A 640pW 32kHz switched-capacitor ILO analog-to-time converter for wake-up sensor applications

This paper presents the architecture and ultra-low power (ULP) implementation of a switched-capacitor injection-locked oscillator (SC-ILO) used as analog-to-time converter for wake-up sensor applications. Thanks to a novel injection-locking scheme based on switched capacitors, the SC-ILO architecture avoids the use of power-hungry constant injection current sources. The SC-ILO design parameters and transfer function, resulting from an analytical study, are determined, and used to optimize the design. The ULP implementation strategy regarding power consumption, gain, modulation bandwidth and output phase dynamic range is presented and optimized to be compatible with audio wake-up sensor application that require ultra-low power consumption but low dynamic range performances. This paper reports SC-ILO circuit experimental measurements, fabricated in a 22 nm FDSOI process. The measured chip exhibits a 129° phase-shift range, a 6kHz bandwidth leading to a 34.6dB-dynamic range for a power consumption of 640pW under 0.4V.