A Magnitude/Phase Bio-Impedance Measurement System with PWM Output

Abstract This paper presents an implantable bio-impedance device for long-term monitoring applications. The proposed magnitude/phase system includes a low-power analog front-end that generates pulse-width-modulated outputs. Additionally, the bio-impedance readout uses a Fibonacci DC-DC converter to convert voltage to time for backscattering communications. The proposed bio-impedance system is designed and simulated in a 0.18 µm CMOS process and occupies 200µm×170µm and measures bioimpedance at 2 kHz over a wide dynamic range of 100 Ω to 4 kΩ with 1.25 Ωrms accuracy while consuming just 4 µA from a 1.8 V supply.