27.1 A 3-Axis MEMS Gyroscope with 2.8ms Wake-Up Time Enabled by a $\boldsymbol{1.5\mu} \mathbf{W}$ Always-on Drive Loop

MEMS gyroscopes are widely used in mobile and wearable devices with human-machine interfaces for motion detection and indoor navigation [1]–[5]. In these applications, the always-on mode (i.e., standby or suspend mode) is required to support event-driven operation and extend battery life [3]–[5]. One of the key design challenges is the trade-off between the always-on current consumption and the wake-up time. To meet this challenge, an always-on MEMS gyroscope with burst-mode phase-locked loop (BPLL) technique was reported, which achieved an always-on current of 737nA and a wake-up time of 5.45ms [6]. However, the BPLL-based drive loop suffers from an instability problem due to the parasitic-relaxation-oscillation (PRO) effect triggered by temperature variation, deteriorating the reliability. This paper presents an always-on MEMS gyroscope employing a duty-cycle-automatic-optimization (DAO) technique to control the PRO, achieving a wake-up time of 2.8ms and ±5% wake-up time stability from -40 to 85°C.