A 0.48$^{\circ}$ Phase Error 91.1 dB SNR Bioimpedance Measurement IC for Monitoring Cardiopulmonary Diseases

Area of Science:

• Biomedical Engineering
• Electrical Engineering
• Medical Devices

Background:

• Cardiopulmonary diseases require continuous monitoring.
• Existing bioimpedance (BioZ) systems face challenges with phase shift and power consumption.
• Integrated circuit (IC) design offers potential for miniaturized and efficient medical monitoring.

Purpose of the Study:

• To develop a low-power, low phase error BioZ measurement IC for cardiopulmonary disease monitoring.
• To introduce a novel phase shift calibration logic for improved impedance accuracy.
• To demonstrate the IC's capability in capturing physiological signals like Impedance Cardiography (ICG).

Main Methods:

• Designed a single-channel, in-phase demodulation-based impedance measurement scheme.
• Implemented a noise-shaping pseudo-sine wave current generator (CG) with data-weighted averaging (DWA).
• Fabricated the IC using a 0.18μm CMOS process, achieving a compact size and low power consumption.

Main Results:

• The IC achieves low power consumption (52.7–97.5μA) and a small footprint (0.73mm²).
• The current generator demonstrates high spurious-free dynamic range (SFDR) and low total harmonic distortion (THD).
• Achieved excellent performance metrics including low input-referred impedance noise, high SNR, wide input range, and minimal phase error (<0.48°).

Conclusions:

• The developed BioZ IC effectively compensates for phase shifts, enabling accurate measurements.
• On-body experiments successfully recorded Impedance Cardiography (ICG) and respiration signals using a 4-electrode setup.
• This technology holds promise for non-invasive, continuous monitoring of cardiopulmonary conditions.