A 255nW 138kHz RC oscillator for ultra-low power applications

An on-chip sub-μW RC oscillator suitable for ultra-low power applications is presented. A technique that cancels both comparator delay and offset are proposed to improve the frequency stability against variations of temperature and supply voltage. This relaxation oscillator is designed and simulated in a 180-nm CMOS technology. The post layout simulation results show that the proposed circuit has a 1-cycle start-up time, and the frequency drift is less than ±0.6%. For the supply voltage changing from 0.9 to 1.2 V, the variation of frequency is -0.72% ~ +0.68% and the temperature coefficient is 75.5 ppm/°C over 0 to 90°C. The power consumption of the proposed oscillator is 255 nW at TT and 27°C.