Development of low phase noise quadrature output digitally controlled CMOS ring oscillator

A 14-bit digitally controlled ring oscillator (DCO) with operating frequency up to 1 GHz in 0.18 μm CMOS technology is designed. The design used digital control to obtain higher output voltage swing and to get lower flicker noise compared to the analog counterpart. To make the oscillator oscillate and to get stable quadrature output in the even number of stages, feed-forward technique is used. Designed DCO has tuning frequency range from 212 MHz to 1 GHz. Phase noise at 4 MHz frequency offset is -137.81 dBc/Hz. Figure of Merit (FoM) calculated as big as -162.25 dBc/Hz, an improvement of about 6 dB from the recently published result.