active-mixer-adopted sub-sampling phase-locked loop (AMASS-PLL) is presented that replaces the passive-mixer-like sample-and-hold switches and charge pump (CP) of a sub-sampling PLL (SSPLL) with an active-mixer and $g_{m}$ -cell, which reduces spurious content by 20 dB while enabling sub-mW power consumption at 2.4 GHz. Specifically, an active-mixer-based phase detector is used to improve the isolation between the voltage-controlled oscillator (VCO) and the sampling mechanism, which helps to address the inherent problem of high reference spurs in SSPLLs. Fabricated in 65 nm, the AMASS-PLL achieves an rms jitter of 161 fs from 10 kHz to 100 MHz with a spur of -67 dBc, all at a power of 0.93 mW, for a figure of merit (FoM) of -256 dB.