A 171µW PPG-based Vitals Monitoring SoC for Asthmatic Patients

Asthma is a long-term lung disease that affects both children and adults and is a recurring illness among children. This paper proposes a low-power and compact PPG-based physiological signals monitoring system-on-chip (SoC) for asthma patients to measure four vitals including heart rate (HR), heart rate variability (HRV), blood oxygen saturation (SpO2), and respiratory rate (RR). The proposed SoC comprises a power-efficient LED driver operating in pulsed mode for red and IR LEDs duty-cycled at 0.625%, along with a PPG readout that provides amplification, filtering, and digitization of the PPG signal. The analog front end employs a transimpedance amplifier followed by a switched integrator that provides both amplification and filtering while digitization of the single-ended PPG signal is achieved using a fully differential second-order, discrete-time, delta-sigma analog to digital converter (ΔΣ-ADC). The digitized PPG data is processed by the vitals extraction processor employing signal processing and feature extraction (FE) to compute vitals. The SoC consumes 171µW and is implemented in a 180nm CMOS process with an area of 4.5mm 2 . The proposed SoC is verified on 34 patients achieving high accuracy with a maximum absolute error percentage of <1% for all vitals.