A Software-Defined Always-On System With 57–75-nW Wake-Up Function Using Asynchronous Clock-Free Pipelined Event-Driven Architecture and Time-Shielding Level-Crossing ADC

This work presents an ultra-low-power software-defined always-on wake-up system to drastically decrease the system power of Internet of Things (IoTs) devices, which usually operate in random-sparse-event (RSE) scenarios. It mainly thanks to a clock-free time-shielding level-crossing ADC (TS-LCADC), software-defined clock-free multi-function detectors, and an asynchronous pipelined event-driven architecture. First, by quantifying RSE noisy signals with clock-free adaptive sampling in a signal-noise-rejecting manner, the proposed TS-LCADC reduces number of sampling points and power, and consumes only 41 nW when on-call waiting for IoT events. Second, the proposed clock-free multi-function detectors with offline and online programmability are able to character the signal features of versatile IoTs events and allow versatile and dynamic wake-up functions. Third, the proposed asynchronous pipelined event-driven architecture minimizes the system activity and thus power, because a power-hungry high-performance system (HPS) is only woken up when a detected parameter crosses its corresponding threshold. As such, the long-term average power (LTA-power) is dominated by the always-on circuits in RSE scenarios. The measurement results achieve 71-75 nW for three typical applications, i.e., heart rate, epilepsy, and keyword envelope detection. The LTA power is only 57 nW when waiting for RSE events, which is 30 × lower than a prior general-purpose wake-up chip. Compared with other works of dedicated voice and acoustic wake-up functions, this work consumes 2 × and 17 × less power, respectively, while featuring 16 × higher signal bandwidth and a broader versatility.