Low power bio-impedance sensor IC with precise phase measurement

Abstract

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. In this dissertation, two low-voltage and low-power ICs are proposed for bio-impedance (Bio-Z) sensing applications, both of which are fabricated in a 65 nm CMOS process. The first IC features a sub-10-μW power consumption operating from a 0.5 V supply, sustaining a sub-1º of phase error even under 10% of supply and 0ºC–70ºC of temperature variations. It exhibits a 15.28 mΩ/√Hz of input-referred impedance noise performance, occupying a 4.83 mm² of active area. Its linearity performance shows that the magnitude and the phase of Bio-Z can be measured within the error of 2% and 0.4º, respectively, given that the magnitude of load impedance is less than 126 Ω, 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. The second IC features a sub-10-μW and a sub-0.1% THD sinusoidal current generator (CG) that is capable of 20 kHz output current driving. This IC also operates from a 0.5 V supply, benefiting from the ultra-low-power nature of near-threshold operation of digital circuit. With a 2 μApp amplitude of sinusoidal current, it assures <1% of driving error up to the load impedance of 2 kΩ, occupying a 0.059mm² of active area.