A 1mW Time Constant Based Impedance Spectroscopy for Non-Invasive Blood Glucose Monitoring

A novel Electrical Impedance Spectroscopy (EIS) system is proposed to provide a non-invasive blood glucose level monitoring. The proposed system estimates the blood glucose by measuring the RC time constant of a 50 KHz pulse signal penetrating through the patient tissue sensed at an on-chip resistor of 1 K Omega. For accurate measurement of the time constant, 1) a threshold detector capable of detecting the signal level at 37% of its original value with minimum effect of PVT variations, and 2) a mixed-signal PVT-resilient Phase Locked Loop (PLL) circuit that provides a clock signal of 100 MHz to operate the time constant measuring circuit are proposed. The proposed system is capable of measuring a capacitance value in the range of 1 nF-10 nF and therefore estimates the blood glucose with mean absolute relative difference of 13.2%. It is simulated with a 65 nm CMOS technology and consumes a power of 1 mW.