A 2.2 GHz -242 dB-FOM 4.2 mW ADC-PLL Using Digital Sub-Sampling Architecture

This paper presents an all-digital phase-locked loop (AD-PLL) using a voltage-domain digitization realized by an analog-to-digital converter (ADC) instead of adopting a traditional time-to-digital converter (TDC) which usually suffers from a tradeoff in resolution and power consumption. It consists of an 18 bit class-C digitally controlled oscillator (DCO), a 4 bit comparator, a digital loop filter (DLF), and a frequency-locked loop (FLL). Implemented in 65 nm CMOS technology, the proposed PLL reaches an in-band phase noise of -112 dBc/Hz and an RMS jitter of 380 fs at a carrier frequency of 2.2 GHz. A figure of merit (FoM) of -242 dB was achieved with a power consumption of only 4.2 mW.