Ultra-Low-Voltage CMOS Crystal Oscillators

In this paper, 32 kHz crystal oscillators operating with only 60 mV supply are presented. Two implementations based on a Schmitt trigger circuit for two different crystals were designed and experimentally characterized. The circuits require 45 μm × 74 μm and 78 μm × 83 μm, respectively, within a 130 nm CMOS process. The power consumptions of the oscillators are 2.26 nW and 15 nW and the temperature stabilities attained are 62 ppm (25-62°C) and 50 ppm (5-62°C), respectively. The dependence on the supply voltage of the current consumption, fractional frequency, start-up time and oscillation amplitude were measured. The Allan deviation is 30 ppb for both oscillators.