A 90μW 12MHz Relaxation Oscillator with a -162dB FOM

Abstract

Both ring oscillators and relaxation oscillators are subsets of RC oscillators featuring large tuning ranges and small areas. Such relaxation oscillators have two advantages with respect to ring oscillators: 1) they have a constant frequency tuning gain; and 2) their phase can be read out continuously due to their triangular (or sawtooth) waveform. A major disadvantage of practical relaxation oscillators is their poor phase-noise compared to ring oscillators.