A 1.28-nW 1.97-kHz Relaxation Oscillator for Ultra-Low Power System

This paper presents a fully integrated 1.97 kHz relaxation oscillator (RXO) based on the 40 nm CMOS process. The RXO is powered by 0. 4V to directly generate a dual phase clock signal with a duty of 50% and the power consumption of only 1. 2SnW, which is suitable for ultra-low-power circuit systems. A proportional-to-absolute-temperature compensation and a complementary-to-absolute-temperature compensation technique are implemented to achieve the temperature stability of output frequency. By adding an enable (EN) signal, the stability of the feedback network can be improved without extra power consumption. The temperature coefficient (TC) of RXO is 170 ppm/°C in the temperature range of −20°C to 80°C. The RXO achieves a Figure of merit (FoM) of 0.649 nW/kHz at room temperature, and its supply voltage coefficient is ± 2.7%/V from 0.4 V to 1.6 V.