A 6nW 0.0013mm2 ILO Bandpass Filter for Time-Based Feature Extraction

Event-driven wake-up sensing methods are emerging functions necessary to increase the autonomy of power-hungry multisensors Internet-of-Things applications. To decrease the power consumption of feature extraction function essential for event-based wake-up, this letter introduces a novel injection-locked oscillator (ILO) filter architecture, to be used in a time-based filter bank for feature extraction. After reviewing the phase shifter property and dynamic behavior of a switched-capacitor injected relaxation ILO, ILO high-pass and bandpass filter designs and transfer functions are presented, resulting in the implementation of a four-channel ILO filter bank in a 65-nm CMOS technological node. Experimental measurements demonstrate the ILO bandpass filtering function works at a power consumption of 6 nW, an active area of 0.0013 mm2 and an output dynamic range of 46 dB. The filter bank average power consumption reaches 3 nW/channel for a total bandwidth from 130 Hz to 5.5 kHz.