A 0.5-V Sub-10-μW 15.28-mΩ/√Hz Bio-Impedance Sensor IC With Sub-1° Phase Error

Continuous monitoring of fluid status through bio-impedance (Bio-Z) measurement of thoracic magnitude or phase is critical in reducing the mortality of chronic heart failure (CHF) patients. However, the stringent power constraints of implantable devices force the design of Bio-Z sensors to be highly challenging. We present a sub-10- $\mu \text{W}$ Bio-Z sensor IC operating from a 0.5 V-supply, sustaining a sub-1° of phase error even under 10% of supply and 0 °C–70 °C of temperature variations. Fabricated in a 65-nm CMOS process, this sensor IC exhibits a 15.28- $\text{m}\Omega /\surd $ Hz of input-referred impedance noise performance, occupying a 4.83 mm ² . Its linearity performance shows that the magnitude and the phase of Bio-Z can be measured within the error of 2% and 0.4°, respectively, given that the magnitude of load impedance is less than 126 $\Omega $ , and thus, it is suitable for fluid status monitoring applications. Experimental measurement on the human chest demonstrates its capabilities of thoracic impedance variance (TIV) and impedance cardiography (ICG) monitoring.