A 206 μW Vital Signs Monitoring System on Chip for Measuring Five Vitals

Abstract

This article presents an area and power-efficient system-on-chip (SoC) for vital signs monitoring to provide patients with remote monitoring. It measures five important vitals including blood oxygen saturation (SpO2), respiration rate (RR), heart rate (HR), HR variability (HRV), and temperature. The proposed SoC utilizes a photoplethysmography (PPG) signal to compute HR, HRV, SpO2, and RR. The PPG signal is amplified and filtered using a PPG readout that includes a transimpedance amplifier (TIA) with a switched integrator (SI) to filter and amplify the signal. A differential second-order, delta-sigma analog-to-digital converter ( $\Delta \Sigma $ -ADC) is adopted to digitize the PPG signal. The SoC also comprises a low-power LED driver for both red and infrared (IR) LEDs which operate in pulsed mode with a 0.625% duty cycle. A vital signs extractor performs feature extraction (FE) and computes the vital signs with a maximum absolute error of less than 1%. In this work, the temperature is also measured by employing a Wheatstone bridge (WhB)-based temperature sensor which integrates thermal resistors into a second-order $\Delta \Sigma $ -ADC. The proposed system shares $\Delta \Sigma $ -ADC for digitizing the PPG signal and the temperature readings to reduce both area and power consumption. The proposed system computes the temperature over the human’s temperature range ( $32~^{\circ }$ C to $42~^{\circ }$ C) with an accuracy of +/ $- 0.09~^{\circ }$ C. The SoC is implemented using a 180 nm CMOS process with an area of 4.8 mm2 while consuming $206~\mu $ W.