A 9.6-nW Wake-Up Timer With <i>RC</i>-Referenced Subharmonic Locking Using Dual Leakage-Based Oscillators

Abstract

This brief presents a nano-watt wake-up timer implemented mainly through digital synthesis. By performing successive subharmonic frequency locks between two leakage-based digitally controlled oscillators (DCOs) and repeatedly switching their roles, the period of the timer can be locked to a scaled RC time, enabling low-frequency generation without the need for substantial RC values. The proposed frequency-lock scheme is applied to design a 360 Hz timer. The implemented timer in a 0.18-mu m CMOS process consumes 9.6 nW and shows a standard deviation of 1.36% without the need for extensive external trimming, mainly due to intra-wafer process variation. The measured supply and temperature sensitivities are 0.32%/V and 395 ppm/degree celsius, respectively.