A 0.6V 785-nW Multimodal Sensor Interface IC for Ozone Pollutant Sensing and Correlated Cardiovascular Disease Monitoring

In this article, we present the design and analysis of a 785-nW multimodal sensor interface IC for ozone pollutant sensing and correlated cardiovascular disease monitoring based on electrocardiography (ECG) and photoplethysmography (PPG). The proposed hybrid <inline-formula> <tex-math notation="LaTeX">$dc$ </tex-math></inline-formula> offset current cancellation (DCOC) along with a 4-<inline-formula> <tex-math notation="LaTeX">$\text{M}\Omega $ </tex-math></inline-formula> gain-regulated cascode transimpedance amplifier (RGC-TIA) enable PPG readout power reduction by <inline-formula> <tex-math notation="LaTeX">$37\times $ </tex-math></inline-formula>, compared with the state-of-the-art PPG sensor interfaces. The ozone sensing channel proposes an adaptive architecture to enable low <inline-formula> <tex-math notation="LaTeX">$V_{\text {DD}}$ </tex-math></inline-formula> operation, achieving a <inline-formula> <tex-math notation="LaTeX">$300\times $ </tex-math></inline-formula> power reduction, compared with the state-of-the-art gas sensing readouts. The ozone sensing channel’s performance was also verified using custom resistive metal-oxide sensors for concentrations from 50 to 900 ppb. The sensor interface IC is fabricated in a 65-nm CMOS, integrating a 165-nW voltage-mode ECG channel, a 532-nW current-mode PPG channel, 76-nW resistive-mode ozone channel, and 12.6-nW peripheral circuits, all at 0.6 V. The total system power consumption including the LED and a custom digital readout IC is 10.98–<inline-formula> <tex-math notation="LaTeX">$15.51~\mu \text{W}$ </tex-math></inline-formula>, which is <inline-formula> <tex-math notation="LaTeX">$41\times $ </tex-math></inline-formula>–<inline-formula> <tex-math notation="LaTeX">$57\times $ </tex-math></inline-formula> less than prior ozone/CVD joint monitoring sensor interface systems.