Abstract: A low-phase-noise wideband ring oscillator with coarse and fine tuning techniques implemented in a standard 65 nm CMOS process is presented. Direct frequency modulation in the ring oscillator is analyzed and a switched capacitor array is introduced to produce the lower VCO gain required to suppress this effect. A two-dimensional high-density stacked MOM-capacitor was adopted as the switched capacitor to make the proposed ring VCO compatible with standard CMOS processes. The designed ring VCO exhibits an output frequency from 480 to 1100 MHz, resulting in a tuning range of 78%, and the measured phase noise is --120 dBc/Hz @ 1 MHz at 495 MHz output. The VCO core consumes 3.84 mW under a 1.2 V supply voltage and the corresponding FOM is --169 dBc/Hz.

Key words: ring oscillator, switched capacitor array, phase noise, MOM-capacitor, standard CMOS