18.5kHz RC Oscillator With Comparator Offset Cancellation

A fully-integrated 18.5kHz RC time-constant-based oscillator is designed in 65nm CMOS for sleep-mode timers in wireless sensors. A comparator offset cancellation scheme achieves 7x temperature stability improvement, leading to an accuracy of ±0.25% over -40 to 90°C and ±0.1% over 0 to 90°C. Sub-threshold operation and low-swing oscillations result in ultra-low power consumption of 120nW. The oscillator has a long-term Allan stability of 20ppm or better for measurement intervals over 0.5s.