Stable ring oscillator for ultra low supply voltages

This paper presents an alternative to crystal based oscillators for reference frequencies in highly integrated SoCs. The frequency reference through the usage of an active bias controlled ring oscillator operating with a supply voltage from 300 to 500 mV for an temperature from -40 to 125 ° C. The oscillator shows a very good temperature and supply voltage frequency stability coming from the active biasing using a stable current reference.